Pressure-controlled fuel injection for internal combustion engines

Abstract

An electronically controlled fuel supply system for an internal combustion engine. The timing of the commencement of fuel injection into each combustion chamber is not fixed relative to the rotational position of the camshaft or other engine components. A unit injector assembly associated with each combustion chamber includes a control module and an accumulator type injector module. The control module contains a solenoid valve and, in some embodiments, a hydraulic pressure intensifier. The accumulator type injector module contains an injector nozzle, a hydraulic accumulator, and a non-return valve for admitting liquid fuel under pressure into the accumulator. In operation, an electrical control system supplies an electrical signal to the control module an appreciable portion of the engine cycle in advance of the time when fuel injection is to be initiated in the particular combustion chamber. In response to that electrical signal, the solenoid valve admits liquid fuel under pressure into the hydraulic pressure intensifier. The output of the intensifier provides a metering and intensifying chamber in which the pressure of the fuel continues to increase until near the time when fuel injection is to commence. As pressure builds up, fuel flows through the non-return valve into the accumulator. Under control of the electrical signal the solenoid valve then shuts off the flow of liquid fuel into the intensifier. The transfer of fuel under high pressure from the intensifier chamber to the accumulator is discontinued due to the non-return valve, and the injector nozzle then fires. Alternatively, the solenoid valve admits liquid fuel under pressure directly through the non-return valve into the accumulator, with the turn-off of the solenoid valve causing the injector nozzle to fire. The control system may be utilized for operating the engine in a modified engine cycle in which firing cycles are selectively eliminated. The control system may also be utilized for controlling different cylinders of an engine differently from each other. The control of engine power is accomplished by either electrical or hydraulic means, or a combination thereof, and does not involve any mechanical adjustments within the unit injector assemblies.

Description

RELATED APPLICATION

This application is a continuation-in-part of copending U.S. patent application Ser. No. 418,688 filed Sept. 16, 1982 by the present applicants and Christian G. Goohs, and which was assigned to the same assignee, BKM, Inc., as is the present application. The prior application has subsequently been abandoned.

two separate fuel inputsdoes provide certain. TheMore specifically, the opening action of the T-valve is as follows: The pressure in compression chamber 150 is applied to recess 187, i.e., the entire cross-sectional area of the T-valve member 180 less the areas of bore diameter 185 containing the needle valve member 190, and circumferential lip 182. The pressure in the accumulator chamber 150a reaches a larger area, that of the member 180 less bore 185. Hence the pressure in compression chamber 150 is initially applied to a smaller area, and must also overcome the force of spring 200. After the valve opens, only the spring force need be overcome.

The next action to take place in the closing of the T-valve 180, returning both valve members 180 and 190 to their initial positions as shown in FIGS. 5a, 5b, 7 and 8. the T-valve 180 to its initial, closed position as shown in FIGS. 5a and 7, while the needle valve member 190 remains in its closed position as shown in FIGS. 5b and 8. This closing action of T-valve 180 is caused by the equalization of forces on both sides of T-valve 180 (upward forces on T-valve 180 of accumulator fluid pressure and T-valve spring 200 becoming equal to downward force on T-valve 180 of fluid pressure in compression chamber 150), or in case such forces have not yet become equalized, by the turning off of the solenoid valve 30, with the resultant pressure drop in the low pressure chamber 145 and in turn in the high pressure chamber 150.

Although the valve positions are the same as previously, the conditions inside the accumulator chamber 150a are now significantly different. That is, the interior of the accumulator body or housing has been charged with an additional quantity of liquid fuel, raising its internal pressure from about 6,000 psi to about 22,000 psi. As a result, differential pressure acting inside the accumulator will cause the needle valve member 190 to be raised off the valve seat 166. Although this action is well known in the prior art, it will be briefly summarized here as well.

The diameter of needle valve 190 beneath the flange 195 is smaller than its diameter above that flange. Internal fluid pressure acting on differential areas as previously described creates a net force upward on the needle valve member. That force must be sufficient to overcome the force of large spring 210. It must, in addition, be sufficient to overcome the force of fluid pressure acting upon the upper end surface 194 of the needle valve member. In this connection, reference is made to the bucking arrows 54 and 55 in FIG. 2 which schematically illustrate the pressure changes taking place at of pressure acting downwardly against the T-valve member 180 and the top end of the needle valve member 190 (schematically check valve 60 of FIG. 2), and of pressure acting upwardly against the T-valve member 180 and needle valve member 190. The differential pressure is sufficient to raise the needle valve off its seat, hence upward movement of the needle valve member occurs, and fuel injection commences through the holes 177 in spray tip 175.

The fuel injection occurs during a time interval of about one to one and a half milliseconds. Internal pressure inside the accumulator chamber 150a quickly falls to the closing pressure for which it was designed, approximately 6,000 psi, depending upon the force of the spring 210 and other design factors. The needle valve member 190 then returns to its closed position. The spherical sealing surface 192 on member 190 reengages spherical seat 166, the seating stress being minimized by the previously described dimensional relationship between surfaces 192 and 166. Both valve members are again in their initial position as shown in FIGS. 5a and 7.

More specifically, the opening action of the T-valve is as follows: The pressure in compression chamber 150 is applied to recess 187, i.e., the entire cross-sectional area of the T-valve member 180 less the areas of bore diameter 185 containing the needle valve member 190, and circumferential lip 182. The pressure in the accumulator chamber 150a reaches a larger area, that of the member 180 less bore 185. Hence the pressure in compression chamber 150 is initially applied to a smaller area, and must also overcome the force of spring 200. After the valve opens, only the spring force need be overcome.

The action of the needle valve is self-centering because of its particular construction. That is, the upper end of the needle valve fits loosely in the opening in the spring separator 170. Similarly, the T-valve member 180 also fits loosely inside the spring separator 170. At the same time, the upper end surface 194 of the needle valve is not laterally restricted in any way by the washer 151 above it, or by the lower face of the block 111. Thus, when the needle valve returns to its normal closed position, it centers itself on the valve seat 166 at the lower end of the accumulator, and the upper end portion of the needle valve member positions itself wherever necessary in order to align with the lower end. It is the support means at the upper end of the needle valve which permits it to function in this matter.

An important feature of the needle valve operation is that it is closed only by the forces of spring 210 and the pressure differential across the needle valve stem. Because the valve face 192 has a slightly smaller radius than valve seat 166, the closing action occurs rapidly and smoothly, with minimal wear on the valve parts.

XI. OPERATION OF THE UNIT INJECTOR ASSEMBLY

PAC (FIGS. 2, 12 and 13)

The operation of the unit injector assembly in accordance with the present invention has already been described in general terms in conjunction with the schematic diagram of FIG. 2.

Now that the specific mechanisms of the preferred embodiment of the unit injector assembly have been described in conjunction with the detailed drawings thereof, it is appropriate to refer to FIGS. 12 and 13 which illustrate an example of the actual operation of the device at 5700 rpm.

As shown in FIG. 12, the voltage pulse 36 causes the solenoid valve to open, but only after a delay of about 3.0 milliseconds. The common outlet port 33 had previously been bled to zero pressure level through the fluid return or drain port 32. The inward flow of fuel from the inlet 31 causes it pressure to initially rise rather rapidly, but then more slowly since it is necessary to perform work in moving the large piston 130 of the hydraulic intensifier downward. Thus as shown in FIG. 12, as the intensifier pistons travel through their range of movement, the pressure in the low pressure chamber 145 rises to the level of the supply pressure (about 1,500 psi). Even before this action is completed, the voltage pulse ends and after a delay of about 2.3 milliseconds the solenoid valve closes.

Closing Assuming that T-valve 180 has not already become closed by balancing of the force of accumulator pressure plus T-valve spring 200 against the force of fluid pressure in compression chamber 150, closing the solenoid valve with consequent venting of low pressure chamber 145 and pressure drop in high pressure chamber 150 causes the T-valve to close. The pressure in the high pressure chamber 150, which is also the pressure applied to the upper end surface 194 of the needle valve, drops sharply (see FIG. 12). The accumulator chamber 150a pressure drops rapidly, but less so. The differential between these two pressures is applied to the needle valve member for driving it upward agains the force of big spring 210. Near the upper part of FIG. 12 is shown the actual motion or displacement of the needle valve member 190. As shown there, the maximum displacement of the needle is only a little over 0.40 millimeter of 0.016 inches, because that is the spacing between the upper end of the needle valve member and the washer 151 which acts as a bumper to limit needle movement.

A very small displacement of the needle is sufficient to initiate a full flow of the fuel through the orifices. The uppermost curve in FIG. 12 illustrates an example of the rate at which fuel is injected into the combustion chamber of an engine cylinder.

XII. TIMING THE INJECTION

The timing of the fuel injection is established by the end of voltage pulse 36, which causes solenoid 30 to return to its closed position (closed to pressure, open to vent)after the aforementioned time delay of about 2.3 milliseconds. The mechanical closing of the solenoid then causes the injection of the fuel to occur almost immediately thereafter, the needle valve member 190 opening in response to the rapid drop in pressure above it in high pressure chamber 150 when the solenoid closure vents the intensifier.

The time duration required for the fuel injection to be completed depends upon various design constants of the apparatus. The completion of the injection is determined by the characteristics built into the unit injector assembly, rather than being timed or controlled from some external source.

XIII ADJUSTING (CONTROLLING) THE FUEL CHARGE

Once the fuel system is primed and the engine is operating at a steady speed and load, the unit injector assembly operates in accordance with the balanced conditions as shown by the curves in FIGS. 12 and 13. That is, after the injection of each fuel charge, the fuel pressure inside the accumulator returns to the residual pressure level for which the accumulator was designed. Upon the next actuation of the hydraulic intensifier, that pressure level must be equalled and slightly exceeded before the T-valve will open and admit additional fuel from the compression chamber.

During this operating condition, a fuel charge whose quantity is selected in terms of its volume at a specified pressure is transferred from the compression chamber into the accumulator. For example, a typical fuel charge is 30 cubic millimeters at atmospheric pressure. The quantity of this fuel charge will be slightly less than the total amount of fuel that was held in the compression chamber 150 and the metering duct 118b which extends between chamber 150 and check valve 119. When this predetermined fuel charge passes into the accumulator, it may increase the total quantity of fuel contained in the accumulator chamber 150a by approximately five percent. This is made possible by the compressibility of the fuel. For example, the internal capacity of the accumulator may be 700 cubic millimeters (i.e., 700×0.05=35 cubic millimeters). Since an operating condition that is in hydraulic balance has been achieved, the quantity of the fuel charge injected from the accumulator into the combustion chamber will be almost precisely the same as the quantity that was transferred from the compression chamber into the accumulator.

It is important to note that with this invention the function of metering the desired mass (as distinguished from volume) of the fuel charge to be injected is accomplished in the accumulator charge of the injector. Specifically, the mass of each fuel charge injected is metered or determined by the selected fixed volume of the accumulator chamber and by (and a direct function of) the difference between the peak pressure inside the accumulator nozzle and the pressure at which the tip valve closes. Although there is a slight pressure drop between the compression chamber and the accumulator (across the T-valve), the mass of the injected fuel charge is also a direct function of the volume of the accumulator chamber and of the difference between the peak pressure in the compression chamber and the nozzle tip valve closing pressure (fuel injection threshold pressure) of the accumulator. The quantity of fuel transferred into the compression chamber simply replaces the previously injected fuel charge.

When it is desired to change the power and/or speed of the engine, positive controls must be exercised. In accordance with the present invention, the preferred method of making such adjustments in the quantity of fuel charge is by adjusting the supply pressure level. This action was discussed previously in connection with the electrical control system 78 and its output line 90 that carries signals to the rail pressure regulator 15.

The quantity of fuel charge may also be adjusted by changing the duration of the time interval through which the hydraulic intensifier operates. That is, the start of the voltage pulse 36 can be advanced to increase the fuel charge or retarded to decrease the fuel charge. In general, the voltage pulse commences an appreciable portion of the engine cycle in advance of the time when injection is to occur, and the intensifier builds up pressure in the compression chamber 150 for at least several milliseconds. See FIG. 11, wherein a combination of a solid line and a dotted line indicate that the point of commencement of the voltage pulse 36 is subject to adjustment. In that connection it will be noted from the particular example of FIG. 12 that a time interval of about 9 milliseconds is required for the intensifier pistons to reach the maximum displacement, and a time interval of about 10 milliseconds is required for the low pressure piston to return to its initial position. Fluid pressure in the low pressure chamber 145 remains at a low pressure until the large piston has returned to its initial upper position; then the pressure in chamber 145 and common output terminal 33 drops to zero. There follows a dead space or unused time interval in the engine cycle, when the capabilities of the unit injector assembly are not being utilized. Increasing or decreasing this unused time interval also involves a concurrent decrease or increase in the period of time that the solenoid valve is open. By making this adjustment to the length of time the solenoid valve remains open, the subsequent length of time that the hydraulic intensifier is able to operate can in turn be increased or decreased, and the quantity of the fuel charge produced by it can be adjusted accordingly.

In addition to adjusting the fuel charge by adjusting the level of the rail pressure, hydraulic control may also be achieved by adjusting the pressure of the fuel return line, or by adjusting pressure of a selected separate source supplying the inlet check valve to the intensifier chamber. Alternately, any combination of the three types of adjustments may be used.

Furthermore, by means of the microprocessor the adjustment of the duration of the voltage pulse, and the adjustment of the hydraulic pressures supplied to the injector unit assembly, may be used in conjunction with each other, in varying degrees, as desired.

XIV. MATHEMATICAL EXPLANATION OF OPERATION

In accordance with the present invention the quantity of each injected fuel charge is defined by the following relationships:

Q=K×V_ac ×(P_max -P_min) (1)

P_max =P_rail ×E×I (2)

(neglecting the small pressure drop across the T-valve)

P_min =P_rail +P_spring (3)

(neglecting the small pressure drop across the T-valve) wherein:

Q is the quantity of fuel that is metered and then injected into the combustion chamber for the next firing;

K is the compressiblity factor for the fuel, a single valued function of pressure and temperature which can be considered a constant for relatively small changes in pressure;

V_ac is the accumulator volume;

P_max is the maximum accumulator pressure;

P_min is the minimum accumulator pressure;

P_rail is the common rail supply pressure;

I is the intensifier ratio;

E is the intensifier effectiveness which is the ratio of actual pressure intensification to theoretical pressure intensification; and

P_spring is that portion of the needle valve closing pressure which is attributable to its spring.

By combining the initial set of equations the following additional relationship is obtained:

Q=K×V_ac ×(P_rail ×E×I-P_rail -P_spring) (4)

This single equation defines the quantity of fuel which is metered in the accumulator injector and is then injected into the combustion chamber for the next firing.

It will be noted that in Equation (4) the only parameters which become variables during the operation of the system are the rail pressure, P_rail and the ratio E which indicates the proportion of available pressure multiplication that is being utilized. It will be realized that the value of E is determined by the "on" time of the solenoid valve, and asymptomatically approaches 1.0 with increasing "on" time.

An important characteristic of the invention is the manner in which changes in the metered fuel charge are achieved. By applying a differential calculus type of analysis to Equation (4) the following additional relationship may be derived:

Q+ΔQ=f(P_rail +ΔP_rail E+ΔE)

where ΔP_rail is a change in rail pressure, ΔE is a change in intensifier effectiveness and ΔQ is a change in the metered charge. The notation f(. . . ) denotes a function of the variables contained within the brackets. Thus, increases or decreases, ΔQ, in the charge to be metered may be controlled by varying either the rail pressure, P_rail or the intensifier effectiveness ratio, E, or both.

XV. OPTIMIZING ENGINE PERFORMANCE

An inherent feature of the fuel supply system of the present invention is that the hydraulic power requirement to operate the fuel injectors is relatively constant throughout the entire engine cycle, so that the peak power demand is greatly reduced.

As mentioned previously, when the engine is idling the timing cycle of the electrical control system can be changed so that it coincides with an integral multiple of the normal number of crankshaft revolutions. Thus, a modified operating cycle of the engine can be accomplished to inject a fuel charge only half or one-fourth as often as the basic operating cycle. These cycles are appropriate for light load operation. A fuel charge is injected into each cylinder of the engine only once during an operating cycle.

This mode of operation not only saves fuel, but reduces the amount of exhaust pollutants. In general, individual injection and ignition cycles are selectively eliminated to improve engine performance.

Another feature of the present invention is the utilization of the electrical control system to control the operations of the individual cylinders differently from each other. That is, for example, in the first cylinder of the engine the hydraulic intensifier unit may be turned on for 9 milli-seconds, while in the second cylinder the hydraulic intensifier may be turned on for 91/2 milliseconds, and in the third cylinder for only 81/2 milliseconds. This method of control makes it possible to accomplish a "fine tuning" action. This compensates for any difference between the cylinders in order to give them a balanced operation and improve the overall efficiency and economy of the engine operation.

XVI. CONTROL CHARACTERISTICS

The basic fuel control methods described previously are utilized in performing the engine governing functions. Maximum speed governing, for example, reduces fuel delivery by any of the described methods in response to signals generated by the pulse generator and subsequent operations performed by the electronic control system. In a similar manner the pulse generator in cooperation with the electronic control system may perform a speed control or speed governing function by increasing the fuel delivery to increase engine speed or decrease fuel delivery to decrease engine speed. Thus a selected minimum speed or any speed within the operating range of the engine may be governed.

According to the present invention a sequence of electronic timing signals is generated, and is repeated once each engine cycle. For improved performance at part load, cycles may be selectively eliminated.

XVII. PRIOR ART DISTINGUISHED

Since Luscomb, and Straubel or Falberg in combination with Luscomb, formed the primary basis of rejection of some of the claims in the original application, the applicants have prepared a detailed analysis giving the significant differences between their devices and the cited prior art. It is respectively submitted this will adequately illustrate both the aplicants' unique and patentable features over Luscomb and that to combine elements of Straubel or Falberg with Luscomb, even if such were obvious, would not duplicate the applicants' invention or its operation.

A few actual and apparent similarities exist between Luscomb and Beck, et al., such as a three-way solenoid valve, an intensifier piston and a needle valve chamber. However, there exist fundamental differences in the method of metering, the actuation of the intensifier piston, and in the manner of initiating, accomplishing, and terminating the injection of the fuel charge into the cylinder.

More specifically, Luscomb meters first, and thereafter accomplishes pressurization and injection as essentially coterminous functions. In Beck the metering and pressurization are accomplished as coterminous functions, and only when they are completed is injection commenced. A further important distinction is that in Luscomb the time duration of the injection event is determined in whole or in part by the time duration of the pressurizing movement of the intensifier piston, while in Beck the injection even is terminated by the spring closing action of the accumulator injector and is independent of piston motion.

These substantial differences in principle, structure and operation offer important advantages in the Beck device, both in simplicity, the cost of manufacturing, and in being potentially more forgiving during the life of the injector in an engine.

Two basic differences between Beck and the cited art of significance are:

1. Unique to Beck is that his intensifier is allowed to achieve nearly its full pressure multiplication, and that his control of metering is more greatly influenced by the supply pressure in the fuel supply rail 16 rather by the influence of the time interval throughout which the solenoid valve 30 is energized. In fact, in the practical form of the Beck invention the duration of "valve on" time is used only to compensate for individual differences among the various cylinders of an engine, while the control of supply pressure becomes the sole means for controlling fuel quantity Q and hence engine power. FIG. 12 of the drawings shows the motion of the intensifier piston 130, 140 in relation to the time it is moving. The slope of its movement curve, particularly as it approaches maximum displacement, is quite gentle. Thus a change in the time that the valve is energized serves more as a trimming function than acting as a major element for metering.

2. Further unique to Beck is that forming the fuel charge with pressure metering, i.e. by controlling the common supply pressure to all injectors, and allowing sufficient time to each injector to reach its maximum pressure, is dependent upon the compressibility and density properties of the fuel.

In distinguishing between Beck and Luscomb it is to be noted that the Luscomb device is not of the accumulator type as he does not store a fuel charge under injection pressure in his chamber (78) between the metering chamber (50) and the nozzle tip prior to injection of the charge into the combustion chamber. The actual injection process is solely a function of, and is in synchronization with the movement of his intensifier piston (64,65). In Beck et al, injection is an independent event not synchronized with the downward movement of the intensifier piston.

A simple analogy of these differences can be made by comparing the injection process of Beck vs. Luscomb with that of a firearm:

In Beck, the "loading" (metering) is accomplished concurrently with the "cocking" (charging of the accumulator chamber 70). Thus by the end of the "loading" (metering) phase, the injector is also "cocked" and ready to "fire". The metering is controlled by the pressure reached in the "loading" phase. "Firing" (injection) occurs when the solenoid moves the control valve to vent the chamber 145 above the large end 130 of the piston and acts to "pull the trigger" to allow the stored energy ("powder charge") in the accumulator (the "cartridge") to power the injection of the charge through the nozzle holes.

In Luscomb, "loading" (metering) is a distinct, separate phase. "Cocking" and "firing" are the linked phases in synchronization with the movement of the intensifier piston.

Luscomb further teaches that prior to the time of the injection event the chamber above the intensifier piston large diameter end 64 is open to the fuel reservoir via passages in the shuttle valve assembly 38 and a throttling orifice 144a, adjustable only during calibration at assembly. In Beck et al at this point the large diameter end is open to source pressure.

In Luscomb the source pressure acts on the small end 66 of the intensifier piston prior to the injection event. In Beck the opposite occurs. The source pressure is on the large diameter end 130 prior to injection.

In Luscomb the outermost point of travel of the intensifier piston (towards the nozzle) always ends at the same place. The innermost point of travel is varied in order to meter a fuel charge, its stroke end-position being a function of the time interval during which the valve is energized and the influence of the calibrated orifice (144a) in the fuel return circuit. Without this manually adjustable resistance, the metered charge quantity could not be varied since the intensifier piston would always travel to the end wall of its large end chamber. Thus Luscomb meters the fuel charge during the movement of the intensifier piston to its innermost position. The accuracy of metering is greatly dependent, therefore, on the time that the solenoid valve's interval of being energized can be controlled and by the variable orifice means.

In Beck, the innermost point of piston travel remains fixed and the outermost point (towards the accumulator chamber and the nozzle tip) is determined by when the force generated against the large end of the intensifier piston from the supply pressure equals the force exerted on the opposite end by the accumulator chamber pressure. Restated, the piston arrives at an equilibrium position based on a pressure balance between the source pressure multiplied by the big end piston area and the injection pressure multiplied by the small end piston area and the reduction in volume of the fuel in the spaces below the piston (accumulator chamber 150a, compression chamber 150, etc.) due to the inherent compressibility of the fuel under the elevated pressures. The pressure determining the force on the piston large end is regulated as a function of engine power needs.

A significant disadvantage of the Luscomb system is that the quantity of fuel metered, or admitted to, the high pressure end of his intensifier is highly dependent on the pressure differential across the adjustable restriction orifice 144a imposed by the needle valve 144, 146 that is positioned when the injector is calibrated at assembly. This adjustable flow orifice also offers the engine operator a simple means during the calibration procedure to tamper with the fuel rate and increase it above that which the engine manufacturer might deem a maximum for a particular model. Further, the effect of temperature on calibration when flow rate control orifices are used is particularly important. Others have found that pressure-time metering requires compensating devices to accommodate variations in viscosity due to temperature changes in the fuel. Beck has no need for this restriction as in his device the piston always returns to the same innermost point.

Of further disadvantage in the Luscomb device is that the time available to fill his metering chamber 50 is severely limited by its being open to source pressure only during the very short time his solenoid can be energized. This greatly magnifies inherent variations in flow resistances, sliding friction of valve parts and solenoid coil characteristics. These variations are additive and, because they constitute a measurable time, can cause a greater cycle to cycle and/or cylinder to cylinder variance of fuel metering which may or may not be overcome by fine tuning of the microprocessor controls.

For example:

1. Luscomb must provide a high-flow second stage valve, as shown by the spool 38, because his system requires very high flow rates over very short time intervals for even relatively small engines. Thus, if 50 mm³ are to be injected into the combustion chamber in one millisecond, then several times this flow rate is required through the valve 38 which because of the intensifier ratio results in a flow rate during the injection phase of approximately 300,000 300 mm³ per second millisecond. Such high flow rates create inertial lags and flow losses that after injection timing and delivery. In the case of a single-cylinder, four-stroke cycle engine running at 2,000 rpm, each engine cycle occupies 60 milliseconds. For these conditions the pump must supply several times the injection delivery in the above mentioned period of about 1 ms. This short duration flow is about 60 times the average flow. For a comparable application Applicants' invention would have a peak flow of less than six times the average flow.

2. The Luscomb valve shuttle pieces have inherently more sliding friction than does the floating ball design of the Beck valve.

3. The small diameter end of the intensifier piston contains a spill port annulus 56. Its purpose is to terminate injection by opening a passage from the metering chamber 50 to conduit 54 and then to the inlet port 46. Thus displacement of the intensifier piston beyond the point at which the spill port opens is of no value as the displaced fuel is simply forced into the inlet passage. None of this displaced fuel is, therefore, delivered to the injector between the time of the opening of the spill port and the bottoming of the large diameter piston 62 on the face of the enlarged annulus 49a. The non-delivery portion of the intensifier stroke is an additional source of fuel metering error as this stroke portion must again be traversed during the retraction (metering) phase of the cycle. More hydraulic power also is required to push the intensifier through the non-productive portion of its stroke. In addition to the annulus 56, the axial and cross ports 70 in the piston end 66 further add to the manufacturing cost of the Luscomb device. The Beck design does not require this.

4. Extremely high pressure, short duration hydraulic pressure pulses or "spikes" would result from the inherent abrupt termination of flow when the intensifier piston bottoms out at the end of injection. Similar inertial pulses would result due to the abrupt shut-off of the shuttle valve 38 which terminates retraction of the intensifier. In the present invention, the flow at termination of pressurization is nearly zero, creating very low hydraulic pressure pulses.

5. A high supply pump pressure is required by Luscomb (5,000 psi is referred to) as the intensifier area ratio is limited to a relatively low value due to low response limitations of the shuttle valve 38. This necessitates heavier lines, fittings, and a more expensive pump in the pressure source system.

Conversely, the Beck et al. invention is importantly different in both function and construction. Features of this invention overcoming the detailed inherent deficiencies in Luscomb are the following:

1. In the Beck et al. injector, the compression chamber pressurizing time, i.e. the interval during which the solenoid is energized, can last at least one crankshaft revolution in a four-stroke cycle engine. The very short time for injection takes little of the overall cycle. Thus, a major portion of the engine operating cycle is available for pressurizing. As a result, variations caused by mechanical or fluid friction, as mentioned above, have little or no effect on the Beck device.

2. The quantity of fuel injected into the combustion chamber is precisely related to the pressure within the accumulator nozzle 70 at the time that injection commences.

3. At the start of injection of fuel into the engine cylinder, the pressure in the chamber 145 above the intensifier piston has been charged at an exponentially decreasing rate and has converged toward (asymtotically approached in a mathematical sense) the pressure in the fuel supply rail 16. The accumulator pressure at this point is the pressure in the chamber 145 multiplied by the intensifier area ratio. FIG. 12 in the drawings shows the accumulator pressure profile for a typical cycle. It can be seen that the rate of change of accumulator pressure approaches zero prior to the start of injection, whereby that pressure has become less sensitive to the duration of the charging phase as the duration continues. Thus, beyond a certain point the duration of the accumulator charging phase has little or no effect on peak accumulator pressure and hence, fuel delivery amount. In Luscomb, the final quantity is directly proportional to solenoid on-time. It is also to be noted that in Beck relatively large changes in the duration of accumulator charging time result in only small changes in injection pressure and fuel delivery. This characteristic permits very accurate adjusting of the fuel charge to be injected.

4. The primary control of fuel delivery in the applicants' injector is by adjustment of fuel supply rail pressure. The idea itself of varying source fuel pressure to meter is not new, one example being the successful Cummins PT (Pressure-Time) injection system; that system, wholly dependent on such a means of control, meters at low pressures (5-200 psi) into its injectors and thereby utilizes pressure and time to control fuel charge volume. However, the applicants' device utilizes the compressibility and density properties of liquids as a function of pressure. (Compressibility is defined as the specific change in density per unit pressure.) Since the compressibility and density for any given liquid are basic physical properties of that liquid, the mass present in a fixed volume is related directly to the pressure of the liquid. A corollary is that a fixed volume of liquid undergoing a change from one discrete pressure to another discrete pressure must also change its mass in an exact relationship to the volume and the two discrete pressure levels. It is thus possible to meter a liquid fuel charge by first selecting a fixed volume accumulator chamber and a needle tip valve closing pressure to set the minimum accumulator pressure, and then, by control means, adjusting the accumulator charging time and hence the maximum accumulator pressure. A slight adjustment of the fuel charge for individual cylinders is accomplished by altering the accumulator charging time.

5. As pressure builds and approaches equilibrium in the accumulator during the metering phase of the cycle, the flow rate of fuel entering the intensifier chamber 145 via the control valve 30 gradually decreases and approaches zero. The valve is thus switched to the "closed-to-supply, open-to-vent" position at this point in the cycle where the flow through the valve approaches zero. Only minimum hydraulic inertial pressure spikes are produced at the valve closing event.

6. Relatively low peak pump flow rate is required. Typically, the system is designed such that the flow into the intensifier 145 from the fuel supply rail would occupy about one complete revolution for a four-stroke engine. As mentioned above, this can be seen in the trace of the intensifier piston motion in FIG. 12. Using the same data as in the example cited for Luscomb's operation of a single cylinder, four-stroke engine running at 2,000 rpm, the maximum instantaneous fuel pumping rate required by the Beck device is less than about six times the average pumping rate, as contrasted with 60 times in Luscomb.

In view of the above explanatory information distinguishing the applicants' device from Luscomb the following brief comparison of the Luscomb-Straubel combination with the Beck et al. device should suffice.

In Straubel, the adjustable regulator 32 in the inlet line 31 is essentially regulated to a constant pressure of about 50 bar (approximately 730 psi). The purpose of adjusting this pressure is to effect pressure changes in the line to the injector in order to compensate for temperature variations of the fuel. It is not the primary fuel metering control nor is it under direct operator control for changing the fuel rate to the engine under such conditions as increased power at constant speed or under acceleration. Thus the applicants' device is not readable on Luscomb in view of Straubel as the use of an adjustable pressure regulator to control metering in conjunction with fuel compressibility and density is not obvious.

A discussion of the Beck et al. device in comparison with Luscomb in view of Falberg is now respectfully submitted to show that the applicants' device could not be achieved as a matter of obvious design choice by substituting the Luscomb nozzle injector 78 for the Falberg accumulator injector 28 and its associated elements.

While it is true that a Luscomb-Falberg combination injector could probably be made to work, it would neither be practical nor efficient and, because of inherent injection timing problems, could cause damage to the engine. In addition such a combination of Luscomb-Falberg would retain most or all of the deficiencies of Luscomb.

It may be logical to assume that the volumetric metering of Luscomb can be substituted for the volumetric metering of Falberg, and thus the two devices may be combined. That would be difficult enough. To further assume, on a highly imaginative basis, that the resulting combination could then be utilized to accomplish Applicants' pressure metering method, would present obstacles that cannot reasonably be overcome. Thus, a comparison of a Luscomb-Falberg combination with the Beck et al. device may be best understood by explaining the operational modifications necessary if the Luscomb-Falberg combination were to be converted to the applicants' system (obvious element deletions will not be itemized):

1. Change the 3-way control valve from "normally open" to "normally closed".

2. Change the metering function to occur when rail pressure is "on" rather than when it is "off".

3. Eliminate the spill port annulus (56) in Luscomb and block passage 98.

4. Change the initiation of injection to occur when the intensifier piston ismoving upward rather than downward.

5. Reach peak pressure in the accumulator chamber when the intensifier piston velocity is nearly zero rather than when the velocity is a maximum.

6. Pressurize the accumulator chamber in a time interval equal to about one rather than about one-fifteenth of an engine revolution.

7. Change the metering function to depend upon rail pressure rather than largely on a calibrated vent orifice and "solenoid on" time.

8. Use an operator-controlled variable rail pressure rather than an essentially fixed rail pressure.

9. Make the metering function primarily independent of solenoid-on time rather than mainly dependent on that time interval.

10. When the solenoid is de-energized, keep the system unpressurized rather than pressurized.

While some of the above changes required to convert a Luscomb-Falberg combination to the applicants' system might be individually obvious, it is submitted that none of the changes 3 to 9 would be obvious. More importantly, it is clear that applicants' invention viewed as a whole would not be obvious in view of these references.

XVIII. ALTERNATIVE FORMS

Many variations are possible in the details of the mechanisms that are illustrated in FIGS. 3 through 10, inclusive. Furthermore, in accordance with the present invention a method of controlling engine operation for optimum performance is provided, which may not depend upon the specific type of unit injector assembly that is schematically described in FIG. 2.

For example, the pump 12 may be of the variable displacement pressure-compensating type with which pressure regulator 15 would not be required.

It will also be understood that FIGS. 12 and 13 illustrate the operation of the invention under one particular set of conditions, and that both the operating speed and the design parameters of the apparatus may be modified with corresponding modification in the operation.

XIX. CASCADED CONTROL VALVES

FIGS. 14 and 15 show the construction of a two-stage electrically operated unit injector assembly which is similar to the previously described construction except that a second valving stage is included having greater flow capacity for larger engines. In this construction the previously described solenoid valve 30 serves as a master or pilot stage to operate a significantly larger slave valve 30A. The larger slave valve 30A is of similar construction to the pilot valve having two ball poppet type valving elements which connect a common port 33A alternately to either the supply line or to the drain line. While the ball valves 31a, 32a of the pilot valve 30 may typically be of 3/32" diameter, the ball valves 31b, 32b of the slave valve 30A are typically of twice that diameter, or 3/16".

A piston 34c having a pusher pin 34d is located coaxial with the slave stage and on the vent end of the slave stage. The end of the pusher pin, which is opposite the piston, abuts the drain ball 32b of the slave stage.

A fluid supply line 33B connects a cavity behind the piston to the common port of the solenoid pilot valve. The common port 33A of the slave stage connects through a fluid passage to the large diameter piston of the intensifier.

Another feature of the embodiment of FIG. 15 is that a modified form of T-valve 181 is controlled by a single spring 211. It will be understood that the T-valve and spring arrangements of FIG. 5 and FIG. 15 are generally interchangeable.

When the solenoid pilot valve 30 is in the open-to-supply position, fuel is supplied to piston 34c which moves the slave stage to the open-to-supply position. Conversely when the solenoid (pilot) valve is in the open-to-drain position, the piston cavity is open to drain, and the slave valve returns to the closed-to-supply, open-to-drain position. Hence, the operation of the slave stage in conjunction with the intensifier, the accumulator injector, and check valves is identical to operation without the slave stage, except that the valve passage sizes are larger, permitting higher flow rates and increased fuel delivery.

XX. CONTROL FROM TWO PRESSURE SOURCES

Either the embodiment of FIGS. 1-13 or the embodiment of FIGS. 14, 15 may, if desired, be controlled from two pressure sources rather than a single source.

Thus as shown in FIG. 14 a cut-off valve 19B may be inserted between fuel supply rail 16 and the check valve 19. An alternate fuel source at a selected pressure may be connected via line 19C to the input side of check valve 19. Then, when valve 19B is cut and line 19C is activated, the fuel charges for the high pressure chamber 40 are supplied solely from the alternate fuel source. At the same time, energy for operating the hydraulic intensifier 40 continues to be provided by the common rail supply line 16, which can be operated either with liquid fuel or with some other liquid having desirable properties.

When the fuels ource and the hydraulic energy source are thus separated, the equation describing the quantity of the fuel charge becomes as follows:

Q=K+V_ac ×(P_rail ×E×I-P_selected source -P_spring) (6)

(again neglecting a small pressure loss across the T-valve)

Thus the control of fuel charges entails three variables--the common rail pressure P_rail, the intensifier effectiveness ratio E (based on "valve on" time), and the pressure of the alternate fuel source.

XXI. PRESSURE CONTROLLED INJECTOR WITHOUT PRESSURE INTENSIFICATION

FIG. 16 shows a schematic diagram while FIGS. 17 and 18 show the actual construction of a simplified unit injector assembly 101 which is similar to assembly 100 shown in FIGS. 2 through 10. In this construction the intensifier has been deleted and the common outlet port 33 of solenoid 30 communicates directly with the modified T-valve member 180A and the flat upper end surface 194 of needle valve member 190. Metering duct 118, check valve 119, check valve 121, and block 111 (FIG. 5a) have also been eliminated in this construction. All other features are retained.

In FIG. 18, cylindrical member 196 is pressfitted into block 110A, and its lower end has a lapped surface which provides a seal against the upper end of modified T-valve member 180A. Thus the modified check valve 60A includes T-valve member 180A, cylindrical member 196, and the cylindrical upper end of needle 190. The concentric inner cylindrical member 197 is loosely fitted and acts as a needle stop, like washer 151 of FIG. 5.

FIGS. 19 and 20 are curves of pressure versus time for the embodiment of FIGS. 16-18, comparable to FIGS. 12 and 13 for the first embodiment. As shown in FIG. 19, after firing of the nozzle the pressure level remaining in the accumulator chamber equals the sum of its spring pressure and the drain line pressure.

The function of the simplified electrically operated unit injector is identical to the previously described injector having an intensifier except that the maximum accumulator pressure is slightly less than the fuel supply or common rail pressure. With the solenoid in the energized position, pressure in the accumulator increases and approaches rail pressure. As in the previously described cases, switching the valve from the open-to-supply to the open-to-drain condition causes the T-valve to close and the pressure on the top surface of the upper portion of the needle valve member to decrease. When the pressure on the top surface of the upper portion of the needle valve member decreases to a sufficiently low level, the needle valve lifts from its seat and causes fuel to be sprayed through holes in the injector tip.

The amount of fuel injected is related to accumulator volume, the maximum and minimum accumulator pressures, and the compressibility factor for the fuel. The minimum accumulator pressure in this case is spring pressure plus drain line pressure rather than spring pressure plus rail pressure. The relationship can be expressed in equation form as follows:

Q=K×V_ac ×(P_rail ×E-P_drain -P_spring) (7)

PERFORMANCE COMPARISON FOR USE OF THE INVENTION FOR GASOLINE AND OTHER SPARK IGNITION ENGINES

The characteristic of the invention which separates the charging event from the injection even permits very short duration of injection without the flow variations typical of conventional pulse-width modulated systems. FIG. 21 shows needle motion, injection rate, and spark timing where fuel injection begins about 360 crankshaft degrees before the spark is fired, such as when injecting fuel into the intake port or engine manifold. FIG. 22 illustrates in-cylinder injection beginning about 70 degrees before the spark is fired. FIG. 23 shows the typical relationship between injection duration vs. quantity. For the conventional low pressure, pulse-width modulated system, precise control of fuel quantity is very difficult to attain for injection durations less than about 2 milliseconds. For the pressure-metered accumulator system of this invention, fuel quantity is essentially independent of injection duration, hence very fast injection becomes quite practical.

The present invention has been described in considerable detail in order to comply with the patent laws by providing a full public disclosure of at least one of its forms. However, such detailed description is not intended in any way to limit the broad features or principles of the invention or the scope of patent monopoly to be granted.

Claims

1. The method of injecting fuel into a combustion chamber of an internal combustion engine, comprising the steps of:

(a) selecting an accumulator type fuel injector having a fuel input, and characterized by the fact that the withdrawal of applied pressure from its input initiates the injection of a fuel charge;

(b) placing said fuel injector in operative relation to the combustion chamber;

(c) selecting an electronically controlled three-way valve for selectively admitting fuel into said accumulator type fuel injector;

(d) coupling said valve to said injector;

(e) coupling a source of liquid diesel fuel to said valve; and

(f) whenever it is desired to inject a fuel charge into the combuation chamber, applying an electronic control signal to said valve to open said valve for a selected period of time;

whereby at the end of said selected period of time when said valve closes to pressure and opens to vent, said accumulator type injector causes the injection of the fuel charge into the combustion chamber to be initiated; the termination of injection of the fuel charge being controlled by said accumulator type fuel injector and not by said valve or said electronic control signal.

2. The method of operating an internal combustion engine having a normal operating cycle during which a single fuel charge is injected once per cycle into each combustion chamber of the engine, comprising the steps of:

(a) generating a periodically repeated sequence of electronic timing signals;

(b) sensing the revolution of a revolving shaft of the engine;

(c) in response to the sensed shaft revolutions, synchronizing said sequence of electronic timing signals with a normal operating cycle of the engine;

(d) then utilizing said sequence of electronic timing signals to control both the injection of fuel charges into the combustion chambers of the engine, and the ignition of said fuel charges, so as to maintain said normal operating cycle of the engine;

(e) then altering said sequence of electronic timing signals so that it occupies a time period which is an integral multiple of the time period it previously occupied, but with the same spacings between the individual injection signals, so that the engine then operates on a modified cycle which corresponds to said integral multiple times the number of engine revolutions contained in the normal operating cycle;

whereby it is possible to maintain substantially the same size of fuel charge supplied to each combustion chamber of the engine while decreasing the number and frequency of such fuel charges, thereby reducing the total fuel comsumption of the engine while maintaining its combustion efficiency.

3. Fuel injection apparatus for a diesel engine comprising, in combination:

(a) a source of liquid at a predetermined common supply pressure;

(b) a separate unit injector assembly associated with each combustion chamber of the engine;

(c) means for supplying one electronic control signal per engine cycle to each of said unit injector assemblies in order to control the repetitive injection of a prescribed fuel charge into the combustion chamber of the associated cylinder;

(d) each of said unit injector assemblies including a pressure intensifier, a solenoid valve for controlling the admission of a fuel charge to said pressure intensifier, an accumulator type injector, and a non-return valve coupling the output of said pressure intensifier to said accumulator injector;

(e) said control signal being operative once in each engine cycle to open said solenoid valve an appreciable portion of said cycle in advance of the injection of the fuel charge, said control signal also being operative to close said solenoid valve at the time when the fuel charge is to be injected;

(f) said pressure intensifier being operative to raise the pressure of the fuel charge received therein to at least several times the pressure level of said source, the closing of said solenoid valve being operative to relieve the pressure in said intensifier;

(g) said non-return valve opening in response to the opening of said solenoid valve when the fuel pressure produced by said pressure intensifier exceeds the residual pressure in said accumulator injector so that fuel at the intensified pressure is transferred to said accumulator injector, and closing in response to the closing of said solenoid valve;

(h) said accumulator injector being responsive to the closing of said non-return valve and the release of pressure in said intensifier for causing the injection of the fuel charge, the injection of the fuel charge being then powered by the differential pressure between the intensified fuel pressure in said accumulator injector and the pressure in the combustion chamber; and

(i) means for adjusting at least one of the pressure level of said common supply pressure, and the time interval during which said solenoid valve is open, in order to correspondingly adjust the magnitude of the fuel charge to be injected into said cylinder.

4. Fuel injection apparatus as in claim 3 wherein the engine includes a plurality of combustion chambers, and said injection apparatus includes a corresponding plurality of unit injector assemblies, each unit injector assembly being associated with the respective one of the engine cylinders.

5. Fuel injection apparatus in accordance with claim 3, wherein said fuel source includes a pump having its output coupled to a pressure regulator, and means for adjusting the pressure level of said regulator.

6. Fuel injection apparatus in accordance with claim 3, which includes an electrical control system having a separate output line coupled to each of said injector assemblies, and having means associated with said output line for generating a voltage pulse during each engine cycle; the leading edge of said voltage pulse causing said electronically controlled valve of the associated injector assembly to open, and the trailing edge causing said solenoid valve to close.

7. Fuel injection apparatus as claimed in claim 6 which further includes a separate output from said electrical control system coupled to said pressure source for adjusting said supply pressure.

8. Fuel injection apparatus as claimed in claim 6 wherein said electrical control system includes means for individually adjusting the various pulses of voltage supplied to the respective output lines coupled to corresponding injector assemblies.

9. Fuel injection apparatus as claimed in claim 3 which includes means for adjusting both the pressure level of said common supply pressure, and the time interval during which said solenoid valve is open, in order to adjust the magnitude of the fuel charge to be injected into said combustion chamber.

10. Fuel injection apparatus as claimed in claim 3 wherein said pressure intensifier includes a large piston and a small piston coupled together, a low pressure chamber to which the operative surface of said large piston is exposed, and a metering and intensifying chamber to which the operative surface of said small piston is exposed.

11. Fuel injection apparatus as claimed in claim 10 which further includes a fuel return line, and wherein said solenoid valve is a three-way valve, the operation being such that when said valve is open and low pressure chamber is coupled to said fuel source but not to said fuel return line, while when said valve is closed the opposite relationship exists.

12. Fuel injection apparatus as claimed in claim 11 which further includes a metering duct coupling said fuel source to said metering and intensifying chamber, whereby said metering and intensifying chamber is always filled with liquid fuel; and a non-return valve positioned within said metering duct to prevent the flow of fuel from said metering and intensifying chamber back to said source.

13. In a fuel injection system for an internal combustion engine wherein said fuel supplied at substantially constant pressure is converted to a series of metered charges at a pressure much greater than the supply pressure, an injector module comprising, in combination:

an elongated housing having an entry port at one end thereof and a spray tip at its other end;

an elongated needle valve member disposed within said housing, one end of said needle valve member having a transverse flat surface which is exposed to said entry port, the other end of said needle valve member having a valve face normally engaging a valve seat formed within the lower end of said housing adjacent said spray tip;

a spring separator diposed within and secured to said housing intermediate the two ends thereof, but locator closer to said entry port than to said spray tip;

said needle valve member having an annular shoulder formed therein intermediate its ends;

a first helical spring extending between said shoulder of said needle valve member and one side of said spring separator for urging said needle valve member against said valve seat, said first spring having a comparatively high spring force;

a valve member having a circular opening, said valve member being disposed within said housing with said one end of said needle valve member extending through said circular opening thereof;

both said valve member and said needle valve member being normally exposed to said entry port; and

a second helical spring extending between said valve member and said spring separator for urging said valve member towards said entry port, said second spring having a low spring force compared to said first spring.

14. The apparatus of claim 13 wherein said valve member is generally cup-shaped, said circular opening being formed in its end wall, and its circumferential wall extending toward said spring separator and surrounding said second helical spring.

15. The apparatus of claim 13 wherein said spring separator is of substantially annular configuration.

16. Fuel injection apparatus in accordance with claim 3, wherein said fuel source includes a variable displacement pressure-compensating type pump, and means for adjusting its output pressure.

17. The method of injecting liquid fuel charges into a combustion chamber of an internal combustion engine, comprising the steps of:

(a) providing a source of liquid fuel under controllable pressure;

(b) selecting a pressure intensifier having an intensifier piston and having a pressure intensifying chamber with a selected volume;

(c) selecting an accumulator type fuel injector having an accumulator chamber with a selected volume;

(d) admitting fuel from said source to fill said intensifying chamber;

(e) once during each firing cycle of said engine, constraining the fuel in said intensifying chamber against returning to said source, so that the fuel in said intensifying chamber may be compressed;

(f) then, commencing an appreciable portion of said engine operating cycle in advance of the time when injection is to be accomplished, and throughout an interval whose duration is longer than the time required for injection, drawing a quantity of fuel from said source and utilizing its pressure to gradually reduce the volume of said intensifying chamber until a selected pressure level of said fuel in said intensifying chamber is reached which is higher than the nozzle tip valve closing pressure of said injector;

(g) placing said pressure intensifying chamber in fluid communication through a non-return valve with said accumulator type fuel injector;

(h) transferring fuel from said intensifying chamber into the accumulator chamber of said accumulator type fuel injector at said selected pressure level; and

(i) when injection is to be initiated, then releasing the pressure within said intensifying chamber by reversing the direction of motion of the intensifier piston, so that the non-return valve immediately closes off the fluid communication between said intensifying chamber and said accumulator chamber of said accumulator type fuel injector, and such release of pressure from within said intensifying chamber causes the nozzle tip valve to open;

whereupon said injector then discharges into the combustion chamber a fuel charge whose mass is determined in part by the fixed volume of the accumulator chamber and is linearly related to the difference between said predetermined pressure level and said tip valve closing pressure.

18. Fuel injection method in accordance with claim 17 wherein said nozzle tip valve closing pressure of said injector is equal to the sum of said source pressure plus a pressure caused by a needle valve spring.

19. In an internal combustion engine fuel injection system, a control module for receiving liquid fuel from a substantially constant pressure supply line and producing a repetitive series of fuel charges of a metered quantity and at a substantially higher pressure level, said control module comprising, in combination:

a three-way solenoid-controlled valve having a fuel inlet port, a fuel drain port, and a common outlet, said valve being operative in one position to couple said common outlet to said inlet port only and being operative in another position to couple said common outlet to said drain port only;

a hydraulic intensifier having a large piston and a small piston in oppositely facing directions, a low-pressure chamber communicating with the face of said large piston, and a high pressure chamber communicating with the face of said small piston;

a metering duct providing direct fluid communication from said fuel inlet port to said high-pressure chamber, and having check valve means for preventing the flow of liquid fuel in the reverse direction;

a passageway coupling said common outlet to said low-pressure chamber so that in said one position of said valve, liquid fuel flows into said low-pressure chamber and advances said small piston so as to pressurize fuel stored in said high-pressure chamber, and in said alternate position of said valve, liquid fuel flows out of said low-pressure chamber to said drain port and causes said small piston to retract; and

said small piston being imperforate, and said high pressure chamber having a single outlet port disposed directly opposite the face of said small piston.

20. The method of controlling the mass of liquid fuel charges injected into a combustion chamber of an internal combustion engine, comprising the steps of:

(a) providing a source of liquid fuel at a selected pressure level which is nominally constant but selectively variable in order to adjust the mass of the fuel charges that are to be injected;

(b) establishing a threshold pressure level for the injection of fuel into the combustion chamber;

(c) periodically selecting a quantity of liquid fuel from said source;

(d) then isolating said selected fuel quantity from said source and storing said selected fuel quantity in a chamber;

(e) multiplying the pressure level of each such selected fuel quantity by a selected multiple such that its pressure level then exceeds said threshold pressure level; and

(f) in response to and under the control of each such selected fuel quantity those selected pressure has been thus multiplied, injecting into the combustion chamber a charge of liquid fuel whose mass is a direct function of the volume of the chamber in which the selected fuel quantity is stored and of the difference between said multiplied source pressure and said threshold pressure level.

21. The method of claim 20 wherein the mass of the fuel charge is adjusted by adjusting the time interval within which pressure multiplication occurs and thereby adjusting said selected multiple of pressure multiplication.

22. The method of claim 20 wherein an accumulator type fuel injector is selected which has a self-contained non-return valve at its input and a closing pressure corresponding to said threshold pressure level, and wherein each such selected fuel quantity having a multiplied pressure level is applied to the fuel input of said accumulator injector.

23. The method of claim 22 wherein the mass of the fuel charge is adjusted by adjusting the time interval within which pressure multiplication occurs and thereby adjusting said selected multiple of pressure multiplication.

24. The method of injecting fuel into an internal combustion engine having at least one cylinder with an associated combustion chamber, and of controlling both the quantity and the timing of each fuel charge that is injected into the combustion chamber so as to thereby control the engine operation, comprising the steps of:

(a) providing a source of liquid fuel under a predetermined pressure;

(b) selecting a unit injector assembly having

(1) a pressure intensifier including a larger and a smaller diameter piston having the capability of raising said fuel source pressure to a desired injection pressure,

(2) an electrically actuated control valve capable of being energized for a variably substantial part of an engine operating cycle to allow said intensifier to generate said injection pressure prior to the injection event; and

(3) an accumulator storage chamber capable of storing liquid fuel under an elevated pressure level, which pressure level determines the fuel charge to be injected;

(c) coupling said fuel source to said control valve of said injector assembly;

(d) turning said control valve on and off once during each power operating cycle of said engine so that whenver said valve is turned on, a chamber adjacent to said large intensifier piston is pressurized, thus causing the movement of said smaller piston through a distance sufficient to displace said fuel charge into said storage chamber under a selected injection pressure;

the movement of said smaller piston when the valve is energized being controlled by a balance of forces resulting from the pressure level of said fuel source, the pressure level on said intensifier pistons and the time interval during which said valve is energized;

(e) de-energizing said solenoid to open said control valve to a vent line and close said valve coupled to said source, thus initiating injection of said fuel charge into said combustion chamber; and

(f) simultaneously with the turning off of said control valve, causing

(1) said chamber adjacent to said larger piston, previously connected to said pressurized fuel source, to be connected to said vent line, said vent line leading to a fuel reservoir supplying said pressurized source and having a minimum flow resistance in order to allow said piston to return to the same fixed point at the end of each venting stroke, and

(2) the discharge from said storage chamber of said fuel charge into said combustion chamber;

the instant of time each said fuel charge begins its injection into said combustion chamber being determined by the time when said control valve is opened to vent;

so as to selectively determine the power and acceleration of said engine.

25. The method according to claim 24 in which only said source pressure is adjusted.

26. The method according to claim 24 in which only the timing of said valve turn-off is adjusted.

27. The method according to claim 24 in which only the time interval throughout which said valve remains turned on is adjusted.

28. The method according to claim 24 in which at least two of said source pressure, duration of time valve is on, and valve turn-off time are adjusted.

29. The method of claim 24 in which all three of said source pressure, duration of time valve is on, and valve turn-off time are adjusted.

30. The method in accordance with claim 24 wherein the engine is a multi-combustion chamber engine having a plurality of unit injector assemblies, one for each combustion chamber, and all of said unit injector assemblies, while operating at different points of time during the engine cycle, are controlled in an identical fashion.

31. The method according to claim 30 wherein said source pressure is common to all injector assemblies.

32. The method according to claim 34 24 wherein the engine is a multi-combustion chamber engine, having a plurality of unit injector assemblies, one or more for each said combustion chamber, and wherein at least one of said source pressure, duration of time the valve is on, and valve turn-off time is adjusted differently for one chamber of the engine than it is for another chamber of said engine.

33. The method of controlling the mass of liquid fuel charges injected into a combustion chamber of an internal combustion engine, comprising the steps of:

(a) providing a source of liquid fuel at a selected pressure level which is normally constant but selectively variable;

(b) providing a pressure intensifying means whose pressure multiplying movement is a function of said source pressure and the compressibility and density properties of the liquid fuel;

(c) establishing a minimum pressure level at which the fuel may be injected into the combustion chamber;

(d) periodically selecting a quantity of liquid fuel from said source;

(e) using said intensifying means to multiply the pressure level of each such selected fuel quantity by a fixed multiple such that its pressure level then exceeds said minimum pressure level;

(f) forcing said selected fuel quantity into an accumulator type storage chamber; and

(g) in response to and under the control of each such selected fuel quantity whose selected pressure has been thus multiplied, injecting into the combustion chamber a charge of liquid fuel whose mass is a direct function of the volume of said chamber in which the selected fuel quantity has been stored and of the difference between said multiplied source pressure and said minimum pressure level.

34. The method of claim 33 wherein the mass of the fuel charge is adjusted either by adjusting said source pressure or by adjusting said minimum pressure level.

35. The method of claim 33 wherein the mass of the fuel charge is a direct function of said fixed multiple of pressure multiplication.

36. The method of claim 33 wherein said accumulator-type chamber has a self-contained, non-return valve at its input, and wherein each such selected fuel quantity having a multiplied pressure level is applied to said fuel input of said accumulator chamber.

37. The method of claim 36 wherein the mass of the fuel charge is adjusted by adjusting said source pressure or by adjusting said minimum pressure level.

38. The method of claim 36 wherein the mass of the fuel charge is a direct function of said fixed multiple of pressure multiplication.

39. An accumulator type fuel injection system for an internal combustion engine comprising, in combination:

(a) a unit injector for each combustion chamber of said engine;

(b) a three-way valve incorporated in each said unit injector and actuated by a corresponding separate solenoid;

(c) a fuel reservoir with passages leading to each of said three-way valves;

(d) a pump means to draw fuel from said reservoir in order to raise the fuel to a predetermined source rail supply pressure and having passages leading to each of said three-way valves;

(e) an accumulator chamber of predetermined volume in each said unit injector having an inlet check valve and an outlet needle valve;

(f) control means to control the level of fuel pressure generated by said pump means and to actuate each of said solenoids;

(g) passages controlled by each said three-way valve to pressurize or depressurize said corresponding inlet check valve as required;

(h) said check valve being in the form of a T-valve having a spring biasing means acting on one end, to serve both as said inlet check valve to said accumulator chamber and as a bushing for said needle valve; and

(i) said needle valve having an upper stem which slideably operates within said T-valve bushing, and having a lower end which abuts a seat adjacent to a nozzle orifice leading into a combustion chamber of said engine;

whereby when said solenoid is energized by said control means the liquid fuel in said accumulator chamber is thereby compressed to both meter and store in said accumulator chamber a fuel charge to be injected whose mass is a function of the volume of said accumulator chamber, the compressibility and density of the fuel, and the pressure in said accumulator chamber; and

whereby when said solenoid is de-energized by said control means the pressure above said T-valve and said upper stem of said needle valve is reduced, and said needle valve is triggered to lift off of said seat causing the injection of said fuel charge into said combustion chamber through said nozzle orifice using the energy of the compressed fuel in said accumulator chamber to accomplish the injection process.

40. An accumulator type fuel injection system for an internal combustion engine comprising, in combination:

(a) a three-way valve actuated by a solenoid;

(b) a fuel reservoir with passages leading to said three-way valve;

(c) a pump means to draw fuel from said reservoir in order to raise the fuel to a predetermined source supply pressure and having passages leading to said three-way valve;

(d) an intensifier piston having input and output ends;

(e) passages alternately connecting the input end of said intensifier piston with said source pressure or with said fuel reservoir as required;

(f) a control means to control the level of fuel pressure generated by said pump means and to actuate said solenoid;

(g) an accumulator chamber of predetermined volume having an inlet check valve, said check valve coupling the output end of said intensifier piston to said accumulator chamber; and

(h) a needle valve seating at a nozzle tip orifice leading into a combustion chamber of said engine;

whereby when said solenoid is energized, the force created by said pressurized fuel source acting on the input end of said piston causes the movement of said piston to both meter, by said piston reaching an equilibrium position based on a balance of the hydraulic force acting on each end of said piston, and load under injection pressure into said accumulator chamber a fuel charge whose mass is a function of the volume of said storage chamber, the compressibility and density of the fuel, and the pressure in said chamber; and

whereby when said solenoid is de-energized said piston input end is vented through passages having a minimum hydraulic resistance, thereby triggering the lifting of said needle valve and using the energy of the compressed fuel in said storage chamber to cause the injection of said fuel charge into said combustion chamber through said nozzle orifice.

41. The method of metering fuel charges and injecting them into a combustion chamber of an internal combustion engine by supplying fuel from a selected pressure source through a pressure intensifier chamber to an accumulator type fuel injector, and controlling the pressure multiplying action of the intensifier from a common rail source through a solenoid valve, in which the fuel quantity to be delivered is linearly related to the pressure of the common rail source, substantially in accordance with the relationship:

Q=K×V_ac ×(P_rail ×E×I-P_selected source -P_spring)

wherein:

Q is the quantity of fuel to be burned that is metered and then injected into the combustion chamber;

K is the compressibility factor for the fuel;

V_ac is the accumulator volume;

P_rail is the common rail supply pressure;

I is the intensifier ratio;

E is the intensifier effectiveness which is the ratio of actual pressure intensification to theoretical pressure intensification;

P_spring is that portion of the needle valve closing pressure which is attributable to its spring; and

P_selected source is the pressure of the selected source supplying fuel to the intensifier chamber.

42. The method of claim 41 wherein the needle valve closing pressure is adjusted by adjusting the pressure level of the selected source.

43. The method of metering fuel charges and injecting them into a combustion chamber of an internal combustion engine by supplying fuel through to a solenoid valve and through a pressure intensifier having an intensifier piston the movement of which is under control of said solenoid valve into an accumulator type fuel injector, such that the quantity of the fuel charge being metered and to be injected is adjusted by adjusting the valve "on" time and hence adjusting the actually utilized proportion of the pressure increase that is available from the pressure intensifier, and the commencement of injection is initiated by turning the valve off and reversing the movement of the intensifier piston.

44. The method of metering fuel charges and injecting them into a combustion chamber of an internal combustion engine by supplying fuel from a common rail source through to a solenoid valve and through a pressure intensifier the movement of which is under control of said solenoid valve into an accumulator type fuel injector, such that timing of the commencement of the injection is controlled by turning the valve off, and the quantity of the fuel charge being metered and injected is in linear relationship to the common rail source pressure.

45. The method of metering fuel charges and injecting them into a combustion chamber of an internal combustion engine by supplying fuel from a common rail source through a solenoid valve into an accumulator type fuel injector, such that timing of the injection is controlled by turning the valve off, and changes in the quantity of the fuel charge being metered and injected are controlled by controlling the common rail source pressure.

46. The method of metering fuel charges and injecting them into a plurality of combustion chambers of an internal combustion engine, comprising the steps of:

supplying liquid fuel from a common rail source to a plurality of solenoid valves associated with corresponding ones of the combustion chambers;

feeding the fuel under control of each solenoid valve and through a respectively associated pressure intensifier and through a check valve into a respectively associated accumulator type fuel injector;

turning each valve on at a substantial part of an engine cycle prior to the time when a fuel charge is to be injected into the associated combustion chamber, so as to allow a substantial time for the associated pressure intensifier to accomplish a build-up of the fuel pressure;

initiating the injection of a fuel charge into each combustion chamber by turning the associated valve off;

controlling the pressure of the common rail source so as to control the quantities of all the fuel charges; and

adjusting the turn-on times of some of the valves relative to the others so as to adjust the proportion of the pressure multiplying capability of each pressure intensifier that is actually utilized, and thereby adjust the relative fuel quantities injected into the various combustion chambers of the engine.

47. The method of injecting fuel into a combustion chamber of an internal combustion engine, comprising the steps of:

(a) selecting an accumulator type fuel injector having a fuel input, and characterized by the fact that the withdrawal of applied pressure from its input initiates the injection of a fuel charge;

(b) placing said fuel injector in operative relation to the combustion chamber;

(c) selecting an electronically controlled three-way valve for selectively admitting fuel into said accumulator type fuel injector;

(d) coupling said valve to said injector;

(e) coupling a source of liquid fuel to said valve; and

(f) whenever it is desired to inject a fuel charge into the combustion chamber, applying an electronic control signal to said valve to open said valve a substantial portion of an engine cycle in advance of the time when injection is to commence; and

(g) immediately prior to the time when injection is to commence, terminating said control signal so as to close said valve to pressure and open it to vent;

whereby said accumulator type injector then causes the injection of the fuel charge into the combustion chamber to be initiated; the termination of injection of the fuel charge being controlled by said accumulator type fuel injector and not by said valve or said electronic control signal.

48. The method of claim 47 wherein the quantity of the fuel charge injected is controlled by adjusting the pressure of said fuel source.

49. The method of claim 47 wherein the quantity of the fuel charge injected is controlled by adjusting the interval of time during which said valve is open.

50. The method of claim 47, wherein the quantity of the fuel charge injected is controlled by adjusting both the pressure of said fuel source and the interval of time during which said valve is open.

51. The method of claim 47 wherein the quantity of the fuel charge injected is controlled either by adjusting the vent pressure or by adjusting the needle valve closing pressure.

52. The method of claim 47 which is applied to a multi-cylinder engine, wherein each accumulator type fuel injector is controlled by a respectively associated electronically controlled valve.

53. Apparatus for injecting fuel into a combustion chamber of an internal combustion engine, comprising, in combination:

(a) an accumulator type fuel injector having a fuel input, said fuel injector being positioned in operative relation to the combustion chamber and characterized by the fact that the withdrawal of pressure from its input initiates the injection of a fuel charge;

(b) an electronically controlled three-way solenoid valve having fuel supply and vent inputs, and a common port which is normally closed to supply and open to vent;

(c) means coupling said common port of said valve to said fuel input of said injector;

(d) a source of liquid fuel coupled to said fuel supply input of said valve;

(e) means for supplying energizing current to said solenoid valve a substantial portion of an engine cycle in advance of the time when injection is to commence, so as to open said common port to supply and close it to vent; and

(f) means for interrupting said energizing current immediately prior to the time when injection is to commence, thereby closing said valve to source pressure and opening it to vent so that said fuel injector then initiates the injection of the fuel charge;

the termination of injection of the fuel charge being controlled by said accumulator type fuel injector and not by said valve.

54. Apparatus as claimed in claim 53 which additionally includes a pressure intensifier coupled between said common port of said valve and said fuel input of said injector, whereby said accumulator injector becomes charged to a pressure level which is a multiple of the source pressure.

55. Apparatus as claimed in claim 53 wherein said common port of said valve is coupled directly to said input of said injector, whereby said accumulator injector becomes charged to a pressure level which approaches the source pressure.

56. The method of operating an internal combustion engine having a normal operating cycle during which a single fuel charge is injected once per cycle into each combustion chamber of the engine, comprising the steps of:

(a) generating a periodically repeated sequence of electronic timing signals;

(b) sensing the revolution of a revolving shaft of the engine;

(c) in response to the sensed shaft revolutions, synchronizing said sequence of electronic timing signals with a normal operating cycle of the engine;

(d) then utilizing said sequence of electronic timing signals to control both the injection of fuel charges into the combustion chambers of the engine, and the ignition of said fuel charges, so as to maintain said normal operating cycle of the engine;

(e) then altering said sequence of electronic timing signals so that individual injection and ignition cycles are selectively eliminated from the normal sequence of events to improve efficiency, and to control power, speed, torque impulses, exhaust emissions and other engine characteristics;

whereby it is possible to maintain substantially the same size of fuel charge supplied to each combustion chamber of the engine while decreasing the number and frequency of such fuel charges, thereby reducing the total fuel consumption of the engine while maintaining its combustion efficiency.

57. The method of claim 56 in which the fuel is injected into the intake port or other passage related to the combustion chamber.

58. Apparatus for injecting fuel into a combustion chamber of an internal combustion engine, comprising, in combination:

(a) an accumulator type fuel injector having a fuel input, said fuel injector being positioned in operative relation to the combustion chamber and characterized by the fact that the withdrawal of pressure from its input initiates the injection of a fuel charge;

(b) an electronically controlled three-way solenoid valve having fuel supply and vent inputs, and a common port which is normally closed to supply and open to vent.

(c) a source of liquid fuel at a predetermined common supply pressure, coupled to said fuel supply input of said valve;

(d) means coupling said common port of said valve directly to said fuel input of said injector;

(e) means for supplying energizing current to said solenoid valve a substantial portion of an engine cycle in advance of the time when injection is to commence, so as to open said common port to supply and close it to vent;

(f) means for interrupting said energizing current immediately prior to the time when injection is to commence, thereby closing said valve to source pressure and opening it to vent so that said fuel injector then initiates the injection of the fuel charge; and

(g) means for adjusting at least one of the pressure level of said common supply pressure, and the time interval during which said solenoid valve is open, in order to correspondingly adjust the magnitude of the fuel charge to be injected into said cylinder;

the termination of injection of the fuel charge being controlled by said accumulator type fuel injector and not by said valve, and the quantity of fuel to be injected being controlled by the peak pressure of the accumulator chamber and the inherent closing pressure of said accumulator type fuel injector.

59. Apparatus as in claim 58 wherein said solenoid valve is of the ball or poppet valve type.

60. Apparatus as in claim 58 wherein said solenoid valve includes:

a plunger, a first ball at the end of said plunger, a plunger extension, and a second ball at the end of said plunger extension;

each of said balls being captured for reciprocating movement to accomplish a valving action;

said inlet port communicating with one of said balls, said drain port communicating with the other of said balls, and said common outlet port being located intermediate to said balls and communicating with both of them.

61. The method of metering a fuel charge and injecting it into a combustion chamber of an internal combustion engine by:

(a) feeding fuel from a common rail source through a pathway controlled by a solenoid valve and through a check valve into an accumulator type fuel injector for a substantial portion of an engine cycle before the charge is to be injected;

(b) turning off the solenoid valve in order to close the pathway and discontinue the feed of fuel and concurrently initiate the injection of the fuel charge into the combustion chamber;

(c) continuing the fuel injection until the injection event is terminated by the spring closing action of the injector so that the quantity of the injected charge is determined by the rail pressure; and

(d) then adjusting the rail pressure in order to adjust the quantity of the next succeeding fuel charge.

62. The method of claim 61 wherein the fuel is fed directly through the solenoid valve to the check valve.

63. In a diesel fuel injection system, a unit injector assembly comprising, in combination:

a pressure intensifier having an intensifier piston, an input end with a low pressure chamber, and an output end with a high pressure chamber;

means for supplying liquid fuel from an adjustable common rail pressure source through a check valve to said high pressure chamber;

a three-way solenoid valve having a fuel inlet adapted to be coupled to said common rail pressure source, a common outlet coupled to said low pressure chamber of said intensifier, and a drain output, said solenoid valve normally being open to the drain output;

electrical control means for selectively energizing said solenoid valve so as to open said valve to its fuel inlet and close said valve to drain, and hence to apply pressure through said hydraulic intensifier to said high pressure chamber so that said fuel supply check valve becomes closed;

an accumulator type fuel injector having an accumulator chamber and an outlet valve;

a non-return valve coupling said high pressure chamber of said hydraulic intensifier to said accumulator chamber;

said electrical control means being operable for keeping said solenoid valve open throughout a time interval which is longer than the duration of an injection event, so that the fuel pressure in said high pressure chamber of said hydraulic intensifier increases exponentially towards a selected multiple of said common rail pressure, and is at the same time transmitted through said non-return valve into said accumulator injector; and

said electrical control means also being operable, whenever a fuel charge is to be injected, for closing said solenoid valve to inlet and opening it to drain, thereby reversing the direction of said intensifier piston, relieving the pressure in said high pressure chamber, and causing said non-return valve to close;

whereby said outlet valve opens and the injection of the fuel charge is then initiated by said accumulator injector and continues until terminated by the spring closing action of the injector, with the result that the mass of the injected fuel charge bears a linear relationship to the then existing pressure level of said common rail pressure.

64. The method of metering fuel charges and injecting them into a plurality of combustion chambers of an engine by

(a) providing fuel from a common rail source,

(b) for each combustion chamber, transferring fuel from the common rail source under control of a separate solenoid valve through a separate pressure intensifier and a separate check valve into a separate accumulator type fuel injector,

(c) selectively turning each solenoid valve off in order to isolate the associated accumulator type injector from the common rail source and thereby initiate the injection of a fuel charge into the associated cylinder, and

(d) adjusting the common rail source pressure from time to time so as to change the fuel charge quantities being injected into all the combustion chambers in linear relationship to said common rail source pressure.

65. The method of metering a fuel charge and injecting it into a combustion chamber of an internal combustion engine by:

(a) feeding fuel from a common rail source through a pathway including a pressure intensifier that is controlled by a solenoid valve and through a check valve into an accumulator type fuel injector for a substantial portion of an engine cycle before the charge is to be injected;

(b) turning off the soleoid valve in order to close said pathway and discontinue the infeed of fuel and concurrently initiate the injection of the fuel charge into the combustion chamber;

(c) continuing the fuel injection until the injection event is terminated by the spring closing action of the injector so that the quantity of the injected charge is determined by the rail pressure; and

(d) then adjusting the rail pressure in order to adjust the quantity of the next succeeding fuel charge.

66. The method of claim 65 wherein the pressure intensifier utilizes a piston, and the turning off of the solenoid valve reverses the direction of travel of the piston so as to close the check valve.

67. A pressure-metered fuel injection method comprising the steps of

(a) selecting microprocessor means for controlling liquid pressure level,

(b) selecting a liquid fuel source having a controllable pressure level that is controllable by said microprocessor means,

(b) (c) supplying liquid fuel from said source through a fluid pathway and a non-return valve to an accumulator injector,

(c) (d) under control of the source pressure, allowing fuel to flow through said pathway and through the non-return valve into the accumulator injector throughout a time interval which is of sufficient duration that the fuel pressure inside the accumulator injector then becomes essentially a function of the source pressure rather than of the parameters of the pathway,

(d) (e) then closing off and venting the pathway so that the non-return valve closes, and the injector injects a fuel charge whose mass is linearly related to the source pressure, and

(e) (f) thereafter adjusting the source pressure by said microprocessor means so as to adjust the mass of the next succeeding fuel charge charges.

68. The method of operating an internal combustion engine having a plurality of combustion chambers, comprising the steps of:

(a) generating a sequence of electronic timing signals to provide a timing cycle,

(b) acquiring an electrical signal from a shaft of the engine for synchronizing the sequence of timing signals with the engine operation,

(c) during each sequence, applying one of the timing signals to a unit injector assembly associated with each of the combustion chambers for initiating the injection of fuel into the associated chamber,

(d) continuously repeating the sequence of electronic timing signals so as to operate the engine through successive firing cycles, and

(e) then modifying the repetition of the sequence of timing signals so as to selectively eliminate selected firing cycles of the engine.