Exhaust gas purification system of internal combustion engine

Abstract

A system for purifying exhaust gas generated by an internal combustion engine including a bypass branching out from the exhaust pipe downstream of a catalyst and merging to the exhaust pipe, an adsorber installed in the bypass, a bypass valve member which closes the bypass, and an egr conduit connected to the bypass at one end and connected to the air intake system for recirculating the exhaust gas to the air intake system. The bypass valve member is opened for a period after engine startup to introduce the exhaust gas such that the adsorber installed in the bypass adsorbs the unburnt HC component in the exhaust gas. The adsorber adsorbs the HC component when the exhaust temperature rises and the adsorbed component is recirculated to the air intake system through the egr conduit. In the system, the bypass valve is provided at or close to the branching point in the exhaust pipe and a chamber is provided close to the branching point such that the conduit is connected to the bypass at the one end in the chamber. The bypass valve member is combined with an exhaust pipe valve member as a combination valve such that when the bypass valve member closes the bypass, the exhaust pipe valve member opens the exhaust pipe. With the arrangement, the system can effectively prevent the exhaust pipe from being clogged even when a valve for closing a bypass is stuck in the closed position. At the same time, the system can provide a relatively short egr conduit for recirculating unburnt HC component adsorbed from the adsorber and the adsorption and desorption are conducted optimally. A system for purifying exhaust gas generated by an internal combustion engine including a bypass branching out from the exhaust pipe downstream of a catalyst and merging to the exhaust pipe, an adsorber installed in the bypass, a bypass valve member which closes the bypass, and an egr conduit connected to the bypass at one end and connected to the air intake system for recirculating the exhaust gas to the air intake system. The adsorber adsorbs the HC component in the exhaust gas when the exhaust gas temperature rises and the adsorbed component is recirculated to the air intake system through the egr conduit. The bypass valve member is combined with an exhaust pipe vale member as a combination valve such that when the bypass valve member closes the bypass, the exhaust pipe valve member opens the exhaust pipe.

Description

B(Z⁻¹)=b₀+b₁z⁻¹+ . . . +b_mz^−m  Eq. 2

$\begin{array}{cc}\begin{array}{c}{\hat{\theta }}^T\left(k\right)=\left[{\hat{b}}_0\left(k\right),{\hat{B}}_R\left(z^{-1},k\right)\widehat{,S}\left(z^{-1},k\right)\right]\\ =\left[{\hat{b}}_0\left(k\right),\hat{r}1\left(k\right),\dots ,r_{m+d-1}\left(k\right),s_0\left(k\right),\dots ,s_{n-1}\left(k\right)\right]\\ =\left[b_0\left(k\right),r_1\left(k\right),r_2\left(k\right),r_3\left(k\right),s_0\left(k\right)\right]\end{array}& \mathrm{Eq}.3\end{array}$

$\begin{array}{cc}\begin{array}{c}{\zeta }^T\left(k\right)=\left[u\left(k\right),\dots ,u\left(k-m-d+1\right),y\left(k\right),\dots ,y\left(k-n+1\right)\right]\\ =\left[u\left(k\right),u\left(k-1\right),u\left(k-2\right),u\left(k-3\right),y\left(k\right)\right]\end{array}& \mathrm{Eq}.4\end{array}$

In the above, the adaptive parameters {circumflex over (θ)} comprises the elements of a scalar quantity {circumflex over (b)}_o⁻¹(k) that determines the gain, an element {circumflex over (B)}_R(Z⁻¹, k) that is expressed by the manipulated variable and an element Ŝ(Z⁻¹, k).

The adaptation mechanism estimates or identifies these elements and outputs to the STR controller as the adaptive parameters {circumflex over (θ)}(shown in Eq. 3). Specifically, the adaptation mechanism calculates the adaptive parameters {circumflex over (θ)} using the manipulated variable u(i) input to the controlled object (plant) and the controlled variable y(j) output from the controlled object such that the error between the desired value and the controlled variable becomes zero. (Here, i, j include past values).

Specifically, the adaptive parameters {circumflex over (θ)} are calculated in accordance with an equation shown in Eq. 5 below.
{circumflex over (θ)}(k)={circumflex over (θ)}(k−1)+Γ(k−1)ζ(k−d)e*(k)  Eq. 5

In Eq. 5, Γ(k) is a gain matrix that is (m+n+d)th order square matrix and determines the estimation/identification speed of the adaptive parameters {circumflex over (θ)}, and e*(k) is an error signal indicative of the generalized estimation/identification error, i.e., an estimation error signal of the adaptive parameters. The feedback correction coefficient KSTR(k) is calculated in accordance with an equation shown in Eq. 6.

$\begin{array}{cc}\text{KSTR(k)}=\frac{\begin{array}{c}\mathrm{KCMD}\left(k-d^{\prime }\right)-s_0\times y\left(k\right)-r_1\times \mathrm{KSTR}\left(k-1\right)-\\ r_2\times \mathrm{KSTR}\left(k-2\right)-r_3\times \mathrm{KSTR}\left(k-3\right)\end{array}}{b_0}& \mathrm{Eq}.6\end{array}$

Based on the above, the calculation or determination of the EGR correction coefficient KEGRN will be explained. Since, however, this is also described in U.S. Pat. No. 5,657,736, the description will be short.

First, the EGR rate is estimated. The rate is defined as a ratio in volume or weight of the exhaust gas relative to the intake air.

It can be assumed that the amount of gas passing through the EGR control valve 84 is determined from the valve opening area (the amount of valve lifting) and the ratio between the upstream pressure and downstream pressure of the valve 84. It can also be assumed that the EGR rate under a steady-state is a value when the amount of actual valve lifting is equal to the valve lifting command value, while the EGR rate under transient-state is a value when the amount of actual valve lifting is not equal to the valve lifting command value.

Thus, it is assumed to be possible to estimate the EGR rate (more precisely, the net EGR rate supplied to the engine cylinder) by multiplying the steady-state EGR rate by the ratio between the gas flow rates under the steady-state and the transient-state as:

• • net EGR rate=(steady-state EGR rate)×{ (gas flow rate QACT determined by actual valve lifting amount and the ratio between upstream pressure and downstream pressure of the valve)/(gas flow rate QCMD determined by command value and the ratio between upstream pressure and downstream pressure of the valve)}

Here, the steady-state EGR rate is calculated by determining a correction coefficient under a steady-state and subtracting the same from 1.0. Namely, calling the correction coefficient under a steady-state KEGRMAP, the steady-state EGR rate can be calculated as follows.

Steady-state EGR rate=(1−KEGRMAP)

The steady-state EGR rate and the correction coefficient under a steady-state are sometimes referred to as the “basic EGR rate” and “basic correction coefficient”, respectively. In addition, as mentioned before, in order to distinguish from the EGR rate under a steady state, the EGR rate is sometimes referred to as the “net EGR rate”.

The EGR control is conducted by determining a command value of the EGR control valve lifting amount on the basis of the engine speed and engine load, etc., and the actual behavior of the EGR control valve lags behind the issued command value. There is a response delay between the actual valve lifting and issuing the command value to do so. Moreover, it takes additional time for the exhaust gas passing through the valve to enter the combustion chamber. Therefore, it is assumed that the exhaust gas passing through the valve remains for a while in a space (chamber) before the combustion chamber and after a pause, i.e., the dead time, will enter the combustion chamber at one time. Accordingly, the net EGR rate is consecutively estimated and is stored in the memory each time the program is activated. Among the stored net EGR rates, one estimated at a previous control cycle corresponding to the delay time is selected and is deemed to be the true net EGR rate.

The above will be explained with reference to the flow chart of FIG. 12. The program is activated at every TDC crank angular position.

The program begins at S200 in which the engine speed Ne, the manifold pressure Pb, the atmospheric pressure Pa, and the actual valve lifting amount named LACT (the stroke of the valve 84 detected by the sensor 123) are read, and proceeds to S202 in which the command value for valve lifting amount LCMD is retrieved from mapped data using the engine speed Ne and the manifold pressure Pb as address data. Like the aforesaid correction coefficient, the mapped data for the command value LCMD is predetermined with respect to the same parameters. The program then moves to S204 in which the basic EGR rate correction coefficient KEGRMAP is retrieved from the mapped data at least using the engine speed Ne and the manifold pressure Pb.

The program then advances to S206 in which it is confirmed that the actual valve lifting amount LACT is not zero, namely it is confirmed that the EGR control valve 84 is opened, and to S208 in which the retrieved command value LCMD is compared with a predetermined lower limit LCMDLL (a least value) to determine whether the retrieved command value is less than the lower limit. When S208 finds that the retrieved command value is not less than the lower limit, the program proceeds to S210 in which the ratio Pb/Pa between the manifold pressure Pb and the atmospheric pressure Pa is calculated and using the calculated ratio and the retrieved command value LCMD, the gas flow rate QCMD corresponding thereto is retrieved from mapped data which has been prepared in advance. The gas flow rate is that mentioned in the equation as “gas flow rate QCMD determined by the command value and the ratio between upstream pressure and downstream pressure of the valve”.

The program then proceeds to S212 in which the gas flow rate QACT is retrieved from mapped data prepared in advance. This corresponds to the term in the equation “gas flow rate QACT determined by actual valve lifting amount and the ratio between upstream pressure and downstream pressure of the valve”. The program then proceeds to S214 in which the retrieved EGR rate correction coefficient KEGRMAP is subtracted from 1.0 and the difference resulting therefrom is deemed as the steady-state EGR rate (basic EGR rate or steady-state EGR rate). The steady-state EGR rate means the EGR rate under which EGR operation is in a stable state, i.e., the EGR operation is not under a transient condition, such as when the operation is being started or terminated.

The program then moves to S216 in which the net exhaust gas recirculation rate is calculated by multiplying the steady-state EGR rate by the ratio QACT/QCMD, and to S218 in which a fuel injection correction coefficient KEGRN is calculated.

FIG. 13 is a flow chart showing the subroutine for calculating the coefficient KEGRN.

In S300 in the flow chart, the net EGR rate (that is obtained at S216 of FIG. 12) is subtracted from 1.0 and the difference resulting therefrom is deemed to be the fuel injection correction coefficient KEGRN. The program then proceeds to S302 in which the calculated coefficient KEGRN is stored in a ring buffer prepared in the ROM 84.

FIG. 14 shows the configuration of the ring buffer. As illustrated, the ring buffer has n addresses which are numbered from 1 to n and are so identified. Each time the programs of the flow charts of FIGS. 12 and 13 are activated at respective TDC positions and the fuel injection correction coefficient KEGRN is calculated, the calculated coefficient KEGRN is consecutively stored in the ring buffer from the top.

In the flow chart of FIG. 13, the program then proceeds to S304 in which the delay time τ is retrieved from mapped data using the engine speed Ne and the engine load with the manifold pressure Pb as address data. FIG. 15 shows the characteristics of the mapped data. Namely, the delay time τ indicates a dead time during which the gas passing through the valve remains in the space before the combustion chamber. Since the dead time varies with engine operating conditions including the engine speed and the engine load, the delay time is set to vary with the parameters. Here, the delay time τ is set as the ring buffer number.

The program then moves to S306 in which one from among the stored fuel injection correction coefficients KEGRN corresponding to the retrieved delay time τ (ring buffer number) is read and is determined to be the correction coefficient KEGRN at the current control cycle. Explaining this in reference to FIG. 16, when the current control cycle (or period) is at A, the coefficient calculated 12 control cycles earlier is, for example, selected as the coefficient to be used in the current control cycle.

Again returning to FIG. 12, when S206 finds that the actual valve lifting amount LACT is zero, this means that no EGR operation is carried out. However, as the correction coefficient KEGRN at this time will be a candidate at the selection in a later control cycle, the program proceeds to S214 and on to calculate the net EGR rate and the correction coefficient KEGRN. In such a case, specifically, the net EGR rate is calculated as 0 at S216 and the fuel injection correction coefficient KEGRN is calculated as 1.0 at S300 in FIG. 13.

When it is found in S208 that the command value for valve lifting amount LCMD is less than the lower limit LCMDLL, the program proceeds to S222 in which the command value LCMDk−1 from the last control cycle k−1 is used.

This is because, when the command value for valve lifting amount LCMD is made zero in order to terminate the EGR operation, the actual valve lifting amount LACT does not immediately become zero due to the delay in valve response. Therefore, when the command value LCMD is less than the lower limit, the previous value LCMDk−1 is kept until S206 finds that the actual valve lifting amount LACT has become zero.

Moreover, when the command value LCMD is less than the lower limit LCMDLL, the command value may occasionally be zero. If this happens, the gas flow rate QCMD retrieved at S210 becomes zero and as a result, division by zero would occur at the calculation in step S216, making the calculation impossible. Since, however, the previous value is kept in S222, the calculation can be successfully carried out in S216.

The program then proceeds to S224 in which the basic correction coefficient KEGRMAPk−1 retrieved at the last control cycle is again used in the current control cycle. This is because, under such engine operating conditions that the command value LCMD retrieved in S202 is found to be less than the lower limit LCMDLL, the basic EGR rate correction coefficient KEGRMAP retrieved in step S14 will be 1.0 based on the characteristics of the mapped data. As a result, there is the possibility that the steady-state EGR rate is determined to be 0 in S204. The retaining of the last value in S224 aims to avoid this.

The EGR correction coefficient KEGRN is included in KTOTAL as mentioned above with reference to FIG. 10 and is used to determine the quantity of fuel injection. Since the air/fuel ratio is accurately converged to the desired value using the correction coefficient in response to the EGR rate and the correction coefficient determined by the adaptive controller, it becomes possible to recirculate the unburnt HC component to the air intake system at any time during the EGR operation, thereby improving the purification efficiency of the system.

With the arrangement, the system can effectively prevent the exhaust pipe from being clogged even when a valve for closing a bypass is stuck in the closed position, and can provide a relatively short EGR conduit for recirculating unburnt HC component adsorbed from the adsorber. Also, the adsorption and desorption are conducted optimally.

FIG. 17 is a view, similar to FIG. 1, but shows the exhaust gas purification system of an internal combustion engine according to a second embodiment of the invention.

Explaining the system according to the second embodiment, the chamber 52 is elongated compared to the one of the first embodiment, and the adsorber 74 is carried on four beds and is housed in the chamber 52. In the second embodiment, thus, the amount of adsorber 74 is increased and hence, the capacity to adsorb the HC component is increased. In the second embodiment and thereafter, the same reference numeral indicates the same member in the first embodiment.

FIG. 18 is a cross-sectional view taken along XVIII-XVIII of FIG. 17. As illustrated, the chamber 52 is almost rectangular in cross section. The adsorber 74 is positioned, not around the exhaust pipe 38, but is situated close to the exhaust pipe 38 so as to receive heat that will expedite the desorption.

In the second embodiment, the exhaust gas flows, as indicated by arrows in FIG. 17, to the bypass 56 when the bypass valve member 60 is opened and the exhaust pipe valve member 58 is closed. Except for the fact that the amount of adsorber 74 is increased and hence, the capacity to adsorb the unburnt HC component is increased, the configuration, the operation, as well as the advantages are the same as that of the first embodiment.

FIG. 19 is a partial cross-sectional plan view of the exhaust pipe 38 schematically showing the exhaust gas purification system according to a third embodiment of the invention.

Explaining this while putting an emphasis on the difference from the foregoing embodiments, the chamber 52 is further enlarged to house the adsorber 74 carried on six beds (which is illustrated schematically for ease of understanding). In the third embodiment, the exhaust pipe 38 is staggered in the chamber 52 such that the adsorber 74 are housed or held in the recess or curved portion (viewing from the top) so as to expedite heating. In the third embodiment, the exhaust gas flows to the bypass 56 as shown by arrows in the figure when the bypass valve member 60 is opened while the exhaust pipe valve 58 is closed. Except for the fact that the amount of adsorber 74 is further increased and hence, the capacity to adsorb the unburnt of HC component is further increased, the configuration, the operation, as well as the advantages are the same as that of the first embodiment.

FIG. 20 is a view, similar to FIG. 4, but showing the exhaust gas purification system of an internal combustion engine according to a fourth embodiment of the invention.

In the fourth embodiment, a time or period for opening the bypass valve member 60 during engine starting is determined in accordance with a parameter relating to the volume or amount of exhaust gas.

Explaining the flow chart, the program begins at S400 in which it is determined whether the engine is starting using the manner mentioned above. When the result is affirmative, the program proceeds to S402 in which the output quantity of fuel injection Tout (mentioned with reference to FIGS. 10 and 11) is read, to S404 in which the bit of a flag FTRPV is set to 1, to S406 in which TPRV 68 is made ON to open the bypass valve member 60, and is terminated.

In a next loop, when the result is again affirmative, the program again proceeds to S402 in which Tout is newly react and is added to the value read in the preceding program loop, to S404 and S406 in which the flag bit is kept to 1 and the valve is kept opened (if not, it is set to 1 or opened), and is terminated. In the flow chart, setting the flag bit to 1 indicates reading and adding of Tout and making the valve 68 ON, while resetting the flag bit to 0 indicates discontinuation or termination thereof.

When the result in S400 is negative in the next or later loop, the program proceeds to S408 in which it is determined whether the flag bit is set to 1. When the result is affirmative, the program proceeds to S410 in which an accumulated value ΣTout of the read output quantity of fuel Tout is calculated. The accumulated value is thus a value accumulated since engine starting (since the flag bit was set to 1).

The program proceeds to S412 in which it is determined whether the accumulated value ΣTout is not less than a predetermined value ToutLMT. ToutLMT is a value corresponding to an upper limit of an accumulated volume or amount of exhaust gas. In the fourth embodiment, the limit of adsorption is determined based on a parameter relating to the volume or amount of exhaust gas (i.e., the accumulated value of the quantity of fuel injection). This is contrast to the first embodiment in which the limit of adsorption is determined based on a parameter relating to the catalyst temperature (i.e., the coolant temperature Tw).

The reason why the accumulated value of the quantity of fuel injection Tout is used as the parameter relating to the volume or amount of exhaust gas, is that, since the quantity of fuel injection Tout is determined such that the air/fuel ratio with respect to the quantity or amount of intake air becomes a predetermined air/fuel ratio (in the embodiment, the stoichiometric air/fuel ratio) and since the quantity or amount of intake air is proportional to the volume or amount of exhaust gas, the accumulated value of the quantity of fuel injection is equivalent to the accumulated value of the volume or amount of exhaust gas. If the desired air/fuel ratio KCMD is changed, the accumulated quantity of fuel injection should be corrected in response to the change of the desired air/fuel ratio.

The upper limit ToutLMT is determined on the basis of the adsorption ability of the adsorber 74, more precisely is determined on the basis of the critical adsorption ability and the volume or amount of the adsorber 74. The critical capacity that the adsorber 74 can adsorb the unburnt HC component is decided, irrespective of the temperature, from its mechanical and chemical limits. The upper limit ToutLMT is a value corresponding to this critical capacity.

Again explaining the flow chart of FIG. 20, when the result in S412 is negative, in other words, when it is determined that the accumulated value has not reached the upper limit, the program proceeds to S414 in which it is determined whether the engine load is high using the same manner mentioned in the first embodiment. When the result in S414 is negative, the program proceeds to S416 in which it is determined whether it is in any failsafe condition as done in the first embodiment. When the result in S416 is negative, the program proceeds to S406 in which the TRPV 68 is made ON or kept ON if it has previously been made ON.

On the other hand, when the result in S408 is negative, the program proceeds to S418 in which TRPV 68 is made OFF. When the result in S412, or S414, or S416 is affirmative, the program proceeds to S420 in which the bit of the flag is reset to zero, and to S418 in which TRPV 68 is made OFF.

In the fourth embodiment, since the adsorption limit of the adsorber 74, in other words, the period during which the bypass valve member 60 is kept open is determined based on the parameter relating to the volume or amount of exhaust gas, the system has the same advantages as those mentioned in the first embodiment. The rest of the configuration is the same as that of the first embodiment.

In the fourth embodiment, it is alternatively possible to correct the upper limit ToutLMT as the increase of the catalyst temperature (or the coolant temperature Tw). If the degradation or deterioration of the adsorber is detected, it is alternatively possible to correct the limit in response to the adsorber degradation.

It is alternatively possible to detect the quantity or amount of intake air by an air flow meter and to determine the time or period by an accumulated value of the detected quantity or amount of intake air. It is alternatively possible to accumulate, instead of the output quantity of fuel injection, the basic quantity of fuel injection TiM-F.

Thus, the embodiments are configured such that the system for purifying exhaust gas generated by an internal combustion engine (10) having an air intake system (air intake pipe 12) and an exhaust system which includes an exhaust pipe (38) extending from an exhaust manifold (36) of the engine and a catalyst (40, 42, 44) installed in the exhaust pipe, the exhaust system exhausting gas generated by the engine to the atmosphere, including a bypass (56) branching out from the exhaust pipe (38) at a location (fork 54) downstream of the catalyst and merging to the exhaust pipe downstream (confluence point 78) of the branching point (fork 54); an adsorber (74) installed in the bypass; a valve means (bypass valve member 60) which closes the bypass (56); a conduit (EGR conduit 82) connected to the bypass (38) at one end and connected to the air intake system (air intake pipe 12) for recirculating the exhaust gas to the air intake system; valve control means (ECU 86) which opens the valve means (bypass valve member 60) for a period (TTRSLMT, ToutLMT) after the startup of the engine to introduce the exhaust gas to the bypass (56) such that the adsorber (74) installed in the bypass adsorbs the unburnt component in the exhaust gas; an EGR control means (ECU 86) which causes the exhaust gas introduced in the bypass to be recirculated to the air intake system through the conduit (EGR conduit 83). In the system, the valve means (bypass valve member 60) is provided at or close to the branching point (fork 54) in the exhaust pipe (38), a chamber (52) is provided close to the branching point (fork 54) such that the conduit (EGR conduit 82) is connected to the bypass at one end in the chamber.

It should be noted in the above that the description saying that “a chamber (52) is provided close to the branching point (fork 54) such that the conduit (EGR conduit 82) is connected to the bypass at one end in the chamber” means that the conduit 82 is connected upstream of the adsorber 84 in terms of exhaust gas flow, or is connected downstream of the adsorber 84 in terms of recirucluated exhaust gas flow.

It should also be noted that the description saying that “for a period (TTRSLMT, ToutLMT) after the startup of the engine”, means for a period after the startup of the engine and a period until a negative pressure is generated to drive the valve means to open when the valve means is operated by the negative pressure.

With the arrangement, the system can effectively prevent the exhaust pipe from being clogged even when a valve for closing a bypass is stuck in the closed position, and can provide a relatively short EGR conduit for recirculating unburnt HC component adsorbed from the adsorber. Also, the adsorption and desorption are conducted optimally.

It is alternatively possible to combine the fourth embodiment into the first embodiment such that the time or period is determined from the accumulated value of fuel injection amount and the catalyst (coolant) temperature.

In the first to fourth embodiments, while the ignition timing retard is used for expedite the catalyst activation, it is one example and should not be limited thereto.

In the first to fourth embodiments, it is alternatively possible to utilize an electric actuator to operate the exhaust pipe valve member and the bypass valve member.

In the first to fourth embodiments, it is alternatively possible to use an adsorber made from activated charcoal.

While the invention has thus been shown and described with reference to specific embodiments, it should be noted that the invention is in no way limited to the details of the described arrangements but changes and modifications may be made without departing from the scope of the appended claims.

Claims

1. A system for purifying exhaust gas generated by an internal combustion engine having an air intake system and an exhaust system which includes an exhaust pipe extending from an exhaust manifold of the engine and a catalyst installed in the exhaust pipe, the exhaust system exhausting gas generated by the engine to the atmosphere, including comprising:

a bypass branching out from the exhaust pipe at a location downstream of the catalyst and merging to the exhaust pipe downstream of the branching point;

an adsorber installed in the bypass;

a valve means which closes the bypass;

a conduit connected to the bypass at one end a location between the valve means and the adsorber and connected to the air intake system for recirculating the exhaust gas to the air intake system;

valve control means which opens operates the valve means to open the bypass for a period since starting of the engine to introduce the exhaust gas to the bypass such that the adsorber installed in the bypass adsorbs the unburnt component in the exhaust gas and then closes the valve means to recirculate the adsorbed unburnt component through the conduit with the exhaust gas after having desorbed from the adsorber; and

an egr control means which causes the exhaust gas introduced in the bypass to be recirculated to the air intake system through the conduit;

wherein the improvement comprises:

the valve means is provided adjacent the branching point in the exhaust pipe; and

a chamber is provided surrounding the branching point such that the conduit is connected to the bypass at one end in the chamber fuel injection quantity determining means for determining a quantity of fuel injection to be supplied to the engine;

air/fuel ratio detecting means for detecting an air/fuel ratio of the exhaust gas;

feedback loop means having an adaptive controller with an adaptive mechanism that estimates an adaptive parameter based on past values of a feedback correction coefficient and the detected air/fuel ratio, the adaptive controller calculating the feedback correction coefficient based on the estimated adaptive parameter such that the detected air/fuel ratio converges to a desired air/fuel ratio;

egr correction coefficient calculating means for calculating an egr correction coefficient when recirculating the exhaust gas to the air intake system; and

fuel injection quantity correcting means for correcting the quantity of fuel injection based on at least the feedback correction coefficient and the egr correction coefficient.

2. A system according to claim 1, wherein the chamber encloses a part of the exhaust pipe such that the part of the exhaust pipe is close to the adsorber.

3. A system according to claim 1, wherein the chamber encloses a part of the exhaust pipe at the branching point and the valve means.

4. A system according to claim 2, wherein the chamber encloses a part of the exhaust pipe at the branching point and the valve means.

5. A system according to claim 1, further including a combination valve comprised of the valve means which closes the bypass and a second valve means which closes the exhaust pipe, the valve means and the second valve means being connected to a shaft such that when the valve means closes the bypass, the second valve opens the exhaust pipe.

6. A system according to claim 2, further including a combination valve comprised of the valve means which closes the bypass and a second valve means which closes the exhaust pipe, the valve means and the second valve means being connected to a shaft such that when the valve means closes the bypass, the second valve opens the exhaust pipe.

7. A system according to claim 1, wherein the valve control means including;

catalyst temperature parameter detecting means for detecting a parameter relating to a temperature of the catalyst;

and determines a the period based on the detected parameter.

8. A system according to claim 7, wherein the valve control means decreases the period with increasing temperature of the catalyst.

9. A system according to claim 7, wherein the valve control means decreases the period when the engine is under high load.

10. A system according to claim 7, wherein the valve control means decreases the period when the engine is in a failsafe condition.

11. A system according to claim 7, wherein the parameter is a coolant temperature of the engine.

12. A system according to claim 11, wherein the valve control means decreases the period with increasing temperature of the catalyst engine.

13. A system according to claim 11, wherein the valve control means decreases the period when the engine is under high load.

14. A system according to claim 11, wherein the valve control means decreases the period when the engine is in a failsafe condition.

15. A system according to claim 1, wherein the valve control means including;

exhaust gas volume parameter detecting means for detecting a parameter relating to a volume of the exhaust gas;

and determines a period based on the detected parameter.

16. A system according to claim 15, wherein the valve control means decreases the period when the engine is under high load.

17. A system according to claim 15, wherein the valve control means decreases the period when the engine is in a failsafe condition.

18. A system according to claim 15, wherein the parameter is a quantity of fuel injection to be supplied to the engine.

19. A system according to claim 18, wherein the valve control means decreases the period when the engine is under high load.

20. A system according to claim 18, wherein the valve control means decreases the period when the engine is in a failsafe condition.

21. A system according to claim 1, further including:

catalyst activation promoting means for promoting activation of the catalyst when the engine is started.

22. A system according to claim 21, wherein the catalyst activation promoting means comprising an ignition timing control means which retards an ignition timing supplied to the engine.

23. A system according to claim 22, wherein the ignition timing means discontinues to retard the ignition timing under a specific engine operating condition.

24. A system according to claim 1, wherein the egr control means including;

fuel injection quantity determining means for determining a quantity of fuel injection to be supplied to the engine;

air/fuel ratio detecting means for detecting an air/fuel ratio of the exhaust gas;

a feedback loop means having a controller which calculates a feedback correction coefficient using a control law expressed in a recursion formula such that the detected air/fuel ratio converges to a desired air/fuel ratio;

egr correction coefficient calculating means for calculating an egr correction coefficient when recirculating the exhaust gas to the air intake system;

fuel injection quantity correcting means for correcting the quantity of fuel injection based on at least the feedback correction coefficient and the egr correction coefficient.