Attitude sensing system for an automotive vehicle relative to the road

Abstract

A stability control system (18) for an automotive vehicle includes a plurality of sensors (28-39) sensing the dynamic conditions of the vehicle. The sensors may include a speed sensor (20), a lateral acceleration sensor (32), a roll rate sensor (34), a yaw rate sensor (20) and a longitudinal acceleration sensor (36). The controller (26) is coupled to the speed sensor (20), the lateral acceleration sensor (32), the roll rate sensor (34), the yaw rate sensor (28) and a longitudinal acceleration sensor (36). The controller (26) determines a global roll attitude and a global pitch attitude from the roll rate, lateral acceleration signal and the longitudinal acceleration signal. The controller determines a roll gradient based upon a past raw roll rate and current raw roll rate, the roll angular rate signal and the lateral acceleration signal, a pitch gradient based upon a past raw pitch rate and current raw pitch rate the calculated pitch angular rate signal and the longitudinal acceleration signal. The controller determines a relative roll and relative pitch as a function of the roll gradient and the pitch gradient.

Description

TECHNICAL FIELD

The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for controlling the system of the vehicle by determining attitude of the vehicle.

BACKGROUND

Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.

In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.

There are two types of vehicle attitudes needed to be distinguished. One is the so-called global attitude, which is sensed by the angular rate sensors. The other is the relative attitude, which measures the relative angular positions of the vehicle with respect to the road surface on which the vehicle is driven. The global attitude of the vehicle is relative to an earth frame (or called the inertia frame), sea level, or a flat road. It can be directly related to the three angular rate gyro sensors. While the relative attitude of the vehicle measures the relative angular positions of the vehicle with respect to the road surface, which are always of various terrains. Unlike the global attitude, there are no gyro-type sensors which can be directly related to the relative attitude. A reasonable estimate is that a successful relative attitude sensing system must utilize both the gyro-type sensors (when the road becomes flat, the relative attitude sensing system recovers the global attitude) and some other sensor signals.

One reason to distinguish relative and global attitude is due to the fact that vehicles are usually driven on a 3-dimensional road surface of different terrains, not always on a flat road surface. Driving on a road surface with large road bank does increase the rollover tendency, i.e., a large output from the global attitude sensing system might well imply an uncontrollable rollover event regardless of the flat road driving and the 3-D road driving. However driving on a three-dimensional road with moderate road bank angle, the global attitude may not be able to provide enough fidelity for a rollover event to be distinguished. Vehicular rollover happens when one side of the vehicle is lifted from the road surface with a long duration of time without returning back. If a vehicle is driven on a banked road, the global attitude sensing system will pick up certain attitude information even when the vehicle does not experience any wheel lifting (four wheels are always contacting the road surface). Hence a measure of the relative angular positions of the vehicle with respect to the portion of the road surface on which the vehicle is driven provides more fidelity than global attitude to sense the rollover event.

The vehicle rollover sensing system used for deploying safety-related devices has been proposed in U.S. Pat. Nos. 6,002,975, 6,038,495, EP 1002709A2, where a stand-alone sensor module including 5 sensors are used including the roll/pitch angular rate sensors, later/longitudinal/vertical acceleration sensors. These systems sense the global attitude of a vehicle without considering the relative attitude of the vehicle with respect to the road surfaces. Due to the stand-alone nature of the sensing module, it does not share internal information with vehicle dynamics control systems.

The rollover control system using brake controls has been proposed in U.S. Pat. No. 6,065,558 (“Anti-Rollover Brake System”), where the claimed sensor setting could be any of the following: (1) a lateral accelerometer; (2) a sensor for measuring the body roll angle; (3) an accelerometer, a gyroscope, a roll rate senor, and sensors measuring the distances between the vehicle and the wheels to measure the roll angle of the vehicle. In the current invention, a different sensor set is used. The used sensors includes those used in the vehicle yaw stability control (lateral/longitudinal accelerometers, yaw angular rate sensor, wheel speeds and steering angle) and an extra roll rate angular sensor. Also, notice that U.S. Pat. No. 6,065,558 does not intend to distinguish between global and relative attitude of a vehicle reflected by the Euler angles.

Another vehicle attitude sensing method has been proposed in U.S. Pat. No. 5,408,411 (“System For Predicting Behavior Of Automotive Vehicle And For Controlling Vehicular Behavior Based Thereon”). Where a sensor module using six linear accelerations is mounted on the vehicle to get vehicular attitude information.

It would therefore be desirable to provide an attitude control system to predict attitude angle for vehicle dynamics control that includes the interdependency among the roll, pitch and yaw motions while compensating for long term maneuvers.

SUMMARY OF THE INVENTION

The present invention aims to estimate and predict the vehicular attitude used in a rollover control system which can prevent the vehicle from rolling over. The estimate and predicted variables are used for setting a rollover control action flag and as the feedback signals to construct the desired control forces for controlling roll stability or activate other safety devices. In detail, the rollover control action needs the information from the vehicle attitude sensing system, the available sensors, and the driving/road condition identifiers. The rollover control flag is set based on a rollover logic process. In case a positive determination of vehicle rollover is deemed from this rollover logic process, the control commands will be computed by feeding back the estimated vehicle attitude variables. The control command output is further sent to the ECU of the hardware to activate the system. In detail, the vehicle attitude sensing system uses all the sensors available for yaw stability control (including a Do

Let l be the half of the wheel track; t_f and t_r be the distances from the center of gravity of the car body to the front and rear axles; h be the distance between the bottom of the vehicle body and the center of gravity of the vehicle along the body z-axis; θ_xbr and θ_ybr are the relative roll and pitch angles. Then in the body frame the four corners of the vehicle body where suspensions are connected with the wheel have the following coordination:
LF Corner: x=t_f, y=l, z=−h
RF Corner: x=t_f, y=−l, z=−h
LR Corner: x=−t_r, y=l, z=−h
RR Corner: x=−t_r, y=−l, z=−h  (2)

Let z_lf,z_rf,z_lr and z_rr be the relative displacements of the vehicle corners at the left-front, right-front, left-rear and right-rear locations, which are measured along the direction perpendicular to the average road surface. By using the transformation in Equation (1), those corner displacements relative to the road surface can be expressed as the function of the relative roll and pitch angles θ_xbr and θ_ybr
z_lf=−t_f sin(θ_ybr)+l sin(θ_xbr)cos(θ_ybr)+(z_cg−h)cos(θ_xbr)cos(θ_ybr)
z_rf=−t_f sin(θ_xbr)−l sin(θ_xbr)cos(θ_ybr)+(z_cg−h)cos(θ_xbr)cos(θ_ybr)
z_lr=t_r sin(θ_ybr)+l sin(θ_xbr)cos(θ_ybr)+(z_cg−h)cos(θ_ybr)cos(θ_ybr)
z_rr=t_r sin(θ_ybr)−l sin(θ_xbr)cos(θ_ybr)+(z_cg−h)cos(θ_xbr)cos(θ_ybr)  (3)
where z_cg is the relative displacement of the center of gravity of the vehicle with respect to the road surface, but measured along the body z-axis.

Referring now to FIG. 3, the four equations of Equation (3) pose four constraints on a set of seven variables: z_lf,z_rf,z_lr,z_rr,z_cg,θ_xbr and θ_ybr. Hence a combination of three variables can be used to compute the rest of the variables. Since θ_xbr and θ_ybr are of interest in the present invention, the possible choices are choosing three variables from z_lf,z_rf,z_lr,z_rr and z_cg to characterize θ_xbr and θ_ybr. The direct measurement of any of z_lf,z_rf,z_lr,z_rr, and z_cg is relatively expensive (for example, expensive laser distance sensors can be used). Hence, measuring any three of z_lf,z_rf,z_lr,z_rr and z_cg may be cost prohibitive in a commercial environment with current technology. However, certain linear combinations of the four corner displacements z_lf,z_rf,z_lr and z_rr can be related to the available sensors through dynamics. When linear combinations are related to the relative roll and pitch Euler angles θ_xbr and θ_ybr, θ_xbr and θ_ybr may be characterized from the available sensor signals. In the following, the effort has been focused on finding those linear combinations of z_lf,z_rf,z_lr,z_rr which bridges between θ_xbr and θ_ybr, and the available sensor signals including the lateral and longitudinal accelerations, the roll and yaw angular rates and the wheel speed sensor signals.

The relative Attitudes Based on the Linear Combinations of the Corner Displacements

The linear combinations of z_lf,z_rf,z_lr,z_rr, which serve as bridges to connect θ_xbr and θ_ybr with the available sensor signals are the following variables, which are called the relative roll and pitch gradients $\begin{array}{cc}{\Theta }_x=\frac{Z_{\mathrm{lf}}-Z_{\mathrm{rf}}+Z_{\mathrm{lr}}-Z_{\mathrm{rr}}}{4l}{\Theta }_y=\frac{Z_{\mathrm{lf}}+Z_{\mathrm{rf}}-Z_{\mathrm{lr}}-Z_{\mathrm{rr}}}{2\left(t_f+t_r\right)}& \left(4\right)\end{array}$
Θ_x and Θ_y is related to the relative roll and pitch attitudes by manipulating the equations in (3). The final formula for the relative pitch Euler angle is
θ_ybr=sin⁻¹{Θ_y}  (5)
and the final formula for the relative roll Euler angle θ_xbr is $\begin{array}{cc}{\theta }_{\mathrm{xbr}}={\sin }^{-1}\left\{\frac{{\Theta }_x}{\cos \left({\theta }_{\mathrm{ybr}}\right)}\right\}& \left(6\right)\end{array}$

On the other hand Θ_x and Θ_y can be further related to the available sensor signals through dynamic equations which describe the vehicle body dynamics. Θ_x and Θ_y will be first broken into two portions, and related to the sensor signals.

Roll and Pitch Gradients Due to Suspension and Wheel Motions

As shown in FIG. 4, a portion of the left front wheel 12b and suspension 52 are illustrated, z_lf can be further expressed as the sum of the two parts: the suspension stroke s_lf as measured by sensor 50 and the wheel displacement w_lf with respect to the road surface along the direction perpendicular to the road surface. The same is true for the rest of the corner locations. The sensor 50 may
z_rf=s_rf+w_rf
z_lr=s_lr+w_lr
z_rr=s_rr+w_rr  (7)

The relative roll and pitch gradients Θ_x and Θ_y may be broken into pieces according to the suspension motion and the wheel vertical motion. The roll and the pitch gradients Θ_x-susp and Θ_y-susp due to suspension motions s_lf,s_rf,s_lf and s_rr may be defined as: $\begin{array}{cc}{\Theta }_{y-\mathrm{susp}}=\frac{s_{\mathrm{lf}}+s_{\mathrm{rf}}-s_{\mathrm{lr}}-s_{\mathrm{rr}}}{2\left(t_f+t_r\right)}{\Theta }_{x-\mathrm{susp}}=\frac{s_{\mathrm{lf}}-s_{\mathrm{rf}}+s_{\mathrm{lr}}-s_{\mathrm{rr}}}{4l}& \left(8\right)\end{array}$
and the roll and pitch gradients Θ_x-whl and Θ_y-whl due to the wheel vertical motion defined as: $\begin{array}{cc}{\Theta }_{y-\mathrm{whl}}=\frac{w_{\mathrm{lf}}+w_{\mathrm{rf}}-w_{\mathrm{lr}}-w_{\mathrm{rr}}}{2\left(t_f+t_r\right)}{\Theta }_{x-\mathrm{whl}}=\frac{w_{\mathrm{lf}}-w_{\mathrm{rf}}+w_{\mathrm{lr}}-w_{\mathrm{rr}}}{4l}& \left(9\right)\end{array}$
Then



Θ_x=Θ_x-susp+Θ_x-whl

The relative Euler angles Θ_xbr, and Θ_ybr can be also written as two parts: $\begin{array}{cc}{\theta }_{\mathrm{ybr}}={\sin }^{-1}\left\{{\Theta }_{y-\mathrm{susp}}+{\Theta }_{y-\mathrm{whl}}\right\}{\theta }_{\mathrm{xbr}}={\sin }^{-1}\left\{\frac{{\Theta }_{x-\mathrm{susp}}+{\Theta }_{x-\mathrm{whl}}}{\cos \left({\theta }_{\mathrm{ybr}}\right)}\right\}& \left(11\right)\end{array}$

Since there are no restrictions in Equation (11), it is valid regardless of if the four wheels of the vehicle contact the road surface or lift from the road, as soon as the accurate characterization of the roll and pitch gradients Θ_x-susp and Θ_y-susp, and Θ_x-whl and Θ_y-whl are available. Hence in the following Θ_x-susp,Θ_y-susp,Θ_x-whl and Θ_y-whl may be computed based on the available sensor signals.

Estimate the Roll and Pitch Gradients

From the formula in Equation (8), the roll and pitch gradients Θ_x-susp and Θ_y-susp are related to the suspension stroke. The estimation schemes are sought for computing Θ_x-susp and Θ_y-susp from the available sensor signals.

Consider in Equation (3) that the distance differences between the left side corners and right side corners are equal, that is:
z_lf−z_rf=z_lr−z_rr  (12)
or:
s_lf−s_rf=s_lr−s_rr+[w_lf−w_rr−w_lf+w_rf]  (13)
Since the tire deflections are much smaller than the suspension stroke, from (13) it is reasonable to say
s_lf−s_rf>>s_lr−s_rr  (14)
or rewrite this as: $\begin{array}{cc}\frac{s_{\mathrm{lf}}-s_{\mathrm{rf}}}{s_{\mathrm{lr}}-s_{\mathrm{rr}}}\approx 1& \left(15\right)\end{array}$
Hence, for any given constant weight k, we have: $\begin{array}{cc}{\Theta }_{x-\mathrm{susp}}\approx \frac{\kappa \left(s_{\mathrm{lf}}-s_{\mathrm{rf}}\right)+s_{\mathrm{lr}}-s_{\mathrm{rr}}}{2/\left(\kappa +l\right)}& \left(16\right)\end{array}$
In the sequential discussion, the Equation (16) may be used to describe the roll gradient Θ_x-susp.

Θ_x-susp and Θ_y-susp must then be related to the available sensor signals. The following dynamic relationship which are obeyed by the car body through the Newton law described around the c.g. of the vehicle body $\begin{array}{cc}{I}_x{\stackrel{.}{\omega }}_x=h_y\sum _{i-1}^4{F}_{\mathrm{yi}}+l\left(K_f{s}_{\mathrm{lf}}+D_f{\stackrel{.}{s}}_{\mathrm{lf}}\right)-l\left(K_f{s}_{\mathrm{rf}}+D_f{\stackrel{.}{s}}_{\mathrm{rf}}\right)+l\left(K_r{s}_{\mathrm{lr}}+D_r{\stackrel{.}{s}}_{\mathrm{lr}}\right)-l\left(K_r{s}_{\mathrm{rr}}+D_r{\stackrel{.}{s}}_{\mathrm{rr}}\right)+K_{\mathrm{anti}-\mathrm{roll}-f}\frac{\left(s_{\mathrm{lf}}-s_{\mathrm{rf}}\right)}{l}+K_{\mathrm{anti}-\mathrm{roll}-r}\frac{\left(s_{\mathrm{lr}}-s_{\mathrm{rr}}\right)}{l}{I}_y{\stackrel{.}{\omega }}_y=h_x\sum _{i=1}^4{F}_{\mathrm{xi}}+l_f\left(K_f{s}_{\mathrm{lf}}+D_f{\stackrel{.}{s}}_{\mathrm{lf}}\right)-l_f\left(K_f{s}_{\mathrm{rf}}+D_f{\stackrel{.}{s}}_{\mathrm{rf}}\right)-t_r\left(K_r{s}_{\mathrm{lr}}+D_f{\stackrel{.}{s}}_{\mathrm{lr}}\right)-t_r\left(K_r{s}_{\mathrm{rr}}+D_r{\stackrel{.}{s}}_{\mathrm{rr}}\right)M_s{a}_y=\sum _{i=1}^4{F}_{\mathrm{yi}}{M}_s{a}_x=\sum _{i=1}^4{F}_{\mathrm{xi}}& \left(17\right)\end{array}$
where I_x and I_y are the momentum of inertia of the car body with respect to the x and y axis respectively; M_s is the sprung mass (the mass of the car body); h_x is the c.g. height of the car body with respect to the top of the suspension; K_f and K_r are the front and rear suspension spring rates with unit N/m. K_anti-roll-f and K_anti-roll-r are the stiffnesses for the front and the rear anti-roll bar, with unit Nm/rad. D_f and D_r are the front and the rear suspension damper rates; F_xi is the ith suspension force applied to the car body along the body fixed direction b₁, and F_yi is the ith suspension force applied to the car body along the body fixed direction b₂.
Define a weight: $\begin{array}{cc}k=\frac{l^2{K}_f+K_{\mathrm{anti}-\mathrm{roll}-f}}{l^2{K}_r+K_{\mathrm{anti}-\mathrm{roll}-r}}& \left(18\right)\end{array}$
Since the damping rates are usually proportional to the spring rates for suspensions, it is reasonable to assume: $\begin{array}{cc}\frac{l^2{D}_f+D_{\mathrm{anti}-\mathrm{roll}-f}}{l^2{D}_r+D_{\mathrm{anti}-\mathrm{roll}-r}}\approx k& \left(19\right)\end{array}$
For a well balanced vehicle, the normal dead loading applied to the vehicle should not generate significant body attitude variation when the vehicle is parked on a flat road. That is, the roll and pitch attitude angles induced by the normal dead loading during flat road parking should be close to zero. For this reason, it is reasonable to assume the following holds:
t_rK_r=t_fK_f  (20)
Similar argument can be used for suspension damping rates.

Through algebraic manipulation the first two equations in Equation (17) can be rewritten as the following: $\begin{array}{cc}{I}_x{\stackrel{.}{\omega }}_x=h_y{M}_s{a}_y+\left({\mathrm{lK}}_r+\frac{K_{\mathrm{anti}-\mathrm{roll}-r}}{l}\right)\left[k\left(s_{\mathrm{lf}}-s_{\mathrm{rf}}\right)+\left(s_{\mathrm{lr}}-s_{\mathrm{rr}}\right)\right]+\left({\mathrm{lD}}_r+\frac{D_{\mathrm{anti}-\mathrm{roll}-r}}{l}\right)\left[k\left({\stackrel{.}{s}}_{\mathrm{lf}}-{\stackrel{.}{s}}_{\mathrm{rf}}\right)+\left({\stackrel{.}{s}}_{\mathrm{lr}}-{\stackrel{.}{s}}_{\mathrm{rr}}\right)\right]I_y{\stackrel{.}{\omega }}_x=h_x{M}_s{a}_x+t_r{K}_r\left(s_{\mathrm{lf}}+s_{\mathrm{rf}}-s_{\mathrm{lr}}-s_{\mathrm{rr}}\right)+t_r{D}_r\left({\stackrel{.}{s}}_{\mathrm{lf}}+{\stackrel{.}{s}}_{\mathrm{rf}}-{\stackrel{.}{s}}_{\mathrm{lr}}-{\stackrel{.}{s}}_{\mathrm{rr}}\right)& \left(21\right)\end{array}$
Using the definition of Θ_x-susp and Θ_y-susp, Equation (21) can be rewritten as:



{dot over (w)}_y=d₀a_x+d₁Θ_y-susp+d₂{dot over (Θ)}_{y-susp
that is, Θx-susp(t) and Θy-susp(t) obeys the 1^st order differential equations, and the coefficients c0,c1,c2,d0,d1 and d2 can be obtained by comparing Equation (21) and Equation (22). Although the analytical solution for Equation (22) are not hard to find, the solutions may be directly implemented in digital environment. On the other hand, the pitch rate signal is not measured, but an estimation of the pitch rate signal can be obtained as a function of the measured signals and the signals computed from the measured signals:
{dot over (w)}y={circumflex over (θ)}ysec({circumflex over (θ)}x)+wz tan({circumflex over (θ)}x)  (23)
where {circumflex over (θ)}x and {circumflex over (θ)}y are the estimated global roll and pitch Euler angles of the vehicle body (with respect to the sea level). The details if this are described in U.S. application Ser. No.
{circumflex over (Θ)}y-susp(k+1)=f0{circumflex over (Θ)}y-susp(k)+f1[RPA_RAW(k+1)+RPA_RAW(k)]  (25)}

The wheel motion-induced roll and pitch gradients are usually much smaller than the suspension motion induced gradients due to the small tire deflections at each wheel/tire assembly. Therefore:
Θ_x-whl<<Θ_x-susp
Θ_y-whl<<Θ_y-susp  (26)
or say:
Θ_x≈Θ_x-susp
Θ_y≈Θ_y-susp  (27)

As described above, the present invention uses Equation (27) to approximately calculate the roll and pitch gradients. The relative roll and pitch attitude angles can be computed as in Equations (5) and (6).

Referring now to FIG. 5, a flow chart summarizing the method of the present invention is illustrated. In step 70 the sensor signals of the sensor set are read. In the present example, a roll rate sensor determines the roll rate of the vehicle, a lateral acceleration sensor generates a lateral acceleration signal of the vehicle body, and a longitudinal acceleration sensor generates a longitudinal acceleration signal of the vehicle body. The yaw rate of the vehicle body is also measured. In step 72, a calculated pitch rate signal is determined from the yaw rate, the roll rate, the lateral acceleration, and the longitudinal acceleration. In step 74 the global roll attitude and global pitch attitude are determined from the calculated pitch rate, the roll rate, the lateral acceleration, and the longitudinal acceleration. In step 78 a roll gradient is determined based upon a past roll rate and the roll rate and the lateral acceleration signal. A relative roll angle is determined in step 80 based upon the roll gradient. In step 82 a pitch gradient based upon the passive past raw pitch rate, the calculated pitch rate, and the longitudinal acceleration is determined. In step 84 the relative pitch angle based upon the pitch gradient is determined. In step 86 a safety device is activated in response to the relative roll angle, the relative pitch angle, the global roll angle and the global pitch angle.

While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.

Claims

1. A control system for an automotive vehicle having a vehicle body comprising:

a first angular rate sensor generating a first angular rate signal corresponding to a first angular motion of the vehicle body;

a second angular rate sensor generating a second angular rate signal corresponding to a second angular motion of the vehicle body;

a lateral accelerometer generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body;

a longitudinal accelerometer generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said first angular rate sensor, said second angular rate sensor, said lateral accelerometer, said longitudinal accelerometer, and said wheel speed sensor, said controller determining a roll gradient based upon a past raw roll rate and current raw roll rate, the first angular rate signal or the second angular rate signal and the lateral acceleration signal, a pitch gradient based upon a past raw pitch rate and current raw pitch rate, the first or second angular rate signal and the longitudinal acceleration signal, determining a relative roll and relative pitch as a function of the roll gradient and the pitch gradient.

2. A system as recited in claim 1 wherein said first angular rate sensor is one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor and said second angular rate sensor comprises is one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor, said second sensor being different than the first sensor.

3. A control system for an automotive vehicle having a vehicle body comprising:

a roll angular rate sensor generating a roll angular rate signal corresponding to a roll angular motion of the vehicle body;

a yaw angular rate sensor generating a yaw motion signal corresponding to a yaw motion of the vehicle body;

a lateral accelerometer generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body;

a longitudinal accelerometer generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said roll angular rate sensor, said yaw angular rate sensor, said lateral accelerometer, said longitudinal accelerometer, and said wheel speed sensor, said controller determining a pitch rate in response to said roll angular rate signal, said yaw motion signal, said lateral acceleration signal, said longitudinal acceleraton signal, and said wheel speed signal, said controller determining a roll gradient based upon a past raw roll rate and current raw roll rate, the roll angular rate signal and the lateral acceleration signal: a pitch gradient based upon a past raw pitch rate and current raw pitch rate, the calculated pitch angular rate signal and the longitudinal acceleration signal, determining a relative roll and relative pitch as a function of the roll gradient and the pitch gradient.

4. A control system as recited in claim 3 further comprising a safety system coupled to said controller, said controller generating a control signal to said safety system in response to said relative roll angle, the relative pitch angle, a global roll attitude and a global pitch attitude.

5. A control system as recited in claim 4 wherein said safety system comprises an active brake control system.

6. A control system as recited in claim 4 wherein said safety system comprises an active rear steering system.

7. A control system as recited in claim 4 wherein said safety system comprises an active front steering system.

8. A control system as recited in claim 4 wherein said safety system comprises an active anti-roll bar system.

9. A control system as recited in claim 4 wherein said safety system comprises an active suspension system.

10. A method of controlling a rollover system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a lateral acceleration of the vehicle body;

measuring a longitudinal acceleration of the vehicle body;

measuring a yaw rate of the vehicle body;

determining a calculated pitch rate signal from the yaw rate, the roll rate, the lateral acceleration and the longitudinal acceleration;

determining a global roll attitude and a global pitch attitude from the calculated pitch angular rate, the roll rate, lateral acceleration and the longitudinal acceleration;

determining a roll gradient based upon a past raw roll rate, the roll rate signal and the lateral acceleration signal;

determining a relative roll angle based upon said roll gradient;

determining a pitch gradient based upon a past raw pitch rate and calculated pitch rate and the longitudinal acceleration signal;

determining a relative pitch angle based upon said pitch gradient; and

activating a safety device in response to the relative roll angle, the relative pitch angle, the global roll and global pitch angle.

11. A method as recited in claim 10 wherein determining a relative pitch angle comprises determining a relative pitch angle using an Euler approximation.

12. A method as recited in claim 10 wherein determining a relative roll angle comprises determining a relative roll angle using an Euler approximation.

13. A method as recited in claim 10 wherein said step of activating a safety device comprises one selected from the group consisting of an active brake control system, an active rear steering system, an active front steering system, an active anti-roll bar system, and an active suspension system.

14. A method of controlling a safety system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a lateral acceleration of the vehicle body;

measuring a longitudinal acceleration of the vehicle body;

measuring a yaw rate of the vehicle body; and

determining a relative roll angle, a relative pitch angle, a global roll and a global pitch angle in response to the roll rate, the yaw rate, the lateral acceleration and the longitudinal acceleration.

15. A control system for an automotive vehicle having a vehicle body comprising:

a first angular rate sensor generating a first angular rate signal corresponding to a first angular motion of the vehicle body;

a second angular rate sensor generating a second angular rate signal corresponding to a second angular motion of the vehicle body;

a lateral accelerometer generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said first angular rate sensor, said second angular rate sensor, said lateral accelerometer and said wheel speed sensor, said controller determining a roll gradient based upon a past raw roll rate and current raw roll rate, the first angular rate signal or the second angular rate signal and the lateral acceleration signal, determining a relative roll as a function of the roll gradient.

16. A system as recited in claim 15 wherein said first angular rate sensor is one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor and said second angular rate sensor comprises one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor, said second sensor being different than the first sensor.

17. A control system for an automotive vehicle having a vehicle body comprising:

a roll angular rate sensor generating a roll angular rate signal corresponding to a roll angular motion of the vehicle body;

a yaw angular rate sensor generating a yaw motion signal corresponding to a yaw motion of the vehicle body;

a lateral accelerometer generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said roll angular rate sensor, said yaw angular rate sensor, said lateral accelerometer and said wheel speed sensor, said controller determining a roll gradient based upon a past raw roll rate and current raw roll rate, the roll angular rate signal and the lateral acceleration signal, determining a relative roll angle as a function of the roll gradient.

18. A control system as recited in claim 17 further comprising a safety system coupled to said controller, said controller generating a control signal to said safety system in response to said relative roll angle.

19. A control system as recited in claim 18 wherein said safety system comprises an active brake control system.

20. A control system as recited in claim 18 wherein said safety system comprises an active rear steering system.

21. A control system as recited in claim 18 wherein said safety system comprises an active front steering system.

22. A control system as recited in claim 18 wherein said safety system comprises an active anti-roll bar system.

23. A control system as recited in claim 18 wherein said safety system comprises an active suspension system.

24. A method of controlling a rollover system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a lateral acceleration of the vehicle body;

measuring a longitudinal acceleration of the vehicle body;

measuring a yaw rate of the vehicle body;

determining a global roll attitude from the roll rate, lateral acceleration and the longitudinal acceleration;

determining a roll gradient based upon a past raw roll rate, the roll rate signal and the lateral acceleration signal;

determining a relative roll angle based upon said roll gradient;

activating a safety device in response to the relative roll angle and the global roll.

25. A method as recited in claim 24 wherein determining a relative roll angle comprises determining a relative roll angle using an Euler approximation.

26. A method as recited in claim 24 wherein said step of activating a safety device comprises one selected from the group consisting of an active brake control system, an active rear steering system, an active front steering system, an active anti-roll bar system, and an active suspension system.

27. A method of controlling a safety system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a lateral acceleration of the vehicle body;

measuring a yaw rate of the vehicle body; and

determining a relative roll angle, a global roll angle in response to the roll rate, the yaw rate and the lateral acceleration.

28. A control system for an automotive vehicle having a vehicle body comprising:

a first angular rate sensor generating a first angular rate signal corresponding to a first angular motion of the vehicle body;

a second angular rate sensor generating a second angular rate signal corresponding to a second angular motion of the vehicle body;

a longitudinal accelerometer generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said first angular rate sensor, said second angular rate sensor, said longitudinal accelerometer, and said wheel speed sensor, said controller determining a pitch gradient based upon a past raw pitch rate and current raw pitch rate, the first or second angular rate signal and the longitudinal acceleration signal, determining a relative roll and relative pitch as a function of the pitch gradient.

29. A system as recited in claim 28 wherein said first angular rate sensor is one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor and said second angular rate sensor comprises one selected from the group of a yaw rate sensor, a pitch rate sensor and a roll rate sensor, said second sensor being different than the first sensor.

30. A control system for an automotive vehicle having a vehicle body comprising:

a roll angular rate sensor generating a roll angular rate signal corresponding to a roll angular motion of the vehicle body;

a yaw angular rate sensor generating a yaw motion signal corresponding to a yaw motion of the vehicle body;

a longitudinal accelerometer generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the center of gravity of the vehicle body;

a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle; and

a controller coupled to said roll angular rate sensor, said yaw angular rate sensor, said longitudinal accelerometer, and said wheel speed sensor, said controller determining a pitch rate in response to said roll angular rate signal, said yaw motion signal, said longitudinal acceleration signal, and said wheel speed signal, said controller determining a pitch gradient based upon a past raw pitch rate and current raw pitch rate, the calculated pitch angular rate signal and the longitudinal acceleration signal, determining a relative pitch angle as a function of the pitch gradient.

31. A control system as recited in claim 30 further comprising a safety system coupled to said controller, said controller generating a control signal to said safety system in response to the relative pitch angle, and a global pitch attitude.

32. A control system as recited in claim 31 wherein said safety system comprises an active brake control system.

33. A control system as recited in claim 31 wherein said safety system comprises an active rear steering system.

34. A control system as recited in claim 31 wherein said safety system comprises an active front steering system.

35. A control system as recited in claim 31 wherein said safety system comprises an active anti-roll bar system.

36. A control system as recited in claim 31 wherein said safety system comprises an active suspension system.

37. A method of controlling a rollover system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a lateral acceleration of the vehicle body;

measuring a longitudinal acceleration of the vehicle body;

measuring a yaw rate of the vehicle body;

determining a calculated pitch rate signal from the yaw rate, the roll rate, the lateral acceleration and the longitudinal acceleration;

determining a global pitch angle from the calculated pitch angular rate, lateral acceleration and the longitudinal acceleration;

determining a pitch gradient based upon a past raw pitch rate and calculated pitch rate and the longitudinal acceleration signal;

determining a relative pitch angle based upon said pitch gradient; and

activating a safety device in response to the relative roll angle, the relative pitch angle, the global roll and global pitch angle.

38. A method as recited in claim 37 wherein determining a relative pitch angle comprises determining a relative pitch angle using an Euler approximation.

39. A method as recited in claim 37 wherein said step of activating a safety device comprises one selected from the group consisting of an active brake control system, an active rear steering system, an active front steering system, an active anti-roll bar system, and an active suspension system.

40. A method of controlling a safety system for a vehicle body of an automotive vehicle comprising:

measuring a roll rate of the vehicle body;

measuring a longitudinal acceleration of the vehicle body;

measuring a yaw rate of the vehicle body; and

determining a relative pitch angle, a global pitch angle in response to the roll rate, the yaw rate, and the longitudinal acceleration.