Process for driving stability control with control via pressure gradients

• US 5,735,584 A
• Filed: 06/07/1995
• Issued: 04/07/1998
• Est. Priority Date: 11/25/1994
• Status: Expired due to Fees

• Current Assignee: ITT Automotive Europe GmbH
• Original Assignee: ITT Automotive Europe GmbH
• Inventors: Eckert, Alfred
• Primary Examiner(s): Poon, Peter M.
• Application Number:
  US08/473,708
• Time in Patent Office: 1,035 Days
• Field of Search: 303/140, 303/146, 303/147, 303/148, 364/426.03, 364/426.01, 364/426.02
• US Class Current: 303/140
• CPC Class Codes: B60G 2400/1042 using at least two sensors
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• CPC Class Codes: B60T 2270/313 with less than three sensors (yaw rate, steering angle, lateral acceleration)
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• CPC Class Codes: B60W 10/184 with wheel brakes
• CPC Class Codes: B60W 2422/95 Measuring the same parameter at multiple locations of the vehicle
• CPC Class Codes: B60W 2520/125 Lateral acceleration
• CPC Class Codes: B60W 2520/14 Yaw
• CPC Class Codes: B60W 2520/20 Sideslip angle
• CPC Class Codes: B60W 2720/14 Yaw
• CPC Class Codes: B60W 2720/30 Wheel torque
• CPC Class Codes: B60W 30/02 Control of vehicle driving stability
• CPC Class Codes: B60W 40/064 Degree of grip

Abstract

A control process for the driving stability control of a motor vehicle is provided. The signal sent out by a control law unit to generate the necessary additional torque is sent to a distribution logic unit, which subsequently sends the pressure signals used to actuate the individual wheel brakes. The superimposition of these pressure signals and the pressure signal characterizing the driver'"'"'s desire to brake (as well as the subsequent superimposition of these adjusting signals to adjusting signals arriving from other brake pressure controllers, such as ABS, TSC, EBV) leads to interfaces in which differing physical variables must be compared or superimposed. The necessary conversion of these variables is expensive and increases the inaccuracy of the control system. Simplified interfaces are provided, to achieve improved processing of the brake pressure desired by the driver, and possibly to avoid the conversion of the individual signal variables. Pressure gradient signals are sent, to the output of the distribution logic unit, and are superimposed with corresponding gradient signals from other brake pressure control circuits. A priority circuit processes the pressure signals of the individual wheels such that commands to reduce the pressure are processed first, after which the commands to hold pressure, and finally the commands to build up pressure are processed.

Claims

1. In a yaw control system of a vehicle having a plurality of wheel brakes, a method for determining pressure adjustments for the brakes, individually, and applying the pressure adjustments to adjust a yawing moment that is applied to the vehicle by the brakes, comprising the steps of:

(1) detecting a condition in which an increase in the brake pressure applied to a first one of the brakes is required to apply the yawing moment to the vehicle while a driver of the vehicle is actuating the brakes to apply a first braking force to the vehicle;

(2) determining a reduction in pressure that is applied to a second one of the brakes, such that a total braking force applied to the vehicle does not exceed the first braking force when the pressure applied to the first brake is increased; and

(3) reducing pressure in the second brake before initiating the increase in the pressure applied to the first brake.

2. A method for controlling driving stability of a vehicle which has sensors for measuring a velocity, a steering angle and a measured yaw variable, and a plurality of brakes to which respective braking pressures are applied, individually, comprising the steps of:

(a) measuring the velocity, the steering angle and the measured yaw variable;

(b) determining a desired yaw variable from the velocity and the steering angle;

(c) determining a difference between the measured yaw variable and the desired yaw variable;

(d) determining a control value representing the rate of change with respect to time of a yawing moment that is applied to the vehicle based on the difference, so that the measured yaw variable approaches the desired yaw variable;

(e) determining pressure adjustments based on the control value that are applied to each brake, individually, to adjust the yawing moment that is applied to the vehicle by the brakes, including the steps of;

(1) detecting a condition in which an increase in the brake pressure applied to a first one of the brakes is required to apply the yawing moment to the vehicle while a driver of the vehicle is actuating the brakes to apply a first braking force to the vehicle,

(2) determining a reduction in pressure that is applied to a second one of the brakes, such that a total braking force applied to the vehicle does not exceed the first braking force when the pressure applied to the first brake is increased, and

(3) reducing pressure in the second brake before initiating the increase in the pressure applied to the first brake.

3. A method according to claim 2, wherein step (e) includes limiting the pressure adjustments for each brake, individually, so that the pressure adjustments do not exceed a permissible slip threshold value.

4. A method according to claim 2, wherein each brake has valve means for adjusting the brake pressure applied to the brake, the method further comprising:

(f) calculating valve switching times, based on the pressure adjustments, which are used to open and close the valve means of each brake, individually, so as to perform the pressure adjustments.

5. A control system according to claim 4, further comprising:

(g) calculating the brake pressures that are applied to each brake, individually, based on the valve switching times.

6. A method according to claim 2, wherein step (e) includes determining the pressure adjustments according to the equation:

##EQU33## where xx is a position of one of the brakes and is selected from the group consisting of front-right, front-left, rear-right, and rear-left, .increment.P_xx is the change in pressure for wheel xx, c_xx is a constant for brake xx, M is the rate of change with respect to time of the yawing moment applied to the vehicle, g_I is a weighting factor, P_brake is a brake pressure applied by a driver of the vehicle, and p_xxist is an actual brake pressure applied to brake xx.

7. A method according to claim 2, further comprising:

(f) providing first values from an anti-lock braking system, for controlling each brake, individually;

(g) providing second values from a traction slip control system for controlling each brake, individually,

(h) providing third values from a brake effort proportioning system for distributing braking pressure between the brakes of a front axle of the vehicle and the brakes of a rear axle of the vehicle;

(i) applying criteria to determine a desired brake pressure that is applied to each brake, individually based on the first, second and third values and the pressure adjustments determined in step (e).

8. A method according to claim 7, wherein step (k) includes:

(1) detecting a condition in which the first, second, and third values and the pressure adjustments indicate that at least two different adjustments from the group consisting of;

(A) a reduction in pressure,

(B) maintaining a constant pressure for a period, and

(C) an increase in pressure are to be applied to the same one of the brakes; and

(2) performing at least one of the steps of;

(A) initiating the reduction in pressure before maintaining the constant pressure for the period;

or

(B) maintaining the constant pressure for the period before initiating the increase in pressure.

9. A method according to claim 7, wherein the first, second and third values each represent a respectively different pressure adjustment.

10. A method for controlling driving stability of a vehicle which has sensors for measuring a velocity, a steering angle and a measured yaw variable, and a plurality of brakes to which respective braking pressures are applied, individually, each brake having valve means for adjusting the brake pressure applied to the brake comprising the steps of:

(a) measuring the velocity, the steering angle and the measured yaw variable;

(b) determining a desired yaw variable from the velocity and the steering angle;

(c) determining a difference between the measured yaw variable and the desired yaw variable;

(d) determining a control value representing the rate of change with respect to time of a yawing moment that is applied to the vehicle based on the difference, so that the measured yaw variable approaches the desired yaw variable;

(e) determining pressure adjustments based on the control value that are applied to each brake, individually, to adjust the yawing moment that is applied to the vehicle by the brakes,

(f) calculating first valve switch timing values, based on the pressure adjustments, for opening and closing the valve means of each brake, individually, so as to perform the pressure adjustments;

(g) providing second valve switch timing values from an antilock braking system for controlling each brake, individually;

(h) providing third valve switch timing values from a traction slip control system for controlling each brake, individually;

(i) providing fourth valve switch timing values from a brake effort proportioning system for distributing braking pressure between the brakes of a front axle of the vehicle and the brakes of a rear axle of the vehicle; and

(j) applying criteria to the first, second, third and fourth valve switch timing values, to determine prioritized valve switch timing values that are used to open and close the valve means of each brake.

11. A control system for controlling driving stability of a vehicle which has a velocity, a steering angle, a sensor for providing signals representing a measured yaw variable, and a plurality of brakes to which respective braking pressures are applied, individually, comprising:

vehicle model means responsive to a first value representing the velocity and a second value representing the steering angle for providing a value representing a desired yaw variable;

comparing means responsive to the signals representing the measured yaw variable and the value representing the desired yaw variable for determining a difference therebetween;

yawing moment control means responsive to the difference for determining a control value representing the rate of change with respect to time of a yawing moment that is applied to the vehicle, such that the measured yaw variable value approaches the desired yaw variable value;

distribution logic means responsive to the control value for determining pressure adjustments that are applied to each brake, individually, to adjust the yawing moment that is applied to the vehicle by the brakes, including logic means for;

(1) detecting a condition in which the distribution logic means determines that an increase in the brake pressure applied to a first one of the brakes is required to apply the yawing moment to the vehicle while a driver of the vehicle is actuating the brakes to apply a first braking force to the vehicle, and

(2) determining a reduction in pressure that is applied to a second one of the brakes, such that a total braking force applied to the vehicle does not exceed the first braking force when the pressure applied to the first brake is increased, and

(3) initiating the reduction in pressure in the second brake before initiating the increase in the pressure applied to the first brake.

12. A control system according to claim 11, wherein the distribution logic means limit the pressure adjustments for each brake, individually, so that the pressure adjustments do not exceed a permissible slip threshold value.

13. A control system according to claim 11, wherein each brake has valve means for adjusting the brake pressure applied to the brake, the control system further comprising:

valve switch timing means, responsive to the pressure adjustments determined by the distribution logic means, for calculating valve switching times which are used to open and close the valve means of each brake, individually, so as to perform the pressure adjustments.

14. A control system according to claim 13, wherein the distribution logic means include means for calculating the brake pressures that are applied to each brake, individually, based on the valve switching times.

15. A control system according to claim 11, further comprising:

an anti-lock braking system that provides first control values for controlling each brake, individually;

a traction slip control system that provides second control values for controlling each brake, individually,

brake effort proportioning means for providing third control values for distributing braking pressure between the brakes of a front axle of the vehicle and the brakes of a rear axle of the vehicle;

prioritizing means, responsive to the first, second, and third values and the pressure adjustments determined by the distribution logic means, for applying criteria to determine a desired brake pressure that is applied to each brake, individually.

16. A control system according to claim 15, wherein the prioritizing means include:

means for detecting a condition in which the first, second, and third values and the pressure adjustments determined by the distribution logic means indicate that at least two different adjustments from the group consisting of;

(1) a reduction in pressure,

(2) maintaining constant pressure for a period, and

(3) an increase in pressure are to be applied to the same one of the brakes;

means responsive to the detecting means for initiating the reduction in pressure before maintaining the constant pressure for the period; and

means responsive to the detecting means for maintaining the constant pressure for the period before initiating the increase in pressure.

17. A control system according to claim 15, wherein the first, second and third values each represent a respectively different pressure adjustment.

18. A control system for controlling driving stability of a vehicle which has a velocity, a steering angle, a sensor for providing signals representing a measured yaw variable, and a plurality of brakes to which respective braking pressures are applied, individually, comprising:

vehicle model means responsive to a first value representing the velocity and a second value representing the steering angle for providing a value representing a desired yaw variable;

comparing means responsive to the signals representing the measured yaw variable and the value representing the desired yaw variable for determining a difference therebetween;

yawing moment control means responsive to the difference for determining a control value representing the rate of change with respect to time of a yawing moment that is applied to the vehicle, such that the measured yaw variable value approaches the desired yaw variable value;

distribution logic means responsive to the control value for determining pressure adjustments that are applied to each brake, individually, to adjust the yawing moment that is applied to the vehicle by the brakes, said distribution logic means including means for determining the pressure adjustments according to the equation;

##EQU34## where xx is a position of one of the brakes and is selected from the group consisting of front-right, front-left, rear-right, and rear-left, .increment.P_xx is the change in pressure for wheel xx, c_xx is a constant for brake xx, M is the rate of change with respect to time of the yawing moment applied to the vehicle, g₁ is a weighting factor, P_brake is a brake pressure applied by a driver of the vehicle, and P_xxist is an actual brake pressure applied to brake xx.

19. A control system for controlling driving stability of a vehicle which has a velocity, a steering angle, a sensor for providing signals representing a measured yaw variable, and a plurality of brakes, each brake having valve means for adjusting the brake pressure applied to the brake, individually, comprising:

vehicle model means responsive to a first value representing the velocity and a second value representing the steering angle for providing a value representing a desired yaw variable;

comparing means responsive to the signals representing the measured yaw variable and the value representing the desired yaw variable for determining a difference therebetween;

yawing moment control means responsive to the difference for determining a control value representing the rate of change with respect to time of a yawing moment that is applied to the vehicle, such that the measured yaw variable value approaches the desired yaw variable value;

distribution logic means responsive to the control value for determining pressure adjustments that are applied to each brake, individually, to adjust the yawing moment that is applied to the vehicle by the brakes

valve switch timing means, responsive to the pressure adjustments determined by the distribution logic means, for calculating first valve switch timing values for opening and closing the valve means of each brake, individually, so as to perform the pressure adjustments;

an anti-lock braking system that provides second valve switch timing values for controlling each brake, individually;

a traction slip control system that provides third valve switch timing values for controlling each brake, individually,

brake effort proportioning means for providing fourth valve switch timing values for distributing braking pressure between the brakes of a front axle of the vehicle and the brakes of a rear axle of the vehicle; and

prioritizing means, responsive to the first, second, third and fourth valve switch liming values, for applying criteria to determine prioritized valve switch timing values that are used to open and close the valve means of each brake.

20. Control process for controlling the driving stability of a vehicle, in which the input variables, which are determined essentially by the desired travel curve, are converted into the desired value of a yaw angle variable on the basis of a vehicle model defined by calculated variables, and this desired value is compared in a comparison unit with the actual value of the yaw angle variable, which was determined by means of a sensor, wherein the difference value determined is sent to a control law unit, in which a torque variable is calculated, and it is used to set pressure variables, which generate an additional yawing moment via the wheel brakes of the vehicle, and this additional yawing moment causes the measured yaw angle variable to approach the calculated yaw angle variable, characterized in that the instantaneous velocity of the additional yawing moment and, if desired, in the form of a pressure signal, the driver'"'"'s desire to brake are sent as the output variable of the control law unit to a distribution logic unit, and that the distribution logic unit sends pressure gradients associated with the individual brakes of the vehicle, and these pressure gradients are subsequently converted into valve-switching rime signals, via which the brake valves on the wheels are actuated, and the pressure in the individual wheel brakes can be individually controlled,

wherein the distribution logic unit is provided with a logic block, which controls the value of the pressure gradient sent out such that the pressure gradients that bring about the pressure build-up on the wheel brake are sent out only when a corresponding reduction in pressure on another wheel below the brake pressure desired by the driver has taken place within the yawing moment control activity.

21. Control process in accordance with claim 20, characterized in that the sending of the pressure gradients by the distribution logic unit is controlled such that the permissible slip determined on a wheel in the longitudinal direction of the vehicle cannot be exceeded.

22. Control process in accordance with claim 20, characterized in that the logic block is provided with a vehicle brake model, which simulates the pressure occurring on the individual wheel brakes on the basis of the pressure gradients sent out.

23. Control process in accordance with claim 20, characterized in that a pressure gradient circuit, which sends the pressure gradients of the individual wheels according to the following relationship:

##EQU35## in which xx is the position parameter of the individual wheels, C is a constant, a is a weighting factor (rating number) and P_Driver =P_F is the brake pressure desired by the driver, is provided in the distribution logic unit.

24. Control process in accordance with claim 20, characterized in that a priority circuit arranged downstream of the distribution logic unit is provided, in which the adjusting signals sent by additional brake control systems including an anti-lock braking system, a traction slip control system, and a brake effort proportioning system are processed with the adjusting signals arriving from the distribution logic unit, wherein signals containing deviating commands with respect to the individual wheel brakes are processed in the following order:

Reduction in pressure, holding pressure, and pressure build-up.

25. Control process in accordance with claim 24, characterized in that the priority circuit is actuated by pressure gradient signals.

26. Control process in accordance with claim 25, characterized in that the priority circuit is actuated by valve-switching time signals, wherein a valve-switching time circuit, which converts the pressure gradient signals of the distribution logic unit into valve-switching time signals, which control the opening and closing of the brake valves, is inserted between the distribution logic unit and the priority circuit.