Hydraulic dual-circuit braking system

• US 4,824,185 A
• Filed: 07/18/1988
• Issued: 04/25/1989
• Est. Priority Date: 07/18/1987
• Status: Expired due to Fees

• Current Assignee: Daimler-Benz AG (Mercedes-Benz Group AG)
• Original Assignee: Daimler-Benz AG (Mercedes-Benz Group AG)
• Inventors: Steiner, Manfred, Leiber, Heinz, Klinker, Walter
• Primary Examiner(s): Reger, Duane A.
• Application Number:
  US07/220,595
• Time in Patent Office: 281 Days
• Field of Search: 303/97, 303/98, 303/99, 303/100, 303/103, 303/106, 303/108, 303/110, 303/111, 303/114, 364/426
• US Class Current: 303/113.5
• CPC Class Codes: B60T 11/24 Single initiating means operating on more than one circuit, e.g. dual circuits multiple master cylinder units B60T11/20
• CPC Class Codes: B60T 13/144 Pilot valve provided inside booster piston
• CPC Class Codes: B60T 2270/203 hydraulic system components
• CPC Class Codes: B60T 8/175 Brake regulation specially adapted to prevent excessive wheel spin during vehicle acceleration, e.g. for traction control safety devices for propulsion unit control responsive to, or preventing, skidding of wheels B60K28/16
• CPC Class Codes: B60T 8/1766 Proportioning of brake forces according to vehicle axle loads, e.g. front to rear of vehicle
• CPC Class Codes: B60T 8/246 Change of direction
• CPC Class Codes: B60T 8/26 characterised by producing differential braking between front and rear wheels using electrical circuitry or regulation means B60T8/17
• CPC Class Codes: B60T 8/447 Reducing the boost of the power-assist booster means to reduce brake pressure
• CPC Class Codes: B60T 8/4845 using a booster or a master cylinder for traction control

Abstract

A hydraulic dual-circuit braking system comprising two main cylinders combined in twin-type construction which is actuated via a torque-equalized rocker operated by an actuating force proportional to brake pedal force, and wherein the main cylinders have position transmitters to detect piston positions, which are indirectly a measure of the brake pressure, and wherein an anti-blocking system enables the front wheel brakes to be blocked off from their main cylinders. The position signals are used by an electronic processing unit to determine the instantaneous front axle/rear axle braking force distribution, and compares this with a value which is ideal in accordance with the vehicle data, and when this comparison shows that the rear axle braking force component is too low, the front-wheel brakes are blocked off from their main cylinders until the rear axle braking force component is increased to such an extent that the ideal braking force distribution has been almost achieved. The front wheel blocking is then halted and both braking forces increase until the next under comparison situation is reached. The cycle of operation is then repeated.

Claims

1. A hydraulic dual-circuit braking system for a road vehicle having front wheel and rear wheel brake means which are controlled by a front axle and a rear axle braking circuit means for supplying separate braking actuating pressures P_VA and P_HA to the front and rear wheel brake means in response to a pedal means applying a force via a braking force amplifier;

each braking circuit means including a main piston-cylinder means arranged in a common housing adjacent to one another in a twin-type construction and including a piston means;

a two armed rocker means having one of its arms connected to each piston means of the piston-cylinder means is provided to cause displacement of each piston means;

said rocker means is supported for displacement by an actuating force in the direction of displacement of the piston means and pivotable about an axis which extends vertically with respect to the displacement direction of movement of the piston means;

the rocker arms having a length L_V and L_H for the front and rear braking circuit means, respectively;

wherein a ratio L_V /L_H of the effective lengths L_V and L_H of the rocker arms corresponds to a ratio of F_H /F_V, wherein F_H and F_V are affective piston areas of the respective main cylinder pistons;

said pedal means acting through said rocker means to provide a permanent balancing of a braking force distribution F_VA /F_HA, wherein F_VA and F_HA are the braking forces applied to the front and rear wheel brakes, respectively, for a dynamically stable braking behavior of the road vehicle in an entire range of variations of vehicle decelerations with highest adhesion-force coefficients between roadway and wheels of the vehicle;

an anti-blocking system means (ABS) having braking pressure actuator means driven by electric output signals of an electronic ABS control unit means;

said anti-blocking system means (ABS) operating to provide braking pressure holding phases at the front wheels of the vehicle, and including;

one position transmitter means for each of the main cylinder pistons, for providing electric output signals of the respective piston positions as information inputs to a processing unit means provided within the electronic control unit means;

wherein said processing unit means evaluates the position output signals of the position transmitters means as indicative of the braking pressures P_VA and P_HA generated in the two main piston-cylinder means, as well as ideal front and rear axle braking force components F_HA and F_VA to produce braking force components F'"'"'_HA and F'"'"'_VA for the front and rear braking means, which are correlated to a particular vehicle deceleration Z;

said processing unit means comparing said rear axle braking force component F'"'"'_HA with an ideal value component F_HAi of the rear axle braking force component determined from measurement data of the vehicle when attempting to provide equal adhesion force closure at the front and rear brakes;

and wherein if the value component F'"'"'_HA determined in this manner is lowered by more than a threshold value F_HA1 than the ideal value component F_HAi, said processing unit means triggers a signal which, in turn, triggers a braking pressure holding phase at the front axle brake to maintain the braking force at the front axle constant, while increasing the braking force at the rear brakes;

and wherein when the rear axle braking force component exceeds a value which is lower by less than a second difference threshold F_HA2, which is smaller than the first threshold value F_HA1, than the ideal value component F_HAi of the rear axle braking force, said signal processing means releases the braking pressure holding phase at the front axle brake to allow the brake pressure at the front brake to increase.

2. A braking system according to claim 1, wherein a pressure switch means is provided to generate an output signal when the braking system is operated with the vehicle stationary and the pressure P_VA generated in the front axle braking circuit exceeds a predetermined threshold valve P_O ;

said output signal and the positions of the piston means in the main cylinder means through the position transmitter means are processed by the signal processing means to determine quantities which are characteristic of the installed braking force distribution;

and wherein said characteristics are then used by the signal processing means as a basis for the determination of the ideal component values.

3. A braking system according to claim 1, wherein the signal processing means contains a computer which determines ideal braking force component F'"'"'_HA and F'"'"'_VA distribution utilized for the comparison with the measured braking force while taking into consideration loading conditions of the vehicle.

4. A braking system according to claim 2, wherein the signal processing means contains a computer which determines ideal braking force component F'"'"'_HA and F'"'"'_VA distribution utilized for the comparison with the measured braking force while taking into consideration loading conditions of the vehicle.

5. A braking system according to claim 1, wherein the value F_HAi'"'"' utilized for the comparison with the measured value of the rear axle braking force component, is lowered by a difference amount Δ

F_HAi when a transverse acceleration acts on the vehicle which exceeds a predetermined threshold value.

6. A braking system according to claim 2, wherein the value F_HAi'"'"' utilized for the comparison with the measured value of the rear axle braking force component, is lowered by a difference amount Δ

F_HAi when a transverse acceleration acts on the vehicle which exceeds a predetermined threshold value.

7. A braking system according to claim 3, wherein the value F_HAi'"'"' utilized for the comparison with the measured value of the rear axle braking force component, is lowered by a difference amount Δ

F_HAi when a transverse acceleration acts on the vehicle which exceeds a predetermined threshold value.

8. A braking system according to claim 4, wherein the value F_HAi'"'"' utilized for the comparison with the measured value of the rear axle braking force component, is lowered by a difference amount Δ

F_HAi when a transverse acceleration acts on the vehicle which exceeds a predetermined threshold value.

9. A braking system according to claim 1, wherein at least one level transmitter means is provided to produce an output signal to the signal processing means which is a measure of longitudinal inclination of the vehicle chassis which deviates from a position of the chassis which is characteristic of minimum loading of the vehicle and is thus a measure of the rear axle load component on the vehicle to determine the ideal value component F_HAi.

10. A braking system according to claim 2, wherein at least one level transmitter means is provided to produce an output signal to the signal processing means which is a measure of longitudinal inclination of the vehicle chassis which deviates from a position of the chassis which is characteristic of minimum loading of the vehicle and is thus a measure of the rear axle load component on the vehicle to determine the ideal value component F_HAi.

11. A braking system according to claim 5, wherein at least one level transmitter means is provided to produce an output signal to the signal processing means which is a measure of longitudinal inclination of the vehicle chassis which deviates from a position of the chassis which is characteristic of minimum loading of the vehicle and is thus a measure of the rear axle load component on the vehicle to determine the ideal value component F_HAi.

12. A braking system according to claim 1, wherein the signal processing means determines from an evaluation of the operating data of engine speed, throttle valve position and gear transmission for transmitting propulsion torque from the engine to the vehicle wheels, the total vehicle weight and the axle load distribution from a comparison of this data with vehicle acceleration data detected by means of wheel speed sensors to be used to determine the ideal value component F_HAi.

13. A braking system according to claim 2, wherein the signal processing means determines from an evaluation of the operating data of engine speed, throttle valve position and gear transmission for transmitting propulsion torque from the engine to the vehicle wheels, the total vehicle weight and the axle load distribution from a comparison of this data with vehicle acceleration data detected by means of wheel speed sensors to be used to determine the ideal value component F_HAi.

14. A braking system according to claim 5, wherein the signal processing means determines from an evaluation of the operating data of engine speed, throttle valve position and gear transmission for transmitting propulsion torque from the engine to the vehicle wheels, the total vehicle weight and the axle load distribution from a comparison of this data with vehicle acceleration data detected by means of wheel speed sensors to be used to determine the ideal value component F_HAi.

15. A braking system according to claim 1, wherein vehicle acceleration is logically combined with the respective braking force distribution by the signal processing means for determining the total vehicle weight and the axle load distribution used to determine the ideal value component F_HAi.

16. A braking system according to claim 2, wherein vehicle acceleration is logically combined with the respective braking force distribution by the signal processing means for determining the total vehicle weight and the axle load distribution used to determine the ideal value component F_HAi.

17. A braking system according to claim 5, wherein vehicle acceleration is logically combined with the respective braking force distribution by the signal processing means for determining the total vehicle weight and the axle load distribution used to determine the ideal value component F_HAi.