Brake system with adjustably variable front/rear axle braking force distribution

• US 5,482,361 A
• Filed: 10/31/1994
• Issued: 01/09/1996
• Est. Priority Date: 01/03/1992
• Status: Expired due to Fees

• Current Assignee: Daimler Chrysler Company LLC (Stellantis NV)
• Original Assignee: Mercedes-Benz AG (Mercedes-Benz Group AG)
• Inventors: Kazan, Sinan, Zimmer, Richard, Burckhardt, Manfred
• Primary Examiner(s): Oberleitner, Robert J.
• Assistant Examiner(s): Muratori, Alfred
• Application Number:
  US08/256,248
• Time in Patent Office: 435 Days
• Field of Search: 303/9.62, 303/9.71, 303/9.73, 303/95-97, 303/103, 303/111, 303/113.2, 303/113.4, 303/113.5, 303/DIG. 4, 303/22.1, 303/24.1, 364/426.01-426.03
• US Class Current: 303/186
• CPC Class Codes: B60T 13/563 with multiple booster units, e.g. tandem booster units
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2270/208 adapted to friction condition
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• 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 8/1755 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: B60T 8/1764 Regulation during travel on surface with different coefficients of friction, e.g. between left and right sides, mu-split or between front and rear
• 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 8/266 using valves or actuators with external control means B60T8/261 takes precedence
• CPC Class Codes: B60T 8/3215 Systems characterised by having means acting on components of the drive line, e.g. retarder, clutch or differential gear B60T8/322 takes precedence
• CPC Class Codes: B60T 8/326 Hydraulic systems
• CPC Class Codes: B60T 8/3275 Systems with a braking assistant function, i.e. automatic full braking initiation in dependence of brake pedal velocity
• CPC Class Codes: B60T 8/345 having more than one brake circuit per wheel
• CPC Class Codes: B60T 8/4059 involving the rate of delivery
• CPC Class Codes: B60T 8/4275 Pump-back systems
• 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 brake system has a variable front/rear axle braking force distribution for a racing car. An electrohydraulic braking force control device with an electronic computer stage is provided in the system to take account of the aerodynamic axle load changes occurring at high speeds. This computer stage forms, from the vehicle speed and dynamically determined magnitudes, or magnitudes assumed to be appropriate, of the coefficient of friction μ_B effective at the vehicle wheels, an optimized braking force distribution factor. The brake pressure connected into the rear wheel brakes is caused to follow up the brake pressure connected into the front wheel brakes in such a way that the rear axle braking force follows the front axle braking force.

Claims

1. A brake system with variable braking force distribution between front and rear axles of a high speed vehicle in which downward aerodynamic forces on the vehicle cause an increase in axle loads as vehicle speed increases, wherein the increase in axle load is greater at the rear axle than at the front axle, comprising front wheel brakes, rear wheel brakes, a brake unit actuatable by a brake pedal and configured to generate at least a brake pressure in the front wheel brakes and operatively associated with the front wheel brakes and the rear wheel brakes that in the event of a specified defined limiting value of an actuation force exerted by a driver of the high speed vehicle, the vehicle has a magnitude of deceleration corresponding to complete utilization of frictional force on the braked vehicle wheels, and a separate pressure source comprising a braking force control device and providing a settable outlet pressure operatively associated between the brake unit and the rear wheel brakes so as to be directly connected as brake pressure into piston pairs of brake calipers of the rear wheel brakes, the source comprising an electronic control unit operatively configured to process at least one signal representative of the vehicle speed and one at least adjustably specifiable magnitude of a friction coefficient present at the vehicle wheels or assumed to be present and set, and to continuously form a value of an optimized braking force distribution factor in accordance with the following linear relationship

View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)

2. The brake system according to claim 1, having a front/rear axle brake circuit division on which the front wheel brakes are jointly connected to an outlet pressure space of the brake unit in which static pressure can be generated as a brake pressure p_v, by actuation of the brake pedal, the rear wheel brakes are arranged to be acted on exclusively by the outlet pressure, p_h, of the controllable pressure source, and the outlet pressure, p_h, is caused to follow up the front axle brake pressure, p_V, in accordance with the relationship

3. The brake system according to claim 2, wherein the brake unit comprises a tandem main cylinder with an outlet pressure space associated with the front wheel brakes and an outlet pressure space associated with the rear wheel brakes, the rear wheel brakes have four-piston calipers of one configuration, each with two piston pairs of one or different configuration, the piston pairs of one brake caliper being connected together with one identically dimensioned piston pair of the other brake caliper via a respective common brake conduit, one brake conduit being connected to a brake unit pressure outlet, associated with the rear wheel brakes and another brake conduit being connected to a pressure outlet of the controllable pressure source.

4. The brake system according to claim 3, wherein the brake unit and cross-section of cylinders of the wheel brakes are configured to fixedly match for stable dynamic vehicle braking behavior over a braking range from partial braking range to full braking range.

5. The brake system according to claim 1, wherein the outlet pressure of the controllable pressure source is set by controlling rotational speed of an electric drive motor of a high-pressure pump.

6. The brake system according to claim 1, wherein the pressure source further comprises one of a pressure supply pump driven with a constant high rotational speed and a pressure reservoir kept at a high pressure level, and the rear axle brakes are selectively connectable thereto by pulse-controllable inlet and outlet valves.

7. The brake system according to claim 1, wherein the sensor device comprises at least one pressure pick-up to monitor brake pressure in the front wheel brakes and generate an output signal characteristic of the outlet pressure of the brake unit connectable into at least one of the front wheel brakes.

8. The brake system according to claim 1, wherein a position pick-up is provided to generate, as representative of the outlet pressure of the brake unit, an output signal characteristic of one of a pedal position and a position of the brake unit piston which is displaceable by the brake pedal.

9. The brake system according to claim 1, wherein a pressure pick-up is provided for recording an actual value of the pressure connected into the rear wheel brakes and is operatively connected to the pressure outlet of the pressure source.

10. The brake system according to claim 1, wherein a computer stage is operatively associated with the system to continuously evaluate wheel peripheral speeds and of at least one driven and one free-running vehicle wheel to form a signal characteristic of a parameter in which drive slip of the vehicle, λ

_a, is given by the following relationship

space="preserve" listing-type="equation">λ

.sub.a =(v.sub.ant -v.sub.f)/v.sub.ant

where v_ant is the driven wheel velocity, and v_f is the free-running wheel velocity, and vehicle longitudinal acceleration is represented by z and, for values of the parameter dλ

_a /dz, which are located within a range between 0.4 and 0.6, and to determine the friction coefficient, μ

_B, associated with values of the vehicle longitudinal acceleration z in accordance with the following relationship

space="preserve" listing-type="equation">μ

.sub.B =Z/(ψ

-Z.sub.χ

)

the friction coefficient, μ

_B, being applied by the computer stage to determine the optimum rear axle braking force proportion, φ

_om, and the optimized braking force distribution factor, DB_om, and thereby provided optimized braking force distribution to the high speed vehicle.

11. The brake system according to claim 1, wherein the vehicle is equipped with an anti-lock brake system for stable dynamic deceleration behavior, and a vehicle deceleration Z_ABS, in relation to the gravitational constant, g, which equals 9.81 m/s², which occurs with a response of the anti-lock brake system on all vehicle wheels, is applied as the friction coefficient, μ

_B, used for the determination of the optimum braking force distribution factor, DB_om.

12. The brake system according to claim 1, wherein the vehicle is equipped with a longitudinal acceleration sensor arranged to generate electrical output signals characteristic of at least one of accelerations and decelerations occurring on the vehicle.

13. A brake system with variable axle braking force distribution between front and rear axles of a high speed vehicle in which downward aerodynamic forces on the vehicle cause an increase in axle loads as vehicle speed increases, wherein the increase in axle load is greater at the rear axle than at the front axle, comprising front wheel brakes, rear wheel brakes, a brake unit, actuatable by a brake pedal and configured to generate at least a brake pressure connectable into the front wheel brakes, and operatively connected with the front and rear wheel brakes such that in the event of a specified defined limiting value of an actuation force exerted by a driver of the high speed vehicle, the vehicle has a deceleration of a magnitude corresponding to complete utilization of frictional force on the braked vehicle wheels, a separate pressure source comprising a braking force control device with an electrically controllable outlet pressure connectable into a control pressure space of the brake unit and thereby additively superimposed on brake pressure generatable by actuation of the pedal alone, which brake pressure is connectable into the rear wheel brakes, the pressure source comprising an electronic control unit operatively configured to process at least one signal representative of the vehicle speed and one at least adjustably specifiable magnitude of a friction coefficient present at the vehicle wheels or assumed to be present and set, and to continuously form a value of an optimized braking force distribution factor in accordance with the linear relationship

View Dependent Claims (14, 15, 16)

14. The brake system according to claim 13, wherein the brake unit comprises a tandem main cylinder in which the front wheel brakes are connected to a primary outlet pressure space thereof and the rear wheel brakes are connected to a secondary outlet pressure space thereof, a housing of the tandem main cylinder having a first bore step forming a boundary fixed to a housing of the secondary outlet pressure space and being bounded therein by an outer piston flange of a secondary piston relative to an unpressurized follow-up space which is movably sealed by an inner piston flange against an inner section of the bore step and which is bounded by an intermediate wall of the housing against a central bore step beginning at a second bore step accommodating a primary piston, a cross-sectional area A₁ of the second bore step being somewhat larger than a cross-sectional area A₃ of the central bore step, an actuating piston is guidably displaceably arranged in a pressure-tight manner in the central bore step and forms an axially movable, inner boundary between the primary outlet pressure space and an unpressurized follow-up space axially bounded by the intermediate wall connected to the housing, the actuating piston having a push-rod configured axially to penetrate the central follow-up space and displaceably to pass through a central hole of the intermediate wall in a pressure-tight manner and further configured to be axially supportable on the inner piston flange of the secondary piston, and the annular space, which is axially movably bounded by the inner piston flange of the secondary piston and axially fixed relative to the housing by the intermediate wall and which is penetrated at a central region thereof by the push-rod, is connected to the pressure outlet of the controllable pressure source.

15. The brake system according to claim 14, wherein an end section of the push rod, acting on the secondary piston is displaceably arranged in a pressure-tight manner in a pocket hole of the secondary piston and is supportable on a bottom portion of the pocket hole.

16. The brake system according to claim 15, wherein the inner piston flange of the secondary piston is provided with a balance hole opening into the pocket hole centrally at the bottom portion to connect the pocket hole with the follow-up space.

17. A method for providing variable braking force distribution between front and rear axles of a high speed vehicle in which downward aerodynamic forces on the vehicle cause an increase in axle loads as vehicle speed increases, with the increase in axle load being greater at the rear axle than at the front axle, comprising the steps of

generating a brake pressure in front wheel brakes of the vehicle

processing at least one signal representative of the vehicle speed and one at least adjustably specifiable magnitude of an actual or assumed friction coefficient to continuously form an optimized braking force distribution factor value in accordance with the following linear relationship

View Dependent Claims (18)

18. The method according to claim 17, wherein the provision of the rear axle braking force, F_BH, comprises the step of utilizing exclusively outlet pressure, p_h, of the controllable pressure source for the rear wheel brakes in accordance with the relationship