Fluid-pressure and analogous brake systems – Speed-controlled – Front-rear axle apportioning or speed difference
Patent
1994-10-31
1996-01-09
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Front-rear axle apportioning or speed difference
303 971, 3031135, 303182, 303198, 36442602, B60T 830
Patent
active
054823617
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a brake system with an adjustably variable front/rear axle braking force distribution for a vehicle designed for high speeds, in particular a racing car, 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 the 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.
At the high speeds of 350 km/h and more which are attained by racing cars on high-speed tracks, and given the aerodynamic shapes of the bodies for such vehicles which usually have a rear-axle drive, drastic increases in axle load occur at both the front axle and the rear axle because of the aerodynamic downward forces which increase quadratically with increasing vehicle speed. In magnitude, these increases in axle load can correspond to a multiple of the vehicle weight, for example twice or three times the stationary vehicle weight. For the designs possible, it is found that with increasing vehicle speed v, the aerodynamic downward forces effective at the rear axle increase more strongly than the aerodynamic downward forces effective at the front axle. This, however, leads to the fact that a brake system, such as one designed for a fixed matching of the braking force distribution, can only be designed in an optimum manner for a narrow speed range and, outside this speed range, is associated with either the danger of unstable dynamic braking behaviour of the vehicle or the disadvantage of a relatively low braking deceleration for a specified actuating force.
This disadvantage can indeed be ameliorated by an anti-lock brake system (ABS) which operates with a speed-dependent change to the response threshold both at the front axle and at the rear axle as discussed in DE 39 35 834 C2. Because, however, the brake system must be basically matched for stable braking behaviour without the influence of the aerodynamic forces, so that the brake coefficient B*.sub.H of the rear axle must of necessity be kept relatively low, a disproportionately large increase in pressure is necessary at the front axle when the anti-lock brake system responds in the high speed range in order to enforce a response of the control system at the rear wheel brakes also. However, the expenditure of force necessary for such an increase in pressure, on the one hand, and the time that elapses before the build-up of pressure is achieved limit the effectiveness of an anti-lock braking system for racing duties and lead, as a result, to time delays in the build-up of brake pressure which lead, as a result, to unacceptable losses of time when racing.
On the other hand, twin main cylinders are also used in racing cars in which "single circuit" main cylinders associated with the front wheel brakes and the rear wheel brakes are actuated by a rocker with a variable point of action of the force, the most favorable positional setting of the point of action of the force being different for each speed. In combination with twin main cylinders, automatically operating adjustment appliances for the point of action of the force on the rocker are also known which would, in principle, also permit a speed-dependent variation in the braking force distribution. Such adjustment appliances, however, have the disadvantage that very high forces act in braking operation on the linkage piece marking the point of action so that the adjustability is necessarily associated with hysteresis and substantial adjustment times have to be accepted, with the result
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Burckhardt Manfred
Kazan Sinan
Zimmer Richard
Mercedes-Benz AG
Muratori Alfred
Oberleitner Robert J.
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