Fluid-pressure and analogous brake systems – Multiple systems – Fluid pressure and electric
Patent
1995-10-16
1998-08-04
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Multiple systems
Fluid pressure and electric
303 11, 303DIG3, B60T 1368, B60T 860
Patent
active
057883378
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP94/00981.
BACKGROUND OF THE INVENTION
This invention relates to an automotive vehicle auxiliary energy brake system having a central pressure source and a hydraulic system which includes pressure medium lines connecting the wheel brakes of the automotive vehicle with the pressure source, electrically controllable hydraulic valves, and pressure medium orifices. Brake systems of this type also include an electronic control unit for generating valve control signals and for controlling the braking pressure in the wheel brakes in dependence on measured pressure signals and a pressure sensor arranged at the outlet of the pressure source.
On principle, an auxiliary energy brake system of this type will always be needed if a wheel brake is to be activated independently of the actuation of the brake system by the driver. A known example of the application of such a system is traction slip control by brake management. In these systems, the braking pressure is controlled in response to the rotational behavior of the spinning or unstable wheels.
Further, there are brake systems conceivable and being developed which will be activated automatically as an accident-preventing measure as soon as the distance between an automotive vehicle and another vehicle in front of it or another obstacle becomes too small. Speed control systems likewise require brake management in some situations. For such systems, the rotational behavior of the wheels is not a suitable control parameter; intervention by means of control does not depend on the instability of any wheel.
Adjusting a preset braking pressure which is variable or depends on certain conditions is difficult. Control systems are known which work with a fixed pulse pattern and, if necessary, modify this pulse pattern in dependence on reactions of the vehicle. These systems are relatively inaccurate and are only able to effect rough pressure changes. Moreover, there is a relatively strong dependence of the braking pressure on the environmental and operating temperatures.
Besides, there are known control systems which cannot function without direct measurement of the braking pressure in the individual wheel brakes. In these systems, a plurality of pressure sensors is needed, namely at least one sensor per brake caliper which, moreover, must be arranged near the brake caliper.
German Patent DE-A-40 29 793 discloses a vehicular hydraulic brake which comprises a central pressure source and hydraulic valves by means of which both a boosting function and anti-lock control and traction slip control are possible. Moreover, this system provides driving dynamics adaptation within the normal braking range and can even function as a remote controlled brake system. For performing these functions, a hydraulic valve interrupts the pressure medium path from the master cylinder of the brake system to the wheel brakes and switches on the auxiliary pressure source. Then, the pressure at the outlet of the master cylinder, i.e., upstream of this point of separation, and the pressure metered in by the pressure source, i.e., the pressure downstream of the point of separation, are measured by pressure sensors and are evaluated for pressure control or pressure regulation. This requires a considerable expenditure.
SUMMARY OF THE INVENTION
The present invention provides an auxiliary energy brake system which permits continuous adjustment of a preset, variable braking pressure and requires a comparatively small manufacturing expenditure. The brake system displays a stable behavior over a wide operative range and is insensitive to variations in the hydraulic parameters, e.g., caused by temperature changes, aging, wear and tear, or manufacturing tolerances.
A brake system according to the present invention develops braking pressure in the wheel brakes as a function of the pressure at the outlet of a pressure source, measured by a pressure sensor arranged there, and of the hydraulic conductance (D) of the
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"Bremstechnische Begriffe und Werte fur Nutzfahrzeuge" der Firms Knorr-Bremse GmbH, Ausg. 1976, S.295.
U.S. patent application labelled "P6400".
Graham Matthew C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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