Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1990-01-19
1991-07-09
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303119, 303114, B60T 832, B60T 844, B60T 1312
Patent
active
050299522
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a slip-controlled brake system comprising a master cylinder whose working chamber communicates with a supply reservoir wherein a pair of pistons cooperate with a shut-off valve to control pressure at an outlet pump.
A like brake system, which is described in German Patent application No. P3726302, bears the advantage that the master brake cylinder is not uncoupled from the wheel brakes during a brake slip control action. Therefore the volume in the master brake cylinder is available as an additional volume, in the event that the rate of delivery of the pump is momentarily insufficient during a brake slip control action. Pedal positioning is effected simultaneously by way of actuation of the shut-off valve by the master brake cylinder piston. The shut-off valve is actuated by means of a ramp on the working piston of the master brake cylinder. The ramp is arranged in such a way that the shut-off valve is in a closed position when the working piston is slid far into the master brake cylinder. The pressure-fluid connection which is controlled by the shut-off valve is open when the working piston assumes a position which is only a small difference from the initial position.
By this arrangement, during a brake slip control action, that is with the pump switched on, the working piston and thus the pedal are set into a position which corresponds to the transition between the two mentioned areas.
The shut-off valve is designed such that the closure member can be pushed open by a ramp-controlled tappet in opposition to the pump pressure. Thus, the full pump pressure acts upon the tappet which takes support on the peripheral surface of the working piston. In doing so, the pressure causes a friction force between the tappet and the peripheral surface of the working piston which hinders the latter in its axial movement. This must be avoided especially during a slip control action, since the additional volume which is to be removed from the master brake cylinder must be supplied very quickly to the wheel brake. A retarded pressure fluid supply would have negative effects on the control quality.
The pressure of the tappet on the peripheral surface as well as the rapid movements of the piston during a brake slip control action cause damages in the area of the control ramp. Hence, it follows that the fatigue durability of the material soon is exhausted. At best, this shortcoming can be counteracted by performing complicated and costly hardening processes.
Therefore, it is an object of the present invention to modify the known brake system in such a fashion that its advantages are preserved (accumulator effect of the master brake cylinder, pedal positioning), on the one hand, and that its fatigue durability is augmented without having to perform intricate hardening measures, on the other hand.
Another disadvantage of the known brake system is that the shut-off valve must be mounted on a conventional master brake cylinder construction so that a new design or construction of the master brake cylinder is necessary. Therefore, another object to be achieved by the present invention is to embody the desired functions in an additional arrangement which can be connected to the existing master brake cylinders.
SUMMARY OF THE INVENTION
This object is achieved in that the working piston of the master brake cylinder is composed of a piston and an additional transmission piston, a hydraulic pressure cushion being formed between these pistons, and in that the closure member of the added shut-off valve is acted upon by the pressure in the pressure cushion in the closing sense and by the pressure at the outlet of the pump in the opening operation. It is therefore accomplished that the closure member of the shut-off valve is substantially pressure-balanced so that no forces are transmitted onto the working piston. Since the pump is switched on only during a brake slip control action, the pressure of the pressure cushion loads the tappet during a conventional braking operation, that is during braking witho
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Burgdorf Jochen
Reinartz Hans-Dieter
Steffes Helmut
Alfred Teves GmbH
Butler Douglas C.
Lewis J. Gordon
Seitter Robert P.
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