Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1993-05-20
1995-02-21
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 10, 3031132, B60T 1314
Patent
active
053909950
DESCRIPTION:
BRIEF SUMMARY
STATE OF TECHNOLOGY
The invention concerns a brake pressure control system for braking systems with anti-locking and drive slip control as set forth hereinafter.
Brake pressure control systems of this type for braking systems with a closed anti-locking control system and a drive slip control system are known, and are in use in various design forms. With these, in the case of a wheel having a tendency to lock, the anti-locking control is actuated, with the brake fluid being returned to the main brake cylinder by means of a recirculating pump, in order to reduce pressure in the respective wheel brake cylinders.
From DE-OS 32 15 739, a drive slip control system for vehicles is known, where in order to reduce brake pressure, a pressure agent is released, by means of a control valve, into a storage chamber, and this pressure agent is then recirculated into the connection between the main brake cylinder and the brake pressure control valve by means of a recirculating pump. In this drive slip control system, the recirculating pump is designed as a suction pump, and between the main brake cylinder and the pump intake a connection duct with a changeover valve is interposed.
In the recirculation of brake fluid, a problem arises in that in the case of particular driving conditions, in order to maintain driving stability with controlled brakes, the brake pressure must be very greatly reduced, whilst on the other hand no negative pressure should arise in the braking system, since this could result in the danger of air entering the system. For this reason, in known recirculating pumps, the opening pressure of an inlet valve located on the recirculating pump is set at >1 bar. By this means, the delivery chamber of the pump is no longer filled at brake pressures of <1 bar, and the recirculation is interrupted. However, a disadvantage here is that no brake fluid can be taken in from the ventilated reservoir by means of the recirculating pump, and so a desired multiple use for the anti-locking or drive slip control system is not possible.
It is possible to limit the brake pressure towards the lower end, generally in the case of recirculation, in principle via an additional servo-valve. Here, the servo-valve is built in upstream of the inlet valve of the recirculating pump, in relation to the return flow, and thus prevents the pressure in the recirculation canal from dropping below the previously set value. Downstream, behind the servo-valve, the duct which is connected to a reservoir, leads into the suction port of the pump. Thus should the need arise, brake fluid can be taken from the reservoir via the recirculating pump, without the pressure in the recirculating pump falling unacceptably.
In familiar servo-valve designs, these are valves with spring-loaded spherical or conical closing bodies through which the flow is in the direction of opening. However, these valves have a relatively large hysteresis between opening and closing pressure, and therefore cannot be set precisely. This results from the fact that the opening and closing of a spring-loaded valve does not occur suddenly, because an ideal and absolutely precisely-shaped seat geometry cannot be realised. Rather, inaccuracies in shape, roughness and guide clearance lead to the situation where on closing the valve, the closing body and the valve seat initially touch each other only in certain places. Only after increasing the closing force, and the alignment, and the elastic deformation associated with it, does the closing body make contact with the full extent of the valve seat, and thus effect a complete seal. The same applies in reverse for the opening process. Between the fully opened and closed state, the closing force must be increased by a certain amount. This necessary closing force difference does decrease with improved seat geometry, but the capabilities of production engineering and the corresponding costs, impose limits.
A small valve hysteresis, i.e. a small pressure difference between the opening and closing of the valve is, however, necessary i
REFERENCES:
patent: 3079946 (1963-03-01), Rosler
patent: 3754567 (1973-08-01), Whitten
patent: 4121619 (1978-10-01), Pauliukonis
patent: 5152586 (1992-10-01), Burgdorf
patent: 5195809 (1993-03-01), Burgdorf
Greigg Edwin E.
Greigg Ronald E.
Muratori Alfred
Oberleitner Robert J.
Robert & Bosch GmbH
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