Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-01-08
2000-05-09
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031133, 3031162, 3031164, B60K 802
Patent
active
060593806
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to a hydraulic brake system for a vehicle having a traction control unit and a dynamic driving control unit.
Known vehicle brake systems of this kind have a brake pressure modulating valve assembly with one inlet valve and one outlet valve for each wheel brake cylinder, and one return feed pump. The return feed pump, when the brake pressure in a wheel brake cylinder drops, pumps brake fluid released from the wheel brake cylinder back into the master cylinder, or pumps it into the wheel brake cylinder in order to raise the brake pressure.
Problems arise if when the master cylinder is not actuated brake pressure is to be built up, an example being during drive slip control and dynamic driving control. The pressureless brake fluid flows only slowly to the return feed pump, and the pressure buildup is therefore delayed. This may still be acceptable for traction control, but for dynamic driving control a very much faster pressure buildup is necessary, to counteract fishtailing of a vehicle at the very outset.
German Published, Non-Examined Patent Disclosure DE-OS 33 37 545 discloses a precharge pump which is disposed between a brake fluid storage container and the master cylinder and pumps into one of the two pressure chambers of the tandem master cylinder. As a result, when the master cylinder is not actuated, brake pressure in the appropriate brake circuit can be built up very quickly, that brake fluid flows under pressure and thus in an adequate volumetric flow to the return feed pump.
However, the known vehicle brake system has the disadvantage that for the conventional brake actuation without anti-lock control, traction control or dynamic driving control, the precharge pump must be capable of having a flow through it in both directions, so as to assure the necessary flow of brake fluid from the storage container into the master cylinder and vice versa. Hence only special types of pump can be used as the precharge pump, namely hydrodynamic pumps such as centrifugal or flyweight pumps, which when at a standstill can have a flow of brake fluid through them in both directions.
A centrifugal pump would have to be embodied with multiple stages, to meet the demands made of a precharge pump. This makes it expensive. A further factor is that because of the high pump rpm, cavitation and the formation of gas bubbles must be expected, which would cause damage to the centrifugal pump and lead to impairment in the function of the brake system.
Other types of pump as the precharge pump have the disadvantage of throttling the flow of brake fluid, that is, of hindering the flow of brake fluid from the storage container to the master cylinder and back. Centrifugal and flyweight pumps are therefore poorly suited as precharge pumps.
ADVANTAGES OF THE INVENTION
In the vehicle brake system of the invention a hydraulic element assures the free flow of brake fluid from the storage container into the master cylinder and in the opposite direction when the precharge pump is stopped. The flow of brake fluid between the storage container and the master cylinder is not hindered by the precharge pump, so that when the precharge pump is not in operation it has no effects whatever on the function of the vehicle brake system. If the master cylinder is not actuated, it is possible with the precharge pump to build up a pilot pressure in the master cylinder and hence in the vehicle brake system that can be rapidly increased with the return feed pump to a necessary brake pressure to enable rapid response of the traction control and dynamic driving control units.
Another advantage of the invention is that the precharge pump need not be capable of having a flow through it in both directions when it is at a standstill, and a wide variety of pumps are therefore available to choose from. Nor is a high-quality, high-efficiency pump necessary, since with the precharge pump only a pilot pressure is generated, which is raised by the return feed pump to the necessary brake pressure. Accordingly, inexpensive pumps, whi
REFERENCES:
patent: 5335981 (1994-08-01), Volz et al.
Pueschel Helmut
Schmidt Guenther
Graham Matthew C.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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