Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Patent
1989-06-15
1992-05-12
Look, Edward K.
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
60579, 60533, 74110, 303113R, B60T 1314, F16D 3102
Patent
active
051116596
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a device for adapting the charging or discharging characteristic force curve of a hydraulic accumulator to the characteristic force-to-travel, curve of a hydraulic pressure consumer.
Today, brake systems of modern vehicles frequently have hydraulic brake boosters equipped with a pressure source consisting of an accumulator and a pump. The pump is required for charging the accumulator which may be of the piston or balloon or other suitable type. A pedal-operated brake valve is provided by means of which the pressure medium is metered from the pressure accumulator into a booster chamber. Generally, the pressure developed in the booster chamber is proportional to the brake pedal force, and displaces a booster piston acting on a master cylinder.
In order to release the brakes, the booster chamber is placed in communication with an unpressurized storage reservoir so that the pressure medium can flow out of the booster chamber. After release of the brakes, or even during braking, the accumulator is recharged, a certain amount of energy being needed to this end. Thus, during any braking action, a certain amount of energy becomes unavailable for the actuation of the booster.
In a brake-slip-controlled system, the energy loss due to accumulator recharging is particularly high. In the prior art, e.g., there are descriptions of slip-controlled brake systems in which the master brake cylinder is returned to its resting position for the purpose of pressure relief of the wheel brake cylinders. This is accomplished by reversing the booster pressure in a cyclic manner or rather in accordance with the provision of control signals generated by a brake slip control device. Any reversing of the booster pressure, however, means a loss of energy as pressure medium is taken out of the accumulator both for the return of the booster, i.e., for the pressure relief of the master brake cylinder, and for a new braking pressure build-up. Such is the case, for instance, in the brake system disclosed in German Published Patent Application (DE-OS) No. 34 44 828.
A further disadvantage of the known accumulators is that, when charged, they are necessarily under a high pressure which drops during pressure medium removal. The characteristic force curve of a hydraulic pressure consumer, however, may be just the reverse. For instance, such is the case in brake systems. As more pressure medium is metered into the hydraulic booster, the booster pressure increases. The charging capacity of the accumulator must therefore be such that, with a master brake cylinder being maximally pressurized, the almost emptied accumulator continues to make sufficient pressure available so as to enable a corresponding pressure to be generated in the master brake cylinder. The accumulator pressure when fully charged must therefore be correspondingly higher, so that charging of the accumulator must take place against high pressures. This, however, means that substantial energy is needed in order to charge the accumulator.
SUMMARY OF THE INVENTION
It is thus an object of this invention to markedly reduce the energy requirements of a hydraulic system, in particular of a brake system. Accordingly a device is suggested for adapting the characteristic charging or discharging force curve of a hydraulic accumulator to the characteristic force-to-travel characteristic curve of a consumer. The device comprises a master cylinder and piston with which the hydraulic accumulator communicates and a slave cylinder and piston with which the consumer communicates. A transmission mechanism is arranged between the pistons of the master and slave cylinders, the force transmission ratio of the transmission mechanism varying in dependence on the positions of the pistons.
Although the above device is described with reference to a brake system, it is envisioned that such a device can be used in all repeated actuating operations characterized by energy accumulation and discharge cycles.
An especially compact and advantageous embodiment of such a transmission mecha
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Alfred Teves GmbH
Lewis J. Gordon
Look Edward K.
Ryznic John
Seitter Robert P.
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