Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1996-03-01
1997-06-03
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60451, F16D 3102
Patent
active
056343353
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydrostatic transmission with a brake valve, for application with open or closed circulation and with constant or variable direction of flow.
Such a hydrostatic transmission is for example known from DE-OS 41 29 667 as a reversible transmission, e.g. having variable direction of flow, and having open circulation, for the drive of excavator vehicles. In load operation of such an excavator vehicle, the hydraulic pump, driven by the drive source, delivers to the hydraulic motor via the first or the second working line--in each case serving as feed line--depending upon the direction of travel determined by means of a travel direction valve, in order to drive this hydraulic motor and thus the vehicle wheels. The brake valve, arranged in both working lines for reason of the reversibility of the transmission, is controlled by means of the working pressure prevailing in the respective feed line in load operation, via a control line, and thereby held in a position in which the brake valve makes possible both the unthrottled pressure medium feed via the feed line and also the unthrottled pressure medium return via the respective other working line serving as return line. Further, the working pressure in the feed line acts upon the setting device as setting pressure, via the first setting pressure line and via the second setting pressure line which is also connected to the first working line because of the reversibility of the transmission, in the direction of maximum displacement volume of the hydraulic motor.
In overrun operation of the hydraulic transmission, that is when the drive of the hydraulic motor is not effected by means of the hydraulic pump but is taken over by the vehicle wheels, for example upon travel down an incline, the working pressure in the feed line, and in the return line section downstream of the brake valve connected via the travel direction valve to the tank, falls and thus is available neither as control pressure for the brake valve nor as setting pressure, via the first setting pressure line, for the setting device. The brake valve hydraulically relieved of pressure in this way then takes up its braking position in which it throttles the pressure medium return by means of cross-sectional reduction of the return line and generates a corresponding backup pressure which brakes the hydraulic motor and thus the vehicle. The backup pressure in the return line acts as setting pressure on the setting device, via the second setting pressure line, in the direction of maximum displacement volume of the hydraulic motor and swings the latter out up to maximum displacement volume through continuous increase as a consequence of feedback. The maximum pressure medium flow generated by the hydraulic motor in this position generates a maximum backup pressure at the brake valve and thus a maximum braking force at the vehicle wheels.
This maximum braking force can, under certain operating conditions of the hydraulic transmission, give rise to undesirably great decelerations, such as for example upon the employment of a subsequently-connected mechanical gear change transmission which increases the braking force generated by the hydraulic motor in correspondence with the transmission ratio.
The object of the invention is to so further develop a hydrostatic transmission of the kind mentioned in the introduction that the braking effect achievable therewith can be adapted to differing operating conditions.
This object is achieved by a relief valve device, preferably in the form of a settable pressure limiting valve, which is controlled by the control pressure taken off from the second setting pressure line via a control line, in overrun operation of the hydrostatic transmission holds the setting pressure in the second setting pressure line at the pressure desired-value set in each case, with the aid of the counter-pressure, expediently in the form of a spring, which set pressure desired-value sets the hydraulic motor--via the setting device--to a corresponding displacement volume. The pre
REFERENCES:
patent: 4481769 (1984-11-01), Nagahara
Brueninghaus Hydromatik GmbH
Lopez F. Daniel
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