Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1980-05-16
1982-08-10
Cohen, Irwin C.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60424, 91 29, 91 33, 91516, 91520, F15B 1116, F15B 1306, F16H 3946
Patent
active
043431518
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a hydraulic control system for supplying pressurized fluid to two work circuits, one of which has priority over the other.
BACKGROUND ART
In many vehicles which have a hydraulic steering motor and a hydraulic implement circuit which receive flow from a single pump, the steering motor is connected upstream of and in series relation with the implement system. As a result, the pump is working against the sum of the load pressures of the steering motor and the implement circuits. The pump, however, can only operate up to its rated operating pressure and can only supply its maximum rated flow rate. Hence, if the implement circuit is experiencing a high load pressure, only a relatively low pressure (a portion of the pump rated operating pressure) is available across the steering motor for operating it. This can lead to low torque stalling of the steering motor. One can utilize a pump with a very high operating pressure and flow ratings, along with a high power engine to drive the pump, but this adds to the weight, size and cost of the vehicle.
Prior art load sensitive hydraulic systems, on the other hand, suffer from the disadvantage that the return flow from the priority work circuit is passed to tank regardless of the pressure requirements of subsequent circuits. This requires the use of a wastefully large pump.
In essence, it would be advantageous to have a system which gave first priority to the steering motor, which utilized a pump primarily sized to the steering motor, wherein the steering motor was not subject to low torque stalling, which provided both high speed turn and high speed implement correction when operating at relatively lower pressures and prevented such dual high speed operation when the implement was operating at a relatively higher pressure level, and which provided underspeed-type engine protection as well.
The present invention is directed to overcome one or more of the problems set forth above.
DISCLOSURE OF INVENTION
According to an embodiment of the present invention, an improvement is provided in a hydraulic system having a pressurized fluid source, a first work circuit having an output flow, a second work circuit, an input flow path connected to deliver flow of pressurized fluid from the source to the first circuit, and a series flow path connected to receive the output flow from the first circuit and to deliver the output flow to the second circuit. The improvement comprises a parallel flow path connected to receive a portion of the flow from the source and to deliver it to the second circuit. A valving structure is in the series flow path and means are provided for opening the valving structure to direct flow to the second circuit in response to load pressure in the second circuit being below a selected value. The valving structure blocks flow to the second circuit when the load pressure in the second circuit is above that value.
Through utilizing an improved hydraulic control system as set out above, motor discharge flow is supplied via series flow to the low pressure implement hydraulic functions, which thereby provides high speed cornering of the vehicle carrying the system and high speed implement correction at relatively lower pressures. Further, discharge from the vehicle steering motor is dumped to tank when implement pressures are high. The system thereby prevents low torque motor stall due to insufficient differential pressure across the steering motor. Also, the system provides underspeed-type engine protection whereby utilization of vehicle horsepower is enhanced.
BRIEF DESCRIPTION OF DRAWING
The drawing consists of a single FIGURE which schematically illustrates an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The drawing illustrates a hydraulic control system 10. The system 10 includes a pressurized fluid source or pump 12. The pump 12 supplies fluid to a first work circuit 14 of primary (higher) priority and to a second work circuit 16 of secondary (lower) priority. The first work
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patent: 3878679 (1975-04-01), Sievenpiper
patent: 4002220 (1977-01-01), Wible
patent: 4043419 (1977-08-01), Larson et al.
patent: 4089169 (1978-05-01), Miller
Caterpillar Tractor Co.
Cohen Irwin C.
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