Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1980-04-07
1982-08-24
Cohen, Irwin C.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60422, 60428, 60430, 91529, 91530, F15B 1116, F15B 1306, F15B 1309
Patent
active
043454364
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates generally to fluid systems having a plurality of pumps for supplying working fluid to a plurality of fluid circuits. More particularly the invention relates to the control and coordination of variable output fluid sources in systems where pump output that is not being used by an associated circuit is made available to another circuit served by another pump.
2. Background Art
Fluid driven devices, such as rotary or reciprocating fluid motors for example, are often operated intermittently, at variable speeds, with variable loading or under some combination of these conditions. Demand for working fluid is therefore variable with respect to both pressure and flow.
Greater efficiency is realized under these conditions if the source of working fluid is controlled so that output pressure and preferably output flow as well varies in accordance with demand. Otherwise, the fluid source must be operated to continually provide a high output pressure and high flow adequate to meet the peak demands of the driven devices. During periods when the demand is below maximum, the fluid source needlessly consumes power and needlessly contributes to heating and aeration of the working fluid.
It is a known practice to avoid these problems by feeding back a pressure signal from the driven device to a control which adjusts the output pressure of the fluid source to match variations in demand and which in some cases adjusts output flow as well.
Fluid source control of this kind is subject to a complication in systems in which a pump supplies fluid to a plurality of devices. At any given time, the feedback signal or control pressure should correspond to the pressure within the one of the several devices which is most highly pressurized and different ones of the devices may become the most highly pressurized one at different stages of operation. Consequently the control system must compare the pressures within each of the devices and transmit the highest pressure to the pump control.
One known form of pump control for this purpose uses a network of resolver valves to compare pressures from several fluid driven devices in order to communicate the most highly pressurized device, at any given time, with the fluid source control.
Pump output control by feedback of a control pressure from a driven device becomes still more complex in fluid systems that have more than one pump each supplying an associated separate circuit of fluid driven devices and which also have fluid exchanging arrangements which make fluid from one pump available to supplement another pump when the pumping capacity of the one pump is not being fully used by its own circuit. In such a system, the pressure comparing function of the pump control of the one circuit must be temporarily extended to include a pressure from another circuit during periods when fluid transfer is occurring.
To accomplish the conditional comparison of pressures from devices served by separate fluid sources without intercommunicating such devices, prior fluid source controls for systems of this kind include check valves or the like in the control pressure lines between the fluid source control and the several devices. Thus the control pressure is transmitted to the fluid source control through a one way flow path. Consequently pressure increases from the most highly pressurized device are directly transmitted to the fluid source control but pressure decreases are not. To cause the control pressure to decrease when the pressure at the most highly pressurized device decreases, it has heretofore been necessary to provide a continually open bleed orifice in the control pressure line. This allows the control pressure to drop following a decrease in pressure within the most highly pressurized device since, owing to the bleed, a continual input of fluid from that device, through the check valve, is needed to maintain the control signal pressure at any given level.
A continual bleeding or draining of fluid from the fluid source control pressure line ha
REFERENCES:
patent: 3693506 (1972-09-01), McMillen et al.
patent: 3987623 (1976-10-01), Bianchetta
patent: 3991571 (1976-11-01), Johnson
patent: 3998053 (1976-12-01), Johnson
patent: 4112821 (1978-09-01), Bianchetta
patent: 4210061 (1980-07-01), Bianchetta
Borg Warner Pressure Compensated Directional Control Valves Brochure #HDS 75-1.
Caterpillar Tractor Co.
Cohen Irwin C.
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