Search Results

In conventional hydraulic systems, a fixed or variable displacement pump is used to supply a number of separate branches of a circuit, each with potentially different flow rate and pressure requirements which can vary widely with time. Conventional approaches to distributing the flow to the individual branches generally involve valves controlling the flow to each individual branch. This can lead to significant energy losses from valve throttling, depending upon the actual flow and pressure requirements of each part of the circuit. In the system discussed in this paper, the entire output of the pump is quickly and sequentially directed to each individual branch of the circuit. The average speed of the actuator is controlled by the proportion of time that the pump flow is being directed to that branch. A small accumulator is incorporated in each branch of the circuit to smooth the velocity of the actuator.

Four alternative fluid power systems were analyzed to determine their efficiencies and standby power consumption while providing hydraulic power for power steering and a hitch for an agricultural tractor operating over a typical duty cycle. The investigation shows that a significant reduction in losses can be achieved with systems incorporating both split flow and variable delivery capabilities. These characteristics reduce losses by providing the required flow and pressure to each function without a large pressure drop for the function operating at the lower pressure. These systems can be used to improve efficiencies whenever there are multiple, simultaneous hydraulic power demands which require significantly different pressures.