Lil4X
Elio Addict
Electric PS systems seem to be based on a variable displacement pump or a bent axis pump that drives a series of axial pistons through a "swash plate" whose angle can be tipped by the demand for flow. Running at a constant speed, when there is no demand for hydraulic pressure, the plate is in a "zero" position, meaning it is not driving the pistons, and can be considered to be "freewheeling". But when fluid pressure drops as the result of its being demanded by a ram or a hydraulic motor, the swash plate tilts, developing progressively more piston stroke, thus flow. While it sounds complex, it's really rather simple, and its advantage is that the pump can run constantly with minimal demands for energy - but when you need volume, its there immediately.
This kind of VDP technology is being used on automotive A/C compressors too. Driving them electrically means the input shaft is rotating at a constant speed and not dependent on engine speed which seriously affects the pump output. An electric pump can dispense with a lot of the control mechanism. Here's a 6 minute video of its operation in an engine-driven compressor, if you can stand the deeply nerdy description by a computer voice . . .
I worked with fairly large pumps like these (32 gpm @ 2000 psi) and they were fairly expensive 25 years ago, but technology has reduced the size and cost to produce some very efficient fist-sized pumps that cost a bit more than a conventional PS pump, but are much better suited to PS duty.
This kind of VDP technology is being used on automotive A/C compressors too. Driving them electrically means the input shaft is rotating at a constant speed and not dependent on engine speed which seriously affects the pump output. An electric pump can dispense with a lot of the control mechanism. Here's a 6 minute video of its operation in an engine-driven compressor, if you can stand the deeply nerdy description by a computer voice . . .
I worked with fairly large pumps like these (32 gpm @ 2000 psi) and they were fairly expensive 25 years ago, but technology has reduced the size and cost to produce some very efficient fist-sized pumps that cost a bit more than a conventional PS pump, but are much better suited to PS duty.
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