Re: HP drawn by the power steering pump.

[Peter Orban <ORBAN@nrcamt.iamt.nrc.ca>]

>>On Nov 29, 10:10pm, Robert (Bob) Myers wrote:
>> Subject: Re: HP drawn by the power steering pump.
>...
>> Pressure-volume work = P*delta V.  If the fluid is imcompressible then
>> delta V = 0 and P*delta V also = 0.
>>
>> The work being done is strictly the work being done comporessing the trapped
>> air in the pressure accumulator and pushing the hydraulic cylinders around
>> plus what is required to overcome friction losses.  This won't amount to
>much.
>
>>-- End of excerpt from Robert (Bob) Myers
>
>	Dead on, I believe.  So, whenever power assist is required, the
>	accumulator loses a bit of pressure which is replenished by the
>	pump, translating to work done by it.  Right?

There is something wrong here. The work done by the pump is the
volume * pressure difference before and after the pump. Now, the pumps
are not a variable displacement pumps, right?
I thought that only the brake is driven from the pressure accumulator.
When there is no assist, nothing to replenish in the accumulator, then
there is still oil pumped around, but it is bled off. So there is a
pressure difference, and there is volume. That is for the brake.
As for the power steering, when the steering is not loaded, the oil
circulates freely, the pressure difference is very little. When the
steering is loaded, the pressure rises, so the work done by the pump
also rises.
Am I cheating somewhere here?

Peter
orban@nrcamt.nrc.ca