# Re: HP drawn by the power steering pump.

• To: quattro@swiss.ans.net
• Subject: Re: HP drawn by the power steering pump.
• Date: Wed, 30 Nov 94 18:33:05 EST
• Sender: quattro-owner

```>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

Peter,

Thanks, I think you have spotted the problem with my calculations.

I was thinking that under no steering load, the pump would just
recirculate oil between its high pressure reservior and the
inlet/intake reservior.

The flow HAS to take place, there is no variable displacement
in the pump mechanism. The inlet reservior is at atmospheric
pressure ( else the plastic bottle on the firewall is at
2200 psi ). However. if the steering regulator valves allow
oil flow when no torque is on the input shaft, and only
restrict flow when assist is needed, viola, almost no pressure
differential to pump against.

The calculation changes from:

> Therefore, Power used = 33.3 x 7 x 7.2 ft-lbs/sec
>                       = 1680 ft-lbs/sec
>                       = 3.05 HP  (  each HP is 550 ft-lbs/sec )

To:

Therefore, Power used = 33.3 x 1 x 7.2 ft-lbs/sec
= 239 ft-lbs/sec
= 0.43 HP  (  each HP is 550 ft-lbs/sec )

At 3000 rpm that would be 1.3 HP.

It is starting to sound better now, sort of when you eliminate
all the alternatives one by one, whatever is left must be
what is happening.

Now, if we were to replace the ( stupid &*%#@ ) pump with
an electrical pump that had the same capacity to help the
steering assist at idle, it would have to be ( go back
to the old calculation, it now applies.. ) 2 to 3 HP.
However, if you were to get the right capacity
reservior for the steering, steady state could be as low
as ZERO HP, with a half HP to "fill-er-up" every now and then.

I think the discussion has proabably run its course, I doubt
anyone will go through all the bother to gut and replace the
"perfect" hydraulic system with something else. It might
be even flakier.

Alan Cordeiro

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