Re: HP drawn by the power steering pump.

[cordeiro@adi.com (Alan Cordeiro)]

Hi,

The discussion about pump substitutes seemed to hinge
on the fact that I had suggested one or two horsepower
as the load required by the pumping system. 

This was a WAG on my part.

So I tried to come up with some scientific basis 
to see what the results would be;

Area of the pistons ( 0.5" dia )  = Pi x .25 x .25 = .196 sq"

Stroke of piston ( approx ) 0.2"

Pressure ( 150 bar ) generated by the piston = 2200 psi

WORK by EACH PISTON per stroke  = 2200 x .196 x .2  in-lbs
                                = 86.5 in-lbs
                                = 7.2 ft-lbs

There are 6 pistons on the steering circuit, and two smaller
ones on the brake circuit, so I will use 7 pistons in my calc.

AT engine speeds of 1000 rpm, the pump is running at 2000 rpm
                    = 33.3 revs/sec

 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 )

WOW, thats is a lot of load at 1000 rpm.

That would work out to 9 HP at 3000 rpm, ( highway cruising
                                          not 55 mph  )


Can someone go over these numbers, I think I'm on the high side
but still hav'nt spotted where the problem is. It may also be
my incomplete understanding of what the pump is doing when
there is no fluid being drawn from any of its outputs.

Since all this power is converted to HEAT if it is not used,
that implies the pump is self heating to the tune of 4 or 5 KW 
at highway cruising speeds. I find this a little steep
and hard to believe.

I still think the pump is running a half HP at 1000 rpm, and
one to two HP at cruising speeds.


Alan Cordeiro