How much energy does it take to turn a power steering pump

[oil pan 4]

I am not asking, I already know.
Many have pondered, some have argued.

I finely got around to measuring how much power it takes to turn a P/S pump. ( about this time last year)
It looks like if you can keep the P/S turning at 850rpms it takes hardly any power to turn, around 150 to 200 watts.
But when you bring it up to a more normal cruse speed say about 2,000 rpms power draw goes up quite a bit. It took a little over 500 watts to keep it turning at that speed.
That is with the pump just spinning with out any input to the steering wheel.
For my suburban 500w gets about half MPG.
That should scale down to about a 2 to 3mpg savings on a small car. Assuming my suburban takes about 35 to 40 horsepower to maintain 60mph and a small car takes about 10 horses to go the same speed, then account for the car engine turning the pump about 3000rpm.

Beyond 2000 RPMs I believe that you will see a proportional increase, wattage doubling as the RPMs double.

[darcane]

Any details on your testing setup? Could you test while turning the steering wheel? Any chance you could test on a different car for more data points? And test at higher RPMs to verify your assumption?

[ecomodded]

The Power steering pump has a large design flaw in that it makes less power when you need it ( at idle) and more when you don't like highway speeds. Its ass backwards, We need a new pump design or is there a electric pump available that runs at a constant rpm ?

You would think they sell one with all the hybrids in development.

[oil pan 4]

No chance of testing in a car any time soon. I tested it on the suburban while I was replacing the radiator and making some other vehicle body modifications.
I used a 120v power drill, varrac, kill-a-watt meter and a hand held optical tachometer.
And it was a very hot day.

[oil pan 4]

This is how much the pump and steering box warms up after a very short 1 mile drive.



I am surprised how fast it warms up.
It must be stopped.

[MkVer]

I wonder if you could put a solenoid controlled bypass line in so at highway speeds the pump pretty much free spins....

Originally Posted by ecomodded

We need a new pump design or is there a electric pump available that runs at a constant rpm ?

You would think they sell one with all the hybrids in development.

(ignoring VW's current woes, other threads have that covered) Most newer TDIs (at least since 2005) have electric assisted steering. At highway speeds it's completely turned off. In the simplest terms its an electric motor attached in parallel to the steering column and controlled by wheel speed. In addition to being a MPG improver, its actually considered a secondary safety feature since it makes it harder to make abrupt inputs at speed.

[Fat Charlie]

Originally Posted by MkVer

In addition to being a MPG improver, its actually considered a secondary safety feature since it makes it harder to make abrupt inputs at speed.

That's one secondary safety system I'm a fan of. I hate the supplemental restraint systems (I'd prefer to simply wear my seatbelt to protect me from collisions than have to wear it to protect myself from the airbags that "supplement" it) and in dodgy traction I hit the dash switch to disable the backup electro-hydraulic traction control. I prefer my foot operated traction control, which most people call a manual transmission.

[California98Civic]

Oilpan... the 3 mpg number you speculate fits nicely with the 2 or 3mpg I thought I saw jn my Civic after removing the PS system.

Originally Posted by MkVer

I wonder if you could put a solenoid controlled bypass line in so at highway speeds the pump pretty much free spins....

Or an electromagnetic clutch for the pulley like most alternators have now. The ECU could just disengage the pulley under certain conditions, as it does a "smart" alternator. "Smart" pulley driven power steering pump is born. Could put such a pulley on an "on/off" switch too and ckntrol it from the dash. So you would only draw power from the engine at the low RPMs that oilpan is saying draw very little power. But his test was without turning the steering wheel, so wouldn't turning the wheel increase power draw somehow?

[jamesqf]

In a reasonably-sized car like a Civic, why do you need power steering, anyway?

[cRiPpLe_rOoStEr]

Originally Posted by California98Civic

Or an electromagnetic clutch for the pulley like most alternators have now. The ECU could just disengage the pulley under certain conditions, as it does a "smart" alternator. "Smart" pulley driven power steering pump is born.

There were some "progressive" power steering setups which decreased their assistance at higher speeds, not sure if they used some sort of electromagnetic clutch...