Re-visiting a clutched power steering pump

[t vago]

Based on both oil pan 4's excellent work on figuring out how much power a power steering pump draws, this Hot Rod article I found that gives a bit more power loss detail for Mopar engines, and the original inspiration for this idea, I've decided to go ahead and try to attach an A/C compressor electric clutch pulley to my power steering pump.

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

Hot Rod: Mopar Engines - Power Vs. Luxury

Ecomodder: Electric Clutch Power Steering

Basically, I want the power steering to be power-assisted at speeds only below 20 MPH, and to disengage while the vehicle is stopped and the engine speed is below 900 RPM and the brake pedal is pressed (with an override, of course)

[oil pan 4]

Ideally clutched is the ultimate way to go. You have normal power steering restored and it draws less than 10 amps and you can run it as long as you want.

I took the easy way out with a 12v hydraulic power unit, it might come back to bite me in the but because I should only run the HPU for 20 or 30 seconds definitely no more than a minute with out a good long cool down. Plus it draws like 110 amps under load and 60 amps no load. The HPU was not cheap, but cheaper than a clutched commercial/industrial hydraulic pump. In theory sticking an AC compressor clutch on some kind of OEM style power steering pump should be the cheapest option.

[jakobnev]

I wonder if it's possible to modify the rack itself to get less assist.

[oil pan 4]

The problem is the power steering hydraulic pump requires quite a bit of power just to circulate fluid around the system when you are not needing any power assist. It actually takes very little hydraulic power to use "power steering" to move the wheels to the left or right when sitting still.
When driving along down the road the power steering takes up to 1 horsepower just to circulate the fluid, when its not even doing anything as far as you are concerned. Then when you need it the power steering only takes around 2 horse power to run the pump its self to push the rack or steering arm one way or the other.

[JRMichler]

All, and I do mean ALL, of that pump power goes into heating the oil. If the system was not wasting that much energy, there would be no need for a power steering oil cooler.

[t vago]

Well, I finished revisiting this idea, and came to the conclusion it'd be simpler just to install an electrohydraulic power steering pump out of a Toyota MR2.

http://ecomodder.com/forum/showthrea...ing-18629.html

[serialk11r]

Originally Posted by oil pan 4

The problem is the power steering hydraulic pump requires quite a bit of power just to circulate fluid around the system when you are not needing any power assist. It actually takes very little hydraulic power to use "power steering" to move the wheels to the left or right when sitting still.
When driving along down the road the power steering takes up to 1 horsepower just to circulate the fluid, when its not even doing anything as far as you are concerned. Then when you need it the power steering only takes around 2 horse power to run the pump its self to push the rack or steering arm one way or the other.

Actually, it takes 2 horsepower all the time, doesn't matter if the wheel is turned or not. The pump is positive displacement so it circulates the same amount of fluid at any given rpm, and the pressure regulator is a simple valve.

If you're turning the steering wheel very fast, it's possible the pump actually uses less power than while the steering wheel isn't being turned because if you turn the wheel fast enough it'll drop the pressure in the system.

Electro-hydraulic pumps make this less of an issue by slowing down the pump to regulate the pressure, but you need the pressure sensor and electronic control over motor speed to make this work. Applying constant voltage to a PS pump motor gives you constant amperage draw.

A clutched PS pump is an okay solution, but grabbing an electrohydraulic pump is better. The clutched pulley weighs quite a bit and when the pump is off the steering effort is going to be much higher since you are forcing hydraulic fluid through all the valves. You can find old EHPS pumps on UK Ebay for ridiculously cheap prices, so why would you go through the trouble of doing a clutched pump?

[oil pan 4]

My tests showed that it takes about 1 horsepower to circulate fluid at 2500 RPM on my vehicle with the stock pump.
The hydraulic power unit I am using to drive the power steering draws 50 to 60 amps free flowing and 110 amp to move the steering sector while sitting still on dirt.

The only time the system develops pressure is when the wheel is turned. The fluid free flows when there is no steering wheel input.

[t vago]

Originally Posted by oil pan 4

My tests showed that it takes about 1 horsepower to circulate fluid at 2500 RPM on my vehicle with the stock pump.
The hydraulic power unit I am using to drive the power steering draws 50 to 60 amps free flowing and 110 amp to move the steering sector while sitting still on dirt.

That current draw does seem a bit high. What speed does your HPU use to drive your power steering? Can it be lowered? Reason I'm asking is because the current draw of the Toyota MR2 pump I'm using draws something like 4 amps at idle, and goes up to almost 50 amps when called upon to operate the rack.