Electric power steering pump

This is the first post in what will probably be a very slowly progressing project to replace the stock serpentine belt driven power steering pump with an electric motor driven power steering pump.

I have done a fair amount of research on the internet regarding converting various vehicle's hydraulically assisted rack and pinion steering from a belt driven pump to an electric motor driven pump. Some conversions were to achieve space near the front of the engine for a supercharger. Others were to reduce engine loss for drag racing. Some were to improve the performance and handling for circle track or road coarse racing. Most were for gas to electric powered vehicle conversions.

There are two types of electric motor power steering assist. One type is an electric motor with shaft and gearing integrated into the steering column that assists the driver in turning the steering shaft. This is the latest technology because it saves power and reduces fuel consumption. Unfortunately, when the system fails the vehicle is nearly impossible to drive. It would also be impractical to retrofit to my Explorer.

The other type replaces the belt driven pump that pressurizes power steering fluid to the steering rack with an integrated electric motor driven pump to perform the same function. This configuration is much easier to retrofit and consequently used electro-hydraulic pumps are in high demand. The only electro-hydraulic pump I found suitable for retrofit on my Sport was used on the early 1991 thru 1995 Toyota MR2 - a mid engine sports car hence no belt driven pump. This particular series has no integrated power steering reservoir allowing it to be short enough (hopefully) to fit under the battery tray. I have seen these used units sold on eBay for $400 and new ones cost over $800. Last night one was advertised with a purchase now price of $90 and I bought it with no hesitation.


I have an electronic copy of the 1991 MR2 wiring diagram which shows several other power steering related electrical components: ECU, relay, power driver module. These are also expensive to purchase and difficult to find. However, the pump will run at full speed continuously with just power applied to 2 pins. The other components reduce the power consumption (up to 80 amps at startup under load) and vary the pump rotation speed for more assist at slow vehicle speeds and less assist at fast vehicle speeds. Many of the later generations have a steering angle sensor (SAS) that increases pump speed when the steering wheel is turned faster. My Tahoe had variable assist power steering with an SAS on the steering column. As it aged the sliding contact surface became coated making the contact unreliable. On occassion when the wheel was turned at 30 mph the power assist would go to full eliminating all steering wheel turning resistance. If I was not quick to respond the vehicle would unsafely oversteer. After I figured out what was going on I periodically cleaned the contacts by spraying with electrical contact cleaner.

I doubt I will purchase any of the other MR2 steering components. I will probably purchase or design and build a high current motor speed controller that uses the Explorer vehicle speed sensor output (same signal that controls radio volume) to vary the power steering motor speed. Instead of a fuse for the motor power I will use an automatically resetting circuit breaker. I will also need a small reservoir and space to locate it as well as a high pressure hose going from the pump output to the steering rack.

big and heavy

The electric power steering pump/motor is bigger and heavier than I realized.

It is about 11 inches tall and 6 inches wide. It weighs a little more than 11 pounds. It will be challenging to find a place to mount it. I'll pull my wheels to change my spark plugs soon and see how much space is under the battery support shelf.

Even though I don't plan to use the ECU that controls the power steering pump I ended up with one because nobody outbid my $11 offer.

I would need the associated driver module to use the ECU and I suspect a 100 amp motor speed controller might result in a simpler system to implement.

I haven't found one from a U.S. supplier yet.

This is interesting since I didn't know that any vehicles used this set up at that time. Many years ago I fabricated my own electric steering set up in my 1988 van using a Dayton hydraulic pump, and several parts that I had to design myself. It has a magnetic reed switch near the steering column with magnets strapped to the column shaft. I had to design the control module since there wasn't anything readily available. The first module wasn't as good since the pump would run too much. The second module was very complicated, and took 5 months to design. The pump's brushes wear out occasionally, and the starter solenoid wears out often since the pump requires a lot of current to run. I had to install a second battery with an isolator, and a high current alternator to compensate.

variable speed?

I assume that the reed switches detect steering column movement to activate the pump motor. That's a good way to save energy consumption. Does the system respond quickly? Does your controller vary the motor speed?

I plan to have my pump run continuously but eventually vary the pump speed based on vehicle speed. From what I've learned the motor start current is much larger than the running current. Also, the current draw is proportional to load. Hopefully, once the hydraulic system is pressurized the current draw will be less than 20 amps except for low speed turning.

P=E*I (13v*20a= 260 watts) HP=260/745.7= 0.35

What is the rating of your pump motor?

Interesting Dale, I'm watching.

I wonder how well an electric fan controller might function to power that pump. I'd contact Brian of DCC to ask for his input. I wonder if a pressure sensor in the PS line could be used to help to demand more current for the "system."

Find out what kind of PS pressure there is in the OEM lines in various places, with and without the PS pump running. Maybe a simple sensor etc, may be used with a DCC device to power that electric PS pump.:scratch:

It only uses one reed switch, but it has several magnets on the shaft. The switch could trigger the controller by either opening the contact when the wheel is moved or closing the contact when the wheel is moved. The pump isn't variable speed. Since the magnets are powerful, and spaced very close to each other, it only requires a slight movement to activate the system. I bought it from Grainger in the early 1990s, and might have the box with the part number in my shed or basement somewhere. I tried using the original power steering pressure switch to trigger the pump, but was unsuccessful since it was wired to the computer. Ford uses a real ground, and a virtual ground for the sensors. The computer in the vehicle will get damaged if you try to make the virtual ground into a real ground. I had to replace the computer as a result, so I speak from experience. Since your model doesn't have the sensor or the PCM wiring, you could remove the factory plug, and connect a sensor from Autozone. They are around $7 or more.

How is your project coming along? The box from my pump says 12 volt Dayton auxiliary hydraulic pump model number 4F689.

no progress

BrooklynBay said:

How is your project coming along? The box from my pump says 12 volt Dayton auxiliary hydraulic pump model number 4F689.

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Thanks for the information and the interest. Unfortunately, family obligations (disposing of my mother's estate) has prevented me from pursuing any automotive activities (except the forum) and likely will continue for several more months. I'm beginning to experience automotive project withdrawal.

Take care there Dale, I understand about the family issues. Stay warm etc, with this winter weather.

I'm sorry to hear about your mother.

I don't have any issues with the current steering set up in my Exp but this might be a good idea for my BMW.
I've had an Eaton M90 sitting in the garage supercharging a shelf for a while now while I figure out how I'm going to fit to the engine and the spot that the steering pump occupies might worth looking at.

I too wonder if it could run an Explorer rack, I want a turbo under the hood if it's possible.

Why don't you use the steering from a new ford truck or mustang gt500 they are both electric.

integrated power steering

Hotrodmk8 said:

Why don't you use the steering from a new ford truck or mustang gt500 they are both electric.

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I don't know specifically about the Mustang and Ford truck but most of the new electric steering systems designed to increase fuel economy use a small motor mounted below the steering wheel that is integrated into the steering column. Also, I think it is computer controlled. Incorporating that into my Explorer would involve replacing the entire steering column and possibly lower steering assembly as well as trying to kluge together an electronic interface to the PCM. I've heard that the integrated systems are nearly impossible to steer when the motor fails or electric power is lost. With the current Explorer steering if the pump fails steering is difficult but not impossible.

I don't think ford would make it impossible to steer if it lost power,but I have a buddy that has a new truck I will find out.

Looks like the mustang has a electric motor on the rack its self. http://www.caranddriver.com/photos-...00-rack-and-pinion-steering-gear-photo-327717

hydraulics

R1dd1cK said:

Looks like the mustang has a electric motor on the rack its self. http://www.caranddriver.com/photos-...00-rack-and-pinion-steering-gear-photo-327717

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Good find! From the photo I suspect the assist is via motor driven gearing instead of hydraulic pressure assist. Unless the gearing disengages when the motor fails it would be very difficult to overcome the mechanical advantage and steer the vehicle.

looking for mounting space

Today I removed the battery, battery tray and fender well to look for a possible mounting spot for the MR2 power steering pump. The photo below was taken looking down from the engine compartment.


The next photo was taken from the wheel well.


I didn't have time to take any measurements but stuffing the pump into that area would require relocating components and a modification to the fender well. I doubt it would be easy to accomplish and would reduce future maintainability by restricting access to components.

How big is the pump? The area next to the battery above the body mount bolt is the only space in that area. Other than that I'm not sure if the other side under the air inlet tube is any larger.

A/C line & VM valve

If I relocate the A/C line and the vapor management valve there may be room for the pump. I was hoping that the V8 may have a different A/C line configuration but this photo by Joe Dirt of his 2000 V8 A/C line looks similar to mine.

Fuel Vapor Management Valve

It looks like the fuel vapor management valve (FVMV) could be relocated from the stock position:


to behind the bumper below the horns and left headlight assembly: