Electrohydraulic Power Steering
 

As the title hints, I think I will pursue installing one of these critters into my Dakota. I have a 2001-2005 Toyota MR2 power steering pump module (a combined electric motor, pump, reservoir, and controller), and I found these nice instructions over here at DIYElectricCar.com.

I should be able to re-install the stock crank pulley (I swapped it with an underdrive pulley a few weeks ago and saw a whopping 1% improvement in FE), and once I do that, I should be able to get a shorter serpentine belt that would bypass the factory power steering pump altogether.

I am looking to get more than a 1% FE improvement. Specifically, I am looking at a target of around 3%, which would raise my average FE from around 20 MPG right now, to around 20.5 MPG. Not much, to be sure, but I already have most of the needed equipment floating around already in my garage - 60 amp rated relay, 4-gauge fuse holder, 4-gauge wires, electrical connectors of all sorts (crimp+solder and Weatherpak) 18-gauge wires, power steering return line, factory service manual, and (of course) the pump unit itself. I just need a pressure hose with a 16mm x 1.5 inverted flare fitting on one end and a 18mm x 1.5 o-ring fitting on the other end, a custom-made mounting bracket (and a mounting point), and a shorter (~82 inch) serpentine belt.

The big challenge I am seeing right now is where to install this thing. It's not very small, and of course the engine bay is a little crowded.

http://image.moparmusclemagazine.com...e_Bay_View.jpg

Not quite my engine bay, but similar enough so that you can see what I'm dealing with.

Very nice, keep us up to date!

looks like your a prime candidate to use George and I's alternator improvement circuit ;)

If you are having too much difficulty finding room to stuff the electro hydraulic unit in there, here is what I would like to put in my car:
Hydraulicstore.com - 877.778.3533 -
Notice the replacement pump clutch section.

Were I do to something like that, I'd disconnect the pump and loop the lines to the box. Or get a manual box if there's one that'll bolt in.

I think I have found a good spot for the electric pump module ("good" meaning that it'll actually fit and be oriented correctly). However, there are a couple of caveats.

First, the stock power steering pump, reservoir, and PS fluid cooler will have to be removed as a unit. I will not be able to keep the stock unit in the engine bay and have the electric pump installed at the same time.

Second, the pump will very likely sit low in the engine bay, which will make checking the power steering fluid level somewhat of a challenge.

I think I can live with both of these caveats. I will make some mounting brackets to mount the electric pump module on the truck chassis, and then wire it up.

After some digging around, I could find the input and output pins on the pump module itself.

A1 - high amperage +12VDC
A2 - high amperage ground

B1 - idle up output to Toyota ECM (active high or active low?)
B2 - 4 pulse/rev speed sensor input
B3 - "TC" diagnostic connector
B4 - N/C
B5 - EHPS relay control (active low)
B6 - WOT cutout input from Toyota ECM (possibly active low)
B7 - "TS" diagnostic connector
B8 - N/C

C1 - switched ignition +12VDC
C2 - "SIL" diagnostic connector
C3 - N/C
C4 - warning lamp output (possibly active high)

So, it should be a simple matter to come up with a T flip-flop to interface my truck's VSS output (8 pulse/rev) to the input of the pump. I will probably rig up a small relay that switches a ground signal, controlled by the idle-up signal, that would be fed as the power steering pressure switch signal into my truck's engine computer. I'll probably end up using some sort of comparator circuit, taking its input from the throttle position sensor, which would provide the WOT cutout input for the pump module. Wiring up the warning light ought to be pretty simple, too.

steering angle sensor
 

Steering angle sensor? Nope.
 

I have not made mention of such a sensor, because this particular module does not require such a sensor. It uses an internal hydraulic pressure sensor to sense demand. The older MR2 EHPS used several modules and sensors, including what you're describing. This one is from a newer MR2, and is almost completely self-contained.

You're right. However, this is not a concern. This module was not designed to be smart enough to require a network for operation - CANBUS, ISO, J-1853, CCD, or otherwise.

The pump will still operate, regardless of whether or not I hook up the WOT cutout wire and idle up command wire. Those two wires are "nice-to-have" wires, but they're not strictly necessary for operation.

The speed signal wire is the most important signal wire, because it will allow the module to determine when to reduce its output power. The warning lamp signal is the second most important signal wire, because that will tell me if something's wrong.

The diagnostic wires are not going to be hooked to anything, since they only went to a diagnostic connector on the MR2 to begin with. This module was never interfaced with the MR2 network.

Not entirely sure how this would work. Do you mean that I should tap the wiring that drives the A/C compressor clutch?

*cough* *cough* *cough*

Wow! This old thread sure gathered a lot of dust! Hope I don't catch a cold from all of this dust I knocked off of it!

Anyhoo, basically gave up on trying to attach an air conditioning clutch to my existing power steering pump, and am re-pursuing this MR2 pump option. I think I found a good spot, too. I'm going to attach the pump to right below where the battery sits. With the existing power steering pump removed, the MR2 EHPS fits right in. I have to get an 82 inch length drivebelt.

Had to order some Summit Racing fittings to construct a supply hose, and the parts should get in by Thursday.

Thinking of programming an Arduino to control the IDUP B1 pin to my truck's PCM, the EFI enabling signal B6 pin to the EHPS, do the necessary divide-by-two of the VSS signal, and drive an LED based off the warning lamp WL C4 pin. The Arduino would also get signals from the transmission control module and the brake lamp switch, so it could turn off the EHPS whenever the truck was in Park, or the brake pedal was pressed.

Some progress... Got the mount fabricated and bolted together. The mount will be attached to the battery brace. I had to remove the front bumper and the left fender for an unrelated reason, and the battery brace was right there for the taking. The stock power steering pump has been removed, and the serpentine belt has been replaced with an 82 inch length one.

The mount is made of aluminum square tubing, 1 in x 1 in, with a thickness of 1/8 inch. The bolts used are 5/16 in 304 stainless steel.

(click on picture for larger view)

Fiat Dakota with left front fender, bumper, grille removed
http://www.tom-viki.com/spgm/gal/Car...1606180000.jpg

Front inner view of mount, off of vehicle
http://www.tom-viki.com/spgm/gal/Car...1606290000.jpg

Rear inner view of mount, off of vehicle
http://www.tom-viki.com/spgm/gal/Car...1606290001.jpg

Installed, inner rear view looking outboard
http://www.tom-viki.com/spgm/gal/Car...1606290002.jpg

Installed, inner rear view looking outboard
http://www.tom-viki.com/spgm/gal/Car...1606290003.jpg

Installed, inner front view looking outboard, next to coolant recovery tank
http://www.tom-viki.com/spgm/gal/Car...1606290004.jpg

It works!

I had to modify the wiring a bit to accommodate the electrical parts I have on hand. The PS unit controls a normal 30 amp automotive relay, which then switches a Toyota PS solenoid relay. That controls 50 amp power to the PS unit.

It was a bit of fun to make the pressure hose from -6an braided stainless steel hose. I could use the return hose with no modification.

The steering feels normal when the PS unit is running, even with the engine turned off.

The system has been flushed of most of the old fluid, and has been bled. I still have to connect up the VSS signal. I will probably leave the IDUP and the EFI signals alone for now, since the engine computer should be able to compensate for an increase in electrical demand caused by the PS unit, and the PS unit powers up by itself.

Two more things of note:

You can find the Toyota FSM for the 2000 MR2 here -> Index of /car/Toyota/mr2 spyder/Repair Information/Repair Manual/05 - Diagnostics

For the Dodge, be sure to either reconnect the stock power steering pressure switch to its electrical connector, or jumper the two connector terminals together. Otherwise, the Dodge engine computer thinks the power steering is under load, and will throw a P0551 code with a CEL when you drive above 40 MPH.

Well done.
I was thinking about using one of those but I was not sure if that P/S pump designed for a rack on a little car would work on a 3/4 ton chevy recirculating ball P/S system. Because I could find no pressure and flow numbers.
Does the Dakota P/S us recirculating ball or is it rack and pinion?

Thanks!

Forgot to mention that the power steering unit got installed into the Durango. I figured that, since we were travelling to Oiho in the Durango anyway to go visit family, and that I'd have a lot of time on my hands while there, and while the Durango has approximately the same engine as the Dakota, I might as well test the installation on the Durango.

I don't know exactly what the flow numbers are, but I can tell you that at idle, and with 16 fluid ounces of fluid in the reservoir, the pump will empty out its reservoir through the gear in about 3 seconds. That works out to approximately 2.5 gpm. I didn't really accurately measure the time, though, so YMMV. The MR2 manual states the pump should develop at least 711 psig at full lock. Other than that, there's not a whole lot of information on the intertubes about this pump.

Both the Dakota and the Durango use rack and pinion steering. I would think that your recirc ball setup would perhaps feel slightly sluggish with this pump. I know that the Durango occasionally has a slight amount of lag, usually when coming to a stop after decelerating. It may have something to do with the fact that the Durango (and the Dakota) outputs a VSS that is 8000 pulses per mile, and the the pump only expects 4000 pulses per mile.

For recirculating ball 700psi is enough.
The hydraulic power unit I use is 2.4gpm at a maximum of 1,400psi.

I can also tell you this much, now: The pump puts out pressure in excess of the 1000 psig rating of the braided stainless pressure hose I fabbed up. The hose burst about 3 inches away from the pump outlet, and sprayed fluid all over the front of the engine. It occurred as my wife was negotiating a parking lot. Time to find a better hose...

Good luck!

Funny you should mention that!

I had DiscountHydraulicHose.com fabricate a hose for me. It's a 3 foot length of 3/8 inch SAE 100R12 hose that's good for pressures up to 4000 psig, and temperatures up to 100 C. One end has a flareless compression fitting to tie into the existing tube, and the other end has a 3/8 JIC fitting which is compatible with the -6AN banjo adapter on the pump itself. It cost me a hair over $40, with shipping extra.

Ordered the hose Wednesday night, got it today, and installed it just now. The Durango power steering works again!

Now to go about making that Arduino-based adapter... I think I figured out how to pull diagnostic codes from the pump computer.

Ha! :D
Do keep us informed.

Cool. And encouraging that you had a five year gap start to finish, but did in fact finish. I have a couple old projects on my car. I hope to finish them this year. Haha

Yah... I can't remember why I abandoned the project to begin with. I had the pump in hand, and was trying to figure out how to plumb it, and then... it just dropped off the radar.

Anyhoo, some promising news. Logged the last few tankfuls with this pump installed. Results are consistent with my estimates, which is good.

The 7/5 return trip from Ohio saw an average fuel economy of about 19.8 MPG, which is really good considering I had a Dakota front bumper lashed to the hitch-mounted cargo carrier.

This latest long trip promises even better numbers. There is no cargo carrier installed this time. Typically, the Durango's trip computer tracks to within 1/2 an MPG of what I calculate, so the below picture indicates some significant fuel savings.

Taken at the Indiana I-80 West Toll Gate (~280 miles on last tank fillup)
http://www.tom-viki.com/spgm/gal/Car...1607120000.jpg

Now that's a result.

I'm curious about what you have learned about how the electric motor control algorithm operates.

Is the VSS input basically used to proportionately control (inversely) the motor's speed and/or turn on sensitivity?

How does it operate when stopped? Is the motor fully off until demand is sensed?

Can any lag be felt between demand and response?

Man, oh man. I will be following subsequent tanks on this vehicle with great interest. That's VERY impressive.

I had been wondering about looping the hydraulic lines on your stock steering rack and a steering quickener - upside-down to become a steering slowener providing extra torque - instead of all this other stuff. But shoot, keeping the power steering but getting that big an improvement is huge.

Makes you wonder just how lossy the stock pump is.

I am not at all sure. From reading the Toyota MR2 service manual, I gather that the pump itself is basically shut off at speeds above 12 MPH. The Durango certainly does not need power assisted steering above 12 MPH, as my wife proved last week when the power steering pressure hose failed on her.

There is about a 1 second delay from when the unit first receives switched ignition power, then it closes its power relay. The unit appears to then command the pump go to full speed for about another 2 seconds, then it slows the pump down to some intermediate speed. After about another 5 seconds, the pump slows down to some lower minimum speed, and remains there until the steering wheel is moved.

Once that happens, I guess that the pump itself slows down as pressure builds up due to the steering wheel being moved. At this point, the unit speeds the pump up to provide the increased pump power necessary to move the rack to comply with the steering wheel movement. After the unit senses no more pressure is required, it will slow the pump down as before.

This relys solely on sensing pump speed as a demand indicator, and does not require a steering wheel rate sensor.

Yah, I sense a little bit of lag when the Durango is stopped, but it's not really enough to be an issue. I figure that I can live with this tradeoff, if I can get better fuel economy.

Right now, though, I do feel the steering become choppy when I am maneuvering in a parking lot, and it can be somewhat unnerving if you're not expecting that to happen. I think that's due to the fact that the unit thinks the Durango is going 12 MPH when it's really going 6 MPH.

Thanks! I was rather surprised to see the results, too. 22 highway MPG on a first gen 4x4 Durango? Nobody gets that sort of mileage.

After all was said and done with regard to that picture, the tank refill saw a fuel economy of about 20.6 MPG, and the trip computer reported 20.8 MPG.

Hm... Interesting idea about the reverse-mounted steering quickener being combined with looping the hydraulic lines. I might have done that if it was just my vehicle, and I might still end up doing that on my Magnum, but I'm not sure how my wife would like that.

Back when I was still considering trying to clutch my existing power steering pump, I figured that my push mower consumed about 0.25 gallons of gasoline per hour, making 4 HP at 3500 RPM, which worked out to about 6 ft-lbf of torque at that engine speed. I then read that typical power steering pumps take anywhere from 5 to 12 ft-lbf to operate, and picked 8 ft-lbf at 2000 RPM to come up with a fuel consumption guesstimate of about 0.19 gallons per hour for my power steering pump.

Now, I can compare similar trips in the Durango, and while there are some differences, I'm going to ignore them as I think the differences would equal out. Here's why:

Both trips were pure highway mileage. Both trips have drivers who have about the same driving skills that prefer fuel economy. Both trips had the same sunny weather. Both trips covered roughly the same distance. Both trips had about the same average speed. Both trips saw extensive A/C usage. Both trips had tire pressures at 40 psig.

The first trip had 6 passengers, while the second trip only had 3, so that means that there was about 330 or so lbs not there on the second trip. That was a slight fuel economy penalty on the first trip, relative to the second trip.

The first trip was a net 200 ft drop in elevation, while the second trip was a net 200 ft rise. Probably negligible over the course of some 350+ miles of distance.

The first trip had about 30 extra highway miles due to choice of gas pump used in Indiana, and about another extra 10 miles due to running errands in-town after arriving in Iowa.

So, the first trip saw a distance of 407.2 miles covered in 7 hours 54 minutes, using 22.133 gallons, for an average speed of 51.5 MPH. The second trip saw a distance of 364.3 miles covered in 7 hours 41 minutes, using 17.709 gallons, for an average speed of 47.4 MPH. Using these numbers, I figure that the first trip saw a fuel consumption rate of about 2.8 gallons/hour, while the second trip saw a fuel consumption rate of about 2.3 gallons/hour.

Now, there are more variables which I have not covered for the sake of brevity. For instance, I never calculated average engine speed for either trip, which would have been better than average vehicle speed. This is only a ballpark estimate. That being said, the numbers tell me that the power steering pump appears to consume about 0.5 gallons of gasoline per hour, just being there. That's over twice as much as I had guesstimated, and that tells me that the existing power steering setup is really lossy.

Thanks for tolerating my questions and for the detailed responses. :thumbup:

I'm guessing you meant pressure instead of speed there.

It sounds like after going through a "prime" routine, it enters a feedback loop that simply attempts to maintain system psi.

Any thoughts on the feasibility of converting an existing pump from being belt driven from the crankshaft to either direct or belt driven from an electric motor?

It seems like it'd be relatively easy. Find a spot to tap in a pressure sensor and then add an Arduino with input from that sensor and the VSS with a PWM output from a PID routine to a motor speed controller. Hmmm.

No problemo. It's good to share information.

I would agree, except there is nothing I can find within either the MR2 service manual or on the intertubes that points to a "pressure sensor," as such.

There are a couple of error codes that the service manual mentions, that point to excessive current draw, and it also mentions that the motor has a speed sensor on it. I know that the combination of current draw and pump speed will directly tell what the loading is, and indirectly what the pump pressure is, so I assume that controlling pump speed is how steering system pressure is controlled.

I did find at one point a picture of a MR2 pump module with the electronics cover off, showing a nice large shiny coil of copper, but I cannot currently find this picture. I'm willing to bet that this coil is key to measuring current.

That's my guess, too.

Sounds like a workable idea. You could probably get away with a 3/4 HP motor, as that is effectively the rating of the Toyota EHPS pump motor. Belt-driven is probably more feasable than direct mounting, especially in a tight engine bay. You'd probably want to convert to some EHPS compatible power steering fluid, to minimize unnecessary pump loading, but you'd also want to make sure this fluid would still be compatible with your existing rack seals. I'm using AMSOIL synthetic universal power steering fluid, which claims to be compatible with both Toyota Type EH power steering fluid and Chrysler MS-9602 (ATF +4) power steering fluid.

I was thinking along similar lines about creating a motor controller for the older 1st generation MR2 pump. That system had a separate computer, motor driver, and pump/motor unit, and the computer and motor driver each were pricy. That system also required the usage of a steering wheel rate sensor, which I'm sure is not necessary. Only thing I'd do differently would be to measure current draw and pump speed, instead of using a pressure sensor.

Just looping the lines the power steering pump it will still take 1 to 2 horsepower just to circulate the fluid.

Rack, not pump.

I got the steering quickener idea from a thread on My Tractor Forum, talking about the pros and cons and alternatives to power steering on large garden tractors. The inverted steering quickener stuck with me and was going to be a project, but then I sold my Farmall and became a moot issue.

Sneaky!

Sneaky.

Completed installing another Toyota EHPS into my Dakota. Now I have both a Durango and a Dakota with this pump installed. It'll be interesting to see what improvement the Dakota will get, especially since the Karen-mobile suffered a broken water pump last week.

Found it! There's the coil, right there!

http://www.tom-viki.com/spgm/gal/Car...1105100001.jpg

It (copper coiled coil over black plastic) looks like a Hall Effect device, probably specially manufactured for Toyota.