Electrohydraulic Power Steering

[California98Civic]

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

[t vago]

Originally Posted by California98Civic

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)

[oil pan 4]

Now that's a result.

[Ardent]

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?

[elhigh]

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.

[t vago]

Originally Posted by Ardent

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

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.

Originally Posted by Ardent

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

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.

Originally Posted by Ardent

Can any lag be felt between demand and response?

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.

[t vago]

Originally Posted by elhigh

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

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.

Originally Posted by elhigh

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.

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.

Originally Posted by elhigh

Makes you wonder just how lossy the stock pump is.

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.

[Ardent]

Thanks for tolerating my questions and for the detailed responses.

Originally Posted by t vago

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

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.

[t vago]

Originally Posted by Ardent

Thanks for tolerating my questions and for the detailed responses.

No problemo. It's good to share information.

Originally Posted by Ardent

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

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.

Originally Posted by Ardent

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

That's my guess, too.

Originally Posted by Ardent

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?

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.

Originally Posted by Ardent

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.

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.

[oil pan 4]

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