EPAS, or E Power Steering

[hoveringuy]

Starting this thread to document my experimenting with an EPowerSteering.com conversion. This uses the ubiquitous Saturn Vue EPAS column assist unit that's pretty much the standard in the field right now. The other vendor is EZ power steering and their setup is a bit different.

First, here's a photo of the an airbag column, the EPAS column and the non-airbag column. The airbag column has two U-joints, as do the non-airbag columns, the difference being that the first U-joint is near the wheel and the second is at the rack input, whereas the early cars have both of them at the rack. The functional difference is that the early cars have a steering wheel that is more tilted forward "like driving a van", and also tilted to the left because the column points to the right.

The EPAS rack is designed to follow the early car layout with a straight shaft and both U-joints at the rack.



Here's a photo of what it looks like if I place the airbag collapsing column on the EPAS unit. Will that fit in the car? It's only a few inches longer. Would be awfully nice, wouldn't it... be able to square the wheel and avoid that sharp jog at the rack.



It fits! The shaft spline is actually 1mm larger than the output of the motor but close enough for figurin' out. Without looking too hard, I see a potential interference between the upper U-joint and the brake pedal switch but probably not.

The bigger issue is that the original engineering depends on the output shaft to support the front of the unit, otherwise it only hangs from those two frangible bolts that let it tip back and forth. If I have a U-Joint there, I'd be allowing the entire unit to pivot, so I'll need to fab a bracket.

Finally, it would be massively convenient if my airbag shaft splines actually fit the output shaft of the EPAS, but it's 1mm bigger so I'll need to do a custom shaft. No bigee...




Why would I bother converting to the airbag style lower shaft and not just use what they gave me? I don't like the jog of the lower shaft, I'd prefer to keep the U-joints straighter if the additional torque of power steering is going through them. Finally, the EPAS unit mounts to the two little flanges that hang down from the dash. Those are common to both early and late cars, and both cases all they're designed to do is support the weight of the column. The EPAS has a bit of twisting force and I'd prefer to have it secured a bit better, but maybe I'm overthinking that.

[Panici]

I see what you're saying about the extra forces. But I don't see it being massively different then muscling a manual rack around.
Granted manual racks typically have a higher ratio to make steering effort less.

You could reinforce, but need to keep in mind how the column/brackets may react in a crash.
Hopefully the original is designed not to punch through your chest like older cars, and that may mean mounting points that yield in a certain direction only.

[hoveringuy]

Panici There are two vendors for e30 EPAS. EZ Power Steering and Epowersteering. The EZ one is based in Netherlands, I think, and seems to be more comprehensive. You don't need to send them your old shaft so I'm pretty sure they fabricate everything from scratch and they have a lower tube that goes through the firewall clamp exactly like stock. Also more expensive.

The Epowersteering unit just has a bearing in the firewall clamp and the strength that keeps the motor from flexing is just in the steering shaft.

The EZ one carries some of the torque reaction load down to the clamp, and has the tube to provide extra rigidity.

The engineering between the two is just a little different, but the Saturn Vue motor that I have doesn't have an easy way to bolt an output tube on whereas the one that EZ uses appears to have that.

[hoveringuy]

Thing done.

The output side of the motor unit has a pin that was a pivot in the original GM installations, so lacking a proper mounting flange I fabricated a bracket that uses that pin. 5/8" ID tubing and some light fabrication later, and I have a bracket that happens to work PERFECTLY! The entire upper assembly is mounted SOLID and all I'm missing is the steering shaft and wiring (which is trivial...)

Additional info: the entire upper motor assembly weighs 18-19lbs and the stock airbag upper assembly was 9lbs, so it's about 9-10lbs heavier. All the PS stuff I took off weighs that much so it's about a wash.

The unit may look low under the dash but it's completely unobtrusive as far as my feet.

[Panici]

Great shots! Think the under dash cover will still fit on there?

Can't wait to hear how it feels to drive

[hoveringuy]

Great shots! Think the under dash cover will still fit on there?

yeah, it was designed to fit with ALL of the usual crap under the dash.

[Victell]

Subscribed.

Can't wait to hear how it feels to drive

The million dollar question.

[hoveringuy]

Subscribed.

The million dollar question.

Yeah, pretty much. I'm guardedly optimistic and believe me, I've been skeptical.

I bought a Vue motor unit just to play with (you should too!) and understand how it works. hubcapboy came over the other day and we played with it to no end, came the conclusion that it should work fine. It's a direct connection between the steering wheel and the rack; furthermore, it can be driven equally well from the wheel to the rack or from the rack to the wheel. It's not a one-way check valve. At full assist my pinky was lifting things off the workbench, smoothly. The biggest risk is that there's some inertia to the attached motor, but it's not a gear driven motor that turns at 2000 rpm, it's very low rpm, direct-drive.

The E85 Z4 had this exact setup, a powered column and a manual rack, and it could be compared directly to the MZ4 which had the hydraulic setup. There's not a lot of debate about which one feels better, but the regular Z4 drivers swear that you wouldn't know it was electric if no one told you. I also suspect that some of the MZ4 "feels better" has to do with a lot of other stuff being better than just the hydro steering.

I also read a lot of the Miata forums and the Grassroots forums and everyone that's done the swap seems happy with it. Some people love the fact that with the IGN on, they can have power steering off the trailer without needing to start the motor.

I think a lot of the negative impressions of "electric steering doesn't give feedback" comes from cars that are probably engineered to feel that way. People driving a Prius or the Saturn Vue don't want steering feel, they want zero road feel and no vibrations and that's what they get. I mean, even the new Porsches have electric steering. https://youtu.be/qxWxq4G7YU4

The controller lets you vary the assist from almost no assist to Cadillac boost. My plan, if I'm ok with the unit, is to re-write the code to bring Vss into the mix and make it speed sensitive. More assist in parking lots below 5mph and then taper off assist until 30mph.

[hoveringuy]

Driven!

So far, the most accurate thing I could say is "it works". I just went to the bank and back and there were still tools adrift on the passenger floor for serious cornering but I did have enough time to play with the assist levels.

At full assist it's massively over-boosted and getting into PIO (Pilot Induced Oscillations) territory and just terrible.
At mid-boost, it seems about right for parking lots and maneuvering around the shopping mall.
At minimum assist it feels about like a stock e30.

My other complaint is that it's a little sluggish coming out of a turn, but I think that's because I'm still moving a lot of hydraulic fluid around and I have AN6 lines going all the way to the trunk. My next move would be to loop the line at the rack to eliminate a lot of that flow resistance, the permanent solution is going to be a manual Z4 rack which is actually made for column assist steering.

I also LOVE the current steering shaft! After ordering and evaluating several, I settled on the Z4 one. It is true telescoping and collapses a good 6". It's also made of steel because it was intended to have the extra torque of the column assist motor. The M3 one below it is aluminum and it's not telescoping, but collapsible with frangible rivets. I had to weld an extension on the Z4 piece. Not a fan of welding steering shafts, but this one is just temporary because the Z4 rack has larger splines.

[Northern]

I genuinely like the electric rack in my R56 (EDIT: apparently only came on some models including the S/JCW/GP2?), but they're ~$1000 for a reman rack and very bulky at the pinion/connecting spline so not a great swap candidate.

What are you using for a controller? I see ebay ones with a potentiometer, is that what you're using for now? I think VSS reference is a must for an electric setup.

[hoveringuy]

I genuinely like the electric rack in my R56, but they're supposedly expensive.

What are you using for a controller? I see ebay ones with a potentiometer, is that what you're using for now? I think VSS reference is a must for an electric setup.

I have both the Bruno steering one from Portugal and the one that Epowersteering gave me. They both have a pot and they function identically.

I'm not at the point of needing Vss because I still need to figure-out how to reduce the assist beyond the minimum setting. Once I get to the point where steering gets difficult in parking lots I would need a Vss input to normalize it.

[hoveringuy]

Update.

I drained the rack of fluid which helped a little bit. Steering feel is awesome for parking lots and slow speed driving.

I *think* I learned why the EPAS units got the reputation of having poor return to zero feel (self-aligning from the caster trying to straighten the wheel). I think what happens is that the torque sensor in the shaft works both ways and reacts to torque coming from the steering wheel by driving the wheels in the desired direction, but also reacts to torque coming FROM the wheels, but since that torque is "backwards", it works to counteract that torque, not amplify it. I need to play with making turns both with the system on and off to verify that, but there is some adjustment that you need to steer into a turn as well as steer out.

Feel at speed is still slightly light for my taste. The Vue EPAS units are somewhat of a "one size fits all solution" and I'm not getting assist low enough.

[Northern]

Yeah I'm really hoping it's possible to dial these issues out with this EPS column because it would be such an elegant solution to every PS issue in these cars.

[hoveringuy]

*Update*

I returned the unit.

It had a 700w motor and it just wasn't possible to trim it down enough to be suitable for the e30. Lesson is that the e30 needs a much smaller motor, like 250w or 400w, so I'm installing my standard hydraulic pump for this track season and I'll re-engage this Fall with something I'll fabricate myself out of a Yaris or such.

I will add that 700w is a tremendous amount of power, almost 1hp, and through the worm gear drive it would easily turn the wheels on a Monster Truck.