EPAS, or E Power Steering

[hoveringuy]

e30davieThat's why I'm interested in getting this to the track, will constant cornering trip it up? Cornering isn't necessarily the same as it turning the wheels, but it's still providing assist.
The Vue unit was way too strong, even at the very least assist setting it was reacting to everything and was almost undrivable.
What's interesting is that the torque sensor is on the steering wheel side of the assist motor, so steering inputs are quickly amplified.
The opposite is not true, steering inputs from the wheels need to go through the motor without amplification, so it's beneficial to have the motor as small as possible
On the newest cars the motor actively unwinds the wheel to fake the caster feel and it's convincing.

[hoveringuy]

Yer i would think you could spike it pretty high under some obscure condition. google suggests some cars have even higher than 30. 80A fusible links etc.

Ok, this surprised me. My other units were easily reading 15-20Amps. The highest I saw on this was max assist with the wheels against the stops it peaked at 3.0Amps. Normal steering it was between about 0.3 and 0.7Amps for the most part.

Remember, 747Watts is 1 HP, so even 30Amps at 13V is 1/2 HP, which is a lot of power going into a steering rack!

[e30davie]

damn that's way less than I thought it be. I suppose the reduction gearbox would mean the motor doesn't need to work too hard.

I suppose you don't want the fuse to blow unless there's a real problem...so a bit bigger is probably advisable.

I just looked at our honda odyssey elec steering fuse - 70a!

[Panici]

The highest I saw on this was max assist with the wheels against the stops it peaked at 3.0Amps. Normal steering it was between about 0.3 and 0.7Amps for the most part.

That is surprising!
If the steering feel ends up being what you want, you've done a good job of taking load off the engine!

[hoveringuy]

e30davie The Vue unit running at full assist would try to break my wrist if I gave it any kind of input on the workbench. It was powerful and violent, and the power cables were huge. A 2300# e30 really doesn't need much assist. It would probably be great with just a manual rack that wasn't as quick as an E36 ratio.

Panici There's an Alfa track day in 3 weeks I have my eye on, I'd like to turn some laps to see if it's annoying, fast, or just transparent. I'm probably gaining a max of 3hp, maybe 4, but also getting rid of a bunch of hot fluid and simplifying things. On-center feel on the freeway is a little bit heavier because the very small adjustments you're constantly making aren't quite enough to trigger the input torque sensor (but I can also turn up the assist for that kind of driving). The biggest tell that it's electric is coming out of corners where the wheel doesn't unwind as strongly. If e30davie lets go of his wheel coming out of a corner in the Odyssey he'll probably notice that it unwinds quickly, but that's a "fake" caster return that's actually being driven by the motor. The modern systems that integrate steering wheel angle, speed, G's, braking force and such are pretty slick.

[Panici]

I'm probably gaining a max of 3hp, maybe 4

I would argue that the power increase is just part of the gains.
Reducing any drag of the accessories (or flywheel weight) will change how the engine free revs, and therefore how sporty it feels on downshifts etc.

Even though it's a bear to drive with a heavy clutch, I absolutely love the 7.5lb flywheel in my E30.

I can see why people buy underdrive pulley kits.

[hoveringuy]

hubcapboy Drove it the other day and didn't think that it sucks...

My next step is to integrate Vss into the control. Presently I can adjust boost with a knob but I shouldn't need to increase it everytime I enter a parking lot.

My little CAN emulator box that I purchased enables the EPAS by providing the proper signals to make it think it's in an Aygo, plus it fakes a "speed" as determined by the rotary knob. I sniffed the signal this morning and I thought I'd find a small handful of different CAN IDs, but there are like 20 or more, so I think someone sniffed the CAN traffic as installed on an Aygo and just duplicated them all instead of figuring-out which ones the EPAS actually needs to see, like engine rpm.

I'll need to get smart on Toyota CAN so I can filter this down to just the few that it needs and make my own controller, which can integrate Vss.

[hoveringuy]

I found the one byte that determines assist level, it's on CAN ID 00000B4 byte #3. Took me a while to find it because it's only updated around once per second, while bytes #1 and #4 just increment each cycle. Now I need get my Arduino Nano to be able to activate the EPS and then in short order i'll have it responding to Vss.

[hoveringuy]

Ok, so last time I updated I was just starting to look a the CAN traffic that made control of the Aygo EPAS possible. I figured all of that out and managed to port the CAN functionality onto my Adafruit CAN feather board ($20 on Amazon). It's neat because it has an MC2040 processor and has a full CAN transceiver built in.

So, there are two versions of controllers that you can purchase from Bruno in Portugal. You can get the version that has a potentiometer to adjust assist as needed, or you can get the GPS enabled version that will change assist with vehicle speed. Both of those worked well, but nobody wants to adjust a potentiometer with changes in speed and I wanted my speed to be read from Vss and not GPS.


Here's my Adafruit board and my test rig.




I used a signal generator to spoof the Vss signal (normal 12v high, goes to ground with each vane, 9 vanes per revolution) I verified that the circuit can decode speed past 7000mph. I think I'm ok!



The black box is the Bruno circuit. Nice benefit of my circuit is I can tune the speed vs assist curve, plus I can read data on the laptop in real time.



It's super compact and integrated.






So, I've driven for a few weeks now with my circuit providing variable assist from Vss speed input. It's mostly completely transparent; without any power steering the assist was really difficult below a few mph and massively annoying unitl 20 or 30 and then it was Ok. The EPAS takes all of the effort out of parking lots and I would still characterize it as "firm", it's not Cadillac easy by any measure.

Effort is perfectly proportional with speed, it just feels natural.

First track day is a week away which will be the big test, but it's cool not having any PS pump, no fluid, no leaks, no cooler, lines, reservoir, etc.

[Panici]

So, I've driven for a few weeks now with my circuit providing variable assist from Vss speed input. It's mostly completely transparent; without any power steering the assist was really difficult below a few mph and massively annoying unitl 20 or 30 and then it was Ok. The EPAS takes all of the effort out of parking lots and I would still characterize it as "firm", it's not Cadillac easy by any measure.

Effort is perfectly proportional with speed, it just feels natural.

First track day is a week away which will be the big test, but it's cool not having any PS pump, no fluid, no leaks, no cooler, lines, reservoir, etc.

This is exactly the kind of electric power steering I could get behind.

Fully adjustable speed vs assist curve, still directly connected to the wheels (not steer-by-wire), and simplifying of engine driven components.

[hoveringuy]

So I took it to the track, but it was a perfect NW kind of day. That is, it was pissing rain but I did have one dry session.

I spun. Twice, but it had nothing to do with the steering. Once because I had too much rear bias on my brake balance bar, and once because the pavement transitions to slipperier pavement EXACTLY at the Apex.

To be fair, all the Pro 3 cars spun at least once but they were also hauling-ass.

Anyway, I had to do another session just to think about the steering because I didn't remember it in all the previous sessions... it was perfectly normal. Felt great at speed, felt great in the corners. When I got back to the paddock the electric motor was just barely warm.

I certainly think the hydraulic steering is "better", depending on how that's defined. It has better feel and a natural return-to-center castor response. The EPAS trades a little bit of feel for eliminating all of the power steering crap and replacing it with a small motor on the column. No more reservoir, pump, engine drag, hoses and leaks.

It's a good trade.

[Striker01]

Congrats on a successful track test! Great work! Can we expect a steering circuit to go with the alternator and fuel calculator circuits.

[Striker01]

I joined the EPAS crew today. Thanks to hoveringuy for getting this all figured out. Also a huge thanks to adam.nonis for the fab work.

Having power steering back is awesome! The unit seems to work well, just have to get used to adjusting on the fly. Like Steve mentioned max assist is more than enough for slow speed maneuvers.

I still have stock E30 ABS, I made room for the unit and it's ECU by relocating the ABS Relay and flipping the ABS ECU upside down, but I think it may have fit without moving things around. I did have to trim a couple inches off the end of the bottom steering column housing and the bolster panel will require some work to fit, the unit hangs down just a little too far.

If anyone can figure out the actual power connector required, I'd love to have that part number but 3/8" spade fitting squeezed down a little work just fine; I did heat shrink both because they are really close together.



I had a hard time coming up with a place to put the assist adjustment knob, then remembered I have an unused hole in the steering column where cruise used to be. I removed the everything from E30 cruise stalk housing and bolted a u-shaped piece of aluminum where the stalk used to exit. Wrapped it in fabric tape to blend in and I like the way it turned out, handy for adjustments as well.

[Striker01]

Took quite a bit of trimming on the bolster piece but I got it to work and the EPAS unit is just barely in view of my eye line when driving.

[hoveringuy]

Striker01 Nice!!

Just for fun here's all the hydraulic stuff. Pump, pulley, Chase Bays reservoir, lines and a heatsink cooler.

9lbs without fluid so probably 10lbs with fluid.

it definitely cleans-up the engine bay!