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Link G4+ PWM output current limits and speed sensitive power steering

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I'm looking at driving the power steering solenoid on the R32 GTR from the Link (this is normally driven by the HICAS ecu to give speed sensitive power assistance). With the base level of assistance you get with the solenoid un-energised the steering is a little heavy for me with 265s and plenty of caster (still much lighter than with no assitance though).

I wanted to figure out if the PWM outputs on the Link g4+ (PNP GTR version) had the oomph to drive this solenoid directly. I can measure the resistance of the solenoid but I need to know how much current the PWM outputs will take. I can't seem to locate this info in any of Link's technical docs. Anyone know this?

Also does anyone have experience of setting up speed sensitive steering on a track car (I'm removing the HICAS ecu). I can measure the duty cycle the HICAS ecu is applying at 0mph but I don't have a good way of monitoring it varying with speed. I do like the way the assistance tapers off in the standard system so ideally I'd like to get as close to that as I can but a fixed increased or switchable level of assistance would be an improvement.

I haven't got experience with Link products, but have used the PWM output from another ECU to control the power steering solenoid from a Toyota Supra steering rack. I don't remember the solenoid resistance, but we measured it and determined it was not low enough to be a problem. Even if you can't observe the stock ECU duty cycle at various speeds, it's a good idea to find what frequency it uses and try to match that with your aftermarket ECU.

Our driver preferred a constant amount of assist, we ended up with the same duty cycle regardless of MPH. I found a copy of the calibration, 60% duty cycle at 100Hz any time the engine is running.

That's helpful info thanks

I read elsewhere that the frequency is 120Hz on the Skyline so very close to the Supra one as you'd expect for a similar solenoid.

Also useful to know the drive preferred the feel of fixed assistance, the feel is what it's all about.

I have been messing with this idea myself recently, but on a z32. Please let us know what you figure out!

I've just run this past Link and can confirm that the aux outputs can sink a max of 2 amps which should be ample for most solenoids. Simon from link suggested you will be fine.

nice one, thanks Andre. So anything down to around 6-7ohm.

I think I read the pas solenoid was 8ohm somewhere on SDU forum, buggered if i can find the post. i'll get outside and check it myself and post up the results.

Hmm measured at the plug on the rack the solenoid comes out between 4.5-5ohms. At 14v that's approaching 3amps which might be a bit rich.

So I guess 100% duty cycle is deffo out of the question. Whether or not a reduced duty cycle is acceptable is beyond me though.

I've put an email into [email protected], will see what they say.

EDIT: just found this in the PC Link help file under " Wiring Information > Output Wiring > Auxiliary Output Wiring"

"The load must not draw more than 2 Amps. This means that a directly connected load should have a resistance exceeding 7Ω. "

Looks like all the auxilary outputs have a flyback diode which is useful, only Aux 5 and 8 can drive from the high side which is how the hicas ecu drives it, however Aux 5 and 8 are limited to 0.5 amps which means they are no good for this. But I can't see there being a big problem wiring it to drive the the PAS solenoid on the low side.

Hook it up to a solid state relay then.

I'd agree with kickerzx - Use a solid state relay and get the Link to drive that.

Link came back and confirmed the 2amp limit on aux outputs.

I guess I could do it with a good automotive grade MOSFET or IGBT, something like this, with a shottky diode and a couple of resistors, probably £5 all in

http://www.mouser.co.uk/Search/m_ProductDetail.aspx?STMicroelectronics%2fVNP35N07-E%2f&qs=lrqjml%252bjt8cDzwoW8nFLmw==

This look a decent SSR option: normal relay pin arrangement, 20A, pwm up to 1khz, built in flyback/freewheel diode, £30

Hella 4RA 007 865-031

I'm new to SSRs so advice welcome.

Probably worth the extra £25 for a chunky heat sink and less hassle.

I have one of those Hellas. Used it to PWM a fuelpump (moved on to a bigger amp relay sinse then...). Good unit.

I suggest getting that one. Just make sure you understand how to wire it up up front. The pin arangement is the same but not the functions. If you wire it wrong and power it you will ruin it.

Like this?

Did you add on extra freewheel diode across the load?

Yeah like that.

I didnt.. I do have one now though.

Any progress on this experiment?

Sorry, not had much time on the car recently.

I have wired the SSR with the Aux11 pin on the Link GTR expansion header switching pin 86 to ground. The SSR just takes one 12v input from switched/ignition and switches the high side of the solenoid which is grounded to the body. On the GTR this is made easier because the consult port under the dash has both 12v ignition source (from the same fuse as normally feeds the HICAS ecu) and a test point for the power steering solenoid output from the HICAS.

I haven't yet enabled Aux11 though. I have been reading about managing flyback. A simple 4007 diode reverse biased across the solenoid would help, and at 120Hz I suspect thay would work. However I took the HICAS ecu apart to see how nissan do it. From what I can see there is massive power transistor, and a 1/2w 0.5ohm power resistor in series with a diode together across the load. It is possible there is a capacitor in there too, making a rcd snubber circuit but I can't quite follow the traces.

I think I have established the SSR doesn't have a diode between the output and ground other than the body diode on the mosfet which will get very hot passing 2amps and potentially let the magic smoke out. So a diode at least is a must, either under the car at the solenoid itself, or easier, up between the SSR output pin and ground pin. You always read flyback should be at the load but nissan had it at the ecu so thay will be good enough for me. Then I just need to assess if I want a power resistor in there too, I don't have one to hand, and I'd be guessing the spec, so that adds a little hassle.

ok Aux 11 is no good as it doesnt do pwm.

the only other aux outputs presented on the expansion headers are aux 7 and 8 do but they are already used, CEL and boost ctrl solenoid. both are also connected to the factory pins for those functions on the eccs connector so cant be reassigned easily.

so I'll use Aux 1 which is wired to pin 106 on the eccs connector on the gtr link pnp. This is meant for fuel pump control but that isn't set up on my car so it is free, and there is a second pwm capable aux out assigned to the other fuel pump control pin on the eccs if I want to pwm the pump in future.

Progress, popped out at lunch today and wired the ssr switching ground into Aux 2 on pin 104. Meant to do Aux 1 but cut the wrong wire, never mind, same idea. Setup a basic gp pwm output in pc link, with a sibgle "control" of rpm>150. With a basic two step cal table; 0kph=100%, 20kph=40%.

It works! I just need to recharge my battery power scope to check the diode is doing its job and confirm the effective pwm control range of the solenoid and ssr.

After 15mins idling on the driveway with 100% pwm or in other words 3amps (12v / 4ohms) going through the ssr and solenoid, the ssr was cold still and the solenoid was very hot to touch. Dialing back the pwm should help. It may be that the hicas only drives it at an maximum (mean) of say 6v or 1.5amps and that is enough to fully open the valve and any more than that and the solenoid coil is just acting as a heater.

Oh! you are back :)

Interesting. one should really scope the solenoid in the systems stock form to see what the module does normaly. Maybe it doesnt work its ass of unless you turn the steeringwheel, but is idleling at say 60% until you do. (just an example). Also it could be that there is no difference in output between say 90% and 100%. Which would let the solenoid run cooler but still do the same work.

Yes i think 100% may be beyond the effective range of contril for the solenoid, and perhaps the SSR too. The service manual says in the hicas "failsafe" mode the voltage should measure 4v so 33% duty. This is what cars that have had hicas disabled will run (most cars) and is a quite nice weight of steering.

50% DC seems to give as much power assistance as 100% without overheating the solenoid, so I've set it up to run 50% at 0 kph and 30% at 20kph. I'll drive it like that for a while and see how it goes. I've put my scope on the output of the SSR and the waveform looks fine so I guess the little 1N4007 flyback diode is doing it's job.