Anyone pulled their power steering fuse?

[CTScott]

From what I have found in my experimentation, fooling the PS ECU in regards to vehicle speed is not enough. I actually have to also override the torque sensor data. The "highway wander" is a good example of why this is necessary. Even at high speeds, there is enough power assist that small changes in the torque sensor feedback result in steering adjustment.

One of the simplest implementations may be to add a DPDT relay in line with the power steering motor leads, and control the relay based on vehicle speed.

[CrankyOldMan]

Originally Posted by CTScott

One of the simplest implementations may be to add a DPDT relay in line with the power steering motor leads, and control the relay based on vehicle speed.

Is this something that could be based on the "vehicle speed" wire on the radio harness? I've only got a basic electronics knowledge at the moment, but I'm sure there's an IC that can read the pulses from this line.

[CTScott]

Originally Posted by CrankyOldMan

Is this something that could be based on the "vehicle speed" wire on the radio harness? I've only got a basic electronics knowledge at the moment, but I'm sure there's an IC that can read the pulses from this line.

If you wanted to do it without a microcontroller, you could use a frequency to voltage converter IC and then feed that through a comparator.

[CrankyOldMan]

Originally Posted by CTScott

If you wanted to do it without a microcontroller, you could use a frequency to voltage converter IC and then feed that through a comparator.

I've located some potential parts for these, but I'm not sure how I'd go about measuring the pulse per mph. Do you by chance already know what it is?

I'm also guessing that the signal is 12V, so you'd have to use a regulator or voltage divider to get down to the 5V input that the F/V chip is expecting. I'm still looking through the datasheet to see exactly how the F/V converter works. Any suggestions on what kind of comparator would be the right type to use?

[CTScott]

Originally Posted by CrankyOldMan

I've located some potential parts for these, but I'm not sure how I'd go about measuring the pulse per mph. Do you by chance already know what it is?

I'm also guessing that the signal is 12V, so you'd have to use a regulator or voltage divider to get down to the 5V input that the F/V chip is expecting. I'm still looking through the datasheet to see exactly how the F/V converter works. Any suggestions on what kind of comparator would be the right type to use?

The VSS signal is actually a 5V signal. If memory serves me correct the frequency is 100 Hz at 40 MPH and about 20 Hz at 10 MPH.

For the comparator, a general purpose one, like the LT1011 would be fine. It is amazing how much more complicated this gets trying to do it with analog, rather than digital. I should just build you up one to experiment with using a microcontroller. I could make a simple little black box that connects to ignition switched power and then has an output to drive the relay coil. I could have a pot on the box to adjust the switch over speed.

[CrankyOldMan]

Originally Posted by CTScott

It is amazing how much more complicated this gets trying to do it with analog, rather than digital.

Why would this be the case? There are a few additional passive components that need to be added around the F/V and comparator, but it seems to be fairly straightforward. Is it a matter of getting a comparator that has enough hysteresis to prevent noise around the switching point from making the output fluctuate? Sorry if those aren't the right terms, I just looked some of this up.

I looked at the EWD and the power steering is already throttled by the ECU based on speed and the torque sensor. According to p 176 of the EWD:

* In order to reduce driver’s steering force, the assist current is calculated from the torque sensor signal and vehicle speed
signal of the meter or CAN communication to output to the motor.

∗ When abnormality occurs in the system, the assist is prohibited by shutting off the power source relay and motor relay in
ECU, and the warning light (P/S) in the meter is lit up.

So if we were to ever crack the ECU, we could in theory change the control algorithm. It seems strange that removing the fuse doesn't turn on the (P/S) light.

[Jason@SportsCar]

I like elec power steering. It rocked in my RX-8, made it one of the most pleasurable cars to autox - past cars I raced with traditional systems always struggled to keep up, our Corvette use to puke power steering parts regularly.

I think the system in the Yaris works great. In the GT/B-Spec cars it works seamlessly, I had no problem on the track with it.

I hated the H Prod car when we first started racing it... Due to some hacked wiring the system never worked, and with a 10" wide slick the car was a beast, always fighting you in the turns. However, with time we were able to work out some of the steering bind, making it easier to drive. Ditching the elec motor and the stock column made it much easier to turn (still not as good as the EPS system), and it actually dropped a good bit of weight.

No brainier for me, in a street car I would keep it.

[CTScott]

Originally Posted by CrankyOldMan

Why would this be the case? There are a few additional passive components that need to be added around the F/V and comparator, but it seems to be fairly straightforward. Is it a matter of getting a comparator that has enough hysteresis to prevent noise around the switching point from making the output fluctuate? Sorry if those aren't the right terms, I just looked some of this up.

I looked at the EWD and the power steering is already throttled by the ECU based on speed and the torque sensor. According to p 176 of the EWD:


So if we were to ever crack the ECU, we could in theory change the control algorithm. It seems strange that removing the fuse doesn't turn on the (P/S) light.

I just mean based on the overall number of components and the little bit of math required for configuring the comparator, etc.

The P/S light id turned on by the combination meter when the EPS reports an issue. If the EPS isn't alive it can't complain.

[CrankyOldMan]

Originally Posted by CTScott

The VSS signal is actually a 5V signal. If memory serves me correct the frequency is 100 Hz at 40 MPH and about 20 Hz at 10 MPH.

Is the pulse width fixed, or is it always 50% duty cycle? I'm trying to do a PSPICE sim of the F/V converter and need some idea of the settings for the VPULSE component.

[CTScott]

Originally Posted by CrankyOldMan

Is the pulse width fixed, or is it always 50% duty cycle? I'm trying to do a PSPICE sim of the F/V converter and need some idea of the settings for the VPULSE component.

It's a 50% duty cycle signal, where the width of the pulse decreases as speed increases. If you need a definite frequency value at a particular speed, let me know, as I have a portable scope.