MagnaSteer power steering rack signal?

[MRDAGERUS]

Hi All,

I'm considering replacing manual steering rack in my 88 Lotus Esprit with a hydraulic power rack.
Whilst investigating possible donors, I found that racks on
BUICK ALLURE 2005-2009, CENTURY 2003-2005, LACROSSE 2005-2009, REGAL 2003-2004,CHEVROLET IMPALA 2000-201, MONTE CARLO 2000-2007,PONTIAC GRAND PRIX 2004-2008 are pretty close to what I need.

Some of them have a Magnasteer variable assist racks (from 2002 on) which would be a wonderful to incorporate.
Dependent on speed, the M/Steer gets 0-5V signal from the BCU on these cars.
...
The electronic brake (and traction) control module (EBCM/EBTCM) controls a bi-directional magnetic rotary solenoid. The solenoid is located in the steering gear. The solenoid adjusts the amount of power steering assist in order to achieve a given level of driver effort in order to turn the vehicle. The EBCM/EBTCM varies the steering assist by adjusting the current flow through the solenoid. The amount of steering assist adjusted for steering is dependent upon vehicle speed.
As the vehicle speed increases, the following actions occur:
The steering assist decreases.
The steering wheel driver effort increases.

As the vehicle speed decreases, the following actions occur:
The steering assist increases.
The steering wheel driver effort decreases.
...
Since '88 Esprit speedometer is mechanical and a car does not have a CPU nor ABS computer, I can not get the speed signal to the M/Steer. Would you be able to recommend where to get a processor which can simulate or substitute BCU output for this one particular function, (i.e. vehicle speed/Volt range)?
Or... is it more complicated than I think?

Any thoughts would be appreciated.
Thank you

 

[BrianPetersen]

Can't prove it but the control of that solenoid smells like PWM rather than a binary 100%-on or 100%-off condition. I can't see them designing it for an instant binary switchover between power-assistance on versus off - that would give a big step in the steering feel if one happened to be turning while passing through the changeover speed.

There's probably a way to control PWM via a simple controller (arduino?) but in view of this system's role in an important safety system in the vehicle, are you sure you want to go that route?

Personally I'd look for a dumb non-Magnasteer steering rack. Or see if a Magnasteer one performs acceptably with the Magnasteer bit of it permanently off. If the car is okay to drive with a manual steering rack, how much power assistance do you really need?

 

[IRstuff]

Please refrain from double posting

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[GregLocock]

Arranging a roadspeed to pulse to voltage signal is not difficult - perhaps the ABS tonewheel from an S4 will fit? Otherwise a capacitive or inductive pickup near the rear UJ would probably work. As I understand it Magnasteer modifies the deflection of the torsion bar, and hence affects the boost. @Brian, yes it is a variable effect, neutral at 45 mph (ie you just get the regular calibration), max assist at 0, less than regular assist at high speed. In a normal HPAS the curve of rack assist vs steering column torque (or T bar twist) is non linear, and tuned around a particular vehicle and tire.

I am a little surprised they didn't do this by modulating the hydraulic system pressure as that would give mpg benefits at high speed.

Cheers

Greg Locock


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