"smarter" VAPS mod?

[nkb93]

I installed the VAPS cutout switch as described on shotimes, and I was overall pleased with the difference. I wanted a heavier steering feel at moderate speeds (say 20-50 mph), and found that 'freezing' the VAPS motor around 75 mph generally yields good results.

The primary drawback is that the steering from 0-10 mph (parking lots) is way too stiff at this setting. This requires 'unfreezing' the VAPS motor to get the boost back at low speeds. Then I'm stuck with the normal boost at moderate speeds until I have the chance to achieve 75mph again and cut the switch.

I was pondering other ways to manually control the VAPS motor position:
The VAPS controller uses the VSS sensor output to control the level of boost. So instead of cutting power, it seems like we would be able to control the boost arbitrarily by feeding a false VSS signal to the VAPS controller.

I assume that the VSS output is something like an alternating square wave whose frequency is proportional to the car's speed. This signal could be emulated by a simple circuit (555 timer) with a potentiometer to adjust the frequency. The dialed in frequency is then fed into the VAPS controller to obtain the desired boost level. This false signal would obviously have to be isolated from the other components that need the real VSS signal.

Does anyone have information about the VSS ouput? (Voltage, frequency range, etc..) Helms doesn't mention it.. just thinking out loud until I can get a 'scope hooked up to check it out.



Nathan

 

[SHO Dude]

The VSS signal is an AC voltage signal. As the speed increases, so does the amplitude and frequency.

Also, the stepper motor in the VAPS module doesn't have any intemediate positions. The orifice only moves about .030".

Our solution to this is to replace the rack itself. We use a Non-VAPS rack from an early model SHO. The power assist is heavier, but cosistant.

Interested, drop me a line...

 

[SHOguy 92]

Variable Assist Power Steering? Is my guess correct? Why would you want that off, or is something in your system messed up? Which year SHO's do and don't have that?

 

[SHO92]

The VAPS is on 93+ SHOs. Most people don't like it, but when it works, its not too bad. The Gen 3 system is much better. The variable resistance part is in steps, so its not smooth when it applies or takes away resistance. That usually happens in the middle of a turn, and jerks the wheel back and forth. I leave mine turned on 99% of the time, and turn it off when I feel like some extra feel in spirited driving. The problem is you need to get to a certain speed determining on how much effort you want in the wheel. More effort, requires a higher speed. 75mph is pretty hard to get to safely around here.