need motor control for 12v dc power steering pump motor

[Deyeme]

I have an electric vehicle, built by a hobbiest, that I drive into town occasionally. His "engineering" leaves a little to be desired. I've already made some improvments, and this is the next one.

A gas engine car typically has a belt-driven power steering pump. This car has an electric pump from a Subaru. The pump is wired so that when the ignition is in the ON position, the pump gets 12v and flows at full power.

What I would like to do is use the vehicle speed sensor, or add another sensor (wheel hub, axle shaft, etc) and as vehicle speed increases, make the power steering pump motor decrease in speed. Finding motor controllers seems easy enough, as there are plenty of options from fields such as battle bots, but I'm having trouble finding anything that will do what I want to do- as frequency from a sensor increases (the OEM VSS provides a +5vdc square wave) make the motor slow down.

Any ideas?

 

[WGJ]

Sounds to me that you need pulse-width modulation of the power to the pump, controlled by an inverted signal from one of the speed-sensitive sources you mention.

A UK company called 4QD does a lot of this stuff for various DC motor applications, I would suggest a browse of their site:

http://www.4qd.co.uk/prod/index.html

http://www.4qdtec.com/pwm-01.html

Bill

 

[MikeHalloran]

I doubt that the pump motor runs all the time in the Subaru.

How many amps is "flows at full power"?



Mike Halloran
Pembroke Pines, FL, USA

 

[Deyeme]

It has a 80amp (at 12v) fuse, so it doesn't pull more than that under any circumstance. It pulls the most amps when the steering wheel is turned a very low vehicle speed.

As far as the original Subaru application, I don't know much about the car (the XT6) that the pump came from, but the controller, from what I understand, is tied into the powertrain control module, and involves steering column sensors in addition to probably using a vehicle speed sensor input. I'm trying to do something MUCH simpler. 5v square wave input. No input = full power. Slow frequency = near full power. Fast frequency = less power. With the number of people converting vehicles to electric, I'm suprised no one has an off-the-shelf solution for this. The damm thing would sell like hot coffee on a cold day.

 

[Fabrico]

Decreasing motor speed as vehicle speed increases might be good for power conservation, but does not sound particularly safe. A steering system needs to be capable of handling the worst case scenario at all times, including at increased speeds. Among the many emergency maneuvers you may have to perform, parking is not one of them.

It may be possible to have a snoozing or perhaps even stopped pump motor, if working in conjunction with a hydraulic accumulator. IMHO, unless you have an entire system capable of accomodating instantaneous demand, there is no practical advantage or application for variable speed.

 

[MacGyverS2000]

Fabrico, the Honda S2000 VGS (JDM-sourced) changes turning speeds based upon forward motion speeds... Variable Geared Steering. It takes some getting used to, but after a week or two it becomes second nature. Steering response at slow speeds is quite quick, but at highway speeds it slows down... it still has the oomph to make an emergency lane switch, but it helps mitigate high-speed turns that tend to let drivers lose control of the vehicle.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[Deyeme]

"Decreasing motor speed as vehicle speed increases might be good for power conservation, but does not sound particularly safe."

Actually, from what I've read of the way the OEM controllers work, this is one of the built-in functions. In reality, if you make use of the power steering assist at full volume at highway speed, the only thing you're going to do is become another traffic report about an overturned vehicle.

"...A steering system needs to be capable of handling the worst case scenario at all times, including at increased speeds. Among the many emergency maneuvers you may have to perform, parking is not one of them..."
As a racecar driver with a wall-full of trophies (okay, a little more than half of them are my WIFES) I'm fairly aware of the need for varying assist at different speeds. Rather than wire up a complex OEM controller, I was hoping for a "quick and dirty" solution, only one that looks nice and clean, and comes in a neat little box. I've driven cars with "speed sensitive power steering", like the Dodge Avenger, that lowers assist level as vehicle speed increases. It gives better road feel. In my application, the pump would never be completely "off" (or could be, with a manual override on/auto/off switch), just under decreased pulsewidth.


...It may be possible to have a snoozing or perhaps even stopped pump motor, if working in conjunction with a hydraulic accumulator. IMHO, unless you have an entire system capable of accomodating instantaneous demand, there is no practical advantage or application for variable speed...
Tell that to the numerous designers that have it integrated into OEM systems. All I'm trying to do is make it so dragracers, autocrossers, and EV converters can do something better than no power steering at all or a crude on/off scenario, which WOULD be unsafe.