Electric Powersteering

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Joined: Thu Mar 03, 2011 3:52 pm

Electric Powersteering

Post by genderen » Wed Oct 09, 2013 2:18 pm


I'm looking for a fully programmable ecu to control a powersteering unit. Basicly there is a torsion bar into the steering shaft wich measures the torque applied while steering.
The ECU uses this signal to control the electric motor from the powersteering unit.
The torsion bar signal is quite simple. When no torque applied the voltage is 2.5volt. When steered to the right the voltage raises to approx. 3volt, when steered to the left, the voltage drops to approx. 2volts. It would be nice if there somehow can be a PWM output to the elecric motor to control this and support the steering. Which means how more torque applied to the steering shaft the more assistance the motor will give.
There also is the possibilty that the system is speed sensitive, which means that there is an electric signal from the speedometer, which causes that the support from the steering system decreases as the speed increases.

The electric motor from the powersteering unit takes peaks from 40Amps. A megasquirt on itself cannot handle this, but perhaps with an addtional board this is possible?

If you have a answer or an idea to get this to work, please let me know.

Thanks in advance.

Kind regards,

Patrick van Genderen

Posts: 3860
Joined: Sat Oct 03, 2009 12:24 pm
Location: Quebec, Canada

Re: Electric Powersteering

Post by jbelanger » Wed Oct 09, 2013 8:53 pm

I don't know if a simple open loop method would work or if a closed loop control would be needed. I'm not sure how the closed loop control would work with your description so I will assume that an open loop control method can be used.

The generic PWM implemented in the TinyIOx and coming soon for the IOx is almost what you need. However, it would need to be modified to use an IOx ADC input as the load and have a dependency on a speed input (timer input). The current version uses CAN data from a MegaSquirt as the load and uses RPM (from the MS also over CAN) on the x-axis. So that should be that big of a change but it might require some TunerStudio tweaks to make it easier to use.

As for the 40A output, you could use a logic level FET. Which type would depend on whether you need to control the 12V side or the ground side of the electric motor.

Having said all that, it is possible that your electric motor needs something a bit more sophisticated than a simple PWM output. That would depend on the type of motor used. Another possible solution would be to use an RC motor speed control suited for the type of motor you have. However, that would require a different signal to control it which is not directly implemented at this time. But it would be possible to simulate it with the current generic PWM outputs but you'd lose some accuracy.


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