I want to drive an electric power steering motor from an European Opel Corsa C in a way that I can control the steering of the car programmatically. I have a steering angle sensor which I will to use as rotary encoder for feedback to be able to set a desired steering angle. Unfortunately I do not know what kind of electric motor it is but I suspect a common DC brushed. Can anyone judge from the part number or use scenario on the motor type or do I have to open it to see the internals?

The whole power steering set includes the motor, ECU and torque sensor. In its normal operation, the torque sensor "reads" the torque (on the steering column) that the human driver's hands apply to the steering wheel and the ECU computes how much additional "assistance" will be applied from the power steering. The operation of the set can be seen on this video (Corsa B has identical parts).

A problem with steering is that the torque applied by motor depends not only on the human input but also on vehicle speed - more torque will be needed when vehicle stands still and less when it is moving fast... The ECU probably has a speed/torque map that it uses. I am trying to figure out how to deal with this - I guess the rotary encoder may solve the issue by giving feedback - in case the steering angle would change too slowly, more torque would be needed.

The motor may likely be driven in following two ways:

  1. Reverse engineer the torque sensor. Input "fake" torque readings to the original ECU and let it drive the motor. This method may be easier but may not give precise control of the motor since the ECU will still behave like a black box and will try to map torque via vehicle speed - this may likely be prevented by not inputting speed to the ECU (by disconnecting it from CAN bus) - the ECU would behave consistently then thinking the speed is 0 (or whatever constant).

  2. Directly control the motor with a custom driver. This may be harder but will give full control over the motor. Rotary encoder may be used to deal with the speed/torque dependency.

The motor looks like this (part number - GM/NSK 1407140):

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This is the whole power steering set (motor, ECU and torque sensor):

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My ECU part number is 13136672:

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    \$\begingroup\$ It is a brushed DC motor. \$\endgroup\$ – HandyHowie Aug 2 '16 at 19:17
  • \$\begingroup\$ It doesn't seem very likely that a 2-wire automotive auxiliary motor is anything other than a permanent-magnet brushed DC motor. There is some possibility that it could be electronically commutated. If it is, the speed may or may not track the voltage down to a low speed. You could easily test that. It seems highly unlikely that it is a wound-field motor. That answers the only specific question that you asked. Asking a very general question about suggesting or commenting on alternatives for the project that you described seems to be off topic for this site. \$\endgroup\$ – Charles Cowie Aug 2 '16 at 22:01

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