by SportsCarRacer on Tue Sep 30, 2008 5:34 pm
Hi, i work in AutomotiveOEM development, and thought i could shed a bit of light on this. EPAS systems are very complicated, and have a lot of built in redundancy for a robust safety case...imagine what would happen if you loose control of your steering (some of those systems can easily develop 200nM of torque on the steering pinion shaft!!!). I would STRONGLY advise AGAINST using ANY other sytem to CONTROL the steering actuator......however, if the system aderives it's SETPOINT request from somewhere else, and has position control circuitry on the acuator, then it is a ripe candidate to control from another ECU. The downside is that the setpoint may be something like a 29bit CAN signal, not easily adaptable!!
Usually it will be one of two types, steering shaft mounted or rack mounted. The rack mounted ones are the newer type, and usually incorporate all the control system & all the actuator mechanism into the one big "breadloaf" box. The earlier type is usually a co-axial actuator mounted in-line with the steering cloumn /shaft, with seperate control system mounted nearby. The latter type is more likely to be harder to control, the breadbox type usually gets a setpoint from a remote controller, and linked in with things like DSC stability control, switchable drive modes, etc.
The problem is, you really need to work out what type it is before you can determine if you can control it. It is not a straightforward job, like say taking over alternator control from the ECU. My recommendation would be to avoid disrupting the system if you can at all work that way.