Functional Description - Electronic Power Steering (EPS) Module

EPS and the Torque Overlay Interface (TOI) 

The TOI is a method by which an external steering torque request by the CADM can be overlaid on top of the driver steering torque input in order to provide torque feedback to the driver. The torque felt by the driver through the steering wheel is measured by the steering column torque sensor and is a direct result of the drivers input. The driver input torque is boosted by the steering motor to produce an assistance torque. Ultimately, a rack torque is produced that is then used to steer the wheels. When the CADM induced TOI is requested by the CADM, motor torque is overlaid on the rack and reflected back to the driver through the steering column. The EPS receives and validates the torque demand in a signal from the CADM. Using the torque demand from the CADM, the EPS motor torque is modified and the EPS status is transmitted to the CADM. The EPS performs limitation and other checks to validate the torque signal from the CADM prior to honoring the request. If the EPS system is unable to honor the request, the CADM TOI is deactivated. Common causes for this condition are low battery voltage, loss of communication issues or EPS motor overheating conditions.