Steering: Description and Operation

Variable Effort Steering System Description and Operation

The Variable Effort Steering (VES) system or MAGNASTEER(R) varies the amount of effort required to steer the vehicle as vehicle speed changes. At low speeds, the system provides minimal steering force for easy turning and parking maneuvers. Steering effort is increased at higher speeds to provide firmer steering (road feel) and directional stability. VES works in parallel with the base torsion bar in the power steering system.

The VES control module communicates on the high speed bus and uses vehicle speed and the steering wheel angle speed to command a current that is most appropriate for each speed to the VES actuator in the steering rack and pinion. The actuator is a ring-shaped electromagnet which, together with a permanent magnet, can act so that the torsion bar that determines servo effect is weakened or stiffened depending on current polarity. At -3A servo effect is maximized and at +3 A is minimized.

At lowest speed, about 5 km/h (3 mph), the current is -3A.

At mid speed, around 70 km/h (45 mph), no current is sent through the coils and steering is assisted by hydraulics only. At high speed, the current is +3 A and high steering force is required. Cars equipped with SADS (Semi Active Damping System) have been set using the Config function so that the steering force is acted on when Sport mode is selected.

The VES control module communicates on the HS GMLAN bus.

The VES control module has the ability to detect malfunctions in the actuator. Any malfunctions detected will cause the system to ramp to zero amps. Steering will be assisted by hydraulics only and a DTC is set.