Active Front Steering
The active front steering (AFS) System will superimpose an angle on driver’s steering input via an electromechanical actuator between the steering wheel and steering gear. The motor controlled angle is based on the vehicle’s dynamic state.
At all times, the mechanical link between the steering wheel and road wheels are maintained. The superimposed steering angle is not limited mechanically. It has as much authority necessary to achieve the desired vehicle dynamics. With this type of system, many
benefits can be added to the functionality of the steering system; including continuously variable steering ratio and enhanced vehicle stability control. The system also provides the driver with tactile feedback of the external forces reacting against the front
tires.
The AFS subsystem contain the following major components:
- Active front steering actuator
- Power steering control module
- Motor and signal harness between power steering controller and actuator
- Intermediate shaft
| • | The system will provide continuously variable steering ratio to reduced low speed steering workload. |
| • | The system will provide continuously variable steering ratio at moderate speeds for a more direct steering feel. |
| • | The system will provide continuously variable steering ratio at high speeds to reduce steering sensitivity. |
| • | The system will provide the ability to counter-steer the driver's input to enhance vehicle stability. |
| • | Transmit steering torque and react road feedback torque. |
| • | The system will provide a fail-safe mode that reverts the steering system to the base steering ratio, under certain faults. |
| • | The system dissipates excessive heat generated by the subsystem and be self protecting. |
| • | The system will include features for quiet operation and to limit vibration generation. |
| • | Absorb high frequency audible NVH from transmitting into the passenger compartment. |
| • | Absorb low frequency chatter bump disturbances from transmitting to the steering wheel. This is not a primary function of AFS but a secondary. |
| • | The AFS subsystem is designed to operate between the temperatures of -40 C to 75 C. |
| • | Standard battery voltage is between 9-16 volts. |
| • | This is on the GMLAN line and a dedicated chassis CAN line. |
| • | Steering Wheel rotation is between 400-650 degrees. |
| • | The AFS actuator is integral with the hydraulic steering rack or steering intermediate shaft. The AFS unit is used to add or subtract steering angle to the steering gear pinion. A position sensor is used to control the angle command from the controller.
The angle change is accomplished through an electric motor and a reduction gear mechanism. |
| • | The AFS controller takes vehicle and driver input signals (such as steering wheel position, vehicle speed, etc.) and converts them to an output current to the electric motor of the AFS actuator. |
| • | The Active Front Steering Electrical subsystem and the Vehicle Stability Control Module (VSCM) participate in, and coordinate the control of Yaw Stability Control. |
| • | Module will need a centering procedure when replaced. |
