The Importance of Precise Measuring Instruments in the Steering Lever
The steering bow is designed as an active actuator with force input and displacement feedback. The driver receives feedback concerning the vehicle’s driving dynamics via the position change detected by the steering bow. This results in the subdivision of the steer-by-wire system’s control concept into two phases: setpoint setting and feedback synthesis.
Setpoint Setting
The force exerted by the driver on the handle element is measured using the multi-axial force sensor. Strain gauges allow for the measurement of forces and moments in the force sensor. These are then amplified, digitized, and evaluated in the real-time computer. Based on the sum of the forces on the left- and right-hand sides (with the sign of the force on the right-hand side being inverted since both sensors give a positive signal for the same direction of actuation), setpoints for the steering angles of the front wheels are calculated as a function of the vehicle speed and the vehicle geometry. In the "E-Jet" concept vehicle, these steering angle setpoints are implemented by steering motors.
Feedback Synthesis
The steering motors output the actually implemented steering angle that depends on the driving situation and the road conditions. Based on the actual steering angles of the wheels and the driving conditions the real-time computer calculates a setpoint for the steering-bow angle. This is implemented by the actuator at the steering bow.