Turning system

A turning system configured to move a turning shaft to turn a left wheel and a right wheel of a vehicle, the turning shaft being configured to couple the left wheel and the right wheel to each other, a torsion bar being engaged with the turning shaft via a steering gear box, the turning system comprising:

• a turning mechanism comprising (i) an electric turning mechanism comprising an electric motor configured to rotate a portion of the torsion bar which is located upstream of the steering gear box and (ii) a hydraulic turning mechanism configured to apply a moving force to the turning shaft in an axial direction, the moving force being produced by a hydraulic pressure;
• and
• an electric-motor controller configured to control the electric motor based on a frictional force in the turning mechanism and a road-surface reaction force that acts between (a) a tire on the left wheel and a tire on the right wheel and (b) a road surface,
• wherein the electric-motor controller comprises a twist-angle obtainer configured to obtain an angle of twist of the torsion bar based on the frictional force in the turning mechanism and the road-surface reaction force, and the electric-motor controller is configured to control the electric motor based on the angle of twist of the torsion bar which is obtained by the twist-angle obtainer,
• wherein the steering gear box comprises a rack-and-pinion mechanism,
• wherein the torsion bar is coupled rotatably and integrally with a pinion gear,
• wherein the pinion gear is engaged in the steering gear box with a tooth portion of a rack bar that is the turning shaft, and
• wherein the electric-motor controller comprises:
• a target-pinion-rotation-angle determiner configured to determine a target pinion rotation angle based on a state of the vehicle, the target pinion rotation angle being a target rotation angle of the pinion gear;
• a current controller configured to control a current to be supplied to the electric motor, such that an actual rotation angle of the electric motor is brought closer to a target motor rotation angle that is a target rotation angle of the electric motor;
• and
• a target-motor-rotation-angle determiner configured to determine the target motor rotation angle to a value obtained by adding the angle of twist of the torsion bar which is obtained by the twist-angle obtainer, to the target pinion rotation angle determined by the target-pinion-rotation-angle determiner.