Steering system for a vehicle

A vehicle steering system operable in a normal mode in which a driver-actuatable steering handle, and steered vehicle wheels are operatively connected to one another via an electric or electronic control system, and in an emergency mode in which the steering handle and the steered vehicle wheels are positively coupled at least one of mechanically and hydraulically, comprising a steering-angle control unit for a steering-angle actuator, which is arranged to actuate the steered vehicle wheels, the control unit comprising a first steering-angle control system which is configured to compare the actual steering-angle values from an actual steering-angle transmitter actuated with the steered vehicle wheels and desired steering-angle values from a desired steering-angle transmitter actuated with the steering handle and, as a function thereof, to actuate the steering-angle actuator, and a manual-torque control unit for a manual-torque actuator configured to actuate the steering handle for simulating manual torques, the manual torque control unit comprising a first manual-torque control system to generate desired manual-torque values correlated with forces acting at the steered vehicle wheels and to compare the forces with actual manual-torque values from an actual manual-torque transmitter actuatable with the steering handle and, as a function thereof, to actuate the manual-torque actuator, the control units being configured to monitor themselves and the steering system for functional reliability and plausibility, and switching between the normal mode and the emergency mode of the steering system as a function of this monitoring, the steering-angle control unit further comprising a second manual-torque control system connected redundantly with the first manual-torque control system of the manual-torque control unit, and the manual-torque control unit further comprising a second steering-angle control system connected redundantly with the first steering-angle control system of the steering-angle control unit.