Secondary steering system unit, secondary steering system, vehicle and a method for secondary steering

A method for secondary steering of a host vehicle by a secondary steering system, wherein the host vehicle has autonomous steering capabilities and includes a main steering system with a steering actuator for providing an overlay torque to the main steering system to steer at least one pair of host vehicle steerable wheels, the host vehicle further having a brake system including a respective wheel brake associated with a respective vehicle wheel that is suspended by a respective wheel suspension, the host vehicle further including one or more sensors and a communication arrangement for acquiring vehicle surrounding information, the secondary steering system including a fault determination arrangement configured to determine a presence of a fault in the main steering system and a path controller configured to generate an upcoming path for the host vehicle based on at least one of information received from the one or more sensors and information received via the communication arrangement, the secondary steering system being operable to steer the host vehicle along the upcoming path by activation of differential braking of at least one wheel brake upon determination that a fault is present in the main steering system, the method comprising:

• controlling, by the secondary steering system, the differential braking in dependence of a yaw torque acting on the host vehicle as a result of the differential braking;
• and
• simultaneously controlling, by the secondary steering system, the differential braking in dependence of a steering angle resulting from a generated alignment torque on a braked steerable wheel caused by an associated wheel suspension scrub radius.

A method for secondary steering of a host vehicle by a secondary steering system, wherein the host vehicle has autonomous steering capabilities and includes a main steering system with a steering actuator for providing an overlay torque to the main steering system to steer at least one pair of host vehicle steerable wheels, the host vehicle further having a brake system including a respective wheel brake associated with a respective vehicle wheel that is suspended by a respective wheel suspension, the host vehicle further including one or more sensors and a communication arrangement for acquiring vehicle surrounding information, the method comprising:

• determining, by a fault determination arrangement of the secondary steering system, a presence of a fault in the main steering system;
• generating, by a path controller of the secondary steering system, an upcoming path for the host vehicle based on at least one of information received from the one or more sensors and information received via the communication arrangement;
• steering, by the secondary steering system, the host vehicle along the upcoming path by activation of differential braking of at least one wheel brake upon determination that a fault is present in the main steering system;
• and
• controlling, by the secondary steering system, the differential braking based on:
• 1) a yaw torque acting on the host vehicle as a result of the differential braking and 2) a steering angle resulting from a generated alignment torque on a braked steerable wheel caused by an associated wheel suspension scrub radius.