Vehicle steering apparatus

Steering apparatus for a vehicle adapted to travel along a predetermined travel path bordered by at least one available guide surface providing directional guidance to the vehicle, the vehicle including at least one steerable wheel, the steering apparatus comprising:

• guide follower means including two rotatable guide wheels located adjacent opposite sides of the vehicle for respectively contacting available guide surfaces to cooperatively follow the contour thereof;
• and steering means operatively connected to said guide follower means for maintaining a selected one of said guide wheels in contact with the cooperative guide surface and turning the steerable wheel to control the direction of travel of the vehicle along the path in response to the position of the selected one guide wheel as it follows the contour of the cooperative guide surface;
• said steering means including bi-directional biasing means for applying opposite biasing forces to said guide wheels to maintain contact with the cooperative guide surfaces, said biasing means including a single source of biasing force providing a predetermined biasing force and biasing force control means operatively associated with said source for continously transmitting said biasing force to said guide wheels in alternate sequence, whereby said guide wheels may be biased without counteracting said source to control the biasing force applied.