Self-centering steering system

A steering system for a vehicle having first and second steerable wheels, said steering system comprising:

• an axle having first and second end portions which are suspended by springs and which support the first and second steerable wheels of the vehicle, said axle having an intermediate portion which at least partially defines a chamber through which a longitudinal central axis of said axle extends, said first steerable wheel being pivotally mounted on said first end portion of said axle for pivotal movement about a first pivot axis which extends transverse to the longitudinal central axis of said axle, said second steerable wheel being pivotally mounted on said second end portion of said axle for pivotal movement about a second pivot axis which extends transverse to the longitudinal central axis of said axle;
• a steering member having a longitudinal central axis, said steering member being supported in said chamber in said axle for axial movement along a linear path relative to said axle, said steering member being movable between a straight ahead position and positions offset from the straight ahead position of said steering member, said steering member having a screw thread portion;
• a spring assembly disposed in said chamber in said axle and connected with said steering member, said spring assembly being effective to provide force which urges said steering member toward the straight ahead position when said steering member is in a position offset from the straight ahead position;
• a ball nut associated with said screw thread portion of said steering member and disposed in said chamber in said axle;
• an electric motor connected with said axle;
• at least one drive member connected with said electric motor and said ball nut to rotate said ball nut to move said steering member away from the straight ahead position against the influence of force provided by said spring assembly upon actuation of said electric motor;
• a motor control system connected with said electric motor and operative to enable generation of back EMF in said electric motor upon movement of said steering member toward the straight ahead position under the influence of said spring assembly, said back EMF generated in said electric motor being effective to oppose movement of said steering member toward the straight ahead position under the influence of force provided by said spring assembly,
• a takeoff assembly connected to said steering member having a portion projecting from an opening in said intermediate portion of said axle, said takeoff assembly being movable with said steering member along the linear path upon rotation of said ball nut;
• first steering linkage connected with said projecting portion of said takeoff assembly and extending along an outer side of said axle to transmit movement from said takeoff assembly to said first steerable wheel, said first steering linkage being pivotally connected to said first steerable wheel to effect pivotal movement of said first steerable wheel about said first pivot axis upon movement of said steering member and said chamber in said axle;
• and
• second steering linkage connected with said projecting portion of said takeoff assembly and extending along the outer side of said axle to transmit movement of said takeoff assembly to said second steerable wheel, said second steering linkage being pivotally connected to said second steerable wheel to effect pivotal movement of said second steerable wheel about said second pivot axis upon movement of said steering member in said chamber in said axle.