US Patent 9744989 Control system for steering a rear caster wheel

A hydraulic control system for steering rear caster wheels of a work machine. The control system has a steering mode that proportionally controls the steering of rear caster wheels while compensating the circuit to keep steering performance independent from the load generated by the rear caster wheels, a no steering mode that maintains the position of the rear caster wheels in the absence of a steering command, and a freewheeling mode that permits the rear caster wheels to rotate freely 360°.