A closed-circuit pump is provided that receives input from a steering unit in
order
to drive a steering cylinder. The closed-circuit pump is preferably a proportional
bi-directional pump. The steering unit includes a steering wheel or similar device
controlled by an operator. In one embodiment, the steering unit is a conventional
hydraulic system that includes a servo pump. In another embodiment, the steering
unit is an electronic displacement control system. The steering cylinder engages
with a steering assembly to perform the steering function by physically turning
the wheels of the vehicle. The inlet of the steering cylinder includes a counterbalance
valve, which prevents flow into the steering cylinder when there is no steering
input from the operator.
