Steering system for turning multiple sets of steerable wheels

A steering system for turning multiple sets of steerable wheels comprising:

• a first steering gear operatively connected to a steering wheel and to a first set of steerable wheels to effect turning of the first set of steerable wheels in response to rotation of the steering wheel, the first steering gear including a first control valve assembly, the first control valve assembly directing pressurized fluid to a first hydraulic fluid motor and allowing fluid to return from the first hydraulic fluid motor, the first hydraulic fluid motor being operatively connected to the first set of steerable wheels;
• a second steering gear operatively connected to the first set of steerable wheels and fluidly connected to the first steering gear to assist in turning of the first set of steerable wheels in response to rotation of the steering wheel, the second steering gear including a second control valve assembly, the second control valve assembly being capable of allowing fluid to return from a second hydraulic fluid motor;
• and
• a third steering gear operatively connected to a second set of steerable wheels and to an output shaft of the second steering gear to effect turning of the second set of steerable wheels in response to rotation of the steering wheel, the third steering gear including a third control valve assembly, the third control valve assembly directing pressurized fluid to a third hydraulic fluid motor and allowing fluid to return from the third hydraulic fluid motor, the third hydraulic fluid motor being operatively connected to the second set of steerable wheels,
• the second hydraulic fluid motor being fluidly connected to the first control valve assembly such that the first control valve assembly directs pressurized fluid to the second hydraulic fluid motor and allows fluid to return from the second hydraulic fluid motor, the output shaft of the second steering gear rotating in response to movement of the first control valve assembly when a torque below a predetermined value is applied to the output shaft, the second control valve assembly remaining in a neutral condition when said torque below a predetermined value is applied to the output shaft, the output shaft rotating to cause the second control valve assembly to assume an actuated condition to direct pressurized fluid away from the second hydraulic fluid motor when a torque above the predetermined value is applied to the output shaft of the second steering gear.