Patent ID: 7984785

Claim:
A control valve assembly for an electro-hydraulic steering system comprising: a first flow path having a fluid inlet, a fluid outlet, a first actuation outlet and a second actuation outlet, wherein the first flow path is adapted to communicate fluid between the fluid inlet, the fluid outlet and the first and second actuation outlets; a first proportional valve disposed in the first flow path, the first proportional valve having a closed position and being adapted to provide selective fluid communication between the fluid inlet and one of the first and second actuation outlets; a second flow path disposed in a parallel configuration with the first flow path, the second flow path having a fluid inlet port, a fluid outlet port, a first control port and a second control port; a second proportional valve disposed in the second flow path, the second proportional valve being adapted to provide selective fluid communication between the fluid inlet port and one of the first and second control ports; an isolation valve system disposed in the first flow path, the isolation valve system being actuated between an open position, in which fluid can be selectively communicated between the fluid inlet and the first and second actuation outlets of the first flow path, and a closed position, in which fluid communication between the fluid inlet and the first and second actuation outlets is blocked, the isolation valve system including an isolation valve being disposed in series with the first proportional valve and having a first end and a second end, the isolation valve being adapted for actuation to the closed position by fluid communicated to the first end from the second flow path, wherein the isolation valve system provides priority to the second flow path.