Patent ID: 8469139

Claim:
A power steering apparatus for a vehicle having at least one steerable wheel movable along a steering stroke towards an axle stop defining the end of the steering stroke, the apparatus comprising: a fluid motor for moving the at least one steerable wheel, the fluid motor comprising a piston axially movable for moving the at least one steerable wheel along the steering stroke, the piston dividing the cylinder into first and second motor chambers on opposite sides of the piston; a first motor line fluidly connected to the first motor chamber and a second motor line fluidly connected to the second motor chamber; a source of high-pressure fluid and an exhaust; a supply line fluidly connected to the fluid source and an exhaust line fluidly connected to the exhaust; a control valve connected to the supply line, the exhaust line, and the first and second motor lines, the control valve placeable in centered and non-centered conditions in response to driver steering input, the control valve when in the non-centered condition fluidly interconnecting the supply line and the first motor line to form a high-pressure line from the high-pressure fluid source to the first motor chamber and fluidly interconnecting the exhaust line and the second motor line to form a low-pressure line from the second motor chamber to the exhaust whereby fluid pressure in the first motor chamber urges the piston towards the second motor chamber; a shutoff valve; when the control valve is in the non-centered condition the shutoff valve is disposed in one of (a) and (b): (a) the high-pressure line and (b) the low-pressure line; the shutoff valve being open when the at least one steerable wheel is away from the axle stop and permitting flow through the line associated with the shutoff valve; and the shutoff valve closing when the at least one steerable wheel approaches the axle stop and thereby blocking flow through the line associated with the shutoff valve.