Patent ID: 6598393
Filing Date: 2003-07-29
Classification: B60R

Abstract:
A steering system for a road vehicle, comprising:a steering gear including a reciprocable steering rack connectable to steerable wheels of the vehicle to turn the wheels right upon reciprocation of the rack in a first direction and to turn the wheels left upon reciprocation of the rack in a second direction; a rotatable steering shaft having a pinion engaging said rack for manually reciprocating said rack in said first and second directions upon rotation of said steering shaft; a hydraulic fluid system for assisting the steering shaft in the reciprocation of said rack; said hydraulic fluid system including a power piston reciprocable in a power cylinder and connected to said rack, a hydraulic fluid pump; a control valve; a pressure conduit and a return conduit extending from said hydraulic fluid pump to said control valve; said control valve being operable by the steering shaft to direct hydraulic fluid from the pump through the pressure conduit to the power cylinder at one side or the other of the piston, depending on the direction of rotation of the steering shaft, and to return hydraulic fluid from the power cylinder at the opposite side of the piston through the return conduit to the pump; a lock valve communicating with at least one of said conduits for selectively closing such conduit to prevent fluid flow in said hydraulic fluid system to releasably lock said rack against movement to prevent steering of the wheels; and wherein said lock valve when closed permits only a relatively small, metered flow of fluid so that steering of the wheel is not completely prevented but is accomplished only with great effort.