Trw Limited

Maurice P Roberts

William T Rabe

A power steering apparatus includes an electric motor having an output member which is drivingly connected with a planetary gear set. An output member of the planetary gear set rotates a ball nut. A member which is connected with a steering linkage has an external thread convolution which is engaged by the ball nut. Upon rotation of a steering wheel, the electric motor is energized to drive the planetary gear set. The planetary gear set in turn drives the ball nut to move the drive member which is connected with the steering linkage.

Steering apparatus

Upon initiation of a steering operation, a gerotor gear set rotates a directional control valve to an actuated condition. Initial rotation of the directional control valve actuates a switch assembly under the influence of forces transmitted from the directional control valve. The switch assembly is located in one section of a housing and the directional control valve is located in another section of the housing. The two housing sections are connected in fluid communication so that there are no seals to impede actuation of the switch assembly upon rotation of the directional control valve. The switch assembly and its housing section are rotatable together with the directional control valve to adjust the initial position of the directional control valve relative to the other housing section. In one embodiment of the invention, actuation of the switch assembly effects operation of an electric motor to increase fluid flow from a pump to a steering control assembly. In another embodiment of the invention, actuation of the switch assembly effects operation of a priority valve to reduce fluid flow to an auxiliary apparatus and increase fluid flow to a steering control assembly.

Control apparatus

An improved steering apparatus includes a piston and cylinder type motor having a hollow piston rod extending out of one end of a motor cylinder. Since the piston rod extends out of only one end of the motor cylinder, the working area on the head end of the piston is greater than the working area in the rod end of the piston. The head end working area is exposed to fluid pressure during turns in one direction and the rod end working area is exposed to fluid pressure during turns in the opposite direction. A compensator chamber is provided in the hollow piston rod. The compensator chamber has a working area on the rod end of the piston. The compensator chamber working area is exposed to fluid pressure during turns in both directions. The size of the compensator chamber working area is equal to the cross sectional area of a tubular wall of the piston rod. Since the compensator chamber working area is the same size as the cross sectional area of the piston rod and is on the rod end of the piston, exposing the compensator chamber working area to fluid pressure during turns in both directions tends to equalize the steering forces in both directions.

A hydrostatic steering controller including a pair of valve members which are relatively movable in opposite directions from a neutral position to a pair of operating positions to control flow between a fluid pressure source and a hydraulic steering motor. In each of the operating positions the valve members include interfacing surfaces which define part of a first passage directing high pressure fluid to the steering motor and a second passage directing low pressure fluid from the steering motor to a reservoir. The interfacing surfaces of the valve members create a pressure dam between the first and second passages when the valve members are relatively moved by a predetermined amount away from the neutral position and to an operating position. The pressure dam minimizes leakage between the first and second passages. The pressure dam is created in a pressure dam groove formed in a surface of one of the valve members. The pressure dam groove is connected with the fluid pressure source, and is disposed in facing relationship with a low pressure return groove formed in a surface in the other valve member when the valve members are in their neutral position. When the valve members move to their operating position a surface on the other valve member moves into facing relation with the pressure dam groove, thus increasing the pressure in the pressure dam groove.

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Lafayette, IN, United States of America

Maurice P Roberts