Abstract: The invention relates to a hydraulic circuit for a steer-by-wire steering system which includes a hydraulic pump, a reservoir, a bi-directional steering actuator, a pair of electronic control units (ECU) for generating electrical steering control signals in response to an operator-generated steering command. There is a need for such a circuit which des not require large expensive valves. The hydraulic circuit includes a pair of solenoid operated directional control valve units and a pair of solenoid operated shut-off valves. Each directional control valve unit and a corresponding one of the shut-off valves are connected in series between the pump, the reservoir and the steering actuator, and are connected to a respective one of the ECUs and controlled thereby. In the absence of a fault condition both shut-off valves are open so that hydraulic flow to and from the actuator is shared by both the first and second directional control valve units.

Abstract: A force sensor has a hollow flexible body with a fixed end and a free end. The force to be measured is applied perpendicular to the axis of the flexible body by a link coupled to the free end. A rigid gauge rod is connected to the free end of the flexible body and extends through the interior of the flexible body. The rod carries on its free end a permanent magnet which is near a Hall-effect sensor which is fixed to the fixed end of the body. The flexible body has a relatively low bending stiffness at its free end (in the area of force application) and an increasing bending stiffness towards its fixed end. The flexible body has a relatively low bending stiffness in the direction of force application and a higher bending stiffness in a perpendicular direction. The permanent magnet is arranged so that its poles are aligned parallel to the direction of force application.

Abstract: A valve control system includes a stepping motor coupled to an eccentric via a clutch. A valve member is urged into engagement with the eccentric by a spring. Rotation of the eccentric causes axial movement of the valve member which controls fluid flow through the valve. A detent releasably holds the eccentric in a neutral position.