Abstract: An electro-hydraulic actuator system (10 or 140) includes a hydraulic actuator (27) having a pair of fluid filled chambers (29, 30) and being operable to provide an actuator output (12) as a function of fluid pressures at the chambers. An electric-hydrostatic actuator (34 or 141) includes an electric motor (35 or 142) responsive to motor control signals for providing an output to a motor shaft (40 or 150), one or more pistons (56 or 166, 170) coupled to the shaft, and one or more hydraulic housings (92 or 160, 162) mounted on the motor and cooperating with the pistons for providing a pair of fluid cylinders (54 or 164, 168) respectively coupled to the fluid chambers at the hydraulic actuator. A solenoid valve (33) is connected between the cylinders, and is responsive to valve control signals for feeding fluid between the actuator chambers and thereby short circuiting the hydrostatic actuator cylinders.

Abstract: An electro-hydraulic actuator system (10 or 140) includes a hydraulic actuator (27) having a pair of fluid filled chambers (29, 30) and being operable to provide an actuator output (12) as a function of fluid pressures at the chambers. An electric-hydrostatic actuator (34 or 141) includes an electric motor (35 or 142) responsive to motor control signals for providing an output to a motor shaft (40 or 150), one or more pistons (56 or 166, 170) coupled to the shaft, and one or more hydraulic housings (92 or 160, 162) mounted on the motor and cooperating with the pistons for providing a pair of fluid cylinders (54 or 164, 168) respectively coupled to the fluid chambers at the hydraulic actuator. A solenoid valve (33) is connected between the cylinders, and is responsive to valve control signals for feeding fluid between the actuator chambers and thereby short circuiting the hydrostatic actuator cylinders.

Abstract: An electro-hydraulic power steering system comprising an elongated vehicle steering linkage rack with a rotatable steering gear in mesh with rack teeth and extending within an elongated power assist cylinder of a rack housing. A rack piston separates the power assist cylinder into first and second power assist working chambers filled with hydraulic fluid. An electric/hydrostatic steering assist module includes a hydraulic actuator cylinder with a linear drive screw extending lengthwise therein and journalled for bi-directional rotation and against axial displacement. An actuator piston is reciprocable but non-rotatable within the actuator cylinder and separates it into first and second hydraulic fluid filled actuating chambers. The drive screw is threadedly engaged with the actuator piston to produce bi-directional linear movement thereof as rotationally bi-directionally driven by a servo motor carried on the module.