초록 ▼

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 p

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. First and second fluid lines respectively communicate the first and second actuating chambers with the first and second power assist chambers such that the hydraulic fluid filling said actuating chambers is force fed to and from said first and second power assist chambers in response to motion of said actuator piston under control of the motor and drive screw. A fluid cross-over by-pass line connects the first and second fluid lines and contains a solenoid by-pass valve that when opened allows fluid to be merely displaced between the power assist chambers in by-pass relation to said actuator chambers. When the vehicle operator provides a steering input to the rack, the resultant motion of said rack and consequent motion of the rack piston creates a pressure differential in the rack power assist chambers which is sensed by two pressure sensors coupled one in each fluid line to thereby generate a corresponding pressure differential signal. An electronic controller utilizes the pressure differential signal to control the servo motor and thereby cause rotation of the drive screw to move the actuator piston in a proper direction to force sufficient hydraulic fluid from one of the actuator chambers into an associated one of the power assist chambers to thereby minimize the fluid pressure differential existing between said two pressure sensors and thus provide steering assist power in the power cylinder to assist the vehicle operator in manually applying torque via the steering wheel to achieve the desired motion of the rack to thereby move the steerable vehicle wheels.

대표청구항 ▼

[ What is claimed is:] [1.]1. An electro-hydraulic power steering system comprising an elongated rack adapted to be connected at opposite ends to the steerable wheels of a motor vehicle, said rack having a series of teeth along a section of its length, a rotatable pinion in mesh with the rack teeth

[ What is claimed is:] [1.]1. An electro-hydraulic power steering system comprising an elongated rack adapted to be connected at opposite ends to the steerable wheels of a motor vehicle, said rack having a series of teeth along a section of its length, a rotatable pinion in mesh with the rack teeth and adapted to be operably connected to a steering wheel of the vehicle by a shaft so as to receive vehicle operator steering input, said rack extending lengthwise within an elongated housing constructed to form an elongated power cylinder and having thereon spaced apart first and second circular interior portions of reduced diameter defining the axially opposite ends of said power cylinder and having a sealed engagement with the rack in order to close opposite ends of said power cylinder, a piston carried by said rack within said power cylinder having a sealed engagement with the interior of the cylinder and separating the cylinder into first and second power assist working chambers filled with hydraulic fluid, a first fluid line communicating with said first power chamber adjacent one end of said power cylinder, a second fluid line communicating with said second power chamber adjacent to the other, axially opposite end of said power cylinder, a hydraulic actuator cylinder sealed at opposite ends by first and second end caps, a linear drive screw extending lengthwise within said actuator cylinder and having its opposite ends rotatably received in said end caps for rotation in both directions about its central longitudinal axis and secured against axial displacement thereof, an actuator piston reciprocable within said actuator cylinder and separating said actuating cylinder into first and second hydraulic fluid filled actuating chambers, said actuator piston being secured against rotation in said actuating cylinder and said drive screw extending through and being threadedly engaged with said actuator piston such that rotation of said drive screw is operable to produce linear movement of said actuator piston in one direction or the other depending upon the direction of rotation of the drive screw, said drive screw extending through said second end cap and being operably rotationally driven connected to a servo motor carried by said second end cap, said first and second fluid lines respectively communicating with said first and second actuating chambers on opposite sides of said actuator piston such that the hydraulic fluid filling said actuating chambers is fed to and from said first and second power chambers on the opposite sides of said rack piston within said power cylinder by motion of said actuator piston under control of said motor and said drive screw, a fluid cross-over by-pass line connecting said first and second fluid lines, a solenoid valve connected in said cross-over line having a valve element normally held open by a valve spring but closed by energization of the valve solenoid such that when said valve is open fluid is merely displaced from one side of the rack piston to the other and thus between said power chambers in by-pass relation to said actuator chambers, first and second pressure sensors operably coupled respectively in said first and second fluid lines such that when the vehicle operator provides a steering input to said rack by means of said pinion, the resultant motion of said rack and consequent motion of said piston within said power cylinder creates a pressure differential in said rack power chambers which is sensed by said pressure sensors to generate a corresponding pressure differential signal, an electronic controller operably coupled to receive the pressure differential signal from said pressure sensors and operably coupled to provide a corresponding control signal to said bypass valve for controlling the same and to said motor so as to command rotation of said drive screw and consequent motion of said actuator piston in a direction to force hydraulic fluid from a system selected one of said actuator chambers into an associated one of said power cylinder chambers so as to minimize the fluid pressure differential existing between said two sensors, said electro-motivally developed motion of said actuator piston and consequent hydraulically-developed fluid flow forces thereby providing steering assist power in said power cylinder to assist the vehicle operator in manually applying torque via said steering wheel to achieve the desired motion of said rack to thereby move the steerable vehicle wheel.