Load sensing power steering system

Claim 1

A fluid control system for selectively effecting actuation of a power steering motor to steer vehicle wheels and an auxiliary device, said system comprising: a. source of pressurized fluid; b. a steering control valve disposed in series flow relationship between said fluid source and the steering motor, said steering control valve defining an inlet port and including valving movable selectively from a neutral position to right turn and left turn positions, a fluid meter including a metering element movable to measure the volume of fluid passing therethrough, and means coupling said metering member and said valving to impart follow-up movement thereto responsive to movement of said metering member; c. said steering control valve and said valving defining fluid passage means including a first variable orifice operable to establish a fluid flow rate through said passage means, a second orifice operable to establish a fluid flow direction through said fluid meter, and a third orifice disposed between said fluid meter and the steering motor; d. a flow control valve disposed in series flow relationship between said fluid source and said first variable orifice of said steering control valve, said fluid source comprising the sole source of pressurized fluid for actuation of the power steering motor and the auxiliary device, said flow control valve including an inlet port in fluid communication with said fluid source, a steering outlet port in fluid communication with said first variable orifice of said steering control valve, and an auxiliary outlet port in fluid communication with the auxiliary device; e. said flow control valve including valve means disposed to control fluid flow from said inlet port to said outlet ports, and means biasing said valve means toward a position permitting substantially all of the system flow to pass from said inlet port to said steering outlet port; f. meanns communicating a first pressure signal from immediately downstream of said first variable orifice to exert a biasing force on said valve means in the same direction as said biasing means; and g. means communicating a second pressure signal from immediately upstream of said first variable orifice to exert a biasing force on said valve means in opposition to that of said biasing means to maintain a generally constant pressure drop across said first variable orifice as said fluid flow rate varies between a minimum and a maximum.

Claim 11

A system for controlling the flow of fluid from a source of fluid which is selectively a fixed displacement pump, a pressure-compensated, variable displacement pump or a flow and pressure compensated, load-sensing pump to selectively effect actuation of a power steering motor and an auxiliary device, which is an open-center type, closed-center type, or a load-sensing type, respectively, said system comprising: a. a steering control valve disposed in series flow relationship between the fluid source and the steering motor, said steering control valve including valving movable from a neutral position to right turn and left turn positions, selectively, a fluid meter including a metering element movable to measure the volume of fluid passing therethrough, and means coupling said metering member and said valving to impart follow-up movement thereto responsive to movement of said metering member; b. said steering control valve including a valve body, said valving body defining fluid inlet and fluid return ports and a pair of motor ports to be connected to said power steering motor, said valve body and said valving defining a fluid passage means including a first variable orifice disposed in series flow relationship between said fluid inlet port and said fluid meter, said valving being configured to have a predetermined pressure drop across said first variable orifice when said valving is in said right turn and left turn positions; c. a priority valve disposed in series flow relationship between the fluid source and said steering control valve, said priority valve including an inlet port in fluid communication with the fluid source, a steering outlet port in fluid communication with said fluid inlet port of said steering control valve, and an auxiliary outlet port in fluid communication with the auxiliary device; d. said priority valve including a valve member disposed to control fluid flow from said inlet port to said outlet ports, and means biasing said valving member toward a position permitting substantially all of the system flow to pass from said inlet port to said steering outlet port, said biasing means exerting a biasing force approximately equivalent to said predetermined pressure drop across said first variable orifice to establish a steering flow rate through said steering outlet port and said first variable orifice; e. means communicating a load pressure signal from the downstream side of said first variable orifice to exert a biasing force acting on said valve member in the same direction as said biasing means; and f. means communicating a pilot pressure signal from a location between said valve member and said first variable orifice to exert a biasing force on said valve member in opposition to that exerted by said biasing means.

Claim 12

A system for controlling the flow of fluid from a source of fluid which is selectively a fixed displacement pump, a pressure-compensated, variable displacement pump or a flow and pressure compensated, load-sensing pump to selectively effect actuation of a power steering motor and an auxiliary device, which is an open-center type, closed-center type, or a load-sensing type, respectively, said system comprising: a. a steering control valve disposed in series flow relationship between the fluid source and the steering motor, said steering control valve including valving movable from a neutral position to right turn and left turn positions, selectively, a fluid meter including a metering element movable to measure the volume of fluid passing therethrough, and means coupling said metering member and said valving to impart follow-up movement thereto responsive to movement of said metering member; b. said steering control valve including a valve body, said valving body defining fluid inlet and fluid return ports and a pair of motor ports to be connected to said power steering motor, said valve body and said valving defining a fluid passage means including a first variable orifice disposed in series flow relationship between said fluid inlet port and said fluid meter, said valving being configured to have a predetermined pressure drop across said first variable orifice when said valving is in said right turn and left turn positions; c. a priority valve disposed in series flow relationship between the fluid source and said steering control valve, said priority valve including an inlet port in fluid communication with the fluid source, a steering outlet port in fluid communication with said fluid inlet port of said steering control valve, and an auxiliary outlet port in fluid communication with the auxiliary device; d. said priority valve including a valve member disposed to control fluid flow from said inlet port to said outlet ports, and means biasing said valving member toward a position permitting substantially all of the system flow to pass from said inlet port to said steering outlet port, said biasing means exerting a biasing force approximately equivalent to said predetermined pressure drop across said first variable orifice to establish a steering flow rate through said steering outlet port and said first variable orifice; e. means communicating a load pressure signal from the downstream side of said first variable orifice to exert a biasing force acting on said valve member in the same direction as said biasing means; and f. means communicating a pilot pressure signal from a location between said valve member and said first variable orifice to exert a biasing force on said valve member in opposition to that exerted by said biasing means.