Hydraulic control system

Claim 2

A valve system having a spool movable within a cylinder and including first and second lands arranged to variable expose first and second load ports to fluid under pressure and to tank in a sense and in an amount determined by an input signal, and which includes third and fourth lands arranged to differentially occlude third and fourth internally connected ports respectively, said third and fourth ports being connected externally to form a part of a fluid passageway originating at a source of fluid under pressure and terminating in the tank, and in which said lands are positioned relative to each other and to said ports so that in a neutral position of said spool said first and second lands completely occlude said first and second ports while said third and fourth ports are substantially unobstructed by said third and fourth lands, and which includes a fluid passageway having a check valve therein which connects said source of fluid under pressure through said check valve to the interior of said cylinder adjacent to said first and second lands, characterized in that said source is connected through first and second restrictors to opposite end spaces in said cylinder and in which said spool is formed to define first and second longitudinal passageways each connected to one of said end spaces and to a radial passageway adjacent to that face of said first and second lands respectively, which is exposed to the fluid pressure within said cylinder, and which includes a pilot state responsive to said input signal for generating a corresponding rate of flow of fluid and conducting said flow to one or the other of said end spaces.

Claim 3

A valve system in accordance with claim 1 in which each of said longitudinal passageways includes a check valve arranged to allow passage of fluid from its associated end space to its associated radial passageway and to prevent the flow of fluid in the reverse direction.

Claim 4

A valve system in accordance with claim 1 in which each of said radial passageways is substantially rectangular in cross section and one wall of which is the face of its associated land.

Claim 5

A valve system in accordance with claim 1 including a spring for urging said spool toward said neutral position.

Claim 6

A valve system in accordance with claim 1 in which said pilot stage includes a first stage valve for controlling the flow of fluid from an additional source into first and second conduits in accordance with an input signal and in which said first and second conduits are connected to opposite end spaces of said cylinder.

Claim 7

A valve system in accordance with claim 5 including a force motor for controlling said first stage valve in accordance with said input signal.

Claim 8

A valve system in accordance with claim 6 in which said first stage valve is a three-way valve including a spool moveable within a hollow cylinder.

Claim 9

A valve system in accordance with claim 6 in which said first stage valve includes first and second poppet valves actuated by said force motor for controlling the flow of fluid to said first and second conduits.

Claim 10

A valve system comprising a source of fluid under pressure, a tank for receiving the fluid returned from the system, a valve housing formed to define a hollow cylinder, said cylinder being formed to define first and second ports connected to first and second load conduits respectively, a valve spool within said cylinder intermediate the end thereof so as to define first and second end spaces at opposite ends of said cylinder, said spool being moveable in each direction from a neutral position, said spool including first and second lands located to occlude said first and second ports when said spool is in its neutral position, said spool also including third and fourth lands located between said first and second lands and said first and second end spaces respectively, said housing being formed to include passageways for interconnecting said tank with the interior of said cylinder between said first and third lands and also between said second and fourth lands, said spool also including fifth and sixth lands both positioned intermediate said first and second lands, said housing being formed to define third and fourth ports cooperating with said fifth and sixth lands respectively, and positioned to be substantially open to the interior of said cylinder when said spool is in said neutral position and to be variably occluded by said fifth and sixth lands respectively as said spool is displaced in opposite directions from said neutral position, said spool and cylinder being formed so that said third and fourth ports are in communication with each other within said cylinder, said third and fourth ports being connected externally so as to form a portion of a passageway originating at said source and terminating at said tank, said housing being formed to define a chamber, a first fluid connection from said source to said chamber, a second fluid connection from the interior of said cylinder between said first and fifth lands to the interior of said cylinder between said second and sixth lands, a check valve hydraulically connected to allow flow of fluid from said chamber to said second fluid connection, and to prevent flow in the opposite direction, characterized in that said system includes a pilot stage having a torque motor and a valve responsive to the sense and magnitude of an input signal for selecting either a first or a second conduit and generating a variable fluid flow therein, said first and second conduits being connected to said first and second end spaces respectively, first and second restrictors connected between said chamber and said first and second end spaces respectively, said spool being formed to define first and second longitudinal passageways in communication with said first and second end spaces respectively, and also in communication with first and second radial passageways, said radial passageways being contiguous to those faces of said first and second of lands which are nearest to said fifth and sixth lands, and two additional check valves, one interposed in each of said longitudinal passageways so as to prevent the flow of fluid from said radial passageways to said end spaces but to permit a flow of fluid in the opposite direction.

Claim 11

A valve system comprising a source of fluid under pressure, a tank for receiving the fluid returned from the system, a valve housing formed to define a hollow cylinder, said cylinder being formed to define first and second ports connected to first and second load conduits respectively, a valve spool within said cylinder intermediate the end thereof so as to define first and second end spaces at opposite ends of said cylinder, said spool being moveable in each direction from a neutral position, said spool including first and second lands located to occlude said first and second ports when said spool is in its neutral position, said spool also including third and fourth lands located between said first and second lands and said first and second end spaces respectively, said housing being formed to include passageways for interconnecting said tank with the interior of said cylinder between said first and third lands and also between said second and fourth lands, said spool also including fifth and sixth lands both positioned intermediate said first and second lands, said housing being formed to define third and fourth ports cooperating with said fifth and sixth lands respectively, and positioned to be substantially open to the interior of said cylinder when said spool is in said neutral position and to be variably occluded by said fifth and sixth lands respectively as said spool is displaced in opposite directions from said neutral position, said spool and cylinder being formed so that said third and fourth ports are in communication with each other within said cylinder, said third and fourth ports being connected externally so as to form a portion of a passageway originating at said source and terminating at said tank, said housing being formed to define a chamber, a first fluid connection from said source to said chamber, a second fluid connection from the interior of said cylinder between said first and fifth lands to the interior of said cylinder between said second and sixth lands, a check valve hydraulically connected to allow flow of fluid from said chamber to said second fluid connection, and to prevent flow in the opposite direction, characterized in that said system includes a pilot stage having a torque motor and a valve responsive to the sense and magnitude of an input signal for selecting either a first or a second conduit and generating a variable fluid flow therein, said first and second conduits being connected to said first and second end spaces respectively, first and second restrictors connected between said chamber and said first and second end spaces respectively, said spool being formed to define first and second longitudinal passageways in communication with said first and second end spaces respectively, and also in communication with first and second radial passageways, said radial passageways being contiguous to those faces of said first and second of lands which are nearest to said fifth and sixth lands, and two additional check valves, one interposed in each of said longitudinal passageways so as to prevent the flow of fluid from said radial passageways to said end spaces but to permit a flow of fluid in the opposite direction.