This disclosure relates to a fluid pump for a linear actuator. In particular, the instant disclosure relates to a fluid pump with an improved valve structure for controlling fluid flow between the actuator and fluid pump and metering fluid flow returning from the actuator to the fluid pump.
In a fluid controlled linear actuator, a double acting piston is disposed within a fluid chamber and connected to an actuator rod extending from the fluid chamber. Fluid is delivered to and removed from the fluid chamber on opposite sides of the piston in order to move the piston within the chamber and extend or retract the rod. Fluid is delivered to and removed from the fluid chamber using a fluid pump.
Linear actuators are frequently used to move loads that are influenced by gravitational forces. In situations where the linear actuator exerts a force in the same direction as the gravitational force, fluid flow may exceed the maximum flow rate of the fluid pump in the actuator and cause pressure chatter or bounce resulting in pressure spikes that exceed relief valve settings in the pump and uncontrolled movement of the load. These conditions can be mitigated by metering fluid flow from the fluid chamber in the actuator to the pump. Conventional methods for metering fluid flow, however, all have significant drawbacks. Orifice plates have relatively small openings that are easily clogged. Further, the plates experience localized heating while metering fluid flow that can impact the rate of metering. Adjustable needle valves require the creation of an additional fluid flow path and lack a closed position. Counterbalance valves require relatively large amounts of space and are relatively expensive.
The inventor herein has recognized a need for a fluid pump for a linear actuator that will minimize and/or eliminate one or more of the above-identified deficiencies.
An improved fluid pump for a linear actuator is provided. In particular, a fluid pump is provided having an improved valve structure for controlling fluid flow between the actuator and fluid pump and metering fluid flow returning from the actuator to the fluid pump.
A fluid pump for a linear actuator in accordance with one embodiment includes a housing defining an inlet port configured for fluid communication with a fluid reservoir and first and second outlet ports configured for fluid communication with first and second portions of a fluid chamber formed on opposite sides of a piston disposed within the fluid chamber. The fluid pump further includes a driven pump element disposed within the housing. The fluid pump further includes a first check valve configured to control fluid flow between the driven pump element and the first outlet port, a second check valve configured to control fluid flow between the driven pump element and the second outlet port, and a shuttle disposed between the first check valve and the second check valve and movable along a shuttle axis extending through the first check valve and the second check valve responsive to fluid pressure in the housing. The first check valve includes a valve member movable between a closed position and an open position defining a fluid flow path between the driven pump element and the first outlet port and a pin extending along the shuttle axis through a bore in the first valve member and configured for engagement with the shuttle. Rotation of the driven pump element in a first rotational direction establishes a first fluid pressure causing the valve member to move from the closed position to the open position. Rotation of the driven pump element in a second rotational direction establishes a second fluid pressure causing the shuttle to move the valve member from the closed position to one of the open position and an intermediate position between the closed position and the open position responsive to a position of the pin along the shuttle axis.
A fluid pump for a linear actuator in accordance with another embodiment includes a housing defining an inlet port configured for fluid communication with a fluid reservoir and first and second outlet ports configured for fluid communication with first and second portions of a fluid chamber formed on opposite sides of a piston disposed within the fluid chamber. The fluid pump further includes a driven pump element disposed within the housing. The fluid pump further includes a first check valve configured to control fluid flow between the driven pump element and the first outlet port, a second check valve configured to control fluid flow between the driven pump element and the second outlet port, and a shuttle disposed between the first check valve and the second check valve and movable along a shuttle axis extending through the first check valve and the second check valve responsive to fluid pressure in the housing. The first check valve includes a valve member movable between a closed position and an open position defining a fluid flow path between the driven pump element and the first outlet port and means for limiting movement of the shuttle in a first direction along the shuttle axis towards the first check valve. Rotation of the driven pump element in a first rotational direction establishes a first fluid pressure causing the valve member to move from the closed position to the open position. Rotation of the driven pump element in a second rotational direction establishes a second fluid pressure causing the shuttle to move in the first direction along the shuttle axis and move the valve member from the closed position to one of the open position and an intermediate position between the closed position and the open position responsive to a position of the limiting means along the shuttle axis
A linear actuator in accordance with one embodiment includes a tube defining a fluid chamber, a piston disposed within the fluid chamber and a pushrod coupled to the piston for movement with the piston. The linear actuator further includes a fluid pump. The fluid pump includes a housing defining an inlet port configured for fluid communication with a fluid reservoir and first and second outlet ports configured for fluid communication with first and second portions of a fluid chamber formed on opposite sides of a piston disposed within the fluid chamber. The fluid pump further includes a driven pump element disposed within the housing. The fluid pump further includes a first check valve configured to control fluid flow between the driven pump element and the first outlet port, a second check valve configured to control fluid flow between the driven pump element and the second outlet port, and a shuttle disposed between the first check valve and the second check valve and movable along a shuttle axis extending through the first check valve and the second check valve responsive to fluid pressure in the housing. The linear actuator further includes a motor coupled to the driven pump element. The first check valve includes a valve member movable between a closed position and an open position defining a fluid flow path between the driven pump element and the first outlet port and a pin extending along the shuttle axis through a bore in the first valve member and configured for engagement with the shuttle. Rotation of the driven pump element in a first rotational direction establishes a first fluid pressure causing the valve member to move from the closed position to the open position. Rotation of the driven pump element in a second rotational direction establishes a second fluid pressure causing the shuttle to move the valve member from the closed position to one of the open position and an intermediate position between the closed position and the open position responsive to a position of the pin along the shuttle axis.
A fluid pump in accordance with the present teachings is advantageous relative to conventional fluid pumps for linear actuators. The valve structure of the fluid pump allows adjustment of fluid flow without adding or removing any parts in the pump. Pumps using orifice plates to meter fluid flow must be disassembled to exchange orifice plates of different sizes or to move the orifice plate in order to change the degree of metering of fluid flow. Further, unlike orifice plates, the valve structure of the fluid pump disclosed herein is able to maintain the size of the fluid flow path despite localized heating while meting fluid flow. The larger mass and surface area of the valve decreases the rate of heating and also reduces the amount of time required for transferring heat out of the valve. The bi-directional nature of the fluid pump disclosed herein also reduces or eliminates the potential for clogs to develop. Unlike adjustable needle valves, the valve structure of the fluid pump is able to meter fluid flow while maintaining a single fluid flow path. Finally, unlike counterbalance valves, the valve structure of the fluid pump requires relatively little space and is relatively inexpensive.
The foregoing and other aspects, features, details, utilities, and advantages of the present teachings will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
Housing 12 provides structural support to other components of actuator 10 and prevents damage to those components from foreign objects and elements. Housing 12 may also define a fluid manifold for routing fluid between pump 24 and actuator tube 14. Housing 12 may include a main body 26, a head 28 and an end cap 30.
Body 26 is provided to support actuator tube 14. Referring to
Lid 46 seals one end of fluid reservoir 32. Lid 46 is configured to be received within section 36 of body 26 and therefore may be substantially oval. It should be understood, however, that the shape of lid 46 may vary and is intended to be complementary to the shape of fluid reservoir 32 defined by section 36 of body 26. Referring to
Springs 48 provide means for biasing lid 46 in one direction. Springs 48 may be disposed about and supported on rods 52. One end of each spring 48 engages and is seated against a side of lid 46 while the opposite end may engage and be seated against a surface of head 28 at the end of reservoir 32. Springs 48 apply a relatively small biasing force to lid 46 sufficient to cause movement of lid 46 in the absence of fluid pressure or a reduction in fluid pressure in reservoir 32 and which may yield to increasing fluid pressure in the fluid in the reservoir 32.
The use of lid 46 and springs 48 provides several advantages relative to conventional actuators. For example, lid 46 and springs 48 allow the volume of the fluid reservoir 32 to vary. As a result, actuator 10 is able to handle changing fluid volumes resulting from varying displacement of fluids during extension and retraction of rod 20 in the actuator 10 as well as from thermal expansion and contraction of the fluid. The variable volume reservoir 32 also permits variation in stroke length for the actuator without the need to change the size of the reservoir housing. Springs 48 also protect against pump cavitation by transferring pressure to the fluid in reservoir 32. Further, because the spring-loaded lid 46 seals the fluid in reservoir 32 from the atmosphere regardless of orientation of actuator 10, lid 46 and springs 48 facilitate mounting of actuator 10 in a wider variety of orientations than conventional actuators including those in which gravity acting on the fluid would otherwise risk atmospheric contamination of the fluid in conventional actuators.
Referring again to
End cap 30 closes the opposite longitudinal end of body 26 relative to head 28 and may support the opposite longitudinal end of each tie rod 40 relative to head 28. End cap 30 may be secured to pump 24 using conventional fasteners such as socket head cap screws 64. End cap 30 may also define at least part of a fluid manifold for transferring fluid between pump 24 and tube 14. A gasket 66 may be disposed between end cap 30 and body 26 to prevent fluid leakage from housing 12 as well as entry of contaminants. A manual release mechanism 68 may be received within end cap 30 and used to release actuator 10 in the event of a mechanical failure. Mechanism 68 may comprise a threaded needle having seals disposed about the needle. During normal operation of actuator 10, when the needle and seals are fully seated within end cap 30, mechanism 68 inhibits fluid communication among conduits leading to fluid chamber 16 and reservoir 32. Rotation of mechanism 68 unseats the needle and seals and establishes fluid communication between the conduits to relieve pressure within actuator 10 and permit manual retraction or extension of rod 20.
Tube 14 is configured to house piston 18 and at least a portion of rod 20 and defines a fluid chamber 16 in which piston 18 is disposed. Tube 14 may be cylindrical in shape and is configured to be received within body 26 of housing 12 and supported on tie rods 40 within housing 12. Referring again to
Piston 18 supports one longitudinal end of rod 20 and moves within fluid chamber 16 of tube 14 responsive to fluid pressure within chamber 16 to extend or retract rod 20. Piston 18 is circular in the illustrated embodiment. It should be understood, however, that the shape of piston 18 may vary and is intended to be complementary to tube 14. One or more fluid seals may be disposed about piston 18 to prevent fluid leakage between portions 70,72 of fluid chamber 16.
Rod 20 causes linear motion in another object (not shown). One longitudinal end of rod 20 is coupled to piston 18. The opposite longitudinal end of rod 20 may be configured as, or may support, a tool 78. It should be understood that the configuration of tool 78 may vary depending on the application of actuator 10.
Motor 22 is provided to drive pump 24 in order to displace liquid within tube 14 and extend or retract rod 20. Motor 22 may comprise an electric motor such as an alternating current motor with a stator and rotor or a brushed or brushless direct current motor. Motor 22 is coupled to pump 24 and may be orientated longitudinally in a direction parallel to actuator housing 12.
Pump 24 is provided to transfer and distribute fluid among reservoir 32 and portions 70, 72 of fluid chamber 16. Referring to
Housing 80 provides structural support to other components of pump 24 and prevents damage to those components from foreign objects and elements. Housing 80 may include several members including gear housing member 104, inlet housing member 106 and outlet housing member 108. Referring to
Gear housing member 104 may be disposed between inlet and outlet housing members 106, 108. Member 104 defines a cavity 112 in the shape of two circles that open into another to form a substantially peanut shaped opening. Cavity 112 is configured to receive driven and idler gears 88, 90 and to allow teeth on gears 88, 90 to engage one another.
Inlet housing member 106, together with end cap 30 of housing 12, defines a fluid manifold for directing fluid between fluid reservoir 32 and gears 88, 90. Referring to
Outlet housing member 108, together with end cap 30 of housing 12, defines a fluid manifold for directing fluid between gears 88, 90 and tube 14. Member 108 defines outlet ports 84, 86 that are configured for fluid communication with portions 70, 72 of fluid chamber 16 and a pair of conduits 120, 122 that are in fluid communication with cavity 112 in gear housing member 104. Member 108 further defines a passageway 124 extending across member 108 configured to receive shuttle 98 and check valves 100, 102.
Referring to
Referring again to
Shuttle 98 and check valves 100, 102 provide means for controlling fluid flow between gears 88, 90, and outlet ports 84, 86. Shuttle 98 and check valves 100, 102 are disposed on an opposite axial side of gears 88, 90 relative to shuttle 92 and springs 94, 96. Shuttle 98 is disposed between check valves 100, 102 and is movable along a shuttle axis 142 extending through shuttle 98 and valves 100, 102 in response to fluid pressure within housing 80. In the absence of fluid pressure in either of conduits 120, 122 (e.g., when gears 88, 90 are not rotating), shuttle 102 may occupy a neutral position (shown in
Check valves 100, 102 may be substantially similar in construction. Check valves 100, 102 and may each include a valve body 148, 150, a valve member 152, 154, a spring 156, 158, a pedestal 160, 162 and means, such as pins 164, 166, for limiting movement of shuttle 98 along the shuttle axis 142 towards check valves 100, 102.
Valve bodies 148, 150 may each comprise two members 168, 170 and 172, 174, respectively, sized to be received within passage 124 of outlet housing member 108. Members 168, 170 define fluid passageways that form a part of fluid paths 144, 146 and connect conduits 120, 122 and outlet ports 84, 86. Members 168, 170 are annular in shape and each of members 168, 170 defines a through bore that may be disposed about, and centered about, shuttle axis 142. Referring to
Valve members 152, 154, open and close fluid flow paths 144, 146. The position of valve members 152, 154 along axis 142 determines whether flow paths 144, 146 are opened or closed and the size of the flow path 144, 146. Valve members 152, 154 are annular in shape and each of members 152, 154 defines a through bore that may be disposed about, and centered about, shuttle axis 142. The bores are sized to receive pins 164, 166. An outboard portion of each bore has a larger diameter configured to receive a fluid seal. The outboard portions of valve members 152, 154 also acts as spring seats for one end of a corresponding spring 156, 158 surrounding the pin 164, 166. Referring to
Springs 156, 158 bias valve members 152, 154 to a closed position. Springs 156, 158 are disposed between members 172, 174, respectively, of valve bodies 148, 150 and valve members 152, 154. In particular, springs 156, 158 are seated within opposed spring seats formed in counterbores in valve body members 172, 174 and on outboard surfaces of valve members 152, 154. Springs 156, 158 surround pins 164, 166, respectively.
Pedestals 160, 162 support pins 164, 166 and enable adjustment of the position of pins 164, 166 along shuttle axis 142. Each pedestal 160, 162 is supported within a corresponding valve body 148, 150 and includes a head 180 and a threaded shank 182. Head 180 is configured to be received within the outboard portion of the through bore in a corresponding member 172, 174 of a valve body 148, 150. Head 180 may define a groove in a radially outer surface configured to receive a fluid seal disposed between head 180 and the radially inner surface of the through bore in member 172, 174 of valve body 148, 150. Each head 180 may further define a recess 184 configured to receive a tool used to adjust the position of pedestal 160, 162 (and therefore pin 164, 166) within valve bodies 148, 150 and along shuttle axis 142. Recess 184 may, for example, define one or more flats and may comprise a hexagonal recess configured to receive a hexagonal drive bit used to rotate pedestal 160, 162. It should be understood, however, that the form of recess 184 may vary to adapt to different tools including conventional screwdrivers. Shank 182 is configured to be received within the intermediate portion of the through bore in a corresponding member 172, 174 of a valve body 148, 150. Shank 182 may include a plurality of threads on a radially outer surface configured to engage corresponding threads formed on the surface of the bore to allow infinite positional adjustment of pedestals 160, 162 (and therefore pins 164, 166) along shuttle axis 142 upon rotation of pedestals 160, 162. Shank 182 further defines a blind bore configured to receive one end of a corresponding pin 164, 166 such that each of pins 164, 166 extends from one end of a corresponding pedestal 160, 162.
Pins 164, 166 provide a means for limiting movement of shuttle 98 along shuttle axis 142 towards check valves 100, 102. Pins 164, 166 limit the travel of shuttle 98 along shuttle axis 142 and, as a result, the travel of valve members 152, 154 along axis 142 caused by shuttle 98. Pins 142 are disposed about, and may be centered about, shuttle axis 142. One end of each pin 164, 166 is fixed to and supported by a corresponding pedestal 160, 162. The other end of each pin 164, 166 extends through a bore in a corresponding valve member 152, 154 and is configured for engagement with a corresponding end of shuttle 98. When shuttle 98 is forced towards one of check valves 100, 102 by fluid pressure within one of conduits 120, 122, shuttle 98 engages a corresponding valve member 152, 154 in the check valve 100, 102 and displaces the valve member 152, 154 along axis 142 to open the check valve 100, 102. The positions of pins 164, 166 determine the degree of travel by shuttle 98 along axis 142 and, therefore, the degree of travel by valve members 152, 154 along axis 142. Referring to
Referring now to
A fluid pump 24 in accordance with the present teachings is advantageous relative to conventional fluid pumps for linear actuators. The valve structure 100, 102 of the fluid pump 24 allows adjustment of fluid flow without adding or removing any parts in the pump 24. Pumps using orifice plates to meter fluid flow must be disassembled to exchange orifice plates of different sizes or to move the orifice plate in order to change the degree of metering of fluid flow. Further, unlike orifice plates, the valve structure 100, 102 of the fluid pump 24 disclosed herein is able to maintain the size of the fluid flow path 144, 146 despite localized heating while meting fluid flow. The larger mass and surface area of the valve 100, 102 decreases the rate of heating and also reduces the amount of time required for transferring heat out of the valve 100, 102. The bi-directional nature of the fluid pump 24 disclosed herein also reduces or eliminates the potential flor clogs to develop. Unlike adjustable needle valves, the valve structure 100, 102 of the fluid pump 24 is able to meter fluid flow while maintaining a single fluid flow path 144, 146. Finally, unlike counterbalance valves, the valve structure 100, 102 of the fluid pump 24 requires relatively little space and is relatively inexpensive.
While the invention has been shown and described with reference to one or more particular embodiments thereof, it will be understood by those of skill in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
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