Electrically operated hydraulic actuator with force feedback position sensing

Information

  • Patent Grant
  • 6637461
  • Patent Number
    6,637,461
  • Date Filed
    Friday, March 8, 2002
    22 years ago
  • Date Issued
    Tuesday, October 28, 2003
    21 years ago
Abstract
A proportional hydraulic valve has a primary control spool with a force feedback actuator attached to one end, wherein the control spool meters flow of fluid to a work port. The force feedback actuator includes a piston coupled to the control spool and defining a first control chamber and a second control chamber on opposite sides of the piston. The surface of the piston has a depression with a first tapered section and a second tapered section. The force feedback actuator includes first electrohydraulic valve with a valve element that meters pressurized fluid selectively to the first and second control chambers to move the piston in opposite directions and produce motion of the control spool. A solenoid exerts a first force that on the valve element. A pilot pin engages the piston and the valve element, whereby, movement of the pilot pin on the first and second tapered sections of the piston applies a second force to the valve element. The second force corresponds to the position of the control spool and closes the valve element when the control spool is at a desired location corresponding to magnitude of the first force.
Description




CROSS-REFERENCE TO RELATED APPLICATIONS




Not Applicable




STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT




Not Applicable




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to electrically operated hydraulic actuators, and more particularly to such actuators of a force-feedback type which are particularly suited to operating linear actuated control valves in hydraulic systems.




2. Description of the Related Art




Construction and agricultural equipment have moveable members which are operated by hydraulic cylinder and piston combinations. The cylinder is divided into two internal chambers by the piston and alternate application of hydraulic fluid under pressure to each chamber moves the piston in opposite directions.




Application of hydraulic fluid to the cylinder historically was controlled by a manually operated valve in which the human operator moved a lever that was mechanically connected to a spool within a bore of the valve. Movement of that lever placed the spool into various positions with respect to cavities in the bore that communicate with a pump outlet, a fluid reservoir or the cylinder. Moving the spool in one direction controlled flow of pressurized hydraulic fluid from the pump to one of the cylinder chambers and allowed fluid in the other chamber to flow to the reservoir. Moving the spool in the opposite direction reversed the application and draining of fluid with respect to the cylinder chambers. By varying the amount that the spool was moved in the appropriate direction, the rate at which fluid flows into the associated cylinder chamber was varied, thus moving the piston at proportionally different speeds.




In addition, some control valves provide a float position in which both cylinder chambers are connected simultaneously via the spool to the fluid reservoir. This position allows the machine member driven by the cylinder to move freely in response to external forces. For example, a snow plow blade is allowed to float against the pavement to accommodate variations in surface contour and avoid digging into the pavement.




There is a trend with respect to construction and agricultural equipment away from manually operated hydraulic valves toward electrically controlled solenoid valves. U.S. Pat. No. 5,921,279 describes coupling a solenoid to the end of the spool to operate a control valve. Because the solenoid was capable of driving the spool in only one direction, a pair of such solenoid operated spool valves was required for each work port of the valve assembly. One of those valves controlled movement of the piston in one direction, while the other valve produced piston movement in the other direction.




It is important that the solenoid be able to accurately position the spool to meter the fluid through the valve at the desired flow rate. In an ideal valve, the position of the spool has a constant relationship to the magnitude of electric current applied to the solenoid. This ideal situation assumes that the other forces acting on the spool remain constant over the life of the control valve. In the real world, friction and other forces which affect spool movement vary as the device ages so that the same magnitude of electric current applied to the solenoid does not move the spool into the same position over time. Thus the fluid flow through the valve at a given electric current level changes during the life of the valve.




It is desirable to provide a control valve assembly that consistently locates the spool at the same position when a given magnitude of electric current is applied to the solenoid, even though when other forces acting of the spool change.




SUMMARY OF THE INVENTION




A proportional hydraulic control valve comprises a body with a bore therein, and having a work port, a supply passage, and a tank passage all of which communicate with the bore. A hydraulic motor can be connected to the work port. A pump can be connected to the supply passage and a fluid reservoir of the hydraulic system receiver fluid from the tank passage. A flow control component, such as a valve spool for example, is accommodated in the bore for reciprocal movement therein to provide a first fluid path between the work port and the supply passage and a second fluid path between the work port and the tank passage.




The proportional hydraulic control valve is operated by a force feedback actuator which has a piston that is coupled to the flow control component. The piston defines a first control chamber and a second control chamber on opposite sides of the piston in the bore. The piston has opposing ends with a depression forming a contoured surface there between that has first and second tapered sections. In the preferred embodiment, the piston has an hourglass shape.




The force feedback actuator includes a valve actuator that has a valve element which meters pressurized fluid selectively to the first and second control chambers thereby producing movement of the piston in opposite directions. That movement of the piston causes the flow control component to move into positions at which the first fluid path and the second fluid path are formed. The valve assembly including an valve actuator which produces a first force that is applied to move the valve element. A pilot pin engages the piston and the valve assembly wherein movement of the pilot pin on the first and second tapered sections of the piston transfers a second force to the valve element.




The first force from the valve actuator corresponds to a desired position for the flow control component. The second, or feedback, force indicates the actual position of the flow control component and places the valve element into a closed state when the control spool is at the desired position.




In the preferred embodiment, the linear actuator comprises first and second electrohydraulic valves. The first electrohydraulic valve includes the actuator and the valve element. The first electrohydraulic valve has a first state in which the pressurized fluid is proportionally metered to a valve outlet connected to the first control chamber, a second state in which the first control chamber is coupled to a tank passage, and a third state in which the first control chamber is isolated from both the tank passage and the source of pressurized fluid. The second electrohydraulic valve has a fourth state in which the second control chamber is coupled to the tank passage, and a fifth state in which the second control chamber is coupled to the outlet of the first electrohydraulic valve.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a cross section through a solenoid operated spool control valve according to the present invention;





FIG. 2

is an isometric view of a piston within the control valve;





FIG. 3

is a cross section through a linear actuator of the control valve in the neutral position;





FIG. 4

is an enlarged cross sectional view of a valve element and pilot pin of the linear actuator in

FIG. 3

;





FIG. 5

is a cross section-through the linear actuator when the control valve is in the extend state;





FIG. 6

is a cross section through the linear actuator when the control valve is in the retract state; and





FIG. 7

is a cross section through the linear actuator when the control valve is in the float state.











DETAILED DESCRIPTION OF THE INVENTION




With initial reference to

FIG. 1

, a control valve


10


comprises a valve block


12


having a bore


14


extending there through. A control spool


16


forms a flow control component and is located in the bore


14


and can move longitudinally in a reciprocal manner to control the flow of hydraulic fluid to a pair of work ports


18


and


20


. A dual action spring assembly


15


is connected to a first end of the control spool


16


to return the spool to the illustrated centered neutral position in the bore


14


. The control spool


16


has a plurality of axially spaced circumferential grooves located between lands which cooperate with the bore


14


to control the flow of hydraulic fluid between different cavities and openings into the bores, as will be described.




The first and second work ports


18


and


20


are respectively connected by the first and second work port passages


22


and


23


to cavities extending around the bore


14


. A separate check valve


24


or


25


is located in each of the first and second work port passages


22


and


23


, respectively. The work ports


18


and


20


are connected to a hydraulic motor such as a cylinder


21


and piston


19


arrangement . In an exemplary hydraulic system, the first work port


18


can be connected to the head chamber of a hydraulic cylinder


21


and the second work port


20


can be connected to the rod chamber of that cylinder, for example. The piston


19


and cylinder


21


form a hydraulic motor and it should be understood that the present control valve can be used with other types of hydraulic motors, such as a single acting cylinder or a rotating motor, for example.




The valve block


12


has a plurality of passages extending perpendicular to the plane of the cross-section of

FIG. 1. A

pair of such passages


26


and


27


are connected to the tank of the hydraulic system of which the valve assembly


10


is a component. Both tank passages


26


and


27


open into a different cavity extending around the spool bore


14


. The valve block


12


also has a supply passage


30


that opens into the spool bore


14


and is connected to the output of a pump (not shown) of the hydraulic system. The supply passage


30


communicates with another bore


32


in the valve block


12


which contains a conventional pressure compensator


34


. The pressure compensator


34


controls the flow of hydraulic fluid from the supply passage


30


to a pair of pump cavities


35


and


36


around the spool bore


14


which are connected by a bridge passage


38


.




The valve block


12


preferably is formed of several segments bolted together to provide an interconnection of the various bores, passages, and ports. It should be understood that the present invention can be used with other types of spool control valves in additional to the specific one being described herein.





FIG. 1

illustrates the control spool


16


in the neutral, or centered, position at which fluid is not flowing into or out of the work ports


18


and


20


. Movement of the control spool


16


to the right in the drawing connects the first work port


18


to the tank passage


26


and connects the second work port


20


to the supply passage


30


via the bridge passage


38


and the pressure compensator


34


. This action applies pressurized hydraulic fluid from the system pump to the rod chamber of cylinder


21


and drains fluid from the cylinder head chamber to the system tank. As a result, the piston rod


39


retracts into the cylinder


21


. Movement of the control spool


16


to the left in the drawing connects the first work port


18


to the supply passage


30


and the second work port


20


to the tank passage


27


. This causes pressurized hydraulic fluid from the system pump to flow to the head chamber of the cylinder


21


and fluid to be drained from the rod chamber, thereby extending the piston rod


39


from the cylinder.




Reference herein to directional relationship and movement, such as top and bottom, left and right, or up and down, refer to the relationship and movement of the components in the orientation illustrated in the drawings, which may not be the orientation of the components in other embodiments of the present invention.




The second end of the control spool


16


, which is remote from the dual action spring assembly


15


, is connected to a force feedback actuator


40


. The force feedback actuator


40


has an end block


48


attached to one side of the valve block


12


so that a bore


46


in the end block is aligned with the spool bore


14


. The end block bore


46


contains a piston


42


that is attached to the second end of the control spool


16


. Alternatively the control spool


16


and the piston


42


may be formed as a single piece. In either construction, the piston


42


and the control spool


16


move reciprocally as a common unit. First and second piston control chambers


47


and


49


are defined within the bore


46


on opposite sides of the piston


42


. Although, the end block


48


is separate from the valve block


12


, the two components could be formed as a single piece and thus collectively are being referred to herein as a body


45


. In a single piece body, the spool bore


14


and the piston bore


46


would comprise a common bore.




With additional reference to

FIG. 2

, the piston


42


has a generally hourglass shape with circular end sections


50


and


51


and a depression forming a contoured surface, preferably in the form of an annular notch


52


, between the end sections. The annular notch


52


has frustoconical tapered sections


53


and


54


extending, respectively, from the relatively thick end sections


50


and


51


to the thinner intermediate piston section


55


at the bottom of the notch. Although the tapered sections


53


and


54


are illustrated with surfaces that taper in a linearly from the end sections to the smallest diameter portion of the notch, other surface contours, such as a concave or convex curved surface, may be employed. A longitudinal groove


56


extends along outer surface of the piston


42


from one circular end


50


to the other


51


. Alternatively instead of a notch


52


, the piston


42


may have a cylindrical shape with a large concave longitudinal groove corresponding to the profile of groove


56


.




Referring to

FIGS. 1 and 3

, a proportional first electrohydraulic (EH) valve


60


is mounted in a first bore


62


which extends into the end block


46


and intersects the piston bore


46


at a right angle. The first EH valve


60


has an electrical actuator comprising a first solenoid


64


which when energized, produces movement of an armature


66


that selectively engages a valve element assembly


68


. With additional reference to

FIG. 4

, the valve element assembly


68


comprises a valve element


70


with an central aperture


71


having an open end facing the piston


42


and an inner end with a small opening


73


there through into which the solenoid armature


66


extends. The valve element


70


has an exterior annular groove


75


and a transverse aperture


77


. As will be described, operation of the armature


66


by the first solenoid


64


moves the valve element


70


to proportionally control flow of fluid into the first and second piston control chambers


47


and


49


.




A cap


72


, within the valve element


70


, is biased by a first spring


74


away from the inner end of the central aperture


71


. A second spring


76


is located between the cap


72


and a disk


78


that faces the open end of the central aperture


71


. A feedback pin


80


extends through the disk


78


and has a first end which engages the cap


72


. A shoulder


82


on the feedback pin abuts the disk


78


. A larger diameter portion


84


of the feedback pin


80


projects from the first EH valve


60


and has a rounded end that is received in the longitudinal groove


56


in the piston


42


(see FIG.


2


). The engagement of the rounded end of the pilot pin


80


with the groove


56


of the piston


42


provides a linear contact between those components. Without providing the groove


56


, the pilot pin would have a point contact with the curved surface of the piston


42


which would produce relatively large stress at the point of contact. The linear engagement of the two components reduces the contact stress.




Referring again to

FIGS. 1 and 3

, a pilot pressure passage


85


communicates with the first bore


62


and receives fluid at a constant regulated pilot pressure (P


ILOT


) for controlling the operation of the piston


42


, as will be described. The end block


48


also has a pilot tank passage


86


which communicates with tank passage


27


in the valve block


12


. The pilot tank passage


86


leads to the intersection of the actuator bore


46


and the first bore


62


for the first EH valve


60


. As a consequence, a cavity


88


between the first EH valve


60


and the piston bore


46


always communicates with the tank passage


27


. A branch passage


90


extends from the first piston control chamber


47


on the spool side of the piston


42


to the first bore


62


. A first transverse passage


91


is a continuation of the branch passage


90


from first bore


62


to passage a second bore


92


which is parallel to the first bore in the end block


48


and opens into the second control chamber


49


. A second transverse passage


94


extends between the chamber


88


in the first bore


62


and the second bore


92


.




A second electrohydraulic valve


95


has an electrical actuator formed by second solenoid


96


which operates an armature


97


to move a valve member


98


within the second bore


92


. The second EH valve


95


is an on/off type valve having two states: energized and de-energized. When the second EH valve


95


is de-energized, the valve member


98


is positioned to connect the first transverse passage


91


to the second piston control chamber


49


. Alternately, when the second EH valve


95


is energized, the second transverse passage


94


, which is coupled to the tank passages


86


and


27


, is connected to the second piston control chamber


49


. However, one skilled in the art will appreciate that the connections provided in the energized and de-energized states of the second EH valve


95


may be reversed with a commensurate reversal of the activation of the second solenoid


96


in the subsequent description of the second EH valve's operation. Furthermore, although specific designs of the valve element


70


and valve member


98


are shown in the drawings, other types of these components which perform the same function are contemplated within the scope of the present invention. For example, valve poppets could be employed.




The first electrohydraulic valve


60


is a proportional device which meters the fluid from the pilot pressure passage


85


to control the position of the spool


16


and thus the rate at which fluid is supplied to the work ports


18


and


20


. The two states of the second electrohydraulic valve


95


determine the direction of movement of the piston


42


and thus of the control spool


16


. The movement direction of the control spool


16


determines whether the piston rod


39


is extended from or retracted into the hydraulic actuator formed by cylinder


21


.





FIGS. 1 and 3

illustrate the control valve


10


in the neutral position in which fluid is not being applied to or drained from the cylinder


21


. In this mode of operation, the first EH valve


60


is maintained in a de-energized state, so that its valve element


70


closes communication with the pilot pressure passage


85


. As a consequence, the valve element


70


is a position in which the branch passage


90


, that opens into the first piston control chamber


47


, is connected to the pilot tank passage


86


and there through to the tank. Thus, the first piston control chamber


46


is at tank pressure. The second EH valve


95


also is de-energized which places its valve member


98


in a position that connects the first transverse passage


91


to the second piston control chamber


49


. As noted previously, the first transverse passage


91


is connected to the outlet of the proportional first EH valve


60


which now is connected to the pilot tank passage


86


that leads to the system tank. Therefore, the second piston control chamber


49


also is at tank pressure. One would also note that even if the second EH valve


95


was energized in this state, its valve member


98


would connect the second transverses passage


94


from the tank chamber


88


of the first EH valve


60


to the second piston control chamber


49


which also places that latter chamber at tank pressure. As a consequence, in the neutral state of the control valve


10


, both of the piston control chambers


47


and


49


are at tank pressure which allows the dual spring assembly


15


to center the control spool


16


in the illustrated position in which the two work port passages


22


and


23


are isolated from the other passages and cavities connected to the spool bore.




With reference to

FIG. 5

, to extend the piston rod


39


from the cylinder


21


, the second EH valve


95


is energized so that its valve member


98


connects the second transverse tank passage


94


to the second piston control chamber


49


. The first EH valve


60


also is energized to move the valve element


70


to a position where the annular groove


75


extends between an inlet


87


and an outlet


89


of the valve and thereby proportionally metering fluid from the pilot pressure passage


85


to the branch passage


90


and into the first piston control chamber


47


. Thus, the first piston control chamber


47


will contain fluid at a relatively high pressure as compared to the pressure in the second piston control chamber


49


. This pressure differential forces the piston


42


to the left in the drawing, producing a corresponding movement of the flow control component, spool


16


. This leftward motion of the control spool


16


connects the second work port passage


23


and second work port


20


to the tank passage


27


. At the same timed the first work port


18


and its passage


22


are connected to the bridge passage


38


which receives fluid at the pump output pressure. As a consequence, the piston within cylinder


21


moves to the left in the drawings thereby extending the piston rod


39


from the cylinder, as is apparent from FIG.


1


.




As the piston


42


of the force feedback actuator


40


moves to the left in the drawings, the force feedback pin


80


rides up the tapered section


54


on the piston which forces the pin


80


into the first EH valve


60


. This exerts upward feedback force on the valve element


70


, which counteracts the downward force from the first solenoid


64


, thereby causing the spool to move in a direction which tends to close communication between the pilot pressure passage


85


and the branch passage


90


. This upward movement of the pilot pin


80


compresses the first spring


74


(

FIG. 2

) exerting an upward pressure on the valve element


70


. This exertion of an upward force on the valve element


70


due to the engagement of the pilot pin


80


with piston's tapered section


54


provides a spool position feedback force which acts on the first EH valve


60


.




Thus, the magnitude of electric current applied to the first solenoid


64


of the first EH valve


60


produces a downward force applied via armature


66


to the valve element


70


. That downward force corresponds to a desired position for the control spool


16


. When the control spool


16


reaches the desired position, the upward force exerted by the pilot pin


80


on the valve element


70


matches the downward force produced by the first solenoid


64


. Thus, the force feedback actuator


40


reaches equilibrium at the desired position of the control spool


16


where the valve element


70


is in a closed position and the pilot pressure P


ILOT


in no longer being applied to the first piston control chamber


74


. Therefore, as other forces acting on the control spool


16


, such as friction and change in the force of the dual action spring assembly


15


occur over time, the force feedback actuator


40


compensates for those changes. Specifically, the force feedback actuator


40


will consistently move the control spool


16


into the desired position where the force exerted by the pilot pin


80


moving on the tapered section


54


of the piston


42


counters the force produced by the electric current in the first solenoid


64


of the first EH valve


60


. This force equilibrium occurs when the spool has moved into the desired position regardless of variation of friction or the force of the dual action spring


15


.




Referring

FIG. 6

, a similar action occurs when it is desired to retract the piston rod


39


into the cylinder


21


. In this mode of operation, the second EH valve


95


is de-energized which places its valve member


98


in a position which provides a connection between the first transverse passage


91


and the second piston control chamber


49


. Thus, as the first EH valve


60


is energized to proportionally meter fluid from the pilot pressure passage


85


into the branch passage


90


and first transverse passage


91


, fluid at that pressure will be applied to both the first and second piston control chambers


47


and


49


. As can be seen in the drawing, the surface of the piston


42


exposed to the first chamber


47


is less than the piston surface area exposed to the second piston control chamber


49


. Preferably, the piston surface area in the second piston control chamber


49


is twice that of the area exposed to the first piston control chamber


47


. In this operating, mode as a result, a greater amount of hydraulic force is exerted on the end of the piston which is remote from the control spool


16


, causing movement of the piston


42


and the control spool to the right in the drawings. This motion places the control spool


16


into a position in which the first work port


18


and passage


22


are connected to the tank passage


26


. In additions the control spool


16


now provides a path from the second work port


20


and its passage


23


to the bridge passage


38


which is at pump supply pressure. As a consequence, the piston of cylinder


21


moves rightward in the drawings, retracting the attached rod


39


into the cylinder.




That rightward movement of the piston


42


causes the pilot pin


80


to ride up tapered section


53


thereby pushing the pilot pin into the first EH valve


60


. This movement of the pilot pin


80


exerts an upward force on the valve element


70


which counteracts the downward force from the armature


66


when the first solenoid


64


is energized. Thus, when the control spool


16


and piston


42


move into the desired position corresponding to the magnitude of electric current applied to the first solenoid


64


of the first EH valve


60


, the upward force from the pilot pin


80


reaches an equilibrium with the downward force exerted by the solenoid armature


66


. When this occurs, the valve element


70


is placed in a position which closes communication between the pilot pressure passage


85


and the branch passage


90


and first transverse passage


91


. At that time, pressurized fluid no longer is being applied to either piston control chamber


47


or


49


and movement of the piston and control spool


16


terminates.




Thus, in the retract mode, the piston


62


engaging the pilot pin


80


provides a force feedback mechanism which indicates when the control spool


16


has reaches the desired position corresponding to the magnitude of electric current applied to the first solenoid


64


. The valve element


70


will reopen communication between the pilot pressure passage


85


and the two piston control chambers


47


and


49


only if the control spool moves to the left due to external forces acting upon it. Thus, in the retract mode, the force feedback actuator


40


accurately positions the control spool


16


even though other forces such as friction and the force of the dual action spring


15


acting on the control spool


16


may change over time.




With reference to

FIG. 7

, the control spool


16


also may be placed into a float position in which both of the work ports


18


and


20


are connected to the tank passages


26


and


27


. When the operator of the machine on which the control valve


10


is incorporated activates an input device designating the float position, a relatively high electric current level is applied to the first EH valve


60


. The second EH valve


95


is placed into a de-energized state in which its valve member


98


provides a path between the first transverse passage


91


and the second piston control chamber


49


. The electric current applied to the first solenoid


64


of the first EH valve


60


forces the valve element


70


downward to provide a relatively large path between the pilot pressure passage


85


and both the branch passage


90


and first transverse passage


91


. This applies pressurized fluid to the two piston control chambers


47


and


49


which, due to the differential of the piston surface areas in each chamber, drives the piston and the connected control spool


16


to the right in the drawings. Because the first solenoid


64


applies a relatively large downward force on the valve element


70


, the upward movement of the pin


80


on ramp surface


58


does not close the communication between the pilot pressure passage


85


and the other passages


90


and


91


. As a consequence, the actuator piston


42


is driven the full available distance to the right, pushing the control spool


16


into a position in which both of the first and second work ports


18


and


20


have their respective passages


22


and


23


connected to the tank passages


26


and


27


, respectively. This enables the piston of cylinder


21


to float, moving in response to external forces exerted upon the piston rod


39


.




The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Although the present force feedback actuator has been described in the context of operating a spool type control valve, the actuator can be use to operate other devices, such as the swash plate of a variable displacement pump for example. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.



Claims
  • 1. A hydraulic apparatus comprising:a machine member; a body with a bore therein; a piston mechanically coupled to the machine member and located within the bore thereby defining a first control chamber and a second control chamber on opposite sides of the piston, the piston has a first end and a second end with a contoured surface there between wherein the contoured surface has oppositely tapering first and second tapered sections; a valve assembly having a valve element which moves to meter pressurized fluid selectively to the first and second control chambers to move the piston in opposite directions which moves the machine member, the valve assembly including an actuator which produces a first force that is applied to move the valve element; and a pilot pin which engages the piston and the valve assembly wherein movement of the pilot pin on the first and second tapered sections exerts a second force to the valve element.
  • 2. The hydraulic apparatus as recited in claim 1 wherein the second force at least partially counteracts the first force.
  • 3. The hydraulic apparatus as recited in claim 1 wherein the valve assembly comprises:a first electrohydraulic valve that includes the actuator and the valve element and having first state in which the pressurized fluid is proportionally metered to an outlet connected to the first control chamber, a second state in which the outlet is coupled to the tank passage, and a third state in which the outlet is isolated from both the tank passage and the pressurized fluid; and a second electrohydraulic valve which has a fourth state in which the second control chamber is coupled to the tank passage, and a fifth state in which the second control chamber is coupled to the outlet of the first electrohydraulic valve.
  • 4. The hydraulic apparatus as recited in claim 1 further comprising a cap, a first spring biasing the cap away from the valve element, and a second spring biasing the cap away from the pilot pin.
  • 5. The hydraulic apparatus as recited in claim 1 wherein the piston has a first surface area in the first control chamber that is smaller than a second surface area of the piston in the second control chamber.
  • 6. The proportional hydraulic control valve as recited in claim 1 wherein the piston has a circular cross sectional shape, and the first tapered section and the second tapered section both have frustoconical shapes each with a larger diameter end adjacent a different one of the first end and a second end.
  • 7. The hydraulic apparatus as recited in claim 1 wherein the first tapered section tapers inwardly going away from the first end, and the second tapered section tapers inwardly going away from the second end.
  • 8. The hydraulic apparatus as recited in claim 1 wherein the piston has a longitudinal groove within which an end of the pilot pin is received.
  • 9. The hydraulic apparatus as recited in claim 1 wherein:the body further comprises a work port, a supply passage, and a tank passage all of which communicate with the bore; and the machine member comprises a flow control component coupled to the piston and movably accommodated in the bore to define a first fluid path between the work port and the supply passage and a second fluid path between the work port and the tank passage.
  • 10. A hydraulic apparatus comprising:a body with a spool bore therein, and having a first work port, a second work port, a supply passage, and a tank passage all of which communicate with the spool bore; a control spool accommodated in the spool bore for reciprocal movement therein, the control spool having a first location at which the first work port is coupled to the supply passage and the second work port is coupled to the tank passage, a second location at which the first work port is coupled to the tank passage and the second work port is coupled to the supply passage, and a third location at which the first work port and the second work port are isolated from the supply passage and the tank passage; a piston coupled to the control spool and defining a first control chamber and a second control chamber on opposite sides of the piston, the piston having a first end and a second end with a depression there between, the depression having a first tapered section and a second tapered section; a first electrohydraulic valve having a first actuator coupled to a valve element which has first state in which the pressurized fluid is proportionally metered to an outlet connected to the first control chamber, a second state in which the first control chamber is coupled to a tank passage, and a third state in which the first control chamber is isolated from both the tank passage and the pressurized fluid; a second electrohydraulic valve which has a second actuator coupled to a valve member which has a fourth state in which the second control chamber is coupled to the tank passage, and a fifth state in which the second control chamber is coupled to the outlet of the first electrohydraulic valve; and a pilot pin which engages the piston and the valve element wherein movement of the pilot pin on the first and second tapered sections exerts a force to the valve element.
  • 11. The hydraulic apparatus as recited in claim 10 wherein the force exerted by the pilot pin varies in response to movement of the spool.
  • 12. The hydraulic apparatus as recited in claim 10 wherein the force exerted by the pilot pin on the valve element has a direction that is opposite to a direction of a force applied by the first actuator to the valve element.
  • 13. The hydraulic apparatus as recited in claim 10 wherein the valve element has an aperture within which an end of the pilot pin is received.
  • 14. The hydraulic apparatus as recited in claim 13 further comprising a cap, a first spring biasing the cap away from the valve element, and a second spring biasing the cap away from the pilot pin.
  • 15. The hydraulic apparatus as recited in claim 10 wherein the body further comprises:a first bore within which the valve element of the first electrohydraulic valve is received; a second bore in communication with the second control chamber and within which the valve member of the second electrohydraulic valve is received; a pilot pressure passage receiving the pressurized fluid and communicating with the first bore; a pilot tank passage communicating with the first bore, the second bore and the tank passage; a branch passage connecting the outlet of the first electrohydraulic valve to the first control chamber; and a transverse passage connecting the outlet of the first electrohydraulic valve to the second bore.
  • 16. The hydraulic apparatus as recited in claim 15 wherein:the first electrohydraulic in the first state connects the pilot pressure passage to both the branch passage and the transverse passage, and in the second state connects the branch passage to the pilot tank passage; and the second electrohydraulic valve in the fourth state couples the second control chamber to the pilot tank passage, and in the fifth state couples the second control chamber to the transverse passage.
  • 17. A hydraulic apparatus comprising:a body with a valve bore therein, and having a first work port, a supply passage, and a tank passage all of which communicate with the valve bore; a flow control component movably accommodated in the valve bore to define a first fluid path between the work port and the supply passage and a second fluid path between the work port and the tank passage; a piston coupled to the flow control component and defining a first control chamber and a second control chamber on opposite sides of the piston, the piston having a first end and a second end with a depression there between, the depression having a first tapered section and a second tapered section; a first electrohydraulic valve having a first actuator coupled to a valve element which has first state in which the pressurized fluid is proportionally metered to an outlet connected to the first control chamber, a second state in which the first control chamber is coupled to a tank passage, and a third state in which the first control chamber is isolated from both the tank passage and the pressurized fluid; and a second electrohydraulic valve which has a second actuator coupled to a valve member which has a fourth state in which the second control chamber is coupled to the tank passage, and a fifth state in which the second control chamber is coupled to the outlet of the first electrohydraulic valve.
  • 18. The hydraulic apparatus as recited in claim 17 further comprising a pilot pin which engages the piston and the valve assembly, wherein movement of the pilot pin on the first and second tapered sections applies force to the valve element.
  • 19. The hydraulic apparatus as recited in claim 18 wherein the force applied by the pilot pin corresponds to a position of the spool.
  • 20. The hydraulic apparatus as recited in claim 18 wherein the force applied by the pilot pin has a direction that is opposite to direction of a force applied by the first actuator to the valve element.
  • 21. The hydraulic apparatus as recited in claim 17 wherein the body further comprises:a first bore within which the valve element of the first electrohydraulic valve is received; a second bore in communication with the second control chamber and within which the valve member of the second electrohydraulic valve is received; a pilot pressure passage receiving the pressurized fluid and communicating with the first bore; a pilot tank passage communicating with the first bore, the second bore and the tank passage; a branch passage connecting the outlet of the first electrohydraulic valve to the first control chamber; and a transverse passage connecting the outlet of the first electrohydraulic valve to the second bore.
  • 22. The hydraulic apparatus as recited in claim 21 wherein:the first electrohydraulic in the first state connects the pilot pressure passage to the branch passage and the transverse passage, and in the second state connects the branch passage to the pilot tank passage; and the second electrohydraulic valve in the fourth state couples the second control chamber to the pilot tank passage, and in the fifth state couples the second control chamber to the transverse passage.
US Referenced Citations (7)
Number Name Date Kind
3653409 Brannon Apr 1972 A
3875849 Patel Apr 1975 A
4011891 Knutson et al. Mar 1977 A
4290447 Knutson Sep 1981 A
4569273 Anderson et al. Feb 1986 A
5715865 Wilke Feb 1998 A
5921279 Barber Jul 1999 A
Non-Patent Literature Citations (1)
Entry
Jack L. Johnson, PE, “Design of Electrohydraulic Systems For Industrial Motion Control,” 1991, pp. 4-15 & 4-16.