Patent Application
20060130914
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to pilot operated hydraulic control valves; and more particularly to electrically operated pilot valves with a position feedback mechanism.
2. Description of the Related Art
Agricultural tractors and other types of hydraulically operated machinery commonly have components that are moved by a hydraulic cylinder/piston arrangement. The piston slides within the cylinder and divides the cylinder interior into two chambers. By selectively applying hydraulic fluid under pressure to one chamber and draining hydraulic fluid from the other chamber, the piston can be forced to move in opposite directions within the cylinder. Such movement drives a rod connected between the piston and a component of the machinery.
With reference to
There is a present trend in agricultural equipment away from manual operation of the hydraulic valves toward electrically operated valves. This not only permits the valves to be located remotely from the operator position, but also enables computer control of the valves which allows more sophisticated functions to be provided. With electrical controls, the operator manipulates a joystick or other type of electrical input device to send signals to a microcomputer based controller, thereby indicating the desired movement of the associated components on the agricultural equipment. The controller interprets the electrical signals from the operator's input device and generates control signals which operate the hydraulic valves that control a hydraulic actuator which produces the desired motion.
In order to move a conventional spool valve in reciprocal directions, solenoid operators typically are attached to opposite ends of the spool. Each solenoid is energized independently to move the spool in the appropriate direction to a position where the proper fluid flow occurs to and from the hydraulic cylinder. Although there is a relationship between the magnitude of electrical current applied to a solenoid and the resultant position of spool, that relationship varies from valve to valve and also changes during the life of each valve due to a number of factors. Therefore, various types of position sensing devices have been attached to the spool valve provide an electrical feedback signal to the controller indicating the actual position of the spool. The controller compares the actual position to the desired position of the spool and adjusts the electric current applied to the solenoid coil to place the spool at the desired position. Although such position sensing feedback mechanisms operated satisfactorily, they required additional electrical components, thus adding to the expense and complexity of the solenoid operated spool valve.
In addition, there is a limit to the force and stroke that a solenoid actuator can apply to the spool control valve, which in turn limits the flow and pressure capability of the valve. To overcome these limitations, the spool control valve can be operated by a pilot valve which is directly controlled by the solenoid actuator. Although a pilot valve operator achieves higher flow and pressure capability from the main control valve, it too has drawbacks in performance, such as hysteresis, position resolution, and the ability to respond to small changes in the commanded position. These limitations result from the open loop nature of pilot operated valve control. Thus, a better control mechanisms are desired for electrically operated spool valves.
A valve assembly has a control spool which selectively controls flow of fluid between at least one workport and supply and return passages. The control spool is operated by a pilot valve that comprises piston bore formed in a body of the valve assembly and into which a section of the control spool extends. A pilot piston is connected to the control spool and is slideably received in the piston bore, thereby defining a first chamber and a second chamber in the piston bore on opposite sides of the pilot piston. A pilot spool is slidably received in the body and is moveable with respect to the control spool to open and close fluid paths between the first chamber and both the supply passage and a return passage, and between the second chamber and both the supply passage and a return passage. A linear actuator, such as a solenoid or a stepper motor, for example, is operably coupled to move the pilot spool with respect to the control spool.
In a preferred embodiment of this valve assembly, the piston bore is aligned with or a section of the bore for the control spool. The piston bore has a first opening which communicates with one of the supply passage and the return passage, and has a second opening communicating with the other of the supply passage and the return passage. The control spool extends through a tubular pilot piston and is connected thereto. A feeder aperture in the pilot piston communicates with the first opening in the body and with a first aperture in the control spool.
A pilot spool is slidably received within a pilot bore in the control spool with the first aperture opening into the pilot bore. The pilot spool has a first position which opens a first passage between the first aperture and the first chamber in the piston bore and opens a second passage between the first aperture and the second chamber in the piston bore. In a second position, the pilot spool opens the first passage and a third passage between the second chamber and the second opening in the piston bore. In a third position, the pilot spool opens the second passage and a fourth passage between the first chamber and the second opening. A linear actuator is operably coupled to move the pilot spool within the control spool.
In another embodiment, the valve assembly body has a piston bore and a separate pilot valve bore that opens into the piston bore. A pilot piston is coupled to the control spool and is slideably received in the piston bore thereby defining the first and second chambers in the piston bore. The pilot piston has a surface with a predefined contour, such as a linear taper, for example. The body further includes a first pilot passage extending from the first chamber to the pilot valve bore, and a second pilot passage that extends from the second chamber to the pilot valve bore. The supply passage also opens into the pilot valve bore.
A tubular pilot sleeve is slidably received in the pilot valve bore and has an outer surface and an inner surface that defines a pilot spool bore. A plurality of transverse passages extend between the inner and outer surfaces and communicate with the supply passage, the first pilot passage and the second pilot passage. The tubular pilot sleeve engages the surface of the pilot piston wherein movement of the pilot piston produces movement of the tubular pilot sleeve. A pilot spool is movable within the tubular pilot sleeve into a plurality of positions which provide fluid paths between selected combinations of the plurality of transverse passages. A linear actuator is coupled to the pilot spool for moving the pilot spool within the tubular pilot sleeve.
Movement of the pilot spool by the linear actuator opens paths for fluid to and from the chambers on opposites sides of the pilot piston, thereby moving the control spool. As the pilot piston moves, the pilot sleeve rides along the contoured pilot piston surface which produces movement of the pilot sleeve within the pilot bore. This provides a feedback indication of the location of the control spool. When the control spool is in the desired location, the pilot sleeve has moved to a position at which the chambers on the opposite sides of the pilot piston are closed off from the supply passage. This terminates further movement of the pilot piston and the control spool until the linear actuator changes the position of the pilot spool.
The conventional manually operated spool valve 16 in
The valve assembly 30 has a housing 32 with a main valve housing 34 with a supply passage 50 connected to the supply line 18 from the pump 22 and a set of tank passages 52 connected to the return line 20. The supply and tanks passages 50 and 52 extend into the plane of the drawing from one valve assembly to the next one. A control spool 36 is received in a bore 38 in the main valve housing 34 and is illustrated in a neutral, center position in which fluid does not flow through the valve. A spring arrangement 47 is connected to one end of the control spool 36 and biases the control spool into the neutral, center position.
The control spool 36 moves in reciprocal directions within the bore 38 by operation of an pilot valve 44 attached to the opposite end of the control spool from the spring arrangement 47. Depending on which direction the control spool 36 moves, paths are created which direct pressurized hydraulic fluid through one of the workports 46 or 48 to the lower or upper chamber 26 or 28 of the cylinder 12, thereby driving the piston 14 up or down, respectively (
To raise the piston 14, the machine operator moves the control spool 36 rightward from the illustrated center position. This opens a path which allows fluid from the supply passage 50 to flow through a metering orifice formed by a set of notches 40 in the control spool 36 and through a conventional pressure compensator 54 into a bridge passage 56. The hydraulic fluid continues to travel from the bridge passage 56 to a first workport passage 58, past a first pressure relief valve 60, and out the first workport 46 to the lower chamber 26 of the cylinder 12.
The pressure thus applied to the lower cylinder chamber 26 causes the piston 14 to move up, which forces hydraulic fluid out of the upper cylinder chamber 28. This exhausting fluid flows into the second workport 48, past a second pressure relief valve 64, and through the second workport passage 62 into the spool bore 38. The present position of the control spool 36 creates a path between the second workport passage 62 and one of the tank passages 52 in the main valve housing 34.
To lower the piston 14, the control spool 36 is moved to the left, which opens a corresponding set of paths so that fluid from the supply passage 50 travels via the bridge passage 56 and the second workport passage 62 to the second workport 48. The new spool position forms another path through which fluid exhausted from the lower cylinder chamber 26 flows through the first workport 46 to the other tank passage 52 in the main valve housing 34.
The control spool 36 is moved in response to forces applied by the pilot valve 44 which has a pilot housing 70 that is attached to the main valve housing 34 by a suitable means, such as machine screws (not shown). Alternatively the pilot housing 70 and the main valve housing 34 may be formed by single metal casting for the body 32. The pilot housing 70 has a piston bore 72 which is aligned with the spool bore 38 in the main valve housing 34. A pilot piston 74 is attached to the end of the control spool 36 that protrudes from the valve housing 34 into the piston bore 72. The pilot piston 74 is fixedly attached to the control spool 36 by a nut 77 (as illustrated), a machine screw, or other suitable mechanism. Therefore, the pilot piston 74 and the control spool 36 slide within the bores 38 and 72 as an integral assembly. Alternatively, the pilot piston 74 and the control spool 36 could be fabricated from a single piece of material.
A first pilot chamber 76 is created in the piston bore 72 between the pilot piston 74 and a land of the control spool 36 and a second pilot chamber 78 is formed between the pilot piston 74 and a plug 80 which closes the open end of the piston bore. The pilot piston 74 has an annular recess 82 with a tapered surface 84 which defines an intermediate pilot chamber 86 between the first and second pilot chambers 76 and 78 and isolated there from by elements of the pilot piston 74. A branch of the tank passage 52 communicates with the intermediate pilot chamber 86.
A pilot valve bore 90 opens into the intermediate pilot chamber 86 and extends orthogonally from the piston bore 72 to a surface of the pilot housing 70. A first pilot passage 92 extends from the first pilot chamber 76 to approximately the mid-point along the length of the pilot valve bore 90. A second pilot passage 94 extends from the second pilot chamber 78 to a location in the pilot valve bore 90 between the opening of the first pilot passage 94 and the piston bore. A branch of the supply passage 50 extends into the pilot housing 70 and opens into the pilot valve bore 90 between the first and second pilot passages 92 and 94. A pilot bridge passage 96 extends between the opening of the supply passage 50 into the pilot valve bore 90 and another point along the pilot valve bore on a remote side of the first pilot passage 92.
A tubular pilot sleeve 98 is slidably received within the pilot valve bore 90 and has a projection 99 which extends into the piston bore 72 and engages the surface of the piston recess 82. The opposite end of the pilot sleeve 98 is biased toward the pilot piston 74 by a first spring 107. The tubular pilot sleeve 98 having a pilot spool bore 95. The pilot sleeve 98 has four sets of transverse passages 101, 102, 103, and 104 extending between its inner and outer diametric surfaces. As the pilot sleeve 98 slides within the pilot valve bore 90, each of these transverse passages 101-104 continues to communicate with one of the passages 94, 50, 92, and 96, respectively, in the pilot housing 70.
A pilot spool 100 is slidably received within the central opening of the pilot sleeve 98, and as biased toward the end of the sleeve with the projection 99 by a second spring 109. The upper end of the pilot spool 100 has a head 108 which engages a slot in a shaft 110 of a stepper motor 112. Rotation of the stepper motor 112 causes the shaft 110 to move linearly into and out of the motor housing, thereby moving the pilot spool 100 up and down within the pilot sleeve 98. As will be described, movement between the pilot spool 100 and the pilot sleeve 98 opens and closes the transverse passages 101-104 in the pilot sleeve. Specifically, notches 105 and 106 in the pilot spool 100 provide passages between those apertures. Although the present invention is being described in the context of a stepper motor 112, which produces linear motion of the pilot spool 100, other types of linear actuators, such as a solenoid coil, can be employed in place of the stepper motor. However, a stepper motor is preferred as providing greater resolution of motion.
In order to move the control spool 36 to the right in the drawings, the stepper motor 112 is activated to turn its shaft 110 in a direction in which moves the pilot spool 100 upward into a position such as the one depicted in Future 4. In this orientation, a path is created along the pilot spool 100 between the second and the third transverse passages 102 and 103 of the sleeve 98. These transverse passages 102 and 103 are aligned with the tank passage and the first pilot passage 92 in the pilot housing 70. This alignment communicates pressurized fluid from the supply passage 50 to the first pilot chamber 76. At the same time, the position of the pilot spool 100 provides another path between the first transverse passage 101 and the interior bore 91 of the pilot sleeve 98. The first transverse passage 101 is aligned with the second pilot passage 94 in the pilot housing 70. This allows fluid to flow from the second pilot chamber 78 into that interior bore 91 and through an end aperture 116 into the intermediate pilot chamber 86 from which the fluid continues to flow into the tank passage 52. This relieves pressure within the second pilot chamber 78. As a consequence, the pressurized fluid being introduced into the first pilot chamber 76 drives the pilot piston 74 and the attached control spool 36 to the right in the drawings, thereby enabling fluid to flow to and from the two workports 46 and 48, as previously described with respect to
As the pilot piston 74 moves to the left, the projection 99 of the pilot sleeve 98 rides up on the tapered surface 84 of the pilot piston 74. This pushes the pilot sleeve 98 upward within the pilot valve bore 90 against the force of first spring 107 and into a position illustrated in
It should be understood that the degree to which the pilot sleeve 98 moves within the pilot housing 70 due to engagement with the tapered surface on the pilot piston 74, corresponds to the degree to which the pilot spool 100 has been moved by the stepper motor 112. This related motion of the pilot sleeve 98 provides a position feedback mechanism which terminated the fluid flow when the pilot piston 74 and the control spool 36 are properly positioned.
Thereafter should other forces produce movement of the control spool 36 and pilot piston 74, the engagement of the pilot sleeve projection 99 with the piston's tapered surface 84 will produce a corresponding movement of the pilot sleeve. This motion of the pilot sleeve reopens the two pilot passages 92 and 94 applying further pressurized fluid to the piston chambers 76 and 78 and returning the control spool to the desired position.
When it is desired to move the pilot piston 74 and the control spool 36 to the left, from the centered position illustrated in
The present orientation of the pilot spool 100 applies pressurized fluid from supply line 50 to both the first and second pilot chambers 76 and 78 on opposite sides of the pilot piston 74. Note that the pressure within the pilot chamber 76 acts on a relatively small surface area of the pilot piston 74 as compared to the combined surface area of the piston in the second pilot chamber 78. Due to this surface area difference, the pressurized fluid in the second pilot chamber 78 forces the pilot piston 74 and the attached control spool 36 to the left in
As the pilot piston 74 moves to the left, the projection 99 of the pilot sleeve 98 moves downward along the tapered surface 84 of the piston due to the biasing action of spring 107, as shown in
From this position, movement of the pilot spool 100 by the stepper motor 112 will again open up communication between various transverse passages 101-104 in the pilot sleeve 98 depending upon the direction of that pilot spool motion. That action applies pressurized fluid to one or both of the piston chambers 76 and 78, as described previously moving the pilot piston 74 into a new desired position.
With reference to
The section of the control spool 206 within the piston bore 204 extends through a tubular pilot piston, thereby defining first and second chambers 234 and 238 in the piston bore 204. Engagement of the pilot piston with the outer circumferential surface of the control spool 206 and the surface of the piston bore 204 provides fluid separation between the first and second chambers 234 and 238. The outer circumferential surface of the pilot piston 210 has a wide, centrally located, annular groove to 222 from which several feeder apertures 224 extend to an interior circumferential surface which abuts the control spool 206. Annular first and second interior grooves 232 and 236 are formed in the inner diametric surface of the pilot piston 210 at opposite ends.
A first set of cross apertures 214 is spaced radially around the control spool 206 to provide fluid paths between the outer circumferential surface and a pilot valve bore 212 in the control spool. An annular notch extends around the outer circumferential surface through the openings of the first set of cross apertures 214 and a first snap ring 216 is located within that annular notch. A similar second set of cross apertures 218 is located through the control spool 216 at the opposite end of the pilot piston 210 and a second snap ring 220 fits within another external groove running through the openings of those cross apertures. The two snap rings 216 and 220 fix the location of the pilot piston 210 around the control spool 206 and transfer force there between.
First radial apertures 226 are spaced radially around the control spool 206 and open into an annular notch in the interior surface of the pilot piston which connects the feeder apertures 224, thereby providing passages into the pilot valve bore 212. Second radial apertures 228 through the control spool 206 are on one side of the first radial apertures 226 and third radial apertures 230 in the control spool 206 are on the opposite side of the first radial apertures 226. The first interior groove 232 at one end of the pilot piston 210 provides a passage between the second radial apertures 228 and the first chamber 234 in the piston bore 204 to one side of the pilot piston 210. The second interior groove 236 of the pilot piston 210 provides a passage between the third transverse passages 230 in the control spool 206 and the second chamber 238 on the other side of the pilot piston 210 in the piston bore 204.
A pilot spool 240 is slidably received in the pilot valve bore 212 at the end of the control spool 206. A bias spring 242 located at the bottom of that pilot valve bore 212 and engages the interior end of the pilot spool 240 tending to force the pilot spool out of the bore. The pilot spool 240 has a primary aperture 244 longitudinally there through. A first set of exhaust apertures 246 extend radially outward from the primary aperture 244 to the exterior surface of the pilot spool 240. The first set of exhaust apertures 246 opens through the exterior surface of the pilot spool at a location that is between the cross apertures 214 and the second radial apertures 228 in the control spool 206, when the control spool is centered in the neutral position in
An overload spring 250 is located within an enlarged portion of the primary aperture 244 through the pilot spool 240 at an end which faces outward from the valve body 200. One end of the overload spring 250 abuts an interior shoulder of the primary aperture 244 and a cup-shaped spring guide 252 is received within the opposite end of the overload spring. A retaining clip 254 fits within an annular notch in the pilot valve bore 212 of the control spool 206 to retain the pilot spool 240 therein.
A stepper motor 256 serves as a bidirectional linear actuator which, when electrically driven, advances or retracts an output shaft 256 into or out of the pilot valve bore 212. The remote end of the stepper motor shaft 256 seats within the bottom of the spring guide 252. The stepper motor 256 is secured in the open end of the piston bore 204.
With continuing reference to
When it is desired to move the control spool 206 to the left in the drawings, the controller for the hydraulic system applies a drive signal to the stepper motor 256 which produces an extension of the shaft 258 into the valve body 200. This motion of the motor shaft 258 does not compress the overload spring 250 which transmits the force of the motion to the pilot spool 240. As a result, the pilot spool moves to the left in the drawing, compressing the bias spring 242. As shown in
Eventually, the control spool 206 and the attached pilot piston 210 move into a position similar to that illustrated in
The spring force of the overload spring 250 is such that it is not compressed during normal operation of the valve assembly. However, if the stepper motor 256 is operated very rapidly, the pilot spool may be driven against the inner shoulder 260 of the pilot valve bore 212 before the pressure differential is established across piston 210. At that time, further motion of the stepper motor 256 can not produce additional movement of the pilot spool and the shaft 258 will slip within the stepper motor. Such slippage alters the relationship between the rotational position of the stepper motor and the linear position of the shaft, which is undesirable. The overload spring 250 prevents slippage by compressing under the exertion of additional force by the stepper motor 256 when the pilot spool is bottomed against the inner shoulder 260 of the pilot valve bore 212.
To return the control spool 206 to the center, neutral position, the stepper motor 256 is energized to partially retract the shaft 258 to the right. The bias spring 242 exerts force which causes the pilot spool 240 to follow the retraction of the stepper motor shaft 258, thereby moving to the right in the drawings. This new orientation of the pilot spool 240 within the pilot valve bore 212 at the end of the control spool 206, opens up passages so that pressurized fluid from the supply line branch 208 is fed into the first chamber 234 and fluid in the second chamber 238 is exhausted to the tank passage 52. Specifically, the new position of the pilot spool 240 enables the pressurized fluid flowing through the first radial apertures 226 in the spool to continue into only the first exterior groove 243 around the pilot spool and through the second transverse passages 228 and first piston interior groove 232 to the first chamber 234. Another passage is created by communication of the second set of exhaust apertures 248 in the pilot spool 240 with the set of cross apertures 218 in the control spool 206. This orientation of apertures allows fluid to flow from the second chamber 238 through the primary pilot spool aperture 244 and the cavity of the bias spring 242 into the tank line 52. These passages apply a greater pressure to the first chamber 234 than in the second chamber 238, thereby exerting a net force which drives the pilot piston 210 and the attached control spool 206 to the right. Eventually, the pilot piston and control spool reach the orientation depicted in
As will be readily appreciated by one skilled in the art, retraction of the stepper motor shaft 258 to the right in the drawings from the center neutral position in
One skilled in the art will appreciate that the supply and return passages 208 and 52 can be reversed with corresponding alteration of the passages formed in the control spool 206, pilot piston 210, and pilot spool 240.
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. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
