Patent Application
20110001077
1. Field of the Invention
The present invention relates to a modulator valve assembly for regulating fluid flow along a fluid flow path, and more particularly to controlling valve positioning and fluid flow in a modulator valve assembly.
2. Description of the Related Art
Fluid flow modulator valve assemblies are known in which a controllably rotated motor, such as a step motor, moves a valve member linearly to variably open a port or opening through which a fluid flows. The position and movement of the valve is controlled through motor actuation to selectively permit and modulate the permitted flow of fluid through the opening and thus through the valve assembly. It is also known to operably engage a reversible rotating motor output and such a linearly moveable valve member through a threaded joint or coupling having interconnected male and female portions, one of which is fixed to rotate with the motor output, the other of which is axially fixed to the linearly moveable valve member. Thus, rotation of the motor is translated by the threaded coupling or joint into linear valve movement, the valve member moved linearly back and forth along an axis between different positions relative to the opening in response to reversible rotation of the motor output.
A problem with such prior valve assemblies is that a certain degree of backlash is experienced when reversing the motor from its most recent direction of rotation, which results in a time delay in the valve movement relative to motor output movement and system hysteresis, which compromises valve control. This occurs because the male and female threaded joint portions have one pair of interfacing thread surfaces slidably engaged during valve movement in one direction, and a different, opposite pair of interfacing thread surfaces slidably engaged during valve movement in the opposite direction, the lash or clearance between the interengaged threads of the joint first requiring traversal before reversed rotation of the motor output effects reversed linear movement of the valve. This traversal may be referred to as “backlash.”
Prior modulator valve assemblies including such threaded couplings or joints between the motor output and the valve member have addressed this concern through selectively matching the threaded male and female portions of the joint to minimize the clearance between their interengaged threads. In other words, the threadably interengaged joint connection portions are selected such that the interfacing surfaces on opposed sides of their interengaged threads are, to some extent, brought into closer proximity with each other and minimizing lash, preferably without compromising the ability of the threadably interengaged male and female portions to easily rotate relative to each other and thus move axially relative to each other. Alternatively, very close thread manufacturing tolerances are maintained to similarly minimize lash without selective matching. Either approach is an expensive and/or time-consuming process, and does not fully address the problems of delay and hysteresis, for with it some backlash will still be present.
Further, the sourcing of the motor, valve member and/or intervening threaded coupling or joint portions may complicate their being assembled in a manner that ensures backlash is minimized. For example, these components may be manufactured by different entities, complicating the coordination and undermining the convenience of selective thread matching or adhering to close thread tolerance requirements.
Achieving greater valve control without resorting to selective thread matching or requiring closer thread manufacturing tolerances is therefore desirable.
Additionally, the poppet valves of prior modulator valve assemblies typically give an output response that resembles a second order polynomial or a logarithmic function of the input. Controlling fluid flow using a modulator valve assembly having such an output response can be problematic with newer controllers, which work best with a linear output. For example, if one were to differentiate a second order polynomial, the result would be an equation representing a straight line. This straight line, however, has a slope other than zero, meaning that the valve assembly output response is more and less responsive per unit input at different positions throughout the valve member's travel, a phenomenon known as the modulator valve assembly having a varying “gain.”
If, however, the modulator valve assembly is designed to have a linear output response per unit input (represented by a straight, sloping line), then its derivative at any point in its valve member's travel will be a constant, meaning that the valve assembly output response for a given unit input is constant throughout the entire range of valve member travel, i.e., the modulator valve assembly gain is constant. Modulator valve assembly controllers are programmed to respond to a given error. However, the same error can occur at any point of the valve travel. Therefore, these controllers work best with a constant gain, which facilitates a consistent, more easily controlled output response.
Notably, however, even if constant gain is achieved, valve assembly output response can be affected by variables such as, for example, supply line pressure. Thus, tailoring the valve assembly output response to achieve desired performance in particular circumstances may also be necessary.
It is therefore also desirable to provide a modulator valve assembly with the ability to have constant gain, but which facilitates easily tailoring the valve assembly output response to deviate from a linear function of its input as circumstances warrant.
Thus, it would be advantageous to provide a modulator valve assembly that overcomes at least one of the aforementioned problems.
An object of the present invention is to eliminate backlash between the rotatable motor output and the linearly movable valve member, which are operably engaged through a threaded joint having interengaged male and female portions, in a modulator valve assembly. An anti-backlash device provides a biasing force that is applied in such a way as to keep one side of the thread of the joint portion axially fixed to the valve member against one side of the thread of the joint portion rotatably fixed to the motor output at all times, regardless of motor rotating direction, whereby a change in rotational direction of the step motor is realized immediately at the valve member, thereby eliminating output hysteresis.
Another object of the present invention is to facilitate easily tailoring a modulator valve assembly output response to account for affecting circumstances particular to its installation, use and application, to achieve desired performance. The output response may be altered through selection of a characteristic insert that may be one of a plurality of interchangeable tubular members removably disposed within the modulator valve assembly housing, its cylindrical axis collinear with the axis of valve travel, the valve moving within the tubular member to create and vary the area size of an opening or port in the wall of the tubular member through which a fluid flows, yielding a valve assembly output response to valve input step. The selected characteristic insert may provide an opening or port shape or profile that produces a linear or a non-linear output response, and that may be tailored to accommodate performance-affecting factors such as, for example, supply line pressure, in achieving desired performance. Quick and easy removal and replacement of the characteristic insert with one providing a different opening or port shape and/or size is facilitated by the present invention.
In addition to, or as an alternative to, providing the modulator valve with a plurality of different characteristic inserts, the valve's output response may be altered through the selective adjustment by a user, of minimum and maximum endpoints of the valve member as it moves toward an open position along a tubular insert member, the stroke endpoints defining the limit of a range of travel over which the control signal is scaled. The adjustment of the minimum and maximum open position endpoints in the stroke can be appropriately matched to a constant supply line pressure, or used with a corresponding adjustment to the supply line pressure, to yield a desired output characteristic. For example, supply line pressure may be increased and the valve's maximum opening stroke endpoint reduced to achieve the same maximum output as can be realized through having lower supply line pressure and greater maximum valve stroke, but with more linear output characteristic. Essentially, the valve may be operated on a narrower portion of the “logarithmic” output characteristic and experience less slope change over the operating range. The opening stroke endpoint position being adjustable between minimum and maximum can be easily facilitated through motor control features.
The present invention provides a modulator valve assembly including a housing defining a fluid inlet passage through which fluid enters the housing, a fluid outlet passage through which fluid exits the housing, and a valve member which moves along an axis within the housing, the valve member having first and second positions separated along the axis and is operably disposed between the fluid inlet and outlet passages. The variable size of an opening through which the fluid inlet and outlet passages are in fluid communication within the housing is at least partially defined by the valve member, the opening having a first size when the valve member is in its first position and a second size when the valve member is in its second position. The modulator valve assembly further includes a motor having a reversibly rotating output, the motor output having an axis of rotation substantially aligned with the axis along which the valve member moves, and a joint having threaded male and female portions through which the motor output and the valve member are operably engaged. The threads of the joint male and female portions are interengaged and the joint male and female portions are relatively rotatable. One of the male and female portions is rotatably fixed to the motor output, and the valve member is axially fixed to the other of the joint male and female portions, whereby the valve member is moved axially in response to rotation of the motor output. The threads of the male and female portions each have a first surface that generally faces a first direction and a second surface that generally faces a second, substantially opposite direction, and the first thread surface of one of the male and female portions is biased into continuous contact with the second thread surface of the other of the male and female portions.
The present invention also provides a modulator valve assembly including a housing having a fluid inlet passage and a fluid outlet passage, an interchangeable characteristic insert removably disposed in the housing, the characteristic insert having a wall in which there is a void defined by an edge, the fluid inlet and outlet passages located on opposite sides of the wall. The modulator valve assembly further includes a valve member disposed in the housing and moveable between variable positions along an axis, the valve member positions sequentially arranged with a common fixed distance between adjacent valve member positions along the axis. The modulator valve assembly further includes a reversible motor having an output, and a joint at all times devoid of backlash disposed between the valve member and the motor output through which the motor output and the valve member are operably engaged. The valve member is in sliding engagement with the wall, and the void edge and the valve member define a port in the wall through which the fluid inlet and outlet passages are placed in fluid communication with each other, the port having a variable flow area size partially defined by the variable position of the valve member. The characteristic insert is a selected one of a plurality of interchangeable characteristic inserts each having a void that is different from the void of another characteristic insert of the plurality.
Further aspects of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of a specific example, while indicating a preferred embodiment of the invention, is intended for purposes of illustration only and are not intended to limit the scope of the invention.
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. While the invention is susceptible to various modifications and alternative forms, a specific embodiment of it by way of example is shown in the drawings and described in detail herein. It should be understood, however, that the drawings and detailed description that follows are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Moreover, it is to be noted that the Figures are not necessarily drawn to scale or to the same scale. In particular, the scale of some of the elements of the Figures may be greatly exaggerated to emphasize characteristics of the elements. Elements shown in more than one Figure that may be similarly configured have been indicated using the same reference numerals.
The following description of a preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention or its uses.
Referring to
Modulator valve assembly housing 22 further includes cover 36 sealably and removably attached to body 37 of housing 22 below valve member 28. Motor mount 38 is sealably affixed to housing body 37 above valve member 28. Attached to motor mount 38 is step motor 40 having a rotor provided with reversible rotatable output 44 (
Valve assembly 20 further includes generally cylindrical valve stem 48 which is provided with threaded bore 50 (
The upper axial end of valve member 28 is provided with centrally located threaded bore 58 in which is received axially extending threaded shaft portion 60 of valve stem 48. Valve member 28 and valve stem 48 are fixed together against relative movement therebetween through the threaded engagement of bore 58 and shaft portion 60. A thread adhesive such as LOCTITE™ may be applied to the threads of bore 58 and shaft portion 60 to ensure the fixed relationship of valve stem 48 and valve member 28.
The upper axial end of valve member 28 is formed with centered annular spring seat 62 disposed about threaded bore 58, planar spring seat 62 extending radially outward and normal to axis 30. The outer diameter of spring seat 62 is sized to be received within bore 56 of motor mount 38, as best shown in
Compression spring 64 is a generally cylindrical coiled spring disposed about motor housing extension 54 and axis 30, with one end in abutting contact with spring seat 62 and the opposite end in abutting contact with annular motor housing shoulder 66 formed about motor housing extension 54. As best understood with reference to
Referring now to
Referring still to
Compression spring 64 exerts equal biasing forces FB in the opposite first and second directions respectively indicated by arrows A1 and A2. These forces bias first surface 74 of thread 70 into continuous abutting contact with second surface 80 of thread 72. In all states of valve operation and regardless of the direction of rotation of motor output 44, surfaces 74 and 80 remain in abutting (or when moving relative to each other, slidably abutting) contact, and there is at no time any separation of threads 70 and 72, which remain in contact through their abutting surfaces 74 and 80. Therefore, the backlash encountered in prior modulator valve assemblies, which typically occurs upon their motor outputs reversing their prior directions of rotation, is eliminated in modulator valve assembly 20. Thus, joint or coupling 42 is provided with an anti-backlash device that includes spring 64, spring seat 62 and shoulder 66 between which spring 64 acts, and interengaged surfaces of threads 70, 72 of the male and female portions of joint or coupling 42. Those of ordinary skill in the art will recognize that the anti-backlash device could alternatively be configured to provide a biasing force that maintains first surface 78 of thread 72 into continuous abutting (or slidably abutting) contact with second surface 76 of thread 70, to produce a similar anti-backlash effect. Thus, the need to selectively match or maintain close manufacturing tolerances of the threads of coupling or joint 42 to minimize delay and hysteresis, as done in prior art modulator valve assemblies, is obviated in modulator valve assembly 20.
Referring to
Referring again to
Projecting from axial end surface 86 of valve head 82, along axis 30, is projection 94 having terminal end or tip 96. Tip 96 is brought into abutting engagement with interior surface 98 of cover 36 when valve member 28 is in its maximum, fully opened position. That is to say, the travel of valve member 28 is limited in its direction away from motor 40 by the abutting engagement of tip 96 and cover surface 98.
Disposed within housing 22 and partially defining passageway 32 is tubular member 100 having opposed axial end surfaces 102 and 104 between which is defined interior cylindrical sidewall surface 106 which is in slidably sealing engagement with cylindrical surface 84 and/or seal 92 of valve head 82. Optional groove 90 and band seal 92 provides enhanced sealing engagement between valve head 82 and cylindrical sidewall surface 106 when modulator valve assembly 20 is in its fully closed position (
Tubular member 100 is provided with void or notch 112 that is cut into the wall thereof, one end of void 112 being open to lower axial end surface 104 of tubular member 100. Void or notch 112 thus extends from axial end surface 104 towards annular, axial end surface 102 of tubular member 100.
The shape of void or notch 112 is selected, defined or calculated to achieve the desired modulator valve assembly output response in view of the factors affecting flow and its modulation, and may be, for example, generally rectangular, generally triangular (as shown), or any other shape determined to provide the desired output response to a unit of input defined as being, or being directly proportional to, each stepped linear movement of valve member 28 along axis 30 responsive to the corresponding stepped angular movement of motor output 44 from one position to the next, which the above-described anti-backlash device ensures to be immediate and without hysteresis.
The illustrated triangular shape of void 112 in tubular member 100 is exemplary only. A rectangular void would produce a more linear modulator valve assembly output response to the incremental linear movement of valve member 28 (and thus a substantially constant gain) but, as mentioned above, in tubular member 100 the defining edge of void 112 (and thus of port 34) may be tailored to any shape determined to yield the desired output response in view of circumstances particular to the installation, use and application of the modulator valve assembly, to achieve the desired performance. The shown substantially triangular shape of the edge defining void 112, which has vertex 114 formed by the intersection of opposite sides 116 and 118 separated by angle θ and the base defined by open segment 120 in otherwise annular axial surface 104, provides a modulator valve assembly output response that may be a second order polynomial.
For the purposes of illustration, with reference to
In reaching the adjacent incremental stepped position of valve member 28 along axis 30, shown in
In reaching the further adjacent incremental stepped position of valve member 28 along axis 30, shown in
Tubular member 100 may be one of a plurality of interchangeable characteristic inserts distinguished by the size and shape of its void 112, each facilitating in modulator valve assembly 20 a different output response (e.g., the change in flow area of port 34) per unit of input (e.g., the fixed incremental amount of travel along axis 30 between D1 and D2, or between D2 and D3). The valve assembly output response may be tailored to accommodate circumstances particular to the installation, use and application, to achieve desired performance, by substituting the shown tubular member 100 for another having a different void-defining edge in its sidewall. Substitution of one characteristic insert for another entails removing cover 36 from housing body 37 (held in place with a plurality of screws 124 as shown in
In addition to, or as an alternative to, providing the modulator valve 20 with a plurality of different characteristic inserts 100, the valve's output response may be altered through the selective adjustment by a user, of minimum and maximum endpoints of the valve member 28 as it moves toward an open position along a tubular insert member 100, the stroke endpoints defining the limit of a range of travel over which the control signal is scaled. The adjustment of the minimum and maximum open position endpoints in the stroke can be appropriately matched to a constant supply line pressure, or used with a corresponding adjustment to the supply line pressure, to yield a desired output characteristic. For example, supply line pressure may be increased and the valve's maximum opening stroke endpoint reduced to achieve the same maximum output as can be realized through having lower supply line pressure and greater maximum valve stroke, but with more linear output characteristic. Essentially, the valve may be operated on a narrower portion of the “logarithmic” output characteristic and experience less slope change over the operating range. The opening stroke endpoint position being adjustable between minimum and maximum can be easily facilitated through motor control features.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or type of fluid medium to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
The instant application claims priority to U.S. Provisional Patent Application Ser. No. 61/222,334, filed Jul. 1, 2009, entitled MODULATOR VALVE ASSEMBLY HAVING AN ANTI-BACKLASH DEVICE, the entire specification of which is expressly incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61222334 | Jul 2009 | US |
