Patent Publication Number: US-2011064590-A1

Title: Valve Arrangement for Peripherally Pivoted Oscillating Vane Machine

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/242,590, filed on Sep. 15, 2009, the entire teachings of the above application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Pressure activated valves restrict the flow of fluids to a single direction, opening and closing under changing pressure in the desired direction of flow. An Oscillating Vane Machine, configured for use as a gas compressor or otherwise, requires separation of flow between the upstream and downstream gas pressures (suction and discharge respectively), typically by way of valve mechanisms, in order for the compression process to be effectively performed. 
     Ansdale (U.S. Pat. No. 4,823,743) discloses an Oscillating Vane Machine, which, in one embodiment, uses pressure activated reed valves. In other embodiments, a cam and spring actuated poppet valves and rotary valves, each with timed opening and closing, are disclosed. 
     Moriarty (U.S. Pat. No. 4,080,114) discloses a novel flow path for the fluid entering the piston chambers through the vane pivots and then through the vanes themselves with the opening and closing of the ports in the vanes being controlled with a flapper valve activated by inertia and pressure differences. He also uses various reed valves in additional embodiments for fluid inlet and discharge. As with all of the previous machines, Moriarty does not provide a fluid path which will support high flow rates while keeping the machine small. 
     Henriksen (U.S. Pat. No. 5,201,644) discloses an arrangement for a compressor with oscillating piston wings with a series of mutually angularly displaced discharge slots arranged in a radially extending end wall between a working chamber of the machine and an oppositely disposed discharge chamber. The discharge slots are covered over by valve members of resilient nature. The valve members may be inserted in the end wall with an end groove in a recessed manner to engage a valve seat about each slot. 
     Chomyszak (US Patent Application 2009/0081061 A1) discloses a peripherally pivoted oscillating vane machine, for which the present invention is of particular benefit in ease of installation and service, and ultimately in improved efficiency of the OVM by way of decreased clearance volume, increased valve flow area, and decreased manifold pulsations. 
     Suction and discharge plenums serve as collection points for working fluid before or after it passes through a valve. They are ubiquitous in positive displacement machinery, including OVMs, and are well understood by those skilled in the art. A peripherally pivoted oscillating vane machine is particularly benefited by the radial location of the suction and discharge plenums into combined suction and discharge volumes, which, when properly sized, provide significant performance enhancement to the operation of the OVM by way of reducing the magnitude of gas pulsations which effect pressure activated valve performance. The proximity of the manifold volumes to suction and discharge valves is an important factor in how effective the volumes can be in absorbing the pulsation energy of the fluid flow through the valve. If the volume is too restrictive, the fluid flow through the valve, into the volume, can cause excessive pressure increase (pulsations) in the volume. Since in most cases the valves are pressure activated, meaning the pressure must be greater on one side in order for the valve to open, e.g. any instantaneous increase in pressure in the discharge manifold volume will require extra lost work by the working chamber in order to overcome the higher pressure differential across the valve. Radial location of these volumes allows the elimination of any intermediate communicating passage between the valve and the volume. A manifold volume that is large in comparison to the displaced volume of the working chamber will facilitate more efficient valve operation. 
     The valve attachment methods proposed in the OVM prior art do not take into account proximity of the valve to the manifold volumes, and ease of assembly of the valve to the stator and manifold volumes, particularly not for peripherally pivoted machines with radially located manifold volumes. Ansdale principally discusses “tubular” pressure activated valves which are designed to transmit the working fluid in and out of the compressor in the axial direction. These tubular valves are referenced to be “shrunk into position in the vane housing”, with each suction and discharge valve having separate installation bores for each compression chamber. Much of the OVM prior art shows valve flow in the axial direction, using valves located in an axial face of the oscillating chamber (Henriksen), or otherwise locating the valves tangential to the oscillatory motion, communicated through a chamber side wall, and then translating the direction of fluid flow from tangential to axial (Ansdale). 
     Moriarty addresses a “means of collecting discharge fluids towards a common discharge point which is not shown”, and which appears to be translated to the axial direction. Moriarty addresses valve attachment where the chamber side walls are readily accessible to the exterior of the machine and “reed valve plates” are clamped adjacent to each compression chamber in the “cylinder head” method described earlier. This method of attaching valve plates is conventional, is referred to as such, and is not a claim of the Moriarty patent, which says “The use of reed valve plates and installation thereof is well known in the art and is not further elaborated upon.” 
     in the majority of designs, the total available space for porting and valves in an OVM is inherently limited by the broad face of the oscillating member, or vane  11 , as shown  FIG. 1  and  FIG. 2 . For an OVM, this available valve space is typically rectangular in shape, reflecting the rectangular side profile of the oscillating vane. As such, maximal flow area is achieved with the use of a rectangular valve that reflects the rectangular shape of this available valve space. This is similar to the space constraint on valves for any reciprocating piston-cylinder design, where the suction and discharge valves must be contained within the area of the cylinder head; in the case of a piston-cylinder design, this available space is circular in shape. Furthermore, the upstream and downstream volumes (suction and discharge respectively) must be isolated from one another in order for the compression process to function. 
     To those skilled in the art, any valve provides only a small fraction of this total available space as actual effective valve area for fluid flow. Fluid flow area, specifically the cross sectional area available to a volume of fluid through which flow can occur, is a critical factor in the characterization of fluid flow. The general design goal of a reed valve is to provide as much fluid flow area as possible in order to minimize irreversible losses through the valve without sacrificing structural integrity of the reed, ability to seal, or exceeding reasonable limitations on the practical design implications of valve size. With no pressure differential, a reed covers a valve port through which fluid flows before it reaches or after it passes through the reed. The cross sectional fluid flow area of the valve port is one important design consideration, but in general, it is not the critical parameter. The nature of operation of a reed valve is that one end of a thin plate (reed) lifts by bending due to a pressure differential, allowing fluid flow, while the other end of the reed is secured in place. As such, the critical flow area is actually the area exposed between the reed counterface (where the reed seals the valve port) and the lifted sealing face of the reed itself, as shown in  FIG. 11 . This flow area is a function of both the perimeter of the valve port (and hence valve port flow area) and more importantly the amount of lift that the reed undergoes when exposed to a pressure differential. However, the amount of reed lift permissible in order to achieve sufficient fatigue life for the reed is a function of the length of the reed and frequency of compression. A short reed cannot have as much lift as a long reed without being subjected to higher mechanical stress. It follows that since a reed is bending when it lifts, the vertical lift of the reed can be increased by increasing the length of the reed, specifically the distance from the stationary end of the reed to the lifting end. A valve assembly for an OVM that is predominantly rectangular in shape, and which may have overlapping reeds, is particularly beneficial to the OVM described because it enables longer valve reeds, and accordingly higher effective flow area. 
     It is therefore advantageous for a peripherally pivoted OVM to have suction and discharge valves that communicate directly with suction and discharge manifold volumes. Furthermore, such a valve should have as much effective fluid flow area as possible in order to maximize output of the machine without suffering efficiency losses. Still, such a valve should be able to be assembled quickly and easily, and must accomplish all of the sealing of leakages, internally and externally, that is required of a valve of this type. 
     SUMMARY OF THE INVENTION 
     The present invention relates to improved integrated valve assemblies, preferably, for use in an oscillating vane machine (OVM) that provide easy assembly and maintenance, direct fluid communication between the working chamber and suction and discharge manifold, and the avoidance of the use of fasteners in contact with or adjacent to the working chamber. 
     A preferred embodiment of the invention incorporates a removable valve assembly, or valve sled, which contains the suction and discharge valves for one side of a double acting OVM chamber, and which facilitates the isolation between upstream and downstream pressure cavities. Referring to  FIG. 3  and  FIG. 6 , the valve sled  34  can be installed into an OVM stator  31  from one end  62 , by sliding into the T-Shaped slot  32  shown in  FIG. 3  and  FIG. 5 . In this configuration, it is desirable to seat the manifold side  56  of the valve sled against the top 54 of the T-shaped slot  32 , with the underside of the valve  55  being exposed to the compression or working chamber  53 . The valve sled contains two grooves  33  for o-rings  35  which seal the valve-stator interface, and which are used to separate the suction gas from the discharge gas. See  FIG. 3  and  FIG. 4 . The novel method of valve attachment to an OVM of the invention achieves this o-ring seal without bolts perpendicular to the valve-stator interface, and allows axial installation of the valve assembly through the end  62  of the stator  31 . 
     One embodiment of the above valve type assembly is the Integrated Suction-Discharge Reed Valve (ISDRV) assembly. In particular, the ISDRV is preferably characterized by a vertical overlap of the suction reeds  4  and discharge reeds  5 , shown in  FIG. 9 . When looking at the cross-section of the ISDRV in  FIG. 10 , the suction valve and fluid flow is on the left and the discharge valve and fluid flow is on the right. The orientation of the suction valve, that is the lifting end  95  of the reed that lifts to permit fluid flow, is preferably opposed 180 degrees to the orientation of the discharge valve and vice versa. As such, the stationary, non-lifting end  94  of both the suction and discharge reeds preferably occupy and overlap the center of the cross-section shown in  FIG. 10 . This vertical overlap of the stationary end of the reeds enables two primary technological advantages: specifically the maximization of fluid flow area in a confined space, and the elimination of the need for fasteners in the working chamber. 
     It will be understood that the valve assemblies of the invention could be used in other machines requiring suction and discharge ports, such as compressors. As such, the references to OVMs through out the specification can be substituted by such other machines. Further, while the invention is illustrated by the suction ports being proximal and discharge ports being distal to the working chamber of the OVM, it will be understood that the reverse configuration can also be designed and is intended to be an embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a cross sectional view of a vane  11  of an OVM. 
         FIG. 2  is a side view of a vane  11  of an OVM. 
         FIG. 3  is an expanded view of a valve sled of the invention and illustrates the taper keys used to secure the sled within the OVM stator. 
         FIG. 4  is a cross sectional view of the sled disposed within the stator. 
         FIG. 5  is a perspective view of the valve assembly disposed within the stator and illustrates a possible relationship between the assembly and the working chamber, relative to the vane. 
         FIG. 6  is an end view of the stator with valves assembled. 
         FIG. 7  is an axial cross section showing suction valve passages. 
         FIG. 8  is across sectional view showing valve proximity to manifold volumes. 
         FIG. 9  is an expanded view of the ISDRV. 
         FIG. 10  is a cross sectional view of the ISDRV. 
         FIG. 11  is perspective view illustrating the reed valve critical flow area. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a novel valve arrangement and method of attachment. It is particularly suited for use with a peripherally pivoted oscillating vane machine, such as the type disclosed by Chomyszak. 
     Integration of the suction and discharge valves for an OVM into a single module that can be installed into the stator is an improvement for ease of assembly, inspection and service over previously proposed valve arrangements. It is desirable to locate the valves in direct communication with the manifold volumes to maximize the effectiveness that the manifold&#39;s ability to absorb pulsation energy has on valve performance. Fluid passageways through the machine, for example in the axial direction as shown in the prior art, diminishes the efficiency of the valves, and in some cases can allow excess heat to be transferred to the suction fluid, another source of loss in positive displacement compressors, as is understood by those skilled in the art. 
     Typically, for a reciprocating piston-cylinder compressor, the reed valve assembly is clamped between the cylinder and the cylinder head. In an OVM, the analog to a cylinder head is the chamber side wall, which is the wall parallel to the vane  11  ( FIG. 1  and  FIG. 2 ) at each extreme of motion. Valve attachment methods analogous to the typical cylinder head design described above but adapted to the side wall of an OVM, have been proposed (see Moriarty). This method of valve attachment makes sealing of the assembly and separation of inlet and discharge gas volumes straightforward, by way of gaskets or o-rings clamped between the flat surfaces of the chamber side walls (or cylinder head). 
     However, for Peripherally Pivoted Oscillating Vane Machines (Chomyszak et al) where multiple chambers are adjacent to one another and sharing inlet and discharge manifold volumes, it is advantageous to attach valves by another means, without having to assemble each valve in conjunction with the side walls of each chamber. The reason for this is that a fundamental function of the valves in a positive displacement machine is to control flow in the desired direction with respect to the working chamber. The valve must therefore seal in the working fluid from leakage to any undesired areas. Of particular concern is the leakage from the working chamber into the suction plenum, leakage from the discharge chamber into the suction plenum, and leakage from the discharge chamber out of the normal fluid path (external leakage) altogether. 
     Another advantage to attaching valves without disassembling chamber side walls is the reduction of the number of components required. In order to achieve the sealing required of a properly functioning valve, each chamber side wall would have to seal with the valve which would have to seal against the working chamber. The suction or discharge plenums formed before or after the valve must then somehow be connected in order to communicate to a single suction and discharge input or output to the multi-chamber OVM. 
     Another advantage is in the ease of installation and accessibility of the valves for inspection, service or replacement. The challenge with valve attachment methods that do not utilize the cylinder head (as used in reciprocating machines) or chamber side wall (as used in OVMs) to apply clamping force to a gasket or o-ring is designing an alternative means of achieving the required force for seating between the valve and the stator. It is also desirable to avoid any attachment methods that require fasteners, bolts, screws etc., or any fastening mechanism that can loosen and become free in the working chamber, as this will lead to catastrophic machine failure. 
     A preferred embodiment of the invention incorporates a removable valve assembly, or valve sled, which contains the suction and discharge valves for one side of a double acting OVM chamber, and which facilitates the isolation between upstream and downstream pressure cavities. Referring to  FIG. 3  and  FIG. 6 , the valve sled  34  can be installed into an OVM stator  31  from one end  62 , by sliding into the T-Shaped slot  32  shown in  FIG. 3  and  FIG. 5 . In this configuration, it is desirable to seal the manifold side  56  of the valve sled against the top 54 of the T-shaped slot  32 , with the underside of the valve  55  being exposed to the compression or working chamber  53 . The valve sled contains two grooves  33  for o-rings  35  which seal the valve-stator interface, and which are used to separate the suction gas from the discharge gas. 
     See  FIG. 3  and  FIG. 4 . The novel method of valve attachment to an OVM of the invention achieves this o-ring seal without fasteners perpendicular to the valve-stator interface, and allows axial installation of the valve assembly through the end  62  of the stator  31 . 
     The preferred method of attaching the valve assembly to the stator in the gas flow path, while also providing separation of upstream and downstream pressure cavities, is to use a set of taper keys  36 , as shown in  FIG. 4 . Each set of taper keys have matching angles such that when the angled surfaces  46  of the taper keys are mated together, the opposite or distal faces  47  of the two keys are parallel with one another. One of the parallel faces  47  contacts part of the T-Shaped key slot while the other face pushes against the valve sled. The valve sled face  37  that has the o-rings (opposite the side that the key contacts) is forced against the seating face of the stator by the taper key set. For installation, the tapered keys are pressed together, such that the angled face of each of the keys slide against one another, which increases the height of the parallel faces. The tapered keys are pushed together until the o-ring face of the valve sled is flush with the sealing face of the stator. As an additional safety factor, the tapered keys can be retained in place by a longitudinal screw  39  in one of the tapered keys. 
     There are numerous alternate configurations of this preferred embodiment that would accomplish the same result, including integrating a tapered surface into the valve sled part or integrating a tapered surface into the T-Shaped slot. In addition, a round tapered hole could be drilled into a split rectangular key, into which a tapered pin would be hammered for virtually the same effect as the tapered rectangular keys. Alternatively, a cam-locking mechanism can be employed. 
     As the valve attachment method described here is designed to withstand a pressure differential and provide sealing, it is important to describe the mechanical self-locking nature of the tapered key attachment method. The valve sled side of the valve-stator sealing interface which makes up one side of the o-ring grooves is held in place by the assembled height of the two taper keys. As pressure against the valve increases, the normal force against this sealing face increases. In order for the sealing joint to fail, the tapered keys would either have to compress in the vertical, parallel direction by deformation, or more likely, slide relatively to one another such that the vertical, parallel height of the taper key assembly is decreased, thereby preventing the o-ring seal from functioning properly. However, a simple free-body-diagram analysis of the tapered key valve attachment method shows that the retention force of the tapered key joint in the axial direction (the direction in which relative motion to allow the failure described above would have to occur) is directly proportional to the external pressure force applied to the valve sled. In the same manner that a mass on an incline will slip only if the tangent of the incline angle is greater than the coefficient of static friction between the mass and the incline, the taper key joint will only slip if the angle exceeds a certain factor relative to the coefficient of friction between the materials. The relationship for the preferred embodiment tapered key joint described above is that the joint will only fail (keys slip) if the coefficient of static friction between the keys is greater than one half of the tangent of the taper angle. The reason for the extra factor of one half in this case as opposed to a traditional “mass on an incline” scenario is that in order for the vertical, parallel height of the keys to be decreased, the keys must slide relative to one another, and as such must simultaneously slide against two surfaces at the same time. This doubles the friction holding power of the joint. As such, the attachment method is self locking against the pressure forces which it is meant to seal. For practical purposes, assuming a static coefficient of friction between the sliding key surfaces of 0.15 (typical for lubricated steel-steel contact) the maximum angle of incline for the taper key would be approximately 16.5 degrees in order to assure a self-locking mechanism, as described above. Higher or lower friction coefficients would allow higher or lower taper angles respectively. 
     An enhancement of the tapered key design includes the use of a fastening mechanism to prevent slippage of the tapered key joint due to vibration for example. Alternatively a spring, elastomer, or adhesive material can be used to further restrain the relative motion of one key against another. 
     This preferred method of valve attachment is effective because of the self-locking, mechanical nature of the sealing joint. This sealing joint can be accomplished in other embodiments, such as many possible configurations of a cam-type self locking profile, such as those commonly found in the tooling industry. The important feature of this sealing joint is that the sealing face of the valve sled, containing the o-rings, is forced to be flush with the mating surface of the stator, and is mechanically held in place against any pressure load. 
     Reed Valve Arrangement 
     One embodiment of the above valve type assembly is the Integrated Suction-Discharge Reed Valve (ISDRV) assembly. In particular, the ISDRV is preferably characterized by a vertical overlap of the suction reeds  4  and discharge reeds  5 , shown in  FIG. 9 . When looking at the cross-section of the ISDRV in  FIG. 10 , the suction valve and fluid flow is on the left and the discharge valve and fluid flow is on the right. The orientation of the suction valve, that is the lifting end  95  of the reed that lifts to permit fluid flow, is preferably opposed 180 degrees to the orientation of the discharge valve and vice versa. As such, the stationary, non-lifting end  94  of both the suction and discharge reeds preferably occupy and overlap the center of the cross-section shown in  FIG. 10 . This vertical overlap of the stationary end of the reeds enables two primary technological advantages: specifically the maximization of fluid flow area in a confined space, and the elimination of the need for fasteners in the working chamber. 
     The vertical overlap design of the ISDRV allows for both the suction and discharge reeds to be longer than would be possible in a given confined space if the reeds were not overlapping. By enabling longer reeds, the vertical overlap enables more lift for both the suction and discharge reeds, more fluid flow area, and consequently better performing valves. In addition, the vertical overlap, and by design the implied separation of reed valve sealing counterfaces (the at-rest position of the reed), enables a larger portion of the available confined space to be used for valve ports. Each reed, suction and discharge, will by necessity have a certain area that is not useful to fluid flow in the space required to fasten the reed at the stationary end. The vertical overlap combines this less useful area for each reed into one space, opening up more of the available confined space for fluid flow. 
     This design is beneficial to a rectangular ISDRV because the entire valve module is contained within the envelope of the working chamber, and as such the valve maximizes use of the space available to valves described above. Though the anchored portion of the reeds is located in a potential fluid flow path, this non-useful area is minimized by combining the non-useful portion of both the suction and discharge valves. 
     Thus, the invention includes an integrated valve assembly for an oscillating vane machine (OVM) comprising:
         a. a valve plate  1  characterized by (i) a distal surface  91  relative to a working chamber of an OVM upon installation and a proximal surface  92  adjacent to the working chamber of the OVM upon installation; (ii) at least one suction port  93  which, when installed in an OVM, provides fluid communication with at least one suction fluid volume  101  or suction manifold  81  and a working chamber  53  in said OVM; (iii) at least one discharge port  96  which, when installed in an OVM, provides fluid communication with at least one discharge fluid volume  102  or discharge manifold  82  and a working chamber  53  in said OVM;   b. a suction pressure activated valve sealing member  4  releasably seated onto each suction port on the proximal surface and a discharge pressure activated valve sealing member  5  releasably seated onto each discharge port on the distal surface.       

     Each sealing member preferably comprises a flexible, thin plate reed. Suitable sealing members can be made of polymer, metal, stainless steel or other resilient material. The sealing members can be optionally activated by springs and can be rectangular, circular, or other shape. The sealing members can be arranged within the confinement of the overall rectangular valve shape to maximize flow area. 
     The valve assembly preferably comprising a suction back stop  2  adjacent to the suction pressure activated valve sealing member(s) and positioned to provide a back stop for the member(s) and a discharge back stop  3  adjacent to the discharge pressure activated valve sealing member(s) and positioned to provide a back stop for the member(s). The back stops are ideally shaped to match the shape of the deformed reed, so as to maximize the supportive area of the backstop when the valve is opened, and can be characterized by, for example, a curved incline that slopes from the center joint of the back stop towards the periphery of the valve plate. 
     The back stops each preferably comprise a back stop joint  99  which is joined to each said sealing member and a key  100  having a distal surface  97  and a proximal surface  98  to each said sealing member  4 , said distal surface being substantially parallel with said sealing member when said sealing member is seated on said port and said proximal surface being inclined. 
     The back stops, sealing members, or reeds, and valve plate are preferably connected or joined through one or more common fasteners  6 , such as a pin, screw or bolt. The fasteners  6  are attached from the distal end  91  of the valve plate  1 , relative to the working chamber. This configuration avoids the risk of fasteners becoming loosened during use and discharged into the working chamber. 
     Just as the reeds are preferably overlapping at the stationary ends thereof, the back stops are overlapping at the back stop joints  99  with the keys  100  of the back stops at approximately the central axis of the valve plate extending to opposing sides or the periphery of the valve plate  1 . 
     Elimination of the Need for Fasteners in the Working Chamber 
     There are numerous advantages to the tapered key attachment method beyond enabling axial assembly or disassembly of the valves to or from the stator. It is impossible for any fasteners to become loose and enter the compression chamber in this configuration. The presence of fasteners in the working chamber of an OVM is undesirable because of the possibility of a fastener becoming disengaged, entangled in the motion of the oscillating vane, and the catastrophic damage that would occur as a consequence. The ISDRV eliminates the need for the presence of fasteners in the working chamber by locating the fasteners for the suction reeds beneath the discharge reeds, such that the suction reed is held in place by clamping between the Valve Plate ( 1 ) and the Suction Reed Back Stop ( 2 ). The Suction Reed Back Stop is pulled against the Valve Plate by blind tapped holes and the Suction Reed fasteners are sealed with O-rings ( 9 ) in order to eliminate potential fluid leak paths. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.