CYLINDER HEAD FOR COMPRESSOR

CROSS REFERENCE TO RELATED APPLICATIONSThis application claims the benefit of and priority toIndian Patent Application No. 2512/DEL/2015, filed August 14, 2015.BACKGROUNDCompressors are commonly used to compress various fluids, such as gasses. Reciprocating compressors typically include a cylinder having a chamber that houses a reciprocating piston, and a cylinder head that encloses the cylinder. During a first intake stroke of the piston, negative pressure builds up in the chamber that draws fluid into the cylinder chamber through an inlet. During a second discharge stroke of the piston positive pressure builds up in the chamber, which forces fluid that has been drawn into the chamber during the intake stroke out of the chamber through the outlet. Compressors typically include a discharge valve at the outlet. The discharge valve allows fluid to flow from the chamber through the outlet once the positive pressure in the chamber is sufficient to open the discharge valve, but prevents fluid from flowing into the chamber from the outlet during the intake stroke. Compressors further typically include an inlet valve at the inlet. The inlet valve allows fluid to flow into the chamber through the inlet once the negative pressure in the chamber is sufficient to open the inlet valve, but prevents fluid from flowing out of the inlet from the chamber during the discharge stroke.Compressors find applications in any number of systems. One such application is a refrigeration system, whereby a compressor receives gaseous refrigerant from an evaporator, and compresses the refrigerant to raise the pressure of the refrigerant. The compressed gaseous refrigerant then travels from the compressor to a condenser, where heat is removed from the refrigerant. The refrigerant undergoes a phase change in the condenser from a gas to a liquid. The liquid refrigerant travels through an expansion valve whereby the refrigerant undergoes a pressure drop. The liquid refrigerant then flows to the evaporator, where it removes heat from the space that is to be cooled, and evaporates into a gas. The gas travels to the compressor as described above.US 6464475 B1discloses a head for an alternating pump for fluids, having an inlet section and an outlet section for the entry and exit of the pumped fluid, and comprising: a rigid structure made of plastic material and comprising a shell portion defining a pressure chamberbetween the inlet section and the outlet section, the pressure chamber being subjected to the pulsating pressure due to the alternation of intake and delivery of the pump; a metal frame integrated in the rigidstructure, the frame comprising points for the attachment of intake and delivery manifolds, elements for fastening the head to a base and ribs for connecting the attachment points to the fastening elements, the ribs being integrated in the shell portion.The compressor often consumes the majority of power in a typically refrigeration system. Thus, the efficiency of the compressor has a great effect on the overall efficiency of the refrigeration system. However, while attending to efficiency issues, care is also taken to ensure that the compressor is reliable in the face of severe working conditions due to the high pressures and temperature associated with the refrigerant during operation of the compressor.SUMMARYThe following Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the invention, nor is it intended to be used to limit the scope of the invention. Reference is made to the claims for that purpose. The invention is defined in claim 1.In one aspect of the present disclosure, a cylinder head is provided for attachment to a cylinder body of a compressor. The cylinder body can include an outer wall having an inner body surface and an outer body surface opposite the inner body surface, wherein the inner body surface partially defines a cylinder chamber. The cylinder head defines an inner head surface that faces the cylinder chamber, an outer head surface that is opposite the inner head surface along a central head axis, and a side wall configured to attach to the cylinder body. The outer head surface defines a concavity along at least one direction. It has been found that the concavity provides high stiffness to the cylinder head against internal pressure in the cylinder chamber. Thus, in one example, the cylinder head deflects less than conventional cylinder heads that do not include the concavity.BRIEF DESCRIPTION OF THE DRAWINGSThe foregoing summary, as well as the following detailed description, is better understood when read in conjunction with the appended drawings. There is shown in the drawings example embodiments. The present invention is not intended to be limited to the specific embodiments and methods disclosed, and reference is made to the claims for that purpose.Fig. 1Ais a perspective view of a reciprocating compressor constructed in accordance with one embodiment, including a cylinder and a cylinder head;Fig. 1Bis a sectional side elevation view of the reciprocating compressor illustrated inFig. 1A, taken along line 1B-1B;Fig. 1Cis a perspective view of a cylinder head of the compressor illustrated inFig. 1Aconstructed in accordance with another alternative embodiment;Fig. 2Ais a perspective view of the cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with one embodiment;Fig. 2B is another perspective view of the cylinder head illustrated inFig. 2A;Fig. 2Cis a sectional side elevation view of the reciprocating compressor illustrated in Fig. 2B, taken along line 2C-2C;Fig. 2Dis a side elevation view of the cylinder head illustrated inFig. 2A;Fig. 2Eis a side elevation view of the cylinder head illustrated in Fig. 2B, taken along line 2E-2E, and shown with ribs removed for the purposes of illustration;Fig. 3is a perspective view of a cylinder head of the compressor illustrated inFig. 1A, but constructed in accordance with an alternative embodiment;Fig. 4Ais a perspective view of a cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with an alternative embodiment;Fig. 4Bis a top plan view of the cylinder head illustrated inFig. 4A;Fig. 5Ais a perspective view of a cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with an alternative embodiment;Fig. 5Bis a top plan view of the cylinder head illustrated inFig. 5A;Fig. 6Ais a perspective view of a cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with an alternative embodiment;Fig. 6Bis a top plan view of a cylinder head similar to the cylinder head illustrated inFig. 6A;Fig. 6Cis a perspective view of the cylinder head illustrated inFig. 6A, but including side stiffeners in accordance with one embodiment;Fig. 7Ais a perspective view of a cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with an alternative embodiment;Fig. 7Bis a top plan view of a cylinder head similar to the cylinder head illustrated inFig. 7A;Fig. 8Ais a perspective view of a cylinder head of the compressor illustrated inFig. 1A, constructed in accordance with an alternative embodiment; andFig. 8Bis a top plan view of a cylinder head similar to the cylinder head illustrated inFig. 8A.DETAILED DESCRIPTIONFigs. 1A-1Billustrate a compressor 20 that includes a cylinder body 22 having an outer wall 24. The compressor 20 further includes a cylinder head 26 that is configured to attach to the cylinder body 22 so as to substantially enclose a cylinder chamber 28. The cylinder chamber 28 can be referred to as substantially enclosed in that the cylinder chamber 28 is enclosed with the exception of an inlet 30 and an outlet 32 that each extend into the cylinder chamber 28. The compressor 20 further includes a piston 34 that is supported in the cylinder chamber 28 by a shaft 35. In particular, the compressor can include a connecting rod 39 that is connected between the piston 34 and the shaft 35. During operation, the shaft 35 is rotatable so as to cause the piston 34 to move cyclically along a longitudinal direction L between an intake stroke and a discharge stroke. During the intake stroke, the piston 34 moves away from the cylinder head 26 so as to create a negative pressure in the cylinder chamber 28. The negative pressure draws fluid 27 into the cylinder chamber 28 through an inlet 30. During the discharge stroke, the piston 23 moves toward the cylinder head 26 so as to compress the fluid 27 and create a positive pressure in the cylinder chamber 28.The cylinder body 22 defines an inner body surface 22a and an outer body surface 22b opposite the inner body surface 22a. The inner body surface 22a partially defines the cylinder chamber 28. The cylinder body 22 further defines a first end 22c and a second end 22d opposite the first end with respect to the longitudinal direction L. The cylinder body 22 can include a base 29 at the first end 22c, such that the first end 22c can be closed. The second end 22d can be open. The cylinder head 26 can be attached to the cylinder body 22 at the second end 22d. The shaft 35 can extend through the outer wall 24 of the cylinder body 22 and into the cylinder chamber 28 along a first direction, such as a transverse direction T, that can be substantially (e.g, within manufacturing tolerance) perpendicular to the longitudinal L. The shaft 35 can extend eccentrically from a bearing37 hat is configured to rotate and cause the piston to reciprocally move between the intake stroke and the discharge stroke. The interface between the bearing 37 and the outer wall 24 can be sealed so as to prevent the leakage of fluid in and out of the interface.The compressor 20 further includes an intake valve that allows the fluid 27 to flow into the cylinder chamber 28 through the inlet 30 under negative pressure in the cylinder chamber 28, and prevents the fluid 27 from flowing out of the cylinder chamber 28 through the inlet 30 under positive pressure in the cylinder chamber 28. For instance, the intake valve can be configured as a flap that overlies the inlet 30. Once the negative pressure inside the chamber 28, for instance between the piston 34 and the cylinder head 26, accumulates to a suitable level, the negative pressure causes the intake valve to open, thereby drawing the fluid 27 into the chamber 28. For instance, the fluid 27 can be drawn into the chamber at a location between the piston 34 and the cylinder head 26.The compressor 20 further includes a discharge valve that allows fluid 27 to flow out of the cylinder chamber 28 through the outlet 32 under positive pressure in the cylinder chamber 28, and prevents fluid 27 from flowing through the outlet 32 and into the cylinder chamber 28 under negative pressure in the cylinder chamber. For instance, the intake valve can be configured as a flap that overlies the outlet 32. Once the positive pressure inside the chamber 28, for instance between the piston 34 and the cylinder head 26, accumulates to a suitable level, the positive pressure causes the discharge valve to open, thereby driving the compressed fluid 27 out of the chamber 28 through the outlet 32. For instance, the fluid 27 that is driven out of the chamber 28 can reside in the chamber 28 between the piston 32 and the cylinder head 26.In one application, the compressor 20 can be included in a refrigeration system, such that the fluid 27 comprises a refrigerant. In this regard, the compressor 20 can draw the fluid 27 into the cylinder chamber 28 through the inlet 30 from an evaporator of the refrigeration system. The compressor 20 can compress the fluid 27 to raise the pressure of the fluid 27, and output the fluid 27 to a condenser of the refrigeration system. It should be appreciated that the fluid 27 can be in a gaseous phase both when it is drawn into the cylinder chamber 28 through the inlet 30 and when it is discharged from the cylinder chamber 28 through the outlet. The fluid 27 then travels from the compressor to a condenser of the refrigeration system, where heat is removed from the fluid. The fluid 27 undergoes a phase change in the condenser from the gaseous phase to a liquid phase. The liquid fluid 27 travels through an expansion valve of the refrigeration system, whereby the fluid 27undergoes a pressure drop. The liquid fluid 27 then flows from the expansion valve to the evaporator, where it removes heat from the space that is to be cooled, and evaporates into a gaseous phase. The gaseous fluid 27 then flowsinto the cylinder chamber 28 in the manner described above.The cylinder head 26 includes a closure member 40 that defines an inner head surface 26a that faces the cylinder chamber 28 when the cylinder head 26 is attached to, or otherwise supported by, the cylinder body 22, and in particular the outer wall 24, and the second end 22d. Thus, the inner head surface 26a can partially define the substantially closed cylinder chamber 28. The closure member 40, and thus the cylinder head 26, further defines an outer head surface 26b that is generally opposite the inner head surface 26a along the longitudinal direction L. The inner head surface 26a can be aligned with the cylinder chamber 28 along the longitudinal direction L. Similarly, the outer head surface 26b can be aligned with the cylinder chamber 28 along the longitudinal direction L. Thus, the inner head surface 26a can be aligned with the outer head surface 26b along the longitudinal direction L. The cylinder head 26 further includes a side wall 42 that extends from the closure member 40. In particular, the side wall 42 can extend from the closure member 40 in a direction that is defined from the second end 22d of the cylinder body 22 toward the first end 22c of the cylinder body 22.The side wall 42 can define an outer perimeter of the cylinder head 26. For instance, the side wall 42 can define a plurality of sides 43 that define the outer perimeter of the cylinder head 26. The plurality of sides 43 can cooperate to impart a round, such as circular, shape to the side wall 42. Alternatively, one or more up to all of the plurality of sides 43 can be substantially linear so as to define a rectangular of other polygonal shape. The cylinder head 26 can include a plurality of recesses 49 that extend into the side wall 42, for instance at intersections between adjacent ones of the sides 43. The recesses can extend from the outer head surface 26b toward but not through the inner head surface 26a. The cylinder head 26 can include mounting apertures 51 that extend through the closure member 40 at the recesses 49. The recesses 49 are configured to receive fasteners, such as screws or bolts or the like, that attach the cylinder head 26 to the cylinder body 22, and in particular to the outer wall 24. Thus, the cylinder head 26 can be separate from the cylinder body 22 and configured to be attached to the cylinder body 22 in any manner desired, for instance at the second end 22d. The cylinder head 26 can define an interior space 44 that is defined by the side wall 42 and the closure member 40. The interior space 44 of the cylinder head 26 can define a portion of the cylinder chamber 28 when the cylinder head 26 isattached to the cylinder chamber 28. It is appreciated that the size and shape of the cylinder body 22, the cylinder head 26, and the cylinder chamber 28 can vary as desired.At least one or both of the inlet 30 and the outlet 32 can be defined by the cylinder head 26. For instance, as illustrated inFigs. 1A-1B, the cylinder head 26 can define both the inlet 30 and the outlet 32. In particular, the inlet 30 can extend through the cylinder head 26. The inlet 30 can extend through the closure member 40 or through the side wall 42. Similarly, the outlet 32 can extend through the cylinder head 26. For instance, as illustrated inFigs. 4A-8B, the cylinder head 26 can define an opening 70 that extends therethrough from the inner head surface 26a to the outer head surface 26b. The opening 70 can define the inlet 30 or the outlet 32. The other of the inlet 30 and the outlet 32 can extend through the inner and outer head surfaces 26a and 26b, or can alternatively extend through the side wall 42. In particular, the outlet 32 can extend through the closure member 40 or through the side wall 42. The cylinder head 26 can define a divider wall in the interior space 44 that separates the inlet 30 from the outlet 32, as desired. Alternatively, the cylinder head 26 can define a first opening 31 as illustrated inFig. 1C. The body 22 can define a second opening. The first opening 31 can define the inlet 30 and the second opening can define the outlet 32. Alternatively, the first opening 31 can define the outlet 32 and the second opening can define the inlet 30. The second opening can extend through the outer wall 24 at a location between the piston 34 and the cylinder head 26 during an entirety of the intake and discharge strokes of the piston 34. Thus, both the first and second openings are in fluid communication with the cylinder chamber 28 when the respective intake and discharge valves are open. The first opening 31 can extend through the cylinder head 26 in the manner described above.It is recognized that the cylinder head 26 can experience cyclical loading during operation, due at least in part to the high negative pressures and positive pressures in the cylinder chamber 28 during use. It is desirable for the cylinder head 26 to be constructed with high stiffness in order to avoid potential negative effects of the cyclical loading.Referring now toFigs. 2A-2D, in one example, the cylinder head 26 can define a concavity 46 at the outer head surface 26b. In particular, the outer head surface 26b, at the concavity 46, can be concave as it extends along at least one direction. Thus, from a view to the outer head surface 26b in a direction defined from the second end 22d toward the first end 22c, the outer head surface 26b can be concave at the concavity 46. Accordingly, a plane that is normal to the longitudinal direction L can intersect the outer head surface 26b at the concavity 46, such that afirst portion of the outer head surface 26b lies on one side of the plane, and a second portion of the outer head surface 26b lies on an opposite side of the plane. The at least one direction can be perpendicular to the longitudinal direction L. For instance, it can be defined by the transverse direction T. Alternatively, the at least one direction can be defined by a lateral direction A that is perpendicular to each of the transverse direction T and the longitudinal direction L. Alternatively still, the at least one direction can be angularly offset to each of the lateral direction A and the transverse direction A. The concavity 46 can have a length along the at least one direction that is perpendicular to the longitudinal direction L. The length can be at least half of an outer dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along a direction parallel to the length that intersects a central head axis 57. For instance, the length can be between half and an entirety of the dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along a direction that intersects the central head axis 57. In one example, the length can be an entirety of the dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along a direction that intersects the central head axis 57. The concavity 46 can have a width that is perpendicular to both the length and the longitudinal direction L. The width can be at least half of an outer dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along a direction parallel to the width that intersects a central head axis 57. For instance, the width can be between half and an entirety of the dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along the direction parallel to the width that intersects the central head axis 57. In one example, the width can be an entirety of the dimension of the cylinder head 26 defined by opposed locations of the side wall 42 along the direction parallel to the width that intersects the central head axis 57. The central head axis 57 can be oriented along the longitudinal direction L, and can be coincident with a central axis 25 of the cylinder chamber 28.In one example, the concavity 46 can be substantially U-shaped along a plane that extends through the concavity 46 along the longitudinal direction L and the at least one direction. Thus, the concavity 46 can be straight and linear along a second direction that is perpendicular to the at least one direction. Accordingly, the concavity 46 can be said to define a shape of an inverted parabola. It has been found that the concavity 46 provides high stiffness to the cylinder head 26 against internal pressure in the cylinder chamber 28. In one example, the concavity 46 can define a lowest point that is aligned with the central axis 25 of the cylinder chamber 28 and oriented along the longitudinal direction L. Otherwise stated, the concavity 46 can be centered about the centralhead axis 57 and the central axis 25 of the cylinder chamber 28 that each extends along the longitudinal direction L. Thus, the concavity 46 can be symmetrical about the central axis 25. The inner head surface 26a can be substantially flat or otherwise shaped in such a manner so as to not match or otherwise be defined by the concavity 46. The inner head surface 26a can alternatively define a convexity that matches the concavity 46 and is complementary to the concavity 46.Alternatively, as illustrated inFig. 3, the outer head surface 26b, at the concavity 46, can be concave as it extends along both a first direction that is perpendicular to the longitudinal direction L and a second direction that is perpendicular to the longitudinal direction L. The second direction is angularly offset with respect to the first direction. For instance, the second direction can be perpendicular with respect to the first direction. The first direction can be perpendicular to a first opposed pair of the sides 43. Similarly, the second direction can be perpendicular to a second opposed pair of the sides 43 that is different than the first pair. In one example, the concavity 46 can be dish shaped. Thus, the concavity 46 can define a round outer perimeter in a plane that is normal to the longitudinal direction L through the concavity 46. For instance, the round shape can be circular. Alternatively the round shape can be elliptical. Alternatively still, the round shape can be irregularly shaped. Alternatively still, the outer perimeter of the concavity in the plane can define any suitable geometry as desired, such as a polygonal geometry. The polygonal geometry can be regular or irregular as desired.Referring toFigs. 2A-2E, each of the sides 43 of the side wall 42 can define an inner side surface 43a that faces the interior space 44, and an outer side surface 43b that is opposite the inner side surface 43a. In one example, at least a portion of the outer side surfaces 43b can be substantially smooth. Substantially smooth is intended to encompass a surface geometry that does not include structure that enhances the stiffness of the cylinder head 26. In one example, the inlet 30 and the outlet 32 extend through opposed sides 43 that have substantially smooth outer side surfaces 43b. The remaining sides 43, other than the sides 43 that define the inlet 30 and outlet 32, can define a plurality of slots 48 that extend into the respective outer side surface 43b so as to define a corresponding plurality of projections 50 that are separated by respective ones of the slots 48 along an outer perimeter of the side wall 42. The slots 48 and projections 50 can be arranged between adjacent ones of the mounting apertures 51. The projections 50 and slots 48 can be alternatingly arranged along a plane that is oriented normal to the longitudinal direction L and intersects the side wall 42, and in particular the sides 43. In one example, the projections 50 can be equidistantlyspaced about the perimeter of the side wall 42 at the sides 43 that include the projections 50. .Alternatively, the projections 50 can be spaced from each other at any interval, wither equidistant or variable, as desired. The projections 50 can define stiffeners that enhance the stiffness of the cylinder head 26 during operation of the compressor 20. It has been found that the projections 50 increase the bending stiffness of the cylinder head 26. As will be described in more detail below, the cylinder head 26 can be an injection molded polymer. Thus, the side wall 42 can be monolithic with the inner head surface 26a and the outer head surface 26b. In one embodiment illustrated inFig. 6C, the projections 50 can be arranged along all of the sides 43.The cylinder head 26 can further include a plurality of stiffening ribs 52 that project out from the outer head surface 26b in a direction defined from the first end 22c to the second end 22d. The ribs 52 can be oriented in any direction as desired, and in one example, are planar along respective planes that include the longitudinal direction L. The ribs 52 can extend radially outward from a common hub 54. The common hub 54 can be defined by a common location to which the ribs 52 extend. The common hub 54 can be an empty space. Alternatively, the common hub 54 can define an intersection of the ribs 52. Alternatively still, the common hub 54 can define a central wall 55. The central wall 55 can define a closed shape along a plane that is normal to the longitudinal direction L and extends through the central wall 55. In one example, the hub 54 can be cylindrical about a central axis that is oriented along the longitudinal direction L. The central axis of the hub 54 can be coincident with the central axis of the cylinder chamber 28. The ribs 52 can be equidistantly circumferentially spaced from each other about the hub 54. Alternatively, the ribs 52 can be variably spaced from each other about the hub 54. The ribs 52 can define a height from the outer head surface 26b. The height can taper toward the outer head surface 26b as the rib extends in the radially outward direction away from the hub 54. For instance, the ribs 52 can terminate without overhanging the outer perimeter of the outer head surface 26b. It has been found that the ribs 52 can provide uniformly high stiffness for the cylinder head 26 against internal pressure in the cylinder chamber 28. Alternatively, as illustrated inFigs. 5A-5B, the height of the ribs 52 can be substantially constant from the hub 54 to the outer ends of the ribs 52 opposite the hub 54. Further, the outer ends of at least one or more of the ribs 52 up to all of the ribs 52 can be coplanar with a respective one of the outer side surfaces 43b.As illustrated inFigs. 4A-7A, the cylinder head 26 can further include an auxiliary stiffening rib 53 that extends out from the outer head surface 26b. The auxiliary stiffening rib 53can at least partially surround the opening 70. For instance, the auxiliary stiffening rib 53 can have a round shape in a plane that is oriented normal to the longitudinal axis L that extends through the auxiliary stiffening rib 53. The auxiliary stiffening rib 53 can be attached to one of the stiffening ribs 52.Referring now toFig. 2E, a cross-section of the cylinder head 26 is shown with the ribs 52 removed for the purposes of clarity. The cylinder head 26 can include at least one flange 56 that projects out from an outer perimeter of the side wall 42. In particular, the at least one flange 56 can project out from one or more up to all of the outer side surfaces 43b. The at least one flange 56 can include a shoulder 58 that extends out from the outer perimeter of the side wall 42 away from the central head axis 57 of the cylinder head that is oriented along the longitudinal direction L. The flange 56 further includes a lip 60 that extends out from the shoulder 58 along the longitudinal direction L. For instance, the lip 60 can extend out from the shoulder 58 in a direction that is defined from the first end 22c to the second end 22d. The lip 60 can be positioned so as to be spaced from the side wall 42 such that an air gap 62 is defined between the side wall 42 and the lip 60. It has been found that the projections 50 described above can prevent the flanges 56 from opening up (e.g., increasing the distance of the air gap 62) under assembly as well as during operating loads created by theinternal pressure in the cylinder chamber 28.With continuing reference toFig. 2E, the cylinder head 26, and in particular the side wall 42, can defines an inner surface 66 configured to interface with the cylinder body 22 when the cylinder head 26 is attached to the cylinder body 22. The compressor 20 further includes a compressible gasket 68 disposed at the inner surface 66. For instance, the gasket 68 can be overmolded by the cylinder head 26. The gasket 68 can compress against the cylinder body 22 so as to define a seal at the interface between the cylinder body and the inner surface 66. In one example, the gasket 68 can be elastomeric. The gasket 68 can have any suitable cross-section as desired, such as circular or polygonal (in one example, rectangular).Referring now toFigs. 6A-6C, the cylinder head 26 can define at least one pocket 72 that extends into the outer head surface 26b. The at least one pocket 72 can terminate in the cylinder head 26 without extending through the inner head surface 26a. The at least one pocket 72 is disposed between adjacent ones of the ribs 52. For instance, the at least one pocket 72 can include a plurality of pockets 72 that each extend into the cylinder head 26 between different adjacent ones of the ribs 52. The pockets 72 can be elongate along a select direction that is perpendicular to thelongitudinal direction L, and respective pairs of the pockets 72 can be aligned with each other along the select direction. A first portion of the pockets 72 can be circumferentially aligned with the ribs 52, and a second portion of the pockets 72 can extend radially outward with respect to the outer ends of the ribs 52.Referring now toFigs. 7A-7B, the cylinder head 26 can further include at least one circumferential rib 74 that extends out from the outer head surface 26b. In one example, the cylinder head can include a pair of circumferential ribs 74, including an inner rib 74a and an outer rib 74b. The inner rib 74a can be disposed between the hub 54 and the outer rib 74b. The circumferential ribs 74 can extend circumferentially about the hub 54, and can intersect at least one up to all of the ribs 52, which can define a first plurality of ribs. The circumferential ribs 74 can further enhance the stiffness of the cylinder head 26 against internal pressure in the cylinder chamber 28. The ribs 52 can each include a first portion that extends from the hub 54 to the inner rib 74a, and a second portion that extends from the inner rib 74a to the outer rib 74b. The first portion of each of the ribs 52 can be inline with the second portion, or can be circumferentially offset from the second portion as desired.Alternatively, as illustrated inFigs. 8A-8B, the cylinder head 26 can be devoid of the ribs 52, 53, and 74. Further, the cylinder head 26 can be devoid of the projections 50 and slots 48. Thus, both the outer head surface 26b of the cylinder head 26 and the outer side surfaces 43b can be substantially smooth, thereby reducing the weight of the cylinder head 26 and further increasing manufacturing efficiency. It should be appreciated that the pockets 72 illustrated inFigs. 8A-8Bcan be constructed as described above, but they are not positioned between adjacent ones of ribs 52.It should be appreciated that the cylinder head 26 as described above with respect toFigs. 1-8Bcan include the concavity 46 described above. It should be further appreciated that while the polymeric cylinder head 26 can be used in the reciprocating compressor 20 as described above, the polymeric cylinder head 26 can also be used in other types of compressors as desired, such as scroll compressors.The cylinder head 26 can be made of any suitable polymer. In one example, the polymer is infused with glass particles that are embedded therein. Accordingly, in one example the cylinder head 26 can be injection molded. Thus, the cylinder head 26, including the closure member 40, the side wall 42, the projections 50 (if present), the ribs (if present, including the ribs 52, the ribs53, and the ribs 74), and the flange 56 (if present), can all be one single unitary monolithic homogeneous component. It has been found that the polymeric cylinder head 26 allows for the gasket 68 to be overmolded as described above. Further, the polymeric cylinder head 26 can avoid corrosion and to further provide thermal insulation with respect to the gaseous fluid that travels through the compressor 20 at high temperatures. Additionally, polymeric cylinder head 26 can have a reduced weight and reduced manufacturing complexity with respect to conventional metallic cylinder heads. The reduced weight can increase the efficiency of the cylinder head 26 with respect to conventional metallic cylinder heads. The polymer can be configured as an ULTEM™polymer, commercially available from Saudi Arabia Basic Industries Corporation (SABIC), having a principal place of business in Riyadh, Saudi Arabia. An ULTEM™polymer is a polymer from the family of polyetherimides (PEI). ULTEM™polymers can have elevated thermal resistance, high strength and stiffness, and broad chemical resistance. As described above, the cylinder head 26 made from ULTEM™polymer can include glass particles embedded into the ULTEM™polymer.The invention is set forth by the appended claims. See more