CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of US Patent Application Ser. No. 61/696,724, filed September 4, 2012, and entitled "Reciprocating Refrigeration Compressor Wrist Pin Retention", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0002] The present disclosure relates to refrigeration compressors. More particularly, it relates to reciprocating piston compressors utilized to compress gases such as low global warming potential (GWP) and natural refrigerants.

[0003] A variety of refrigerant compressor configurations are in common use. Among these configurations are: screw compressors; scroll compressors; and reciprocating piston compressors. In a reciprocating compressor a piston head is driven between a lower position at which a fluid to be compressed enters the compression cylinder, and an upper or "top" position at which the compressed fluid is driven outwardly of the cylinder

[0004] An exemplary reciprocating piston compressor has a pin coupling each piston to the associated connecting rod. Such wrist pins may be in a journaled rotating fit to one or both of the piston and rod. In one exemplary configuration, a central portion of the pin is journaled in an end portion of the rod and end portions of the pin are journaled in associated bores in the piston. The pin may be retained against axial movement by clips abutting ends of the pins and partially captured in open channels in the piston bores. Alternative retainers include polymeric washers.

[0005] Separately, in the piston engine field, a proposal has been made to use plugs (US Patent Nos. 5289758 and 6048126) to position a wrist pin. In the compressor art, concealed plugs have been proposed in US Patent No. 5850777. Additionally plugs have been proposed in US Patent No. 6358026.

SUMMARY

[0006] One aspect of the disclosure involves a compressor having a case and a crankshaft. The case has a number of cylinders. For each of the cylinders, the compressor includes a piston mounted for reciprocal movement at least partially within the cylinder. A connecting rod couples each piston to the crankshaft. A pin couples each connecting rod to the associated piston. Each pin has first and second end portions mounted to first and second receiving portions of the associated piston and a central portion engaging the associated connecting rod. For each of the pistons a pair of first and second at least partially non-metallic plugs have respective stems received in the pin first and second end portions and respective heads facing a wall surface of the associated cylinder.

[0007] In various implementations, an electric motor within the case may be coupled to the crankshaft. The plugs may comprise a non-metallic material. They may comprise such material at least along the heads. The material may be a polybutylene terephalate. The plugs may consist of such material or consist essentially of such material. For each pin, the respective end portions may be journaled fit in the associated piston receiving portions. The central portion may be journaled fit in the associated connecting rod. The pins may be axially retained by a cooperation of the associated plug heads with the cylinder. They may be retained only via such cooperation. The plugs may comprise a pressure relief channel along the stem. The pressure relief channel may extend along an underside of the head. The heads may have a doubly convex outer surface having a principal radius of curvature within 5% of a transverse radius of curvature of the associated cylinder.

[0008] Other aspects of the disclosure involve a refrigeration system including such a compressor. The refrigeration system may include a recirculating flowpath through the compressor. A first heat exchanger may be positioned along the flowpath downstream of the compressor. An expansion device may be positioned along the flowpath downstream of the first heat exchanger. A second heat exchanger may be positioned along the flowpath downstream of the expansion device. The refrigerant charge may comprise at least 50% carbon dioxide or fluorocarbon by weight. The system may be a refrigerated transport system. The refrigerated transport system may further comprise a container. The second heat exchanger may be positioned to cool an interior of the container. The system may be a fixed refrigeration system. The fixed refrigeration system may further comprise multiple refrigerated spaces. There may be a plurality of said second heat exchangers, each being positioned to cool an associated such refrigerated space.

[0009] Another aspect of the disclosure involves a compressor wrist pin retaining plug comprising the unitarily molded combination of a hollow stem for receipt in a bore of a pin and a head. The stem protrudes from an underside of the head. A pressure relief channel is at least partially on the stem and head.

[0010] In various implementations, the channel may be an open channel extending continuously along the stem and the underside of the head to a periphery of the head. The stem may comprise a tapered end. The plug may comprise a polybutylene terepthalate. The plug may consist of polybutylene terepthalate. [0011] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a side view of a compressor.

[0013] FIG. 2 is a vertical longitudinal sectional view of the compressor of FIG. 1.

[0014] FIG. 3 is a partial vertical longitudinal sectional view of a cylinder of the compressor of FIG. 1.

[0015] FIG. 3A is an enlarged view of a wrist pin end of the cylinder of FIG. 3.

[0016] FIG. 4 is a partial transverse longitudinal sectional view of the cylinder of FIG. 3, taken along line 4-4 of FIG. 3.

[0017] FIG. 5 is a view of a wrist pin plug for the compressor of FIG. 1.

[0018] FIG. 6 is an end view of the plug of FIG. 5.

[0019] FIG. 7 is a longitudinal/axial sectional view of the plug of FIG. 6, taken along line 7-7 of FIG. 6.

[0020] FIG. 8 is a partial radial inward view of a channel in the plug of FIG. 6, taken along line 8-8 of FIG. 6.

[0021] FIG. 9 is a schematic view of a refrigeration system.

[0022] FIG. 10 is a schematic view of a fixed commercial refrigeration system.

[0023] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0024] FIGS. 1 and 2 show an exemplary compressor 20. The compressor 20 has a housing (case) assembly 22. The exemplary compressor includes an electric motor 24 (FIG. 2). The exemplary case 22 has a suction port (inlet) 26 and a discharge port (outlet) 28. The housing defines a plurality of cylinders 30, 31, and 32. Each cylinder accommodates an associated piston 34 mounted for reciprocal movement at least partially within the cylinder. Exemplary multi-cylinder configurations include: in-line; V (vee); and horizontally opposed. The exemplary in-line compressor includes three cylinders. Each of the cylinders includes a suction location and a discharge location. For example, the cylinders may be coupled in parallel so that the suction location is shared/common suction plenum fed by the suction port 26 and the discharge location is a shared/common discharge plenum feeding the discharge port 28. In other configurations, the cylinders may share suction locations/conditions but have different discharge locations/conditions. In other configurations, the cylinders may be in series. An exemplary fluorocarbon-based refrigerant is R-410A. An exemplary carbon dioxide (C0 ₂ )-based (e.g., at least 50% C0 ₂ by mass/weight) refrigerant is R-744.

[0025] Each of the pistons 34 is coupled via an associated connecting rod 36 to a crankshaft 38. The exemplary crankshaft 38 is held within the case by bearings for rotation about an axis 500. The exemplary crankshaft is coaxial with a rotor 40 and stator 42 of the motor 24. Each piston 30-32 is coupled to its associated connecting rod 36 via an associated wrist pin 44. FIG. 3 shows the pin 44 as having a central portion 46 mounted for rotation in an aperture 48 in a distal end portion 50 of the connecting rod 36. In various

implementations, the aperture may be in a bushing interference fit in a main piece of the connecting rod. The pin has first and second end portions 52 and 53 mounted in apertures 54 and 55 of associated receiving portions 56 and 57 of the piston (e.g., in a non-interference journaled fit).

[0026] The exemplary piston has a distal end face 60 and a lateral/circumferential surface 62. One or more sealing rings 64 may be carried in corresponding grooves 66 in the surface 62. To seal with the cylinder lateral wall (bore) surface 70. In alternative cylinders, at least a portion of the cylinder wall/surface 70 is formed by the interior surface of a sleeve (e.g., press fit in the cylinder block 76).

[0027] As so far described, the compressor may be representative of any of a number of possible reciprocating piston compressors to which the following teachings may be applied.

[0028] FIG. 3 shows a pair of plugs 80 mounted in the associated pin end portions 52 and 53. Each of the plugs has a stem 81 (FIG. 3A) inserted into end portions of a channel (e.g., a bore) 77 in the pin 59. The stem 81 depends from the underside 82 of a head 83. The head undersides abut pin ends (rims) 78 and 79. As is discussed further below, the heads have a doubly convex outer surface 84. Exemplary head outer surfaces 84 are in close facing relation or contacting the cylinder wall 70. The exemplary curvature is such that, as seen in the transverse sectional view of FIG. 4, the surface 84 along a transverse centerplane 522 (FIG. 6) is concentric with the cylinder wall (FIG. 4). Exemplary plug heads are rotationally symmetric about the axis 520 except for the channel 100 and thus have similar curvatures along the transverse centerplane 522 and vertical centerplane 524. It is noted that the plugs need not be limited to this orientation. Additionally, other channel configurations may be featured as may other stem and head configurations. The exemplary configuration matches head radius of curvature Rep to within 10% (more narrowly, 5%) with the transverse radius of curvature Rcc of the cylinder wall surface along a majority of a circumferential length of the head along such transverse plane (Rep thus typically being lower than Rcc- Overall axial (relative to the pin axis but diametric for the cylinder) clearance is twice the illustrated centered clearance AR. The float of the pin may close the gap at either end. Wear of the head may expand the clearance. Exemplary combined clearance at the heads of the two plugs is 3-6mm, more particularly 4.0-5.5mm or 4.1-5.4mm when new. With a cylinder inner diameter (ID) of about 62.1mm, an exemplary wrist pin length is 54.6mm or at least 85% thereof, more particularly 85-92% or 87-90%.

[0029] FIG. 5 shows further details of the exemplary plug 80. The stem 81 extends to a distal end 85. In the exemplary embodiment, the end 85 is formed as a rim surrounding a central compartment/channel 86. The exemplary compartment 86 extends along a central axis 520 (FIG. 6) to the head or near the head. FIG. 7 shows the exemplary compartment defined by a surface comprising a tapering surface 88 (at an exemplary constant half angle θι) extending inward from the rim 85 to a nearly semi- spherical surface 89 forming a base/end of the compartment. FIG. 7 also shows a stem length Ls from an intact (discussed later) planar portion of the head underside 82 to the rim 85. FIG. 7 also shows a compartment depth Dc which may be very close to or coincident to Ls. In terms of additional dimensions, FIG. 7 shows the head as having an approximately cylindrical peripheral/lateral surface 90 having a diameter DH- A height of the head is shown as LH- In this embodiment, exemplary DH is 21mm, more broadly 19-22mm. Other sizes would be appropriate for other compressors. Similarly, exemplary L _s from is 7mm, more broadly 5- 10mm. Exemplary stem diameter is 10mm, more particularly about 9.6mm [0030] Returning to FIG. 5, the exemplary stem is shown as having a varied cross-section or diameter. Proximally of the rim 85 is a frustoconical bevel 92. The exemplary bevel 92 has a length LB (FIG. 7) and a half angle θ ₂ and a length LB- Proximally of the surface portion 92 is a shallower main surface portion 94 (e.g., frustoconical) extending over a length LM at a half angle θ ₃ . A generally cylindrical surface portion 96 extends proximally of the surface portion 94 and along with a radiused transition 97 (at a stem root 98) to the head underside extends for a length LR. Head height LH and perimeter height Lp are advantageously low enough to allow sufficient length of engagement between pin and piston, but advantageously thick enough to provide wear resistance and ease of molding. Exemplary DH is slightly lower than the wrist pin diameter D _P (e.g., 90-100%, more particularly 92-99% or 93-98%).

Exemplary Lp are l-3mm, more particularly, 1.0-2.0mm. With the exemplary cylinder diameter of 62mm and 31 mm radius, exemplary principal head radius of curvature is within 10% or 5% of this as noted above, more particularly 95-100% (29-3 lmm for this example).

[0031] As is discussed further below, the plug includes a pressure relief channel 100 (FIG. 5). The exemplary pressure relief channel includes a first portion 102 along or through the stem and a second portion 104 along or through the head. The exemplary channel is open along both these portions 102 and 104. The portion 102 extends from a distal end 106 to a proximal end at a junction with the portion 104 at the stem root. The portion 104 extends radially outward along the head underside 82 to a second end 108. FIG. 6 shows the channel as including a first rim 110 and a second rim 112 with a base 114 therebetween. Exemplary channel depth Dc along the stem is nominal 1.3mm, with a +/-0.5 mm tolerance. More broadly, exemplary depth is 0.5 -2.0mm. Exemplary depth along the head underside may be smaller (due to less deformation; the stem is subject to a deforming press-fit, whereas the head has less contact force). Exemplary depth along the head is at least 0.05 mm, more particularly 0.05-0.02mm. Exemplary width Wc is greater than the depth along the stem (e.g., about twice, more broadly 1.5-3.0 times or 2.6+/-0.5mm in this example). The exemplary channel is arcuate in cross-section (e.g. of an essentially constant radius of curvature).

[0032] Exemplary plugs are entirely or at least along outboard portions thereof polymeric/resinous. Exemplary polyester resin is a semi-crystalline polybutylene terepthalate (PBT) such as VALOX 310 from SABIC Innovative Plastics Holding B V, Riyadh, Saudi Arabia. Exemplary such plugs are injection molded.

[0033] In the installed condition, the pin bore 59 surface and associated pin rim laterally enclose the channel 104 to allow venting between the pin interior and the associated space between the head and cylinder wall. This resists any tendency of any excess of pressure in the pin driving the plugs outward into contact with the cylinder wall which would encourage wear of the head.

[0034] FIG. 9 shows an exemplary refrigeration system 140 including the compressor 20. The system 120 includes a system suction location/condition 150 at the suction port 26. A refrigerant primary flowpath 152 proceeds downstream from the suction location/condition 150 through the compressor cylinders in parallel to be discharged from a discharge location/condition 154 at the discharge port 28. The primary flowpath 152 proceeds downstream through the inlet of a first heat exchanger (gas cooler/condenser) 156 to exit the outlet of the gas cooler/condenser. The primary flowpath 152 then proceeds downstream through an expansion device 162. The primary flowpath 152 then proceeds downstream through a second heat exchanger (evaporator) 164 to return to the suction condition/location 150.

[0035] In a normal operating condition, a recirculating flow of refrigerant passes along the primary flowpath 152, being compressed in the cylinders. The compressed refrigerant is cooled in the gas cooler/condenser 156, expanded in the expansion device 162, and then heated in the evaporator 164. In an exemplary implementation, the gas cooler/condenser 156 and evaporator 164 are refrigerant- air heat exchangers with associated fan (170; 172)-forced airflows (174; 176). The evaporator 164 may be in the refrigerated space or its airflow may pass through the refrigerated space. Similarly, the gas cooler/condenser 156 or its airflow may be external to the refrigerated space.

[0036] Additional system components and further system variations are possible (e.g., multi-zone/evaporator configurations, economized configurations, and the like). Exemplary systems include refrigerated transport units and fixed commercial refrigeration systems.

[0037] An exemplary fixed commercial refrigeration system 250 (FIG. 10) includes one or more central compressors 20 and heat rejection heat exchangers 156 (e.g., outside/on a building 255) commonly serving multiple refrigerated spaces 256 (e.g., of retail display cabinets 258 in the building). Each such refrigerated space may have its own heat absorption heat exchanger 164' and expansion device 162' (or there may be a common expansion device). Other rack-mount situations include building heating, ventilation and air

conditioning (HVAC).

[0038] The compressor may be manufactured via otherwise conventional manufacturing techniques. The pistons, pins, rods, and cylinder block may be cast and/or machined as may other components. The assembly may involve mounting the connecting rods to the pistons via the pins. This may be performed by hand. Similarly, the plugs may be installed by hand with the surface portion 92 of FIG. 5 guiding insertion into the pin bore. This may eliminate the use of press-fitting or clip-applying tools in a baseline compressor. The pistons may be inserted into the cylinders. The connecting rods may be mated to the crankshaft. The case may be assembled over the crankshaft (e.g., by mating a sump to the cylinder block). The remaining elements may be assembled.

[0039] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering of an existing (baseline) compressor configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.