Patent Grant
7175400
1. Field of the Invention
The present invention relates to reciprocating piston compressors, and more particularly, to reciprocating piston compressors having an improved piston design and a vented cylinder.
2. Description of the Related Art
Conventional reciprocating compressors commonly include a hermetically sealed housing defining an interior plenum. The housing includes a suction inlet and a discharge outlet, through which a compressible fluid respectively enters and exits the compressor assembly. A motor is generally disposed in the interior plenum to rotationally drive a shaft. The shaft typically includes a journal that defines an axis offset from the rotational axis of the shaft thereby causing the journal to travel through a circular arc centered on the rotational axis of the shaft. A cylinder block will also generally be disposed in the interior plenum and define a compression cylinder having a single diameter. A substantially cylindrical piston having a single diameter is disposed within the cylinder. A wrist pin is often used to connect the piston with a piston rod. The piston rod is also secured to the journal whereby the rotational motion of the shaft is converted to reciprocating movement of the piston along the axis of the compression cylinder. The compressible fluid is drawn into the cylinder and compressed by the reciprocation of the piston within the cylinder.
Converting the rotational movement of the shaft into the reciprocating movement of the piston generates side loads that are transverse to both the rotational axis of the shaft and to the axis of the cylinder. These side loads typically result in a portion of the piston bearing against the sidewall of the cylinder. Normal operation of the compressor may also result in a relatively large load being placed on the wrist pin that connects the piston rod with the piston. When using a refrigerant that must be compressed to a relatively high pressure, such as carbon dioxide, these loads can become significant and may, thereby, adversely affect the performance and durability of a conventional reciprocating compressor design.
The present invention provides a reciprocating compressor assembly having a cylinder block defining a two part cavity for receiving the piston wherein part of the cavity is vented.
The present invention comprises, in one form thereof, a compressor assembly that includes a cylinder block defining a cavity having a first cavity portion and a second cavity portion. The cavity defines a central axis extending through each of the first and second cavity portions. The cylinder block defines an inlet and an outlet, both in communication with the first cavity portion and by which a compressible fluid enters the first cavity portion at a suction pressure and is discharged through the outlet at a discharge pressure. A piston is reciprocatingly disposed along the central axis and includes a first piston portion and a second piston portion. The first piston portion is at least partially disposed within the first cavity portion and defines a compression chamber within the first cavity portion. Reciprocation of the piston relative to the cavity compresses the compressible fluid within the compression chamber. The second piston portion is at least partially disposed within the second cavity portion and is reciprocable therein. The second piston portion has a radially outer surface at least partially engageable with a sidewall of the second cavity portion. Forces transverse to the central axis are transferable between the radially outer surface and the sidewall. A variable volume space is defined by the second piston portion and the second cavity portion and is disposed axially adjacent the first cavity portion. A vent passage is in communication with the variable volume space.
The present invention comprises, in another form thereof, a compressor assembly that includes a cylinder block defining a cavity having a first substantially cylindrical cavity portion and a second substantially cylindrical cavity portion. The first and second cavity portions are coaxially disposed and define a central axis. The second cavity portion defines a larger diameter than the first cavity portion. The compressor assembly defines an inlet and an outlet both in communication with the first cavity portion whereby a compressible fluid enters the first cavity portion at a suction pressure and is discharged at a discharge pressure. A piston is at least partially disposed in the cavity wherein the piston reciprocates along the central axis. The piston includes a first piston portion and a second piston portion. The first piston portion defines a substantially cylindrical shape having a diameter substantially similar to the first cavity portion. The second piston portion defines a substantially cylindrical shape having a diameter substantially similar to the second cavity portion. A vent passage is in communication with a variable volume space, which is defined by the second piston portion and the second cavity portion and is disposed axially adjacent the first cavity portion. A crankshaft having a rotational axis is disposed substantially perpendicular to the central axis. A linkage assembly drivingly couples the crankshaft to the piston. During reciprocation of the piston in the cavity, the first piston portion compresses a fluid in the first cavity portion.
The present invention comprises, in yet another form thereof, a method of compressing a refrigerant vapor that includes the steps of providing a cylinder block having a cavity with a first cavity portion and an adjacent second cavity portion wherein the first and second cavity portions define a central axis. The method also includes providing a piston having a first piston portion and a second piston portion, the first and second piston portions having differing cross sectional configurations; disposing the piston at least partially within the cavity wherein the first piston portion defines a compression chamber within the first cavity portion and the second piston portion defines a variable volume space within the second cavity portion; reciprocating the piston along the central axis wherein reciprocation of the piston compresses the refrigerant vapor in the compression chamber and varies the volume of the variable volume space; and venting fluids contained within said variable volume space during reciprocation of said piston.
One advantage of the present invention is that it facilitates the use of a piston having multiple cross sections wherein a first portion of the piston is used for compressing a fluid and a second portion of the piston is used for coupling the piston to a shaft by venting that portion of the cylinder block cavity which is not used for compressing the fluid.
The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates an embodiment of the invention, in one form, the embodiment disclosed below is not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.
Referring first to
Referring now to
A one-piece stepped piston 52 is reciprocatingly disposed along central axis A within stepped cavity 38. As shown in FIGS. 2 and 4–7, stepped piston 52 includes a first or compression portion 54, which is at least partially disposed within compression cavity 40 and, together with piston rings 58, cooperates with sidewall 41 to define compression chamber 40a within which a compressible fluid, e.g., carbon dioxide, is compressed as discussed in greater detail below. Stepped piston 52 also includes a second or guiding portion 56, which is at least partially disposed within guide cavity 42 and bears against sidewall 43 to transfer side loads from piston 52 to cylinder block 36. As piston 52 reciprocates within stepped cavity 38, guide portion 56 and sidewall 43 define a variable volume space 42a within guide cavity 42.
Compression portion 54 and guide portion 56 include radially outer surfaces 55, 57 each of which have a shape that is substantially cylindrical. Axially adjacent compression portion 54 and guide portion 56 are coaxial and when positioned in stepped cavity 38 the axes of compression portion 54 and guide portion 56 are aligned and collinear with axis A of cavity 38 as best seen in
In the illustrated embodiment, piston 52 is formed from a single integral metal casting. In alternative embodiments, compression and guide portions 54, 56 may be formed separately and then affixed together using fasteners, welding or other suitable means.
As shown in
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As illustrated in
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As can be seen in
As shown in
In operation, motor 28 rotationally drives shaft 34 about axis 33. A linkage assembly including piston rod 68 and wrist pin 66 couples shaft 34 to piston 52. Axis 73 of journal portion 70 is offset from rotational axis 33 of shaft 34 as seen in
As piston rod 68 drives piston 52, sleeve 112 and journal 70 as well as sleeve 108 and wrist pin 66 are subject to relative rotational movement and the transfer of forces therebetween. By providing an enlarged guide portion 56 on stepped piston 52, the size of wrist pin 66 and sleeve 108 may be larger than if sleeve 108 and wrist pin 66 were connected within compression portion 54. Similarly, the area of contact between pin 66 and piston 52 may also thereby be relatively larger. Providing a guide portion 56, wrist pin 66 and sleeve 108 that have relatively large bearing surface areas facilitates the reduction of the stress in the material of these parts.
As piston rod 68 reciprocates, the wall of bore 110 oscillates about, and bears against, wrist pin 66 imparting a reciprocating motion to stepped piston 52. As stepped piston 52 is pulled towards the rotational axis of shaft 34 in an intake stroke, one-way check valve 96 flexes away from inlet openings 88 due to differential pressure and a refrigerant, e.g., carbon dioxide in the illustrated embodiment, is drawn into the compression chamber 40a defined within compression cavity 40 from inlet passageway 76 through openings 88. As stepped piston 52 moves away from the rotational axis of shaft 34 in a compression stroke, compression portion 54 of piston 52 compresses the refrigerant within compression cavity 40. When the refrigerant within compression chamber 40a has a pressure that is sufficient to bias valve member 81 away from outlet 86, the refrigerant is discharged through outlet 86 into discharge chamber 78. From discharge chamber 78, the high pressure refrigerant enters internal discharge line 48 and is then discharged from compressor assembly 10.
During operation of compressor assembly 10, journal 70 imparts a circular motion to bearing part 112. The motion of sleeve 108, however, is constrained to a reciprocating motion along axis A due to its connection with piston 52 which is located within stepped cylinder 36. Confining the movement of sleeve 108 to a reciprocating movement along axis A generates side load forces oriented perpendicular to both axis A and the rotational axis of shaft 34. These side load forces are transmitted from sleeve 108 to wrist pin 66 to guide portion 56 of piston 52 resulting in a side load being placed on stepped cavity 38 by stepped piston 52. As described above, the second clearance distance defined between outer surface 57 of guide portion 56 and sidewall 43 of guide cavity 42 is smaller than the first clearance distance defined between outer surface 55 of compression portion 54 and sidewall 41 of compression cavity 40. Consequently, it is the relatively larger guide portion 56 of piston 52 that bears against cylinder block 36 instead of the smaller diameter compression portion 54. Guide portion 56 thereby maintains the alignment of stepped piston 52 within stepped cavity 38 and limits or prevents direct contact between compression portion 54 of piston 52 and sidewall 41 of compression cavity 40. This facilitates the performance and longevity of piston rings 59 which engage sidewall 41 and are disposed in grooves 59 located in surface 55 to form a seal between piston 52 and sidewall 41 at one end of compression chamber 40a.
As mentioned above, outer surface 57 of the relatively large diameter guide portion 56 provides a large bearing surface, relative to compression portion 54, for bearing the side load placed on piston 52. The larger diameter guide portion 56 is also capable of defining a larger transverse void 64 compared to compression portion 54. This permits the use of a relatively large wrist pin 66 and sleeve 108 thereby also relatively increasing the surface area of bore 110 that bears against wrist pin 66. By providing an increased area for these bearing surfaces, the stress at these bearing surfaces can be reduced. The reduction of these stresses is particularly useful in compressors that utilize a refrigerant that must be compressed to a relatively high pressure such as carbon dioxide because an increase in the discharge pressure, without other compensating changes, will result in greater forces being applied to the piston. For example, when carbon dioxide is used as a refrigerant it is typically compressed to a supercritical pressure that is in excess of 1100 psia.
During the reciprocating movement of piston 52, guide portion 56 defines a varying volume 42a within cavity 42. In order to prevent a pressure differential between interior volume 20 and variable volume 42a from acting on the guide portion 56 of piston 52 and thereby degrading the performance of the compressor, stepped piston 52 includes a flat 102 defined on outer surface 57 of guide portion 56. Vent gap 104 is defined between flat 102 and sidewall 43 of guide cavity 42 and communicates with variable volume 42a to provide a vent passage through which oil and air may escape variable volume 42a during the compression stroke and enter variable volume 42a during the suction stroke. By positioning flat 102 in a horizontal orientation and so that it forms gap 104 along the upper section guide portion 56, the reduction in the surface area available for transferring horizontally directed side loads between guide portion 56 and guide cavity 42 caused by flat 102 is minimized. It should be understood that more than one flat may be defined on outer surface 57 to provide multiple gaps.
Referring to FIGS. 4 and 6–7, in addition to flat 102, stepped piston 52 also includes a plurality of vent holes or passageways 106 defined in guide portion 56. Vent passageways 106 extend from the end of guide portion 56 opposite end face 60 to central void 62 which is open to interior volume 20 via opening 61 in end face 60 thereby defining an axially extending passage for venting variable volume 42a. Thus, in addition to gap 104, air and oil within variable volume 42a may also be vented through passageways 106. Although
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.
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|---|---|---|
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| Number | Date | Country | |
|---|---|---|---|
| 20050129543 A1 | Jun 2005 | US |
