US3781135A - Refrigerant compressor for vehicles - Google Patents

Abstract

Compressor apparatus for use with a variable speed power plant to compress refrigerant vapor in an air conditioning system. The compressor includes a plurality of cylinders having pistons which are sequentially operated. Each of the cylinders is provided with refrigerant vapor from multiple chambers of limited capacity in communication with each other and with a plenum chamber of the compressor by metering structures so that the volume of refrigerant vapor being compressed is directly proportional to the speed of the vehicle and the condenser pressure of the system.

Description

United States Patent Nickell Dec. 25, 1973 [5 REFRIGERANT COMPRESSOR FOR 3,685,923 8/1972 Hutchins 417 273 VEHICLES 3,692,434 9 1972 Schnear 417/266 [75] Inventor: Claude II. Nickell, Dearborn, Mich. FOREIGN PATENTS OR APPLICATIONS 731 Assignees: Claude H. Nickel], Deal-born; 608,892 ll/l960 Canada 4I7/539 Winfred D. Weldon, Detroit; Manuel Pinko; Adam Pianga, Primary ExaminerWilliam L. Freeh Dearborn, Mich. Attorney-A. Yates Dowel], Jr.

[22] Filed: May 19, 1972 21 Appl. No.2 255,235 [57] ABSTRACT Compressor apparatus for use with a variable speed power plant to compress refrigerant vapor in an air [2%] C(il. conditioning System. The compressor includes a p d 539 273 rality of cylinders having pistons which are sequen- 1 0 care 4111/53; tially operated. Each of the cylinders is provided with refrigerant vapor from multiple chambers of limited capacity in communication with each other and with a [56] References cued plenum chamber of the compressor by metering struc- UNITED STATES PATENTS tures so that the volume of refrigerant vapor being 1,916,130 6/1933 Torrey 417/441 compressed is directly proportional to the speed of the 2.819,678 l/l958 e" 417/571 vehicle and the condenser pressure of the system. 3,174,436 3/1965 Wanner 417/273 3,456,874 7/1969 Craper 417/534 8 Claims, 31 Drawing Figures Tn m9,

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SHEET 13 0F 15 PATENTEDUEEZS ma SHEET 15 HF 15 F/az r REFRIGERANT COMPRESSOR FOR VEHICLES BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention relates generally to refrigeration systems of various kinds and relates particularly to compressor mechanism used with variable speed power plants for compressing refrigerant vapor and discharging the same to a conventional refrigerant condenser.

2. Description of the Prior Art.

Heretofore manyefforts have been made to provide refrigerant compressors for use with motor vehicles such as automobiles, buses, trucks and the like, as well as other apparatus having a variable speed power plant. The problems of efficient cooling of motor vehicles are separate and distinct from'the problems encountered in refrigerant systems for buildings and other structures having a constant speed power input. An engine driven vehicle is subject to constantly and sometimes rapidly changing conditions, including changes in weather, air currents, and changes inspeed and direction of the vehicle. As an example, when an automobile is idling or traveling at a slow speed, the greatest amount of compressed refrigerant vapor is required for the comfort of the passengers of the vehicle. When the vehicle is travelingat a relatively high speed, such vehicle functions as a heat exchange member since the vehicle is traveling at a rapid speed through the surrounding atmosphere. Also, at idle speeds the crankcase back pressure of the compressor is at its highest because of the boil-off rate of the evaporator.

In most refrigerant compressors of the prior art, the vapor inlets of the cylinders are in direct communication with the crankcase plenum chamber so that the volume and pressure of the vapor being introduced into the cylinders is in direct proportion to the volume and pressure within the crankcase. In this arrangement, rapid acceleration quickly scavenges the vapor from the crankcase plenum chamber and thereby reduces the efficiency of the compressor while increasing the power requirements for operating the same.

Most vehicle compressors include a pair of generally parallel cylinders having relatively large cross-sectional areas and the pistons within such cylinders have relatively long strokes to produce the necessary compression required by the refrigerant system. Normally, in a two-cylinder compressor, the lobes of the crankshaft are disposed on opposite sides so that the shaft can be statically and dynamically balanced. In some twocylinder compressors, the cylinders are arranged in a V-shape so that the compression has not been equal. In other words, during the first portion of crankshaft rotation, the cylinders will compress refrigerant vapor through approximately 90 of rotation of the shaft and then for approximately 270 of rotation no compressing will take place. This creates an unbalanced condition resulting in vibration and chatter in the compressor. Also, the first cylinder receives a full charge of vapor; however, the second cylinder, which is compressed 90 later, may receive less than a full charge since the plenum chamber may not have been completely recharged after the first cylinder evacuated the vapor therein. Some examples of the prior art are disclosed in the patents to Scott 2,350,537, Atchison 2,759,333, and Heidorn 3,252,296.

Summary of the Invention The present invention relates to a refrigerant compressor for vehicles including a housing having a crankshaft located within a crankcase or plenum chamber. The housing normally includes four cylinders with two cylinders on each side and such crankshaft is provided with two lobes or crank pins which are offset from each other and adapted to operate pistons on opposite sides of the housing alternately. Each of the cylinders has a plurality of limited capacity chambers with the first chambers being in communication with the crankcase plenum chamber through metered orifices or by means of a throttling valve, and the second chambers being in communication with the first chambers through other metered orifices. The operation of the pistons causes vapor within the second chambers to be drawn into the cylinders during the suction strokes and compresses and discharges such vapor during the compression strokes. During the compression stroke, vapor flows from the first chambers into the second chambers and from the plenum chambers into the first chambers.

In two modifications, the cylinders and pistons are located in a generally horizontal housing with a pair of cylinders disposed on each side of a crankshaft and with the cylinders on one side being offset slightly from the cylinders on the opposite side along the length of the crankshaft. In a third modification, the cylinders are located within a generally V-shaped housing disposed at an angle of approximately 45 to a horizontal plane and such cylinders are offset slightly from each other along the length of the crankshaft. If desired, a throttling valve can be provided which is fully open when the condensing pressure is low and which operates automatically to open and close the inlet opening to the limited capacity chambers in accordance with the pressure in the condenser of the refrigerating system.

It is an object of the invention to provide a compressor for a refrigeration system having a variable speed power plant in which the compressor has a plurality of cylinders with each cylinder associated with multiple chambers of limited capacity in communication with each other and with the plenum chamber of the compressor by means of restricted orifices or by one or more throttling valves.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.

FIG.

FIG 3.

FIG. FIG. FIG.

5 is a section on the line 5-5 of FIG. 1. 6 is a section on the line 6-6 of FIG. I. 7 is a section on the line 7-7 of FIG. 1.

FIG. 8 is a section on the line 8-8 of FIG. 1.

FIG. 9 is a fragmentary enlarged section on the line 9-9 of FIG. 1.

FIG. 10 is a section similar to FIG. 9 showing the compression stroke of the piston.

FIG. 11 is an enlarged vertical section of a plenum chamber shield.

FIG. 12 is a section on the line 12-12 of FIG. 11.

FIG. 13 is a transverse section of a modified form of the invention.

FIG. 14 is a fragmentary section on the line 14-14 of FIG. 13.

FIG. 15 is a side elevation along the line 15-15 of FIG. 13.

FIG. 16 is a section on the line 16-16 of FIG. 13.

FIG. 17 is a section on the line 17-17 of FIG. 13.

FIG. 18 is a top plan view of a further modified form of the invention with the cylinders arranged in a V- shape.

FIG. 19 is a longitudinal section on the line 19-19 of FIG. 18.

FIG. 20 is a transverse section on the line 20-20 of FIG. 18.

FIG. 21 is a section on the line 21-21 of FIG. 20 illustrating the interior configuration of the cylinder head.

FIG. 22 is a section on the line 22-22 of FIG. 20 illustrating one side of the valve plate.

FIG. 23 is a section on the line 23-23 of FIG. 20 illustrating the opposite side of the valve plate.

FIG. 24 is a section on the line 24-24 of FIG. 20 illustrating one side of the cylinder housing.

FIG. 25 is an enlarged fragmentary section illustrating the metering valve in use.

FIG. 26 is a schematic layout of a refrigerating system.

FIG. 27 is a perspective view of an offset crankshaft.

FIG. 28 is a perspective view of one of the balancing units.

FIG. 29 is a fragmentary top plan view of the crankshaft with balancing units mounted thereon.

FIG. 30 is a section on the line 30-30 of FIG. 29.

FIG. 31 is a section on the line 31-31 of FIG. 29.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. l-12 of the drawings, a compressor 30 is provided including a cylinder block or housing 31. An inlet port 32 is located at the top of the housing 31 adjacent to one end thereof for introducing refrigerant vapor from an evaporator E (FIG. 24) into a plenum chamber 33 within the housing. An outlet port 34 is provided adjacent to the other end of the housing 31 for conducting compressed gasses from the housing to a conventional condenser C of a refrigeration system (FIG. 26).

Within the housing 31 a crankshaft 35 is provided having offset lobes or crank pins 36 and 37 extending radially from the longitudinal axis of the crankshaft substantially at 90 rotation relative to each other. As illustrated in FIG. 4, one end of the crankshaft 35 is freely rotatably mounted within the housing 31 by a roller bearing 38 or other friction-free member, while the opposite end of such crankshaft is freely rotatably mounted in a bushing 39. In order to drive the crankshaft 35, one end of such crankshaft extends through the housing 31 and is keyed or otherwise connected to the hub 40 of a drive plate 41. A drive pulley 42 is freely rotatably mounted on the hub 40 and such pulley includes a sheave 43 adapted to receive a V-belt (not shown) driven by the crankshaft of the vehicle engine.

-A conventional electromagnetic or other clutch 44 is provided for selectively drivingly connecting the drive plate 41 to the drive pulley 42 in a conventional manner when desired. It is contemplated that the crankshaft 35 could be driven directly from the engine crankshaft by means of a pair of universal joints. Such direct drive could eliminate peak loading of the V-belt as well as belt jerk, high torque peaks and high starting torque.

The housing 31 is provided with a pair of horizontally disposed cylindrical bores 48 on each side of the crankshaft 35 and each of such bores has a liner or sleeve 49 forming a cylinder 50 which slidably receives a piston 51. Each piston has a wrist pin 52 on which one end of a connecting rod 53 is swingably mounted. The opposite end of each connecting rod is attached to an insert bearing 54 rotatably mounted on one of the lobes 36 or 37 of the crankshaft 35. As illustrated in FIG. 4, a nair of connecting rods 53, extending toward opposite sides of the housing 31, are rotatably mounted on each of the lobes 36 and 37. Since the lobes are disposed at an angle of substantially 90 to each other, one of the pistons will fully compress a charge of refrigerant vapor every 90 of rotation of the crankshaft 35.

In order to introduce refrigerant vapor to be compressed into the cylinders 50, the housing 31 is provided with an inwardly extending recess defining a generally C-shaped chamber of limited capacity 55 extending partially around each of the cylinders 50. Each of the chambers 55 is in communication with the plenum chamber 33 through a restricted or metering orifice 56 in the wall of the housing 31. Preferably a shield 57 is disposed in front of each of the orifices 56 and each shield has an inclined opening 58 to permit free access of refrigerant vapor from the plenum chamber 33 into the orifice 56. The openings 58 are inclined so that any oil entrained in the regrigerant vapor and which condenses on the walls of the shield 57 will drain back into the plenum chamber.

The crankshaft 35 includes one or more counterweights 59 for lubricating the pistons 51 and other moving parts within the compressor housing and the shields 57 prevent droplets of oil from being thrown directly into the orifices 56. A pool or supply of oil maintained in an oil pan 60 at the bottom of the housing 31 at all times to reduce frictional wear on the moving parts.

A valve plate 61 is located exteriorly of the housing 31 adjacent to the cylinders 50 and a cylinder head 62 is mounted on the opposite side of the valve plate and connected to the housing 31 by a plurality of bolts or other fasteners 63. Each cylinder head 62 includes a generally C-shaped recess or pocket defining a chamber of limited capacity 64 extending partially around each of the cylinders 50 and each of such chambers is in communication with the corresponding chamber 55 of the housing by means of a restricting or metering orifree 65 extending through the valve plate 61. The orifices 65 are located adjacent to the bottom of the valve plate 61 and if desired an oil bleed hole 66 may provide communication between the chamber 55 and the chamber 64 adjacent to the upper portion of the valve plate.

As illustrated best in FIG. 5, the cylinder head 62 has an imperforate rib 67 disposed along the lower portion of the vertical axis of the head to separate the chambers 64. The rib 67 is connected to an imperforate wall 68 defining a pair of recesses or pockets 69 substantially in alignment with the cylinders 50. Such pockets 69 are in communication with each other and with a channel 70 formed by the wall 68. The channel 70 on each side of the compressor communicates with the outlet port 34 through passageways 71 formed in the housing 31.

A plurality of bosses 72 are located within the chambers 64 through which the fasteners 63 extend. As illustrated, the bosses are connected by ribs 73 to the wall 68 and by ribs 74 to side walls 75 of the cap. The ribs 74 do not extend the full length of the bosses 72 to provide for free flow of vapor fluid within the chambers 64.

The valve plate 61 is provided witha plurality of angularly disposed openings or orifices 76 providing communication between the chamber 64 and the interior of the cylinder 50. A flexible disk valve 77 is mounted by a' fastener 78 on the inner side of valve plate 61 and within the cylinder 50 so that when the piston 5 ll is retracted, the suction 01" negative pressure created within the cylinder will open the disk valve and permit refrigerant vapor to flow from the chamber 64 into the cylinder. The orifices 70 are located on a generally C- shaped bolt center disposed within the chamber 64 so that vapor within the recess 64 only can be drawn into the cylinder.

A plurality of orifices 85 extend through the valve plate 61 and provide communication between the cylinder 50 and the pockets 69 in the cylinder head 62. A disk valve 86 is mounted on the exterior of the valve plate 61 and within each pocket 69 to normally close the orifices 83. A buffer 87 having an inclined face 88 is mounted on the fastener 78 within the pockets 69. The inclined face 88 permits the disk valve 86 to open a limited amount when the vapor within the cylinder has been compressed to discharge the compressed gas into the pocket 69 and through the channel 70 and passageways 71 to the outlet port 34.

Pressure within the plenum chamber 33 forces oil from the oil pan 60 upwardly through a screen and oil tube 90 and into an oil line 91 which discharges such oil into a passage 92 extending generally centrally of the crankshaft 35. If desired, an oil pump (not shown) could be provided to receive oil from the oil pan 60 and pump such oil under pressure into the passage 92. An oil port 93 extends from the passage 92 to each of the connecting rod bearings 54 for lubricating such bearings. As illustrated in FIG. 4, the insert bearings 54 have openings 94 and the connecting rods 53 have a central bore 95 in alignment with one of the openings 94 for lubricating the connection between the outer end of the connecting rods and wrist pins 52.

A rotary shaft seal 96 is carried by the crankshaft 35 and such seal bears against an insert 97 carried by the housing 31 to prevent oil or vapor from within the housing from seeping out along the crankshaft. In order to lubricate the shaft seal 96, an oil port 98 extends outwardly from the passage 92 to the area surrounding the seal 96. Normally the roller bearing 38 is provided with a pair of shields 99 which interrupt the flow of oil from the seal 96 back to the oil pan 60- To permit the passage of oil from the seal 96, as well as to lubricate the roller bearing, each of the shields 99 is provided with one or more openings 100 which permit oil to flow from the area of the shaft seal through the roller bearing 38 and back to the oil pan.

in the operation of this modification of the device, refrigerant vapor enters the inlet port of the compressor 30 from the evaporator E. Such vapor is under pressure or back pressure from the evaporator and completely fills the plenum chamber 33 above the level of the oil in the oil pan 60. Refrigerant vapor passes through the opening 58 in each of the shields 57 and through each of the restricted orifices 66 into the limited capacity chambers 55. From the chambers 55, the vapor passes through orifices 65 into the limited capacity chambers 64 within the cylinder head 62. As long as the compressor is not operating, the pressure of the vapor within the plenum chamber 33 and the chambers 55 and 64 will reach equilibrium with the crankcase back pressure. If the vapor pressure within the chambers 64 is great enough to unseat the disk valves 77, then the cylinders likewise will be filled with vapor. When the clutch 44 is energized, the crankshaft 35 is rotated by the drive pulley 42 to cause the pistons 51 to be reciprocated within the cylinders 50. One of the pistons 51 is fully closed every 90 of rotation of the crankshaft 35 and when one piston is in closed position, the other piston on the same crankshaft lobe is in fully open position. The pistons on the other lobe are in intermediate positions, one being midway through the suction stroke and the other midway through the compression stroke.

The lobes 36 and 37 of the crankshaft are offset only a short distance of approximately one-half inch so that the stroke of the pistons 51 is relatively short and the surface speed is slower in feet per minute than conventional compressor pistons and, therefore, vibration and rocking action are substantially reduced. At an idling speed of approximately 600 rpms, the back pressure from the evaporator is greatest and the refrigerant vapor is forced into the chambers and 64 as rapidly as possible. At this time, the pistons 51 are reciprocating at their slowest speed and as each piston is retracted, vapor is withdrawn through the orifices 76 and the disk valve 77 into the cylinder. At the end of the suction stroke, the disk valve 77 closes the orifices 76 so that when the direction of movement of the piston 51 is reversed on the compression stroke, the vapor within the cylinder is compressed. During the compression stroke when the vapor within the cylinder reaches the head pressure, the disk valve 86 opens and vapor under pressure is discharged from the cylinder through the orifices 85 into the pockets 69 from which the compressed gas flows through the channel 70, passageway 71, and through the outlet port 34 to the condenser.

When the engine of the vehicle is accelerated, the back pressure within the plenum chamber 33 is reduced and simultaneously the pistons 51 which are moving more rapidly quickly scavenge the vapor from the chamber 64. Due to the reduced pressure within the plenum chamber, and the restricted orifices 56 and 65, the amount of vapor which can flow into the chamber 64 during the compression stroke of the piston is limited, such amount being a factor of time, pressure, and capacity of vapor which can flow through the orifices, as well as the pressure of the vapor within the plenum chamber. The metered orifices 56 and are designed to supply the greatest amount of fluid to the cylinders 50 at idle or low speeds and variations of the crankcase back pressure and rotational speed of the. crankshaft automatically change the output volume and pressure at the outlet port 34. When the vehicle speed increases, the demand for refrigerant decreases thereby cutting down the output of the compressor which permits high speed driving for long periods of time.

With reference to FIGS. 13-17, a modified form of compressor is illustrated including a housing 104 having a plenum chamber l05-with a crankshaft 35 rotatably mounted therein. The housing 104 includes a pair of horizontally disposed bores 106 on each side in which liners 49 forming cylinders 50 are mounted. Each of the cylinders slidably receives a piston 51 connected by a wrist pin 52 to one end of a connecting rod 53, as previously described. The opposite end of each connecting rod is rotatably mounted on one of the lobes of the crankshaft 35. An oil pan is mounted on the bottom of the housing 104 to supply lubricant for the pistons 51 through the oil passage 92 in the crankshaft 35. If desired, the housing 104 may have recesses 107 located adjacent to the lower portion of the bores 106 to provide for an increased oil capacity.

In order to introduce refrigerant vapor into the cylinders 50, the housing 104 is provided with a recess defining a chamber of limited capacity 108 extending partially around each of the cylinders 50. In this modification, each of the chambers 108 is connected by passageway 109 to a central manifold chamber 110 communicating with the plenum chamber 105 of the hous ing by a bore 111. Preferably a shield 112 is disposed across the open end of the bore 1 11 and such shield has an inclined passageway 113 which permits free access of refrigerant vapor from the plenum chamber 105 to the bore 111. The shield 112 prevents oil from being thrown by the crankshaft oil slingers 59 directly into the bore 111.

A valve plate 115 is located at each side of the housing adjacent to the cylinders 50 and a cylinder head 116 is mounted on the opposite side of each valve plate and is connected to the housing 104 by a plurality of bolts or other fasteners 117. Each cylinder head 116 includes a generally C-shaped recess defining a chamber of limited capacity 118 extending partially around each of the cylinders 50 and each of the chambers 118 is in communication with the corresponding chamber 108 of the housing by means of a plurality of orifices 119 extending through the valve plate 115. The orifices 119 provide substantially free flow of refrigerant vapor from the chamber 108 to the chamber 118 at slow and idling speeds, but restrict flow of vapor at high speed because of the lesser demand.

As illustrated best in FIG. 16, the cylinder head 116 has an imperforate rib 120 disposed along the lower portion of the vertical axis of the head to separate the chambers 118. The rib 120 is connected to an imperforate wall 121 extending most of the way around the cylinders 50 and define a pair of pockets 122 substantially in alignment with such cylinders. The pockets 122 are in communication with each other by means of a channel 123, which, in turn, communicates through a bore 124 in the valve plate 115 with a passageway 125 in the housing 104. The passageway 125 leads to a pressure dome or collector chamber 126 forming an upward extension of such housing. The pressure dome is closed by a cap 127 and is in communication with the condenser C of the refrigerating system by an outlet line (not shown).

The valve plate 115 has a plurality of angularly disposed openings or orifices 76 providing communication between the chamber 118 and the interior of the cylinder 50 and a plurality of orifices 85 .providing communication between the cylinder 50 and the pockets 122 of the cylinder head. Disk valves 77 and 86 are mounted on the valve plate 115 in the same manner as previously described with reference to valve plate 61 to control the flow of vapor into and gas out of the cylinder 50.

It is desirable to begin compression of refrigerant vapor as soon as the compressor is started in order to build up pressure within the condenser C and to control the amount of vapor or gas being compressed when the condenser pressure rises to a predetermined level. To do this, a throttling valve 130 is provided including a valve housing 131 forming a part of the housing 104 and extending upwardly into the pressure dome 126. The.valve housing 131 has a bore 132 and a counterbore 133 extending therethrough with the bore 132 being open to the manifold chamber 110 and in axial alignment with the bore 111. A valve 134 is located within the counterbore 133 and such valve has a stem 135 projecting downwardly through the bore 132. A series of bellville springs or other resilient means, such as a calibrated coil spring 136, is disposed between the valve 134 and the bottom of the counterbore to urge the valve stem 135 away from the bore 111.

Preferably the end of the valve stem 135 remote from the valve 134 is hollow for at least a portion of its length and is provided with one or more orifices 137 providing communication between the hollow interior of the stem and the manifold chamber 110 so that the flow of vapor cannot be entirely interrupted. As illustrated in FIG. 13, the cap 127 of the pressure dome is provided with a recess 138 in the area of the upper end of the valve housing 131 so that gas under pressure within the pressure dome will have free access to the upper surface of the valve 134.

With reference to FIGS. 18-26, another modified form of the invention is disclosed including a compressor housing having a crankcase or plenum chamber 151 in which a crankshaft 152 is rotatably mounted. In this modification, the housing is substantially V-shaped in cross-section and includes a pair of bores 153 on each side with each of such bores being disposed at an angle of approximately 45 to a horizontal plane. Each of the bores 153 is provided with a liner 49 defining a cylinder 50 in which a piston 51 is reciprocably mounted. Each piston 51 is connected by a wrist pin 52 to one end ofa connecting rod 53 and the opposite end of such connecting rod is rotatably mounted on bearings 54 mounted on lobes 154 and 155 of the crankshaft 152.

The lobes 154 and 155 are offset from opposite sides of the central axis of the crankshaft 152 so that such lobes are substantially 180 apart. One connecting rod from each side of the housing is connected to each of the crankshaft lobes so that when one piston carried by the lobe 154 is fully open, as illustrated in FIG. 20, the piston of the other connecting rod carried by the same lobe will be in an intennediate position. Simultaneously, one of the pistons carried by the lobe 155 will be fully closed while the other piston will be in an intermediate position. When the crankshaft is rotated, the piston which is fully open begins to close, the piston which is fully closed begins to open, and the two intermediate pistons move toward open and closed positions, respectively.

Refrigerant vapor from the evaporator E is introduced through an inlet passage 156 into the plenum chamber 151 and such vapor flows through a bore 157 into a central manifold chamber 158. Preferably a shield 159 having laterally extending passageways 160 is located across the end of the bore 157 to prevent oil

Claims (8)

1. In a compressor for use with a variable speed power plant, said compressor having a housing with at least one cylinder, a piston reciprocably mounted within said cylinder, means for reciprocating said piston, and means for discharging compressed vapor from said compressor; the improvement comprising a plenum chamber within said housing for receiving all of the vapor to be compressed, a first chamber of limited capacity spaced from and communicating with said plenum chamber, first flow control means for controlling the flow of vapor from said plenum chamber to said first chamber, a second chamber of limited capacity spaced from and communicating with said first chamber, second flow control means for controlling the flow of vapor from said first chamber to said second chamber, and valve means selectively providing communication between said second chamber and said cylinder, whereby said first and second chambers and said first and second flow control means provide a flow responsive control to the inlet for the cylinder so that the suction stroke of the piston causes said valve means to open and causes vapor from said seconD chamber to flow into said cylinder and vapor from said first chamber to flow into said second chamber and vapor in said plenum chamber to flow into said first chamber, and the compression stroke of said piston causes the vapor in said cylinder to be compressed and discharged through said discharging means.

2. The structure of claim 1 in which said first flow control means includes a restricted orifice.

3. The structure of claim 1 in which said first flow control means includes throttling valve means.

4. The structure of claim 1 in which said second flow control means includes a restricted orifice.

5. The structure of claim 1 in which said housing includes a plurality of cylinders, each of said cylinders having independent first and second chambers of limited capacity and first and second flow control means providing communication with said plenum chamber.

6. The structure of claim 5 in which said housing includes a plurality of cylinders disposed on opposite sides of the longitudinal axis of said housing.

7. The structure of claim 6 in which the axes of said cylinders are substantially coplanar.

8. The structure of claim 6 in which the axes of the cylinders on one side of said housing are disposed at an angle to the axes of the cylinders on the other side of said housing.

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