Two-speed Compressor

Abstract

A refrigerant compressor having a two-speed compressor motor therein for driving a compression mechanism selectively at a relatively high speed and at a relatively low speed to effect capacity control. For example, a two-winding four-pole motor would, during two-pole operation, rotate at about 3,600 r.p.m., and during four-pole operation at about 1,800 r.p.m. A two-stage pump is provided for cooperating with the crankshaft to provide for adequate lubrication of the crankshaft bearing surfaces during both high-speed and low-speed operation of the compressor motor.

Description

BACKGROUND OF THE INVENTION

This invention relates to a hermetic refrigerant compressor utilizing a motor operable at different predetermined increments for driving the compression mechanism so as to effect capacity control. In another aspect, this invention relates to a hermetic refrigerant compressor having a motor operable at different fixed increments, for example, full-speed and half-speed, with a two-stage pump associated with the crankshaft for assuring adequate lubrication at both speeds of operation.

Refrigerant compressors have generally been designed to operate at a relatively constant speed. In use, the load on the refrigeration system in which the compressor is utilized may vary, resulting in several off-on cycles as well as inefficient operation of the compressor unless the capacity of the compressor can be varied to comply with system variation. One method of effecting capacity control has been to bypass discharge gases from the discharge line directly to the suction line or suction side of the refrigeration system--a highly inefficient method. Still another arrangement requires the use of capacity control valving and solenoids within or in association with the compressor in order to vent the discharge of cylinders to the suction manifold. This method is more efficient than the discharge gas bypass arrangement, but still less efficient than desired.

An object of the present invention is to provide an improved refrigerant compressor employing a compressor motor operable at different fixed increments of speed for effecting capacity control.

Another object of this invention is to provide an improved hermetic compressor having a drive motor operable at different fixed increments of speed, such compressor including multistage pump means to assure adequate lubrication of the crankshaft bearing surfaces during all operating speeds. Other objects and advantages of the present invention will become more apparent hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

The attached drawing illustrates a preferred embodiment of the invention in which like numerals refer to like elements and in which:

FIG. 1 is a side elevational view, partially in section and with parts broken away, of a hermetic refrigerant compressor embodying the present invention;

FIG. 2 is an enlarged cross-sectional view of the two-stage pump mechanism of the present invention;

FIG. 3 is a bottom view of the two-stage pump mechanism of FIG. 2; and

FIG. 4 is a cross-sectional view of the pump impeller.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated a compressor embodying the present invention. The compressor 10 comprises a gastight, hermetically enclosed outer casing or housing including an upper shell 12 and a lower shell 14 integrally joined to one another, as, for example, by welding. To the bottom of the exterior surface of the lower shell 14 are welded a plurality of legs 16 by means of which legs the compressor may be supported in an upright position within a condensing unit or an air-conditioning unit.

Supported within the outer casing of the compressor 10 is a compression mechanism 18 which includes a compressor block having a crankcase portion 20 and a motor flange portion 22. An annular sleeve 24 made from sheet metal surrounds the crankcase portion 20 of the compressor block and cooperates therewith to define an annular discharge gas cavity 23 in the compression mechanism. A heat shield 26 is disposed about the annular sleeve in spaced relationship thereto.

The annular sleeve 24 includes an out-turned upper flange 28. Secured to the lower shell 14 of the outer casing is an annular flange member 29. Spring means 32 cooperate between the flange 28 and flange member 29 for resiliently supporting the compression mechanism 18 within the outer casing of compressor 10.

Provided within the compressor block are a plurality of radially oriented cylinders 30. Though a four-cylinder compressor is illustrated, it will be understood that the present invention may be used in a hermetic refrigerant compressor having other cylinder configurations. Cylinder sleeve or liners 33 are provided in each of the cylinders 30 and a piston 34 is slidably mounted for reciprocation within each of the cylinder liners 33. Each piston 34 has mounted therein a wrist pin 36 upon which is journaled one end of a connecting rod 38. The other end of each connecting rod 38 is affixed to the eccentric portion 40 of drive shaft or crankshaft 42.

Provided at the end of each cylinder 30 for closing the end of each cylinder cavity is a valve assembly 60. The valve assemblies 60 each comprise a discharge valve unit and a suction valve unit operable in a known manner. Each valve assembly 60 is held in place in the end of a cylinder 30 by a cylinder head or cap 62. A Belleville spring 64 and a retaining ring 66 cooperate with the cylinder head 62 to maintain the head in position closing the end of the cylinder. The annular space 23 provided within the compression mechanism between the compressor block and the sleeve 24 communicates each of the cylinders and receives the discharge gases from the cylinders and conveys them to the discharge line 72.

The drive shaft 42 is disposed in an upright position within the compression mechanism 18 and is connected at its upper end to the rotor 44 of the electric drive motor 46. The motor includes a stator 48 which is supported within the motor flange portion 22 of the compressor block and the rotor 44 which is inductively connected to the stator 48.

Enclosing the top of the motor 46 is an end cap 50 which is suitably connected to top of the motor flange portion 22 of the compressor block.

Drive shaft 42 is journaled at its lower end within a lower bearing 52 mounted in lower bearing head 54. The lower bearing head 54 is maintained in position by a suitable wedge-lock spring or retaining ring 56 seated within an annular groove in the lower crankcase portion 20 of the compressor block. Intermediate its ends the drive shaft 42 is journaled within the spaced bearings 57 and 58 in the hub portion or partition portion 21 of the compressor block.

Suction gas enters the outer casing or housing of the compressor via the suction line inlet 74 and flows into a first compartment defined between the outer casing and the compression mechanism below the flange 29. The gas passes from the first compartment into a second compartment or annular space defined between the flanges 29 and 28 and then into a third compartment defined between the outer casing and the top of the compression mechanism 18. From the third compartment, the suction gas passes through the opening 51 in the top of the end cap 50 over the electric motor 46 for cooling same and then through the openings 76 in the compressor block into the cylinders 30. The gases are compressed within the cylinders and forced through the valve assemblies 60 into the annular discharge gas cavity 23. From the annular discharge gas cavity 23, the compressed gas passes through the discharge line 72 to the condenser of the refrigeration system in which the compressor is utilized.

A plurality of terminals 78 are provided in the top of the upper shell 12 in order to conduct electric current from a suitable source to the electric motor 46 and to provide for connection of suitable motor protection while preserving the hermetic nature of the compressor.

In larger size refrigerant compressor, for example, on the order of 10-ton capacity and four cylinders, it is sometimes difficult to employ mechanical unloaders because of balance and control problems. A unique solution to the problem of capacity control in such compressors is to provide a multipole electric motor operable at different fixed increments of speed by which the capacity of the refrigeration system can be varied. For example, a four-pole two-winding electric motor can be utilized to provide full capacity during two-pole operation and one-half capacity during four-pole operation. The characteristics of one form of motor embodying the present invention would be as follows: ##SPC1## ##SPC2##

It is seen that in such motor the minimum speed during high-speed or two-pole operation would be on the order of 3,235--3,510 r.p.m. At half-speed or four-pole operation the motor speed would be on the order of 1,620--1,750 r.p.m.

It has been found that by taking advantage of total refrigeration system characteristics and reducing the maximum load requirement during low-speed operation, minimum required efficiencies of not less than about 80 percent can be maintained during both high-speed and low-speed operation with a less expensive motor design than, say, a constant torque two-speed motor.

In use, the known pump means of the prior compressors would function satisfactorily in the novel compressors of this invention during high-speed operation, but provided inadequate lubrication during low-speed operation. The hermetic compressor 10 of the present invention has been provided with unique two-stage pump means 80 for assuring adequate lubrication of the crankshaft bearing surfaces during both high-speed and low-speed operation. The upright drive shaft or crankshaft 42 is provided with a longitudinally disposed pump passage 81 which has at its upper end radially disposed passages 82 and 84 for lubricating the bearing surfaces between the crankshaft 42 and bearings 57 and 58. The passages 83 and 85 communicate with the upper end of the pump passage 81 to vent refrigerant from the pump passage at startup of the compressor. Lubricant is supplied to the lower bearing 52 through the radially disposed passage 86.

Disposed in an opening in the bottom of the lower bearing head 54 and fixedly secured thereto is a thrust plate 90. Openings 91 in the thrust plate 90 provide inlet opening means for communicating the rotating elements of two-stage pump 80 with lubricant in the sump defined between the compression mechanism and the lower shell 14. Lubricant passes from the openings 91 through an inlet opening 92 in the pump impeller 93 into radially disposed or transversely disposed passage 94 in the pump impeller 93. The passage 94 provides for the first-stage pressurization of the ingested lubricant. Lubricant is discharged from passage 94 into the annular space 96 between the rotating pump impeller 93 and the inner wall of the lower bearing head 54. The impeller 93 is connected to the drive shaft 42 by suitable fastening means, for example, machine screws 98. The lubricant passes from the annular space 96 through a transverse passage 100 in the fixed thrust plate 90 and then upwardly through a central passage 102 in the pump impeller 93 into a recess 103 in the bottom of the drive shaft. From recess 103, the lubricant passes into the radially disposed passage 86 and then into the pump passage 81 for transfer to the crankshaft bearing surfaces. A second-stage pressurizing of the lubricant is effected in the passage 86.

In operation it has been found that the lubricant will be supplied to the radially disposed outlets 86, 84 and 82 during both high-speed and low-speed operation of the compressor under desired pressure. The use of a conventional single-stage pump was found inadequate to supply desired lubricant pressure during low-speed operation. Screen 110 is affixed to the lower bearing head to prevent impurities in the sump from entering the two-stage pump 80.

Referring to FIGS. 2, 3 and 4 there is better illustrated the details of the two-stage pump of the present invention. The thrust plate 90 has four openings 91 therein which serve as inlet openings for communicating the two-stage pump with the oil in the sump. A continuous annular groove 112 is provided in the top of the thrust plate 90 for providing continuous feed of lubricant to the pump impeller 93. Provided in the thrust plate 90 in a plane generally transverse or at right angles to the axes of the four openings 91 is a bore 100. The pump impeller 93 of the two-stage pump 80 rests upon the thrust plate 90 during normal operation. The pump impeller 93 is fixed to the drive shaft or crankshaft 42 for rotation therewith by means of the fastening means 98. Lubricant will be ingested through the passages 91 in the thrust plate 90, into the annular groove 112 in the top of the thrust plate, through the inlet opening 92 in the pump impeller 93 into the radially disposed passage 94 of the pump impeller 93 where the first-stage pressurization occurs. The lubricant will then pass from the radially disposed passage 94 through passage means defined in part by annular chamber 96 between the impeller 93, washer or thrust plate 90 and lower bearing head 54, the bore 100 in the thrust plate 90 and the axially aligned upright bore 102 in the impeller 93 for passage through the second-stage pressurized passage 86 into the upright axially offset passage 81. The two-stage pump of the present invention functions effectively during both high-speed and low-speed operation of the compressor motor to provide adequate lubricant pressurization during all modes of operation. A minimum number of components are required to be added to the compressor mechanism while maintaining the desired lubrication.

There has been provided by the present invention a hermetic compressor utilizing a motor for driving the compression mechanism within the compressor selectively at different fixed increments of speed so as to provide for capacity control without auxiliary components such as capacity control valving and solenoids. In one presently preferred form, the motor is a two-winding four-pole motor, with two-pole operation providing the higher speed (about 3600 r.p.m.) and four-pole operation providing the lower speed (about 1,800 (r.p.m.). The hermetic compressor is further provided with a novel two-stage pump means which will maintain desired pressurized lubrication during both high-speed and low-speed operation of the compressor motor.

While there has been shown and described a presently preferred embodiment of the invention, it will be obvious that other embodiments will be apparent to those skilled in the art. It is, therefore, intended that the invention be limited only within the scope of the appended claims.

Claims

We claim:

1. In a refrigerant compressor including compression mechanism within a sealed outer casing, said compression mechanism including an upright crankshaft means having at least one longitudinally extending pump passage therein offset from the rotational axis of the crankshaft means for supplying lubricant to surfaces to be lubricated, motor means within the outer casing for actuating the compression mechanism, and a lubricant sump in the compressor, the improvement characterized by said motor means comprising a four-pole two-winding drive motor for driving the compression mechanism at a first high speed and a second lower speed to control capacity of the compressor, two-pole operation providing said high speed and four-pole operation providing said lower speed, and a two-stage pump mechanism operatively driven by the drive motor for assuring adequate lubrication whether the drive motor is operating at said high speed or said lower speed, said pump mechanism including means defining first inlet opening means offset from the rotational axis of the crankshaft means for ingesting lubricant from the sump, a first-stage pressurizing opening transversely disposed in said crankshaft means, said first-stage pressurizing opening communicating with said first inlet opening means, a second-stage pressurizing opening transversely disposed in said crankshaft means, passage means communicating with said first-stage pressurizing opening with said second-stage pressurizing opening, said second-stage pressurizing opening also communicating with said pump passage, the two-stage pump mechanism assuring adequate lubrication of said surfaces to be lubricated at said lower speed operation of said drive motor.

2. A refrigerant compressor as in claim 1 wherein the means defining first inlet opening means comprises a thrust washer fixed in said compression mechanism below the crankshaft means and having at least one axially offset inlet opening therein, said thrust plate having a transversely disposed bore separate from said inlet opening, said transversely disposed bore defining a portion of said passage means.

3. A refrigerant compressor as in claim 2 wherein the crankshaft means includes crankshaft and a pump impeller connected thereto, said first-stage pressurizing opening being in said pump impeller.

4. A refrigerant compressor as in claim 3 wherein said passage means includes an axial bore in said crankshaft which communicates at one end with an axial bore in said thrust washer that in turn communicates with the tranversely disposed bore in the thrust washer, whereby lubricant ingested through said inlet opening passes through the first-stage pressurizing opening, passage means, and second-stage pressurizing opening to the pump passage.

5. A refrigerant compressor as in claim 3 wherein the passage means includes an annular chamber defined between the thrust washer, pump impeller and compression mechanism, said annular chamber communicating with said first-stage pressurizing opening and said transversely disposed bore in said thrust washer.

6. A refrigerant compressor as in claim 5 wherein the thrust washer has a continuous annular groove in the top surface thereof communicating with the inlet opening means, the top surface of the thrust washer abutting the bottom surface of the pump impeller, said annular groove providing continuous feed of lubricant from the inlet opening means to said first-stage pressurizing opening in the pump impeller.