US2302448A - Refrigerative compressor - Google Patents

Description

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. f aErar'GEaArIvE COMPRESSOR William D. Leonard, York, Pa., assignor' to York Ice Machinery Corporation,

porat'ion of Delaware York, Pa a cor- Application October .24, 1940, Serial No. 362,691 f a scam I01. zed-190) This invention relates to compressors and is of particular utility in compressors intended for use in refrigeration circuitsof the compressor, cn-. denser and evaporator type. 1

In'the refrigeration art it is usual to use single acting pistons and closed crank cases with splash lubrication, and to operate the crank case at the suction pressure ofthe circuit. The reason for this is that the suction pressure most nearly ap-' proximates atmospheric pressure, and this, fact reduces the pressure diiierential againstwhich the crankshaft seal must be. effective. Another reason is that since the refrigerant is in the vapor phase on the low side of the system,,1the tendency of refrigerant to mix with oil in the crank case is minimized.-

The oil problem in refrigerative circuits is a serious matter, particularly with those refrig-- erants which are freely miscible with the lubricating oil. ,In order to resist the tendency of lubricating oil to leave the compressor with compressed refrigerant, it is common practice to use a trunk pistonof the hourglass type having the sealing ring or rings above the wrist pin and near the head of the piston, and having an oil scraping ring with oil drainage ports in the skirt of the piston below the wrist pin.

In such a construction the intake ports are in the cylinder wall in such a position that they always lie between the head and the skirt of the piston, that is, in the reduced or hourglass portion of the piston. This is important for several reasons. The intake is not drawn directly from the crank case which, if the compressor operates at relatively high speed, is filled with a fog of oil.

Further, if the compressor be used in one of those circuits in which some oil is withdrawn from the evaporator and returned to the intake of the com pressor with. refrigerant in the vapor phase, the use ofan oil scraping ring and drainage ports is essential; to the separation of the oil from the refrigerant at the compressor intake. The example'discussed' is typical," but there are other constructions'in which the'crank case is not in free communication with-the compressor suction. Use of such construction" has involved difflcul-' ties. The crank case operates at a pressure which sometimes closely approximates suction pressure, but at other times, particularly when a compressor is first started up, tends to rise'considerably, above suctionpressure. This, followsirom the fact: that somerefrigerant inevitably. becomes mixed with the oil and when the oil. is first whipped by the cranks it is heated suiiiciently to vaporize a part of the refrigerant with the result that the crank case pressure tends to riseunless the evolved vapor is freely vented. Such ventin schemes as have been tried have proved unsatisfactory. In prior art constructions the oil ,foams, and oil pumpingtends to occur, 'with'attendant increase in the discharge of oil with compressed refrigerant. The present invention contemplates active pumping out of refrigerant vapor from the crank case so thatthe refrigerant content of the "oil is kept low.

The conditions stated also cause dimculties where a group of compressors are used in a single refrigeration circuit, and are selectively shut down to vary compressor capacity. Variations of crank ca'se pressure as between the different compressors sometimes cause destruction of a compressor as the result of loss of its oil by displacement through the ofl level equalizing connection required between the various compressor crank cases. The present invention assures a low crank case pressure for every operating compressor.

An important feature of the present invention is the arrangement of the intake valve in such a way that when the compressor. operates, refrigerant vapor is pumped from the crank case. This tends to keep crank case pressure at a value equal to the suction pressurein the system whenever a compressor is in operation. However, when a compressor is shut down, the suction line and the crank case are not in free'communication but are substantially isolated from each other. This prevents or. at least minimizes drainage of refrigerant to the crank case, alone or with oil, during shut down periods.

The arrangement is such that the development of pressure in the crank case tends to create an opening tendency on the suction inlet valve. This increases the ease with which that valve operates and increases the lift of the valve. A free opening inlet valve increases the volumetric efllciency of the compressor and consequently reduces the suction pressure developed in the suction line by operation of the compressor. The action varies automatically with the speed of the compressors, an important consideration since a given sizecompressor may be operated at various speeds, depending on the installation. Speeds as low as 200 R. P. M. are used, but some compressors driven by 'direct connected motors run at speeds" as high as 1800 R. M. P, .The crank case pump out action of the present invention can be arranged to operate over thiswide speed range. Thus the invention permits the retention of all the advantages heretofore secured in -compressors of this type'and in addition afiords'stabilization of crank case pressure and better inlet valve operation.

One embodiment of the invention will now bedescribed in connection with the accompanying drawing. That drawing illustrates a portion of a small two cylinder compressor having a disc type inlet valve and a feather type exhaust valve. A small compressor is chosen because precise valve action is particularly important in compressors of small piston displacement In small compressors, clearanciosses and losses due to sluggish valve action are particularly serious.

In the drawing:

Figure 1 is a view partly in vertical section through one cylinder of a two cylinder single acting compressor.

Fig. 2 is a section through the cylinder casting one the plane of the center of the inlet ports.

Fig. 31s a fragmentary axial section of the cylinder as viewed in Fig. l, drawn on a reduced scale and with the piston removed to render the inlet port visible.

Fig. 4 is a diagram showing the compresso connected in a refrigerating circuit. 9

Referring first to Fig. 4, the compressor has a' crank case 6, cylinder casting 1, and head 8, and

may be driven by any suitable means, such as the motor 9. The high pressure discharge line H leads to a condenser 12 of any suitable type in which the compressed refrigerant is cooled and assumes the liquid phase. Liquid refrigerant is led from the expansion valve l3 to an evaporator l4 which is connected by the suction line l5 to the suction intake of the compressor.

The compressor is of the type having a closed crank case containing oil for lubrication. This lubrication may be of the splash type or partly splash and partly force feed, the important thing being that the crank case of the compressor does contain oil. It is also to be understood that in the ordinary operation of such compressor some refrigerant inevitably mixes with the oil in the crank case. v

The evaporator may be of any preferred type and may include means not illustrated in the drawing, but well lmown in the art, for causing some oil to pass with the vaporous refrigerant from the evaporator to the compressor. It is deemed unnecessary to illustrate this feature because various arrangements are known for causing oil to return from the evaporator to the compressor. Use of such a scheme is optional so far as the present invention is concerned, the purpose of mentioning it being to indicate that the compressor is well adapted for use in these as well as more conventional circuits. I

Referring now to Figs. 1 to 3, the crank case is indicated generally at 6 and the cylinder casting at 1. In the small compressor illustrated they are cast as a single unit. The inlet connection to the compressor is indicated in Figs. 2 and 3 at [8 and is protected by a thimble strainer l9. It has two branch passages 2| and 22 which lead to the interior of the two cylinders 23 and 24 respectively. The discharge connection is through the head 8 and thence through port 26 in the cylinder casting 1 (see Fig. 2), the discharge connection 21 being visible in Fig. 1.

Only the cylinder 23 is shown in complete section in Fig. 1, cylinder 24 being a mirror duplicate. In cylinder 23 is illustrated a piston 26 of the hourglass type, that is it has a reduced middle portion in which the wrist pin 29 is mounted and has above this reduced middle portion a head 3| and below it a skirt 32. The piston packing means are mounted in the head 3| and in Fig. 1 a single ring 33 is illustrated in conjunction with two grooves 34, one above and the other below the ring 33. The number of rings to be used and the presence or absence of the grooves 34 are matters of design and are controlled in some degree by the size of compressor, the speed of operation, and the pressures to be developed.

In the skirt 32 is a slotted oil scraping ring 35. The groove in which the ring 35 works has drain ports 36 at its back and these communicate with the drainage slots 31 in the oil ring 35. The oil ring may take various forms, there being a number of commercial forms of ring which are well adapted to this service. The purpose of the ring 35 is to scrape oil from the cylinder walls on the down stroke of the piston, thus causing the oil to be returned to the crank case 6.

One of the crank shaft bearings appears at 38 and the crank shaft proper is indicated generally at 39. In the small compressor illustrated use is made of eccentrics 4i instead of crank throws so that the connecting rod 42 takes the form of an eccentric strap. The rod 42 is centered on the wrist pin 29 by means of the spring washers 43, as clearly shown in the drawing.

It will be observed that the head of the rod 42, where it engages the wrist pin 29, is rather closely confined in, but not sealed in, a pocket in piston 23 and this has the purpose and effect of protecting a port 44 from oilsplashed in the crank case by rotation of the crank shaft. The port 44 leads to the top face of the piston head and is normally closed by the central portion of the disc type inlet valve 45. This valve is circular in form and is clamped at its center by a convex retainer 46. held in place by screw 41 threaded into the piston head.

The inlet passages through the piston are indicated at 48 and are arranged in a circular series a short distance within the periphery of the valve disc 45. There are two circular seats 49, one within and the other without the circular row of ports 46. Outside the port 44 and inside the inner seat 43 is a relief groove 5| intended to insure tight sealing of the disc valve 45 against the seats 49. Only one port 44 is shown but more may be used if desired.

To avoid expensive coring, the cylinder head, generally indicated by the numeral 3, is not made in a single piece. Instead it comprises a flat plate l6 and an overlying inverted cuplike member I1, the joints between the parts I6 and I1 and between the part I6 and the cylinder casting 1 being sealed by gaskets 25, as shown. The plate I6 is formed with a discharge port, formed to receive the valve retainer 46. In this way the clearance is kept small and still the retainer 46 may be made of substantial size.

The discharge valve for each cylinder comprises a feather valve 52 seating on plate l6 and controlling flow through the port which receives the retainer 46. The valve 52 is guided on two studs 53 set in plate l6 so that the valve may move in a straight line toward and from its seat. A spring retainer plate 54 is held on the upper ends of the studs 53 by'the nuts 55. The bow-shaped valve spring 56 is retained by the studs, reacts at its ends against the plate 54 The retainer 46 isa somewhat lower suction pressure.

andat its middle reacts downwardfly upon the discharge valve 52. w

The valve 52 is mounted in the chamber l formed in the head 8 between its component parts I6 and I1. In this chamber are mounted] the discharge valves for both the cylinders of a" two cylinder compressor.

compressed vaporous refrigerant through the I I From the cavity 51 v the passage 26. leads to the exhaust connection line H. Small quantities of oil inevitably .pass to the condenser I2 and where'the refrigerant lsv of the type freely miscible with the oil, amixture of oil and liquidrefrigerant is developed grad.-

. ually in the condenser l2 as the system operates.

It follows that the expansion valve l3 delivers not only refrigerant but oil to the evaporator l4.

Some means must be provided to remove the oil from theevaporator and one'common practice is to cause the oil to return with the vaporous refrigerant through the suction line l5 to the intake line 18 of the compressor. Where this is done it is particularly desirable that the ring 35 be of the oil scraping variety because the oil separation. occurs at the compressor inlet.

If the compressor is started up and the crank case pressure starts-to rise, as already suggested, or if pressure is developed in the crank case for any other reason, it is quickly dissipated because the port 44 allows the crank case pressure to react upon the lower face of the valve disc 45. This increases the opening tendency of the valve disc and thus permits the compressor to develop Opening of the valve entails opening of the port 44 to the intake passages 48 with the result that there is an actual pumping action from the crank case which tends to maintain crank case pressure at, or only slightly below, suction pressure so long as the compressor is in operation. When, however, the compressor stops, closure of the inlet disc valve 45 against its seat isolates the crank case not only from the working space of the compressor but also from the suction inlet port 2|. This closure of the port 44 is quite important because it prevents drainage of any liquid refrigerant or a mixture of liquid refrigerant and oil from the working space to the crank case. This action is enhanced by the fact that the upper end of the port 44 is at the extreme top of the piston and consequently above the inlet passages.

It follows that crank case pressure is kept at a desirable low value at all times when the compressor is operating without the use of any special relief valve or check valve and without requiring free communication between the inlet port and the crank case. Because of the operative characteristics of the compressor it is possible when two are used in the same circuit to provide a simple oil equalization connection between the crank cases of the two compressors. Any compressor which is operating will maintain its crank case at the lowest pressure in the system, hence oil will not be displaced by pressure differentials from the crank case of the operating compressor. Similarly, if any compressor which has been shut down is started up, the immediate reduction of crank case pressure insures return of oil to its crank case, if for some reason oil has been displaced from the crank case during a shut down.

While I prefer to use the disc valve mounted on the piston head, other types of valves can be andcontrolling a pressure equalizing connection to the particular valve'mech'a nls'm' shown is not contemplated. 'Whiletheinvention is believed to attain its greatest'utility in a 'refrigcrating circuit, it does so because insuch-a circuit there is the problem""of undesired circulation of oil and the importance of avoiding oil pumping and the disturbing factors incident to the presence of other refrigerant mixed with the oil. The valve arrangement could, however,

be used in any compressor in which the compressed medium is likelyto become mixed with lubricant oil'and to cause account.

I claim:.

1. A refrigerating diffici lties on that compressor comprising in combination, a cylinder having a working'space and an inlet thereto; a crank casecontaining a 1 lubricant; a reciprocating piston which substantially isolates said working space and inlet from said crank case; an i'nlet valve controlling com munication through the inlet to the working tion between the crank case and the inlet, the parts being so arranged that said connection is open when the inlet valve is open and closed when'the inlet valve is closed.

2. The combination definedin claim 1 in which the equalizing connection is formed in the piston and the inlet valve is carried by the piston.

3. A refrigerative compressor comprising a cylinder with side inlet port; a closed crank case adapted to contain a lubricant; a trunk piston reciprocable in said cylinder, said piston having a reduced middle portion in communication with the'cylinder inlet port and having a circumferential sealing portion above said reduced portion and lubricant, scraping means below said reduced portion; a suction operated inlet valve mounted on the piston and serving to control flow from the reduced portion of the piston to the working space above the piston within the cylinder; and means affording a passage from the upper portion of the crank case to a seated portion of the inlet valve and so arranged that pressure developed in the crank case reacts on the inlet valve in an opening direction and opening of the inlet valve connects said passage with said working space.

4. A compressor for use in a refrigerating circuit of the compressor condenser evaporator circuit type containing a volatile refrigerant, said compressor comprising a valve mechanism and a crank case containing a lubricant, into which crank case refrigerant may enter as an incident to compressor leakage; and means associated with the valve mechanism of the compressor to cause the compressor to pump refrigerant vapor from its own crank case when it runs and to isolate the crank case from the refrigerant circuit when the compressor stops, whereby the refrigerant content of the crank case is kept at a minimum.

5. The combination defined in claim 4 in which the parts are so arranged that the opening of the inlet valve connects the crank case with that part of the refrigerative circuit which is at the lowest pressure, and the closure of the inlet valve isolates the crank case from the circuit.

6. A compressor for use in a refrigerating circuit of the compressor condenser evaporator circuit type containing a volatile refrigerant, said compressor comprising a crank case containing a lubricant and a cylinder having a side inlet port,

used in I accordance with the 'inventionand ex cept as specifically stated in the claims limita-' tion of the crankcase to the inlet valve so arranged that pressure developed in the crank case reacts on the inlet valve in a valve opening direction and so that opening of the inlet valve connects the crank case with said working space.

'7. The combination defined in claim 6 in which the trunk piston is formed with a concentric series of inlet ports in communication with the cylinder inlet port, the inlet valve is of the flexible plate type mounted on the head of the piston and the passage from the upper portion of the crank case leads to a portion of the plate valve adjacent the piston inlet ports. I

.8. A compressor for use in a refrigerating circuit oi the compressor condenser evaporator circuit type containing a volatile refrigerant, said compressor comprising a crank case containing a lubricant and a cylinder having a side inlet port, a trunk piston having piston packing means above said inlet port and a lubricant scraping ring below the inlet port, the cylinder and Piston enclosing a working space, and a suction operated inlet valve controlling flow from the inlet port to the working space, there being means affording a passage from the upper portion of the crank case to the inlet valve and so arranged that pressure developed in the crank case reacts onthe inlet valve in an opening direction and opening of the inlet valve connects the crank case with said working space.

9. A compressor for use in a refrigerating circuit of the compressor condenser evaporator circuit t'ype containing a volatile refrigerant, said compressor comprising a crank case containing a a lubricant with which the refrigerant is miscible,

a cylinder having a-side inlet port and a trunk piston having a reduced middle portion in communication with said inlet port, packing means carried by the piston above the inlet port and an oil scraping ring carried by the piston below the inlet port, the cylinder and piston enclosing a working space, and a suction operated inlet valve of the plate type mounted on the head of the piston and controlling flow from the reduced portion of the piston to the working space, there being means affording a passage from the upper portion of the crank case to a portion of the inlet valve adjacent the inlet passages in the piston, the parts being 50 arranged that pressure developed in the crank case reacts on the inlet valve in an opening direction and opening of the inlet valve connects the crank case with said working space.

WILLIAM D. LEONARD.

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