US2202175A - Refrigerating apparatus - Google Patents

Description

May 28,1940. w. H. TEETER 2,202,175

REFRIGERATING APPARATUS Filed March 15, 1937 2 Sheets-Sheet 1 WJ//IINVENTOR.

May 28, 1940.

w. H. TEETER 2,202,175

REFRIGERAT'ING APPARATUS Filed March 15, 1937 2 Sheets-Sheet 2 g i g 102. z

llHllll llllllll l compressors and pumps.

Patented May 28, 1940' PATENT OFFICE,

REFRIGERATING APPARATUS Wilford H. Teeter, Dayton, Ohio, assignor to General. Motors Corporation, Dayton, Ohio, a corporation of Delaware Application March 15, 1937, Serial No. 130,859

4 Claims. I (01. 230-198) This invention relates to refrigerating ap paratus and more particularly to refrigerant Two-stage pumps have often been proposed to provide compressors of improved efliciency. In such compressors, difficulty has been encountered in obtaining a construction which had an even torque in its power requirements and in which the output and efficiency are commensurate with the additional structure required to provide a twostage compressor instead of a single-stage compressor.

It is an object of my invention to provide an improved two-stage pump having an even torque load.

It is another object of my invention to improve the eficiency of a two-stage pump and to increase its output.

More specifically, it is another object of my invention to improve the charging of the secondstage cylinder of a two-stage pump;

It is another object of my invention to prevent the super-heating of the fluid drawn into the first stage of the pump.

It is still a further object of my invention to decrease the heat transfer between the head ends of the cylinders of different stages.

It is another object of my invention to provide an improved drive shaft and eccentric connec-.

tion.

It is another object of my invention to provide an improved piston for a two-stage pump.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a vertical sectional view through one form of my improved pump together with the remaining elements of a refrigerating system;

Fig. 2 is a sectional view taken along the lines 2-2 of Fig. 1;

Fig. 3 is a sectional view through the firststage piston taken along the lines 3--3 of Fig. 4;

Fig. 4 is a sectional View of the first-stage piston taken along the lines 44 of Fig. 3; and

Fig. 5 is a sectional View through the eccentric member and counterweight mounted upon the drive shaft. a Briefly, I have shown a refrigerating system including a two-stage compressor havinga large and a small cylinder which are separated attheir head ends by a slot to prevent heat transfer therebetween. The first-stage cylinder is, of

course, larger than the second-stage; and fluid is pumped from the first-stage cylinder into the crank case, and from the crank case the fluid is pumped into the second-stage cylinder and dischar edtherefrom.

Bo h of the pistons are connected to eccentrics located in the same position with respect to the drive shaft so that they are both at top dead center at the same time. By this construction the first-stage piston does work upon the down stroke in drawing gas into the cylinder against the crank case pressure and does little work in transferring this gas to the crank case upon the up stroke. In the second-stage cylinder, the piston does little work on the down stroke in transferring fluid from the crank case to the second-stage cylinder but does its major work upon its up stroke in expelling the gas from the cylinder against discharge pressure.

The eccentrics are clamped to the shaft by screws which extend into the counterweight. The first-stage piston is separated above the wrist pin so that the piston valve may be inserted between the piston head and the wrist pin without the useiof a gasket joint.

Referring now to the drawings and more particularly Fig. 1, there is shown a refrigerating system including the compressor 20 for compressing the refrigerant and for forwarding compressed refrigerant to a condenser 22, where the compressed refrigerant is liquefied and collected in a receiver 2t. From the receiver 2%, the liquid refrigerant is forwarded through a supply conduit to an evaporating means 26 where the refrigerant evaporates under reduced pressure and is returned to the compressor through the return conduit 28. i

The compressor 20 is driven by an electric motor 30 through pulley and belt means under the control of thd'snap-acting temperature-responsive switch means 32.

The body of the compressor 20 is formed of a casting 34 provided with the first stage or low pressure cylinder 36, the high pressure or secondstage cylinder 38, and a crank case 40 which communicates directly with the cylinders 36 and 38 in its upper portion and which is closedat the bottom by a pressed metal member 42 fastened to the lower edge of the crank case walls by cap screws 44. The crank case walls 40 are provided with bosses 46 and 48 which are machined to provide bearings for supporting the drive shaft 50. The bearing in the boss 46 is closed to the outside by a plug 52, while at the opp ite bearing the shaft projects to form a taper for receiv- Heretofore, in two-stage compressors, it has been customary to place the eccentric or cranks 180 degrees apart upon the drive shaft in compressors of this type. This tended to statically balance the eccentrics and the pistons and also provided a partial dynamic balance. It, however, produced an extremely uneven torque load for the driving motor to overcome. In this construction both pistons were working at the same time and both of them were idle at the same time so that practically all of the power to drive the compressor was required in half a revolution and, therefore, large fluctuations of voltage and current in the electric supply line occurred. This disturbs the operation of other electrical equipment and makes electric lights flicker. In order to avoid this it is necessary to employ an exceedingly heavier flywheel and a larger motor.

The eccentric member 54 surrounds the portion of the drive shaft within the crank case. This eccentric member comprises two eccentrics 56 and 58 which have hollow portions turned toward each other. Between the two eccentrics 58 and 58 is a plurality of laterally extending bosses 60 which receive cap screws 82 extending into a counterweight 64. This counterweight has a portion which extends into a fiatted portion 66 of the drive shaft. Thus, for this construction, the screws 62 tightly clamp the counterweight onto the flat of the drive shaft to lock both the counterweight and the eccentrics to the drive shaft. I

These eccentrics may be moved laterally upon the drive shaft to adjust the clearance between the face 63 of the boss 48, the ring 65, and the adjacent end of the eccentric member 54 so that end play of the drive shaft 58 is kept at a sumciently small amount to prevent any noise resulting therefrom. This adjustment is made after the plug 52 is in place. This plug 52 prevents movement of the drive shaft in the opposite direction. The eccentrics are locked 180 degrees from the counterweight, and the counterweight is made sufiiciently heavy to substantially balance not only the eccentrics but also the connecting rods and pistons.

The eccentric 55 is provided with a connecting rod 66 which receives a hollow wrist pin 68 in its wrist pin bearing. This wrist pin is supported in wrist pin bearings in the bosses I0 provided in the lower half 12 of the first-stage piston. The hollow wrist pin 68 floats in the connecting rod as well as in the wrist pin bearings. Buttons are provided at the opposite ends of the wrist pin to hold it in place. The lower half I2 of the first-stage piston is connected by long screws I4 to the upper half or head portion 16. The joint between these two halves of the piston is made by a ground step joint. The piston is split in this manner so that the valve mechanism may be inserted in the head of the piston. By splitting the piston in the middle, it is not necessary to provide gaskets at the joint since a sufiicient skirt is provided in the head portion of the piston to prevent any flow of gas or oil through the joint.

The head end of the piston is provided with a plurality of valve ports I8 which are provided with seats on the inside of the head. These seats are adapted to be closed by a valve disc which is resiliently held in place by a light' valve spring 82. This light valve spring 82 is supported by a pressed metal ring which is provided with a shoulder for this purpose.

The upper portion of this pressed metal ring rests against the top wall of the piston to prevent the collapsing of the valve spring 82. A shoulder is also provided which supports the upper end of a still spring 86 which is provided for normally holding the ring 84 in position. The lower end of this stifi spring 86 is supported by a fiattened portion 88 provided upon the top of the wrist pin bosses ID. This construction is provided so that if any large amount of oil or liquid should enter the first-stage compression chamber in such an amount that it could not be handled by the valve 80 and its valve spring 82, under such circumstances the stiff spring would be compressed to act as a relief valve and thereby would permit the passage of the liquid through the valve with sufiicient rapidity to prevent the injury of either the inlet or outlet valve of this cylinder or any other parts of the compressor such as the connecting rod or crank shaft.

The top of the first-stage cylinder 36 is closed by a valve plate 90. This valve plate 90 is provided with an inlet valve comprising a supporting disc 92, a valve spring and valve disc which are supported and held in place by the disc 92, and a plurality of ports 94 which are provided with valve seats in their lower ends. The disc 92 is held to the valve plate 90 by a bolt 96. Above the inlet valve is a chamber 98 formed in an inlet head castin'g I02 through which pass the long screws I04 which clamp the valve plate and its gaskets between this head and the cylinder and also hold the head onto the cylinder. This completes the description of the mechanism of the first-stage.

In the mechanism of the second stage there is provided a connecting rod I06 upon the eccentric 58 which rod has its upper bearing receiving a hollow wrist pin I08provided with buttons at its Opposite ends to keep the wrist pin in place. I

In the head end of this cylinder is a discharge valve H2, and the top of a piston is provided with a tapered knob .or boss II4 which fits into an opening in the valve plate '6, which is provided with a discharge valve I I8. Above this discharge valve H8 is the discharge chamber I20 formed within a cylinder head casting I22. Screws I24 extend through the cylinder head casting and the valve plate into the walls of the cylinder 38 to hold the valve plate and the cylinder head in place on top of the cylinder.

Beginning the operation of the compressor, starting from the position shown in Figs. 1 and 2, as the drive shaft 50 is turned by the motor 30 both pistons begin to move downwardly. The first-stage piston 'I2I6 moves downwardly and, at the same time, its valve prevents any gas from the crank case from entering" the compression chamber of the cylinder 36. This creates a low pressure within the compression chamber, thus making it possible for gas to enter from the cylinder head chamber 98 through the ports 94 into the compression chamber. At the same time, the second-stage piston I09 is moving downwardly at the same speed. The valve H2 in this piston, however, permits gas to fiow from the 7 crank case into the compression chamber of the cylinder 38. I

In this movement through 180 degrees fluid is compressed in the crank case because of the gradually reducing, volume of the chamber enclosed by the crank case, the cylinder walls 36 and 38, and the pistons. When the eccentrics 56 and 58 have been turned through 180 degrees, so that the two pistons are at the bottom of their strokes, the pressure within the crank case will be at a maximum. At this time the fluid in the crank case has full access to the compression chamber of this second-stage cylinder at a time when this second-stage compression chamber is at its greatest volume. This will, of course, insure that the maximum amount of fluid under pressure will flow through the valve N2 of the second-stage piston I89 into. its compression chamber. Since the pressure within the crank case fluctuates rather widely, this provides considerably improved charging of the second-stage compression chamber. Furthermore, the movement of the gas from the cylinder 36 into the cylinder 38 and into the compression chamber will set up a current of fluid in the direction of the cylinder 38 which will have a slight amount of inertia, sufiicient to supercharge the compression chamber of this sec0ndstage cylinder by reason of the current of gas or fluid set up and the effect of its inertia which tends to make it begin to move and continue to move in that direction.

During this time the first-stage cylinder has been doing substantially all the work in compressing the gas in the crank case and pushing the compressed gas into the compression chamber of the second-stage cylinder 38. At the same time this first-stage cylinder 36 is drawing into its compression chamber a charge of gas from the evaporator.

During the next half revolution, both pistons move upwardly, but at this time the work shifts to the second-stage piston I09, which is required to push the gas out of the second-stage compression chamber of the cylinder 38 up through the valve I I8 into the disha'rgechamber against the pressure of the gas within the discharge chamber. In the meantime, the first-stage piston I2I6 is moving upwardly, forcing the gas from the compression chamber of the cylinder 38 into the'crank case. Since the pressure upon the crank case side of the piston is at all times greater or substantiallyequal to the pressure on the top of this first-stage piston, no appreciable amount of work will berequired to move the flrststage piston upwardly to its top dead-center position. Thus, during one-half of each revolution, substantially all the work is done by the first-stage piston: and during the second half of each revolution, substantially all the work is done by the second-stage piston.

In this operation the cylinder head I02 of the first-stage cylinder is kept substantially at the temperature of the gas from the evaporator which is drawn into it and through it. This is also true of the valve plate 90 and the upper portion of the cylinder 38. Howevr'erj because of the work done in compression, the fluid discharged from the compression chamber ofthe secondstage cylinder 38 is rather hot. This makes the cylinder head I of the second-stage cylinder as well as the valve plate II 6 and the upper end of the cylinder wall of the cylinder 38 rather.

warm. Normally, these cylinder heads and valve plates for both the stages have been made in one piece. This, however, permits "the warming of the gas coming into the first-stage by the hot gas which leaves the second stage. This superheats the incoming gas from the suction line, and thus raises the crank case pressure, resulting in increased power requirements to rotate the crankshaft. And in order to avoid this, I have provided a slot I26 and a passage I28 between the cylinder heads, the valve plates, and the upper portion of the cylinders of the responsive stages. If desired, for purposes of strength, these members may be connected together by one or more connections of low heat conducting structure. However, if the casting 34 is made sufficiently rigid, this is not necessary.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A two cylinder two stage pump including means forming cylinders and a crankcase communicating therewith, pistons within said cylinders, the first stage piston and cylinder being larger than that of the second stage, means for reciprocating said pistons in said cylinders in substantially the same direction toward the crankcase at substantially the same time, said pump being provided with fluid control means and passages to pump fluid first into the larger one of the cylinders, then discharging the fluid pumped into the crankcase, and then. conducting the fluid from the crankcase into the smaller of the cylinders, said crankcase having an efiective volume greater than the displacement of said piston. i

2. A two cylinder two stage pump including means forming first and second cylinders, piston means within said cylinders, the first stage piston and cylinder being larger than that of the second stage, one of said means being provided with fluid inlet control means for admitting fluid into the larger one of said cylinders, one of said means being provided with fluid outlet control means for said larger cylinder, one of said means being provided with fluid inlet control means for the smaller of said cylinders, one of said means being provided with fluid outlet control means for said smaller cylinder, the fluid outlet means of said larger cylinder communicating with the fluid inlet means of said smaller cylinder, and

means for reciprocating the piston means of said larger and said smaller cylinder in the same direction at substantially the same time, said cylin-. ders being parallel to each other and on the same side of said reciprocating means.

3. A two cylinder two stage pump including means forming cylinders, piston. means within said cylinders, the first stage piston and cylinder being larger than that of the second stage, one of said means being provided with fluid inlet control means for admitting fluid into the larger one of said cylinders, one of said means being provided with fluid outlet control means for said larger cylinder, one of said means being provided with fluid inlet control means for the smaller of said cylinders, one of said means being provided with fluid outlet control means for said smaller cylinder, a crankcase communicating with said cylinders, means for reciprocating the piston means of said larger and said smaller cylinder in substantially the same direction toward the crankcase at substantially the same time, the

fluid outlet control means ofsaid larger cylinder and said fluid inlet control means of said smaller cylinder being connected to the interior of said crankcase, the interior of said crankcase having a volume greater than the displacement of said piston means.

4. A two-stage compressor for compressible fluids comprising a primary compression means, and a secondary compression means, each consisting of a cylinder and a piston reciprocable therein, said primary compression means being of greater displacement than said secondary compression means, means for reciprocating said primary piston and said secondary piston in the same direction at the same time in parallel paths,

and a crankcase chamber between said primary and secondary compression means, said primary compression means compressing fluid into said Y crankcase chamber and said secondary compression means pumping the fluid out of said crankcase chamber, the fluid pressure in said crankcase chamber being maintained, at all times during the operation of the compressor, at a pressure substantially higher than the pressure at which the fluid is introduced into the primary compression means; said primary and secondary cylinder being located in parallel relation on the same side of the crankcase.

WILFORD H. 'ITEETER.

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