CA1156989A - Dual capacity compressor with reversible motor and controls arrangement therefor - Google Patents

Abstract

14 47,635B1 A B S T R A C T
DUAL-CAPACITY HERMETIC REFRIGERANT
COMPRESSOR WITH REVERSIBLE MOTOR
The invention relates to a dual-capacity her-metic refrigerant compressor of the reciprocating type, the capacity of which can be changed by reversing the crankshaft rotation.

Description

DUAL-CAPACITY ~ERMETIC ~EFRIGERAN~
COMPRESSOR WITH REVERSIBLE MOTOR
The invention relates to a dual-capacity refrig-erant compressor for air conditioning units and especially heat pumps.
Studies of heat pump economics have shown that, if a heat pump operating in a heating mode were capable of running efficiently at lower capacity on mild days and at higher capacity on cold days, definite economic advantages would be obtained. The problem is, however, that the compressor capacity of heat pumps operating in a heating mode decreases with falling temperatures because the latter cause the suction gas temperature and density to drop so that less refrigerant is fed to the compressor.
Thus, the compressor capacity actually is decreasing when, ideally, it should increase in order to compensate for the lower ambient by supplying more heat. Several ways of handling this problem have been proposed, among them the use of multispeed compressors, of compressors having multiple cylinders which are partially unloadable, and of compressors deliberately oversized to meet all heating needs anticipated (which results in rather poor economics, having regard to the moderate cooling needs experienced in northern regions and to the moderate heating demands to be satisfied on mild days).
From earlier patents it is further known that the output of a pump, or other apparatus employing a reciprocating member, can be changed by changing the eccen-tricity of the orbiting means driving the connecting rod ..~

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as~oclatecl with the reclprocating member. Thusg the prior art teache~ how such an ad~ustment of eccentrlcity ~an be effected by manually operatlng a gear or other means, whilst other prior ar-t provides ~or eccentricity changes -to be brought about by changlng the hydraulic pressure ln a lubricating system. Of course, it .~5 impractica~le to adjust ~he eccentr~c means in a hermeti~ally ~ealed com~
pressor from the outside of the hermetic compresæor shell.
As for the ~nown arran~ement relying upon hydraullc pressure 10 changes 9 it also has its drawbacks in~o~ar as it calls for hydraulic ~luid actuated mean~ to be mounted on ~the crankshaft and to ro~ate with itg and requlres the lubrication pre~ure to be varied by mean~ either o~ a m~nually ~perable pressure regulator or an a~tomatically operated pr~ssure re~ator controlled by the load on the com~ressor, whlch again would be undes~rable with respect to a hermetic system~
Likewise known are arrangements in which varia-ble stroke lengths are obtained through rever~als o~ the operating directlon o~ driving mean~ mu~ one particular piece of prlor art teache~ a dlrection sensltive linkage-lengthening arrangement particularly for use with vehicle-windshield wiper mechanlsms, wh~reas ~n the U.S. patent specification No. 3,4829458 lssued December 9, 1969 there is disclosed a dual stroke-length mechanism particularly applicable to reciprocating saw~ng machines ln whlch a pair o~ llnks associated with a rotating plate will give different stroke lengths depending up~n the rotating directlon of the plate. Neither o~ the~e arrangements w~uld be suitable ~or use i~ a he~metic re~rigerant compressor, particularly in view o.~ the considerable di~erence in magnitude between the forces required ln a compressor and those which linkages of these known types could handle.
It i~ the principal obJect Q~ the inven-tion to provide a her~etic refrig~rant compressor o~ the recipro-cating type ~ith relatively inexpensi~e yet durable means for automatically adjusting the effective piston-stroke length upon each reversal of crankshaft operation.
The invention accordingly resides in a dual-capacity hermetic refrigerant compressor comprising a rotatable ~rankshaft having a crankpln which is eccentric with respect to the crankshaft, a reversible motor for driving the crankshaft in either rotary direction, at least one cylinder having a piston therein connected to the crankshaft through a connecting rod having an end bearing encircling the crankpin, and piston stroke adjust-ing means for automatically changing the stroke length of the piston upon each directional reversal of crankshaft rotation, said piston-stroke adjusting means comprising an eccentric ring rotatably supported on said crankpin and journaled in said end bearing of the connecting rod, coupling means interposed between the crankpiIl and the eccentric ring in such manner as to cause the latter, during rotation of the crankshaft, to move together with the crankpin without any angular relative displacement occurring between the crankpin and the ring, said coupling means having a predetermined amount of play enabling a limited eccentricity-altering angular relative displace-ment to occur between the crankpin and the eccentric ring during an initial portion of crankshaft rotation following each directional reversal thereof, and means effective during said initial portion of crankshaft rotation to dampen impacts otherwise resulting when said predetermined amount of play is taken up.
In a preferred embodiment of the invention, the impact dampening means is an elastic member which serves also as part of the coupling means permitting the limited eccentricity-altering angular relative displacement to occur between the crankpin and the eccentrlc disc upon each reversal of crankshaft rotation. In another embodi-ment, impacts are dampened with the aid of a dashpoteffect. If desired, such dashpot effect may also be employed with the first-mentioned embodiment to assist the elastic member in dampening impacts.

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The preferred embodiment of the invention will now be described, by way of example, in detail with refer-ence to the accompanying drawings, in which:
Figure l is a side elevational and partly sec-tional view of a kind of hermetic refrigerant compressorto which the invention is applicable;
Fig. 2 is a detail sectional view, taken along line II-II in Fig. 1, of the preferred embodiment of the invention;
Fig. 3 is a fragmentary sectional view taken along line III-III of Fig. 2;
Fig. 4 is a diagrammatic view ill~strating the change in stroke length obtained with the mechanism of Figs. 2 and 3 when the motor drives the crankshaft in one direction and alternatively in the other;
Fig. 5 is a sectional view of another embodiment of the invention; and Fig. 6 is a fragmentary sectional view taken on line VI-VI of Fig. 5.
The invention is applicable to hermetic refrig-erant compressors having either a single cylinder or multiple cylinders, although its best application at present is thought to be with the latter type. The com-pressor shown in Fig. l is of a type similar tQ the one ,~ ssv~ 6G
described in U.S. patent specification 3,259,307-~to which reference may be had for a more detailed description.
Briefly, with reference to Fig. l, the refrigerant com-pressor illustrated therein comprises a generally cylin-drical, hermetically sealed shell lO having an inlet 12 through which suction gas refrigerant is admitted to the shell, and one or more discharge tubes 14 through which the compressed gas exits from the shell. The upper part of the shell houses a reversible electric motor 16, the rotor 18 of which is fixed to the upper end of the crank-shaft20.
The compressor is shown as having two cylinders 22 containing pistons 24 which are connected to the crank-pin portion of the crankshaft 20 through connecting rods26.
The lower end portion of the crankshaft 28 includes lubricant inlet means 30 for admitt.ing oil from a sump 32 into a passage 34 extending axially through the crankshaft and carrying oil to the crankshaft bearings, as known.
Referring now to Figs. 2 and 3, the dash-llne circle 36 (Fig. 2) indicates the location of the part of the crankshaft 28 which is journaled in the main bearings while the solid-line circle 38 shows the location of the crankpin which is eccentric with respect to said part of the crankshaft, the centerlines of the crankshaft and of the crankpin being indicated at 36a and 38a, respectively.
An eccentric ring 40, which derives its eccentricity from its progressively varying wall thickness, is rotatably mounted on the crankpin 38, the riny consisting of two sections 40a and 40b which are held together along the lines 42 by the encl bearing 26a of the crankshaft 26, in which end bearing the eccentric ring 40 is journaled. The end bearing 26a likewise is composed of two sections bolted together.
With the arrangement as just described, it will be appreciated that an angular relative displacement of the eccentric ring 40 and the crankpin 38 with respect to one another will result in a change of the total eccen-tricity affecting the stroke length of the connecting rod 26 and, hence, of the piston 24. As shown in the draw-ings, the degree of such relative displacement is limited, the means for limiting it comprising, in the emhodiment of Figs. 2 and 3, a cylindrical key 44 movably disposed in a space which is defined, between the crankpin 38 and the ~ccentric ring 40, by a relieved area 46 extending along an arcuate portion of the outer circumference of the crankpin, and a relieved area 48 extending along an arcu~
ate portion of the inner circumference of the eccentric ring. The depth of each of the two relieved areas corre-sponds substantially to half the diameter of the key 44or, in other words, the diameter of the latter exceeds the depth of either relieved area 46 or 48 so that any angular relative displacement occurring between the crankpin 38 and the eccentric ring 40 upon initial rotation of the crankshaft in either direction will be terminated due to engagement of the key 44 with one of the opposite end surfaces of the two relieved areas 48, continued crank-shaft rotation in the same direction thereafter causing the eccentric ring 40 to be carried along without any further angular relative displacement occurring between it and the crankpin 38. Thus, the key 44 and the end sur-faces of the relieved areas 46, 48 in effect form coupling means having a predetermined amount of play which enables a limited, eccentricity-altering angular relative dis placement to occur between the crankpin and the eccentric ring during an initial portion of crankshaft rotation following each directional reversal thereof, the coupling means after such limited relative displacement forcing the eccentric ring to move with the crankpin without any further relative displacement occurring therebetween.
Referring now to Fig. 4, there is shown therein the manner in which angular relative displacements of the eccentric ring 40 and the crankpin 38 with respect to each other will change the stroke length of the piston 24. In Fig. 4A, the crankpin and eccentric ring are shown in a top dead-center position, and with the crankpin moving clockwise as indicated by the arrow. Fig. 4B shows the same parts in a bottom dead~center position and still moving clockwise. The dash-line projections 50 toward the center of the drawing indicate the maximum stroke length achieved upon clockwise rotation of the cranXshaft to-gether with its crankpin 38.
If the compressor is stopped and is then re-started and driven in the opposite direction by the re-versible electric motor 16, the crankpin 38 will first turn within the eccentric ring 40 counterclockwise until the key 44 reaches and engayes the opposite end surface or shoulder of the relieved area 48 of the ring 40, as shown in Fig. 4C, and, upon further counterclockwise rotation, drives the eccentric ring 40 along to move together with the crankpin 38, as indicated in Fi~. 4D. It can be seen from Fig. 4 that this directional reversal of crankshaft rotation and the consequential angular relatlve displace~
ment between the crankpin and the eccentric ring have resulted in a reduction of the stroke length. A subse-quent reversal of the crankshaft rotation will increasethe stroke length again, as shown in the left-hand portion of Fig. 4.
In the embodiment illustrated in Figs. 5 and 6, a key 60 is fixed to the crankpin 62 and projects radially therefrom into a recess 66 which, extending through a predetermined angle, is formed in the inner circumference of the eccentric ring 64 and, together with a portion of the outer circumference of the crankpin 62, defines an arcuate space in which the projecting portion of the key is movable. It is conceivable that the arrangement could be reversed in the sense of providing a recess similar to recess 66 in the outer circumference of the crankpin 62, and affixing a k0y similar to the key 60 to the eccentric ring 64 so that a portion of the key would extend radially from the inner circumference of the ring and into the recess of the crankpin.
In order to minimi~e wear and tear resulting from impacts occurring when the play in the coupling means between the crankpin and the eccentric ring is taken up, provision is made for dampening such impacts. In the embodiment according to Figs. 5 and 6, the means for dampening impacts comprises passageways 68 formecl in the crankpin 62 and extending from the previously mentioned lubricant supply passage 34 radially in opposite direc-tions to the outer peripheral surface of the crankpin.Another passageway 70 formed in the eccentric ring 64 is provided to permit lubricant to flow from the arcuate 3~

space 66 to the bearing surfaces between the eccentric ring and the end bearing of the connecting rod 26. The passageways 68 and 70 are arranged iII such manner as to place the arcuate space 66 in 1uid-flow communication with the l~bricant supply and with said bearing surfaces throughout rotation of the crankshaft, yet to impede lubricant flow from the arcuate space 66 during an initial portion of crankshaft rotation immediately following a directional reversal of the latter, thereby providing an impact dampening dashpot effect in the following manner.
Supposing the compressor was stopped, with the key 60 positioned as shown in Fig. 5, and is now restarted with the shat rotating in the clockwise direction. As the crankpin begins to rotate clockwise within the still stationary eccentric ring, the key 60 will push oil in the arcuate space 66 ahead of it and out through the passage-way 70 as well as into the oil passage 68. When the key has moved past the passageway 70 and the passageway in the crankpin has moved out of registry with the space 66, any oil remaining in the latter ahead of the key 60 can escape only through normal clearances in the assembly, thus encountering a high flow resistance which produces the above-mentioned dashpot effect. When all of the oil ahead - of the key 60 has been slowly forced from the space 66 through these clearances, the key will have reached the opposite end of the space 66 and have gently engaged the adjacent end surface of the recess in the eccentric ring.
At the same time, the opposite end of the passageway 68 will have come into registry with the space 66, thus reestablishing normal lubricant flow from the passage 34 into the space 66. When the compressor is stopped again and restarted in the opposite direction, the same sequence will occur in reverse.
In the embodiment illustrated in Figs. 2 and 3, impact dampening is achievd by means of the key 44 which is so constructed as to have a sufficient degree of elas-ticity to absorb impact forces. Thus, the key 44, as t~
g shown, is in the form of a spiral spring which will effec-tively cushion impacts due to the play in the coupling means between the crankpin 38 and the eccentric ring 40 being taken up. It is conceivable that a key consisting of a cylindrical me~nber made of a suitable elastomer which is sufficiently heat resistant, strong and elastic might be employed instead of a spiral spring.
If desired, the crankpin 38 and the eccentric rinq 40 of the embodiment illustrated in Figs. 2 and 3 may be provided, as indicated in the latter, with passageways 68a and 70a, respectively, enabling a dashpot effect to be obtained in a simi'ar manner as described above. Such dashpot effect, whilst probably not required in most instances in which the embodiment utilizing the elastic key 44 is employed, would assist the latter in dampening impacts.
As mentioned hereinbefore, the invention is applicable to both single-cylinder and multiple-cylinder types of compressors, the compressor to which it is shown applied herein having two cylinders. ~eferring in this connection to Figs. 3 and 6, it will be seen therefrom that the arrangement embodying the inventio~ is readily adaptable for use with multiple cylinders by using a crankpin and eccentric ring having axial dimensions suffi-cient to accommodate the end bearings of all connecting rods side-by-side in axial alignment with each other.
With this arrangement, the single ring 40 or 64 serves to adjust the stroke length of all connecting rods 26 simul-taneously.
It will be appreciated that the degree of stroke reduction may vary from case to case, depending upon the degree of eccentricity of the eccentric ring selected for use. An example would be a stroke reduction of, say, about 30%. With a high-capacity stroke length of unity, and with a clearance ratio of, say, 5%, this 30% stroke reduction, when effected by reversing the operating direc-tion of the compressor, will result in a new clearance ratio of 28.6%:~r the redtlced ~troke length. It will be appreciated and is apparent ~rom Flg~ 4 that with the arrangement as sho~, the reductio~ o~ the stroke length occurs both a-t the top dead-center position and~e bottom dead-center po~ltlonO
A contrcl arrangement particularly suitable for use in controlling and revers~ng a her~etic re~rigerant compres~or ~ach as de~cribed herein, e~peclally when employeà wlth heat pump~ di~clo~ed and claimed in Applic~nt's copending Canadian applicatiQn No. 363Jo63 filed October 23, 1980.

Claims (3)

What is claimed is:

1. In a dual capacity hermetic refrigerant com-pressor of the reciprocating piston type:
a rotary crankshaft having an eccentric crankpin rotating therewith;
an eccentric ring having an inner and outer circum-ference mounted on said crankpin and rotatable relative thereto;
a connecting rod having a strap end encompassing the outer circumference of said eccentric ring in rotatable relation and its other end connected to reciprocate a piston in a cylinder as the crankshaft rotates;
means limiting the rotation of said ring relative to said crankpin between one end point and an opposite angularly displaced end point, said ring at said one-end point adding the maximum eccentricity of said ring to the eccentricity of said crankpin, said ring at said opposite end point adding only a part of the maximum eccentricity of said ring to the eccentricity of said crankpin, so that with said ring at said the end point the stroke length of said rod is at a maximum and at said other end point the stroke length is reduced therefrom;
reversible motor means for rotating said crankshaft, said motor operating in one direction effecting the angular displacement of said ring relative to said crankpin to said one end point, and in the opposite direction effecting the angular displacement of said ring relative to said pin to said opposite end point;
said rotation limiting means comprises key means located at the interface of said ring inner circumference and the crankpin outer circumference; and said crankpin includes a relieved area along an arcuate portion of its circumference, and said ring in-cludes a relieved area along an arcuate portion of its inner circumference, and said key means is interposed in the space between said relieved areas.

2. In a dual capacity hermetic refrigerant com-pressor of the reciprocating piston type:
a rotary crankshaft having an eccentric crankpin rotating therewith;
an eccentric ring having an inner and outer cir-cumference mounted on said crankpin and rotatable relative thereto;
a connecting rod having a strap end encompassing the outer circumference of said eccentric ring in rotatable relation and its other end connected to reciprocate a piston in a cylinder as the crankshaft rotates;
means limiting the rotation of said ring relative to said crankpin between one end point and an opposite angularly displaced end point, said ring at said one end point adding the maximum eccentricity of said ring to the eccentricity of said crankpin, said ring at said opposite end point adding only a part of the maximum eccentricity of said ring to the eccentricity of said crankpin, so that with said ring at said one end point the stroke length of said rod is at a maximum and at said other end point the stroke length is reduced therefrom;
reversible motor means for rotating said crankshaft, said motor operating in one direction effecting the angular displacement of said ring relative to said crankpin to said one end point, and in the opposite direction effecting the angular displacement of said ring relative to said pin to said opposite end point;
said crankpin and said eccentric ring both have an axial extent adequate to accommodate the strap ends of two connecting rods in side-by-side relation; and said compressor includes a second connecting rod in opposed relation to the first and having its strap end encompassing said eccentric ring in rotatable relation therewith adjacent the strap end of the first connecting rod.

3. In a dual capacity hermetic refrigerant com-pressor of the reciprocating piston type:
a rotary crankshaft having an eccentric crankpin rotating therewith;
an eccentric ring with an inner and outer cicum-ference mounted on said crankpin and rotatable relative thereto;
a connecting rod having one end encompassing the outer circumference of said eccentric ring in rotatable relation and its other end connected to reciprocate a piston in a cylinder as the crankshaft rotates;
said ring and said crankpin including means forming an arcuate shaped chamber through a predetermined angle at the interface area of said ring and said crankpin, said chamber having one end point and an opposite end point;
means carried by said crankpin and movable through the circumferential extent of said chamber between the one and opposite end points to limit rotation of said ring relative to said crankpin;
said crankpin including lubricant passage means disposed to place said chamber in communication with a lubricant supply in both end point positions and to reduce the communication through at least a part of the movement of said means carried by said crankpin through the chamber to provide a dash pot effect throughout at least a part of said movement in both directions of said means carried by said crankpin; and reversible motor means for rotating said crankshaft, said motor operating in one direction effecting movement of said means carried by said crankpin through said chamber to said one end point and in the opposite direction effecting movement of said means carried by said crankpin to said opposite end point in said chamber, said chamber and said means carried by said crankpin being disposed relative to the eccentricity of said ring and said crankpin to provide different degrees of total eccentricity of said ring and crankpin at said one and said opposite end positions of said means carried by said crankpin.