CA1309698C

CA1309698C - Variable capacity compressor

Info

Publication number: CA1309698C
Application number: CA000559240A
Authority: CA
Inventors: Teruo Maruyama; Yoshikazu Abe; Tatuhisa Taguti
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1987-02-20
Filing date: 1988-02-18
Publication date: 1992-11-03
Anticipated expiration: 2009-11-03
Also published as: JPS63205479A; JPH0833158B2; US4815944A

Abstract

ABSTRACT OF THE DISCLOSURE

In a variable capacity compressor having a capacity control mechanism so as to keep the suction pressure of the compressor constant by detecting the suction pressure, plural return ports, a return passage and an exit are provided for bypassing refrigerant gas from a volume-decrease-step space in a cylinder compartment to a volume-increase-step space. A guide passage wherein a slider slides by the pressure of the refrigerant gas is provided for controlling the amount of bypassing gas, whereby it is possible to control capacity correctly and stably.

Description

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TITLE OF THE INVENTION
Variable capacity compressor FIELD OF THE INVENTION AND REL~TED ART STATEMEN~
1. FIELD OF THE INVENTION
The present invention relates to a compressor which is applicable, for instance, to an air conditioner for a car, and more particularly relates to an improvement in a variable capacity compressor.

2. DESCRIPTION OF THE PRIOR ART
Recent ~mprovements in compressors for use in motor vehicle air conditioners have included the development of a varlable capacity compressor for enabling power saving and improved comfort. In 1986, a rotary type compressor, which is superior to a reciprocating type compressor in respect of compactness and silence and which has the possibility of controlling capacity by providing a by-pass cylinder, was put on the market by Nippon denso Co., Ltd. Such a control system is described in more detail below, but may be summarized as requiring a spool valve which reciprocates linearly in a cylinder. For reasons explained fully below, the linear travel of the valve imposes limits upon the variable capacity range of the compressor.
Also, there is a tendency for refrigerant leakage past the valve when a large cooling capacity is required - i.e. during maximum-capacity driving.
Finally, this arrangement requires the use of a spring which is frequently expanded and contracting during operation and thereby is susceptible to metal fatigue over the course of time.

OBJECT AND SUMMARY OF THE IMVENTION
The ob~ect of the present invention is to provide a variable capacity rotary compressor which is capable of having a wide variable capacity range and stable characteristics for correctly controlling capacity.
The variable capacity compressor in accordance with the present invention comprises:
a rotor;
an enclosure containing the rotor rotatably therein and having a cylinder compartment wherein a volume sectioned by the rotor is changed cyclically by rotation of the rotor, a plurality of return ports formed on a :

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wall of volume-decrease-step space in the cylinder compartment, a return passage which connects to the cylinder compartment through the return ports, an exit formed on the wall of volume-increase-step space in the cylinder compartment for connecting the return passage with the cylinder compartment, and a guide passage which has a first orifice for leading control pressure on an end thereof, a second orifice for leading high pressure on the other end thereof, a third orifice for leading suction pressure on an intermediate part thereof and an aperture for connection to the return passage;
a slider which slides gas-tightly in the guide passage with a first compartment for leading the control pressure and a second compartment for leading the high pressure remaining ln both end parts of the guide passage and has a cut-ofE part thereon for making a narrow passage connecting the second compartment to the third orifice with a variable fluid friction between the slider and the guide passage and has an aperture thereon for opening the return port; and a pressure control means for adjustably supplying the control pressure to the first compartment.
The above-mentioned variable capacity compressor has the advantage that the second compartment operates like a spring, but has no change in the characteristics of expansion and contraction after a long period of use thereof. Therefore, it is possible to control the capacity correctly and stably without any change in characteristics for a long service time.
The invention will hereinafter be described further and by way of example only, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF TaE DRAWINGS
FIG. 1 is a cross-sectional view showing one embodiment of a variable capacity compressor according to the present invention.
FIG. 2 is a cross-sectional view taken on line II-II in FIG.l FIG. 3 is a schematic illustration showing the control mechanism of an embodiment of a variable capacity compressor of the present invention.
FIG. 4 is a graph showing the relationship between pressure P2 and angle 0 of a slider in accordance with the present invention.
FIG. 5 is a basic structural view of a conventional variable capacity compressor.
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1 3~n?6q~3 DETAILED DESCRIPTION OF THE PRIOR ART
Referring to FIG. 5, a spool valve 42, which is cylindrical and is slidably disposed inside an enclosure 40 having a cylindrical inner wall 41 therein, is urged by a sprlng 43 in a direction exposing two by-pass holes 44, which are provided in the enclosure 40 and connected to a high pressure compartment of a cylinder (not shown). Refrigerant ~as is fed to the cylinder from a suction compartment 45, which is provided ad~acent and connected to the enclosure 40. The gas exhausted from the cylinder enters the enclosure 40 through the by-pass holes 44 and returns to the suction compartment 45. A pressure control compartment 46 is located above the spool valve 42 and has a pressure applied thereto which is close to the exhaust pressure 50 of the cylinder. The pressure in compartment 46 is adjusted by automatically controlled opening of a valve 48 in a pressure regulator 47 by means of the pre~sure difference between the pressure of the suction compartment 45 and the atmospheric pressure 49, so as to keep the pressure of the suction compartment 45 constant. Thus, opening of the by-pass holes 44 is automatically adjusted, hence to control the amount of outflow of the gas into the suction compartment 45.
The above-mentioned conventional variable capacity compressor has the following shortcomings.
Firstly, in the above-mentioned structure, since the spool valve 42 reciprocates in a straight line, freedom of arrangement of the by-pass holes 44 around a cylinder or a cylindrical compartment having circular cross-section and cross-sectional area of the passages of the bypass holes 44 are restricted. In fact, the variable capacity range of the compressor of this type is not sufficiently wide (i.e. it is about 50--100 percent of the cooling capacity).
Secondly, when a large cooling capacity is required, the spool valve 42 is pushed with a high pressure, and the by-pass holes 44 are thereby closed. In such a state, since the pressure regulator 47 always applies a high pressure, which is close to the exhaust pressure, to the pressure control compartment 46, the gas is likely to leak to the suction compartment 45 past the circumference of the spool valve 42. Thereby the cooling capacity is decreased.
Thirdly, since the spring 43 is frequently and repeatedly required to expand and contract, the spring 43 develops metal fatigue after a long . J
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period of use. As a result, the performance of the spring 43 deteriorates, whereby it becomes impossible to control the spool valve 42 correctly.

DESCRIPTION OF ~ PREF~RRED ENBODI~NT
Referring now to FIGS. 1-4, a preferred embodiment of the invention will be described. In FIG. 1, a shaft 1 is held by needle-roller bearings 4 which are provided in a front plate 2 and a rear plate 3. A rotor 6 which is sweated on the shaft 1 rotates in a direction shown by an arrow 35 (FIG.
2) within a cylinder 5. A first intermediate plate 7 having an arcuate guide passage 8 (FIGS. 1, 2) therein and a second intermediate plate 9 10 having an arcuate return passage 10 are located between the cylinder 5 and the front plate 2. In FIG. 2, vanes 12 are slidably located in a plurality of slits 6a which are formed in the rotor 6. A cylinder-head cover 13 has a suction compartment 16 and an exhaust compartment 17 therein for respective connection to a suction inlet 14 and an exhaust outlet 15, which are formed 15 in the cylinder 5. Plural return ports 18 are formed in the first intermediate plate 7 so as to connect to the guide passage 8 a volume-decrease-step space, which is a space sectioned by the vanes 12 in a compartment 5a within cylinder 5 and which is decreased in volume by rotation of the rotor 6. As shown in FIG. 2, the return ports 18 are 20 disposed in an arcuate array such that the diameters thereof decrease one by one in the rotating direction 35 of the rotor 6. The compression ratio increases with rotation of the rotor 6, and thereby the amount of re-expansion of the high pressure refrigerant gas increases. Therefore, the arrangement described above is desirable in its ability to obtain high 25 cooling efficiency for the compressor. An exit 19 is formed through the first intermediate plate 7 and the second intermediate plate 9 so as to connect the return passage 10 formed in the second intermediate plate 9 with a volume-increase-step space of the cylinder compartment 5a. A slider 20 is provided slidably and gas-tightly in the guide passage 8. The slider 20 has 30 a surface which covers the return ports 18 for closing them and an arcuate aperture 21 formed in that surface for exposing the return ports 18 and providing a through-path thereto. The arcuate aperture 21 is connected to the return passage 10 through a passage 22 formed in the slider 20 and a vent 23 formed in the second intermediate plate 9. The passage 22 and the vent 23 are so formed as to communicate with each other at any position of ~ ,, ,`i . .
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the slider in the guide passage 8. When the slider 20 is positioned at the counter-rotating-directional end of the rotor 6 (namely the clockwise end of FIG. 2) in the guide passage 8, all of the return ports 18 are closed by the slider 20. When the slider 20 is positioned at the rotating-directional end S of the rotor 6 (namely the anticlockwise end of FIG. 2) in the guide passage8, all of the return ports 18 are open by virtue of the aperture 21 of the slider 20. In the guide passage 8, a first pressure compartment 24 is formed between the clockwise end of the guide passage 8 and the slider 20, and a second pressure compartment 25 is formed between the anticlockwise end of the guide passage 8 and the slider 20. As shown in FIG. 3, control pressure is applied to the first pressure compartment 24 from a pressure controller 30 via a pressure lead-in pipe 26. Further, high pressure PH is applied to the second pressure compartment 25 from a high pressure lead-in orifice 27. A suction pressure lead~in orifice 28 is provided at a mid-point region of an external circumference of the guide passage 8, and a variable-length passage 29, which connects the suction pressure lead-~n orifice 28 to the second pressure compartment 25 with a very small cross-sectional area thereof, is formed between a circumference of a cut-off part 20a of the slider 20 and the guide passage 8. When the slider 20 moves in the guide passage 8, the effective length of the variable-length passage 29 varies between the second pressure compartment 25 and the suction pressure lead-in orifice 28, thereby to vary the fluid friction RX which is determined by the effectlve length of the passage 29. The pressure controller 30 comprises a bellows 31, a valve spring 34, a valve 35, a valve seat 36 and a rod 32 which is fixed to the bellows 31. The bellows 31 expands/shrinks according to the differential between the suction pressure PS and the atmospheric pressure Po, and thereby the rod 32 pushes/releases the valve 35 which is energized to open or close relative to the valve seat 36. Control pressure which is applied by the exhaust of the pressure controller 30 is led to the first pressure compartment 24 through the pressure lead-in pipe 26.
The, operation of the above-mentioned variable capacity compressor will now be described.
The air conditioner (not shown) of the car has a compressor which is generally rotated by the engine via a belt or the like means. Therefore, when temperatures outside/inside the car are kept constant, the cooling 1 3"qS9~

capacity and input characteristic of the air conditioner having a fixed displacement compressor shows a tendency that the suction pressure gradually decreases and the cooling capacity gradually increases with increase of rotation speed of the compressor. The load upon the engine increases substantially in proportion to the rotation speed of the compressor.
Therefore, the capacity coefficient showing efficiency of cooling capacity relative to the power consumption of the engine decreases with increase of the rotation speed. This embodiment of the invention keeps the suction pressure from dropping below a predetermined value irrespective of increase of the rotation speed above a predetermined value, thereby to restrain increase of the cooling capacity and consequent power consumption.
In the first pressure compartment 24, the control pressure Pl is supplied from the pressure controller 30 via the pressure lead-in pipe 26.
In the second pressure compartment 25, the high pressure PH is supplied from the high pressure lead-in orifice 27 with a fluid friction R2 and the suction pressure PS is led through the variable-length passage 29 which has an effective length responding to the position of the slider 20. The slider 20 comes to a stop at a position where the pressure Pl of the first pressure compartment 24 becomes equal to the pressure P2 of the second pressure compartment 25. When the rotation speed of the compressor i9 not too high, the pressure P1 is low and nearly equal to the suction pressure Ps. At that time, the slider 20 comes to the stable position where the capacity of the first pressure compartment 24 is at a minimum and that of the second pressure compartment 25 is at a maximum, thereby to decrease the pressure P2 to be nearly equal to the suction pressure Ps. Such position is shown by a maximum angle of a (75 in FIG. 4) in FIG. 3. In this state, the aperture 21 of the slider 20 does not uncover any of the return ports 18, and the return ports 18 are therefore closed by the slider 20. After that, in the pressure controller 30, when the suction pressure PS decreases below a predetermined value by increase of the rotation speed, the bellows 31 expands, and the rod 32 pushes the valve 35 against the valve spring 34, so that a gap 33 is created between the valve 35 and the valve seat 36. Then, the high pressure PH is applied through the gap 33, and thereby the control pressure increases. As a result, the pressure Pl in the first pressure compartment 24 increases, so that the slider 20 moves in the rotating direction of the rotor 6 (anticlockwise in FIG. 3) against the pressure P2 -`-, ' , :

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in the second pressure compartment 25. Then, the effective length of the variable length passage 29 is increased, hence increasing the fluid friction Rx, and thereby the pressure P2 in the second pressure compartment 25 increases. Again, the slider 20 reaches a stable position where the pressure Pl becomes equal to the pressure P2. In that position, some return ports 18 are opened by the aperture 21, and high pressure refrigerant gas then bypasses through the return ports 18, the aperture 21, the passage 22, the vent 23, the return passage 10 and the exit 19 in this order, and returns to the volume-increase-step space of the cylinder compartment 5a.
Thus, the amount of the gas which is exhausted from the compressor decreases as a result of the bypassing through the exit 19, and thereby the pressure balance between the suction pressure PS and the exhaust pressure in the refrigeration cycle is changed, and hence the suction pressure Ps increases. When the suction pressure increases over the predetermined value, the gap 33 between the valve 35 and the valve seat 36 is made small, and thereby the control pressure Pl in the first pressure compartment 24 decreases. Thereby, the slider 20 slides clockwise under the pressure P2 in the second pressure compartment 25. The above-mentioned operation of the slider 20 is repeated until the suction pressure PS becomes equal to the predetermined value, and the slider 20 reaches a stable position, though negligibly slight ~luctuations may arise.
As shown in FIG. 4, the relationship between the pressure P2 of the second pressure compartment 24 and the angle 0 (FIG. 3) between the anticlockwise end of the guide passage 8 and the anticlockwise end of the slider 20 is linear and follows a gradient determined by the fluid frictions R2 (FIG. 3) and RX (FIG. 3). In FIG. 3, a compression spring (not shown) having an equivalent characteristic to that shown in FIG. 4 could be used in the second pressure compartment 25 instead of leading the high pressure PH.
However, in such a case, friction would occur between the spring and the inner wall of the second pressure compartment 25 caused by contact between the spring and the wall under the pressure of the spring. Thereby, the spring would develop a hysteresis, thereby resulting in such an undesirable state that the slider 20 could not be controlled correctly. Moreover, there would be the problem that the characteristic of the spring would change by abrasion and metal fatigue thereof. Using the second pressure compartment in place of a spring eliminates problems induced by the above-mentioned hysteresis and the change of spring characteristic.

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In the above-mentioned embodiment, since the slider 20 slides in the arcuate guide passage 8, the operational range of the return ports 18 and the cross-sectional area of the return ports 18 can be made wide, and thereby the range of variable capacity can be made wide in comparison with the conventional linear guide passage wherein the slider reciprocates in a straight line. For instance, a variable range of capacity from 15 to lO0 percent may be realized according to this invention.
Further, since the pressure Pl of the first pressure compartment 24 and the pressure P2 of the second pressure compartment 25 are both low at the maximum-capacity driving time when all of the return ports 18 are closed by the slider 20, leakage of the gas is avoidable. Therefore, high efficiency of the compressor can be maintained.
In the above-mentioned embodiment, though the variable capacity compressor having the arcuate guide passage 8 and the slider 20 is shown, it is also possible to apply this invention to the type of variable capacity compressor wherein the slider reciprocates in a straight line.
Although the above-mentioned embodiments of the present invention are for a rotary compressor of sliding vane type, the present invention is also applicable to a compressor of elliptical cylinder type and to throughslot vane type compressors, and the application can be expanded to rolling piston type compressors and scroll type compressors.
Uhlle specific embodiments of the invention have been illustrated and described herein, it is realized that other modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all modifications and changes as fall within the true spirit and scope of the invention.

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Claims

1. A variable capacity compressor comprising:
a rotor;
an enclosure containing said rotor rotatably therein and having a cylinder compartment wherein a volume sectioned by said rotor is changed cyclically by rotation of said rotor, a plurality of return ports formed on a wall of volume-decrease-step space in said cylinder compartment, a return passage which connects to said cylinder compartment through said return ports, an exit formed in said wall of volume-increase-step space in said cylinder compartment for connecting said return passage with said cylinder compartment, and a guide passage which has a first orifice for leading control pressure on an end thereof, a second orifice for leading high pressure on the other end thereof, a third orifice for leading suction pressure on an intermediate part thereof and an aperture for connection to said return passage;
a slider which slides gas-tightly in said guide passage with a first compartment for leading said control pressure and a second compartment for leading said high pressure remaining in both end parts of said guide passage and has a cut-off part thereon for making a narrow passage connecting said second compartment to said third orifice with a variable fluid friction between the slider and said guide passage and has an aperture thereon for opening said return ports; and a pressure control means for adjustably supplying said control pressure to said first compartment.

2. A variable capacity compressor in accordance with claim 1, wherein said return passage connects to said return port through an inner space of said slider and said aperture of the guide passage.

3. A variable capacity compressor in accordance with claim 1, wherein said guide passage is disposed between said return passage and said cylinder compartment.

4. A variable capacity compressor in accordance with claim 1, wherein pressures in said first and second compartments are substantially equal to said suction pressure in maximum-capacity driving.

5. A variable capacity compressor comprising:
a rotor;
an enclosure containing said rotor rotatably therein and having a cylinder compartment wherein a volume sectioned by said rotor is changed cyclically by rotation of said rotor, a plurality of return ports formed on a wall of volume-decrease-step space in said cylinder compartment, an arcuate return passage which connects to said cylinder compartment through said return port, an exit formed on said wall of volume-increase-step space in said cylinder compartment for connecting said return passage with said cylinder compartment, and an arcuate guide passage which has a first orifice for leading control pressure on an end thereof, a second orifice for leading high pressure on the other end thereof, a third orifice for leading suction pressure on an intermediate part thereof and an aperture for connection to said return passage;
an arcuate slider which slides gas-tightly in the guide passage with a first compartment for leading said control pressure and a second compartment for leading said high pressure remaining in both end parts of said guide passage and has a cut-off part thereon for making a narrow passage connecting said second compartment to said third orifice with a variable fluid friction between the slider and said guide passage and has an aperture thereon for opening said return port; and a pressure control means for adjustably supplying said control pressure to said first compartment.

6. A variable capacity compressor in accordance with claim 5, wherein said return passage connects to said return port through an inner space of said slider and said aperture of the guide passage.

7. A variable capacity compressor in accordance with claim 5, wherein said guide passage is disposed between said return passage and said cylinder compartment.

8. A variable capacity compressor in accordance with claim 5, wherein pressures in said first and second compartments are substantially equal to said suction pressure in maximum-capacity driving.

9. A variable capacity compressor in accordance with claim 5, wherein said return ports are gradually made smaller one by one in a rotating direction of said rotor.