REFRIGERANT CIRCUIT WITH PASSAGAWAY CONTROL MECHANISM

Abstract: A refrigerant circuit with passageway control mechanism is disclosed which includes a compressor (1), a condenser (2), and an evaporator (5) connected to each other in series. The passageway control mechanism (26) is disposed between an inlet side of the evaporator (5) and an inlet side of compressor (1) and operates to change an opening area of a passageway therebetween responsive to pressure difference between high and low pressure within compressor (1). Therefore, torque shock is prevented from occuring at start of driving of compressor (1).

Description: This invention relates to a refrigerant circuit with a passageway control mechanism for use in an air conditioning system according to the precharacterizing part of claim 1. A refrigerant circuit for use in an air conditioning system is generally well known which includes a compressor, a condenser, an orifice, an evaporator and an accumulator, which is called an orifice type. Also, another type refrigerant circuit, which is called an expansion valve type is well known which includes a compressor, a condenser, a receiver dryer, an expansion valve and an evaporator. In a refrigerant circuit for use in an air conditioning system as mentioned above, start of the compressor in condition of which the gas pressure at an inlet side equals the gas pressure at an outlet side causes increase of drive torque for the compressor as the compressor carries out a large volume of refrigerant gas from the inlet side to the outlet side in a short time and thereby causing reduction of rotation frequency of a drive source. For instance, in the refrigerant circuit for an automotive air conditioning system, reduction of rotaion frequency of an automotive engine may cause torque shock. Furthermore, in a refrigerant circuit including a compressor with a variable capacity mechanism for controlling suction pressure uniformly, pressure loss increases with increase of passageway resistance between an outlet of an evaporator and an inlet of the compressor in accordance with increase of flow rate of refrigerant. Accordingly, refrigerant pressure at the outlet of the evaporator increases responsive to increase of the pressure loss, thereby increasing temperature of air which is passed through the evaporator, and reducing the air conditioning capacity thereto. Thus, comfortableness for passengers is made worse. The above compressor maintains suction pressure to be uniform, and thereby temperature of air which is passed through the evaporator also is maintained fixed. As a result, temperature of air which is passed though the evaporator can not be relevantly controlled from the outside in accordance with variation of the circumstance for the automobile or desire of the passengers. To cope with the above indicated problems, Patent Abstracts of Japan JP 57-159980 disclose passageway control means between the outlet of the evaporator and the inlet of the compressor to control the opening of said passageway as a function of the pressure difference between suction chamber and discharge chamber. It is a primary object of this invention to provide a refrigerant circuit with such passageway control mechanism which prevents said torque shock at the start of driving of the compressor by a simple device. It is another object of this invention to provide a refrigerant circuit with a passageway control mechanism which can prevent variation of the temperature of air passed through the evaporator in accordance with changes of flow rate of refrigerant. It is a further object of this invention to provide a refrigerant circuit with a passageway control mechanism which can adjust the temperature of air passed through the evaporator by controlling the pressure of refrigerant at the outlet of the evaporator. A refrigerant circuit with passageway control mechanism according to the present invention is indicated in claim 1. Further aspects of this invention will be better understood from the detailed description of embodiments of this invention with reference to the annexed drawings. Figure 1 is a schematic view of a refrigerant circuit with a passageway control mechanism in accordance with one embodiment of this invention. Figure 2 is a cross-sectional view of a wobble plate type compressor with a variable displacement mechanism provided with a passageway control mechanism in accordance with one embodiment of this invention. Figure 3 is a cross-sectional view of a passageway control mechanism according to one embodiment of this invention. Figure 4 is a cross-sectional view illustrating operation of the compressor as shown in Figure 2. Figure 5 is a graph illustrating the relationship between discharge pressure and flow volume of refrigerant. Figure 6 is a graph illustrating the relationship between an operating area of a passageway and pressure difference between high and low pressure sides in a refrigerant circuit. Figure 7 is a graph illustrating the relationship between drive torque and time on driving of a compressor. Figure 8 (a) is a graph illustrating the relationship between pressure and flow volume of refrigerant. Figure 8 (b) is a graph illustrating the relationship between pressure and flow volume of refrigerant. Figure 9 is a graph illustrating the relationship between pressure and flow volume of refrigerant. Figure 10 is a cross-sectional view of a passageway control mechanism in accordance with another embodiment of this invention. Figure 11 is a cross-sectional view of a passageway control mechanism in accordance with the other embodiment of this invention. Referring to Figure 1, there is shown a block diaphram for a refrigerant circuit. The refrigerant circuit comprises compressor 1 with a variable displacement mechanism, condenser 2, receiver dryer 3, expansion valve 4, evaporator 5 and passageway control mechanism 26 which are connected to each other by turns. The refrigerant sucked through inlet 1a is compressed by compressor 1 and discharged to condenser 2 through outlet 1b thereby. The refrigerant discharged from compressor 1 is changed into liquid refrigerant at condenser 2 and accumulated in receiver dryer 3. The liquid refrigerant in receiver dryer 3 is sent to evaporator 5 through expansion valve 4, changed into gas at evaporator 5 and returned to inlet 1a of compressor 1 through passageway control mechanism 26. Referring to Figures 2 and 3, the construction of a wobble plate type compressor with a variable displacement mechanism in accordance with one embodiment of this invention is shown. Compressor 1 includes a closed housing assembly formed by cylindrical compressor housing 10, front end plate 11 and a rear end plate in the form of cylinder head 12. Cylinder block 101 and crank chamber 102 are located in compressor housing 10. Front end plate 11 is attached to one end surface of compressor housing 10, and cylinder head 12 which is disposed on the other end surface of compressor housing 10 is fixed on one end surface of cylinder block 101 through valve plate 13. Opening 111 is formed in the central portion of front end plate 11 to receive drive shaft 14. Drive shaft 14 is rotatably supported on front end plate 11 through bearing 15. An inner end portion of drive shaft 14 also extends into central bore 102 formed in the central portion of cylinder block 101 and is rotatably supported therein by bearing 16. Rotor 17, disposed in the interior of crank chamber 103, is connected to drive shaft 14 to be rotatable with the drive shaft and engages inclined plate 18 through hinge mechanism 19. Hinge mechanism 19 comprises tab portion 191 which is formed on inner end surface of rotor 17, and has pin portion 191a, and tab portion 192 which is formed on one end surface of inclined plate 18 and has longitudinal hole 192a. The inclined angle of inclined plate 18 with respect to drive shaft 14 can be adjusted by hinge mechanism 19. Wobble plate 20 is disposed on the other side surface of inclined plate 18 and bears against it through bearing 21. A plurality of cylinders 104, one of which is shown in Figure 2, are equiangularly formed in cylinder block 101, and piston 22 is reciprocatingly disposed within each cylinder 104. Each piston 22 is connected to wobble plate 20 through connecting rod 23, i.e., one end of each connecting rod 123 is connected to wobble plate 20 with a ball joint and the other end of each connecting rod 23 is connected to one of pistons 22 with a ball joint. Guide bar 24 extends within crank chamber 103 of compressor housing 10. The lower end portion of wobble plate 20 engages guide bar 24 to enable wobble plate 20 to reciprocate along guide bar 24 while preventing rotating motion. Pistons 22 are thus reciprocated in cylinders 104 by a drive mechanism formed of drive shaft 14, rotor 17, inclined plate 18, wobble plate 20 and connecting rods 23. Drive shaft 14 and rotor 17 are rotated; and inclined plate 18, wobble plate 20 and connecting rods 23 function as a coupling mechanism to convert the rotating motion of the rotor into reciprocating motion of the pistons. Cylinder head 12 is provided with suction chamber 121 and discharge chamber 122, both of which communicate with cylinders 104 through suction holes or discharge holes 132 formed through valve plate 13, respectively. Also, cylinder head 12 is provided with inlet port 123 and outlet port 124 which place suction chamber 121 and discharge chamber 122 in fluid communication with a refrigerant circuit. A bypass hole or passageway 105 is formed in cylinder block 101 to communicate between suction chamber 121 and central bore 102 which is communicated with crank chamber 103. The communication between chamber 121 and 103 is controlled by a control valve mechanism 25. Control valve mechanism 25 is located between cylinder block 101, and cylinder head 12 and includes bellows element 251. Operation of bellows element 251 is determined by pressure difference between the pressure of refrigerant in suction chamber 121 and the pressure in crank chamber 103. Passageway control mechanism 26 is disposed within one end of cylinder head 12 and comprises valve 261 which includes piston 261a and valve portion 261b, coil spring 262, and screw mechanism 263 which includes spring seat 263a. Cylinder portion 125 is formed within cylinder block 12 to communicate suction chamber 121 and inlet port 123 with discharge chamber 122. Piston portion 261a of valve 261 is reciprocably fitted within cylinder portion 125. Valve portion 261b of valve 261 varies the opening area between suction chamber 121 and inlet port 123 in accordance with operation of piston portion 261a. Coil spring 262 is disposed between valve portion 261b and spring seat 263a attached to valve portion 261b at one end and supported on the inner end of spring seat 263a at the other end. Coil spring 262 always urges valve portion 261b to close the opening against the refrigerant pressure in discharge chamber 122. The recoil strength of coil spring 262 may be adjusted by screw mechanism 263, as shown in Figures 10 and 11. Further, with reference to Figure 4, the operation of passageway control mechanism 26 is described below. When compressor 1 is started by a driving source through electromagnetic clutch 30 in condition that refrigerant pressure in suction chamber 121 equals that in discharge chamber 122, piston portion 261a of valve 261 in passageway control mechanism 26 is urged downward by the recoil strength of coil spring 262 to close the opening between suction chamber 121 and inlet port 123, thereby maintaining the opening area therebetween at a minimum value. Thereafter, when compressor 1 actually is driven by rotation of drive shaft 14, the flow volume of refrigerant which is sucked into suction chamber 121 is limited since the opening area therebetween is at a minimum, thereby, the refrigerant pressure in cylinder 104 is rapidly reduced. Accordingly, refrigerant pressure in crank chamber 103 becomes higher than that in suction chamber 121, thereby increasing the pressure difference therebetween. Thus, the angle of inclined plate 18 with respect to drive shaft 14 decreased, and the nutational volume of wobble plate 20 also decreases. Therefore, the stroke volume of piston 22 is reduced, thereby keeping the drive torque of compressor 1 at a minimum. If compressor 1 is continued to be driven, refrigerant pressure in discharge chamber 122 increases since refrigerant at inlet port 123 is sucked into suction chamber 121 through the minimum opening area between suction chamber 121 and inlet port 123. Piston portion 261a of valve 261 is urged upward against recoil strength of coil spring 262 by increased refrigerant pressure discharged in discharge chamber 122. As shown in Figure 5, the discharge pressure of compressor 1 increases in proportion to the flow volume of refrigerant. Accordingly, when the flow volume of refrigerant increases, and the refrigerant pressure discharged in discharge chamber 122 becomes higher than the recoil strength of coil spring 262, piston portion 261a of valve 261 is moved upward within cylinder portion 124 together with valve portion 261b. Accordingly, the opening area of passageway between suction chamber 121 and inlet port 123 is increased and if discharge pressure becomes higher than a certain value, e.g., 13 bar, valve 261 is moved upward to open the opening area therebetween to a maximum. Referring to Figure 6, the relationship between the opening area of a passageway for flowing refrigerant and the pressure difference between high and low pressure sides in a refrigerant circuit is illustrated by solid line C. The opening area increases with increase of the pressure difference. When the pressure difference is below pressure difference Po1, the opening area is at a constant minimum value. On the other hand, when the pressure difference is higher than pressure difference Po2, the opening area is at a constant maximum value. The minimum and maximum values can be freely predetermined by suitably selecting size of valve 261 in a passageway between suction chamber 121 and inlet port 123 or location between suction port 123 and valve 261. Furthermore, the value of pressure difference Po2-Po1 to change the opening area from the minimum into maximum value can be also predetermined by suitably varying recoil strength of coil spring 262 toward value 261 due to adjusting the position of spring seat 263a. Dotted line C' illustrates a characteristic for the relationship therebetween in the condition that the recoil strength of coil spring 262 toward valve 261 is increased by moving spring seat 263a downward due to screwing screw mechanism 263. Referring to Figure 8, the relationship between drive torque and time on driving of a compressor is shown. The changes of drive torque in a refrigerant circuit having a passage control mechanism in accordance with the present invention is very small as compared with that in a conventional refrigerant circuit. In a conventional refrigerant circuit, the pressure in a suction chamber of a compressor is about 2 bar to prevent frost from being on an evaporator even though the flow volume of refrigerant is reduced as shown by line d in Figure 8 (a). However, if the flow volume of refrigerant is increased, the pressure at the outlet side of the evaporator is increased by pressure loss in a passageway between the inlet of the compressor and the outlet of evaporator as shown by dotted line C in Figure 8 (a). Accordingly, pressure difference is increased thereby causing the above mentioned problems. On the other hand, a passageway control mechanism according to the present invention increases the opening area with an increase of pressure difference between high and and low pressure sides in the refrigerant circuit which is caused by increase of the flow volume of refrigerant, and thereby decreases the pressure at the inlet side of passageway control mechanism as shown by dotted line e in Figure 8 (b). Accordingly, the pressure at the outlet side of the evaporator is not influenced by the flow volume of refrigerant, and is maintained to be a certain value. Therefore, the temperature of air which is passed through the evaporator can be maintained to be about a certain value. The temperature of air which is passed through an evaporator is determined in accordance with the pressure of refrigerant at the outlet side of the evaporator. The pressure of refrigerant at the outlet side of the evaporator can be optionally predetermined by adjusting a passageway control mechanism. For instance, as mentioned above, the characteristic for the relationship between an opening area and pressure difference between high and low pressure sides in a refrigerant circuit can be changed from line C to line C' (Fig.9) by varying the recoil strength of coil spring 262 of passageway control mechanism 26. Accordingly, if the pressure at the inlet side of passageway control mechanism 26 decreases, as shown by line e in Figure 9, the pressure at the outlet of evaporator 5 also decreases, as shown by line C' in Figure 9. This invention is not limited to the above mentioned embodiment. In the above embodiment, a passageway control mechanism is formed within one end of a cylinder block of a compressor. However, the efficiency and object of this invention can be also achieved by disposing the passageway control mechanism anywhere between an outlet side of an evaporator and an inlet side of a compressor or in an evaporator. Furthermore, in the above embodiment, although this invention is applied to a refrigerant circuit including an expansion valve, this invention can be also applied to a refrigerant circuit including an orifice. The efficiency and object of this invention can be achieved by disposing a passageway control mechanism somewhere between an outlet side of an accumulator and an inlet side of a compressor. Furthermore, in the above embodiment, although a cylinder and a valve with a piston portion is used as drive means of a passageway control mechanism, a drive means of drivable response to pressure difference, i.g., bellows 264 as shown in Figure 10 or diaphram 265 as shown in Figure 11 can be used as drive means of a passageway control mechanism instead of the above elements.

Claims: A refrigerant circuit including a compressor (1), a condenser (2) and an evaporator (5) connected to each other in series, valve means (26) being disposed between the outlet side of said evaporator (5) and the inlet side of said compressor (1) which operate to change the opening area of the passageway therebetween responsive to the pressure difference between the suction chamber (121) and the discharge chamber (122) of said compressor, said valve means comprising a piston (261a) and a valve portion (261b), characterized in that said valve portion (261b) is formed as a hollow cylindrical member being displaceable and having its axis extending in direction substantially transversely to the direction of said passageway, said hollow cylindrical member housing a coil spring (262) which is disposed between a bottom of said cylindrical member and a spring seat (263a) opposite said valve portion (261b). The refrigerant circuit according to claim 1, wherein the end of said piston (261a) is subjected to the pressure in said discharge chamber (122), and said valve portion (261b) is subjected to the pressure in said suction chamber. The refrigerant circuit according to claim 2, wherein a bellows portion (264) is fixedly connected to said piston (261a), the inside of said bellows portion communicating with said discharge chamber (122). The refrigerant circuit according to claim 2, wherein a diaphragm (265) is provided, one side of said diaphragm communicating with said discharge chamber (122). The refrigerant circuit according to claim 1, characterized in that said compressor is a compressor (1) with a variable displacement mechanism.

Inventors: KAZUHIKO, TAKAI
Applicants: SANDEN CORPORATION
Application year: 1988
Main classification: F25B41
IPC codes: F04B49, F04B27, F25B1