SLANT PLATE TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A slant plate type refrigerant compressor, such as a wobble plate compressor, with a variable displacement mechanism dependent on crank chamber pressure. One control mechanism (l6) controls the pressure in the crank chamber (22) in response to the pressure in a suction chamber (40) and another control mechanism (l7) controls the pressure in the crank chamber in response to the temperature of refrigerant gas in the suction chamber.

Description: The present invention relates to a slant plate type refrigerant compressor, such as a wobble plate compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system. One way of adjusting the capacity of a slant plate type compressor, particularly a wobble plate compressor, is disclosed in US-A-386l829. This discloses a wobble plate compressor which has a driving device including a cam rotor to reciprocate a plurality of pistons, and variation of the angle of inclination of a slant surface of the cam rotor changes the stroke length of the pistons. Since the stroke length of the pistons within the cylinders is directly responsive to the angle of the slant surface, the displacment of the compressor is easily adjusted by varying the angle of inclination. Furthermore, variations in the angle can be effected by the pressure difference between a suction chamber and a crank chamber in which the driving device is located. In such a prior art compressor, the angle of the slant surface is determined by the pressure in the crank chamber. The pressure in the crank chamber is controlled in the following manner: the crank chamber communicates with the suction chamber through an aperture formed through the cylinder block, and the opening and closing of the aperture is controlled by a valve mechanism. The valve mechanism generally includes a bellows and a needle valve, and is located in the suction chamber so that the bellows operates in accordance with changes of pressure in the suction chamber. In the above compressor, the pressure in the suction chamber is controlled by the valve mechanism to maintain uniform pressure therein. Therefore, if the predetermined pressure in suction chamber is set at a low value, there is possibility of frosting on an evaportor in an associated refrigeration circuit. Thus the predetermined set pressure in the suction chamber should be at a sufficiently high value so as to prevent frosting on the evaporator. However, if the predetermined set pressure is comparatively high and the compressor is driven at a high rotational speed, the cooling ability of the compressor is inferior to that of the same type of compressor without a variable displacement mechanism. That is, if the temperature in the compartment of an automobile is high, the pressure in a suction chamber of the compressor usually becomes high. However, if the compressor is driven at a high rotational speed, the pressure in the suction chamber suddenly decreases even though the temperature in the compartment of the automobile and thermal load on the evaporator is still high. Therefore, the variable displacement mechanism is operated to decrease the capacity of the compressor even if the environmental condition requires large a capacity of compressor. The cooling operation in the compartment of the automobile is thus insufficient. US-A-386l829 discloses a capacity-adjusting mechanism used in a wobble plate compressor. As is typical in this type of compressor, the wobble plate, which is disposed at an inclination relative to the drive axis, nutates but does not rotate, and couples the pistons to the drive source. This type of capacity adjusting mechanism, using selective fluid communication between the crank chamber and the suction chamber, however, can be used in any type of compressor which uses a slant plate or surface in the drive mechanism. For example, US-A-4664604 discloses this type of capacity adjusting mechanism in a swash plate compressor. The swash plate, like the wobble plate, is disposed at an inclination and couples the pistons to the drive source. However, while the wobble plate only nutates, the swash plate both nutates and rotates. The term slant plate type compressor will therefore be used herein to refer to any type of compressor, including wobble and swash plate types, which use an inclined plate or surface in the drive mechanism. Our earlier European application No. 87306436.4 discloses a slant plate type compressor of a kind (hereinafter referred to as of the kind described) for use in a refrigeration circuit and comprising a compressor housing having a front end plate at one end of the housing and at the other end of the housing a rear end plate in the form of a cylinder head defining a suction chamber and a discharge chamber, the housing having a cylinder block provided with a plurality of cylinders and a crank chamber adjacent to the cylinder block; a plurality of pistons slidably fitted within respective ones of the cylinders; a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft rotatably mounted in the housing, a rotor coupled to the drive shaft and rotatable therewith, and coupling means for coupling the rotor to the pistons such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a member having a surface disposed at an inclination relative to the drive shaft, and the angle of inclination of the member being adjustable to vary the stroke length of the pistons and the capacity of the compressor; and control means for varying the capacity of the compressor by adjusting the angle of inclination of the members, the control means including at least one passageway interconnecting the crank chamber and the suction chamber, and valve means for controlling the opening and closing of the passageway(s), and hence the pressure in the crank chamber, the valve means being responsive to refrigerant pressure in the compressor and to a temperature. As particularly described in that earlier application, the valve means is responsive to crank chamber pressure and to a temperature in a compartment of a car with which an air conditioning system incorporating the compressor is used. According to the present invention, a compressor of the kind described is characterised in that the valve means is responsive to refrigerant pressure and temperature in the suction chamber. In the accompanying drawings: Figures l and 2 are cross-sectional views of first and second examples of a wobble plate compressor with a variable displacment mechanism in accordance with this invention; Figure 3(a) is a graph illustrating the relationship between time and the pressure or temperature of refrigerant gas in the suction chamber of a slant plate type compressor with a conventional variable displacement mechanism or with a variable displacment mechanism in accordance with this invention; Figure 3(b) is a graph illustrating the relationship between time and the capacity of a slant plate type compressor with a conventional variable displacement mechanism or with a variable displacement mechanism in accordance with this invention; and, Figure 3(c) is a graph illustrating the relationship between time and the temperature in a compartment of a car when a slant plate type compressor with a conventional variable displacement mechanism or with a variable displacement mechanism in accordance with this invention. As shown in Figure l, a compessor l includes a closed housing assembly formed by a cylindrical housing 2, a front end plate 3 and a rear end plate in the form of a cylinder head 4. A cylinder block 2l and a crank chamber 22 are formed in the compressor housing 2. The front end plate 3 is attached to one end surface of the compressor housing 2, and the cylinder head 4 is fixed on one end surface of the cylinder block 2l with an interposed valve plate 5. An opening 3l is formed in a central portion of the front end plate 3 for the penetration of a drive shaft 6. The drive shaft 6 is rotatably supported by the front end plate 3 through a bearing 7. A shaft seal (not shown) is disposed between the inner surface of the opening 3l and the outer surface of the drive shaft 6 at the outside of the bearing 7. An inner end portion of the drive shaft 6 also extends into a central bore 23 formed in the central portion of the cylinder block 2l and is rotatably supported therein by a bearing 8. A rotor 9, which is disposed in the interior of the crank chamber 22, is connected to the drive shaft 6 so as to be rotatable with the drive shaft and engages an inclined plate l0 through a hinge portion 90. The angle of inclination of the plate l0 with respect to the drive shaft 6 can be adjusted by the hinge portion 90. A wobble plate ll is disposed on the other surface of the inclinded plate l0 and bears against it through a bearing l2. A plurality of cylinders 24, one of which is shown in Fig. l are equiangularly formed in the cylinder block 2l, and pistons 4 are reciprocatably disposed one within each cylinder 24. Each piston l3 is connected to the wobble plate ll through a connecting rod l4, i.e., one end of each connecting rod l4 is connected to the wobble plate l2 by a ball joint and the other end of each connecting rod l4 is connected to one of the pistons l3 by a ball joint. A guide bar l5 extends within the crank chamber 22. The lower end portion of the wobble plate ll engages the guide bar l5 to enable the wobble plate ll to reciprocate along the guide bar l5 while preventing rotating motion of the wobble plate. The pistons l3 are thus reciprocated in the cylinders 24 by the drive mechanism formed by the drive shaft 6, rotor 9, inclined plate l0, wobble plate ll and connecting rods l4. The drive shaft 6 and rotor 9 are rotated, and the inclined plate ll, wobble plate l2 and connecting rods l4 function as a coupling mechanism to convert the rotating motion of the rotor into reciprocating motion of the pistons. The interior space of the cylinder head 4 is divided by a partition wall 47 into a suction chamber 40 and a discharge chamber 4l both of which communicate with the cylinders 24 through suction holes 50 or discharge holes 5l formed through the valve plate 5, respectively. Also, the cylinder head 4 is provided with an inlet port 42 and an outlet port 43 which place the suction chamber 40 and the discharge chamber 4l in fluid communication with an associated refrigerant circuit. A first bypass hole 25 is formed in the cylinder block 2l and, with a first hollow portion 26, which is also formed within the cylinder block 2l, and a first communication hole 52, which is formed through the valve plate 5, forms a first bypass passage which interconnects the crank chamber 22 and the suction chamber 40. The communication between the chambers 22 and 40 is controlled by a first control device l6. The first control device l6 is located in the first hollow portion 26 and comprises a bellows l6l and a needle valve l62. The needle valve l62 is fixed on one end surface of the bellows l6l and controls opening and closing of the end of the first bypass hole 25, and hence of the first bypass passage, in accordance with the motion of the bellows l6l. The interior of the bellows l6l is evacuated so as to prevent operation in dependence on the temperature of the refrigerant gas in the suction chamber 40 and the bellows l6l is provided with a coil spring (not shown) to determine its operating point, i.e., a predetermined pressure Psl is determined. A second bypass hole 27 is also formed within the cylinder block 2l and, with second hollow portion 28, which is also formed within the cylinder block 2l, and a second communication hole 53, which is formed through the valve plate 5, forms a second bypass passage which interconnects the crank chamber 22 and the suction chamber 40. The communication between the chambers 22 and 40 is controlled by a second control device l7, which comprises a bellows l7l and a tappet valve l72. The bellows l7l is located in the suction chamber 40 so as to correctly detect and respond to the temperature of refrigerant gas in the suction chamber 40. The tappet valve l72 is fixed on the free end surface of the bellows l7l and extends within the interior of the second hollow portion 28 so as to control the opening and closing of the second communication hole 53, and hence of the second bypass passage, in accordance with the motion of bellows element l7l. Gas with low saturated vapour pressure, such as refrigerant, is enclosed in the interior of the bellows l7l so as to respond to the temperature of the refrigerant in the suction chamber 40. When the refrigerant enclosed in the bellows l7l is in the state of a wet gas, i.e., the refrigerant gas enclosed in the bellows l7l is saturated vapour, the pressure of the refrigerant in the bellows l7l is equal to that in the suction chamber 40, and the bellows l7l operates so that the tappet valve l72 closes the second communication hole 53. At that time, if the pressure in the suction chamber 40 is below the predetermined operating point Psl, i.e, the recoil strength of the bellows element l6l is greater than the gas pressure in the hollow portion 26, the bellows l6l is extended to the left (as seen in Figure l), and the needle valve l62 closes the end of the first bypass hole 25. Therefore, the communication between the crank chamber 22 and the suction chamber 40 through both the first bypass passage and the second bypass passage is obstructed. Under this condition, the pressure in the crank chamber 22 gradually increases, because gas leaks into the crank chamber 22 through any gaps between the inner wall surfaces of the cylinders 24 and the outer wall surfaces of the pistons l3. Gas pressure in the crank chamber 22 acts on the rear surface of the pistons l3, and changes the balance of moment on the inclined plate relative to the drive shaft 6, which is thereby decreased; and the stroke of the pistons l4 is thus also decreased. As a result, the volume of refrigerant gas taken into the cylinders 24 is decreased and the capacity of the compressor is thus decreased. In contrast, when the pressure in the suction chamber 40 is greater than the predetermined operating point Psl of the bellows l6l, the bellows l6l contracts to the right, and the needle valve l62 opens the first bypass passage. Communication between the crank chamber 22 and the suction chamber 40 is then obtained. The refrigerant gas in the crank chamber 22 then flows into the suction chamber 40 through first bypass passage. Gas pressure which acts on the rear surface of the pistons 24 thus decreases in accordance with the decrease in the gas pressure in the crank chamber 22. The balance of moments acting on the inclinded plate l0 thus increases so that the angle of the inclined plate l0 relative to drive shaft 6 also changes. The stroke of pistons l4 is thus increased, and the volume of refrigerant gas being compressed is increased. As mentioned above, if refrigerant gas in the suction chamber 40 is not superheated, i.e, the communication between the crank chamber 22 and the suction chamber 40 through the second bypass passage is obstructed, the communication between the crank chamber 22 and the suction chamber 40 is controlled in accordance with operation of the first control device l6 which is responsive to the pressure in the suction chamber 40. When refrigerant gas enclosed in the bellows l7l is in the state of dry gas, i.e, refrigerant enclosed in bellows l7l is in the state of superheated gas as a result of heat exchange with superheated refrigerant in the suction chamber 40, the vapour pressure of the refrigerant enclosed in the bellows l7l relatively increases. Therefore, if the temperatures in the interior and exterior of bellows l7l are equal each other, the bellows l7l pushes the tappet valve l72 to the left. The second communication hole 53 is thus opened to interconnect the crank chamber 22 and the suction chamber 40 through the second bypass passage. As mentioned above, when the refrigerant in the suction chamber 40 is superheated, i.e, the communication between the crank chamber 22 and the suction chamber 40 through the second bypass passage is maintained, this communication is obtained independently of operation of the first control device l6, which is operated in response to the pressure in the suction chamber 40. Figure 2 shows another example of slant plate type compressor with a variable displacement mechanism and in accordance with the invention. Since the construction of this compressor is substantially same as that of the first example except for the variable displacement mechanism, repeated description of the common parts is omitted but the same reference numerals are accorded to the same parts. One bypass passage 29 is formed within the cylinder block 2l to interconnect the crank chamber 22 and the suction chamber 40. The communication between the crank chamber and the suction chamber 40 is controlled by a control device l8. The control device l8 is located in the suction chamber 40 and comprises a bellows l8l, a needle valve l82 fixed on one end of the bellows l8l and a U-shaped sensor l83. One end surface of the U-shaped sensor l83 is fitted against the other end surface of the bellows l8l and the other end surface of the U-shaped sensor l83 is attached to an inner surface of the suction chamber 40. The interior of the bellows element l8l is evacuated so as not to be responsive to the temperature of refrigerant gas in the suction chamber 40 and the bellows l8l is provided with a coil spring (not shown) in the inside thereof to maintain its predetermined operating point. When the pressure in the suction chamber 40 is below the predetermined operating point of the bellows l8l, the bellows l8l extends to the left. In contrast, when the pressure in the suction chamber 40 is greater than the predetermined operating point of the bellows l8l, the bellows l8l contracts to the right and opens the passage 29. The U-shaped sensor l83 is a bimetal strip, so that the position of the bellows l8l is changed in accordance with changes of temperature of the refrigerant in the suction chamber. That is, the U-shaped sensor l83 pushes the bellows l8l towards the bypass hole 29 under the high temperature conditions in the suction chamber, and conversely pulls the bellows l8l under lower temperature conditions. In this construction, if the pressure in the suction chamber 40 is below the predetemined operating point of the bellows l8l, the bellows l8l extends to the left so that the needle valve l82 closes the bypass passage 29. At that time, if the temperature of the refrigerant gas in the suction chamber 40 is higher than a predetermined temperature, i.e, the refrigerant gas in the suction chamber 40 is superheated, the left end of the U-shaped sensor l83 bends toward the right. That is the bellows l8l is shifted towards the right together with the valve element l82. The bypass passage 29 is thus opened to interconnect the crank chamber 22 and the suction chamber 40, thus overriding the action of the bellows. When the refrigerant gas in the suction chamber 40 is not superheated, the U-shaped sensor l83 does not move. Therefore, the communication between the crank chamber 22 and the suction chamber 40 is controlled by operation of the bellows element l8l in response to the pressure in the suction chamber 40. As mentioned above, the slant angle of the inclined plate is thus controlled by the condition of pressure and temperature of refrigerant in the suction chamber, therefore the capacity of the compressor is controlled in accordance with actual environmental condition, as shown in Figures 3(a) and 3(b). Therefore, cooling down of an associated refrigerating apparatus is improved, as shown in Figure 3(c)

Claims: 1. A slant plate type compessor for use in a refrigeration circuit, the compressor comprising a compressor housing (2) having a front end plate (3) at one end of the housing and at the other end of the housing a rear end plate (4) in the form of a cylinder head defining a suction chamber (40) and a discharge chamber (4l), the housing having a cylinder block (2l) provided with a plurality of cylinders (24) and a crank chamber (22) adjacent to the cylinder block; a plurality of pistons (l3) slidably fitted within respective ones of the cylinders; a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft (6) rotatably mounted in the housing, a rotor (9) coupled to the drive shaft and rotatable therewith, and coupling means (l0,ll,l4) for coupling the rotor to the pistons such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a member (l0) having a surface disposed at an inclination relative to the drive shaft, and the angle of inclination of the member being adjustable to vary the stroke length of the pistons and the capacity of the compressor; and control means (l6,l7,l8) for varying the capacity of the compressor by adjusting the angle of inclination of the members, the control means including at least one passageway (25,26,52;27,28,53;29) interconnecting the crank chamber and the suction chamber, and valve means (l6,l7;l8l,l83) for controlling the opening and closing of the passageway(s), and hence the pressure in the crank chamber, the valve means being responsive to refrigerant pressure in the compressor and to a temperature; characterised in that the valve means is responsive to refrigerant pressure and temperature in the suction chamber. 2. A compressor according to claim l, wherein the or each passageway extends through the cylinder block (2l). 3. A compressor according to claim l or claim 2, wherein the valve means comprises a first control device (l6) to control the opening and closing of a first passageway (25,26,52) in response to suction chamber pressure, and a second control device (l7) to control the opening and closing of a second passageway (27,28,53) in response to suction chamber temperature. 4. A compressor according to claim 3, wherein the first and second control devices each comprises a bellows (l6l,l7l) and a valve element (l62,l72). 5. A compressor according to claim 4, wherein the bellows (l6l) of the first control device is evacuated and the bellows (l7l) of the second control device contains a gas with a low saturated vapour pressure. 6. A compressor according to claim l or claim 2, wherein the valve means comprises a first control device (l8l,l82) to control the opening and closing of a passageway (29) in response to suction chamber pressure, and a second control device (l83) to control the opening and closing of the same passageway (29) in response to suction chamber temperature. 7. A compressor according to claim 6, wherein the first control device is a bellows (l8l) and a valve element (l82), and the second control means is a bimetal strip (l83) which forms a movable support for the bellows.

Inventors: TERAUCHI, KIYOSHI
Applicants: SANDEN CORPORATION
Application year: 1987
Main classification: F04B1
IPC codes: F04B27, F04B25