SLANT PLANT TYPE COMPRESSOR WITH VARIABLE DISPLACEMENT MECHANISM

Abstract: A wobble plate type compressor with a capacity adjusting mechanism is disclosed. The compressor includes a housing (2) having a cylinder block (21) provided with a plurality of cylinders (24) and a crank chamber (23). A piston (13) is slidably fitted within each of the cylinders and is reciprocated by a swash plate mechanism (10,11) driven by a shaft (6). The swash plate has a hinge mechanism (91) for changing its slant angle. The slant angle is controlled by the pressure situation in the crank chamber which in turn is controlled by a control mechanism comprising a passageway between the crank chamber and the suction chamber (40) and including a valve mechanism (17) to control the closing and opening of the passageway. The valve mechanism includes a valve element (177) directly controlling the closing and opening of the passageway, a first valve control device (171), which controls operation of the valve element in response to pressure in the suction chamber, and a second valve control device (175) which controls the predetermined operating point of the first valve control means. The operation of the second valve control means is controlled in response to external control signals.

Description: The present invention relates to a slant plate type compressor, and more particularly, to a compressor such as a wobble plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system. Generally, in air conditioning apparatus, thermal control is accomplished by intermittent operation of the compressor in response to a signal from a thermostat located in the room being cooled. Once the temperature in the room has been lowered to a desired temperature, the refrigerant capacity of the air conditioning system generally need not be very large in order to handle supplemental cooling because of further temperature changes in the room or to keep the room at the desired temperature. Accordingly, after the room has cooled down to the desired temperature, the most common technique for controlling the output of the compressor is by intermittent operation of the compressor. However, this intermittent operation of the compressor results in the intermittent application of a relatively large load to the driving mechanism of the compressor in order to drive the compressor. In automobile air conditioning compressors, the compressor is driven by the engine of the automobile through an electromagnetic clutch. Automobile air conditioning compressors face the same intermittent load problems described above once the passenger compartment reaches a desired temperature. Control of the compressor is normally accomplished by intermittent operation of the electromagnetic clutch which couples the automobile engine to the compressor. Thus, the relatively large load which is required to drive the compressor is intermittently applied to the automobile engine. Furthermore, since the compressor of an automobile air conditioner is driven by the engine of the automobile, the rotation frequency of the drive mechanism changes from moment to moment, which causes the refrigerant capacity to change in proportion to the rotation frequency of the engine. Since the capacity of the evaporator and the condenser of the air conditioner does not change when the compressor is driven at high speed, the compressor performs useless work. To avoid performing useless work, prior art automobile air conditioning compressors often are controlled by intermittent operation of the electromagnetic clutch. However, this again results in large loads being intermittently applied to the automobile engine. One solution to above mentioned problems is to control the capacity of the compressor in response to refrigeration requirements. One construction to adjust the capacity of a slant type compressor, is disclosed in US-A-3861829 which discloses a wobble plate type compressor which has a cam rotor driving device to drive a plurality of pistons and varies the slant angle of a slant surface to change the stroke length of the pistons. Since the stroke length of the pistons within the cylinders is directly responsive to the slant angle of the slant surface, the displacement of the compressor is easily adjusted by varying the slant angle. Furthermore, variations in the slant angle can be effected by pressure difference between a suction chamber and a crank chamber in which the driving device is located. In such compressors, the angle of the slant surface is controlled by pressure in the crank chamber. The crank chamber communicate with the suction chamber through an aperture and the opening and closing of this aperture is controlled by a valve. The valve is generally formed by a bellows element and a needle valve and is disposed in the suction chamber to allow the bellows element to operate in accordance with changes in pressure in the suction chamber. The acting point of the valve to open or close the aperture is determined by the pressure of the gas contained in the bellows element. However, the predetermined acting point of the bellows element is fixed at a predetermined value. The bellows element therefore operates only at a certain change of pressure in the suction chamber, and cannot respond to various changes of refrigerating conditions. Furthermore, since the predetermined acting point of the bellows element cannot be changed, the valve cannot be made responsive to requirements such as when the air conditioner requires an especially low evaporating temperature or the compressor must operate with small volume for decreasing thermal loads. Also, for the purpose of reducing the number of parts, the electromagnetic clutch may be omitted and the compressor can be directly connected to a driving source. In this type of compressor, the compressor is driven whenever the driving source is operating. Operation of this type of compressor is especially difficult when the value of the predetermined operating point of the bellows element cannot be changed with changes in the thermal load of an evaporator in a refrigerant circuit. US-A-3861820 discloses a capacity adjusting mechanism used in a wobble plate type compressor. As is typical in this type of compressor, the wobble plate is disposed at a slant or incline angle relative to the drive axis, nutates but does not rotate, and drivingly 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 slanted plate or surface in the drive mechanism. For example, US-A-­ 4664604 discloses this type of capacity adjusting mechanism in a swash plate type compressor. The swash plate, like the wobble plate, is disposed at a slant angle and drivingly 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 a slanted plate or surface in the drive mechanism. It is a primary object of the invention to provide a slant plate type compressor with a variable displacement mechanism wherein the capacity control can be adjusted. Another object of this invention is to provide a slant plate type compressor with a variable displacement mechanism which can be utilized in various types of refrigerating apparatus. According to the invention there is provided a slant type plate compressor including a compressor housing having a cylinder block provided with a plurality of cylinders and a crank chamber adjacent the cylinder block, a piston slidably fitted within each of the cylinders and reciprocated by a swash plate drive by an drive mechanism, a front end plate disposed on the compressor housing for rotatably supporting the drive mechanism, a rear end plate disposed on the opposite end of the compressor housing and defining a suction chamber and a discharge chamber, a passage connecting the crank chamber and the suction chamber, and a valve mechanism for controlling the closing and opening of the passage to vary the volume of the compressor, the valve mechanism including a valve element directly controlling the closing and opening of the passage; characterized by: first valve control means for controlling movement of the valve to open and close the passage in response to changes of pressure in the suction chamber; and second valve control means coupled to the first valve control means for changing the operating point of the first valve control means in response to an external condition. Examples of compressors constructed in accordance with this invention will now be described with reference to the annexed drawings, in which:- Figure 1 is a cross-sectional view of a first wobble plate type compressor with a variable displacement mechanism; Figure 1a is a schematic drawing of a conventional refrigerant circuit within which the compressor of the present invention can be used; Figure 2 is a cross-sectional view of a second wobble plate type compressor with a variable displacement mechanism; Figure 3 is a cross-sectional view of a further wobble plate type compressor with a variable displacement mechanism; and, Figure 4 is a cross-sectional view of a fourth wobble plate type compressor with a variable displacement mechanism. Figure 5 is a cross-sectional view of a fifth wobble plate type compressor with a variable displacement mechanism; Referring to Figure 1, a wobble plate type compressor 1 is shown which includes a cylindrical compressor housing 2 having a cylinder block 21 and a crank chamber 22. A front end plate 3 is attached to one end surface of the compressor housing 2 and a cylinder head 4 is disposed on the other end surface of the compressor housing 2 and is fixed on one end surface of the cylinder block 21 through a valve plate 5. An opening 31 is formed in the central portion of the front end plate 3 to receive a drive shaft 6. The drive shaft 6 is rotatably supported on the front end plate 3 by a 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 21 and is rotatably supported by a bearing 8. A rotor 9, disposed in the interior of the crank chamber 22, is connected to the drive shaft 6 for rotation and engages an inclined plate 10 through a hinge portion 91. The angle of incline of the inclined plate 10 relative to the drive shaft 6 can be adjusted by the hinge portion 91. A wobble plate 11 is disposed on the other side surface of the inclined plate 10 through a bearing 12. A plurality of cylinders 24 are equiangularly formed in the cylinder block 21 and a piston 13 is reciprocably disposed within each cylinder 24. Each piston 13 is connected to the wobble plate 11 through a connecting rod 14, i.e., one end of each connecting rod 14 is connected to wobble plate 11 with a ball joint and the other end of each connecting rod 14 is similarly connected to one of the pistons 13. A guide bar 15 extends within the crank chamber 22 of the compressor housing 2. The lower end portion of the wobble plate 11 engages the guide bar 15 to enable the wobble plate 11 to reciprocate along the guide bar 15 while preventing rotational motion. The pistons 13 are thus reciprocated in the cylinders 24 by a drive mechanism formed of the drive shaft 6, rotor 9, inclined plate 10, wobble plate 11 and connecting rods 14. The drive shaft 6 and rotor 9 are rotated; and the inclined plate 10, wobble plate 11 and connecting rods 14 function as a coupling mechanism to convert the rotating motion of the rotor into reciprocating motion of the pistons. The cylinder head 4 is provided with a suction chamber 40 and a discharge chamber 41, which communicate with the cylinder 24 through suction holes 50 and discharge holes 51 respectively formed through the valve plate 5. Also, the cylinder head 4 is provided with an inlet port 42 and an outlet port 43 which connect the suction chamber 40 and discharge chamber 41 respectively with a refrigerant circuit. Figure 1a schematically illustrates a typical refrigerant circuit wherein compressor 1 is connected in series to a condenser 201, an orifice tube 301 as an expansion device, an evaporator 401 and an accumulator 501. A bypass hole or passage 25 is formed in the cylinder block 21 to provide communication between the suction chamber 40 and the crank chamber 22. The communication between the chambers 40 and 22 is controlled by a control valve mechanism 17 which is disposed in the suction chamber 40 and comprises a bellows element 171 and a solenoid actuator 172. The solenoid actuator 172 comprises a casing 173 a T-shaped core 174, a solenoid (coil) 175 and a movable cylinder 176. Casing 173 is generally cylindrical, and has a U-shaped section with openings 173a, 173b which provide communication between the crank chamber 22 and the suction chamber 40. The solenoid 175 is disposed on the outer surface of the axis of the core 174 and a cylindrical movable cylinder 176, which is U-­ shaped in section, is axially movably disposed within the casing 173 and covers the solenoid 175. An opening 173b is formed through an end plate portion of the casing 173 to connect with one end opening of the passage 25 and is selectively closed by a projection 177 formed on one end plate portion of the cylinder 176. The cylinder 176 has a predetermined radial gap between it and the interior of the casing 173 and further openings 173a surface of the pistons 13. Gas pressure in the crank chamber acts on the rear surface of the pistons 13, and changes the balance of moment on the inclined plate 10. The angle of inclined plate 10 relative to the drive shaft 6 is decreased and the stroke of pistons 13 is thus also decreased. As a result, the volume of refrigerant gas taken into the cylinders 24 is decreased thus varying the volume of the compressor. On the other hand, if the pressure in the suction chamber 40 exceeds the stiffness or spring effect of the bellows element 171, the bellows element 171 the cylinder 176 are pushed to the right, and the projection 177 opens the opening 173b. Accordingly, the crank chamber 22 is placed in communication with the suction chamber 40 through the passage 25. The refrigerant gas in the crank chamber 22 flows into the suction chamber 40, and the pressure in the crank chamber 22 is decreased with decreasing gas pressure in the crank chamber 22. The balance of moments on the inclined plate 10 increases so that the angle of the inclined plate 10 relative to the drive shaft 6 also changes. The stroke of the pistons 13 is thus increased, and the volume of refrigerant gas being compressed is increased. When the solenoid 175 is energized, a magnetic force attracting the movable cylinder 176 to the right is produced. The inherent stiffness or spring effect of the bellows element 171 is set to be greater than the magnetic force, so that the opening 173b is closed by the projection 177 of the movable cylinder 176 even when the solenoid is energized. However, since the magnetic force attracting the movable cylinder 176 acts against the bellows element 171, the bellows element 171 is more easily collapsed than when solenoid 175 is not energized. Solenoid actuator 172 thus acts as a mechanism which reduces the amount of biasing force provided by the bellows element 171; and since the amount of magnetic force is adjustable, as will be explained, this reduction in biasing force is likewise adjustable. In other words, the acting point of the bellows element 171 i.e., the pressure level within suction chamber 40 which causes bellows element 171 to collapse and projection 177 to move between the closed and open positions, is changed by energization of solenoid 175, is changed by energization of the solenoid 175. The strength of the magnetic force produced by the solenoid 175 is changed by varying the electric current supplied to the solenoid and the acting point of the bellows element 171 is, therefore, controlled by the electric current which in turn can be controlled by external conditions. The stroke of the pistons 13 can thus be changed in accordance with any change of thermal load of an evaporator in a refrigerant circuit or any other requirements specified from driving conditions such as engine start or car acceleration. The structure of the valve mechanism may be modified to the simpler structure shown in Figure 2. In this structure, the control valve mechanism 18 comprises a bellows element 181 and a solenoid actuator 182. The solenoid actuator 182 comprises a cylindrical casing 183 which is U-shaped in section and has openings 183a, 183b to provide communication between the crank chamber 22 and the suction chamber 40, a core 184, a solenoid 185 which is dosposed around the axis of the core 184 and a T-shaped movable member 186 which is axially movably disposed within the bellows element 181. The bellows element 181 is provided with a projection 187 and is attached at one end to the surface of a deviding wall 183c. The projection 187 is connected with one end of the movable member 186 whose motion is controlled by the solenoid 185. A communicating channel 188 is formed within the cylinder head 4 in order to connect the interior of the bellows 181 with ambient air. The inherent stiffness or spring affect of bellows element 181 provides the bias force to the left, closed position as in Figure 2; or, if more force is needed to reinforce the stiffness of bellows element 181, a spring 181a can be incorporated in the interior of bellows element 181 as shown in Figure 2. Since operation of the control valve mechanism 18 is similar to that described in the first embodiment, further description of the operation of control valve mechanism 18 is omitted. In the second embodiment, since the interior of the bellows 181 communicates with ambient air, it is not necessary to seal the solenoid 185. Referring to the Figure 3 example, a control valve mechanism 19 is shown which comprise a bellows element 191 and a diaphragm actuator 192. The diaphragm actuator 192 comprises a casing 193 provided with openings 193a,193b which connect the suction chamber 40 with the crank chamber 22, a diaphragm 194, a coil spring 195 and a connecting rod 196 which is movably and axially disposed within the bellows element 191. The bellows element 19 is provided with a needle valve 197 attached at on one end and is attached at the other and to the surface of a dividing wall 193c. The diaphragm 194 is disposed on the other end surface of the dividing wall 193c. A spring 191a is disposed within bellows element 181 and bears against the dividing wall 193c. A connecting rod 196 is connected to the needle 197 through the bellows element 191 and the other end of the connecting rod 196 is connected to one end surface of the diaphragm 194. An inner end surface of the casing 193 is connected to the other end surface of the diaphragm 194 through a coil spring 195. A communicating channel 198 is formed within the dividing wall 193c and the cylinder head 4 to communicate the interior of the bellows element 191 and diaphragm 194 with ambient air. An opening 199 is formed which communicates the exterior of the diaphragm 194 with a tube communicating air pressure for control purposes through an opening 193d, the force on the diaphragm controlling the force applied to the rod 196. Since operation of the control valve mechanism 19 is similar to that described in the first embodiment, the description of the operation of the control valve mechanism 19 is omitted. That is, as varying amounts of electric current are supplied to solenoid 175 in response to changing external conditions, varying amounts of negative pressure are supplied to opening 199 in a conventional manner due to sensed changes in external conditions. Referring to Figure 4, a control valve mechanism 20 comprises a bellows element 201 which is disposed in the suction chamber 40. The bellows element 201 is provided with a needle valve 202 on one end surface thereof and the other end of the bellows element 201 is attached to an inner end surface of the cylinder head 4. A spring 201a id disposed within the bellows element 201. An opening 203 is formed through the cylinder head 4 to communicate the interior of the bellows element 201 with a tube providing air pressure control. Therefore, the predetermined acting point of the bellows element 201 is controlled by air pressure added through tube 203 for control, as with the Figure 3 example. Referring now to Figure 5, the above mentioned bellows element 201 may be replaced with a diaphragm 260 which is disposed in the suction chamber 40. The diaphragm 260 is provided with a needle valve 261 and is fixed on a projecting portion 401 of the suction chamber 40 by a stopper 402. The diaphragm 260 is biassed by a coil spring 403. An opening 404 is formed through the cylinder head 4 to communicate the exterior of the diaphragm 260 with a tube providing air pressure for control. The predetermined opening point of the needle valve 261 is controlled by air pressure through the opening 404.

Claims: 1. A slant type plate compressor including a compressor housing (2) having a cylinder block (21) provided with a plurality of cylinders (24) and a crank chamber (22) adjacent the cylinder block, a piston (13) slidably fitted within each of the cylinders and reciprocated by a swash plate drive (10, 11) by an drive mechanism (6), a front end plate (3) disposed on the compressor housing for rotatably supporting the drive mechanism (6), a rear end plate (4) disposed on the opposite end of the compressor housing and defining a suction chamber (40) and a discharge chamber (41), a passage (25) connecting the crank chamber (22) and the suction chamber (40), and valve mechanism (17) for controlling the closing and opening of the passage to vary the volume of the compressor, the valve mechanism including a valve element (171) directly controlling the closing and opening of the passage; characterized by: first valve control means (171) for controlling movement of the valve to open and close the passage in response to changes of pressure in the suction chamber; and second valve control means (175) coupled to the first valve control means for changing the operating point of the first valve control means in response to an external condition. 2. A compressor according to claim 1, wherein the first valve control means is a bellows element (191) and the second valve control means is a diaphragm (194). 3. A compressor according to claim 1, wherein the first valve control means is a bellows element (171) and the second valve control means is a solenoid (175,185) which controls the operating point of the first valve control means. 4. A compressor according to claim 1, wherein the second valve control means is a pressure sensing means (194) which controls the predetermined operating point of the first valve control means in response to negative pressure. 5. A compressor according to claim 1, wherein the first and second valve and control means comprise a single pressure sensing means, the operating point of which is controlled in response to negative pressure. 6. A compressor according to claim 5, wherein the second pressure sensing means is a bellows element (201). 7. A compressor according to claim 5, wherein the second pressure sensing means is a diaphragm (260). 8. A compressor according to claim 1, wherein the first valve control means comprises a bellows element (171) applying a biasing force in a direction toward the closed position of the valve, and the second valve control means comprises means (175) for applying an adjustable force to the bellows element to adjustably reduce the biasing force. 9. A compressor according to claim 8, wherein the means for applying an adjustable force to the bellows element includes a solenoid actuator having a solenoid (175) for generating an adjustable electromagnetic force. 10. A compressor according to claim 8, wherein the means for applying an adjustable force to the bellows element includes a conduit (199) for coupling to a source of variable negative pressure.

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