Control apparatus used for refrigerant circuit having a compressor with a variable displacement mechanism

Abstract: An automobile air conditioning system including a refriger­ ant circuit having a condenser, expansion element, evaporator and wobble plate type compressor with a variable displacement mechanism. Two passages (813, 823) communicate between the crank chamber (13) and the suction chamber (151) in the cylinder block (10). A bellows (811) is disposed in a first passage (813) and controls the communication between the crank chamber (13) and the suction chamber (15) response to crank chamber pressure. A control valve (82) is disposed in the second passage and controls communication between the crank chamber (13) and the suction chamber (15) in the second passage in response to a signal regarding the temperature of the air immediately leaving from the evapora­ tor. An electric clutch (93) is mounted on the compressor in order to intermittently transmit the rotational motion from an automobile engine to a drive shaft of the compressor in response to the sig­ nal. The automobile air conditioning system is provided with a demist switch for preventing the poverty of visibility through window shields of the automobile. The operation of the control valve overrides the operation of the bellows with regardless of the signal when the demist switch is turned on.

Description: The present invention relates to an improved automobile air conditioning system. More particularly, the present invention relates to a refrigerant circuit having a slant plate type compressor with a variable displacement mechanism suitable for use in an automobile air conditioning system. One construction of a slant plate type compressor, particularly a wobble plate type compressor, with a variable capacity mechanism which is suitable for use in an automobile air conditioning system is disclosed in U.S. -A- 3,861,829. '829 discloses a wobble plate type compressor which has a cam rotor driving device to drive a plurality of pistons. The slant or incline angle of the slant surface of the wobble plate is varied to change the stroke length of the pistons which changes the displacement of the compressor. Changing the incline angle of the wobble plate is effected by changing the pressure difference between the suction chamber and the crank chamber in which the driving device is located. In the compressor of '829, the slant angle of the slant surface is controlled by the pressure in the crank chamber. Typically this control occurs in the following manner. The crank chamber communicates with the suction chamber through an aperture and the opening and closing of the aperture is controlled by a valve mechanism. The valve mechanism generally includes a bellows element and a needle valve, and is located in the suction chamber so that the bellows element operates in accordance with changes in the suction chamber pressure. The pressure of the suction chamber is compared with a predetermined value by the valve mechanism. However, when the predetermined value is below a certain value, there is a possibility of frost forming on the evaporator in the refrigerant circuit. Thus, the predetermined value is usually set higher the critical value to prevent frost from forming on the evaporator. However, since suction pressure above this critical value are higher than the pressure in the suction chamber when the compressor operates at maximum capacity, the cooling characteristics of the compressor are inferior to those of the same compressor without a variable displacement mechanism. This fact is evidently shown in Figure 1. As shown in Figure 1, temperature of the air leaving from the evaporator can not fall to the temperature of the air leaving from the evaporator when the compressor operates at maximum capacity. The air leaving from the evaporator is conducted into a passenger compartment of the automobile through a duct member in order to cool the air in the passenger compartment. Hereinafter, "the air leaving from the evaporator" is abbreviated to "the leaving air" for purposes of illustration. In Figure 1, T2 is the temperature of the leaving air corresponding to the critical value, for example, 4 centigrade. T1 is the temperature of the leaving air when the compressor operates at maximum capacity, for example, 2 centigrade. Accordingly, in the automobile air conditioning system including the compressor of '829 , an inner surface of the window shields of the automobile is not rapidly demisted when required, because that the cooling characteristics of the compressor are inferior to those of the same compressor without a variable displacement mechanism. . '829 discloses a capacity adjusting mechanism used in a wobble plate type compressor. As is typical in this type of compressor, the wobble plate type is disposed at a slant or incline angle relative to the drive shaft 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 can be used in any type of compressor which uses a slanted plate or surface in the drive mechanism. For example, U.S. -A- 4,664,604 discloses this type of capacity adjusting mechanism in a awash 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, including wobble and swash plate types, which use a slanted plate or surface in the drive mechanism. A single controlled compressor solenoid valve in combination with a pressure actuated bellows valve is disclosed in U.S. -A- 4,778,348 to improve cooling characteristics and temperature control in the passenger compartment. In a starting so-called "cool down" stage of an air conditioning system including such a compressor for initially cooling the passenger compartment, the second valve control device works to connect the crank chamber to the suction chamber due to a heat load on the evaporator of the air conditioning system being exceedingly above a single predetermined value. Once the heat load drops to the same predetermined value, the second valve control device closes the valve and only may reopen the valve if the heat exceeds that single predetermined value which will normally occur after the air conditioning system has been turned off and then restarted after a certain time period. Once the second valve control device closes the second valve, the first valve control device solely controls the capacity of the compressor. That is, after the cool down stage, the compressor similarly operates to the compressor of '829. Therefore, the drawback of '829 as described above substantially has been still remained in the operation of the automobile air conditioning system disclosed in '348 Furthermore, in general, when a switch of an automobile air conditioning system is turned on, the so-called "idle up device" is sequentially turned on. The idle up device is used for increasing the number of rotations of an engine in order to compensate decrease in the number of rotations of the engine when the compressor is driven in the idling stage of the engine. At this time, the temperature of the air outside the automobile is low, the compressor operates with the controlled displacement because that the heat load on the evaporator is small. This decreases the driving power to the compressor from the engine. Therefore, the unnecessary increase in the number of rotations of the engine is occurred in the idling stage of the engine due to the operation of the idle up device, thereby causing the unnecessary fuel consumption in the engine. Accordingly, it is an object of the present invention to provide an air conditioning control apparatus which can prevent decline of the demisting capability of an automobile air conditioning system even when a compressor with a variable displacement mechanism is used in a refrigerant circuit of an automobile air conditioning system. According to the present invention a refrigerating system including a refrigerant circuit, comprising a condenser, expansion element, evaporator and compressor, the compressor including a variable displacement control mechanism, cancelling means for cancelling the operation of the variable displacement control mechanism, detecting means for detecting the thermal condition of the evaporator as an electric signal, first control means for controlling the operation of the compressor in response to the electric signal received from the detecting means, second control means for controlling the operation of the cancelling means in response to the electric signal received from the detecting means, is characterised by selecting means for selecting one operation from the operation of the second control means and the operation of the cancelling means, the cancelling means starting to operate regardless of the electric signal of the thermal condition of the evaporator when the selecting means selects the operation of the cancelling means. In the accompanying drawings: Figure 1 is a view illustrating the temperature changes of the air leaving from the evaporator in operation of an automobile air conditioning system which includes the compressor of '829. Figure 2 is a vertical sectional view of the wobble plate type compressor with a variable displacement mechanism in accordance with one embodiment of the present invention. Figure 3 is a schematic block diagram of a control apparatus used in an automobile air conditioning system which includes the compressor shown in Figure 2. Figure 4 is a circuit diagram of a first embodiment of the control apparatus shown in Figure 3. Figure 5 is a view illustrating output response of each comparator in Figure 4 to temperature. Figure 6 is a flow chart illustrating the operation of the compressor of Figure 1 controlled by the first embodiment of the control apparatus of Figure 3. Figure 7 is a view illustrating the temperature changes of the air leaving from the evaporator in operation of the automobile air conditioning system which includes the first embodiment of the control apparatus of Figure 3. Figure 8 is a circuit diagram of a second embodiment of the control apparatus shown in Figure 3. Figure 9 is a view illustrating output response of a comparator as a third operational amplifier shown in Figure 8. Figure 10 is a flow chart illustrating the operation of the compressor of Figure 1 controlled by the second embodiment of the control apparatus of Figure 3. Figure 11 is a view illustrating the temperature changes of the air leaving from the evaporator in operation of the automobile air conditioning system which includes the second embodiment of the control apparatus of Figure 3. Figure 12 is a circuit diagram of a third embodiment of the control apparatus shown in Figure 3. Figure 13 is a block schematic diagram of a first switching device shown in Figure 12. Figure 14 is a view illustrating output response of a comparator of the first switching device shown in Figure 12. Figure 15 is a view illustrating the turning on-off response of a second switching device shown in Figure 12. Figure 16 is a flow chart illustrating the operation of the compressor of Figure 2 controlled by the third embodiment of the control apparatus of Figure 3. With reference to Figure 2, a wobble plate type compressor which is associated with the respective control apparatuses in accordance with the respective embodiments of the present invention is shown. Compressor 10 includes a closed cylindrical housing assembly 11 formed by a cylinder block 12 crank chamber 13 within cylinder block 12, front end plate 14 and rear end plate 15. Front end plate 14 is mounted on the left end portion of crank chamber 13, as shown in Figure 2, by a plurality of bolts (not shown). Rear end plate 15 and valve plate 150 are mounted on cylinder block 12 by a plurality of bolts (not shown). Opening 131 is formed in front end plate 14 for receiving drive shaft 16 which is rotatably supported by front end plate 14 through bearing 132 which is disposed within opening 131. An inner end portion of drive shaft 16 is also rotatably supported by cylinder block 12 through bearing 122 which is disposed within central bore 121. Central bore 121 provides a cavity in a center portion of cylinder block 12. Thrust needle bearing 133 is disposed between an inner end surface of front end plate 14 and an adjacent axial end surface of cam rotor 20. Front end plate 14 has annular sleeve portion 141 projecting from a front end surface thereof for surrounding drive shaft 16 to define a shaft seal cavity. Shaft seal 17 is disposed between an inner surface of annular sleeve portion 141 and an outer surface of drive shaft 16. Electromagnetic clutch 90 is disposed on annular sleeve portion 141 and connected to an outer end portion of drive shaft 16 to intermittently transmit the rotational motion from an external power source, for example, an automobile engine to drive shaft 16 of compressor 10. Electromagnetic clutch 90 preferably comprises rotor 91 rotatably supported on annular sleeve portion 141 through ball bearing 92, electromagnetic coil 93 fixed on front end plate 14, and armature plate 94. Cam rotor 20 is fixed on drive shaft 16 by pin member 18 which penetrates cam rotor 20 and drive shaft 16. cam rotor 20 is provided with arm 21 having pin 22. Slant plate 30 has opening 33 formed at a center portion thereof. Spherical bushing 19, slidably mounted on drive shaft 16, slidably mates with an inner surface of opening 33 which is spherically concave in shape. Slant plate 30 includes arm 31 having slot 32 in which pin 22 is inserted. Cam rotor 20 and slant plate 30 are joined by hinged joint 40 including pin 22 and slot 32. Pin 22 is able to slide within slot 32 so that the angular position of slant plate 30 can be changed with respect to a longitudinal axis of drive shaft 16. Wobble plate 50 is rotatably mounted on slant plate 30 through bearings 31 and 32. Rotation of wobble plate 50 is prevented by fork-shaped slider 60 which is attached to an outer peripheral end of wobble plate 50 and is slidably mounted on sliding rail 61 held between front end plate 14 and cylinder block 12. In order to slide slider 60 on sliding rail 61, wobble plate 50 wobbles without rotation even though cam rotor 20 rotates. Cylinder block 12 has a plurality of annularly arranged cylinders 70 in which respective pistons 71 slide. All pistons 71 are connected to wobble plate 50 by a corresponding plurality of connecting rods 72. Ball 73 at one end of rod 72 is received in socket 75 of pistons 71, and ball 74 at the other end of rod 72 is received in socket 51 of wobble plate 50. It should be understood that, although only one such ball socket connection is shown in the drawings, there are a plurality of sockets arranged peripherally around wobble plate 50 to receive the balls of various rods 72, and that each piston 71 is formed with a socket for receiving the other ball of rods 72. Rear end plate 15 is shaped to define suction chamber 151 and discharge chamber 152. Valve plate 150, which is fastened to the end of cylinder block 12 by plurality of the bolts together with rear end plate 15, is provided with a plurality of valved suction ports 151a connected between suction chamber 151 and respective cylinders 70, and a plurality of valved discharge ports 152a connected between discharge chamber 152 and respective cylinders 70. Suitable reed valves for suction ports 151a and discharge ports 152a are described in U.S. Pat. No. 4,011,029 issued to Shimizu. Gaskets 15a and 15b are placed between cylinder block 12 and an inner surface of valve plate 150, and an outer surface of valve plate 150 and rear end plate 15, to seal the mating surfaces of cylinder block 12, valve plate 150 and rear end plate 15. Suction inlet port 151b and discharge outlet port 152b are formed at rear end plate 15 and connected to an external fluid circuit. A variable displacement actuation mechanism comprises first valve control device 81 and second valve control device 82. The devices actuate the displacement of slant plate 30 with respect to drive shaft 16. First valve control device 81 includes a bellows valve 811 which is disposed within chamber 812 formed in cylinder block 12. Chamber 812 is connected to crank chamber 13 through a hole or passage 813 formed in cylinder block 12, and is also connected to suction chamber 151 through a hole or passage 814 formed in valve plate 150. Hole 813, chamber 812 and hole 814 provide fluid communication between crank chamber 13 and suction chamber 151. Bellows valve 811 comprises bellows element 811a of which one end is attached to an inner end surface of chamber 812, and needle valve element 811b which is attached to the other end of bellows element 811a in order to face hole 814. Bellows element 811a is axially expanded and contracted in response to crank chamber pressure thereby causing needle valve element 811b to close and open hole 814 to keep the crank chamber pressure generally constant. Accordingly, first valve control device 81 controls fluid communication between crank chamber 13 and suction chamber 151 to keep the crank chamber pressure generally constant in response to changes in the crank chamber pressure. When the crank chamber pressure is kept constant, the suction chamber is also kept generally constant. Second valve control device 82 includes solenoid valve 821 which is disposed within cavity 154 formed in rear end plate 15. Solenoid valve 821 comprises casing 821a which defines control chamber 822 and encases solenoid coil 821b surrounding needle valve element 821c therein. Holes 821d and 821e are formed in casing 821a. Hole 821d is formed at a top portion of casing 821a and faces later mentioned hole 823. Hole 821e is formed at a lower side wall portion and faces hole 824 formed at partition wall 153. Needle valve element 821c is urged toward hole 821d by restoring force of bias spring 821f. Wire 821g conducts a later mentioned signal generated at a location outside the compressor to solenoid coil 821b. Hole 823 is formed in valve plate 150 and connects hole 821d and conduit 825 formed in cylinder block 12. Therefore, crank chamber 13 is in fluid communication with control chamber 822 through conduit 825, hole 823 and hole 821d. Control chamber 822 communicates with suction chamber 151 through hole 821e and 824. When the external signal does not energize solenoid coil 821b, needle valve element 821c closes hole 821d by virtue of the restoring force of bias spring 821f so that the communication between crank chamber 13 and suction chamber 151 is blocked. When the external signal energizes solenoid coil 821b, needle valve element 821c moves right in viewing Figure 2 and against the restoring force of bias spring 821f so that crank chamber 13 communicates with suction chamber 151 via conduit 825, hole 823, hole 821d, control chamber 822, hole 821e and hole 824. When communication between crank chamber 13 and suction chamber 151 is established through conduit 825 by the operation of second valve control device 82, the operation of first valve control device 81 is overridden. Therefore, pressure in crank chamber 13 is reduced to and then maintained pressure in suction chamber 151 to thereby maintain the maximum angle of inclination of slant plate 30 and wobble plate 50 with respect to the axis of drive shaft 16, and thus the maximum displacement of compressor 10 is also maintained. Furthermore, the construction of solenoid valve 821 may be modified in a manner such that the closing of needle valve element 821c is retarded by spring 821f. Accordingly, the external signal would have to be reversed to appropriately actuate the valve. With reference to Figure 3, control apparatus 200 for controlling temperature of the leaving air is shown. Control apparatus 200 includes thermistor 210 and demist switch 220. Thermistor 210 is mounted on the evaporator or in a duct (not shown) in which the air flows from the evaporator into a passenger compartment of an automobile in order to sense temperature of the leaving air. The following description will be made as to the case where thermistor 210 is mounted on the evaporator surface at its outlet portion of the air to be cooled. Demist switch 220 manually turns on in order to energize solenoid coil 821b of solenoid valve 821. Control apparatus 200 sends a signal to electromagnetic coil 93 of electromagnetic clutch 90 in response to the operation of demist switch 220 and the temperature of the leaving air sensed by thermistor 210 to control the operation of electromagnetic coil 93. Control apparatus 200 also sends a signal as the external signal described above to solenoid coil 821b in response to the operation of demist switch 220 and the temperature of the leaving air sensed by thermistor 210 to control the operation of solenoid coil 821b. With reference to Figure 4, an electric circuit of a first embodiment of the control apparatus 200 is shown. The electric circuit comprises voltage comparator 201 such as a first operational amplifier. Thermistor 210 as a temperature sensor and resistor R1 form voltage divider 230, the divided voltage Vt of which is applied to inverting input terminal (-) of comparator 201. The divided voltage VT of voltage divider 230 changes according to the temperature variation of the leaving air and, therefore, is a signal representing the temperature of the leaving air. The sensed temperature signal VT is compared at comparator 201 with a reference voltage VR1 which is generated from voltage divider 240 formed by resistors R2 and R3. Reference voltage VR1 is designated to be equal to temperature signal VT sensed at a time when the leaving air is at a predetermined temperature T1, for example, 2 centigrade, and is applied to a non-inverting input terminal (+) of comparator 201. When the temperature of the leaving air is higher than the predetermined temperature T1, the output of comparator 201 is maintained high in voltage level because the reference voltage VR1 is higher than the temperature signal VT. On the other hand, when the temperature of the leaving air is lowered below the predetermined temperature T1, the output of comparator 201 is changed low in voltage level because the reference voltage VR1 is lower than the temperature signal VT. Comparator 201 has feed-back resistor R7 so that the input-output response has a hysteresis. That is, in course of increase of the temperature signal VT from a level lower than reference signal VR1, the output changes from the high level to the low level at a time when temperature signal VT becomes equal to reference signal VR1. However, in course of decrease of temperature signal VT from a level higher than reference signal VR1, the output changes from the low level to the high level at not a time when temperature signal VT becomes equal to reference signal VR1 but a time when tempeature signal VT becomes lower than reference signal VR1 by a certain amount. As a result, the output response of comparator 201 to the temperature has a hysteresis as shown by (a) in Figure 5. Temperature difference delta T1 is determined by the resistance of resistor R7, that is, temperature T2, for example, 4 centigrade higher than T1 by delta T1 is determined by the resistance of resistor R7. Another voltage comparator 202 such as a second operational amplifier compares temperature signal VT with another reference signal VR2 which is generated by another voltage divider 250 comprising resistors R4 and R5. Reference voltage VR2 is designated to be equal to temperature signal VT which will be sensed at a time when the leaving air is at a predetermined temperature T3, for example, 3 centigrade. The temperature T3 is determined higher than temperature T1. It will be easily understood that the output of comparator 202 is a high level at a time when the temperature of the leaving air is higher than the predetermined temperature T3. On the other hand, it is low level at a time when the temperature of the leaving air is lower than predetermined temperature T3. Comparator 202 has feedback resistor R6 to provide a hysteresis so that the output of comparator 202 may change from the low level to the high level at an elevated temperature T4, for example, 6 centigrade higher than not only T3 but also T2. The output response of comparator 202 to the temperature is as shown by (b) in Figure 5. Transistor 203 forms a switching circuit. Resistors R8, R9 and R10 are bias resistors. Relay 205 is connected in a collector circuit of transistor 203, and its operating contact 205a is connected in series with electromagnetic coil 93 of electromagnetic clutch 90. A base of transistor 203 is connected to connection point "B" between resistors R9 and R10. When transistor 203 is conductive, relay 205 is in an operative condition so that electromagnet coil 93 is energized. Output of comparator 201 is connected to connection point "A" between resistors R8 and R9 through diode D1. Therefore, when any one of outputs of comparator 201 is the low level, the level of connection point "A" is also low so that transistor 203 is switched off. Therefore, relay 205 is not energized and, therefore, its contact 205a is open, so that electromagnet coil 93 is not energized. Transistor 204 forms a switching circuit. Resistor R12, R13 and R14 are bias resistors. Relay 206 is connected in a collector circuit of transistor 204, and its operating contact 206a is connected in series with solenoid coil 821b of solenoid valve 821. A base of transistor 204 is connected to connection point "D" between resistors R13 and R 14. When transistor 204 is conductive, relay 206 is in an operative condition so that solenoid coil 821b of solenoid valve 821 is energized. Output of comparator 202 is connected to connection point "C" between resistors R12 and R13 through diode D2. Therefore, when any one of outputs of comparator 202 is the low level, the level of connection "C" is also low so that transistor 204 is switched off. Therefore, relay 206 is not energized and, therefore, its contact 206a is open, so that solenoid coil 821b is not energized. One contact of demist switch 220 is connected to input terminal (+) of a power supply through resistor R11. Another contact of demist switch 220 is connected to connection point "D". When demist switch 220 is turned off, solenoid coil 821b is intermittently energized in response to the output of comparator 202. On the other hand, when demist switch 220 is turned on, solenoid coil 821b is maintained the energized condition. Figures 6 shows a flow chart which illustrates the operation of the first embodiment of control apparatus 200. With reference to Figure 6 in addition to Figures 2-5, compressor 10 used in the automobile air conditioning system operates as follows. After the automobile air conditioning switch is turned on at step 101, whether demist switch 220 is turned on or not is judged at step 102. In step 102, when the visibility through the window shields of the automobile is poor due to the mist, demist switch 220 is turned on. On the other hand, when the visibility is good, demist switch 220 is not turned on. When demist switch 220 is not turned on, the sensed temperature signal VT representing temperature "T" of the leaving air is compared at comparator 202 with reference voltage VR2 at step 103. In step 103, when temperature signal VT is in course of increase from a level lower than reference signal VR2, the output changes from the high level to the low level at a time when temperature signal VT becomes equal to reference signal VR2. That is, when temperature "T" is in course of drop from a higher value than temperature T4, the output changes from the high level to the low level at a time when temperature "T" becomes equal to temperature T3 as shown by (b) in Figure 5. Therefore, relay 206 is not energized and, therefore, its contact 206a is open, so that solenoid coil 821b is not energized as shown by step 104. Accordingly, needle valve element 821c closes hole 821d by virtue of the restoring force of bias spring 821f so that the communication between crank chamber 13 and suction chamber 151 is blocked. Thereby, the displacement of compressor 10 is controlled by only first valve control device 81 in response to changes in the crank chamber pressure as already described above. When temperature signal VT is in course of decrease from a higher level than reference signal VR2, the output changes from the low level to the high level at not time when temperature signal VT becomes equal to reference signal VR2 but a time when temperature signal VT becomes lower than reference signal VR2 by the certain amount. That is, when temperature "T" is in course of rise from a lower value than temperature T3, the output changes from the low level to the high level at a time when temperature "T" becomes equal to temperature T4 as shown by (b) in Figure 5. Therefore, relay 206 is energized and, therefore, its contact 206a is closed, so that solenoid coil 821b is energized as shown by step 105. Accordingly, needle valve element 821c moves right in viewing Figure 2 and against the restoring force of bias spring 821f so as to open hole 821d. Thereby, compressor 10 is maintained the maximum displacement as already described above. On the other hand, when demist switch 220 is turned on, solenoid coil 821b is energized without regard of temperature "T" of the leaving air as shown by step 105. Each of steps 104 and 105 goes to step 106 in which the sensed temperature signal VT representing temperature "T" of the leaving air is compared at comparator 201 with reference voltage VR1. In step 106, when temperature signal VT is in course of increase from a level lower than reference signal VR1, the output changes from the high level to the low level at a time when temperature signal VT becomes equal to reference signal VR1. That is, when temperature "T" is in course of drop from a higher value than temperature T2, the output changes from the high level to the low level at a time when temperature "T" becomes equal to temperature T1 as shown by (a) in Figure 5. Therefore, relay 205 is not energized and, therefore, its contact 205a is open, so that electromagnetic coil 93 is not energized as shown by step 107. Accordingly, transmission of the rotational motion from the automobile engine to drive shaft 16 of compressor 10 is interrupted in order to interrupt the operation of compressor 10. When temperature signal VT is in course of decrease from a higher level than reference signal VR1, the output changes from the low level to the high level at not time when temperature signal VT becomes equal to reference signal VR1 but a time when temperature signal VT becomes lower than reference signal VR1 by the certain amount. That is, when temperature "T" is in course of rise from a lower value than temperature T1, the output changes from the low level to the high level at a time when temperature "T" becomes equal to temperature T2 as shown by (b) in Figure 5. Therefore, relay 205 is energized and, therefore, its contact 205a is closed, so that electromagnetic coil 93 is energized as shown by step 108. Accordingly, the rotational motion of the automobile engine is transmitted to drive shaft 16 of compressor 10 in order to operate compressor 10. Each of steps 107 and 108 returns to step 102. In the event, the first embodiment of control apparatus 200 controls the temperature of the leaving air as shown in Figure 7. With reference to Figure 7, when the automobile air conditioning switch is turned on without turning on demist switch 220 at a time when temperature of the leaving air is higher than T4 and the visibility through the window shields of the automobile is good, the change in tempeature of the leaving air is illustrated at time period "a". In time period "a", compressor 10 continuously operates with the maximum displacement. When the temperature of the leaving air falls to T3, time period "a" is terminated. After time period "a", the change in temperature of the leaving air is illustrated at time period "b". In time period "b", compressor 10 starts to operate with the controlled displacement by operation of only first valve control device 81 in order to maintain the degree of temperature of the leaving air constant, for example, immediately above T2. In this period, when the visibility through the window shields of the automobile becomes poor, demist switch 220 is turned on, and time period "b" is simultaneously terminated. After time period "b", the change in temperature of the leaving air is illustrated at time period "c". In time period "c", compressor 10 operates with the maximum displacement again, but intermittently by virtue of the intermittent operation of electromagnetic clutch 90. Thereby, the temperature of the leaving air is cyclically controlled from T2 to T1 in order to recover the good visibility through the window shields of the automobile. When the good visibility through the window shields of the automobile is recovered, demist switch 220 is turned off, and time period "c" is simultaneously terminated. After time period "c", the change in temperature of the leaving air is illustrated at time period "d". In time period "d", compressor 10 operates with the controlled displacement again as same as time period "b". In the mention-later second and third embodiments of control apparatus 200, the same numerals are used to denote the corresponding elements shown in Figures 2-7 so that the substantial explanation thereof is omitted. Figure 8 illustrates a circuit diagram of a second embodiment of control apparatus 200. As depicted in Figure 8, the circuit of the second embodiment of control apparatus 200 is formed by adding timer circuit 260, which includes comparator 301 as a third operational amplifier, to the circuit of the first embodiment of control apparatus 200 and replacing demist switch 220 which demist switch 221 having contacts 221a and 221b. Comparator 301 compares reference voltage VR3 at point "E" determined by resistors R15 and R16 with the voltage at point "F" determined by the charging-discharging condition of capacitor C1. Comparator 301 has feed-back resistor R17 so that the input-output response has a hysteresis. That is, in course of charging to capacitor C1 from a level lower than reference signal VR3, the output changes from the high level to the low level at a time when the voltage at point "F" becomes equal to reference signal VR3. However, in course of discharging from capacitor C1 from a level higher than reference signal VR3, the output changes from the low level to the high level at not a time when the voltage at point "F" becomes equal to reference signal VR3 but a time when the voltage at point "F" becomes lower than reference signal VR3 by a certain amount. As a result, the output response of comparator 301 to the voltage at point "F" has a hysteresis. The above-mentioned certain amount of the voltage is determined by the resistance of resistor R17. When contact221b of demist switch 221 is closed, the charging amount to capacitor C1 is determined by resistors R18 and R19. Since the voltage at point "F" is determined by resistors R18 and R19 so as to be lower than reference signal VR3, the output of comparator 301 is maintained the high level as shown by (a) in Figure 9. When contact 221b of demist switch 221 is closed, contact 221a is consequentially open. Therefore, solenoid coil 821b is intermittently energized in response to the output of comparator 202. On the other hand, when contact 221a of demist switch 221 is closed, solenoid coil 821b is maintained the energized condition, and contact 221b of demist switch 221 is consequentially open. Therefore, capacitor C1 begins to be charged by the voltage of the output of comparator 301. In a charging condition of capacitor C1, when the voltage at point "F" rises to reference signal VR3, the output of comparator 301 changes from the high level to the low level. Thereby, solenoid coil 821b is deenergized. Simultaneously, capacitor C1 begins to discharge. In a discharging condition of capacitor C1, when the voltage at point "F" falls to the voltage which is lower than reference signal VR3 by the certain amount, the output of comparator 301 changes from the low level to the high level. Thereby, solenoid coil 821b is energized again. Simultaneously, capacitor C1 begins to be charged by the voltage of the output of comparator 301. The change of the output of comparator 301 from the high level to the low level and the change of the output of comparator 301 from the low level to the high level are alternately repeated as shown by (b) in Figure 9 until contact 221a of demist switch 221 is opened. Figure 10 shows a flow chart of the second embodiment of control apparatus 200. As depicted in Figure 10, the flow chart of the first embodiment shown in Figure 6 can be changed to the flow chart of the second embodiment by adding step 401 after "yes" of step 102. Furthermore, the second embodiment of control apparatus 200 controls the temperature of the leaving air as shown in Figure 11. With reference to Figure 11, when the automobile air conditioning switch is turned on without closing contact 221a of demist switch 221 at a time when temperature of the leaving air is higher than T4 and the visibility through the window shields of the automobile is good, the change in temperature of the leaving air is illustrated at time period "a". In time period "a", compressor 10 continuously operates with the maximum displacement. When temperature of the leaving air falls to T3, time period "a" is terminated. After time period "a", the change in temperature of the leaving air is illustrated at time period "b". In time period "b", compressor 10 starts to operate with the controlled displacement by operation of only first valve control device 81 in order to maintain the degree of temperature of the leaving air constant, for example, immediately above T2. In this period, when the visibility through the window shields of the automobile becomes poor, contact 221a of demist switch 221 is closed, and time period "b" is simultaneously terminated. After time period "b", the change in temperature of the leaving air is illustrated at time period "c". In time period "c", compressor 10 operates with the maximum displacement again, but intermittently by virtue of the intermittent operation of electromagnetic clutch 90. Thereby, temperature of the leaving air is cyclically controlled from T2 to T1. When the certain time elapsed from the start of time period "c", time period "c" is terminated, but simultaneously starts time period "e". In time period "e", compressor 10 operates with the controlled displacement by operation of only first valve control device 81 in order to maintain the degree of temperature of the leaving air constant, for example, immediately above T2 as same as time period "b". When the certain time elapsed from the start of time period "e", time period "e" is terminated, but simultaneously starts time period "c" again. These time periods "c" and "e" are alternately repeated in order to recover the good visibility through the window shields of the automobile. When the good visibility through the window shields of the automobile is recovered, contact 221a of demist switch 221 is opened, and time periods "c" or "e" is simultaneously terminated. After time periods "c" or "e", the change in temperature of the leaving air is illustrated at time period "d". In time period "d", compressor 10 operates with the controlled displacement again as same as time period "b". In the second embodiment, compressor 10 operates with the controlled displacement in addition to the maximum displacement in the closed stage of contact 221a so that the energy consumption of the automobile engine for compressor 10 is decreased in comparison with the first embodiment. Figure 12 illustrates a circuit diagram of a third embodiment of control apparatus 200. As depicted in Figure 12, the circuit of the third embodiment of control apparatus 200 is formed by providing first and second switching devices 520 and 530, which are connected in series each other between input (+) of the power supply and connection point "D", to the circuit of the second embodiment of control apparatus 200. With reference to Figures 12 and 13, first switching device 520 includes ignition pulse sensor 521, comparator 522 and relay 523 having contact 523a. Ignition pulse sensor 521 detects the number of ignition pulses as the number of rotations of the automobile engine. Comparator 522 receives a signal representing the number of rotations of the automobile engine from ignition pulse sensor 521, and compares the signal with the mention-later predetermined values in order to generate the high-low level signal which controls relay 523. An input-output response of comparator 522 has a hysteresis. That is, of course of increase of the number of rotations of the engine from a level lower than the number of idling rotations N1, the output changes from the high level to the low level at not a time when the number of rotations becomes equal to the number of idling rotations N1 but a time when the number of rotations becomes higher than the number of rotations N2 which is higher than N1 by certain numbers. However, in course of decrease of the number of rotations of the engine from a level higher than the number of rotations N2, the output changes from the low level to the high level at a time when the number of rotations becomes equal to the number of idling rotations N1. As a result, the output response of comparator 522 to the number of rotations of the automobile engine has a hysteresis as shown in Figure 14. When relay 523 receives the high level signal from comparator 522, contact 523a of relay 523 is closed. When relay 523 receives the low level signal from comparator 522, contact 523a of relay 523 is opened. Second switching device 530 turns on and off with a mechanical hysteresis in response to temperature of air outside the automobile. That is, in course of rise in temperature of the air outside the automobile from a level lower than the predetermined temperature To1, second switching device 530 changes from the turning on stage to the turning-off stage at not a time when the temperature becomes equal to the temperature To1 but a time when the temperature becomes higher than the other predetermined temperature To2 which is higher than To1 by a certain amount. However, in course of fall in temperature of the air outside the automobile from a level higher than the other predetermined temperature To2, second switching device 530 changes from the turning off stage to the turning-on stage at a time when the temperature becomes equal to the temperature To1. As a result, the turning on-off response of second switching device 530 to the temperature of air outside the automobile has a hysteresis as shown in Figure 15. Figure 16 shows a flow chart of the third embodiment of control apparatus 200. As depicted in Figure 16, the flow chart of the second embodiment shown in Figure 10 can be changed to the flow chart of the third embodiment by adding steps 501 and 502 after step 101. In this embodiment, either when the output of first switching device 520 is the high level or when second switching device 530 is the turning-on stage, or neither when the output of first switching device 520 is the high level nor when second switching device 530 is the turning-on stage, first and second switching device 520 and 530 do not override demist switch 221, that is, the third embodiment of control apparatus 200 controls compressor 10 as same as the second embodiment of control apparatus 200. On the other hand, both when the output of first switching device 520 is the high level and when second switching device 530 is the turning-on stage, first and second switching devices 520 and 530 override demist switch 221. Thereby, solenoid coil 821b is maintained the energizing stage, that is, the operation of the compressor is maintained in the maximum displacement. In result, the unnecessary increase in the number of rotations of the engine in the idling stage of the engine can be prevented, that is, the unnecessary fuel consumption in the engine in the idling stage can be prevented. Furthermore, the temperature changes of the leaving air in operation of the automobile air conditioning system including the third embodiment of control apparatus 200 is similar to the second embodiment so that a graph illustrating thereof is omitted. In every embodiment, the following switching device can be used as the demist switch. The switching device includes a lever slidably moving in a slot formed at an air conditioning operation panel in a dash board, and is designed that when the lever is positioned at the point marked "DEMIST" on the panel, the switch is turned on so as to energize solenoid coil 821b.

Claims: A refrigerating system including a refrigerant circuit, comprising a condenser, expansion element, evaporator and compressor (10), the compressor including a variable displacement control mechanism (81), cancelling means (82) for cancelling the operation of the variable displacement control mechanism, detecting means (210) for detecting the thermal condition of the evaporator as an electric signal, first control means (201) for controlling the operation of the compressor in response to the electric signal received from the detecting means, second control means (202) for controlling the operation of the cancelling means in response to the electric signal received from the detecting means, characterised by selecting means (220) for selecting one operation from the operation of the second control means and the operation of the cancelling means, the cancelling means starting to operate regardless of the electric signal of the thermal condition of the evaporator when the selecting means selects the operation of the cancelling means. A system according to claim 1, wherein the selecting means is a switching device. A system according to claim 1 or 2, wherein the thermal condition of the evaporator is the temperature of air immediately leaving the evaporator. A system according to any one of the preceding claims, wherein the compressor is driven by an internal combustion engine of an automobile, and the cancelling means (82) starts to operate regardless of the electric signal of the thermal condition of the evaporator both when the number of rotations of the internal combustion engine is lower than a predetermined value and when the temperature outside the automobile is lower than a predetermined value. A refrigerating system according to claim 1, wherein the compressor includes a compressor housing (11) having a central portion (12), a front plate (14) at one end and a rear plate (15) at its other end, a cylinder block (12) including a plurality of hollow cylinders (70), with a piston (71) slidably fitted within each of the cylinders, a drive mechanism coupled to the pistons to reciprocate the pistons within the cylinders, the drive mechanism including a drive shaft (16) rotatably supported in the housing, the drive shaft coupled to rotational motion transmitting means (90) for transmitting a rotational motion from a power source thereto, a rotor (20) coupled to the drive shaft and rotatable therewith, and coupling means (30,40,50,72) for drivingly coupling the rotor (20) to the pistons (71) such that the rotary motion of the rotor is converted into reciprocating motion of the pistons, the coupling means including a member (30) having a surface disposed at an incline angle relative to the drive shaft (16), the incline angle of the member (30) being adjustable to vary the stroke length of the pistons and thus the capacity of the compressor, the rear plate (15) having a suction chamber (151) and a discharge chamber (152), the variable displacement control means for controlling angular displacement of the adjustable member, including first (81) and second (82) valve control means, the second valve control means providing the cancelling means and being capable of overriding and cancelling the effect of the first valve control means, a temperature control circuit including the detecting means (210) for detecting the temperature of the air leaving the evaporator, the second valve control means (82) responsive to the temperature control circuit and switching means (220) providing the selecting means for overriding the temperature control circuit and activating the second valve control means. A refrigerating system according to claim 5, wherein the temperature control circuit further includes first reference signal source means (250) for generating a first reference signal equal to the output signal of the temperature detecting means (210) corresponding to a first temperature (T3), first comparing means (202) providing the second control means for comparing the output from the first temperature detecting means (210) with the first reference signal and providing an output at a first level when the detected temperature is higher than the first temperature (T3) and at a second level when the detected temperature is lower than the first temperature, first hysteresis means (R6) for causing the output of the first comparing means to display a hysteresis effect, first stop-signal generating means (204,206) coupled with the output of the first comparing means (202) for generating a first stop signal for stopping the operation of the second valve control means (82), the first hysteresis means (R6) prohibiting the first stop signal from reaching the second valve control means (82) until a time when a predetermined second temperature (T4) higher than the first temperature (T3) is detected by the temperature detecting means (210). A refrigerating system according to claim 6, wherein the temperature control circuit further comprises second reference signal source means (240) for generating a second reference signal equal to the output signal of the temperature detecting means (210) corresponding to a third temperature (T1), second comparing means (201) for comparing the output from the temperature detecting means (210) with second reference signal and providing an output at a third level when the detected temperature is higher than the third temperature (T1) and at a fourth level when the detected temperature is lower than the third temperature, second hysteresis means (R7) for causing the output of the second comparing means to display a hysteresis effect, second stop-signal generating means (203,205) coupled with the output of the second comparing means (201) for generating a second stop signal for stopping the operation of the rotational motion transmitting means (90), the second hysteresis means (R7) prohibiting the second stop-signal from stopping the operation of the rotational motion transmitting means (90), until a time when a predetermined fourth temperature (T2) higher that the third temperature (T1) is detected by the temperature detecting means (210).

Inventors: TAGUCHI YUKIHIKO, TAGUCHI, YUKIHIKO
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1990
Main classification: F04B1
IPC codes: F25B1, F04B27, F04B49, B60H1