JP2997269B2 - External control device for variable capacity compressor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for externally controlling a variable capacity compressor called an internal capacity variable type in an air conditioner mounted on a vehicle. 2. Description of the Related Art Conventionally, as a vehicle air conditioner of this type, a compressor (compressor) that is drivingly connected to an on-vehicle engine via an electromagnetic clutch mechanism and a gas refrigerant discharged from the compressor are heated by air. A condenser (condenser) that cools by exchange and condenses to a liquid state, and an evaporator (evaporator) that evaporates the liquid refrigerant passing through the condenser and cools the vehicle interior by the heat of vaporization. When the evaporating temperature of the refrigerant drops below a predetermined temperature, this is detected by a frost switch, and the operation of the compressor is stopped by turning off the electromagnetic clutch mechanism. Have been. That is, when the engine speed increases, the amount of refrigerant discharged from the compressor driven by the engine increases, and a large amount of refrigerant circulates in the refrigerant circuit. Since the load is substantially constant, the capacity becomes surplus, and the drive of the compressor is stopped to eliminate this surplus portion. However, in that case, from the viewpoint of reducing the driving force for driving the compressor of the engine and improving the EER (energy consumption efficiency), rather than temporarily stopping the compressor and restarting it thereafter, the compressor is It is more preferable to continue the operation while reducing the capacity of the fuel cell from the steady state. For example, among compressors, condensers, and evaporators, the dependence of these devices on the coefficient of performance shows that the smaller the capacity of the compressor, the lower the work capacity of the compressor itself, but the higher the contribution rate of the condenser and the evaporator. And the overall coefficient of performance increases. In other words, although the work capacity of the compressor is reduced, the overall enthalpy is equal, and the EER is increased. Therefore, as a compressor that satisfies such requirements,
Hitherto, as disclosed in Japanese Patent Application Laid-Open No. Sho 60-261721, a compressor with a variable internal capacity has been proposed. this is,
When the compressor capacity becomes excessive, a part of the refrigerant sucked into the compressor body is bypassed from the middle of the compression stroke and returned to the suction side, so that the capacity of the compressor can cope with the heat load in the cabin. Is controlled automatically. (Problems to be Solved by the Invention) On the other hand, when using the proposed variable internal capacity compressor, the capacity of the compressor is automatically controlled to a capacity corresponding to the heat load in the vehicle compartment. The following problems arise. That is, for example, when the vehicle is accelerating or climbing a hill, the load on the engine is large. Therefore, it is preferable to transmit the output of the engine to the driving wheels as much as possible. However, if the heat load in the cabin at that time is large, the compressor is automatically controlled to have a large capacity, and the ratio of the engine output consumed for driving the compressor increases, and accordingly,
The power to the driving wheels is reduced, and the acceleration performance and the climbing performance are sacrificed to some extent. The present invention has been made in view of such a point, and its object is to perform the internal capacity control according to the external conditions in addition to the original automatic internal capacity control in the variable internal capacity compressor as described above. In this way, the load on the engine for driving the compressor during vehicle acceleration and climbing uphills is reduced as much as possible while taking advantage of the characteristics of the internal capacity control type compressor, thereby improving the vehicle acceleration. The purpose is to improve performance and climbing performance. (Means for Solving the Problems) In order to achieve this object, for example, a solution of the present invention is to reduce the number of revolutions of an engine and the number of turbine revolutions in a torque converter for transmitting engine output to an automatic transmission. In comparison, a state in which the engine speed is higher than the turbine speed by a predetermined value or more, that is, a state in which so-called slip loss is large is regarded as a state in which the load for traveling of the vehicle is large, so that the engine load is increased by a predetermined amount or more. At this time, the execution of the internal capacity control of the air conditioner compressor is temporarily prohibited, and the capacity is fixedly held at the minimum capacity. Specifically, the configuration of the present invention includes a suction port for sucking the refrigerant, a discharge port for discharging the refrigerant that has been sucked from the suction port and has passed through the compression stroke, and a suction port on the suction side of the refrigerant during the compression stroke of the refrigerant. A bypass passage for bypassing to the suction side, and a bypass valve for opening and closing the bypass passage according to a pressure difference between a suction chamber communicating with the suction side and a pressurization chamber having a higher pressure than the suction chamber. A variable displacement mechanism that operates to control the refrigerant discharge capacity by opening and closing a bypass passage by a bypass valve by changing the pressure of the pressurizing chamber according to the suction pressure of the refrigerant during control, and is driven by an onboard engine; An external control system in which the variable capacity mechanism is controlled by the variable capacity mechanism according to the heat load of the air conditioner from the outside when controlling the air conditioner. Directed to an apparatus. Further, the compressor has a communication passage that communicates the suction chamber and the pressurization chamber of the variable capacity mechanism with the variable capacity mechanism, and an opening / closing valve that opens and closes the communication passage. A capacity setting mechanism is provided to reduce the pressure in the pressurizing chamber and open the bypass valve so that the refrigerant discharge capacity of the compressor is kept to a minimum. A load discriminating means for detecting a load of the engine and outputting a command signal when the engine load is greater than a predetermined value; and controlling the capacity setting mechanism of the compressor based on the command signal from the load discriminating means. Means are provided. (Operation) With this configuration, according to the present invention, when the vehicle is running, the load determining means determines a state in which the engine load is equal to or greater than a predetermined value, and when the engine load is not higher than the predetermined value, the engine load for driving the vehicle is determined. Is in a low state,
The capacity setting mechanism does not operate due to non-operation of the control means, the compressor is maintained in the internal capacity control state by the variable capacity mechanism, the pressure in the pressurizing chamber is changed according to the suction pressure of the refrigerant, and the bypass valve opens and closes. The discharge amount of the refrigerant is controlled according to the suction pressure so that the bypass passage is opened and closed by the opening and closing operation of the bypass valve so that the suction pressure becomes substantially constant. However, when the engine load is higher than a predetermined value, the engine load for running the vehicle is in a high state.
A command signal is output from the load discriminating means, and the operation of the control means receiving the command signal prohibits the internal capacity control of the compressor, and the opening of the on-off valve of the capacity setting mechanism causes the pressurization of the variable capacity mechanism. The refrigerant gas in the chamber flows into the suction chamber via the communication path, the pressure in the pressurizing chamber decreases, the bypass valve opens, and the capacity of the compressor is forcibly fixed to the minimum capacity. Due to the fixed holding of the minimum capacity of the compressor, the load on the engine required for driving the compressor becomes extremely small, and the reduction in the load on the compressor increases the power transmission rate to the driving wheels of the engine, thereby increasing the acceleration performance of the vehicle. And climbing performance can be improved. In addition, the variable displacement mechanism of the compressor with variable internal capacity is controlled by the displacement setting mechanism to keep the discharge capacity of the refrigerant at a minimum. It does not require a separate variable displacement mechanism for displacement control by an external controller of the compressor. In addition, even in the external control state, the compressor is controlled in the same manner as in the internal capacity control state, and natural external control can be performed without giving an uncomfortable feeling to the occupant (particularly, the driver) of the vehicle. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration of an embodiment of the present invention, and 1 shows an electronic fuel injection engine 12 and an electronically controlled transmission (both not shown) that is drivingly connected to the engine 12 via a torque converter. An air conditioner mounted on a vehicle equipped with the air conditioner, the air conditioner 1 includes a compressor 2 (compressor) which is drivingly connected to the on-vehicle engine 12 via an electromagnetic clutch mechanism 13 and a transmission belt 14, and an engine of a vehicle body. A condenser 3 (condenser) which is disposed at the front end of the room and cools the gas refrigerant by heat exchange with traveling wind or the like and condenses it into a liquid refrigerant; a receiver tank 4 (liquid receiver) for storing the liquid refrigerant; An expansion valve 5 (expansion valve) whose degree of opening is adjustable to reduce the pressure to a pressure suitable for vaporization and is disposed in the vehicle interior, and vaporizes the liquid refrigerant to generate air in the vehicle interior by the heat of vaporization. An evaporator 6 (evaporator) for cooling is provided, and a refrigerant circuit 8 is configured by connecting these devices 2 to 6 by a refrigerant pipe 7. Reference numeral 9 denotes the compressor 2 from the evaporator 6.
The temperature-sensitive cylinder attached to the refrigerant pipe 7 returns to the
Is connected to the expansion valve 5 via a heat transfer tube 10, and the opening of the expansion valve 5 is automatically adjusted so that the temperature of the gas refrigerant vaporized by the evaporator 6 becomes constant. Reference numeral 11 denotes a fan attached to the evaporator 6. The compressor 2 is composed of a vane type variable displacement compressor. The basic structure of the variable displacement compressor 2 is the same as that of a normal vane compressor. That is, the main body 20 of the compressor 2 is airtightly joined to a ring-shaped side housing 23 and front and rear surfaces of the side housing 23 as shown in an enlarged detail in FIG. Front and rear housings 25 and 26 forming a columnar working chamber 24, and a cylindrical rotor rotatably fitted in the working chamber 24 of the side housing 23 so as to be offset with respect to the center of the working chamber 24.
27, and a pair of through vanes 28, 28, which are supported by the rotor 27 so as to be able to protrude and retract from the outer peripheral portion thereof, and whose ends are in sliding contact with the inner peripheral wall of the working chamber 24 to partition the working chamber 24, The housing 25 is formed with a suction port 21 for sucking refrigerant into the working chamber 24 and a suction chamber 29 communicating with the suction port 21. The side housing 23 has a discharge port 22 for discharging the refrigerant having passed through the compression stroke, and the rear housing 26 has a discharge chamber (not shown) communicating with the discharge port 22. Further, the rotating shaft 31 of the rotor 27 is connected to the electromagnetic clutch mechanism 13, and when the electromagnetic clutch mechanism 13 is turned on, the engine 12
The rotation of the rotor 27 by the output of the above, the volume of the part partitioned by the vanes 28, 28 in the working chamber 24 in the side housing 23 gradually decreases and changes with the rotation of the rotor 27, the side housing 23 The gas refrigerant sucked from the suction port 21 is compressed and discharged from the discharge port 22. In this basic configuration, a spool valve 32 is provided in the front housing 25 of the compressor body 20. Further, a pressure regulator 40 composed of a needle valve is attached to a lower portion extending over both the side housing 23 and the rear housing 26. As shown in FIG. 3, the spool valve 32 is slidably fitted in a cylindrical valve housing 33 and the valve housing 33. A pressurizing chamber 36 is provided with a port 33a of the valve housing 33 and the port 3a.
A predetermined gap between the front housing 25 and the side housing 23 in the compressor body 20 is communicated through a communication passage 37 connected to 3a, and the internal pressure is determined by the suction pressure and the discharge pressure of the gas refrigerant. The pressure is set to a substantially intermediate pressure. A valve body 34 is provided in the spring chamber 35 in a pressurizing chamber.
A spring 38 biasing toward the side 36 is compressed, and the spring chamber 35 communicates with the suction chamber 29 in the front housing 25 via a port 33b. further,
The valve housing 33 has four bypass holes 39a to 39b in the middle of the sliding range of the valve body 34 inside the valve housing 33. The bypass holes 39a and 39b are opposed to each other in the diameter direction of the housing 33, and the bypass holes 39a and 39b are Housing between 39a (39b, 39b)
The bypass holes 39a, 39a located on one side of the housing 33 (the right side in FIG. 2) correspond to the middle of the refrigerant compression stroke in the working chamber 24. In the part, the other side (same left side) bypass hole 39b,
The working chamber 39b is communicated with the suction chamber 29 by a bypass hole 39a, 39b diametrically opposed to the housing 33 and a part of the spring chamber 35 located between the bypass holes 39a, 39b. Bypass passages 39, 39 are formed to bypass the refrigerant to the suction chamber 29 (suction side) in the middle of the compression process of the refrigerant compressed in the inside 24. Then, the urging force of the intermediate pressure in the pressurizing chamber 36 against the valve element 34 is applied to the refrigerant suction pressure in the spring chamber 35 by the spring 38 therein.
When the force is greater than the urging force obtained by adding the spring force of
Is moved downward in FIG.
On the other hand, when the bypass passages 39 and 39 are closed by closing the bypass passages 39 and 39, the valve body 34 is moved upward in FIG.
It is made to open 9,39. On the other hand, the pressure regulator 40 includes a valve housing 44 in which first and second two pressure chambers 42 and 43 communicating with each other via a valve port 41 are formed, and the valve port 41 in the valve housing 44. A valve body 45 fitted so that it can be opened and closed,
A diaphragm 46 is fitted in the second pressure chamber 43 of the valve housing 44 and partitions the second pressure chamber 43 into a suction pressure chamber 43a and an atmospheric pressure chamber 43b.
Is integrally connected to the valve body 45 via a rod 47, and a diaphragm 46 is provided in the atmospheric pressure chamber 43b.
(In the direction in which the valve body 45 communicates with the first and second pressure chambers 42 and 43) is compressed. The first pressure chamber 42 is connected to the communication path 37 (a predetermined gap between the front housing 25 and the side housing 23 in the compressor main body 20) via a communication path 49, and the suction in the second pressure chamber 43. The pressure chambers 43a communicate with the suction chambers 29, respectively.
Is open to the atmosphere, and when the urging force of the diaphragm 46 due to the refrigerant suction pressure in the suction pressure chamber 43a is larger than the urging force obtained by adding the spring force of the spring 48 inside the atmospheric pressure chamber 43b to the atmospheric pressure. The diaphragm 46 is moved downward in FIG. 3 to close the valve port 41 by the valve body 45 integrated with the diaphragm 46, thereby cutting off the communication between the first pressure chamber 42 and the suction chamber 29, and reversely. When it is small, the diaphragm
46 is moved upward in the same figure to open the valve port 41, and the first pressure chamber is opened.
42 and the suction chamber 29 are communicated. Therefore, the spool valve 32 and the pressure regulator 40 automatically control the opening and closing of the bypass passages 39 and 39 in accordance with the refrigerant suction pressure so that the refrigerant suction pressure of the compressor body 20 is kept substantially constant. When the rotation speed (engine speed) is low and its capacity is low, the pressure regulator 40 is closed and the bypass passages 39, 39 are closed by increasing the pressure in the pressurizing chamber 36 of the spool valve 32. While the capacity of the compressor 2 is maintained at the maximum capacity, when the capacity of the compressor 2 is increased due to an increase in the rotation speed, the pressure in the suction chamber 29 is reduced and the pressure regulator 40 is opened. Accordingly, the pressure in the pressurizing chamber 36 of the spool valve 32 is reduced, the valve body 34 is moved upward in the figure, and the bypass passages 39, 39 are opened. By bypassing the gas refrigerant to the suction side, the capacity of the compressor 2 is reduced in accordance with the increase in the number of revolutions, that is, when the capacity of the compressor 2 exceeds the heat load in the passenger compartment, Variable capacity mechanism 50 that eliminates the ability
Is configured. Further, the first pressure chamber of the pressure regulator 40
A communication passage 49 that communicates the communication passage 42 with the communication passage 37 and the suction chamber 29 in the front housing 25 are communicated by a communication passage 51. The normally closed solenoid valve SV that opens and closes the communication passage 51 is connected to the communication passage 51. Is disposed, and in a closed state of the solenoid valve SV,
While the variable capacity mechanism 50 is operated to bring the compressor 2 into the internal capacity control state, when the solenoid valve SV is opened,
The operation of the variable displacement mechanism 50 is stopped, the pressure in the suction chamber 29 is set to the intermediate pressure, and the valve body 34 of the spool valve 32 is positioned at the rising end position by the spring force of the spring 38, and the bypass passages 39, 39 are fully opened. The capacity setting mechanism 52 is configured to fix the capacity of the compressor 2 to the minimum capacity by controlling the variable capacity mechanism 50 so as to keep the bypass amount of the refrigerant to the maximum so as to keep the compressor 2 at the minimum capacity. Then, as shown in FIG. 1, the operation of the solenoid valve SV is controlled by the control unit 100. The control unit 100 includes an engine rotation sensor 101 that detects the rotation speed of the engine 12 and a turbine rotation sensor 10 that detects the rotation speed of a turbine in a torque converter that drives and connects the engine 12 and the transmission.
2 and each output signal is input. Control unit 100, engine rotation sensor 1
The detailed configuration of 01 and the turbine rotation sensor 102 will be further described with reference to FIG. The above engine rotation sensor 10
1 detects the engine speed based on an energization signal when energizing the ignition coil 12a of the engine 12 by turning on the transistor Tr. The turbine rotation sensor 102 is constituted by an electromagnetic induction coil disposed close to the turbine of the torque converter, and is originally provided for controlling the operation of the transmission, and its output signal is an EA for transmission control.
It is input to the T control unit 103. The control unit 100 includes a first waveform shaper 104 that shapes the waveform of the output signal of the engine rotation sensor 101, and a second waveform shaper that converts the frequency signal shaped by the first waveform shaper 104 into a voltage signal. 1 F / V converter 105,
A second waveform shaper 106 for waveform shaping the output signal of the turbine rotation sensor 102, and a second F / V converter 107 for converting the frequency signal shaped by the second waveform shaper 106 into a voltage signal And The output signals of the first and second F / V converters 105 and 107 are output from a comparator 1 as a load determining means.
08, the comparator 108 compares the magnitude of the engine speed and the turbine speed and the magnitude of the difference between the engine speed and the turbine speed with a predetermined reference value, and determines that the engine speed is greater than the turbine speed by a reference value or more. That is, when the engine load is equal to or more than the predetermined value, the comparator 108 outputs Hi as a command signal.
A level signal is output. The output of the comparator 108 is connected to the transistor Tr2, and the collector of the transistor Tr2 is connected to the solenoid 109a of the relay 109.
The normally OFF relay switch 109b is connected to the solenoid valve SV. Therefore, in this embodiment, when the transistor Tr and the relay 109 output a Hi level signal (command signal) from the comparator 108 as a load determining means, the solenoid valve SV operates based on the Hi level signal. The control means 110 is configured to output a signal to operate the capacity setting mechanism of the compressor 2. Next, the operation of the above embodiment will be described. Basically, with the ON operation of the operation switch of the air conditioner 1, the compressor 2 is operated by being driven by the engine 12, and the gas refrigerant discharged from the compressor 2 is condensed by the condenser 3 to become a liquid refrigerant, This liquid refrigerant expands with the expansion valve 5 and then the evaporator 6
Then, the refrigerant is sucked into the compressor 2 and the interior of the vehicle is cooled by the heat of vaporization of the refrigerant in the evaporator 6. During the operation of the air conditioner 1, the rotation speed of the engine 12 is detected by the engine rotation sensor 101 and the engine 12
The rotation speed of the turbine in the torque converter drivingly connected to the turbine is detected by a turbine rotation sensor 102. The detected engine speed and turbine speed are compared in magnitude with each other in the comparator 108 of the control unit 100. If the engine speed is not higher than the turbine speed by a reference value or more, the state is determined by the running of the vehicle. Is considered to be in a low engine load state. At this time, the output signal level of the comparator 108 becomes L ₀ level, the transistor Tr does not operate ON, the solenoid valve SV in the compressor 2 is kept closed, and the capacity of the compressor 2 is controlled by the operation of the variable capacity mechanism 50. Driven in state. That is, when the rotation speed of the compressor 2 is low and its capacity is low, the pressure regulator 40 is closed, and the bypass passages 39 and 39 are closed by the increase in the pressure in the pressurizing chamber 36 of the spool valve 32, so that the compressor 2 is closed. While the capacity of the compressor 2 is maintained at the maximum capacity, when the capacity of the compressor 2 increases due to an increase in the rotation speed, the pressure in the suction chamber 29 decreases and the pressure regulator 40 opens. As a result, the pressure in the pressurizing chamber 36 of the spool valve 32 decreases, the valve body 34 moves to open the bypass passages 39, 39, and the gas refrigerant is bypassed inside the compressor 2 to the suction side. , The capacity of the compressor 2 is controlled so as to decrease in accordance with the increase in the number of rotations. On the other hand, if the engine speed is higher than the turbine speed and the difference is equal to or greater than the reference value, the state is an acceleration state or an uphill state of the car, and the engine load for the traveling is high. Therefore, it is considered that the slip loss in the torque converter is large. At this time, a Hi-level signal is output from the comparator 108, the transistor Tr is turned ON, the solenoid valve SV is opened, the control operation of the variable displacement mechanism 50 is stopped, and the pressure in the suction chamber 29 is reduced. Becomes the intermediate pressure and the valve element 34 of the spool valve 32
Is located at the rising end position in FIG.
By holding the 9, 39 in the fully open state, the bypass amount of the refrigerant to the suction chamber 29 side is maximized, thereby fixing the capacity of the compressor 2 to the minimum capacity. This compressor 2
, The power consumed for driving the compressor 2 of the engine 12 is reduced, the load on the engine 12 is reduced, and the acceleration performance and climbing performance of the automobile can be improved. Further, since the variable displacement mechanism 50 of the variable internal capacity compressor 2 is controlled by the capacity setting mechanism 52 to keep the discharge capacity of the refrigerant fixed to the minimum, the variable capacity control by the external control device of the compressor 2 is applied to the compressor 2. It can be performed using the internal variable capacity mechanism 50 and the compressor 2
Does not require a separate variable displacement mechanism for external displacement control, and the compressor 2 is controlled in the external control state in the same manner as the internal displacement control state. ) Can perform natural external control without giving a feeling of strangeness. If the compressor 2 is kept in the minimum capacity state during acceleration or climbing a slope, the capacity of the air conditioner 1 is reduced. It does not adversely affect indoor drivers. Further, in the above-described embodiment, a through-vane type compressor is adopted as the variable displacement compressor 2, but it is a matter of course that other types of variable displacement compressors such as a swash plate type may be adopted. (Effects of the Invention) As described above, according to the present invention, in the vehicle air conditioner, the capacity of the compressor for the air conditioner driven by the onboard engine is reduced by the bypass to the suction side of the refrigerant during compression. A variable capacity compressor that has a variable capacity mechanism that is variable according to the air conditioner and that is capacity controlled according to the heat load of the air conditioner by the variable capacity mechanism at the time of air conditioning control. When determined, the internal capacity control of the compressor is prohibited, the bypass amount of the refrigerant during compression is maximized, and the capacity is fixedly held at the minimum capacity state. The engine load can be reduced when the vehicle is accelerating or climbing a hill while taking advantage of the automatic control of the capacity by the vehicle. Can be effectively improved. Also, since the variable displacement mechanism of the variable internal capacity compressor is controlled to keep the discharge capacity of the refrigerant fixed to a minimum, the variable displacement control by the external control device of the compressor requires a special variable displacement mechanism separately. In addition, the control can be performed in a natural control state without giving a feeling of strangeness to the vehicle occupant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the present invention, FIG. 1 is an overall configuration diagram, FIG. 2 is an expanded sectional view showing a variable displacement mechanism of a compressor,
FIG. 3 is a schematic cross-sectional view, and FIG. 4 is an electric circuit diagram showing a configuration of the control unit. 1 ... air conditioner, 2 ... compressor, 12 ... engine, 21 ... suction port, 22 ... discharge port, 32 ... spool valve, 39 ... bypass passage, 40 ... pressure regulator, 50 ... variable Capacity mechanism, 51: Communication path, 52: Capacity setting mechanism, SV: Solenoid valve, 100: Control unit, 101: Engine rotation sensor, 102: Turbine rotation sensor, 108: Comparator, 110 ... Control means.

Continuing from the front page (72) Inventor Hirofumi Nagaoka 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Yoshihisa 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda shares In-house (56) References JP-A-57-195884 (JP, A) JP-A-59-119994 (JP, A) JP-A-61-187992 (JP, U) JP-A-59-126714 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B60H 1/32 623 L

Claims (1)

(57) [Claims] A suction port for sucking the refrigerant, a discharge port for discharging the refrigerant that has been sucked from the suction port and passed through the compression stroke, a bypass passage for bypassing the refrigerant to the suction side in the middle of the compression stroke of the refrigerant, and a communication with the suction side And a bypass valve that opens and closes the bypass passage according to a pressure difference between the suction chamber that performs cooling and the pressure chamber that is higher than the suction chamber. A variable capacity mechanism operable to change the pressure of the pressure chamber to open and close the bypass passage by a bypass valve to control the refrigerant discharge capacity, and to be driven by an engine mounted on a vehicle and to control the air conditioner. An external control device configured to externally control a variable displacement compressor for an air conditioner whose capacity is controlled by a variable displacement mechanism according to the heat load of the air conditioner, The compressor has a communication passage communicating with the suction chamber and the pressurization chamber of the variable capacity mechanism, and an opening / closing valve for opening and closing the communication passage. A capacity setting mechanism is provided to open the bypass valve by reducing the pressure of the pressurizing chamber so that the discharge capacity is kept to a minimum, and a load that outputs a command signal when the load of the engine is larger than a predetermined value. An external control device for a variable displacement compressor, comprising: a determination unit; and a control unit that activates the compressor capacity setting mechanism based on a command signal from the load determination unit.