GB2396689A

GB2396689A - Vehicle air conditioner having refrigerant cycle with hot gas bypass heating function

Info

Publication number: GB2396689A
Application number: GB0326277A
Authority: GB
Inventors: Satoshi Izawa; Kazuo Kito; Toshiya Nagasawa
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2002-11-15
Filing date: 2003-11-11
Publication date: 2004-06-30
Anticipated expiration: 2023-11-11
Also published as: DE10353061A1; KR20040043083A; JP3960207B2; JP2004161219A; KR100555961B1; GB2396689B; GB0326277D0

Abstract

An air conditioner for a vehicle comprises a case 22 through which air flows into a passenger compartment of the vehicle, the air conditioning case 22 having an inside air inlet 71, an outside air inlet 70 and an inside/outside air switching means 72 to switch between an outside air suction mode in which at least outside air is introduced and in an inside air suction mode in which only inside air is introduced. The air conditioner further comprises a refrigerant cycle system featuring a compressor 10, an exterior heat exchanger 14, an interior heat exchanger 18, a hot gas bypass passage 20 through which refrigerant discharged from the compressor 10 is directly introduced into the interior heat exchanger 18 while bypassing the exterior heat exchanger 14 and a control unit 26. The control unit 26 determining whether or not the suction mode is the outside air suction mode to direct the coolant flow through the hot gas bypass passage 20 when the suction mode is the outside suction mode. The refrigerant cycle system may further include a pressure reducing device for decompressing refrigerant. The compressor may be a fixed displacement compressor that is operated or stopped by using an electromagnetic clutch 11.

Description

VEHICLE AIR CONDITIONER

HAVING REFRIGERANT CYCLE WITH HEATING FUNCTION

The present invention relates to a vehicle air conditioner having a hot gas heating function using an interior heat exchanger (evaporator) as a radiator by directly introducing a gas refrigerant (hot gas) discharged from a 10 compressor into the interior heat exchanger.

In a conventional vehicle air conditioner, hot water (i.e., engine cooling water) is circulated in a heating heat exchanger during a heating operation in winter to heat air in 15 the heating heat exchanger by using the hot water as a heat source. In this case, when the hot water temperature is low, the temperature of air to be blown into a passenger compartment is lowered and thus may be insufficient for a heating capacity.

20 Thus, JP-A-5-272817 proposes a vehicle air conditioner which has a heating function by using a hot gas heater cycle. When the hot water temperature is lower than a predetermined value as just after the startup of an engine, gas refrigerant discharged from a compressor is introduced 25 into an interior heat exchanger while bypassing a condenser to release the heat from the gas refrigerant to the air in the interior heat exchanger to obtain an auxiliary heating -1-

function. Generally, the hot gas heater cycle is operated in a refrigerant cycle system of the air conditioner when the hot water temperature flowing into the heating heat exchanger is 5 low. Thus, when the hot gas heater cycle is operated, the air temperature to be blown into the passenger compartment is in a relatively low state. In this case, a windshield temperature of the vehicle becomes in a low temperature close to the outside air temperature. Accordingly, when an inside air 10 suction mode is selected as an inside/outside air suction mode, inside air having a high humidity is blown into the passenger compartment, and air around the inner surface of the windshield is cooled by the windshield to reach a dew point.

Therefore, the windshield is readily fogged.

15 Further, when the hot gas heater cycle operates, a capacity control of the compressor is performed by detecting a high-pressure side refrigerant pressure. For example, when a fixed displacement compressor is used, an intermittent control of the compressor is performed in accordance with the high 20 pressure side refrigerant pressure. In this case, when the air suction mode is switched to the inside air suction mode, a low- pressure side refrigerant pressure increases because a heat radiating amount in the interior heat exchanger is greatly decreased as in the outside air suction mode. Thus, an 25 increase speed of the high-pressure side refrigerant pressure becomes larger, and an intermittent frequency of the operation of the compressor increases. In this case, troubles such as -2-

shocks and noises due to the frequent intermittent of the compressor may be readily caused.

In view of the above-described problems, it is an 5 object of the present invention to prevent the above-described problems. Further, it is another object of the present invention to prevent a windshield of a vehicle from being fogged in a heating mode using a hot gas heater cycle.

According to the present invention, a vehicle air 10 conditioner includes an air conditioning case (22) for defining an air passage through which air flows into a passenger compartment of the vehicle, an inside/outside air switching means (72) for opening and closing an inside air suction port (71) and an outside air suction port (70) to set 15 one of an outside air suction mode where at least outside air is introduced from the outside air suction port (70) and an inside air suction mode where only inside air is introduced from the inside air suction port (71), and a refrigerant cycle system. The refrigerant cycle system includes a compressor 20 (10) for compressing refrigerant, an exterior heat exchanger (14) disposed outside the air conditioning case (22), an interior heat exchanger (18) disposed inside the air conditioning case (22) and a hot gas bypass passage (20) through which refrigerant discharged from the compressor (10) 25 is directly introduced into the interior heat exchanger (18) while bypassing the exterior heat exchanger (14). The refrigerant cycle system is constructed to set a hot gas -3-

heater cycle (H) where the refrigerant discharged from the compressor (10) is directly introduced to the interior heat exchanger (18) through the hot gas bypass passage (20), and a control unit (26) controls operation of the refrigerant cycle 5 system to set a heating mode for heating air in the interior heat exchanger (18) by using the hot gas heater cycle (H). In the air conditioner, the control unit includes suction mode determining means (S40) for determining whether the suction mode is the outside air suction mode, and control means (S50) 10 that performs operation of the heating mode when the suction mode is the outside air suction mode. Because the heating mode due to the hot gas heater cycle is performed when the suction mode is the outside air suction mode, outside air having a relatively low humidity is heated and is blown into the 15 passenger compartment, so it can prevent a windshield of the vehicle from being fogged even when the temperature of air to be blown into the passenger compartment is not sufficiently increased. For example, the outside air suction mode includes a 20 first outside air mode where the inside/outside air switching means (72) opens the outside air suction port (70) and closes the inside air suction port (71), and a second outside air mode where the inside/outside air switching means (72) opens both of the outside air suction port (70) and the inside air 25 suction port (71).

Preferably, the control means performs the heating mode when the suction mode is the outside air suction mode, -4-

and prohibits the heating mode when the suction mode is the inside air suction mode. Alternatively, when the suction mode is the inside air suction mode, the control means performs the heating mode after the outside air suction mode is forcibly 5 set from the inside air suction mode. In this case, it can accurately prevent the windshield from being fogged.

Other objects, features and advantages of the present invention will become more apparent from the following 10 detailed description made with reference to the accompanying

drawings, in which: FIG. 1 is a schematic diagram showing a general structure of a vehicle air conditioner according to a first embodiment of the present invention; 15 FIG. 2 is a block diagram of an electric control portion of the vehicle air conditioner according to the first embodiment; FIG. 3 is a flow diagram showing a control process in a hot gas heating mode in accordance with the first 20 embodiment; and FIG. 4 is a flow diagram showing a control process in a hot gas heating mode in accordance with a second embodiment of the present invention.

25 Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

(First Embodiment) FIG. 1 shows the general structure of a vehicle air conditioner in accordance with the first embodiment of the present invention. A compressor 10 is driven through an 5 electromagnetic clutch 11 by a water-cooled vehicle engine 12, and is constructed, for example, of a fixed displacement type swash plate compressor.

The discharge side of the compressor 10 is connected through a solenoid valve 13 for cooling to a condenser 14. The 10 outlet side of the condenser 14 is connected to a liquid receiver 15 for separating the refrigerant into gas refrigerant and liquid refrigerant, and the liquid refrigerant is stored in the receiver 15. The condenser 14 is an exterior heat exchanger which is arranged together with the compressor 15 10 or the like in a vehicle engine room. The condenser 14 exchanges heat with the outside air (or cooling air) blown by an electric cooling fan 14a. The electric cooling fan 14a is driven by an electrical motor 14b.

Moreover, the outlet side of the liquid receiver 15 20 is connected to a thermal expansion valve 16 that is a pressure reducing device for cooling. The outlet side of this thermal expansion valve 16 is connected through a check valve 17 to an evaporator 18. The outlet side of the evaporator 18 is connected through an accumulator 19 to the suction side of 25 the compressor 10.

An ordinary cooling refrigerating cycle C is constructed of a closed circuit from the discharge side of the -6-

above-mentioned compressor 10 to the suction side of the compressor 10 through the solenoid valve 13 for cooling, the condenser 14, the liquid receiver 15, the thermal expansion valve 16, the check valve 17, the evaporator 18 and the 5 accumulator 19, in this order.

The thermal expansion valve 16, as is well known in the art, regulates its valve opening (or refrigerant flow rate) so that the degree of superheat of the outlet refrigerant of the evaporator 18 can be kept at a 10 predetermined value in an ordinary refrigerating cycle operation (i.e., in a cooling mode). The accumulator 19 separates the refrigerant into the gas refrigerant and the liquid refrigerant, so that the gas refrigerant and a small quantity of liquid refrigerant (in which the oil dissolves) in 15 the vicinity of the bottom are sucked into the compressor 10.

On the other hand, between the discharge side of the compressor 10 and the inlet side of the evaporator 18, a hot gas bypass passage 20 through which refrigerant from the compressor 10 is directly introduced into the evaporator 18 20 while bypassing the condenser 14 is provided. A solenoid valve 21 for heating and a throttle 21a are disposed in series in the hot gas bypass passage 20. The throttle 21a is a pressure reducing unit for the heating operation. The throttle 21a can be constructed with a fixed throttle such as an orifice or a 25 capillary tube. A hot gas heater cycle H for the heating operation is constructed of a closed circuit from the discharge side of the compressor 10 to the suction side of the -7-

compressor 10 through the solenoid valve 21 for heating, the throttle 21a, the evaporator 18 and the accumulator 19, in this order.

An air conditioner case 22 of the vehicle air 5 conditioner defines an air passage through which air flows into a passenger compartment. The air is blown in the air conditioner case 22 by an electric air conditioning blower 23.

The air conditioning blower 23 is shown by an axial-flow type to simply show it, but, in reality, is a centrifugal blower 10 having a centrifugal fan. The air conditioning blower 23 is rotated by a blower motor 23a controlled by a blower drive circuit. Here, it is possible to change the quantity of air blown by the blower 23 in the embodiment continuously or stepwise by adjusting a blower control voltage applied to the 15 blower motor 23a.

Further, on the suction side of the air conditioning blower 23a, an outside air suction port 70 for sucking and introducing air outside the passenger compartment (hereinafter referred to as ioutside air"), and an inside air suction port 20 71 for sucking and introducing air inside the passenger compartment (hereinafter referred to as inside air") are provided. The inside air suction port 71 and the outside air suction port 70 are opened and closed by an inside air/outside air switching door (inside air/outside air switching means) 72 25 Here, the inside air/outside air switching door 72 is driven via a link mechanism (not shown) by an actuator such as a servo-motor to switch at least an outside air suction mode for -8-

sucking the outside air from the outside air suction port 70 and an inside air suction mode for sucking the inside air from the inside air suction port 71.

The evaporator 18 is an interior heat exchanger 5 which is disposed in the air conditioner case 22. The refrigerant is circulated in the cooling mode by the refrigerating cycle C for the cooling operation to cool the air blown by the air conditioning blower 23 through the refrigerant evaporation t treat absorption) in the evaporator 18 10 On the other hand, in the heating mode, a hot gas refrigerant (hot gas) from the compressor 10 flows into the evaporator 18 through the hot gas bypass passage 20 to heat the air in the evaporator 18, so that the evaporator 18 functions as a radiator. 15 Here, in the air conditioning case 22, a discharge port 22a for discharging the condensed water generated in the evaporator 18 is provided at the lower portion of the evaporator 18, so that the condensed water is discharged to the outside of the passenger compartment through a discharge 20 pipe (not shown) connected to the discharge port 22a.

In the air conditioning case 22, at the downstream side of the evaporator 18 in the air flow direction, a hot water type heating heat exchanger 24 for heating the air from the evaporator 18 by using the hot water (engine cooling 25 water) from the vehicle engine 12 as a heat source is disposed A hot water circuit from the vehicle engine 12 to the heating heat exchanger 24 is provided with a hot water valve 25 for _9_

controlling the flow amount of the hot water.

By the way, the hot water type heating heat exchanger 24 constitutes a main heating unit for heating air to be blown to the passenger compartment. Relative to the main 5 heating unit, the evaporator 18 (interior heat exchanger) functioning as a heat radiator by the hot gas heater cycle H constitutes an auxiliary heating unit.

On the other hand, on the most downstream side of the air conditioning case 22 in the air flow direction, plural 10 air outlet ports 31-33 are provided. The plural air outlet ports 31-33 includes a defroster (DEF) blowing port 31 for blowing out conditioned air toward the inside surface of the vehicle front windshield, a face (FACE) blowing port 32 for blowing out conditioned air (mainly, cooled air) toward the 15 face portion (upper half of the body) of an occupant in the passenger compartment, and a foot (FOOT) blowing port 33 for blowing out conditioned air (mainly, warm air) toward the foot portion (lower half of the body) of the occupant. Moreover, a plurality of mode switching doors 34 - 36 for selectively 20 opening and closing these blowing ports 31 - 33 are provided.

Here, these mode switching doors 34 - 36 construct an air outlet mode switching unit, and are driven by an actuator such as a servo-motor via a link mechanism (not shown).

An air conditioning electronic control unit (herein 25 after referred to as "ECU") 26 is constructed of a microcomputer and its peripheral circuits, and performs a predetermined computation in accordance with preset programs -10

to open and close the solenoid valves 13, 21 and to control the actions of the remaining electronic devices (11, 14a, 23, 25 and the like).

FIG. 2 is an electric control block diagram of the 5 first embodiment. Detection signals are applied to the ECU 26 from a set of sensors including a water temperature sensor 27a of the vehicle engine 12, an outside air temperature sensor 27b, an air temperature sensor 27c of the evaporator 18, a refrigerant pressure sensor 27d for detecting a refrigerant 10 pressure discharged from the compressor 10, an inside air temperature sensor 27e, and a solar radiation sensor 27f for detecting the amount of solar radiation entering into the passenger compartment.

Also, control signals of a group of control switches 15 29a-29f are applied to the ECU 26 from an air conditioning operation panel 28 that is disposed in the vicinity of a dashboard in the passenger compartment. That is, an air conditioning switch 29a commands the start and stop of the compressor 10 in the refrigerating cycle system, and functions 20 as a cooling switch for setting the cooling mode. A hot gas switch 29b sets the heating mode by the hot gas heater cycle H and functions as a heating switch.

Further, the air conditioning operation panel 28 is provided with a blowing mode selecting switch 29c for 25 switching the blowing mode of the air conditioner, a temperature setting switch (temperature setting unit) 29d for setting the temperature in the passenger compartment at a - 11-

desired temperature, a blower switch 29e for commanding turning on/off the blower 23 and switching the flow amount of air, and an inside air/outside air selection switch 29f for commanding switching between the outside air suction mode and 5 the inside air suction mode.

Next, in the above construction, the operation of the vehicle air conditioner according to the above embodiment will now be described. First, the operation of the refrigerating cycle system will be described. When the air 10 conditioning switch 29a is turned on to set the cooling mode, the solenoid valve 13 for cooling is opened and the solenoid valve 21 for heating is closed by the ECU 26. Thus, when the electromagnetic clutch 11 becomes in the connecting state and the compressor 10 is driven by the engine 12, the gas 15 refrigerant discharged from the compressor 10 flows through the solenoid valve 13 for cooling, which is in the open state, into the condenser 14.

In the condenser 14, the refrigerant is cooled and condensed by the outside air that is blown by the cooling fan 20 14a. Then, the refrigerant having passed through the condenser 14 is separated by the liquid receiver 15 into the gas refrigerant and the liquid refrigerant. The separated liquid refrigerant is exclusively reduced in pressure by the thermal expansion valve 16 so that a gas-liquid two-phase refrigerant 25 with low temperature and low pressure is obtained.

Next, the low-pressure refrigerant passes through the check valve 17 and flows into the evaporator 18, and -12

evaporates in the evaporator 18 by absorbing heat from the air blown by the blower 23. The air cooled in the evaporator 18 flows into the passenger compartment to cool the passenger compartment. The gas refrigerant evaporated in the evaporator 5 18 is sucked into the compressor 10 through the accumulator 19 to be compressed in the compressor 10.

When the hot gas switch 29b is turned on in winter to set the heating mode by using the hot gas heater cycle H. the solenoid valve 13 for cooling is closed and the solenoid 10 valve 21 for heating is opened by the ECU 26 so that the hot gas bypass passage 20 is opened. As a result, the high temperature gas refrigerant (or the superheated gas refrigerant) discharged from the compressor 10 passes through the heating solenoid valve 21 in the open state and is reduced 15 in pressure by the throttle 21a and then flows into the evaporator 18. That is, the superheated gas refrigerant (hot gas) from the compressor 10 bypasses the condenser 14 and the like and directly flows into the evaporator 18 through the hot gas bypass passage 20.

20 At this time, the check valve 17 prevents the gas refrigerant from flowing from the hot gas bypass passage 20 to the thermal expansion valve 16. As a result, in the heating mode, the refrigerating cycle is operated by the closed circuit (i.e., the hot gas heater cycle H) constructed of the 25 discharge side of the compressor 10, the solenoid valve 21 for heating, the throttle 21a, the evaporator 18, the accumulator 19 and the suction side of the compressor 10.

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Thus, the superheated gas refrigerant having been reduced in pressure by the throttle 21a heats the blown air by releasing its heat to the blown air in the evaporator 18. Here, the heat quantity to be released from the gas refrigerant in 5 the evaporator 18 corresponds to the compression workload of the compressor 10. The gas refrigerant having released its heat in the evaporator 18 is sucked into the compressor 10 to be compressed after passing through the accumulator 19.

When the temperature of water (engine-cooling water) 10 is lower than a predetermined temperature (e.g., 30 C) as just after the start-up of the engine 12, a stop state of the air conditioning blower 23 is maintained even when the blower switch 29e is turned on. Thereafter, when the hot water temperature in the engine 12 increases to a predetermined 15 temperature, the air conditioning blower 23 starts its operation by a low air flow amount. That is, a warm-up control of the air conditioning blower 23 is performed so that a rotation speed (corresponding to air flow amount) of the air conditioning blower 23 is increased as the hot water 20 temperature increases. By flowing the hot water through the hot water valve 25 into the hot water type heating heat exchanger 24, the blown air having heated by the evaporator 18 can be further heated in the heating heat exchanger 24.

Therefore, even in the cold weather, the warm air, which is 25 heated by both of the evaporator 18 and the hot water type heating heat exchanger 24 to have a higher temperature, can be blown into the passenger compartment.

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Next, the operation control of the heating mode of the hot gas heater cycle H in accordance with the first embodiment will be described specifically with reference to FIG. 3. The control routine of FIG. 3 is started by turning ON 5 the ignition switch of the vehicle engine 12, for example.

Specifically, as shown in FIG. 3, operation signals from the switches 29a - 29f of the air conditioning operation panel 28 are input at step S10, and detection signals from the sensors 27a - 27f are input at step S20.

10 Next, at step S30, it is determined whether or not the hot gas switch 29b of the air conditioning operation panel 28 is turned ON. When the hot gas switch 29b is turned ON, that is, when the hot gas heating mode is instructed, it is determined whether or not the suction mode set by the 15 inside/outside air switching door 72 is the outside air suction mode at step S40.

When the outside air suction mode is set at step S40, the control program proceeds to step S50, and the hot gas heating mode using the hot gas heater cycle H is started and 20 performed. That is, at step S50, the solenoid valve 21 for heating is opened, the solenoid valve 13 for cooling is closed, and the electromagnetic clutch It is turned on so that the compressor 10 is operated.

On the other hand, when it is determined that the 25 outside air suction mode is not set at step S40, that is, when it is determined that the inside air suction mode is set as the suction mode at step S40, the control process returns to -15

step S10, and the hot gas heating mode is not started. Because the operation of the hot gas heater cycle H is prohibited in the inside air suction mode, it can prevent heated inside air having a high humidity from being blown toward the inner 5 surface of the windshield, thereby preventing the windshield from being fogged.

Further, according to the first embodiment of the present invention, when the hot gas heater cycle H operates, a high-pressure side refrigerant pressure is detected by the 10 refrigerant pressure sensor 27d. In this case, when the high pressure side refrigerant pressure is higher than a first predetermined pressure, the electromagnetic clutch 11 is turned off, and the operation of the compressor 10 is stopped.

When the high-pressure side refrigerant pressure is decreased 15 lower than a second predetermined pressure that is lower than the first predetermined pressure by a predetermined value, the electromagnetic clutch 11 is turned on, and the compressor 10 is re-started so that the discharge capacity (e.g., interruption operation) of the compressor 10 is controlled.

20 According to the first embodiment, the discharge capacity of the compressor 10 is controlled in the hot gas heater cycle, when the outside air suction mode is set.

Further, when the inside air suction mode is set, the operation of the hot-gas heater cycle is prohibited. Therefore, 25 it can prevent the interruption frequency of the compressor 10 from being increased in the hot gas heating mode, and it can prevent problems such as shocks and noises due to frequent -16

interruptions of the compressor 10.

(Second Embodiment) The second embodiment of the present invention will be now described with reference to FIG. 4.

5 In the above-described first embodiment, when the suction mode is the inside air suction mode, the operation of the hot gas heater cycle is prohibited. However, in the second embodiment, when the inside air suction mode is determined at step S40, the control program processes to step S60, and the 10 outside air mode is forcibly set at step S60. Thereafter, at step S50, the operation of the hot gas heater cycle is performed. According to the second embodiment of the present invention, even when the inside air suction mode is set as the 15 suction mode, the outside air suction mode is forcibly set and the hot gas heater cycle H is started when the hot gas switch is turned on. Therefore, a trouble in the hot gas heater cycle H due to the inside air suction mode can be prevented.

In the second embodiment, the other parts are 20 similar to those of the above-described first embodiment, and advantages described in the first embodiment can be obtained.

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted 25 that various changes and modifications will become apparent to those skilled in the art.

For example, in the above embodiments, when the

outside air suction mode is set as the suction mode at step S40, the hot gas heating mode is started. However, the outside air suction mode can include a mode where at least the outside air suction port 70 is opened by the inside/outside air 5 switching door 72 so that at least the outside air is introduced. That is, the outside air suction mode includes a first outside air mode where the outside air suction port 70 is opened and the inside air suction port 71 is closed, and a second outside air mode where both of the outside air suction 10 port 70 and the inside air suction port 71 are opened. In this case, when the outside air suction mode for sucking and introducing outside air from the outside air suction port 70 is set at step S40, the hot gas heating mode can be started.

In the above-described first embodiment, when 15 suction mode is the inside air suction mode, the control process returns to step S10 from step S40, and the start operation of the hot gas heater cycle is prohibited. In this case, the operation prohibition of the hot gas heater cycle due to the setting of the inside air suction mode can be 20 indicated by using a suitable display device.

In the above-described first embodiment, the fixed displacement compressor is used as the compressor 10, and the capacity control of the compressor 10 is performed by interrupting the operation of the compressor 10. However, a 25 variable displacement compressor for changing the discharge capacity of the compressor 10 continuously or stepwise can be used as the compressor 10. In this case, the capacity control -18

of the compressor 10 can be performed by controlling the discharge capacity of the compressor 10.

Further, when a variable displacement compressor in which its discharge capacity can be changed approximately 5 between 100% capacity and 0% capacity is used as the compressor 10, the electromagnetic clutch 11 can be eliminated When the electromagnetic clutch 11 is not used, the discharge capacity of the variable displacement compressor is controlled at a predetermined capacity in place of the turning-ON 10 operation (connection operation) of the electromagnetic clutch 11. In the abovedescribed first and second embodiments of the present invention, an instruction means for instructing the hot gas heating mode is constructed with the hot gas 15 switch 29b that is manually operated. However, when a maximum heating determining means for determining a maximum heating state of a temperature adjusting means is provided, the instruction means for instructing the hot gas heating mode can be constructed with the maximum heating determining means, and 20 outputs an instruction signal for setting the hot gas heating mode in the maximum heating state of thetemperature adjusting means. Here, the temperature adjusting means adjusts an air heating amount by the heater core 24, and becomes in maximum when the air heating amount by the heater core 24 becomes 25 maximum. Specifically, the temperature adjusting means is an air mixing door that adjusts a flow ratio of an air amount passing through the heater core 24 and an air amount bypassing -19

the heater core 24, or the temperature control valve 25 that adjusts a flow amount or a temperature of hot water flowing into the heater core 24.

Such changes and modifications are to be understood 5 as being within the scope of the present invention as defined by the appended claims.

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Claims

CLAIMS:

1. An air conditioner for a vehicle, comprising: an air conditioning case for defining an air passage through which air flows into a passenger compartment of the vehicle, the air conditioning case having an inside air suction port from inside air of the passenger compartment is introduced and an outside air suction port from which outside air outside the passenger compartment is introduced; an inside/outside air switching means for opening and closing the inside air suction port and the outside air suction port, to set one of an outside air suction mode where at least outside air is introduced from the outside air suction port and an inside air suction mode where only inside air is introduced from the inside air suction port, as a suction mode; a refrigerant cycle system including a compressor for compressing refrigerant, an exterior heat exchanger disposed outside the air conditioning case, an interior heat exchanger disposed inside the air conditioning case and a hot gas bypass passage through which refrigerant discharged from the compressor is directly introduced into the interior heat exchanger while bypassing the exterior heat exchanger, the refrigerant cycle system being constructed to set a hot gas heater cycle where the refrigerant discharged from the compressor is directly introduced to the interior heat exchanger through the hot gas bypass passage; and a control unit for controlling operation of the -21

refrigerant cycle system to set a heating mode for heating air in the interior heat exchanger by using the hot gas heater cycle, wherein the control unit includes suction mode determining means for determining whether the suction mode is the outside air suction mode, and control means that performs operation of the heating mode when the suction mode is the outside air suction mode.

2. The air conditioner according to claim 1, wherein: the outside air suction mode includes a first outside air mode where the inside/outside air switching means opens the outside air suction port and closes the inside air suction port, and a second outside air mode where the inside/outside air switching means opens both of the outside air suction port and the inside air suction port.

3. The air conditioner according to claim 2, wherein the control means performs the operation of the heating mode only in the first outside air mode.

4. The air conditioner according to any one of claims 1 and 2, wherein the control means performs the heating mode when the suction mode is the outside air suction mode, and prohibits the heating mode when the suction mode is the inside air suction mode.

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5. The air conditioner according to any one of claims 1 and 2, wherein, when the suction mode is the inside air suction mode, the control means performs the heating mode after the outside air suction mode is forcibly set from the inside air suction mode. 6. The air conditioner according to any one of claims 1 - 5, further comprising heating mode instruction means for outputting an instruction signal of the heating mode, wherein the suction mode determining means performs the determination of the suction mode when the instruction signal of the heating mode is output from the heating mode instruction means.

The air conditioner according to any one of claims 1 - 6, wherein: the refrigerant cycle system further includes a pressure reducing device for decompressing refrigerant, and is constructed to switch between the hot gas heater cycle and a cooling refrigerant cycle where refrigerant discharged from the compressor is returned to the compressor through the exterior heat exchanger, the pressure reducing device and the interior heat exchanger; and the control unit controls the operation of the refrigerant cycle system to set a cooling mode for cooling air -23

in the interior heat exchanger by using the cooling refrigerant cycle, and the heating mode.

8. The air conditioner according to any one of claims 1 - 7, wherein the control unit controls a heating capacity of the interior heat exchanger for heating air in the heating mode by controlling a capacity of the compressor.

9. The air conditioner according to claim 8, wherein: the compressor is a fixed displacement compressor that is operated or stopped by using an electromagnetic clutch; and the electromagnetic clutch is controlled in accordance with a high-pressure side refrigerant pressure in the hot gas heater cycle in the heating mode.

10 An air conditioner substantially as described herein with reference to Figs. 1, 2 and 3 or 4 of the accompanying drawings.

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