Abstract:
A vehicular air conditioner includes a reversible heat pump having an air distribution fan positioned upstream of an indoor heat exchanger, a coolant heat exchanger positioned downstream of the indoor heat exchanger, and a damper arranged adjacent to a coolant heat exchanger. An engine cooling water system is connected to the coolant heat exchanger. A subassembly is used for positioning the damper in the fully opened condition such that the coolant heat exchanger is made an air intake flow path in addition to an air flow path of an air bypass space during a cooling operation. The engine cooling water system includes a coolant bypass valve connected between a primary side flow path and a secondary side flow path for engine cooling water to bypass the coolant heat exchanger. When the damper fully opens a full quantity of the engine cooling water flows to the secondary side flow path.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a vehicular air conditioner which is installed in vehicles such as automobiles, and in particular to a vehicular air conditioner where a vehicular air conditioner using a heat pump is provided with a heating heat exchanger with the engine cooling water as a heat source.  
         [0003]     2. Description of the Background  
         [0004]     Recently, there has been an increasing demand for introducing a low-pollution vehicle and alternative energy vehicle, accompanied with demands for improving the air environment and eliminating environmental problems. When the energy source is replaced by natural gas, this is basically a change only in the fuel, and there is no need to change the basic structure of an air conditioning apparatus (hereinafter referred to as an air conditioner), since there is still an internal combustion engine (hereinafter referred to as an engine).  
         [0005]     If however a conventional air conditioner is used as is, in an electric vehicle or a hybrid vehicle (using both an electric motor and an engine as a drive source) which is one of the strong candidates for the alternative energy vehicle, it is necessary to reconsider the heat source during the heating operation and the compressor drive source during the cooling operation.  
         [0006]     That is to say, a problem arises in that during the heating operation, with electric vehicles there is no engine cooling water to serve as the heating source as in the conventional vehicles, and in hybrid vehicles there is a motor travelling mode in which the engine is stopped and the vehicle is driven only by the electric motor, and hence sufficient warm water cannot be obtained.  
         [0007]     Moreover, during the cooling operation, the drive source for the compressor cannot rely only upon the engine as with conventional vehicles, and another drive source must be provided. For example, in the case of a hybrid vehicle, there is a motor travelling mode in which the vehicle is driven only by the electric motor, or even if the vehicle is driven by the engine, at the time of stopping, the engine is stopped so as not to run in idle. Hence stable operation of the air conditioner is not possible when only the engine is used as the drive source for the compressor.  
         [0008]     From this background, a heat pump type air conditioner used in household cooling/heating air conditioners has been adopted as the air conditioner installed in vehicles such as; the electric vehicles and hybrid vehicles.  
         [0009]      FIG. 3  shows a schematic structural diagram of a conventional vehicular air conditioner using a heat pump. In  FIG. 3 , there is shown an indoor heat exchanger  1 , a compressor unit  2 , an outdoor heat exchanger  3 , and a fan  4  for drawing in outside air. In this case, the outdoor heat exchanger  3  is installed inside of an engine: compartment together with the compressor unit  2  and the like. By activating the fan  4  for drawing in outside air, the outside air can be drawn into the engine compartment.  
         [0010]     With the above described conventional construction, a refrigerant is circulated as described below to effect cooling and heating in the vehicle cabin.  
         [0011]     The refrigerant during the heating operation circulates in a clockwise direction, as shown by the solid arrow in  FIG. 3 . The refrigerant which is changed to a high-temperature and high-pressure gas by the compressor in the compressor unit  2  is sent to the indoor heat exchanger  1  to exchange heat with the air outside the vehicle (the outside air) or with the air inside the vehicle (the inside air). As a result, the outside air or the inside air (hereinafter referred to as intake air) becomes hot air by absorbing heat from the high temperature and high-pressure gas refrigerant, and at the same time, the high-temperature and high-pressure gas refrigerant loses heat to be changed into a condensate, and becomes a high-temperature and high-pressure liquid refrigerant.  
         [0012]     Subsequently, the high-temperature and high-pressure liquid refrigerant passes through the compressor unit  2  where it is expanded to become a low-temperature and low-pressure liquid refrigerant and is sent to the outdoor heat exchanger  3 . In the outdoor heat exchanger  3 , the low-temperature and low-pressure liquid refrigerant draws up heat from the outside air and is evaporated and gasified to become a low-temperature and low-pressure gas refrigerant. This low-temperature and low-pressure gas refrigerant is again sent to the compressor unit  2  and compressed, to become a high-temperature and high-pressure gas. Hereafter, the above-described process is repeated.  
         [0013]     That is to say, during the heating operation, the outdoor heat exchanger  3  functions as an evaporator, and the indoor heat exchanger  1  functions as a condenser.  
         [0014]     The refrigerant during the cooling/dehumidifying operation circulates in the counterclockwise direction as shown by the broken line arrow in  FIG. 3 . The refrigerant which is changed to a high-temperature and high-pressure gas by the compressor in the compressor unit  2  is sent to the outdoor heat exchanger  3  to exchange heat with the outside air. As a result, the refrigerant gives up heat to the outdoor air and is changed into a condensate, becoming a high-temperature and high-pressure liquid refrigerant. The refrigerant which becomes the high-temperature and high-pressure liquid refrigerant as described above passes through a throttling resistance in the compressor unit  2  to become a low-temperature and low-pressure liquid refrigerant, and is then sent to the indoor heat exchanger  1 .  
         [0015]     Subsequently, the low-temperature and low-pressure liquid refrigerant absorbs heat from the vehicle cabin air, in the indoor heat exchanger  1  to cool the air. Hence cool air can be supplied to the vehicle cabin, and at the same time, the refrigerant itself is evaporated and gasified to become a low-temperature and low-pressure gas refrigerant. The refrigerant which becomes the low-temperature and low-pressure gas refrigerant is again sent to the compressor in the compressor unit  2 , and compressed to become a high-temperature and high-pressure gas. Hereafter, the above described process is repeated. That is, during the cooling operation, the indoor heat exchanger  1  functions as an evaporator, and the outdoor heat exchanger  3  functions as a condenser.  
         [0016]     In the case where the above described conventional vehicular air conditioner using a heat pump is mounted in a vehicle incorporating an internal combustion engine, such as a conventional vehicle or a hybrid vehicle, it is desirable to effectively utilize the waste heat from the engine during the heating operation.  
         [0017]     That is to say, under operating conditions when travelling with the engine as the drive source and hence the high temperature cooling water can be sufficiently used as the heat source, then if a heating heat exchanger, referred to as a heater core, is provided, and the high temperature engine cooling water is introduced thereto, then the intake air passing through the heater core can be heated to enable heating.  
         [0018]     As an example of conventional technology of such a vehicular air conditioner, there is the apparatus described in Japanese Patent Application No. 61-94811. With this conventional technology, as shown in  FIG. 4 , temperature adjustment is affected by air mixing. Hence the heater core with the engine cooling water as the heat source, is provided at an incline, and a damper which adjusts the quantity of the passing air in accordance with the opening thereof, is provided as a device for controlling the heat exchange capacity of the heater core.  
         [0019]     The apparatus of Japanese Patent Application No. 61-94811 is effective, however if higher performance is required.  
         [0020]     In consideration of the above situation, it is an object of the present invention to provide a vehicular air conditioner which can shorten the heating start up time at the time of the heating operation, and improve the heating capacity, and for which the load on the air distribution fan is reduced.  
         [0021]     The apparatus of Japanese Patent Application No. 61-94811 originated from giving priority to keeping the flow path which does not pass through the heater core as large as possible at the time of the cooling operation, and to air mixing performance. Consequently the flow of the intake air tends to become complicated. For example, if the heater core is installed in an inclined condition, the through flow distance is increased, and hence the pressure loss of the intake air passing through the heater core is increased. As a result there is the problem of an increase in the load on the distribution fan. Moreover, since with the operation of fully closing the heater core inlet with the damper, the area through which the intake air can pass is reduced and there is an increase in flow resistance from the pressure loss due to the heater core itself. Consequently, there is also an increase in the load on the distribution fan.  
         [0022]     If the load on the distribution fan is increased in this way, then there is the problem that the power consumption of the electric motor serving as the fan drive source is increased, and the operating noise of the air conditioning apparatus is increased. Furthermore, the complicated air flow due to air mixing is a source of an increase in load on the distribution fan, and air conditioning noise. In particular, in the case of a hybrid vehicle having a motor drive mode, since there is no engine noise, then the air conditioning noise becomes noticeable, and since power consumption is increased, then the possible travelling distance is shortened.  
       SUMMARY OF THE INVENTION  
       [0023]     To address the above problems, the following features employed in the present invention.  
         [0024]     The vehicular air conditioner according to a first aspect of the present invention is a vehicular air conditioner with an air conditioner using a heat pump, with a compressor unit equipped with a compressor, a throttling resistance and a four way valve, connected by a refrigerant path to an indoor heat exchanger for effecting heat exchange between a refrigerant and intake air, and an outdoor heat exchanger for effecting heat exchange between a refrigerant and outside air, which executes a cooling operation and a heating operation by          i of the flow of the refrigerant, provided with an air distribution fan, and a          ger connected to an engine cooling water system, wherein there is          iitioning unit with the indoor heat exchanger and the heating heat           in sequence from an upstream side in a casing which serves as a flow          ir, and an air flow path formed in a part above the heating heat exchanger,          i open/close device for switching the air flow path between a fully closed          ondition.          he heating heat exchanger is preferably installed upright in the casing,           is preferably a variable capacity type.           vehicular air conditioner, since the construction is such that the air flow          eating heat exchanger is switched between fully closed and fully opened          ng device, then the passage for the intake air can be shut off by the          ice so that the area becomes zero. As a result, the pressure loss of the          uced, and the load on the distribution fan can be reduced. Moreover,           intake air is uniform, the discharge temperature can be easily adjusted by          lume from the distribution fan.           the heating heat exchanger is installed upright, then the length of the          heating heat exchanger is reduced, and hence the pressure loss of the          ger itself can be reduced.           by using the variable capacity type compressor, then temperature control          omes unnecessary.          r air conditioner according to a fourth aspect of the present invention is a          oner with an air conditioner using a heat pump, with a compressor unit          pressor, a throttling resistance and a four way valve, connected by a          i indoor heat exchanger for effecting heat exchange between a refrigerant          i outdoor heat exchanger for effecting heat exchange between a          de air, which executes a cooling operation and a heating operation by          i of the flow of the refrigerant, provided with an air distribution fan, and a          ger connected to an engine cooling water system, wherein a bypass valve          gine cooling water system, so as to be able to form an engine cooling          th which bypasses the heating heat exchanger.          alve in this case is preferably a flow control valve.  
         [0025]     With such a vehicular air conditioner, in the case where heating is not required, then the full amount of engine cooling water is introduced to the bypass flow path so that the engine cooling water is not supplied to heating heat exchanger. Consequently, the situation where the intake air which has become cold air from passing through the indoor heat exchanger is heated by the heating heat exchanger so that the temperature rises, can be avoided.  
         [0026]     Moreover, by making the bypass valve a flow control valve, then the flow quantity of the engine cooling water supplied to the heating heat exchanger and of the engine cooling water introduced to the bypass passage can be controlled, enabling adjustment of the discharge temperature.  
         [0027]     The vehicular air conditioner according to a sixth aspect of the present invention is a vehicular air conditioner with an air conditioner using a heat pump, with a compressor unit equipped with a compressor, a throttling resistance and a four way valve, connected by a refrigerant path to an indoor heat exchanger for effecting heat exchange between a refrigerant and intake air, and an outdoor heat exchanger for effecting heat exchange between a refrigerant and outside air, which executes a cooling operation and a heating operation by switching a direction of the flow of the refrigerant, and provided with an air distribution fan, and a heating heat exchanger connected to an engine cooling water system, wherein a cooling water pump is provided in the engine cooling water system for operating when the engine is stopped.  
         [0028]     With such a vehicular air conditioner, because of the cooling water pump which operates when the engine is stopped, engine cooling water can be supplied to the heating heat exchanger even when the engine is stopped. Therefore the heat held by the engine cooling water can be effectively used even when the engine is stopped. This use of waste heat in the engine cooling water is particularly effective for hybrid vehicles where the engine is frequently stopped. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a schematic flow diagram showing a construction of a vehicular air conditioner according to one embodiment of the present invention.  
         [0030]      FIG. 2  is a plan view showing an arrangement of a hybrid vehicle mounted with the vehicular air conditioner using a heat pump shown in  FIG. 1 .  
         [0031]      FIG. 3  is a schematic flow diagram showing an outline construction of a vehicular air conditioner using a heat pump, being a conventional example.  
         [0032]      FIG. 4  is a diagram showing conventional technology for a vehicular air conditioner. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     A description of a hybrid vehicle mounted with a vehicular air conditioner, as one embodiment of the present invention, follows with reference to the appended drawings.  
         [0034]     In  FIG. 2 , a hybrid vehicle  10  is equipped with a drive unit  12  in the front part of the vehicle body, having a motor  11  housed therein for driving front wheels, and an engine  13  in an engine compartment in the rear part of the vehicle body, for driving rear wheels. The hybrid vehicle  10  runs as a front-wheel-drive vehicle at the time of low speed driving, using the motor  11  as a drive source, and runs as a rear-wheel-drive vehicle at the time of high speed driving exceeding a certain speed, by switching the drive source to the engine  13 . Since the motor  11  is provided in the front part of the vehicle body, the engine  13  is arranged in the rear part of the vehicle body, in consideration of the freedom of installation space and reduction in air resistance (Cd value).  
         [0035]     In addition, there is a case where the engine  13  and the motor  11  are activated as the drive source at the same time, to run as a four-wheel-drive vehicle.  
         [0036]     In  FIG. 2 , a battery  14  is a power source for the motor  11 , and a motor generator unit  15  converts the driving force of the engine  13  into electrical power and storing the electrical power in the battery  14 . An electrical power generation motor (not shown) is mounted in the motor generator unit  15 , and electrical power is generated by transmitting the driving force from the engine  13  to the electrical power generation motor. Moreover, the motor generator unit  15  has a function to convert electrical power stored in the battery  14  into the driving force, by driving the electrical power generation motor with the electrical power.  
         [0037]     I/C (inter-cooler) EGR system  50  is also provided in the engine  13 .  
         [0038]     A radiator  16  cools the engine  13 ; a radiator  17  cools the power elements and is provided together with the radiator  16  for cooling the engine  13 . The radiator  16  for the power elements is for cooling the driving motor  11 , and the motor generator unit  15 . The radiator  16  for cooling the engine and the radiator  17  for the power elements are equipped with a radiator cooling fan  18  which passes outside air drawn in from the side face of the vehicle body through the radiators  16  and  17  and thereby releases heat to the air in the inner periphery of the engine room.  
         [0039]     Moreover, there is provided a battery heat exchanger  19  for transferring heat from the engine  13  to the battery  14 .  
         [0040]     Next is a description of an air conditioner mounted in the hybrid vehicle  10 .  
         [0041]     With the first embodiment shown in  FIG. 1  and  FIG. 2 , there are a compressor unit  20  with a variable refrigerant supply capacity, an outdoor heat exchanger  21 , a fan  22  for drawing in outside air, and an air conditioning unit  23  referred to as an HPVM (Heat Pump Ventilating Module). As seen in  FIG. 1  only, the unit  23  incorporates equipment such as a blower fan  24  provided as a distribution fan, an indoor heat exchanger  25  and a heater core  26  serving as a heating heat exchanger, arranged sequentially in the flow direction inside a casing serving as a flow path for intake air.  
         [0042]     The outdoor heat exchanger  21  is arranged on the right side face in the engine room disposed in the rear part of the vehicle body, for forcibly exchanging heat between outside air drawn in from an opening on the side face of the vehicle body by operation of the fan  22  for drawing in outside air, and refrigerant flowing inside the heat exchanger. The air conditioning unit  23  is arranged in the middle of the rear part of the vehicle body, with a front face of the unit  21  connected to a duct  27 , shown in  FIG. 2  only, extending to the front of the vehicle body along a center of a lower part of the vehicle body. The duct  27  is formed in a tubular shape and is provided with air outlet sections  28  and  29  in the central portion and in the front end of the duct  27 , respectively. In this case, the air outlet section  28  is for the rear seats, and the air outlet section  29  is for the front seats, but these may be increased or decreased according to need.  
         [0043]     The air conditioning unit  23  is a module for executing cooling, heating and dehumidifying to effect air conditioning, by making outside air drawn in from outside the vehicle body or inside air drawn in from the vehicle cabin with the operation of the blower fan  24 , as seen in  FIG. 2  only, pass through the indoor heat exchanger  25  and the heater core  26 .  
         [0044]     The indoor heat exchanger  25  is connected by a refrigerant path  30  to the compressor unit  20  and the outdoor heat exchanger  21  to constitute the air conditioner using a heat pump. The compressor unit  20  comprises a variable capacity compressor  31 , an accumulator  32 , a four way valve  33  and a throttling resistance  34  such as an expansion valve, and operates the variable capacity compressor  31  to circulate the refrigerant which is quantity controlled according to air conditioning load, to thereby execute the heat pump operation. In this case, temperature adjustment of the discharge air is effected by controlling the refrigerant supply quantity with the variable capacity compressor  31 .  
         [0045]     Moreover, in the abovementioned air conditioning unit  23 , there is provided an air flow path  35  formed in a part above the heater core  26  which is installed upright inside the casing and there is provided a damper  36  serving as an open/close device for selectively switching the air flow path  35  between either of fully closed and fully opened. The damper  36  is attached to the upper wall interior of the casing with a hinge  36   a  so as to be able to swing relative thereto.  
         [0046]     Consequently, with the damper  36  fully closed, the intake air drawn into the blower fan  24  passes in full through the indoor heat exchanger  25  and the heater core  26 , to be air conditioned. In this case, since the heater core  26  is upright, the through flow distance of the intake air flow path is smaller than for when this is inclined, and hence the pressure loss due to passing through the heater core  26  can be reduced by that amount.  
         [0047]     Moreover, with the damper  36  fully open, the intake air drawn into the damper  36  is branched into two, and flows through the air flow path  35  and the path through the heater core  26 . At this time, the air flow path on the heater core  26  side has a substantial pressure loss compared to the air flow path  35  side, and hence the intake air actually flowing through the heater core  26  is a reduced quantity. Consequently, the overall flow path area is greater compared to when the heater core  26  is covered by a damper or the like, and hence the pressure loss is reduced by that amount.  
         [0048]     The heater core  26  is connected to the engine cooling water system  37  of the engine  13  and is supplied by high temperature engine cooling water, and thus has a heating function for heating the passing intake air. The engine cooling water system  37  of the engine  13  is a circuit in which engine cooling water which is circulated inside the engine  13  by a pump (not shown in  FIG. 1 ) which is operated by taking part of the output from the engine  13  as a drive force, and thus becomes a high temperature, is sent to the radiator  16  and cooled by dissipating heat to the outside air.  
         [0049]     Here, while not shown in  FIG. 1 , with a normal engine cooling water system  37  a thermostat valve is provided. The thermostat valve remains closed until the engine cooling water becomes a high temperature above a predetermined value, thus preventing circulation to the radiator  16  so that to engine cooling water is warmed up in a short time.  
         [0050]     A description of the air conditioning operation by the abovementioned air conditioner follows and is considered separately for the cooling/dehumidifying operation and for the heating operation.  
         [0051]     First, the heating operation will be described. The normal heating operation employs a mode where the damper  36  is fully closed and the engine cooling water flows in the heater core  26 . In this case, the inside air or outside air (referred to hereunder as the intake air) drawn into the casing by operation of the blower fan  24  passes through the indoor heat exchanger  25  and then passes through the heater core  26  to be heated by the heat of the engine cooling water. As a result, as seen in  FIG. 2 , warmed up intake air is introduced to the duct  27  and discharged from the respective discharge sections  28 ,  29 . Hence heating of the vehicle cabin can be effected using this intake air. Under travelling conditions with the engine  13  driving, if there is a normal heating load, then this can be adequately met with such a heating operation.  
         [0052]     Here, depending on requirements, if a cooling/dehumidifying operation as described later is executed as seen in  FIG. 1  with the heat pump air conditioning apparatus, then dehumidified intake air which has passed through the indoor heat exchanger  25  can also be heated to give heating.  
         [0053]     Incidentally, with the heating operation with the above described heater core  26 , when the outside air is not extremely cold, or when the engine  13  is operating so that high temperature engine cooling water is sufficiently supplied, there is no particular problem. However, in the case where these conditions are not met, for example when the engine cooling water temperature is low, or when the heating load is high, then an insufficient heating capacity occurs, such as taking time for the heating operation to start up. When in this way the heating requirements go above a certain level, the variable capacity compressor  31  inside the compressor unit  20  is driven so that the heating operation by the air conditioner using a heat pump is executed at the same time as that by the heater core  26 .  
         [0054]     The level for the heating requirement can be judged for example by detecting the discharge temperature.  
         [0055]     A description of the heating operation of the air conditioner using a heat pump follows. At this time, the refrigerant flow is clockwise in  FIG. 1  (shown by the solid line arrow).  
         [0056]     The variable capacity compressor  31  draws in and compresses the low-temperature and low-pressure gas refrigerant and outputs an amount of refrigerant corresponding to the cooling load to the four way valve  33  as a high-temperature and high-pressure gas refrigerant. At this time, since the four way valve  33  is so set as to send the refrigerant to the indoor heat exchanger  25 , the high-temperature and high-pressure gas refrigerant is sent to the indoor heat exchanger  25  through the refrigerant path  30 , and heat is exchanged with the intake air drawn in by the blower fan  24  to warm the air. That is to say, the heat of the high-temperature and high-pressure gas refrigerant is absorbed by the intake air, and the high-temperature and high-pressure gas refrigerant is changed to a condensate and becomes a high-temperature and high-pressure liquid refrigerant. At the same time, the intake air passing through the indoor heat exchanger  25  is heated by this heat and supplied to the vehicle cabin as warm air. The indoor heat exchanger  25  in this case functions as a condenser.  
         [0057]     The refrigerant exiting from the indoor heat exchanger  25  as the high-temperature and high-pressure liquid refrigerant is decompressed and expanded by the throttling resistance  34  in the compressor unit  20  to become a low-temperature and low-pressure liquid refrigerant, and is then sent to the outdoor heat exchanger  21  installed along the side face of the vehicle body. Outside air drawn in by the fan  22  passes through the outdoor heat exchanger  21 , and the outdoor heat exchanger  21  exchanges heat with outside air to draw up the heat. Therefore, the low-temperature and low-pressure liquid refrigerant is warmed by the outside air which has a relatively higher temperature, and is evaporated and gasified to become a low-temperature and low-pressure gas refrigerant. The outdoor heat exchanger  21  in this case functions as an evaporator.  
         [0058]     The refrigerant which has become the low-temperature and low-pressure gas is then sent to the four way valve  33  and directed to the accumulator  32  where the liquid component is removed, after which the gas is again drawn into the compressor  31  and compressed. Hereafter, the same refrigeration cycle is repeated to effect heating of the vehicle cabin.  
         [0059]     On the other hand, the intake air which has passed through the indoor heat exchanger  25  to become warm air passes in full through the heater core  26  since the damper  36  is fully closed, and is reheated. Consequently, compared to heating with the heater core  26  alone, this is heated in two stages by the indoor heat exchanger  25  and the heater core  26 . Hence the amount of heat heating the intake air is increased. Moreover, the heating due to the heater core  26  is performed on high temperature intake air. Therefore, the heating performance is increased so that, when initiating the heating operation, the temperature can be raised quickly. Moreover, even in the case where the temperature of the intake air is low, the warmed warm air can be discharged until the desired temperature is reached to enable heating.  
         [0060]     At this time, if air quantity control is executed by the blower fan  24 , then the discharge temperature can be easily controlled. That is, with the damper  36  fully closed, conditions on the flow path side do not change. Hence if the heating conditions of the indoor heat exchanger  25  and the heater core  26  are constant, then by increasing the quantity of intake air, the discharge temperature is decreased while conversely by decreasing the air quantity, the discharge temperature is increased.  
         [0061]     Here, since the heater core  26  is upright, then the pressure loss when passing through the heater core  26  is minimized, and hence the load on the blower fan  24  is reduced.  
         [0062]     On the other hand, in the case where the temperature of the engine cooling water is low, then the heating operation is substantially performed only by the air conditioner using a heat pump. Hence at first, the damper  36  is opened fully, so that heating is mainly by the warm air passing through the air flow path  35 . The heating operation by the air conditioner using wheat pump continues until the engine cooling water temperature supplied to the heater core  26  goes above a predetermined value. Since with the operation with the damper  36  fully opened, there is a flow of warm air passing through the air flow path  35  and the heater core  26 , the area of the flow path is large so that the resistance value is low. Consequently, the pressure loss is reduced, and the load on the blower fan  24  is also reduced. Moreover, the flow of intake air (warm air) becomes a uniform flow being approximately a straight flow. Hence from this point also the load on the blower fan  24  is reduced, and hence the noise accompanying the air conditioning operation can be reduced.  
         [0063]     At the time of executing the heating operation with only the abovementioned air conditioner using a heat pump, by fully closing the damper  36 , the engine cooling water inside the heater core  26  can be heated. Hence the temperature of the engine cooling water which reduces the discharge temperature, can be raised to a predetermined value quickly so that the heating operation with the abovementioned two stage heating can be executed in a short time.  
         [0064]     Next is a description of the cooling operation. The damper  36  at this time is in the fully open position, and the flow of the refrigerant is in the counterclockwise direction in  FIG. 1  (shown by the broken line arrow).  
         [0065]     The variable capacity compressor  31  draws in and compresses the low-temperature and low-pressure gas refrigerant, and outputs refrigerant with the supply quantity changed corresponding to cooling load, to the four way valve  33  as a high-temperature and high-pressure gas refrigerant. At this time, since the four way valve  33  is so set as to send the refrigerant to the outdoor heat exchanger  21 , the high-temperature and high-pressure gas refrigerant is sent to the outdoor heat exchanger  21  through the refrigerant path  30 , and heat is exchanged with outside air drawn in by the fan  22  for drawing in outside air. As a result, the heat of the high-temperature and high-pressure gas refrigerant is absorbed by the outside air which has a relatively lower temperature, and the high-temperature and high-pressure gas refrigerant is changed to a condensate and becomes a high-temperature and high-pressure liquid refrigerant. The outdoor heat exchanger  21  in this case functions as a condenser.  
         [0066]     Hereafter, the high-temperature and high-pressure liquid refrigerant is sent to the throttling resistance  34 , and decompressed and expanded in passing through the throttling resistance  34  to become a low-temperature and low-pressure liquid refrigerant. The low temperature and low-pressure liquid refrigerant is then sent to the indoor heat exchanger  25  and exchanges heat with the intake air drawn in by the blower fan  24 , and absorbs heat from the intake air to effect cooling. As a result, the low-temperature and low-pressure liquid refrigerant is evaporated and gasified to become a low-temperature and low-pressure gas refrigerant. At the same time, the intake air becomes cool air and passes through the air flow path  35  and the heater core  26  to be supplied to the vehicle cabin. At this time, the area of the flow path through which the cold air flows is increased by the part that can pass though the heater core  26 . Hence the pressure loss is reduced, so that the load on the blower fan  24  is reduced. Moreover, the noise accompanying the air conditioning operation is also reduced. The indoor heat exchanger  25  in this case functions as an evaporator.  
         [0067]     Moreover, the low-temperature and low-pressure gas refrigerant exiting from the indoor heat exchanger  25  is sent to the accumulator  32  through the four way valve  33 , and the liquid component in the refrigerant is removed. The low-temperature low-pressure gas refrigerant is then again drawn into the compressor  31  from the accumulator  32  and compressed, after which the same refrigeration cycle is repeated to effect cooling of the vehicle cabin.  
         [0068]     Next is a description of a second embodiment of a vehicular air conditioner according to the present invention with reference to  FIG. 1 . With this embodiment, a bypass valve  38  is provided in the engine cooling system  37 , so as to be able to form a bypass flow path which bypasses the heater core  26 . The bypass valve  38  is connected between a primary side flow path  37   a  which introduces engine cooling water to the heater core  26  from the engine  13 , and a secondary side flow path  37   b  which returns the engine cooling water to the engine  13  from the heater core  26 , so as to be able to selectively form a bypass flow path which returns to the engine  13  without passing through the heater core  26 . That is to say, by opening and closing the bypass valve  38 , then one or the other of a normal engine cooling water flow path from the engine  13  passing through the heater core  26  and returning to the engine  13 , or an engine cooling water bypass flow path from the engine  13  returning to the engine  13  via the bypass valve  38  can be selected.  
         [0069]     For this bypass valve  38 , for example a fully closed/fully opened type such as a solenoid valve may be used. For example, a flow control valve which can control the flow quantity of engine cooling water such as with a butterfly valve is preferable.  
         [0070]     By providing such a bypass valve  38 , then at the time of the cooling operation, the full quantity of engine cooling water can be switched so as to flow to the bypass flow path. Hence the situation where the intake air which has become cold air from passing through the indoor heat exchanger  25  is heated by the heat of the engine cooling water supplied to the heater core  26 , can be avoided. That is, the situation where the intake air which has been cooled by the indoor heat exchanger  25  is heated by the heating heater core  26  so that the temperature rises can be avoided, and hence there is no loss in cooling capacity.  
         [0071]     Moreover, if a flow control valve is employed for the bypass valve  38 , then the flow quantity of engine cooling water bypassing the heater core  26  can be appropriately adjusted within a range from 0˜100%. Therefore, the intake air which has been cooled by the indoor heat exchanger  25  or the intake air which has simply passed through the indoor heat exchanger  25  can be appropriately heated by the heater core  26 , enabling the discharge temperature to be adjusted. That is, this can be set so that, if the flow quantity of the engine cooling water flowing to the heater core  26  is increased, the heating amount is increased with this increase so that the discharge temperature is increased. Conversely, if the flow quantity of engine cooling water flowing to the heater core  26  is reduced, the discharge temperature is reduced.  
         [0072]     With the second embodiment described here, in addition to the single application, this may be combined with the abovementioned first embodiment. In particular, during the cooling operation, since in order to reduce the pressure loss, the heater core  26  is placed in an intake: air flow path in addition to the air flow path  35 , this embodiment can prevent the reduction in the cooling capacity due to heating of the cold air which has been expressly cooled by the indoor heat exchanger  25 .  
         [0073]     In addition to temperature adjustment of the intake air passing through the indoor heat exchanger  25  by controlling the supply amount of refrigerant with the variable capacity compressor  31 , if a flow control valve is employed for the bypass valve  38  to adjust the temperature of the intake air passing through the heater core  26 , then it is possible to finely adjust the temperature of the discharge air with a uniform flow of intake air.  
         [0074]     Next is a description of a third embodiment of a vehicular air conditioner according to the present invention with reference to  FIG. 1 .  
         [0075]     With this embodiment, a cooling water pump  39  is provided in the engine cooling water system  37 . The cooling water pump  39  has an electric motor (not shown in  FIG. 1 ) operated for example by a battery as a drive source. When the engine  13  is operating, the power supply to the electric motor is stopped. Furthermore, when the engine  13  is stopped, then particularly at the time of the heating operation, the power supply to the electric motor is started as required to operate the cooling water pump  39  so that engine cooling water is circulated to the heater core  26  by the cooling water pump  39 .  
         [0076]     When the engine  13  is operating, then a normal pump (not shown) housed in the engine  13  is operated to circulate the engine cooling water.  
         [0077]     When such a cooling water pump  39  is provided, high temperature engine cooling water can be supplied to the heater core  26  even after the engine  13  has stopped, and used in the heating operation. That is, in the case of the abovementioned hybrid vehicle, since normally high speed travelling is performed with the engine  13 , then after engine travelling has continued for more than a certain amount, the engine cooling water will remain at a high-temperature for quite a while even after switching to the motor travelling mode.  
         [0078]     Consequently, if the heat of this engine cooling water is supplied to the heater core  26  and effectively utilized, then heating can be obtained without operating the air conditioner using a heat pump, and hence power consumption of the battery  14  in  FIG. 2  can be restrained.  
         [0079]     Moreover if, as described for the first embodiment in  FIG. 1 , the heater core  26  and the air conditioner using a heat pump are used together, then the heating capacity of the vehicular air conditioner can improve the time limit due to the engine cooling water being at a low temperature.  
         [0080]     Needless to say, the third embodiment also can be suitably combined with the above mentioned first embodiment and second embodiment and executed.  
         [0081]     Moreover, with the above described vehicular air conditioner, the variable capacity compressor  31  has been used in the air conditioner using a heat pump. However it is also possible to use a constant volume compressor, and effect operation by on/off control with a clutch.  
         [0082]     In the above description, the vehicle in which the vehicular air conditioner is installed is a hybrid vehicle. However needless to say, this may be applicable to a vehicle having an internal combustion engine as with conventional vehicles.  
         [0083]     With the vehicular air conditioner of the present invention as described above, the following effects are obtained.  
         [0084]     (1) Since there is provided an air conditioning unit with the indoor heat exchanger and the heating heat exchanger arranged in sequence from an upstream side in the casing which serves as a flow path for the intake air, and the air flow path is formed in the art above the heating heat exchanger, and the open/close device switches the air flow path between the fully closed and the fully open condition, then during the heating operation, the air flow path provided in the part above the heating heat exchanger can be closed and set so that the full amount of intake air passes through the heating heat exchanger. Consequently, in the case of a large heating load with the air conditioner using a heat pump in the heating operation condition, the intake air can be heated successively in two stages by the indoor heat exchanger and the heating heat exchanger. Therefore, the heating capacity can be improved and the heating start up time can be shortened. At this time, if the air quantity is controlled by the distribution fan, then the discharge temperature can be easily adjusted.  
         [0085]     (2) When the open/close device is fully closed, since the heating heat exchanger is installed upright, the passage distance is shorter than when install and inclined, hence the pressure loss due to the through flow of intake air can be reduced. Moreover, when the open/close device is fully open, the air flow path and the heating heat exchanger become the through flow path for the intake air, and hence the through flow area is increased so that the pressure loss is reduced. Consequently, the load on the distribution fan can be reduced, enabling a reduction in the power consumption of the drive source and in the noise during air conditioning operation.  
         [0086]     (3) Reduction of the power consumption of the distribution fan and of the air conditioning noise is particularly desirable with hybrid vehicles. That is to say, a reduction in power consumption reduces the consumption of the battery so that the travelling distance using the motor is increased. Moreover, a reduction in air conditioning operating noise improves comfort at the time of motor travelling.  
         [0087]     (4) Since a bypass valve is provided in the engine cooling water system, and a bypass path is formed for passing engine cooling water which bypasses the heating heat exchanger, then in the case where heating is not required, the full amount of engine cooling water can be introduced to the bypass flow path, thereby preventing the supply of engine cooling water to the heating heat exchanger (heater core). Consequently, the intake air which has been cooled by passing through the indoor heat exchanger is not heated by the heating heat exchanger so that the temperature is not increased, and hence there is no drop in the cooling capacity.  
         [0088]     (5) Since a flow control valve is employed for the bypass valve, then the flow quantity of the engine cooling water supplied to the heating heat exchanger and of the engine cooling water introduced to the bypass path can be controlled, enabling temperature adjustment during heating.  
         [0089]     (6) Since the cooling water pump which can be operated when the engine is stopped is provided in the engine cooling water system, then engine cooling water can be supplied to the heating heat exchanger even when the engine is stopped. Consequently, the heat of the engine cooling water can be effectively used even when the engine is stopped, enabling an improvement in the heating capacity of the vehicular air conditioner.