Abstract:
In an automotive air conditioner, there is provided an air guide arrangement for achieving an effective mixing between cooled air from an evaporator and warmed air from a heater under a bi-level mode. The air guide arrangement is placed in the vicinity of an outlet opening of a warmed air passage extending from the heater. The air guide arrangement forces a warmed air from the outlet opening of the warmed air passage to effectively mix with a cooled air which flows in a direction from the evaporator toward a ventilation air outlet opening.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates in general to automotive air conditioners, and more particularly to the automotive air conditioners of a type that has a bi-level mode wherein conditioned air is blown out from both a ventilation air blow opening and a foot air blow opening at the same time. More specifically, the present invention is concerned with the automotive air conditioners that, under bi-level mode, can provide an air mixing chamber thereof with a unique mixing between cooled air and warmed air thereby permitting the ventilation air blow opening to blow out an air mass having a desired temperature.  
           [0003]    2. Description of Related Art  
           [0004]    In order to clarify the task of the present invention, one automotive air conditioner of a related art will be briefly described with reference to FIG. 10 of the accompanying drawings.  
           [0005]    The automotive air conditioner  100  shown in the drawing is of the type having a bi-level mode, which comprises a unit case  101 . Within the unit case  101 , there are installed an evaporator  102 , a heater  103  and an air mix door unit  104  which is arranged between the evaporator  102  and the heater  103 .  
           [0006]    The air mix door unit  104  is constructed to have a heater side passage  105  which allows air to flow from the evaporator  102  toward the heater  103 , a bypass passage  106  which allows air to flow from the evaporator  102  directly to an air mix chamber  108 , and an air distribution slide door  107  which distributes air from the evaporator  102  to the heater side passage  105  and bypass passage  106  at a controlled rate. A warmed air passage  113  extends from the heater  103  to the air mix chamber  108 . Thus, under the bi-level mode of the air conditioner  100 , in the air mix chamber  108 , cooled air flowing from the evaporator through the bypass passage  106  and warmed air from the heater  103  through the warmed air passage  113  are mixed at a controlled ratio thereby to produce a temperature-controlled air in the air mix chamber  108 . From the air mix chamber  103 , there extend a ventilation air passage  109  and a foot air passage  110 . Usually, the ventilation air passage  109  has outlets facing a vertically middle zone of a passenger room and the foot air passage  110  has outlets facing a lower zone of the passenger room. The ventilation and foot air passages  109  and  110  are equipped with pivoting control doors  111  and  112  respectively. Thus, by controlling the working angle of the control doors  111  and  112 , a controlled amount of temperature-controlled air is blown into the passenger room from each of the outlets of the passages  109  and  110 . The control door  112  is arranged and constructed to distribute the temperature-controlled air in the air mix chamber  108  to both the ventilation and foot air passages  109  and  110  at a controlled rate. For this controlling, the control door  112  pivots between a first position to close the foot air passage  110  while opening the ventilation air passage  109  and a second position to close the ventilation air passage  109  while opening the foot air passage  110 . Under the bi-level mode, the control door  112  takes a halfway position between the first and second positions as shown. Thus, under this condition, the temperature-controlled air in the air mix chamber  108  can be led to both the ventilation and foot air passages  109  and  110 .  
           [0007]    However, due to an inherent construction, the air conditioner  100  has the following weak point. That is, as is seen from FIG. 4A of the accompanying drawings, under the bi-level mode, the control door  112  largely projects into the air mix chamber  108  as shown. Under such condition, cooled air from the evaporator  102  through the bypass passage  106  and warmed air from the heater  103  through the warmed air passage  113  are not effectively mixed in the air mix chamber  108  due to obstruction by the largely projected control door  112 . In fact, due to such incomplete mixing in the air mix chamber  108 , the ventilation air passage  109  tends to intake air mass whose temperature is cooler than a desired temperature and the foot air passage  110  tends to intake air mass whose temperature is higher than a desired temperature. This means that air blown into the passenger room from the ventilation air passage  109  and air blown into the passenger room from the foot air passage  110  have a remarkable temperature difference, which makes the passengers uncomfortable. This phenomenon becomes much severe when the size of the air mix chamber  108  is reduced.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an object of the present invention to provide an automotive air conditioner which is free of the above-mentioned undesired phenomenon.  
           [0009]    That is, according to the present invention, there is provided an automotive air conditioner which, under a bi-level mode, can feed respective given portions (viz., passenger chest and feet zones) of the passenger room with air masses which have a reduced temperature difference therebetween.  
           [0010]    According to a first aspect of the present invention, there is provided an automotive air conditioner which comprises a case having an air inlet opening, a ventilation air outlet opening and a foot air outlet opening; an evaporator installed in the case; a heater installed in the case; an upstream air flow passage defined in the case and extending from the air inlet opening to the evaporator; an air mix chamber defined in the case, the air mix chamber having a downstream portion which is communicated with the ventilation air outlet and foot air outlet openings; a bypass passage extending from the evaporator to the air mix chamber bypassing the heater; a first heater passage extending from the evaporator to the heater; a second heater passage extending from the heater to the air mix chamber, the second heater passage having an outlet opening exposed to the air mix chamber; an air mix door unit installed in the case in such a manner as to vary a sectional area of at least the bypass passage; and an air guide arrangement provided at a position downstream of the air mix door unit, the air guide arrangement including a raised structure that extends across the bypass passage from a first position near the outlet opening of the second heater passage to a second position that is opposite to the first position with respect to the bypass passage.  
           [0011]    According to a second aspect of the present invention, there is provided an automotive air conditioner which comprises a case having an air inlet opening, a ventilation air outlet opening and a foot air outlet opening; butterfly-type pivot doors respectively provided by the ventilation and foot air outlet openings, each pivot door having a center axis about which a valve proper rotates; an evaporator installed in the case; a heater installed in the case; an upstream air flow passage defined in the case and extending from the air inlet opening to the evaporator; an air mix chamber defined in the case, the air mix chamber having a downstream portion which is communicated with the ventilation air outlet and foot air outlet openings; a bypass passage extending from the evaporator to the air mix chamber bypassing the heater; a first heater passage extending from the evaporator to the heater; a second heater passage extending from the heater to the air mix chamber, the second heater passage having an outlet opening exposed to the air mix chamber; an air mix door unit installed in the case in such a manner as to vary a sectional area of both the bypass passage and the first heater passage; and an air guide arrangement provided at a position downstream of the air mix door unit, the air guide arrangement including a raised structure that extends across the bypass passage from a first position near the outlet opening of the second heater passage to a second position that is opposite to the first position with respect to the bypass passage, so that the raised structure of the air guide arrangement forces a first air flow from the outlet opening of the second heater passage to mix with a second air flow which runs in a direction from the bypass passage toward the ventilation air outlet opening. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a vertically sectional view of an automotive air conditioner which is a first embodiment of the present invention;  
         [0014]    [0014]FIG. 2A is a perspective view of an area of the air conditioner of the first embodiment where an air mix chamber is provided;  
         [0015]    [0015]FIG. 2B is a schematically illustrated sectional view taken along the line IIB-IIB of FIG. 2A;  
         [0016]    [0016]FIG. 3A is a sectional view of ventilation air blow opening of an air conditioner with an air guide removed, showing a temperature distribution possessed by the air flow in the opening;  
         [0017]    [0017]FIG. 3B is a view similar to FIG. 3A, but showing a temperature distribution in case of the first embodiment;  
         [0018]    [0018]FIG. 4A is a schematically illustrated sectional view of the air conditioner of the related art, showing air flow in the air mix chamber;  
         [0019]    [0019]FIG. 4B is a view similar to FIG. 4A, but showing air flow in the first embodiment of the present invention;  
         [0020]    [0020]FIG. 5A is a graph showing the air temperature in a foot air blow opening and that in a ventilation air blow opening under a bi-level mode in case of the air conditioner of the related art;  
         [0021]    [0021]FIG. 5B is a graph similar to FIG. 5A, but showing the air temperature in case of the first embodiment of the present invention;  
         [0022]    [0022]FIG. 6A is a view similar to FIG. 2A, but an automotive air conditioner of a second embodiment of the present invention;  
         [0023]    [0023]FIG. 6B is a schematically illustrated sectional view taken along the line VIB-VIB of FIG. 6A;  
         [0024]    [0024]FIG. 7A is a view similar to FIG. 2A, but showing an automotive air conditioner of a third embodiment of the present invention;  
         [0025]    [0025]FIG. 7B is a schematically illustrated sectional view taken along the line VIIB-VIIB of FIG. 7A;  
         [0026]    [0026]FIG. 8 is a view similar to FIG. 7B, but showing a first modification of the third embodiment of the present invention;  
         [0027]    [0027]FIG. 9 is a view also similar to FIG. 7B, but showing a second modification of the third embodiment of the present invention; and  
         [0028]    [0028]FIG. 10 is a vertically sectional view of an automotive air conditioner of a related art. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0029]    In the following, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
         [0030]    For ease of description, substantially same parts and constructions of the embodiments are denoted by the same numerals and repeated explanations of such parts and constructions will be emitted from the following.  
         [0031]    Furthermore, for ease of understanding, various directional terms, such as, right, left, upper, lower, rightward, etc., are included in the following description. However, such terms are to be understood with respect to only a drawing or drawings on which the corresponding part or portion is illustrated.  
         [0032]    Referring to FIG. 1 to FIG. 5B, especially FIG. 1, there is shown an automotive air conditioner  100 A which is a first embodiment of the present invention.  
         [0033]    As is seen from FIG. 1, the automotive air conditioner  100 A of the first embodiment comprises a unit case  2 , an electric fan  3  installed at an upstream part in the unit case  2 , an air filter  4  positioned downstream of the fan  3 , an evaporator  5  positioned just downstream of the air filter  4 , an air mix door unit  6  and a heater  7 .  
         [0034]    The unit case  2  is constructed to have an air flow passage “P” defined therein. At a position upstream of the electric fan  3 , the case  2  has an air inlet opening (not shown) through which outside air and/or inside air (viz., air in a passenger room) is led into the passage “P” by the fan  3 . At a downstream part of the air flow passage “P”, there are provided a defroster air outlet opening  9 , a ventilation air outlet opening  10  and a foot air outlet opening  11 . As shown, the openings  9  and  10  are provided at a rear upper portion of the unit case  2 , while the opening  11  is provided at a rear lower portion of the case  2 . More specifically, the opening  11  is formed at a leading end of a duct structure  15  which extends downward in the case  2 . Denoted by numeral  11 A is an inlet opening of a branch duct which extends to another given lower portion from the duct structure  15 .  
         [0035]    The defroster air outlet opening  9  is directed to an inner surface of a windshield (not shown) of an associated motor vehicle, and the ventilation air outlet opening  10  is connected to both a center ventilation duct (not shown) that blows air toward a chest zone of passengers and side ventilation ducts (not shown) that blow air toward side window panes of the vehicle. The foot air outlet opening  11  is connected to both a front foot duct (not shown) that blows air toward a foot area of front passengers and a rear foot duct (not shown) that blows air toward a foot area of rear passengers.  
         [0036]    The electric fan  3  is located at the upstream part  8  of the air flow passage “P” to drive the inputted air downstream in the passage “P”.  
         [0037]    The air filter  4  filters out dusts from air flowing in the air flow passage “P”. Due to this air filter  4 , cleaned air is led into the passenger room and at the same time, heat exchanging fins of the evaporator  5  and those of the heater  7  are protected from ducts and thus the performance of these devices  5  and  7  is kept good for a longer time.  
         [0038]    The evaporator  5  is an element of a cooling system, through which a refrigerant flows for cooling air flowing through the evaporator  5 . The heater  7  is fed with an engine cooling water from a water jacket of an associated engine of the vehicle. Thus, the heater  7  warms air flowing therethrough.  
         [0039]    The air mix door unit  6  is arranged between the evaporator  5  and the heater  7  and comprises a door case  61  and a slide door  62  slidably disposed on the door case  61 . The door case  61  has an air inlet aperture  63  which faces a rear surface of the evaporator  5 , a lower (or first) air outlet opening  65  which faces a front surface of the heater  7  and an upper (or second) air outlet opening  67  which faces toward an after-mentioned air mix chamber  14 . The lower air outlet opening  65  forms part of a heater side passage  64  which extends from the evaporator  5  to the heater  7 , and the upper air outlet openings  67  forms part of a bypass passage  66  which extends from the evaporator  5  to the air mix chamber  14  bypassing the heater  7 . As shown, a warmed air passage  12  extends upward from the heater  7  to the air mix chamber  14 . The slide door  62  slides generally vertically along a given way to vary the open degree of the outlet openings  65  and  67  distributing a cooled air from the evaporator  5  to the heater side passage  64  and bypass passage  66  at a controlled rate.  
         [0040]    As shown, the heater  7  is positioned near the lower air outlet opening  65 . The heater  7  has an upper end held by a holding lib  30  which is projected from the door case  61 . The warmed air passage  12  extends upward along the duct structure  15  that has the foot air outlet opening  11 .  
         [0041]    As is shown, an outlet opening  13  of the warmed air passage  12  is directed toward the air outlet opening  67  of the bypass passage  66 . It is to be noted that the outlet opening  13  and the outlet opening  67  are both exposed to the air mix chamber  14  where cooled air from the bypass passage  64  and the warmed air from the warmed air passage  12  are mixed to provide a temperature-controlled air in the air mix chamber  14 .  
         [0042]    Just above the outlet opening  13 , there is defined an inlet opening  16  of the duct structure  15  of the foot air outlet opening  11 . Just above the inlet opening  16 , there is defined an inlet opening  18  of a ventilation air passage  17  that is connected to the ventilation air outlet opening  10 , and at a front upper position of the inlet opening  18 , there is defined an inlet opening  20  of a defroster air passage  19  that is connected to the defroster air outlet opening  9 .  
         [0043]    As shown, the inlet openings  16 ,  18  and  20  of the air passages  15 ,  17  and  19  are respectively provided with pivot doors  21 ,  22  and  23  of a butterfly type. For ease of understanding, these doors  21 ,  22  and  23  will be called foot door, ventilation door and defroster door respectively. Although not shown in the drawings, these doors  21 ,  22  and  23  are pivotally actuated by an electric actuator when mode setting and temperature setting knobs on an instrument panel are manipulated.  
         [0044]    In the first embodiment  100 A of the present invention, the following constructional features are provided.  
         [0045]    As is seen from FIG. 1, the foot door  21  is pivotal about its center pivot axis  21   h  and so arranged as to pivot between a closed position to close the inlet opening  16  of the foot air passage  15  and an open position to open the inlet opening  16 . As shown, in the closed position, upper and lower ends of the foot door  21  abut against projections (no numerals) formed on a peripheral portion of the inlet opening  16 , while, in the open position, the opposed side parts, viz., the upper and lower ends of the door  21  are projected but slightly into the air mix chamber  14  and the foot air passage  15  respectively. The upper and lower ends of the foot door  21  serve as means for limiting pivoting movement of the foot door  21  in the air mix chamber  14 .  
         [0046]    As is seen from FIGS. 1 and 2, behind the air outlet opening  67  of the bypass passage  66 , there is provided a vertically extending air guide  24  which projects into the air mix chamber  14 . That is, as is seen from FIG. 2, the air guide  24  is located at a laterally middle portion of the outlet opening  67 , extending vertically from the holding lib  30  to an inside case wall  2 A that defines the upstream part  8  of the air flow passage “P”.  
         [0047]    More specifically, as will be seen from FIGS. 2A and 2B, the air guide  24  is constructed to have a generally T-shaped cross section, comprising an elongate base plate  25  that extends vertically across the upper air outlet opening  67  and a baffle plate  26  that is perpendicularly raised from a laterally middle portion of the base plate  25  into the air mix chamber  14 . The air guide  24  may be a part integral with the door case  61 .  
         [0048]    As is seen from FIGS. 2A and 2B, due to provision of the baffle plate  26 , cooled air flow from the evaporator  5  from the bypass passage  66  is separated into two flows.  
         [0049]    Furthermore, as is seen from FIG. 2A, between the inside case wall  2 A of the case  2  and an upper wall of the door case  61 , there laterally extends an elongate plate portion. With this plate portion, there is formed a laterally extending recess  32  which faces the air mix chamber  14 . A laterally middle portion of the recess  32  has an upper end of the baffle plate  26  mounted thereon, as shown. As will be seen from FIGS. 1 and 2A, under operation of the air conditioner  100 A, warmed air from the warmed air passage  12  is guided by the baffle plate  26  and then diffused by the recess  32  in lateral directions.  
         [0050]    Furthermore, as is seen from FIGS. 1 and 4B, in the first embodiment  100 A, an air guide opening  27  is formed on the outlet end of the warmed air passage  12 , which is bent toward the air guide  24 . More specifically, the air guide opening  27  comprises a gently curved upper inner wall of the outlet end of the warmed air passage  12 .  
         [0051]    In the following, advantageous phenomena of the first embodiment  100 A having the above-mentioned constructional features will be described in the following.  
         [0052]    First, as is understood from FIG. 4B, the foot door  21  is of a butterfly type arranged to pivot about its center pivot axis  21   h . This means that the foot door  21  projects into the air mix chamber  14  in a small degree as compared with in case of the related art of FIG. 4A wherein the foot door  112  (see FIG. 10) is pivoted about an upper end thereof. Thus, when the automotive air conditioner  100 A assumes bi-level mode wherein the foot door  21  takes a half-open position as shown in FIG. 4B, the cooled air from the bypass passage  66  and the warmed air from the warmed air passage  12  are effectively mixed in the air mix chamber  14 . That is, in the first embodiment  100 A of the invention, air mass blown out from the ventilation air passage  17  and that blown out from the foot air passage  15  can have a less temperature difference, which makes the passengers comfortable.  
         [0053]    For investigating the above-mentioned advantage of the invention, an experiment was carried out by the applicants by using the air conditioner  100  of FIG. 4A of the related art and the air conditioner  100 A of the first embodiment of the invention. In the experiment, in each of the air conditioners  100  and  100 A, the temperature of air blown out from the foot air passage  110  or  11  and that of air from the ventilation air passage  109  or  10  were measured with respect to the open degree of the foot door  112  or  21 .  
         [0054]    Results of the experiment are depicted in the graphs of FIGS. 5A and 5B. As is seen from these graphs, the first embodiment  100 A showed only 15 C. ° as the largest temperature difference while the related art  100  showed 30 C. ° as the difference. In fact, it occurred that, under a same bi-level mode, the air mass from the foot air passage  110  and that from the ventilation air passage  109  of the related art  100  showed 45 C. ° and 15 C. ° respectively (viz., temperature difference is 30 C. °) in case of the related art  100 , while in case of the first embodiment  100 A, corresponding air masses showed 40 C. ° and 16 C. ° respectively (viz., temperature difference is 24 C. °).  
         [0055]    Second, as is seen from FIG. 2, due to provision of the air guide  24 , the warmed air from the warmed air passage  12  is forced to flow in the air mix chamber  14  in such a manner as is indicated by arrows. That is, due to provision of the air guide  24 , the warmed air can be led to the upper portion of the air mix chamber  14 , and thus, as is seen from FIG. 1, the mass of warmed air becomes to have a higher possibility of being blown toward the ventilation air outlet opening  10  by the cooled air from the bypass passage  66 . Thus, the above-mentioned temperature difference is much reduced. As is seen from FIG. 2B, due to interference by the base plate  25  of the air guide  24 , the mass of cooled air is enforcedly separated into two flows helping the upward flow of the warmed air in the air mix chamber  14 , which promotes the reducing of the above-mentioned temperature difference.  
         [0056]    As is seen from FIGS. 1 and 2A, due to provision of the laterally extending recess  32  defined between the inside case wall  2 A and the upper wall of the door case  61 , the warmed air running upward along the baffle plate  26  is guided laterally outward, which also promotes the reducing of the above-mentioned temperature difference.  
         [0057]    In order to investigate the advantageous function of the air guide  24  in the first embodiment  100 A under the bi-level mode, an experiment was carried out.  
         [0058]    This experiment will be described with reference to FIGS. 3A and 3B, which depict a temperature distribution of air mass flowing in the ventilation air blow opening of tested air conditioners. In each drawing, denoted by numeral  10   a  is a center blow opening, and denoted by numeral  10   b  are side blow openings.  
         [0059]    In the experiment, two types of air conditioners were used, one being a type  100 A′ of FIG. 3A having no air guide and the other being a type  100 A of FIG. 3B having the air guide  24 .  
         [0060]    As is seen from FIG. 3B, in the type  100 A of the first embodiment, the warmed air was seen to flow along an upper zone “A” in the ventilation air outlet opening  10 . This proves that under such bi-level mode, the warmed air from the warmed air passage  12  (see FIG. 1) is subjected to a course change and directed toward the ventilation air outlet opening  10 . In other words, with the provision of the air guide  24 , the cooled air from the bypass passage  66  and the warmed air from the warmed air passage  12  are approximately or uniquely mixed in the air mix chamber  14 . While, in case of the type  100 A′ having no air guide, the warmed air was seen to flow along side walls of the air outlet opening  10  exclusively. The temperature distribution shown in the ventilation air outlet opening  10  is changed or controlled by varying the size, length and position of the air guide  24 .  
         [0061]    In the first embodiment  100 A, the air guide opening  27  is provided, which is constructed to face the air guide  24 , and thus, the warmed air from the warmed air passage  12  is assuredly guided by the air guide  24 .  
         [0062]    Referring to FIGS. 6A and 6B, especially FIG. 6A, there is shown an automotive air conditioner  100 B which is a second embodiment of the present invention.  
         [0063]    Since the conditioner  100 B of this second embodiment is similar to that  100 A of the above-mentioned first embodiment, only parts or portions which are different from those of the first embodiment  100 A will be described in detail in the following for ease of description. Substantially same parts and portions as those of the first embodiment  100 A are denoted by the same numerals.  
         [0064]    As is seen from FIG. 6A, in the second embodiment  100 B, an air guide  28  of a channel-shape is used, which is mounted behind the air outlet opening  67  of the bypass passage  66 . More specifically, the air guide  28  comprises an elongate base plate  29  that extends vertically across the upper air outlet opening  67  and two baffle plates  30 A and  30 B which are raised from lateral ends of the base plate  28  into the air mix chamber  14 . Thus, between the two baffle plates  30 A and  30 B, there is defined a warmed air guide groove  31 .  
         [0065]    As is seen from FIG. 6A, due to the air guide groove  31  provided by the air guide  28 , the warmed air from a laterally middle portion of an outlet opening of the warmed air passage  12  is enforcedly led into the air guide groove  31 , and thus, led into an upper portion of the air mix chamber  14  (see FIG. 1). Thus, the mass of warmed air directed toward the ventilation air outlet opening  10  is increased thereby reducing the above-mentioned temperature difference between air blown from the ventilation air passage  17  and air blown form the foot air passage  15 .  
         [0066]    Referring to FIGS. 7A and 7B, especially FIG. 7A, there is shown an automotive air conditioner  100 C which is a third embodiment of the present invention.  
         [0067]    Since the conditioner  100 C of this third embodiment is also similar to that  100 A of the above-mentioned first embodiment, only parts or portions which are different from those of the first embodiment  100 A will be described.  
         [0068]    As is seen from FIGS. 7A and 7B, in the third embodiment  100 C, an air guide  33  having an anchor-shaped cross section is used, which is mounted behind the air outlet opening  67  of the bypass passage  66 . More specifically, the air guide  33  comprises an elongate base plate  34  that extends vertically across the upper air outlet opening  67 , a center major baffle plate  35  that is raised from a laterally middle portion of the base plate  34  and two smaller baffle plates  36 A and  36 B that are raised from lateral end portions of the base plate  34 . In the illustrated embodiment, the smaller baffle plates  36 A and  36 B have each a length that is substantially the same as the length of the upper air outlet opening  67 .  
         [0069]    In the third embodiment  100 C, two air guide grooves (no numerals) are provided at either sides of the major baffle plate  35 . Due to the air guide grooves provided by the air guide  33 , upward flow of the warmed air from the warmed air passage  12  is smoothed or enhanced, and thus, like in the above-mentioned second embodiment  100 B, the mass of warmed air directed toward the ventilation air outlet opening  10  (see FIG. 1) is increased, and thus, the above-mentioned temperature difference between the ventilation air passage  17  and the foot air passage  15  is reduced.  
         [0070]    If desired, the third embodiment  100 C may be modified like first and second modifications  100 C- 1  and  100 C- 2  which are shown in FIGS. 8 and 9 respectively. That is, in the first modification  100 C- 1  of FIG. 8, the two smaller baffle plates  36 A and  36 B are raised from lateral ends of the base plate  34 . In the second modification  100 C- 2  of FIG. 9, two air guides  37 A and  37 B are used, which are arranged abreast behind the air outlet opening  67  of the bypass passage  66 . Each air guide  37 A comprises an elongate base plate  38  that extends vertically across the opening  67  and a smaller baffle plate  39  that is raised from a laterally middle portion of the base plate  38 .  
         [0071]    The entire contents of Japanese Patent Application 2001-076991 filed Mar. 16, 2001 are incorporated herein by reference.  
         [0072]    Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.