Abstract:
A cabin for a work vehicle comprises: a driver&#39;s seat positioned within the cabin; cabin frames including at least a transverse frame located in a rear region of the cabin; a roof supported by at least some of the cabin frames; at least one air-conditioning duct located within the roof; an air-conditioning unit located rearwardly with respect to a rearward end of a seat portion of the driver&#39;s seat and adjacent the transverse frame for conditioning air and for feeding air-conditioned air into the at least one air-conditioning duct.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of co-pending U.S. patent application Ser. No. 12/832,104 filed Jul. 8, 2010, which is a divisional application of U.S. patent application Ser. No. 11/371,357 filed Mar. 8, 2006, now U.S. Pat. No. 8,033,899, which claims priority to JP2005-251643, JP2005-251644, and JP2005-251645, each filed Aug. 31, 2005. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a cabin for a work vehicle, and more particularly to an air-conditioning unit within the cabin roof. 
     2. Description of Related Art 
     For arranging the air-conditioning unit, the forward half of the roof is formed as a low ceiling portion bulging downward. The air-conditioning unit is arranged in a front portion of the low ceiling portion (e.g., JP Publication No. 2005-1537 (paragraph number [0016], FIG. 1 and FIG. 2). 
     In the above construction, the roof includes a low ceiling portion that accommodates the air-conditioning unit. This leads to narrowing of an upper forward field of view. Then, when performing a front loader operation, the driver seated on the driver&#39;s seat has difficulty in ascertaining a position of the bucket near an upper position, resulting in a possibility of lowering working efficiency. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide an air-conditioning structure for a cab of a working vehicle with an improved upper forward view by providing a better arrangement for the air-conditioning unit. 
     A cabin for a work vehicle in accordance with the present invention comprises: a driver&#39;s seat positioned within the cabin; cabin frames including at least a transverse frame located in a rear region of the cabin; a roof supported by at least some of the cabin frames; at least one air-conditioning duct located within the roof; an air-conditioning unit located rearwardly with respect to a rearward end of a seat portion of the driver&#39;s seat and adjacent the transverse frame for conditioning air and for feeding air-conditioned air into the at least one air-conditioning duct. 
     Since the air-conditioning unit is disposed rearwardly with respect to the rear end of the seat portion of the driver&#39;s seat, a low ceiling portion for accommodating the air-conditioning unit need not be formed in a front portion of the roof of the cabin. A windshield position can be set high. As a result, an improved upper forward field of view is provided. 
     Moreover, since the position of the air-conditioning unit is set rearwardly of the rear end of the seat portion of the driver&#39;s seat, a low ceiling portion formed in the rear of the roof in order to accommodate the air-conditioning unit would not diminish the forward field of view of the driver seated on the driver&#39;s seat, but can alleviate a narrowing of overhead space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side elevation of a tractor; 
         FIG. 2  shows a perspective view showing a structural framework in a first embodiment; 
         FIG. 3  shows a side view in vertical section showing a cabin interior in the first embodiment; 
         FIG. 4  shows a plan view in cross section showing an inner surface of an inner roof portion seen from an outer roof in  FIG. 2 ; 
         FIG. 5  shows a front view showing a duct disposed laterally of a roof; 
         FIG. 6  shows a perspective view showing a structural frame in a second embodiment; 
         FIG. 7  shows a side view in vertical section side showing a mounting structure for an air-conditioning unit in the second embodiment; 
         FIG. 8  shows a perspective view showing a structural framework in a third embodiment; 
         FIG. 9  shows a side view in vertical section side showing a mounting structure for an air-conditioning unit in the third embodiment; 
         FIG. 10  shows a perspective view showing a structural framework in a fourth embodiment; 
         FIG. 11  shows a side view in vertical section side showing a mounting structure for an air-conditioning unit in the fourth embodiment; 
         FIG. 12  shows a plan view in cross section showing a different embodiment of the air-conditioning duct; 
         FIG. 13  shows a plan view in cross section showing a different embodiment of the air-conditioning duct; 
         FIG. 14  shows a rear view showing an arrangement of the air-conditioning duct in  FIG. 13 ; 
         FIG. 15  shows side view in vertical section side showing an upper frame serving also as a duct; 
         FIG. 16  (A) shows a perspective view showing upper ends of front posts higher than fore and aft frames; 
         FIG. 16  (B) shows a principle view showing an upper forward field of view for the driver in  FIG. 16  (A); 
         FIG. 17  (A) shows a perspective view showing upper ends of front posts arranged rearwardly of forward ends of fore and aft frames; and 
         FIG. 17  (B) shows a principle view showing an upper forward field of view for the driver in  FIG. 17  (A). 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While several embodiments will be described below, a combination of a feature in one embodiment with another in a different embodiment is understood to be within the scope of the present invention unless such combination leads to a contradiction. 
     An agricultural tractor will be described as an example of the maintenance vehicle. As shown in  FIGS. 1 and 2 , the agricultural tractor has a cab  1  formed of vertical frames  2  of a structural framework B constituting a framework, boarding and alighting side doors  3 , rear side windows  4  and a rear window  5  having transparent glass planes covering portions surrounded by the vertical frames  2 , an annular upper frame  6  extending over upper surfaces of the vertical frames  2 , and a roof  7  placed on the upper frame  6 . 
     The cabin  1  defines a driving and control section  8  therein. The driving and control section  8  includes a steering wheel  11  attached to a steering column  10  disposed adjacent an engine hood  9 , and a driver&#39;s seat  12  disposed rearwardly of the steering column  10 . The rearward end of the seating portion of the driver&#39;s seat  12  means a rear end of the top surface where the driver sits. When the seat  12  has a seat pad portion and a separate seat back, the rearward end of the seating portion of the driver&#39;s seat  12  may mean the rearward end of the seat pad portion. 
     The roof  7  supports an air-conditioning unit A for air-conditioning the interior of the cab  1 . 
     First Embodiment 
     Different forms of attaching the air-conditioning unit A will be described hereinafter. A first embodiment will be described first, in which, as shown in  FIGS. 2 and 3 , the air-conditioning unit A is mounted above a rear end of the annular upper frame  6  extending over the upper surfaces of the vertical frames  2  constituting the structural framework B. A rear frame portion  6 B located in a rear position of a hood portion  7  of the annular upper frame  6  is called a transverse frame herein. 
     The construction of the structural framework B for supporting the air-conditioning unit A will be described. As shown in  FIG. 2 , right and left vertical frames  2  are erected at connecting bend portions between fore and aft frame portions  6 A and rear frame portion  6 B acting as the transverse frame of the annular upper frame  6 , to serve also as window frames of the rear side windows  4 . A support frame  6 C is laid to extend between the two vertical frames  2  and at a height level a step lower than the rear frame portion  6 B. 
     The air-conditioning unit A is placed in a state of being dropped on the upper surface of the support frame  6 C and between the neighboring vertical frames  2  supporting the support frame  6 C. The support frame  6 C is called herein an air-conditioning unit mounting portion. 
     As shown in  FIG. 3 , a pair of right and left brackets  16  are attached in a fore and aft posture to the upper surface of the support frame  6 C. The air-conditioning unit A enclosed in a unit case  24  is placed on and fixed by bolts to the right and left brackets  16 . 
     The construction of the roof  7  will be described. 
     As shown in  FIGS. 3 through 5 , the roof  7  includes an outer roof  13  and an inner roof  14 , each attached to and supported by the upper frame  6 . The inner roof  14  is an integral resin molding article, has a rearward half thereof above the driver&#39;s seat  12  formed as a low ceiling portion bulging downward. The air-conditioning unit A is mounted in this low ceiling portion. 
     As shown in  FIGS. 2 and 3 , the outer roof  13  is laid on the upper surface of the upper frame  6 , and is in the form of a flat plate larger than the support surface. A seal ring  19  of rectangular section formed in the shape of a ring is attached to a downward-facing surface of the outer roof  13 . In the state of the outer roof  13  laid on the upper frame  6 , part of the section of the seal ring  19  contacts the upper surface of the upper frame  6 , to stop circulation of air to and from the exterior. 
     As shown in  FIGS. 3 through 5 , ambient air intake openings  13 B are formed in downward surfaces of sideways eaves portions  13 E of the outer roof  13  projecting from opposite sides of the upper frame  6 . An ambient air feed opening  13 C communicating with the above ambient air intake openings  13 B is formed in a position inwardly of the seal ring  19 . Numeral  33  in the drawings denotes dust filters provided for the ambient air intake openings  13 B. 
     Air drawn in through the ambient air intake openings  13 B is guided forwardly of the vehicle body through a communicating path “b” acting as an ambient air feed duct formed in the double wall of the outer roof  13 , and is blown off from the ambient air feed opening  13 C formed forwardly of the communicating path “b” into a space “a” leading to the air-conditioning unit A described hereinafter. 
     The internal structure of the inner roof  14  will be described. As shown in  FIGS. 1 through 4 , the air-conditioning unit A includes an evaporator  20 , and a heater  21  disposed forwardly thereof. The evaporator  20  cooperates with a compressor, an expansion valve and a condenser to constitute a coolant circulation circuit. The heater  21  is connected through piping to a radiator  22  mounted in the engine hood  9 . 
     A sirocco fan  23  is disposed at the right-hand side of the evaporator  20  for feeding the ambient air drawn in through the ambient air feed opening  13 C toward the evaporator  20  and heater  21 . 
     As shown in  FIG. 3 , the ambient air introduced through the ambient air feed opening  13 C, is drawn and guided through the space “a” formed between the downward surface of the outer roof  13  and the inner roof  14  acting as a circulation path, to a guide bore  24   a  of the sirocco fan  23  enclosed in the unit case  24 . 
     As shown in  FIGS. 3 and 4 , the evaporator  20  and sirocco fan  23  are surrounded by the unit case  24 . A rear air-conditioning duct  15 A continuous with the unit case  24  extends transversely for guiding conditioning air from the air-conditioning unit A, from opposite lateral ends of the evaporator  20  to the right and left sides. Lateral air-conditioning ducts  15 B extend forward from opposite lateral ends of the rear air-conditioning duct  15 A for guiding the conditioning air forwardly of the vehicle body. 
     The right and left air-conditioning ducts  15 B and  15 B will be described. As shown in  FIGS. 3 through 5 , each of the right and left air-conditioning ducts  15 B has inwardly directed blow-off openings  15   b , and the rearward blow-off opening  15   b  is located for directing an appropriate amount of cool air near the driver&#39;s face. On the other hand, each lateral air-conditioning duct  15 B has blow-off openings  15   a  arranged adjacent the forward thereof and directed forward and downward for blowing off the conditioning air toward a windshield  25  of the cab  1 , and a blow-off opening  15   d  disposed rearwardly of the blow-off openings  15   a  for blowing off defrost air toward the door glass. 
     As shown in  FIGS. 2 and 3 , branch ducts  15 C extend rearward from the opposite ends of the rear air-conditioning duct  15 A, and blow-off openings  15   c  are formed at extension ends thereof for blowing off the conditioning air to the rear side windows  4  and rear window  5 . The above lateral air-conditioning ducts  15 B and the like are located in the inner roof  14 , and are mounted in low ceiling portions formed at opposite sides of the inner roof  14  as shown in  FIG. 5 . 
     As shown in  FIG. 3 , the inner roof  14  includes a circulation opening  14 A disposed forwardly of the portion accommodating the air-conditioning unit A for drawing in air of the cab interior. A wall surface extends upward along the unit case  24  from an upper surface of a slope of a bottom inner roof  14   b  defining the low ceiling portion, and the circulation opening  14 A is formed in a horizontal portion at the upper end of the vertical surface  14   c . The vertical surface  14   c  of the top inner roof  14   a  is called herein an interior air introducing duct. 
     On the other hand, the ambient air feed opening  13 C and circulation opening  14 A are vertically opposed to each other, and a switching valve  17  is disposed therebetween to act as a valve mechanism for opening and closing the ambient air feed opening  13 C and circulation opening  14 A. Thus, a switching is made between a state of drawing ambient air through the ambient air intake openings  13 B into the space “a” formed between the inner roof  14  and outer roof  13 , and a state of shutting off ambient air and circulating the air in the cab interior through the space “a”. 
     The valve mechanism may be the slide type rather than the pivoting type. Although not shown, the valve mechanism is operable by a switching lever erected to a level above and adjacent the driver&#39;s seat  12 . 
     As shown in  FIG. 3 , the inner roof  14 , which has the circulation opening  14 A for drawing in air of the cab interior, includes a rear top inner roof portion  14   a  defining the circulation opening  14 A, and a forward inner roof portion  14   b  located in the forward part of the cab  1 . The inner roof  14  has a fore and aft intermediate position thereof in tight contact with the outer roof  13 . The intermediate position in tight contact separates the rear inner roof portion  14   a  and forward inner roof portion  14   b . A CD radio cassette recorder  29  or the like is mounted in a space of the forward inner roof portion  14   b  having the above construction. The back pressure of the interior air taken in from the circulation opening  14 A does not directly act on the CD radio cassette recorder  29  or the like, so that the CD radio cassette recorder  29  or the like has a reduced chance of drawing in dust and the like. 
     As shown in  FIGS. 3 through 5 , the ambient air intake openings  13 B are arranged adjacent the air-conditioning unit A. Consequently, the communicating path b formed in the outer roof portion  13  and communicating with the ambient air intake openings  13 B may be shortened, and the sirocco fan  23  may have a reduced suction resistance. 
     A support cover  18  extends rearwardly of the support frame  6 C for covering the air-conditioning unit A. The rear window  5  is supported by the support frame  6 C and on the undersurface of the support cover  18  to be pivotable rearward about a transverse axis X. In a closed state, the rear window  5  does not protrude a large extent rearward, thereby to avoid interference with a linkage mechanism and the like supporting a tilling implement, though these components are not shown in the drawings. 
     Second Embodiment 
     Next, a second embodiment will be described, in which, as shown in  FIG. 6 , the air-conditioning unit A is mounted forwardly of the rear end of the annular upper frame  6 . 
     As shown in  FIGS. 6 and 7 , an outer roof  13  and an inner roof  14  are arranged to surround the air-conditioning unit A. An ambient air feed opening  13 C is formed in the outer roof  13  forwardly of the air-conditioning unit A, and an ambient air intake opening  13 B is formed in a downward surface of an eaves portion  13 A of the outer roof  13  projecting rearwardly for feeding ambient air to the ambient air feed opening  13 C. The inner roof  14  has a circulation opening  14 A opposed to the ambient air feed opening  13 C for drawing in air from the interior of the cab  1 . A switching valve  17  is disposed between the ambient air feed opening  13 C and circulation opening  14 A to act as a valve mechanism for opening and closing the ambient air feed opening  13 C and circulation opening  14 A. A switching may be made between a state of drawing ambient air through the ambient air intake opening  13 B into a space “a” formed between the inner roof  14  and outer roof  13 , and a state of shutting off ambient air and circulating the air in the cab interior through the space “a”. 
     Air taken into the space “a” is drawn into the sirocco fan  23  via a guide bore  24   a  formed in the upper surface of the unit case  24  of the air-conditioning unit A. After being conditioned by the evaporator  20  and the like, the air is delivered to the air-conditioning ducts  15 A and  15 B. 
     As shown in  FIG. 4 , the rear air-conditioning duct  15 A extends from opposite lateral ends of the evaporator  20  as described hereinbefore, and lateral air-conditioning ducts  15 B extend forward from opposite lateral ends of the rear air-conditioning duct  15 A for blowing off conditioning air into the cab as in the first embodiment. 
     Next, a mounting structure for the rear side windows  4  and rear window  5  will be described.  FIG. 7  shows the air-conditioning unit A disposed forwardly of the rear end of the annular upper frame  6 . In order to employ the construction for arranging the air-conditioning unit A forwardly of the rear end of the annular upper frame  6 , the rear end of the annular upper frame  6  is displaced rearwardly of the position of the rear window  5 . For this reason, rear pillars acting as the vertical frames  2  located at boundaries between the rear window  5  and rear side windows  4  are connected to the upper frame  6  through connecting frames  30  to increase connecting strength of the frames. The rear window  5  is supported, to be pivotable rearward to an open position, by pivot arms  32  pivotally connected to brackets  31  attached to the rear frame portion  6 B of the upper frame  6 . 
     Third Embodiment 
     Next, a third embodiment will be described, in which, as shown in  FIG. 8 , the air-conditioning unit A is mounted below a suspending frame portion  6 D formed on the rear frame portion  6 B acting as the transverse frame. 
     The construction of the structural framework B for supporting the air-conditioning unit A will be described. As shown in  FIGS. 8 and 9 , right and left vertical frames  2  are erected at connecting bend portions between fore and aft frame portions  6 A and rear frame portion  6 B of the annular upper frame  6 , to serve also as window frames of the rear side windows  4 . The suspending frame portion  6 D is laid to extend between the two vertical frames  2  and at a height level a step higher than the rear frame portion  6 B. 
     The air-conditioning unit A is suspended in a state of being slipped under the lower surface of the suspending frame portion  6 D and between the neighboring vertical frames  2  supporting the suspending frame portion  6 D. The suspending frame portion  6 D is called herein an air-conditioning unit mounting portion. 
     As shown in  FIG. 9 , a pair of right and left brackets  27  are attached in a fore and aft posture to the lower surface of the suspending frame portion  6 D. The air-conditioning unit A enclosed in a unit case  24  is fixed by bolts to the right and left brackets  27 . 
     As shown in  FIG. 9 , an outer roof  13  and an inner roof  14  are arranged to surround the air-conditioning unit A. An ambient air feed opening  13 C is formed in the outer roof  13  forwardly of the air-conditioning unit A, and ambient air intake openings (not shown) are formed in eaves portions (not shown) of the outer roof  13  projecting laterally of the vehicle body for feeding ambient air to the ambient air feed opening  13 C. The inner roof  14  has a circulation opening  14 A opposed to the ambient air feed opening  13 C for drawing in air from the interior of the cab  1 . A switching valve  17  is disposed between the ambient air feed opening  13 C and circulation opening  14 A to act as a valve mechanism for opening and closing the ambient air feed opening  13 C and circulation opening  14 A. A switching may be made between a state of drawing ambient air through the ambient air intake opening  13 B into a space “a” formed between the inner roof  14  and outer roof  13 , and a state of shutting off ambient air and circulating the air in the cab interior through the space “a”. 
     Air taken into the space “a” is drawn into the sirocco fan  23  via a guide bore (not shown) formed in the upper surface of the unit case  24  of the air-conditioning unit A. After being conditioned by the evaporator  20  and the like, the air is delivered to the air-conditioning ducts  15 A and  15 B. 
     As shown in  FIG. 4 , the rear air-conditioning duct  15 A extends from opposite lateral ends of the evaporator  20  as described hereinbefore, and lateral air-conditioning ducts  15 B extend forward from opposite lateral ends of the rear air-conditioning duct  15 A for blowing off conditioning air into the cab as in the second embodiment. 
     As shown in  FIG. 9 , the rear window  5  is supported by the undersurface of a portion of the inner roof  14  projecting rearwardly of the vertical frames  2 . The rear window  5  does not protrude a large extent rearward, thereby to avoid interference with a linkage mechanism and the like supporting a tilling implement, though these components are not shown in the drawings. 
     Fourth Embodiment 
     Next, a fourth embodiment will be described, in which, as shown in  FIG. 10 , the air-conditioning unit A is mounted further rearwardly of the rear frame portion  6 B acting as the transverse frame. 
     The construction of the structural framework B for supporting the air-conditioning unit A will be described. As shown in  FIGS. 10 and 11 , right and left vertical frames  2  are erected at connecting bend portions between fore and aft frame portions  6 A and rear frame portion  6 B of the annular upper frame  6 , to serve also as window frames of the rear side windows  4 . 
     As shown in  FIG. 11 , a pair of right and left brackets  27  are attached in a fore and aft posture to the lower surface of the rear frame portion  6 B. The air-conditioning unit A enclosed in the unit case  24  is fixed by bolts to the right and left brackets  27 . 
     As shown in  FIG. 11 , a rear cover  28  is attached to the rear frame portion  6 B to surround the air-conditioning unit A attached to the rear frame portion  6 B. The outer roof  13  is supported by the rear frame portion  6 B, and the inner roof  14  is supported by the rear cover  28 . 
     An ambient air feed opening  13 C is formed in the outer roof  13 , and ambient air intake openings (not shown) are formed in eaves portions (not shown) of the outer roof  13  projecting laterally of the vehicle body for feeding ambient air to the ambient air feed opening  13 C. The inner roof  14  has a circulation opening  14 A opposed to the ambient air feed opening  13 C for drawing in air from the interior of the cab  1 . A switching valve  17  is disposed between the ambient air feed opening  13 C and circulation opening  14 A to act as a valve mechanism for opening and closing the ambient air feed opening  13 C and circulation opening  14 A. The switching valve  17  switches between a state of drawing ambient air introduced through the ambient air intake opening  13 B, via a space between the inner roof  14  and outer roof  28 , into an inner space “a” of the rear cover  28 , and a state of shutting off ambient air and circulating the air in the cab interior through the inner space “a”. Reference “b” in the drawing denotes an ambient intake guide, and  14   c  denotes an interior air intake guide. 
     Air taken into the space “a” is drawn into the sirocco fan  23  via a guide bore  24   a  formed in the upper surface of the unit case  24  of the air-conditioning unit A. After being conditioned by the evaporator  20  and the like, the air is delivered to the air-conditioning ducts  15 A and  15 B. 
     As shown in  FIG. 4 , the rear air-conditioning duct  15 A is disposed forwardly of the evaporator  20 , and lateral air-conditioning ducts  15 B extend forward from opposite lateral ends of the rear air-conditioning duct  15 A for blowing off conditioning air into the cab as in the first to third embodiments. 
     The rear window  5  is supported by an undersurface of a connection between the inner roof  14  and rear cover  28 . The rear window  5  does not protrude a large extent rearward, thereby to avoid interference with a linkage mechanism and the like supporting a tilling implement, though these components are not shown in the drawings. 
     Other Embodiments 
     The following modified constructions should be understood as applicable to the first to fourth embodiments described hereinbefore. 
     (1) A modified construction of the air-conditioning duct  15  will be described. A construction in which ducts  15  are arranged in the cab  1  and in a transversely middle position of the roof  7  will be described here. As shown in  FIG. 12 , an evaporator  20  and a sirocco fan  23  are surrounded by a unit case  24 . A rear air-conditioning duct  15 A continuous with the unit case  24  extends transversely for guiding conditioned air from the air-conditioning unit A, from opposite lateral ends of the evaporator  20  to the right and left sides. A central air-conditioning duct  15 E acting as a main air-conditioning duct extends forward from a transversely middle portion of the rear air-conditioning duct  15 A for guiding the conditioned air forwardly of the vehicle body. 
     As shown in  FIG. 12 , the central air-conditioning duct  15 E include right and left intermediate branch air-conditioning ducts  15 F acting as branch air-conditioning ducts extending right and left from intermediate positions in the fore and aft direction, and front air-conditioning ducts  15 G extending to full extents right and left from positions forwardly of the intermediate branch air-conditioning ducts  15 F. Each of the right and left intermediate branch air-conditioning ducts  15 F has blow-off openings  15   f  formed therein. The blow-off openings  15   f  are located to blow off an appropriate quantity of cool air to near the driver&#39;s face. On the other hand, the front air-conditioning ducts  15 G have front blow-off openings  15   a  formed therein for blowing off conditioning air forward and downward toward the windshield  25  of the cab  1 , and blow-off openings  15   d  formed rearwardly of the front blow-off openings  15   a  for blowing off defrost air toward the door glass panes. 
     As shown in  FIG. 12 , branch ducts  15 C extend rearward from opposite lateral ends of the rear air-conditioning duct  15 A, and have blow-off openings  15   c  formed therein for blowing conditioning air to the rear side windows  4  and rear window  5 . 
     (2) A different modified construction of the air-conditioning duct  15  will be described. In this construction, the duct  15  is arranged in the cab  1  to cover the entire surface of the roof  7 . As shown in  FIGS. 13 and 14 , an evaporator  20  and a sirocco fan  23  are surrounded by a unit case  24 . A full surface air-conditioning duct  15 H continuous with the unit case  24  extends forward from opposite lateral ends of the evaporator  20  for guiding conditioned air forward from the air-conditioning unit A. 
     As shown in  FIG. 13 , the full surface air-conditioning duct  15 H has blow-off openings  15   f  formed in intermediate positions in the fore and aft direction. The blow-off openings  15   f  are located to blow off an appropriate quantity of cool air rearward to near the driver&#39;s face. On the other hand, blow-off openings  15   a  are formed in the cab  1  for blowing off conditioning air forward and downward toward the windshield  25  of the cab  1 . Blow-off openings  15   d  are formed rearwardly of the front blow-off openings  15   a  for blowing off defrost air toward the door glass panes. 
     As shown in  FIG. 13 , the full surface air-conditioning duct  15 H has blow-off openings  15   b  formed therein for blowing conditioning air to the rear side windows  4  and rear window  5 . The air-conditioning duct  15  covering substantially the entire surface as described above has an advantage of allowing the blow-off openings to be formed in desired positions. 
     As a structure for introduces external air into the full surface duct  15 H having such construction, as shown in  FIGS. 13 and 14 , ambient air feed openings  13 B are formed in eaves portion  13 E of the outer roof  13  projecting laterally of the vehicle body. 
     (3) Although not shown, bellows-like connectors may be provided in the connections between the right and left air-conditioning ducts  15 B and  15 B and rear air-conditioning duct  15 A. Then, the connecting state is stabilized by the elasticity of the duct itself and by absorbing manufacturing errors, for example. 
     (4) As shown in  FIG. 13 , a hose  26  extends from the unit case  24  to discharge dew water from the evaporator  20 . The hose  26  extends out of the vehicle body through the interior of the vertical frame  2  present adjacent the unit case  24 . 
     (5) A mode of using the upper frame  6  as air-conditioning ducts  15  will be described next. As shown in  FIG. 15 , an ambient air intake opening (not shown) is formed in a rearward eaves portion (not shown) of the outer roof  13 . Air is taken in from a communicating path “b” of the outer roof  13  into a space “a” formed with the inner roof  14 , and introduced through a guide bore  24   a  into the air-conditioning unit A. As shown in  FIG. 15 , ambient air and interior air introduced are sent out of an exit  24 A of the unit case  24  after being adjusted by the air-conditioning unit A. The exit  24 A communicates with the interior space of the upper frame  6 , so that the fore and aft frame portions  6 A of the upper frame  6  serve as the air-conditioning ducts  15 . 
     Thus, as shown in  FIG. 15 , air blow-off openings  6   a  of conditioned air are formed in inner surfaces of the fore and aft frame portions  6 A. Since the upper frame  6  is used also as air-conditioning ducts, there is no need to provide air-conditioning ducts separately. 
     The mode of supporting the air-conditioning unit A is the same as in the first embodiment. 
     (6) The following framework construction may be adopted for the cab  1 . As shown in  FIG. 16  (A), (B), right and left front struts  2 , supporting the windshield  25 , of the structural framework B project above the right and left, fore and aft frame portions  6 A of the upper frame  6 , and an upper front frame portion  6 E extending transversely and connecting upper ends of the front struts  2  is installed above the right and left, fore and aft frame portions  6 A. Since these components are located above the right and left, fore and aft frame portions  6 A, the windshield  25  may be located in a correspondingly elevated position, to provide an excellent, enlarged field of view for the driver. 
     As shown in  FIG. 17  (A), (B), right and left front struts  2  are curved so that upper end regions  2 A are located further rearward than lower regions of the front struts  2 . An upper front frame portion  6 E is placed to extend between the upper ends of the front struts  2 . The upper front frame portion  6 E and the right and left, fore and aft frame portions  6 A are set to the same height. 
     With this construction, the upper front frame portion  6 E can be located further rearward than the lower regions of the front struts  2 . The driver can look up with an enlarged field of view, to be able to see an increased height. 
     (7) The outer roof  13  may have eaves portions projecting laterally or fore and aft from the upper frame  6 , to prevent direct rays entering the cab having large glass surfaces. 
     (8) The foregoing embodiments have been described as applying this invention to the agricultural tractor. The invention may be applied to other agricultural machines such as a combine or to construction equipment. 
     (9) A lateral air-conditioning duct  15 B may be provided for only one of the right and left sides. 
     (10) The ambient air intake opening  13 B may be provided only to one of the eaves portions  13 E. Especially when it is provided on the left side (i.e. the side the operator often gets in and out of the cabin) of the roof ( 7 ), the filter in the ambient air intake opening  13 B may more easily be accessed for checking and maintenance. Also, since the fan  23  is located on the right hand area of the roof  7 , the air flow speed can be increased due to funneling effect since the opening  13 B is located at a distance from the fan  23 , leading to an increased efficiency of the fan  23 .