Abstract:
There is provided a cab structure that a joint portion of a cab and a chassis frame has sufficient shear strength and which can disperse external force to the entire cab or chassis frame to reduce the burden of load and can sufficiently resist the impact load in the longitudinal direction. 
     A front end portion of a cab-under-frame fixed to the outer surface of the floor panel is extended toward a front upper side, and a cab mount bracket is also extended toward a front upper side so that they are integrally joined with a front mounting rail. As a result, these three components are firmly fastened to disperse the incoming force in the longitudinal direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a joint structure of a cab mounting portion for joining a cab of a forward control vehicle to a chassis frame. 
     2. Description of the Related Art 
     As a cab structure of a forward control vehicle, one shown in FIG. 13 is generally adopted. A cab  504  is surrounded by front pillars  509  provided on both right and left sides of a front portion, a front mounting rail  506  provided on an outer surface of the front lower portion, a roof panel  511 , a rear panel  512 , a side panel  513  and others, and a floor panel  507  is provided on a floor face. Further, cab-under-frames  508  are fixed to the outer surface of the floor panel  507 . The cab of the forward control vehicle is coupled to a cab mount bracket which is rotatably provided on a chassis frame in a cab mounting portion. 
     FIGS. 14 and 15 show an example of the structure of a joint portion for the cab and the chassis frame in the prior art. A cab mount bracket  501  b has a shape allowing contact with a lower surface or a side surface of the cab-under-frame  508  and a rotation center hole  514  for tilt of the cab  504  is formed thereto. Further, as shown in the drawings, the cab-under-frame  508  is fixed to an outer surface of the floor panel  507 , and a front end portion of the cab-under-frame  508  is coupled to the front mounting rail  506  side. 
     In the above-described structure of the joint portion for the cab and the chassis frame, the cab  504  is supported by fastening the cab-under-frame  508  to the cab mount bracket  501   b  fixed to the chassis frame, and it is configured so as to sufficiently resist vertical external force applied from a road surface side during normal running. However, when a vehicle clashed head-on or bumped from behind, an impact load larger than that obtained during normal running acts in the longitudinal direction. Thus, in the structure of the conventional joint portion for the cab and the chassis frame, since the cab-under-frame  508  and the cab mount bracket  501   b  are fastened mainly in the vertical direction there is a possibility that the structure can not sufficiently resist the impact load in the longitudinal direction. 
     On the other hand, as an example of a well-known technique concerning the periphery of the cab mounting member, there are Japanese Utility Model Applications Laid-open Nos. 116277/1981 and 171653/1986. “The floor structure of a tilt cab” in Japanese Utility Model Application Laid-open No. 116277/1981 is a floor constituent member of a tilt cab, in which a front end of a main sill is flange-coupled to a convex shoulder surface of a front cross member constituting the convex shoulder surface on a rear surface side, and a front end of a cab hinge bracket fixed to the main sill is fixed to the convex shoulder surface. In the case of this well-known technique, the rigidity of the coupling portion is insufficient and the coupling rigidity of the cab hinge bracket relative to the main sill is insufficient because the cab hinge bracket is coupled to the convex shoulder surface on the rear surface of the front cross member having the front-open-section. Therefore, the strength against the external force in the longitudinal direction may be possibly insufficient. On the other hand, in “the cab structure of an automobile” disclosed in Japanese Utility Model Application Laid-open No. 171653/1986, a grill bracket is attached to a front surface of a floor frame which supports a outer surface of a floor panel and to which a cab mounting bracket is fixed, and the grill bracket is fixed to the front grill so that the front grill can function as a strength member. However, this structure cannot sufficiently resist the impact load in the longitudinal direction. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, it is an object of the present invention to provide a cab structure that a joint portion for a cab and a chassis frame has the sufficient shear strength and which can disperse external force across the cab or the chassis frame to reduce the burden of load and which can sufficiently resist an impact load in the longitudinal direction. 
     To achieve this aim, there is provided a cab mounting portion structure in which a “inside surface portion of a front mounting rail” provided on a cab front lower side is coupled to a “front end portion upwardly extending a cab-under-frame” fixed to a floor outer surface, a cab mount bracket is also extended upwardly to be coupled to a vehicle front outer portion of the coupling portion, and these three members are integrally fixed to improve the joint strength. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view vertical to a horizontal plane, showing main members of a joint portion  5  for a cab and a chassis frame in an embodiment according to the present invention; 
     FIG. 2 is a perspective view of a cab mount bracket  1 ; 
     FIG. 3 is a cross sectional view vertical to a horizontal plane, showing that a cab-under-frame  8  and the cab mount bracket  1  in FIG. 1 are fastened to constitute the joint portion  5  for the cab and the chassis frame; 
     FIGS. 4 and 4B are cross sectional views taken along the line A—A and the line B—B in FIG. 3; 
     FIG. 5 is a perspective view showing the component relationship between front pillars  9 , a front mounting rail  6  and the cab-under-frame  8 ; 
     FIG. 6 is a perspective view showing the state in which an upward portion  8 a at an end of the cab-under-frame  8  is engaged with a cab mount bracket  1 ; 
     FIG. 7 is an enlarged perspective view of the cab mount bracket  1  depicted in FIG. 6; 
     FIG. 8 is a perspective view showing the state in which constituent members of the joint portion  5  for the cab and the chassis frame are assembled as a whole; 
     FIG. 9 is a longitudinal cross section view vertical to a horizontal plane, showing main members of the joint portion  5   a  for the cab and the chassis frame in another embodiment according to the present invention; 
     FIG. 10 is a longitudinal cross section view vertical to a horizontal plane, showing that the cab-under-frame  8  and the cab mount bracket  1   a  in FIG. 9 are fastened to constitute the joint portion  5   a  for the cab and the chassis frame; 
     FIG. 11 is a perspective view showing the state in which the upward portion  8   b  at an end of the cab-under-frame  8  is engaged with the cab mount bracket  1   a;    
     FIG. 12 is a perspective view showing the state in which constituent members of the joint portion  5   a  for the cab and the chassis frame are assembled as a whole; 
     FIG. 13 is a perspective view showing a cab structure of a general forward control vehicle; 
     FIG. 14 shows an example of the structure of a joint portion for a cab and a chassis frame in a prior art; and 
     FIG. 15 shows the example of the structure of the joint portion for the cab and the chassis frame in the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  8  show an embodiment of the present invention. FIG. 1 is a longitudinal cross section view vertical to a horizontal plane, showing main members of a joint portion  5  for a cab and a chassis frame. As shown in  5 FIG. 1, a front mounting rail  6  having a hat-like cross section is provided on the front lower side of a cab  4  (FIG.  5 ). A front end  7   a  of a floor panel  7  forming a floor face of the cab  4  uprises to close an opening portion of the front mounting rail  6  and is fixed. On the other hand, a cab-under-frame  8  is brought into contact with the outer surface of the floor panel  7  to be fixed, and an upward portion  8   a  which extends toward the front upper portion of the cab is formed to the front end of the cab-under-frame  8  and fixed to a front vertical surface  18  of the front mounting rail  6 . FIG. 5 is a perspective view showing the component relationship between front pillars  9 , the front mounting rail  6  and the cab-under-frame  8 . 
     A cab mounting bracket  1  configuring one of constituent parts of the joint portion  5  for the cab and the chassis frame is made up of a bracket bend  2  and a bracket plate  3 . FIG. 2 is a perspective view of the cab mount bracket  1 , and FIG. 3 is a longitudinal cross section view vertical to a horizontal plane showing that the cab-under-frame  8  and the cab mount bracket  1  in FIG. 1 are fastened to constitute the joint portion  5  for the cab and the chassis frame. FIG. 4A is a cross sectional view taken along the line A—A in FIG. 3, and FIG. 4B is a cross sectional view taken along the line B—B in FIG.  3 . As shown in FIG. 2, the racket bend  2  is composed of an upper surface portion  15  which has a substantially-C-like cross section and forms a profile matching with a curved surface of an outer surface of the cab-under-frame  8 , and a profile portion  16  which forms a largest cross section at a substantially central part by curving the substantially-C-like cross section from the front end toward the rear end. A flat portion  17  is formed on the front end side of the upper surface portion  15 , and this flat portion  17  comes into contact with the front vertical surface  18  of the front mounting rail  6  as shown in FIG.  3 . The flat portion  17  and the vicinity thereof form together with a part of the profile portion  16  an upward portion  100  which extends toward the front upper part of the cab along the cab-under-frame  8 . 
     On the other hand, the bracket plate  3  is formed by a tabular member as shown in FIGS. 1,  2  and  3 . In this example, the bracket plate  3  is fixed to each of the both side surfaces of the bracket bend  2  in the state that a curved profile portion  20  is substantially matched with the profile portion  16  of the bracket bend  2 . In this state, a curved portion  19  of the bracket plate  3  is formed so as to largely protrude from the upper surface portion  15  of the bracket bend  2 . This protruding portion is fixed on the side surface of the cab-under-frame  8  by spot welding or arc welding. As shown in FIGS. 1,  2  and  3 , a tilt shaft hole  14  is provided to the cab mount bracket  1 , and this hole serves as a bearing portion engaged with a tilt shaft for tilting the cab  4  and simultaneously bearing the load applied to the cab  4 . FIG. 6 is a perspective view showing the state in which the upward portion  8 a at the end of the cab-under-frame  8  is engaged with the cab mount bracket  1 , and FIG. 7 is an enlarged perspective view showing the cab mount bracket  1  illustrated in FIG.  6 . FIG. 8 is a perspective view showing that constituent parts of the joint portion  5  for the cab and the chassis frame are assembled as a whole. The upward portion  100  of the cab mount bracket  1  is exposed on the outer surface of the front mounting rail  6 . 
     The bracket bend  2  is provided in such a manner that the upper surface portion  15  is brought into contact with the outer surface of the cab-under-frame  8  and the flat portion  17  on the front end side thereof is brought into contact with the front surface  18  of the front mounting rail  6 . The bracket bend  2  is coupled and fixed to these portions by mechanical fastening using a bolt  21  and a nut  22  (FIGS. 1,  3  and  4 ) or spot welding or arc welding. In this state, the bracket plate  3  is fixed on each of the both side surfaces of the cab-under-frame  8  by spot welding or arc welding as illustrated by a welding portion  10  in FIG.  4 B. As described above, the cab mount bracket  1  is stiffly coupled to the front mounting rail  6  and the cab-under-frame  8 , and the entire rigidity of the periphery of these members becomes much higher than that of the prior art structure. 
     On the other hand, as shown in FIG. 8, the front mounting rail  6  to which the cab-under-frame  8  or the cab mount bracket  1  according to the present invention is fixed is coupled with the front pillars  9  and  9  at the both ends thereof. Therefore, when external force acts on the cab  4  having the above-described structure in the longitudinal direction, a part of this external force acts on the front surface of the front mounting rail  6 . However, the periphery of the front mounting rail  6  is formed so as to have the high rigidity as described above, and the surrounding constituent parts accepts the external force as a whole. Therefore, shear force and the like applied to the individual constituent parts can be greatly reduced. Further, the external force which has acted on the front mounting rail  6  side is transmitted to the entire cab  4  through the front pillars  9  and  9 , and the external force is dispersed. Thus, the influence of the external force can be greatly reduced, and it is possible to sufficiently resist the large impact load. 
     FIGS. 9 to  12  show another embodiment according to the present invention. FIG. 9 is a longitudinal cross section view vertical to a horizontal plane, showing main members of the joint portion  5   a  for the cab and the chassis frame. FIG. 10 is a longitudinal cross section view vertical to a horizontal plane, showing that the cab-under-frame  8  and the cab mount bracket  1   a  depicted in FIG. 9 are fastened to constitute the joint portion  5   a  for the cab and the chassis frame. The structure of the cab mount bracket  1   a , the bracket bend  2   a  and the bracket plate  3   a  has the structural influence which is similar to that of the cab mount bracket  1  and others in the above-described embodiment. In the above-mentioned embodiment, the upward portion  100  of the cab mount bracket  1  is coupled by bringing the flat portion  17  of the bracket bend  2  into contact with the front vertical surface  18  of the front mounting rail  6 . However, in the present embodiment, as shown in FIGS. 9 and 10, the upward portion  100   a  of the cab mount bracket  1   a  is inserted into the inner side of the front mounting rail  6 , and the flat portion  17   a  is brought into contact with and fixed to the front end  7   a  of the floor panel  7 . The front end portion of the cab-under-frame  8  constitutes the upward portion  8   b  and does not extend to a position at which it is directly joined with the front mounting rail  6 . However, when the upward portion  8   b  is abut on the cab mount bracket  1   a  to be fastened and it is then fixed with the cab mount bracket  1   a  through the bracket plate  3   a  by welding and the like, the high strength of the joint portion  5   a  for the cab and the chassis frame can be assured. 
     FIG. 11 shows the state where the upward portion  8   b  at the end of the cab-under-frame  8  is engaged with the cab mount bracket  1   a . FIG. 12 is a perspective view in which the constituent parts of the joint portion  5   a  for the cab and the chassis frame are assembled as a whole. The front end portion of the cab mount bracket  1   a  is hidden inside without being exposed on the outer surface of the front mounting rail  6 . 
     When the external force in the longitudinal direction acts on the cab  4  having the above-described structure, this external force partially acts on the front surface of the floor panel  7 . However, the floor panel  7  is reinforced by the front mounting rail  6  to be formed with the high rigidity, and the entire surrounding constituent members accept the external force. Therefore, as similar to the above-described embodiment, the shear force and the like applied to the individual constituent elements is dispersed and greatly reduced. Further, the external force which has acted from the floor panel  7  through the front mounting rail  6  is transmitted to the entire cab  4  through the front pillars  9  and  9 . Therefore, the entire vehicle bears the external force, and the influence of the external force can be greatly reduced to sufficiently resist the large impact load. 
     The rigidity of the joint portion for the cab and the chassis frame can be greatly improved, and the external force in the longitudinal direction can be entirely transmitted to the cab and the chassis frame. Further, the influence of the external force can be largely reduced, and it is possible to sufficiently resist the impact load. Moreover, displacement of the cab can be reduced, and an accommodation space can be assured.