Abstract:
An industrial vehicle has a frame and an axle swingalbly connected with the frame, wherein a cylinder interposed between the frame and the axle selectively extends and retracts so as to absorb a swinging motion of the axle. The cylinder is coupled to the frame and the axle in a rotatable manner within a plane intersecting an axis of a center about which the axle swings.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a structure for supporting cylinders, which are employed in vehicles such as forkifts and arranged between axles and body frames to restrict the movement of the axles. 
     Forklifts having rear axles that are supported pivotally with respect to its body frame to permit tilting, or roll, of the forklift are known in the prior art (e.g., Japanese Unexamined Patent Publication No. 58-183307). In such a forklift, a hydralic cylinder is arranged between the body frame and the axle to restrict the pivoting of the axle with respect to the body frame. The hydraulic cylinder locks the axle and restricts tilting of the forklift to maintain stability. For example, the tilting of the forklift is restricted when the forklift carries heavy loads, holds loads at high positions, or turns to change directions at high traveling speeds. 
     The hydraulic cylinder may be connected to the body frame and to the rear axle. In such case, a bracket having a connecting shaft, which extends in the longitudinal direction of the forklift (the direction of the roll axis), is fixed to the body frame. The hydraulic cylinder has a cylindrical housing. One end of the housing is secured to an anchor. The anchor is pivotally connected to the connecting shaft by means of a bearing such that the hydraulic cylinder is pivotal with respect to the body frame about the connecting shaft. A piston rod extending from the other end of the housing is connected to the rear axle such that the piston rod is pivotal. That is, like the housing of the hydraulic cylinder, the piston is pivotal about an axis that extends in the longitudinal direction of the forklift. Accordingly, the hydraulic cylinder is pivoted relative to the body frame and the rear axle, a pair of axes that extend in the direction of the roll axis. 
     The rear axle is assembled as a unit, or an assembly, before being connected to the body frame. The dimensional tolerances allowed for the components constituting the rear axle assembly may offset the position of the rear axle relative to the body frame from the ideal location in the longitudinal direction of the forklift. Furthermore, parts connecting the rear axle to the body frame may become loose during use of the forklift. This may also offset the relative position of the rear axle and the body frame. Such conditions would apply excessive force on the connecting shaft, the anchor, the bracket, and other parts of the hydraulic cylinder. 
     These problems may be solved by a structure such as that shown in FIG.  5 . In a similar manner to the structure of the Japanese publication, a bracket  70  fixed to a body frame  75  has two support plates  72  to support a connecting shaft  71 . A hydraulic cylinder  77  secured to a rear axle  76  is connected to the connecting shaft  71  with a bearing  74 . The structure of FIG. 5 differs from the structure of the Japanese publication in that the distance between the support plates  72  is longer and that the connecting shaft  71  is longer than the diameter of the anchor  73 . This permits the anchor  73  to move in the axial direction of the connecting shaft  71 , or longitudinal direction of the vehicle. Thus, if the position of the rear axle  71  relative to the body frame  75  is offset longitudinally from the ideal location, the movement of the anchor  73  with respect to the connecting shaft  71  compensates for the offset distance. This prevents excessive force from acting on the bracket  70 , the anchor  73 , and other parts, while permitting the hydraulic cylinder  77  to pivot about a pair of longitudinally extending axes. 
     In the structure of FIG. 5, the hydraulic cylinder  77  is moved with its anchor  73  connected to the long connecting shaft  71 . Thus, when the rear axle  76  is pivoted with respect to the body frame  75 , a bending force is applied to the connecting shaft  71  by the anchor  73 . The bending force may deform the connecting shaft  71 . Therefore, the dimensions of the connecting shaft  71  and the bracket  70  must be enlarged to withstand the bending force. This increases the space required by the bracket  70 . 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide a cylinder supporting structure that prevents the application of excessive force on parts used to support the cylinder without enlarging the dimensions of the supporting structure. 
     To achieve the above objective, the present invention provides an industrial vehicle having a frame and an axle swingably connected with the frame. The vehicle includes a center shaft of the swinging motion of the axle. The center shaft has an axis. The frame is connected with the axle by the center shaft. The axle swings about the center shaft. A cylinder is interposed between the frame and the axle. The cylinder is arranged to selectively extend and retract so as to absorb the swinging motion of the axle. A coupling device couples the cylinder with the frame and the axle. The cylinder is rotatable within a plane intersecting the axis of the central shaft. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a schematic side view, partially in cross-section, showing a cylinder supporting structure according to the present invention, as seen in a direction normal to the longitudinal direction of the vehicle; 
     FIG. 2 is a diagrammatic rear view showing the body frame and the rear axle of FIG. 1; 
     FIG. 3 is a rear view, partially in cross-section, showing the hydraulic cylinder of FIG. 1, as seen in the direction of the longitudinal axis of the vehicle; 
     FIG. 4 is a schematic rear view, partially in cross-section, showing a further embodiment of a cylinder supporting structure according to the present invention; and 
     FIG. 5 is a schematic side view, partially in cross-section, showing a prior art cylinder supporting structure, as seen in a direction normal to the longitudinal direction of the vehicle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A cylinder supporting structure according to the present invention will now be described with reference to FIGS. 1 to  3 . The supporting structure is employed in industrial vehicles such as a forklift. 
     FIG. 2 is a schematic view showing the rear view of a forklift. As shown in the drawing, the forklift has a body frame  1 . A rear axle  2  is arranged at the rear lower section of the forklift. The rear axle  2  is supported such that it is pivotal about a center pin  3  in the roll direction of the forklift. In other words, the rear axle  2  moves relatively to the body frame  1  in a plane extending normal to the longitudinal axis of the vehicle. An elastic member  4  for dampening the impact produced by the pivoting of the rear axle  2  is provided between the body frame  1  and the rear axle  2 . Wheels  5 , which are steered to change the direction of the forklift, are mounted on each end of the rear axle  2 . 
     A multiple action type hydraulic cylinder  6  is arranged between the body frame  1  and the rear axle  2 . As shown in FIG. 3, the cylinder  6  includes a housing  7 , which accommodates a piston  8 . The piston  8  defines a lower chamber Ri and an upper chamber R 2  in the housing  7 . A piston rod  9  is fixed to the piston  8 . As shown in FIG. 1, the piston rod  9  is connected to a bracket  10 , which is fixed to the rear axle  2 . An end piece  11  is provided at the upper end of the housing  7 . The end piece  11  is connected to a bracket  12 , which is fixed to the body frame  1 . 
     As shown in FIG. 2, the lower chamber R 1  is connected to an electromagnetic control valve  14  through a passage  13   a,  while the upper chamber R 2  is connected to the control valve  14  through a passage  13   b.  The control valve  14  is further connected to an accumulator  15 . The control valve  14  is normally closed. Therefore, when the control valve  14  is de-excited, the control valve  14  is shifted to a disconnected position  14   a.  At the disconnected position  14   a,  movement of hydraulic oil between the lower and upper chambers R 1 , R 2  is prohibited. The control valve  14  is shifted to a connected position  14   b  when excited. At the connected position  14   b,  hydraulic oil is permitted to move between the lower and upper chambers R 1 , R 2 . 
     A controller  16  is electrically connected to the control valve  14 . When the forklift engine (not shown) is running, the controller  16  continuously excites the control valve  14 . However, if certain conditions are satisfied, the controller  16  de-excites the control valve  14 . 
     As shown in FIG. 1, the bracket  12  fixed to the body frame  1  has two support plates  18 ,  19 . An upper connecting shaft  20  extending parallel to the longitudinal axis (the roll axis) of the forklift is supported by the two support plates  18 ,  19 . A threaded portion  20   a  is defined on one end of the connecting shaft  20 . A nut  23  is engaged with the threaded portion  20   a  to fasten the connecting shaft  20  to the bracket  12 . A washer  22  is held between the support plate  18  and the nut  23 . Another washer  21  is held between the support plate  19  and the connecting shaft  20 . 
     Two identical collars  24  are fitted to the connecting shaft  20  between the support plates  18 ,  19 . Each collar  24  has a large diameter portion  25  and a small diameter portion  26 . Each large diameter portion  25  is located on the outer side of the collar  24  adjacent to the associated support plate  18 ,  19 . A spacer  27  is fitted on each large diameter portion  25 . Each spacer  27  contacts the inner wall of the associated support plate  18 ,  19 . 
     A male bushing  28  is fitted on the small diameter portions  26  of the two collars  24 . That is, the male bushing  28  is held between the large diameter portion  25  of the collars  24  and between the support plates  18 ,  19 . The male bushing  28  has a convex surface  28   a  and is made of a sintered metal, in which lubricating oil is impregnated. 
     An upper anchor  17  is defined at the upper portion of the end piece  11 . The upper anchor  17  has a bore  29  through which the connecting shaft  20  is inserted. A large diameter portion  30  and a small diameter portion  31  are defined in the support bore  29 . A female bushing  32  is fitted in the large diameter portion  30  and abuts against the wall, or step, formed between the large and small diameter portions  30 ,  31 . The abutment of the female bushing  32  against the wall determines the position of the female bushing  32 . In the same manner as the male bushing  28 , the female bushing  32  is made of a sintered metal, in which lubricating oil is impregnated, and has a concave surface  32   a.  The concave surface  32   a  slides against the convex surface  28   a  of the male bushing  28 . 
     The end piece  11  is connected to the connecting shaft:  20  by engaging the male bushing  28  with the female bushing  32  such that the convex surface  28   a  comes into spherical surface contact with the concave surface  32   a.  The engagement between the male and female bushings  28 ,  32  permits the upper anchor  17  to pivot relative to the connecting shaft  20  when the end piece  11  and the bracket  12  are connected to each other. In other words, the angle defined between the axis of the bore  29  and the axis of the connecting shaft  20  can be changed arbitrarily in accordance with the pivoting of the hydraulic cylinder  6 . The male and female bushings  28 ,  32  are commercially available and sold in sets. Furthermore, the male and female bushings  28 ,  32  define a universal joint. 
     The bracket  10  fixed to the rear axle  2  also has two support plates  34 ,  35 . A lower connecting shaft  36  extending parallel to the longitudinal axis of the forklift is supported by the support plates  34 ,  35 . A bearing portion  37  is defined at the axially middle part of the connecting shaft  36 . The bearing portion  37  has a curved surface  37   a.  A flange  38  extends radially and integrally from one end of the connecting shaft  36 . A bolt  39  fastens the connecting shaft  36  to the bracket  10  with the flange  38  engaged with the support plate  35 . The other end of the connecting shaft  36  projects from the support plate  34 . A cotter pin  48  is inserted radially through the connecting shaft  36  to keep the connecting shaft  36  held in the bracket  10 . 
     A spacer  40  is fitted on the connecting shaft  36  at each side of the bearing portion  37 . Each spacer  40  contacts the inner wall of the associated support plate  34 ,  35 . An oil conduit  41  extends through the connecting shaft  36  from its flanged end to the curved surface  37   a  of the bearing portion  37 . An oil supplying device (not shown) delivers lubricating oil to the oil conduit  41 . 
     A lower anchor  42  is defined on the end of the piston rod  9  projecting from the cylinder housing  7 . The lower anchor  42  includes a bore  43  through which the connecting shaft  36  is inserted. A small diameter portion  44  is defined at the axially middle section of the bore  43 , while a large diameter portion  45  is defined at each end of the bore  43 . A bearing sleeve  46  is fitted into the small diameter portion  44 . The inner wall of the bearing sleeve  46  defines a slide surface  46   a.    
     The lower anchor  42  is connected to the connecting shaft  36  by engaging the bearing portion  37  with the bearing sleeve  46  such that the curved surface  37   a  slides against the slide surface  46   a.  The engagement between the bearing portion  37  and the bearing sleeve  46  permits the lower anchor  42  to pivot relative to the lower connecting shaft  36 . In other words, the angle defined between the axis of the bore  43  and the axis of the lower connecting shaft  36  can be changed arbitrarily in accordance with the pivoting of the hydraulic cylinder  6 . A seal  47  is arranged in each large diameter portion  45  to seal the space formed between the curved surface  37   a  and the slide surface  46   a.  The seal  47  may be made of synthetic rubber. The connecting shaft  36  and the bearing sleeve  46  define a universal joint. 
     Accordingly, the hydraulic cylinder  6  is supported between the body frame  1  and the rear axle  2  by two universal joints such that the cylinder  6  is pivotal about each joint in a plane that intersects the roll axis of the vehicle. 
     As shown in FIG. 3, the housing  7  of the hydraulic cylinder  6  has a lower opening closed by a rod piece  50  and a higher opening closed by a head piece  51 . 
     A guide rod  52  is fixed to the upper end of the piston  8  in the housing  7 , as viewed in FIG.  3 . The cross-sectional area of the guide rod  52  is equal to that of the piston rod  9 . The piston rod  9  has an upper end that extends through the piston  8  and into the upper chamber R 2 . A threaded section  9 a is defined on this end. The other end of the piston rod  9  extends through the rod piece  50  and out of the housing  7 . The guide rod  52  has a lower end located in the upper chamber R 2 . A threaded bore  52   a  is defined in this end. The threaded bore  52   a  is fastened to the threaded section  9   a  of the piston rod  9 . Accordingly, the piston rod  9  and the guide rod  52  are fastened to each other with the piston  8  held in between. In the hydraulic cylinder  6 , the pressure-receiving area of the upper end of the piston  8  is equal to that of the lower end of the piston  8 . In other words, their axially projected areas are the same. Also, the cross-sectional areas of the chambers R 1 , R 2  are the same. 
     The head piece  51  has a support bore  51   a  to slidably accommodate the upper end of the guide rod  52 . The end piece  11  has a retaining bore  11   a  for retaining the upper end of the guide rod  52 . The guide rod  52  moves axially in the retaining bore  11   a.    
     When assembling the rear axle  2  to the body frame  1 , the machining tolerances allowed for each component and the assembling tolerances allowed for the assembled components may offset the position of the rear axle  2  relative to the body frame  1  from the desirable position in the longitudinal direction of the forklift, or in a direction parallel to the roll axis. In such case, if the hydraulic cylinder  6  is connected to the bracket  12  of the body frame  1  and to the bracket  10  of the rear axle  2 , the hydraulic cylinder  6  will be tilted in a vertical plane that is parallel to the roll axis as shown in FIG.  1 . That is, the upper and lower ends of the hydraulic cylinder  6  will be pivoted about horizontal axes that are normal to the roll axis. Furthermore, if the position of the rear axle  2  relative to the body frame  1  is offset from the ideal position in the lateral direction of the forklift, the hydraulic cylinder can also be tilted in a vertical plane, that is normal to the roll axis. 
     In there is lateral offset and if the rear axle  2  is pivoted relative to the body frame  1 , the lower anchor  42  pivots about the connecting shaft  36  as the slide surface  46   a  of the bearing sleeve  46  slides against the curved surface  37   a  of the bearing portion  37  while the axis of the bore  43  pivots relative to the axis of the connecting shaft  36 . Simultaneously, the end piece  11  is pivoted about the connecting shaft  20  as the convex surface  28   a  of the male bushing  28  slides against the concave surface  32   a  of the female bushing  32  while the axis of the bore  29  pivots relative to the axis of the connecting shaft  20 . 
     Accordingly, the pivoting of the rear axle  2  relative to the body frame  1  permits the brackets  10 ,  12  to pivot in two parallel planes, respectively, that are each perpendicular to the roll axis if the brackets  10 ,  12  are offset from each other in the direction parallel of the rolling axis. The piston rod  9  is projected from or retracted into the hydraulic cylinder  6  in accordance with the pivoting of the rear axle  2  relative to the body frame  1 . 
     Since the pressure-receiving area of the upper end of the piston  8  is equal to that of the lower end of the piston  8 , and the cross-sectional area of the upper chamber R 2  is the same as that of the lower chamber R 1 , the amount of hydraulic oil discharged from one of the chambers R 1  R 2  is equal to that sent into the other chamber R 1 , R 2  during actuation of the hydraulic cylinder  6 . Therefore, the piston  8  moves in the same manner whether the piston rod  9  projects out of or retracts into the hydraulic cylinder  6 . This permits smooth pivoting of the rear axle  2  relative to the body frame  1 . 
     When the controller  16  de-excites the electromagnetic control valve  14 , the control valve  14  is shifted from the connected position  14   b  to the disconnected position  14   a.  This prohibits the movement of hydraulic oil between the lower and upper chambers R 1 , R 2  in the hydraulic cylinder  6  and locks the hydraulic cylinder  6 . Accordingly, the hydraulic cylinder  6  prohibits pivoting of the rear axle  2  relative to the body frame  1 . 
     The preferred and illustrated embodiment of the cylinder supporting structure has the advantages described below. 
     (a) The rear axle  2  is pivotal relative to the body frame  1  in the roll direction of the forklift. The universal joints (the joints defined by the bushings  28 ,  32  and by the connecting shaft  36  and the bearing sleeve  46 ) further support the hydraulic cylinder  6  such that the cylinder  6  is permitted to pivot in a vertical plane intersecting the rolling axis. Accordingly, if the positions of the joint between the cylinder  6  and the body frame  1  and the joint between the cylinder  6  and the rear axle  2  are offset from the ideal location in the longitudinal direction of the forklift, the rear axle  2  is pivoted relative to the body frame  1  while the cylinder  6  pivoted in a plane that is parallel to the rolling axis. This structure prevents the application of excessive force to the brackets  10 ,  12 , the anchors  17 ,  42 , and other parts. 
     Furthermore, a mechanism for connecting the brackets  10 ,  12  with the associated anchors  17 ,  42  of the hydraulic cylinder  6  to permit relative movement therebetween in the longitudinal direction of the vehicle, like the vehicle of FIG. 5, becomes unnecessary. Thus, the brackets  10 ,  12  need not be enlarged to support such connecting mechanisms. 
     (b) The connecting shaft  20 , which extends in the longitudinal direction of the forklift, is supported by the body frame bracket  12  with the male bushing  28  fitted on the connecting shaft  20 . The female bushing  32  is fitted into the bore  29  of the upper anchor  17  such that the concave surface  32   a  of the female bushing  32  engages the convex surface  28   a  of the male bushing  28 . Thus, the upper anchor  17  of the hydraulic cylinder  6  is connected to the connecting shaft  20  of the bracket  12  such that the axis of the bore  29  is permitted to pivot to an arbitrary angle relative to the axis of the connecting shaft  20 . In this state, the bushings  28 ,  32  are in spherical surface contact with each other. Accordingly, the force produced when the rear axle  2  pivots relative to the body frame  1  is applied to the hydraulic cylinder  6  over a wide area. This enhances the durability of the bushings  28 ,  32 . Furthermore, the bushings  28 ,  32  are easily obtained since they are commercially available. 
     (c) The connecting shaft  36 , which extends in the longitudinal direction of the forklift, is supported by the rear axle bracket  10 . The lower anchor  42  of the hydraulic cylinder  6  is connected to the connecting shaft  36  with the cylindrical slide surface  46   a  of the bearing sleeve  46  engaged with the curved surface  37   a  defined on the bearing portion  37  of the connecting shaft  36 . Thus, the lower. anchor  42  is connected to the bracket  10  such that the axis of the bearing sleeve  46  is permitted to pivot to an arbitrary angle relative to the axis of the connecting shaft  36 . Accordingly, production costs are saved by supporting the hydraulic cylinder  6  with the connecting shaft  36  and the bearing sleeve  46 . 
     (d) In the hydraulic cylinder  6 , the pressure-receiving area of the upper end of the piston  8  is equal to that of the lower end of the piston  8 . Also, the cross-sectional area of the upper chamber R 2  is the same as that of the lower chamber R 1 . Accordingly, the amount of hydraulic oil discharged from one of the chambers R 1 , R 2  is equal to that sent into the other chamber R 1 , R 2  during actuation of the hydraulic cylinder  6 . Therefore, the hydraulic cylinder  6  operates smoothly and allows smooth pivoting of the rear axle  2 . 
     (e) The preferred embodiment according to the present invention is applied to the hydraulic cylinder  6  employed in a forklift that restricts the pivoting of the rear axle  2  relative to the body frame  1 . This structure prevents excessive force from being applied to the brackets  10 ,  12 , the anchors  17 ,  42 , and other parts. Furthermore, this cylinder supporting structure compensates for the offset distance of the rear axle  2  with respect to the body frame  1  in either the longitudinal or the lateral direction of the vehicle. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. 
     In the preferred and illustrated embodiment, the present invention is applied to a vehicle having only one cylinder for restricting the movement of the axle. However, there are vehicles that require two cylinders to restrict the movement of the axle. In such vehicles, the present invention may be applied to each cylinder. 
     The male bushing  28  having the convex surface  28   a  and the female bushing  32  having the concave surface  32   a  may be employed to connect the hydraulic cylinder  6  to the rear axle  2 . On the other hand, the connecting shaft  36  and the bearing sleeve  46  may be employed to connect the hydraulic cylinder  6  to the body frame  1 . In other words, the hydraulic cylinder may be inverted from the position illustrated. 
     The connecting shafts  20 ,  36  need not extend parallel to the longitudinal axis of the vehicle. For example, the connecting shafts  20 ,  36  may be inclined with respect to the longitudinal axis. This would also prevent the application of excessive force on parts used to support the cylinder  6 , while compensating for the offset distance of the rear axle  2  relative to the body frame  1  without increasing the amount of occupied space. 
     The male and female bushings  28 ,  32  need not be made of sintered metal. For example, the bushings  28 ,  32  may be made of a synthetic resin that has a self-lubricating property and superior wear resistance property. 
     An oil conduit may be formed extending through the connecting shaft  20  and the collars  24  to supply lubricating oil to the convex and concave surfaces  28   a,    32   a  of the bushings  28 ,  32 . 
     The electromagnetic control valve  14  may be normally opened. 
     As shown in FIG. 4, the hydraulic cylinder  6  may be connected to the body frame  1  or the rear axle  2  by employing a ball joint  55  having a spherical socket  53  and a joint  56  having a spherical surface  54 . The engagement of the spherical cavity  53  with the spherical surface  54  would permit the hydraulic cylinder to pivot in any direction. 
     The application of the present invention is not limited to forklifts. For example, the present invention may be applied to other types of industrial vehicles such as shovel loaders. 
     In addition to the hydraulic cylinder  6 , the present invention may be applied to other cylinders that dampen impacts. 
     The present invention may be applied to other types of cylinders used in industrial vehicles. For example, the present invention may be applied to suspending cylinders, vertical motion dampening cylinders, and vertical motion restricting cylinders. 
     The present invention may also be applied to cylinders operated by liquid pressure and gas pressure (e.g., pneumatic pressure) instead of hydraulic pressure. 
     The application of the present invention is not limited to industrial vehicles. For example, the present invention may also be applied to any type of industrial machinery that employs cylinders connected to two members that move relatively to each other. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.