Abstract:
A crawler vehicle comprises a body frame and an auger mounted to the body frame at a front portion thereof, the body frame being mounted to a rear portion of a crawler frame via a pivot shaft to allow the crawler frame carrying a crawler belt to swing vertically. The pivot shaft is located forwardly of a lower idle wheel rotatably mounted to the crawler frame. Positioning of the pivot shaft forwardly of the lower idle wheel allows the auger to move downward even when a front portion of the crawler belt is lifted. This causes the auger to move downward regardless of new snow or hard snow, enabling the auger to carry out snow-removing operation in a highly efficient manner.

Description:
REFERENCE TO RELATED APPLICATION 
     The application is a U.S. national stage application of copending International Application Serial No. PCT/JP01/01766 filed Mar. 7, 2001 and published in a non-English language. 
     TECHNICAL FIELD 
     This invention relates generally to a crawler vehicle and, more particularly, to an improvement in a snow-removing machine. 
     BACKGROUND OF THE INVENTION 
     A crawler vehicle having at its front portion a working member (snow-removing section) is disclosed in, for example, Japanese Patent Publication No. SHO-51-30378 entitled “Snow-Removing Machine”. This snow-removing machine comprises a body frame connected to a rear portion of a crawler frame, which has a front portion equipped with a driven wheel and a lower portion equipped with two guide wheels, through a pivot shaft for vertical swinging movement, a snow-removing section mounted at a front portion of the body frame and serving as a working member, an engine mounted on the body frame, a drive wheel mounted to a rear portion of the body frame, and a crawler belt trained around the drive wheel, the driven wheel and the guide wheels. 
     In addition, during traveling of the crawler vehicle with its snow-removing section held in an inoperative state, a jack is extended to allow the body frame to swing clockwise about the pivot shaft, lifting the snow-removing section to thereby prevent the snow-removing section from hitting an obstacle on the road surface. 
     FIGS. 6A and 6B hereof are schematic side elevational views showing operations of the aforementioned conventional snow-removing machine. More specifically, FIG. 6A shows that the snow-removing machine in snow removing operation, while FIG. 6B shows a state in which a jack  101  remains in an extended condition to allow a body frame  103  to swing clockwise about a pivot shaft  102  such that a snow-removing section  104  is lifted. 
     When the snow-removing section  104  is lifted, a drive wheel  105  moves downward as shown by arrow {circle around ( 1 )}. As a result, the distance M between the center of a driven wheel  106  and the center of the drive wheel  105  slightly varies such that the distance N between the center of the drive wheel  105  and the center of the rearmost guide wheel  107  decreases. As the distances M and N vary in such a manner, tension of a crawler belt  108  also varies. When the tension of the crawler belt  108  exceeds an excessive level, the crawler belt  108  encounters a breakdown. In contrast, when the tension of the crawler belt  108  is too small, the crawler belt  108  is apt to be dislocated from the drive wheel  105  or the driven wheel  106 . 
     Now, discussion will be made as to an operation of the snow-removing machine when it accidentally runs on hard snow during snow-removing operation with reference to FIGS. 7A to  7 C. 
     In FIG. 7A, the crawler belt  108  is held in close contact with road surface  100 , with the body frame  103  and an auger  104  located at the front portion of the crawler vehicle being held at a given height from the road surface  100  by the action of a pivot shaft  102  mounted at a rear portion of a crawler frame  109  located inside the crawler belt  108  and the jack  101  located forwardly of the pivot shaft  102 . Reference numeral  110  designates a sleigh which serves as a member for suitably maintaining the auger  104  at the given height from the road surface  100  or as a member for reducing weight and load of the auger  104  to be applied to the body frame  103 . A pentagon is formed by connecting the sleigh  110 , the auger drive shaft  112 , the pivot shaft  102 , the center of the guide wheel  107 , and the sleigh  110  (hereinafter referred to as a “pentagon X”). 
     It has been proposed to provide a snow-removing practice wherein, when an object to be removed is new snow, the auger  104  is intentionally lowered with a view to remove an increased amount of snow. In such a practice, the jack  101  is retracted to allow of the body frame  103  to rotate counterclockwise about the pivot shaft  102 , thereby lowering the auger  104 . 
     However, when the snow-removing machine accidentally comes across hard snow with the jack  101  held in the retracted state, the snow-removing machine encounters the following problems. In this event, the sleigh  110  runs on hard snow, causing the crawler belt  108  to be lifted up from the road surface  100  in the vicinity of the driven wheel  106 . That is, the crawler belt  108  is caused to rotate clockwise as a whole at an angle θ 1  about the pivot shaft  102 . In parallel with such a movement, the pentagon X shown in FIG. 7A varies in a manner as described below. 
     The center  107  a of the guide wheel  107  is caused to swing clockwise at the angle θ 1  about the pivot shaft  102 . Since, in this instance, the center  107   a  remains at a fixed height from the road surface  100 , the pivot shaft  102  is lowered. Since, in this event, the sleight  110  and the body frame  103  form a common rigid structure to which the auger shaft  112  and the pivot shaft  102  are interconnected, the line segment connected between the sleigh  110  and the auger shaft  112  and the line segment connected between the auger shaft  112  and the pivot shaft  102  intersects at an angle α which remains unchanged at a constant value. 
     When the pivot shaft  102  is lowered with the angle α held constant, the auger shaft  112  is apt to swing clockwise about the sleigh  110 , causing the auger shaft  112  to rise. Pentagon formed during such a movement is referred to as the pentagon Y. 
     FIG. 7C shows the pentagons X and Y in an overlapped state. When the center  107   a  is caused to swing clockwise at the angle θ 1  about the pivot shaft (provided that, since the level of the center  107   a  remains unchanged, the pivot shaft  102  swings clockwise about the center  107   a  by appearance), the pivot shaft  102  is lowered by the distance Δ 1  and, in link motion therewith, the auger shaft  112  swings clockwise at the angle θ 2  about the sleigh  110 , thereby lifting up the auger shaft  112  by the distance Δ 2 . 
     Thus, when the auger shaft  112  is raised and the pivot shaft  102  is lowered, the auger  104  shown in FIG. 7B is tilted upward more than that shown in FIG. 7A, thereby deteriorating biting effect of the snow. 
     As discussed above, in the conventional snow-removing machine, if the auger is lowered when the snow-removing machine removes snow deeply, the auger is apt to be tilted upward with a resultant decrease in performance efficiency of the snow-removing operation. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a crawler vehicle which has an improved performance efficiency in snow-removing operation and is able to minimize the variation in tension of a crawler belt. 
     According to an aspect of the present invention, there is provided a crawler vehicle comprising a crawler frame having a front portion carrying a driven wheel and a lower portion carrying at least one lower idle wheel, a body frame connected vertically swingably to a rear portion of the crawler frame, a working member mounted to a front portion of the body frame, an engine mounted to the body frame, a drive wheel mounted to a rear portion of the body frame, and a crawler belt trained around the drive wheel and the driven wheel, characterized by a pivot shaft positioned forwardly of the lower idle wheel for allowing the vertical swinging movement of the body frame. 
     When the front portion of the crawler belt is lifted up from the road surface, the center of the lower idle wheel is apt to swing about the pivot shaft. Since, in this event, the pivot shaft is located forwardly of the lower idle wheel, the swing movement of the lower idle wheel causes the pivot shaft to be lifted. Due to this lifting movement of the pivot shaft, the auger shaft swings about the sleigh and is lowered. Consequently, it is possible for the auger to be lowered regardless of soft snow or hard snow, thereby carrying out snow-removing operation in an efficient manner. 
     In a preferred form, the lower idle wheel comprises a plurality of lower idle wheels while the pivot shaft is located forwardly of a lower rearmost one of the idle wheels. However, the pivot shaft should be positioned rearward of a lower idle wheel which is located next to the rearmost lower idle wheel at a front area thereof. 
     It is desirable that the pivot shaft for connecting the body frame to the crawler frame is positioned forwardly of the lower idle wheel, the drive wheel is positioned rearwardly of the lower rearmost idle wheel, the lower idle wheel is positioned at a lower intermediate position between the pivot shaft and the drive wheel, and an upper idle wheel is mounted to the crawler frame for supporting the crawler belt at an upper intermediate position between the pivot shaft and the drive wheel. 
     By connecting the body frame to the crawler frame with the pivot shaft, the body frame is enabled to arbitrarily swing, thereby allowing the front working member to be adjusted in height relative to ground surface or road surface. During such an adjustment, although the drive wheel is raised or lowered, provision of the additional upper idle wheel allows the total length of the crawler belt to be maintained at a substantially constant value for thereby minimizing the variation in tension to be exerted to the crawler belt. This results in remarkably extended life of the crawler belt. 
     In a specific form, the working member comprises a snow-removing section. More specifically, it comprises an auger or a blade for pushing and removing earth and sand as well as arable soil. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a crawler vehicle according to the present invention; 
     FIG. 2 is an exploded side view of relevant parts of the crawler vehicle shown in FIG. 1; 
     FIGS. 3A and 3B are schematic views illustrating a relationship among an upper idle wheel, a drive wheel and a lower idle wheel; 
     FIGS. 4A and 4B are views illustrating variations in the total length of the crawler belt; 
     FIGS. 5A to  5 C are schematic views illustrating a mode of operation of the crawler vehicle according to the present invention, wherein the crawler vehicle runs on hard snow; 
     FIGS. 6A and 6B are schematic views showing a conventional crawler vehicle illustrative of a mode of operation of the conventional crawler vehicle, wherein an auger is lifted up; and 
     FIGS. 7A to  7 C are schematic views illustrating a mode of operation of the conventional crawler vehicle as it runs on hard snow. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, which is a side view of a preferred embodiment of a crawler vehicle according to the present invention, there is shown the crawler vehicle as applied to an example of a snow-removing machine. 
     The snow-removing machine  10 , which serves as the crawler vehicle, includes a crawler frame  16  which has a pair of driven wheels  11  rotatably supported at a front portion of the crawler frame  16 , and three pairs of lower idle wheels  12 ,  13  and  14  which are mounted at a lower portion of the crawler frame  16 . A rear portion of the crawler frame  16  is connected to a body frame  21  to allow the same to swing in upward or downward directions. A front portion of the body frame  21  is mounted with a snow-removing section  30  which serves as a working member. An engine is mounted on the body frame  21 . A drive wheel  23  is rotatably mounted at a rear portion of the body frame  21 . A crawler belt  24  is tensioned between the pair of driven wheels  11  and the drive wheel  23 . The crawler frame  16  and the body frame  21  are connected to one another via a pivot shaft  25 . The rearmost idle wheel  14  is located in a lower position intermediate between the pivot shaft  25  and the drive wheel  23 . The pivot shaft  25  is located forwardly of the pair of the rearmost idle wheels  14 . The drive wheel  23  is located rearward of the pair of rearmost idle wheels  14 . An upper idle wheel  26  is mounted on the crawler frame  16  in an upper position intermediate between the pivot shaft  25  and the drive wheel  23  to exert a tension to the crawler belt  24 . 
     A snow-removing section  30  includes an auger  31  driven by a drive source composed of the engine  22 , a blower  32 , a snow-remover housing  33 , a sleigh  34  and a snow discharge shooter  35 . The engine produces a power output which is sequentially delivered through a small pulley  36 , a belt  37 , a large pulley  38 , a drive shaft  39  and an auger shaft  42  to rotate the auger  31 . Rotation of the auger  31  allows snow over the road surface to be gathered and transferred to the blower  32  through which snow is discharged via the shooter  35  due to a centrifugal force of the blower  32 . Reference numeral  41  designates a gear case and a reference numeral  43  designates an engine cover. Reference numeral  44  designates an engine cooling fan. Reference numeral  45  designates an output pulley which drives and rotates the drive wheels  23  via the belt. 
     FIG. 2 is an exploded view of an essential part of the snow-removing machine according to the present invention. In FIG. 2, the body frame  21  is connected to the crawler frame  16  via a bracket  47  and the pivot shaft  25  to allow the body frame  21  to swing upward or downward. Upward and downward movement is implemented with a hydraulic cylinder  50  for auger height adjustment which is mounted between an upper bracket  48  of the body frame  21  and a lower bracket  49  of the crawler frame  16 . 
     That is, the body frame  21  is interconnected to the crawler frame  16  in a manner as shown by an arrow {circle around ( 2 )} and the crawler belt  24  is engaged with the drive wheels  23  in a manner as shown by an arrow {circle around ( 3 )}. The hydraulic cylinder  50  is mounted to the crawler frame  16  in a manner as shown by an arrow {circle around ( 4 )} and subsequently the hydraulic cylinder  50  is caused to expand and contract, thereby allowing the body frame  21  to swing about the pivot shaft  25 . As a result, the drive wheel  23  shown by a phantom line in FIG. 2 is moved upward or downward about the pivot shaft  25 . 
     Now, the upward and downward movement of the drive wheel  23  is described below in detail with reference to FIGS. 3A and 3B. 
     In FIG. 3A, assuming that a line segment connected between the center of the lower rearmost idle wheel  14  and the center of the upper idle wheel  26  is designated by L 1  while a line segment connected between the center of the pivot shaft  25  and the center of the drive wheel  23  is designated by L 2 , the line segments L 1  and L 2  are shown as intersecting with one another at right angles. In this instance, the distance between the center of the upper idle wheel  26  and the center of the drive wheel  23  is assigned with A 1 , and the distance between the center of the rearmost lower idle wheel  14  and the center of the drive wheel  23  is assigned with B 1 . 
     In FIG. 3B, the drive wheel  23 , which is not linked to the crawler frame  16 , moves upward and downward around the rotational center of the pivot shaft  25  previously described above. In this event, the distance between the upper idle wheel  26  and the drive wheel  23  varies in length between A 2  and A 3 , and the distance between the drive wheel  23  and the lower idle wheel  14  varies between B 2  and B 3 . 
     FIG. 4A, assuming that the distance between the point P 1  on an ellipse and one focus F 1  is a 1  and the distance between the point P 1  and the other focus F 2  is a 2 , the sum (a 1 +a 2 ) is constant. That is, assuming that the distance between the other point P 2  on the ellipse and the one focus F 1  is a 3  and the distance between the point P 2  and the other focus F 2  is a 4 , the sum (a 3 +a 4 ) equals the sum (a 1 +a 2 ). Thus, the ellipse has a characteristic in that the sum of distances between arbitrary point on the ellipse and respective focuses F 1  and F 2  becomes constant at all times. 
     In FIG. 4B, when a circle R 2  with a radius of a line segment L 2  is drawn about the pivot shaft  25 , it is regarded that the circle R 2  closely resembles part of the ellipse shown in FIG.  4 A. That is, it is regarded that the circle R 2  extremely resembles the ellipse which is described with one focus provided by the center of the upper idle wheel  26  and with the other focus provided by the center of the other lower idle wheel  14 . As a result, the sum (A 4 +B 4 ) of the distances A 4  and B 4  becomes constant regardless of the swing angle of the line segment L 2 . 
     It is thus deemed that, in FIG. 3B, the relationship (A 2 +B 2 )=(A 3 +B 3 ) is obtained. Accordingly, it is seen that the total length and the tensioned state of the crawler belt  24  is not varied regardless of the upward or downward movement of the drive wheel  23 . 
     Thus, non-variation in the total length of the crawler belt  24  is reflected by the fact that the lower idle wheel  14  and the upper idle wheel  26  are located at a symmetrical position with respect to the center of the line segment L 2  shown in FIG.  3 A. 
     However, the upper idle wheel  26  is not required to be necessarily located at the symmetrical position relative to the lower idle wheel  14 . There exist no inconvenience for the upper idle wheel  26  to move left and right on the plane of the drawing as long as the line segment L 1  intersects the line segment L 2 . For this reason, even when the line segment L 2  is out of intersection relative to the line segment L 1 , the above operation may be carried out. 
     In the preferred embodiment, accordingly, the pivot shaft  25  is located forwardly of the lower idle wheels  14  while the drive wheels  23  are located rearwardly of the lower idle wheels  14  such that the rearmost lower idle wheels  14  are located at the lower intermediate position between the pivot shaft  25  and the drive wheel  23 . In addition, the upper idle wheel  26 , which supports the respective crawler belts, is mounted onto the crawler frame  16  at the upper and intermediate position between the pivot shaft  25  and the drive wheel  23 , with a resultant success in limiting variation in tension of the crawler belt  24 . In this manner, as the variation in tension of the crawler belt  24  remains in a minimum range, the crawler belt  24  does not encounter breakage troubles, thereby remarkably extending the life of the crawler belt  24 . 
     In the conventional crawler vehicles, although it has been a usual practice to have the crawler vehicle equipped with a tension adjustment mechanism composed of basic mechanical elements such as a spring, a bolt and a nut etc., application of such a complicated tension adjustment mechanism in the snow-removing machine causes the work load of the operator to remarkably increase owing to indispensable removing work for ice and snow adhered to the spring etc. 
     In contrast, if the variation in tension of the crawler belt  24  is kept within a minimum range as attained by the concept of the present invention, the complicated tension adjustment mechanism is not required and, even when a slight amount of tension adjustment is required, such a slight adjustment can be sufficed with a simplified tension adjustment mechanism. Consequently, the concept of the present invention is useful for a crawler vehicle of a general type equipped at its front side with a working member (such as, for example, a snow-removing section) and is useful especially for a snow-removing machine whose adhesion of snow and ice is to be considered. 
     Also, it is to be noted that the working member of the present invention may involve a blade for pushing out earth and sand as well as arable soil or a blade for pushing and removing snow, thus making it possible for the present invention not to be limited to the snow-removing machine but to be applied to bulldozers for civil engineering or agricultural machineries. 
     In the preferred embodiment, although the crawler vehicle has been shown and described as including three lower idle wheels, the crawler may have at least one lower idle wheel and at least one upper idle wheel wherein the number of idle wheels is arbitrarily determined. 
     Now, operation of the snow-removing machine for improving a snow-removing efficiency to cause the auger to achieve an improved biting effect is described in detail below with reference to FIGS. 5A to  5 C. 
     FIG. 5A shows a normal operating state of the snow-removing machine. In this event, the sleigh  34 , the auger  42 , the pivot shaft  25  and the center  14   a  of the lower idle wheel  14  form a pentagon X. Here, the line segment connected between the pivot shaft  25  and the center  14   a  of the lower idle wheel  14  is assigned with Lf. 
     FIG. 5B shows an operating state wherein, when the hydraulic cylinder  50  is retracted and the sleigh  34  runs into hard snow, a front portion of the crawler belt  24  is lifted from the road surface. As the crawler belt  24  rotates clockwise at an angle of θ 1 , the line segment Lf is caused in link motion with the crawler belt  24  to swing clockwise at an angle of θ 1  about the pivot shaft  25 . Since, in this instance, the center  14   a  of the lower idle wheel  14  remains at a constant height from the ground surface, the pivot shaft  25  is consequently lifted. Since the angle α around the auger shaft  42  remains unchangeable in the same manner as discussed above with reference to FIG. 7B, the lift of the pivot shaft  25  necessarily causes the auger shaft  42  to swing counter-clockwise and to move downward around the sleigh  34 . The pentagon shown in FIG. 5B is assigned with the pentagon Y. 
     In the pentagon Y shown in FIG. 5C, the line segment Lf swings clockwise at the angle of θ 1 , with a resultant lifting of the pivot shaft by a value σ 1 . At the same time, the auger shaft  42  swings counter-clockwise at an angle θ 2  about the sleigh  34 , resulting inn a downward movement of the auger shaft  42  by a value σ 2 . 
     Thus, the downward movement of the auger shaft  42  allows the auger  31  to increase its biting property to a higher level than that obtained in the normal operating state shown in FIG. 5A, improving the snow-removing work efficiency. 
     In FIG. 5A, also, assuming that an angle defined between a vertical line and the line segment Lf is ψ, the operating state shown in FIG. 5C is established provided that the angle ψ exceeds a value 0 (zero). 
     Accordingly, the condition wherein the pivot shaft is located forwardly of the lower idle wheel should meet a condition which satisfies 0≦ψ. However, location of the pivot shaft  25  in an extremely forward position conflicts a requirement in that the orientation (i.e., the auger angle) of the auger  31  is to be gently varied. Accordingly, it is arranged such that the pivot shaft  25  is not located forward beyond the second idle wheel  13  closest to the rearmost idle wheel  14 . 
     In the preferred embodiment, while the snow-removing section has been shown as composed of the auger, the snow-removing section may comprise a blade for pushing and removing snow. 
     INDUSTRIAL APPLICABILITY 
     As previously noted above, the present invention allows a pivot shaft, which rotatably interconnects a body frame to a rear portion of a crawler frame, to be located forwardly of a lower rearmost idle wheel among lower idle wheels. Lift of a front portion of a crawler belt from a road surface causes the center of the lower idle wheel to swing about the pivot shaft. During such a swing movement, since the pivot shaft remains forwardly of the lower idle wheel, the pivot shaft is lifted due to the above swing movement. As the pivot shaft is lifted up, an auger shaft is moved downward about a sleigh. Accordingly, the auger can be moved downward regardless of soft or hard snow, with a resultant highly improved snow-removing efficiency to provide a highly reliable snow-removing machine. In addition, the crawler vehicle of the present invention may also be suitably applied to bulldozers for civil engineering or agricultural machineries.