CA2214474A1

CA2214474A1 - Crawler vehicle

Info

Publication number: CA2214474A1
Application number: CA 2214474
Authority: CA
Inventors: Yoshiaki Kimura; Shunichi Shibasaki
Original assignee: Individual
Current assignee: Toyota Motor Corp
Priority date: 1996-09-20
Filing date: 1997-09-11
Publication date: 1998-03-20
Also published as: JP3282548B2; JPH10147267A; AU3831297A; AU697098B2

Abstract

A crawler vehicle includes: a driving wheel fixed to a drive shaft which is rotatively driven by receiving a driving force, the driving wheel being adapted to rotate with the drive shaft; a front rolling wheel and a rear rolling wheel which are arranged at positions lower than the driving wheel in a longitudinal direction of a vehicle, respectively; a crawler wound around the driving wheel, the front rolling wheel, and the rear rolling wheel, and adapted to move in a winding direction as the driving wheel rotates;
a fixed frame supported by a vehicle body in a state of being unrotatable about the drive shaft, the fixed frame being adapted to pivotally support the drive shaft; and a swingable frame for interconnecting the front rolling wheel and the rear rolling wheel and for pivotally supporting the front rolling wheel and the rear rolling wheel, the swingable frame being connected swingably to the fixed frame such that a swinging center axis of the swingable frame is located below the drive shaft.

Description

CRAWLER VEHICLE

BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to a crawler vehicle which travels by causing crawlers each wound around a driving wheel, a front rolling wheel, and a rear rolling wheel to move in a winding direction by rotatively driving the driving wheel.
Description of the Related Art:
As a method for changing an ordinary vehicle with tires mounted thereon into a crawler vehicle, there is a method in which crawler units each having the shape of an isosceles triangle in a side view are mounted instead of the tires.
An arrangement which can be used as a crawler unit of this type is disclosed in Japanese Utility Model Application Laid-Open (JP-U) No. 62-25286, and will be described hereinunder.
As shown in Fig. 18, a crawler unit 100 is comprised, as its main component elements, of a sprocket-shaped driving wheel 104 detachably mounted on a drive shaft 102 of a vehicle; a pair of rolling wheels 106 arranged at positions lower than the driving wheel 104 in a longitudinal direction of a vehicle; a substantially inverse T-shaped frame 108 for pivotally supporting the driving wheel 104 and the pair of rolling wheels 106 and interconnecting them; and a pair of intermediate rolling wheels 110 disposed at a lower end portion of the frame 108 at a predetermined interval therebetween in the longitudinal direction of the vehicle.
More specifically, a plurality of engaging holes 116, with which teeth 114 of the driving wheel 104 are engaged, are formed at predetermined intervals in a widthwise central portion of a crawler 112. In addition, projections 118 are formed at a predetermined intervals on widthwise opposite sides of the engaging holes 116 in the crawler 112, and the crawler 112 is arranged to rotate as the pair of rolling wheels 106 and the pair of intermediate rolling wheels 110 come into contact with spaces between the projections 118 (i.e., the engaging holes 116) (see Fig. 19). Further, rolling center shafts 120 of the intermediate rolling wheels 110 are interconnected by a pair of leaf springs, and the pair of intermediate rolling wheels 110 are constantly pressed and urged in the downward direction of the vehicle by the urging forces of the leaf springs 122.
In accordance with the above-described arrangement, since the teeth 114 of the driving wheel 104 are engaged in the engaging holes 116 of the crawler 112, when the driving wheel 104 is rotatively driven, the crawler 112 moves by being guided by the rolling wheels 106 and the intermediate rolling wheels 110 arranged in the longitudinal direction of the vehicle with respect to the driving wheel 104. At this time, since only the center of the bottom portion of the crawler 112 projects downward via the intermediate rolling wheels which are subjected to the urging forces of the leaf springs 122, even if the weight of the vehicle is added, the area of the tread of the crawler 112 is reduced. For this reason, the swiveling of the vehicle is facilitated. In addition, if the intermediate rolling wheels 110 are made to be pivotally supported directly by the lower end of the above-described frame, although there is a disadvantage in that the frame 108 vibrates vertically when the intermediate rolling wheels 110 ride over the engaging holes 116 of the crawler 112, since the vertical motion of the intermediate rolling wheels 110 can be absorbed by the elastic deformation of the leaf springs 122 in accordance with the above-described arrangement, it is possible to suppress the transmission of the vibrations of the intermediate rolling wheels 110 to the frame 108. Such are the main contents of the arrangement disclosed in the above-described publication.
However, with the arrangement disclosed in the above-described publication, since the frame 108 for pivotally supporting the driving wheel 104 and the pair of rolling wheels 106 arranged in the longitudinal direction of the driving wheel and for interconnecting them is formed as a rigidly integral component, when the rolling wheels 106 ride over irregularities on the road surface, the frame 108 must swing like the motion of a pendulum about the drive shaft 102 serving as a swinging center axis of the frame 108. In other words, with the above-described arrangement, in order to ride over irregularities on the road surface, it is necessary to ride them over without deforming the shape of the crawler (the shape of the isosceles triangle) in ~ side view, which is formed by the driving wheel 104 and the pair of rolling wheels 106. For this reason, when the frame 108 has swung about the drive shaft 102, the front rolling wheel 106 or the rear rolling wheel 106 projects forward or rearward by a large degree, and the projecting rolling wheel 106 (to be accurate, the portion of the crawler 112 wound around that rolling wheel 106) is liable to interfere with the vehicle body.
Accordingly, in a case where the above-described arrangement is to be adopted, it is necessary to devise a measure, such as the securing in advance (at a design stage) of a large installation space for the crawler unit 100 (or the tire installation space if the interchangeability with a tire is taken into account) in the swinging direction of the frame 108 (in the longitudinal direction of the vehicle), or the provision of stoppers for preventing the interference between the vehicle body and the crawler 112.

S~DMARY OF THE INVENTION
In view of the above-described circumstances, it is an object of the present invention to provide a crawler vehicle which makes it unnecessary to make the installation space for the crawler unit large in the longitudinal direction of the vehicle, and to provide stoppers for preventing interference with the vehicle body.
To this end, in accordance with a first aspect of the present invention, there is provided a crawler vehicle comprising: a driving wheel fixed to a drive shaft which is rotatively driven by receiving a driving force, the driving wheel being adapted to rotate with the drive shaft; a front rolling wheel and a rear rolling wheel which are arranged at positions lower than the driving wheel in a longitudinal ~
direction of a vehicle, respectively; a crawler wound around the driving wheel, the front rolling wheel, and the rear rolling wheel, and adapted to move in a winding direction as the driving wheel rotates; a fixed frame supported by a vehicle body in a state of being unrotatable about the drive shaft, the fixed frame being adapted to pivotally support the drive shaft; and a swingable frame for interconnecting the front rolling wheel and the rear rolling wheel and for pivotally supporting the front rolling wheel and the rear rolling wheel, the swingable frame being connected swingably to the fixed frame such that a swinging center axis of the swingable frame is located below the drive shaft.
In accordance with a second aspect of the present invention, in the crawler vehicle according to the first aspect of the invention, the swinging center axis of the swingable frame in a side view is disposed in a region below a segment connecting a rolling center axis of the front rolling wheel and a rolling center axis of the rear rolling wheel.
In accordance with a third aspect of the present invention, the crawler vehicle according to the first aspect of the invention further comprises: an intermediate rolling shaft disposed between the front rolling wheel and the rear rolling wheel such that a position of a rolling center of the intermediate rolling wheel and a position of a swinging center of the swingable frame coincide with each other.
In accordance with a fourth aspect of the present invention, in the crawler vehicle according to the first aspect of the invention, the fixed frame is provided in such a manner as to be supported by the drive shaft on both sides of the driving wheel in a thicknesswise direction thereof.
In accordance with a fifth aspect of the present invention, in the crawler vehicle according to the first aspect of the invention, at least one of the front rolling wheel and the rear rolling wheel is formed in an annular shape permitting elastic deformation in a radial direction.
In accordance with a sixth aspect of the present invention, the crawler vehicle according to the fifth aspect of the invention further comprises: a restricting member for restricting a swinging angle of the swingable frame within a fixed range by coming into contact with at least one of the front rolling wheel and the rear rolling wheel formed in the annular shape permitting elastic deformation.
In accordance with a seventh aspect of the present invention, in the crawler vehicle according to the sixth aspect of the invention, the restricting member is a rotary member disposed rotatably about a shaft parallel with a center of rotation of the contacting one of the front rolling wheel and the rear rolling wheel.
In accordance with an eighth aspect of the present invention, the crawler vehicle according to the first aspect of the invention further comprises: a contacting member provided on the fixed frame and adapted to restrict a swinging angle of the swingable frame within a fixed range by coming into contact with the swingable frame.
In accordance with the first aspect of the present invention, when the drive shaft is rotatively driven by receiving a driving force, the driving wheel concurrently rotates. For this reason, the crawler which is wound àround the driving wheel and the front rolling wheel and the rear rolling wheel, which are arranged at positions below the driving wheel on a front and a rear side, moves in its winding direction. Consequently, the crawler vehicle travels.
Here, in the present invention, the arrangement provided is such that, instead of pivotally supporting the driving wheel, the front rolling wheel, and the rear rolling wheel by a single integral and rigidly-formed frame, the frame is divided into the fixed frame for pivotally supporting the driving wheel and the swingable frame for pivotally supporting and interconnecting the front rolling wheel and the rear rolling wheel, the fixed frame being supported by the vehicle body in a state of being unrotatable about the drive shaft, the swingable frame being connected swingably to the fixed frame such that the swinging center axis of the swingable frame is located below the drive shaft. Accordingly, as the swingable frame swings about its swinging center axis in correspondence with irregularities on the road surface during traveling, it is possible to deform the shape of the crawler (the shape of the isosceles triangle) in a side view, which is formed by three component members, i.e., the driving wheel, the front rolling wheel, and the rear rolling wheel. For this reason, by making use of this deformation, it is possible to reduce the amount of forward or rearward projection of the front rolling wheel or the rear rolling wheel. Consequently, an outstanding advantage can be obtained in that it is unnecessary to enlarge the installation space for the crawler unit in the longitudinal direction of the vehicle or provide stoppers for preventing interference with the vehicle body.
In accordance with the second aspect of the present invention, since the swinging center axis of the swingable frame in a side view is disposed in a region below a segment connecting the rolling center axis of the front rolling wheel and the rolling center axis of the rear rolling wheel, a segment connecting the rolling center axis of the front rolling wheel and the swinging center axis as well as a segment connecting the rolling center axis of the rear rolling wheel and the swinging center axis are inevitably inclined upward. For this reason, if an example is cited in which a load has been inputted to the rolling center axis of the front rolling wheel during riding over a bump on the road surface, a component force for displacing a load-input side end of the swingable frame rearwardly upward occurs at that end of the swingable frame. On the other hand, if an example is cited in which a load has been inputted to the rolling center axis of the rear rolling wheel during riding over a bump on the road surface, a component force for displacing a load-input side end of the swingable frame forwardly upward occurs at that end of the swingable frame.
Therefore, in accordance with the present invention, it is possible to minimize, i.e., eliminate, the amount of forward or rearward projection of the front rolling wheel or the rear rolling wheels when the swingable frame swings. As a result, it is possible to positively obtain advantages in that the installation space for the crawler unit can be reduced and the stoppers can be disused.
In accordance with the third aspect of the present invention, since the position of the rolling center of the intermediate rolling wheel, which is disposed between the front rolling wheel and the rear rolling wheel, and the position of the swinging center of the swingable frame are made to coincide with each other, one system (unit) which is comprised of the driving wheel, the front rolling wheel, the rear rolling wheel, the crawler, the fixed frame, the swingable frame, and the intermediate rolling wheel can be made compact by the portion in which the positions of the centers of the two elements are located coaxially (i.e., by the portion in which the positions of the centers of the two elements are not disposed eccentrically). In addition, in a case where the intermediate rolling wheel is added, it is possible to obtain an outstanding advantage in that the installation space for the crawler unit can be reduced.

The operation in accordance with the fourth aspect of the present invention is as follows. During the traveling of the vehicle, the road surface load is inputted to the swingable frame from the bottom portion of the crawler via the front rolling wheel and the rear rolling wheel, and is then transmitted to the fixed frame. Finally, that load is transmitted to a point at which the fixed frame is supported on the vehicle body.
Here, in the present invention, since the fixed frame is supported by the drive shaft, i.e., an element on the vehicle body side, on both sides of the drive wheel, the fixed frame is supported by the vehicle body side on both sides of the driving wheel. Consequently, it is possible to obtain an outstanding advantage in that the rigidity of the fixed frame and, hence, the crawler unit with respect to the shaking in the transverse direction of the vehicle can be improved.
In accordance with the fifth aspect of the present invention, even if the shape of the crawler (the shape of the isosceles triangle) in a side view, which is formed by the three component members, i.e., the driving wheel, the front rolling wheel, and the rear rolling wheel, has become deformed, and the winding length of the crawler has changed, since at least one of the front rolling wheel and the rear rolling wheel undergoes elastic deformation in the radial direction, the difference between the length of the crawler itself and the winding length of the crawler can be absorbed. Hence, it is possible to prevent the crawler from becoming disengaged from the driving wheel, the front rolling wheel, and the rear rolling wheel.
In accordance with the sixth aspect of the present invention, the swinging angle of the swingable frame is restricted within a fixed range, and the swingable frame does not swing excessively, so that it is possible to prevent the crawler from becoming disengaged from the driving wheel, the front rolling wheel, and the rear rolling wheel. The restricting member comes into contact with the front rolling wheel or the rear rolling wheel formed in the annular shape permitting elastic deformation in the radial direction, so as to restrict the swinging angle of the swingable frame within a fixed range, so that the impact at the time of contact can be alleviated. Consequently, the durability of the restricting member improves, and the occurrence of abnormal noise during contact can be prevented.
In accordance with the seventh aspect of the present invention, when the restricting member comes into contact with the front rolling wheel or the rear rolling wheel, the restricting member rotates together with the front rolling wheel or the rear rolling wheel. As a result, since the rotary member (restricting member) does not rub against the front rolling wheel or the rear rolling wheel, the rotational resistance of the front rolling wheel or the rear rolling wheel does not increase. Further, it is possible to prevent the occurrence of damage of or the frictional sound from the restricting member, the front rolling wheel, and the rear rolling wheel.
In accordance with the eighth aspect of the present invention, since the swinging angle of the swingable frame is restricted within a fixed range, and the swingable frame does not swing excessively, it is possible to prevent the crawler from becoming disengaged from the driving wheel, the front rolling wheel, and the rear rolling wheel.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an enlarged schematic diagram of essential portions of a crawler unit in a crawler vehicle in accordance with a first embodiment of the present invention;
Fig. 2 is a cross-sectional view, taken along line 2 -2, of the crawler unit shown in Fig. 1;

Fig. 3 is a schematic diagram of the crawler vehicle equipped with the crawler unit shown in Fig. 1;
Fig. 4 is an enlarged schematic diagram of the essential portions of the crawler unit for describing an advantage of the first embodiment in comparison with a conventional type;
Fig. 5A is an explanatory diagram explaining another advantage of the first embodiment;
Fig. 5B is an explanatory diagram explaining the other advantage of the first embodiment;
Fig. 6A is an explanatory diagram for describing the other advantage of the first embodiment in comparison with the conventional type, and corresponds to Fig. 5A;
Fig. 6B is an explanatory diagram for describing the other advantage of the first embodiment in comparison with the conventional type, and corresponds to Fig. 5B;
Fig. 7 is an enlarged schematic diagram of essential portions of a crawler unit in a crawler vehicle in accordance with a second embodiment of the present invention;
Fig. 8 is a cross-sectional view, taken along line 8 -8, of the crawler unit shown in Fig. 7;
Fig. 9 is a side elevational view illustrating a crawler unit in accordance with a third embodiment of the present invention;

Fig. 10 is a cross-sectional view, taken along line 10 - 10, of the crawler unit shown in Fig. 9;
Fig. 11 is a cross-sectional view, taken along line 11 - 11, of the crawler unit shown in Fig. 9;
Fig. 12 is an enlarged perspective view illustrating a torsion bush of the crawler unit in accordance with the third embodiment;
Fig. 13 is graph illustrating the elastic characteristic of rubber constituting the torsion bush of the crawler unit in accordance with the third embodiment;
Fig. 14 is a cross-sectional view, taken along line 14 - 14, of the crawler unit shown in Fig. 9;
Fig. 15 is an enlarged perspective view illustrating a damper member of the crawler unit in accordance with the third embodiment;
Fig. 16 is a side elevational view illustrating a state in which a swingable frame of the crawler unit in accordance with the third embodiment has swung;
Fig. 17 is a side elevational view illustrating a state in which the swingable frame of the crawler unit in accordance with the third embodiment has swung;
Fig. 18 is a side elevational view of a crawler unit in accordance with a conventional example; and Fig. 19 is a cross-sectional view, taken along line 19 - 19, of the crawler unit shown in Fig. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Figs. 1 to 6, a description will be given of a first embodiment.
Fig. 3 shows a schematic diagram of a crawler vehicle 10 in accordance with this embodiment. As shown in this drawing, the crawler vehicle 10 is comprised of an ordinary vehicle body 12 as in a recreational vehicle (RV) and crawler units 16 which are respectively mounted in tire installation spaces 14 in the vehicle body 12 instead of tires of front and rear wheels.
Fig. 1 schematically shows an enlarged structural diagram of essential portions of the above-described crawler unit 16. Fig. 2 shows a central vertical cross-sectional view of the crawler unit 16. Hereafter, a description will be given of the arrangement of the crawler unit 16 with reference to these diagrams.
The crawler unit 16 has as its main component elements a driving wheel 18, a pair of front rolling wheels 20, a pair of rear rolling wheels 22, two pairs of intermediate rolling wheels 24, a crawler 26, a fixed frame 28, and a swingable frame 30. A description will be given of each component element in the order mentioned.
A drive shaft 32 which is rotatively driven by receiving a driving force from the vehicle is pivotally supported in a hub bearing case 34. The driving wheel 18 having the shape of a sprocket is concentrically fixed to a distal end portion 32A side of the drive shaft 32.
Accordingly, when the drive shaft 32 is rotatively driven, the driving wheel 18 is also rotatively driven.
Incidentally, the distal end portion 32A of the drive shaft 32 is passed through the driving wheel 18. In addition, a drum brake 36 for braking the driving wheel is disposed adjacent to a vehicle transverse direction inner side of the driving wheel 18.
The pair of front rolling wheels 20, whose diameter is smaller than that of the driving wheel 18 and which are juxtaposed in the transverse direction of the vehicle, are disposed below the driving wheel 18 on the vehicle front side thereof. In addition, a pair of rear rolling wheels 22, whose diameter is identical to that of the driving wheel 18 and which are juxtaposed in the transverse direction of the vehicle, are disposed below the driving wheel 18 on the vehicle rear side thereof. Further, two pairs of front and rear intermediate rolling wheels 24, whose diameter is smaller than that of the front rolling wheels 20 and the rear rolling wheels 22 and which are juxtaposed in the transverse direction of the vehicle, are disposed between the front rolling wheels 20 and the rear rolling wheels 22.
The relationship of relative sizes of the driving wheel 18, the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24 is changed, as required, in the light of the reduction gear ratio, i.e., the gear ratio (an element for the driving wheel 18), the stepped-portion riding-over performance (an element for the front rolling wheels 20 and the rear rolling wheels 22), the stability of the tread (an element for the intermediate rolling wheels 24), the interference with other members, i.e., mountability, and the like. In addition, the reason that the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24 are juxtaposed in the transverse direction of the vehicle is to avoid the interference of the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24 with the driving wheel 18 and to stabilize the tread by uniformly distributing pressing points (pressing area) for the crawler 26 in the longitudinal and transverse directions of the vehicle.
The crawler 26 in the shape of an endless belt is wound around outer peripheral portions of the above-described driving wheel 18, front rolling wheels 20, rear rolling wheels 22, and intermediate rolling wheels 24 in a state in which a predetermined tension is applied to the crawler 26.
Accordingly, the crawler 26 in a side view forms a closed loop having the shape of an isosceles triangle.

A protrusion 38 whose width is set to a predetermined dimension smaller than the width of the crawler is formed integrally on a widthwise intermediate portion of an inner peripheral surface of the crawler 26. The front rolling wheels 20, rear rolling wheels 22, and intermediate rolling wheels 24 which are respectively juxtaposed are positioned on both sides of the protrusion 38 in such a manner as to sandwich the same. Accordingly, this protrusion 38 functions as a positioning means for positioning the widthwise direction of the front rolling wheels 20, rear rolling wheels 22, and intermediate rolling wheels 24, and also functions as a restricting means for restricting their widthwise movement. A plurality of rectangular parallelopiped-shaped engaging recesses 40 which teeth 18A
of the driving wheel 18 having the shape of a sprocket are capable of engaging are formed in a widthwise intermediate portion of the protrusion 38 at predetermined intervals in conformity with the pitch of the teeth 18A of the driving wheel 18. Accordingly, the teeth 18A of the driving wheel 18 are always in a state of being engaged with the engaging recesses 40 of the crawler 26. The arrangement provided is such that when the driving wheel 18 is rotatively driven, the crawler 26 receives the rotatively driving force and moves in its winding direction, and its moving direction is changed by the front rolling wheels 20 and the rear rolling wheels 22, respectively.
Here, in this embodiment, a frame for supporting the above-described driving wheel 18, the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24 is divided into two parts, i.e., the fixed frame 28 and the swingable frame 30. Hereafter, a detailed description will be given of the fixed frame 28 and the swingable frame 30.
The fixed frame 28 is arranged as having the shape of a substantially rectangular frame with an open section.
Specifically, the fixed frame 28 is comprised of a shaft-shaped bottom po-rtion 28A which is disposed below the driving wheel 18 and whose longitudinal direction coincides with the axial direction of the driving wheel 18 (this bottom portion 28A corresponds to a "swinging center axis"), a pair of side portions 28B and 28C which respectively project upward from longitudinal ends of the bottom portion 28A and are arranged in parallel with each other in such a manner as to sandwich the driving wheel 8, and a pair of top portions 28D and 28E which are respectively bent at upper ends of the side portions 28B and 28C toward the driving wheel 18 side and are arranged in parallel with thé bottom portion 28A.

Of the top portions of the fixed frame 28, the vehicle transverse inner side top portion 28D is fixed to a lower end of the aforementioned hub bearing case 34. In addition, a bearing accommodating portion 42 having the shape of a hollow cylinder is formed integrally in the vicinity of an inward end of the vehicle transverse outer side top portion 28E of the top portions of the fixed frame 28. A bearing 44 (its inner race and outer race are not illustrated), into which the distal end portion 32A of the drive shaft 32 is press fitted for pivotally supporting the same, is accommodated in the bearing accommodating portion 42.
Accordingly, the drive shaft 32 for transmitting the driving force to the driving wheel 18 is pivotally supported by the top portions 28D and 28E of the fixed frame 28 (i.e., upper end portions of the fixed frame 28) via the hub bearing case 34 and the bearing 44.
Further, as can be appreciated from the above-described arrangement, in an assembled state, the fixed frame 28 does not rotate about the drive shaft 32, and the fixed frame 28 is supported by the drive shaft 32, i.e., a vehicle body-side element, at two points (i.e., supported on both sides) on both sides of the driving wheel 18 (at the position where the hub bearing case 34 is disposed and the position where the bearing 44 is disposed on the drive shaft 32).

In addition, as shown in Fig. 1, a plate-shaped supporting plate 29 is formed integrally with the fixed frame 28 in such a manner as to project substantially from a vertical center of the fixed frame 28 in the forward and rearward directions of the vehicle. Rubber members 31 serving as contact members are fixed to the bottom of the supporting plate 29 on both the vehicle front and rear sides thereof. Accordingly, the rubber members 31 are provided on the fixed frame 28 via the supporting plate 29.
Each of these rubber members 31 is formed substantially in the shape of an inverse circular cone which is tapered off toward its lower end.
In a state in which the swingable frame 30 has not been swung, a lower end of each rubber member 31 is opposed to an upper surface of the swingable frame 30 at a predetermined interval therewith. However, when the swingable frame 30 is swung, the upper surface of the swingable frame 30 presses the rubber member 31, so that the rubber member 31 undergoes elastic deformation. By virtue of this elastic deformation, the rotary kinetic energy due to the swinging of the swingable frame 30 is absorbed, and an angle of swinging is restricted to a fixed range.
It should be noted that the structure in which the rubber members 31 are fixed is not limited to the above-described one insofar as the arrangement makes it possible to restrict the angle of swinging to a fixed range as the rubber members 31 come in~o contact with the swingable frame 30 which has been swung. For instance, the rubber members 31 may be attached directly to the fixed frame 28 without the supporting plate 29. In addition, the contact members are not limited to the aforementioned rubber members 31 formed of rubber, and it suffices if the contact members are formed of an elastically deformable material. Further, the shape of the contact members is neither limited to the above-described one.
On the other hand, the swingable frame 30 is an elongated member whose longitudinal direction coincides with the longitudinal direction of the vehicle. The swingable frame 30 is comprised of a base portion 30A which is disposed horizontally such that its longitudinal direction as seen in a side view extends along the axial direction of the bottom portion 28A of the fixed frame 28; a front inclined portion 30B which is bent at a front end of the base portion 30A and extends forwardly upward; and a rear inclined portion 30B which is bent at a rear end of the base portion 30A and extends rearwardly upward.
A front rolling shaft 46 serving as a rolling center axis of the front rolling wheels 20 is pivotally supported at a distal end portion of the front inclined portion 30B.
Similarly, a rear rolling shaft 48 serving as a rolling center axis of the rear rolling wheels 22 is pivotally supported at a distal end portion of the rear inclined portion 30C. Further, a pair of intermediate rolling shafts 50 serving as rolling center axes of the intermediate rolling shafts 24 are pivotally supported on the front end side of the base portion 30A (i.e., between the base portion 30A and the front rolling shaft 46) and the rear end side of the base portion 30A (i.e., between the base portion 30A and the rear rolling shaft 48), respectively. Accordingly, the aforementioned front rolling wheels 20, rear rolling wheels 22, and intermediate rolling wheels 24 are connected to each other by the swingable frame 30.
Further, the swingable frame 30 is pivotally supported swingably on the bottom portion 28A of the fixed frame 28 by means of a pair of bearings 54. Accordingly, the bottom portion 28A of the fixed frame 28 functions as the swinging center axis of the swingable frame 30. Further, the swinging center axis of the swingable frame 30 (i.e., the bottom portion 28A of the fixed frame 28) is disposed in close proximity to a bottom portion 26A of the crawler 26 which constitutes the tread. Therefore, a segment R which connects the swinging center axis (bottom portion 28A) of the swingable frame 30 and the front rolling shaft 46, i.e., the rolling center of the front rolling wheels 20, as well as the rear rolling shaft 48, i.e., the rolling center of the rear rolling wheels 22, is substantially horizontal in a side view. More specifically, the swinging center axis of the swingable frame 30 is offset downward by a predetermined distance from a segment P which connects the front rolling shaft 46 and the rear rolling shaft 48.
Hereafter, a description will be given of the operation and advantages of this embodiment.
When the drive shaft 32 rotates by receiving the driving force, the driving wheel 18 fixed to the drive shaft 32 rotates. Since the teeth 18A of the driving wheel 18 are engaged in the engaging recesses 40 of the crawler 26, when the driving wheel 18 rotates, the crawler 26, which is wound around the driving wheel 18, the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24, moves in the winding direction (along the closed loop of the crawler formed in the shape of an isosceles triangle in a side view), and is thereby set in a traveling state.
Here, when traveling on a flat road surface, the crawler vehicle 10 in accordance with this embodiment travels while maintaining the shapes of the crawlers in the normal state (i.e., in the shape of isosceles triangles), as shown by the solid lines in Fig. 1. On the other hand, when traveling on a road surface having many irregularities, such as snowy land, cultivated land, sandy land such as shores, marshy land, and muddy land, the crawler vehicle 10 travels while changing the shape of each crawler from the shape of an isosceles triangle to the shape of a triangle excluding the isosceles triangle. Hereafter, a description will be given by placing emphasis on this point.
For example, as shown in Fig. 4, in the case of a crawler unit 58 (in the case of an arrangement corresponding to a conventional structure) in which a frame 56 for pivotally supporting and interconnecting the driving wheel 18, the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24 is arranged as a rigid integral component as illustrated in the drawing, if an attempt is made to ride over a bump located in front on the road surface, the swinging center axis of this frame 56 becomes the drive shaft 32, so that the frame 56 swings clockwise about the drive shaft 32 like the motion of a pendulum and raises the front rolling wheels 20 upward.
Moreover, in this case, a segment Q which connects the front rolling shaft 46, i.e., the rolling center of the front rolling wheels 20, and the drive shaft 32, i.e., the swinging center of the frame 56, becomes downwardly inclined with a relatively large gradient. For these reasons, the locus of movement of the front rolling wheels 20 accompanying the swinging motion of the frame 56 inevitably becomes in the forward direction of the vehicle (and in the upward direction of the vehicle), so that the amount of forward projection of the front rolling wheels 20 increases.
Consequently, if the crawler unit 58 having the above-described frame structure is mounted within the tire installation space 14 of the vehicle body 12 in the crawler vehicle 10 in accordance with this embodiment, the front rolling wheels 20 (to be accurate, the crawler 26 wound therearound) interfere with a vehicle body-side component member such as a wheel housing. Incidentally, the same holds true of the rear rolling wheels 22 as well.
Accordingly, to overcome the above-described drawback, it is necessary to provide a measure, such as enlarging in advance the tire installation space 14 in the swinging direction of the frame 56 (i.e., in the longitudinal direction of the vehicle) or providing stoppers for restricting the swinging motion of the crawler 26 before the crawler 26 interferes with a vehicle body-side component member. In this respect, such a conventional arrangement is disadvantageous.
In contrast, in this embodiment, the frame is divided into the fixed frame 28 for pivotally supporting the driving wheel 18 and the swingable frame 30 for pivotally supporting and interconnecting the front rolling wheels 20 and the rear rolling wheels 22. Further, the fixed frame 28 is supported by the vehicle body side in the state of being unable to rotate about the drive shaft 32, and the swingable frame 30 is swingably connected to the fixed frame 28 such that the bottom portion 28A of the fixed frame 28 serving as the swinging center axis is located below the drive shaft 32.
Therefore, when riding over irregularities on the road surface, the crawler 26 is able to ride over it since the fixed frame 28 remains immobile, and only the swingable frame 30 swings about the swinging center axis (bottom portion 28A) located in close proximity to the tread of the crawler 26, changing the shape of the crawler from the shape of an isosceles triangle to the shape of a triangle excluding the isosceles triangle. Accordingly, if the deformation of the shape of the crawler is made use of, it is possible to reduce the amount of forward or rearward projection of the front rolling wheels 20 or the rear rolling wheels 22. As a result, in accordance with this embodiment, even if the crawler unit 16 is mounted in an ordinary tire installation space 14, the front rolling wheels 20 or the rear rolling wheels 22 are prevented from interfering with a vehicle body-side component member.
Hence, in accordance with this embodiment, as compared with the case where the above-described conventional structure is adopted, it is possible to reduce the tire installation space 14 and disuse the stoppers.
Further, since the stoppers are disused, it is impossible to reduce the number of parts used and cost, and prevent the occurrence of abnormal noise and vibrations due to contact with the stoppers. In addition, in a conventional case where an arrangement is adopted in which the stoppers are provided instead of enlarging the tire installation space 14, the height of the irregularities over which the crawler unit 58 is able to ride is consequently limited (i.e., the crawler unit 58 is unable to ride over large irregularities). In accordance with this embodiment, however, such a disadvantage does not occur.
Further, in this embodiment, the bottom portion 28A of the fixed frame 28 serving as the swinging center axis is disposed in a region below the segment P which connects the front rolling shaft 46 serving as the rolling center axis of the front rolling wheels 20 and the rear rolling shaft 48 serving as the rolling center axis of the rear rolling wheels 22 in a side view. Therefore, both the segment connecting the swinging center axis and the front rolling shaft 46 and the segment connecting the swinging center axis and the rear rolling shaft 48 are inclined upward. For this reason, if an example is cited in which a load is inputted to the rolling center axis 46 of the front rolling wheels 20 when riding over a bump on the road surface, a component of force for displacing a load input-side end portion of the swingable frame 30 rearwardl~ upward is produced at that end portion. On the other hand, if an example is cited in which a load is inputted to the rolling center axis 48 of the rear rolling wheels 22 when riding over a bump on the road surface, a component of force for displacing a load input-side end portion of the swingable frame 30 forwardly upward is produced at that end portion. Accordingly, in accordance with this embodiment, it is possible to minimize, i.e., eliminate, the amount of forward or rearward projection of the front rolling wheels 20 or the rear rolling wheels 22 when the swingable frame 30 swings. As a result, it is possible to positively obtain the above-described advantages (the reduction of the tire installation space 14 and the disuse of the stoppers).
In addition, in accordance with this embodiment, since the fixed frame 28 for pivotally supporting the driving wheel 18 and swingably supporting the swingable frame 30 is supported by the vehicle body side (drive shaft 32) on both sides of the driving wheel 18, it is possible to improve the rigidity with respect to the swaying (shaking) of the fixed frame 28 and, hence, the crawler unit 16 in the transverse direction of the vehicle. That is, the load surface load acting during the traveling of the crawler vehicle 10 is inputted from the bottom portion 26A of the crawler 26 to the swinging frame 30 via the front rolling wheels 20, the rear rolling wheels 22, and the intermediate rolling wheels 24, is then transmitted to the fixed frame 28 to which the swingable frame 30 is connected, and is finally transmitted to the supporting points where the fixed frame 28 is supported by the vehicle body side. Here, if the fixed frame is supported by the vehicle body side in a cantilevered manner, the transmission of the load from the fixed frame to the vehicle body side would become unstable.
However, if the fixed frame 28 is supported by the drive shaft 32, i.e., a vehicle body-side element, on both sides of the driving wheel 18 as in this embodiment, the load transmission path of the load which is transmitted from the fixed frame 28 to the vehicle body side becomes stable.
Accordingly, it is possible to improve the rigidity with respect to the swaying (shaking) of the fixed frame 28 and, hence, the crawler unit 16 in the transverse direction of the vehicle.
Further, in accordance with this embodiment, since the swingable frame 30 is swingably connected to the fixed frame 28, and the shape of the crawler is arranged to be changeable from the shape of an isosceles triangle to the shape of a triangle excluding the isosceles triangle, even if the bump on the road surface is a right-angled step 60, as shown in Figs. 5A and 5B, it is possible to reliably ride over the step 60.
That is, as shown in Figs. 6A and 6B, in the case where the frame which interconnects the driving wheel 18, the front rolling wheels 20, and the rear rolii.~g wheels 22 is a rigid integral component (in the case of the struc~ure shown in Fig. 4 referred to earlier), if the driving wheel 18 moves along an advancing direction A (see Fig. 6A), and the front rolling wheels 20 abut against the right-angled step 60, the front rolling wheels 20 receives from this step 60 a relatively large pushing force F acting in a direction opposite to the advancing direction A. For this reason, the crawler unit 58 is subjected to inverting moment M about the drive shaft 32 serving as the swinging center of the frame.
Consequently, as shown in Fig. 6B, the crawler unit 58 rotates in the direction in which the inverting moment M
acts, with the result that it becomes difficult for the crawler unit 58 to ride over the step 60.
In contrast, in this embodiment, since the swingable frame 30 is swingably connected to the fixed frame 28, and the shape of the crawler is arranged to be changeable from the shape of an isosceles triangle to the shape of a triangle excluding the isosceles triangle, whèn the front rolling wheels 20 abut against the step 60 as shown in Fig.
5A, the front rolling wheels 20 receives the pushing force F
from the step 50, but the swingable frame 30 swings in a direction B due to the action of the pushing force F.
Consequently, in accordance with this embodiment, the crawler unit 16 is able to easily ride over the step 60, as shown in Fig. 5B.
Further, in this embodiment, since the bottom portion 28A of the fixed frame 28 is also used as the swinging center axis of the swingable frame 30, it is possible to simplify the structure as compared with a case where an exclusive-use swinging center axis is provided.
In addition, in this embodiment, since the crawler unit 16 is arranged to be in the shape of a flat isosceles triangle as a whole in a side view, it is possible to secure a long longitudinal length of the bottom portion 26A
constituting the tread of the crawler 26. For this reason, it is possible to reduce the tread pressure of the bottom portion 26A of the crawler 26.
Further, in this embodiment, when the swinging angle of the swingable frame 30 reaches a fixed amount, the upper surface of the swingable frame 30 abuts against the rubber member 31 to restrict the swinging motion. For this reason, the crawler 26 is prevented from becoming disengaged from the crawler unit 16 due to the excessive swinging of the swingable frame 30.
Next, referring to Figs. 7 and 8, a description will be given of a second embodiment. In addition, the same component parts as those of the above-described first embodiment will be denoted by the same reference numerals, and a description thereof will be omitted.
As shown in these drawings, in a crawler unit 70 in accordance with this embodiment, a fixed frame 72 having a bilaterally asymmetrical cross-sectional configuration with respect to the driving wheel 18 is used. More specifically, a side portion 72C disposed on the vehicle transverse direction outer side of the fixed frame 72 is disposed in close proximity to the driving wheel 18, thereby allowing a bottom portion 72A of the fixed frame 72 functioning as the swinging center axis of a swingable frame 76 to project more outwardly in the transverse direction of the vehicle than the side portion 72C (hereafter, this projecting portion will be referred to as a projecting portion 72A'). In addition, due to the fact that the side portion 72C of the fixed frame 72 is disposed in close proximity to the driving wheel 18, the vehicle transverse direction dimension of a vehicle transverse direction outer side top portion 72E
becomes short. Incidentally, other portions of the fixed frame 72 (i.e., a vehicle transverse direction inner side portion 72B and an inner top portion 72D) are similar to those of the aforementioned fixed frame 28.
In this embodiment, the intermediate rolling wheels 24 which are disposed between the front rolling wheels 20 and the rear rolling wheels 22 are pivotally supported by the projecting portion 72A' of the bottom portion 72A in t~e above-described fixed frame 72 by means of bearings 74.
That is, this embodiment is characterized in that a pair of the intermediate rolling wheels 24 disposed between the front rolling wheels 20 and the rear rolling wheels 22 are provided as a single unit, and that the intermediate rolling wheels 24 together with the swingable frame 76 are pivotally supported by making use of the bottom portion 72A of the fixed frame 72.
It should be noted that although the shape of the swingable frame 76 is slightly altered in the light of the above-described arrangement, the function of the swingable frame 76 is similar to that of the swingable frame 30 in accordance with the first embodiment.
In accordance with the above-described arrangement, since all the arrangements adopted in the above-described first embodiment are provided, it is possible to obtain the operation and advantages similar to those of the first embodiment. Namely, in accordance with this èmbodiment as well, it is possible to minimize (i.e., eliminate) the amount of forward or rearward projection of the front rolling wheels 20 or the rear rolling wheels 22 when the swingable frame 76 swings.
In addition, in accordance with this embodiment, since the arrangement provided is such that the pair of the intermediate rolling wheels 24 as a single unit are disposed between the front rolling wheels 20 and the rear rolling wheels 22, as compared with the case where two pairs of the intermediate rolling wheels 24 are juxtaposed in the longitudinal direction of the vehicle, it is possible to make the crawler unit 70 compact in the longitudinal direction of the vehicle. For this reason, a segment P' which connects the front rolling shaft 46 and the rear rolling shaft 48 becomes shorter than the segment P shown in the above-described first embodiment. Accordingly, the deformation of the shape of the crawler when the swingable frame 76 swings becomes small as a whole, so that the possibility of interference with a vehicle body-side component member such as a wheel housing is eliminated more positively. For this reason, it is possible to further reduce the tire installation spaces 14. In this context, the crawler unit 70 in accordance with this embodiment is generally suitable for a passenger vehicle and the like having a smaller wheel housing than the crawler vehicle 10 of the RV type shown in Fig. 3.
Further, in accordance with this embodiment, not only can the number of intermediate rolling wheels 24 installed be reduced, but also the bottom portion 72A of the fixed frame 72 can also be used as the rolling center axis of the intermediate rolling wheels 24, so that it becomes unnecessary to separately provide the rolling center axis.
For this reason, it is possible to further reduce the number of parts used, thereby contributing to a reduction in cost.
It should be noted that although, in the above-described embodiments, the intermediate rolling wheels 24 are disposed between the front rolling wheels 20 and the rear rolling wheels 22, the intermediate rolling wheels 24 may not necessarily be disposed. For instance, instead of the intermediate rolling wheels 24, an urging means, such as a leaf spring in which a ball is rollably accommodated at a top of its curved portion, may be disposed on the swingable frame 30 or 76 so as to ensure the safety of the bottom portion 26A for forming the tread of the crawler 26.
Next, referring to Figs. 9 to 17, a description will be given of a crawler unit 130 in accordance with a third embodiment. In addition, the same component parts as those of the above-described first and second embodiments will be denoted by the same reference numerals, and a description thereof will be omitted.
As shown in Figs. 9 and 10, an outer fixed frame member 132 is pivotally supported at an upper end of the distal end portion 32A of the drive shaft 32 by means of the bearing 44. A substantially hollow cylindrical drive-shaft accommodating portion 134 is formed at an upper end of the outer fixed frame member 132, and the distal end portion 32A

of the drive shaft 32 is accommodated in the drive-shaft accommodating portion 134. The outer fixed frame member 132 in a side view is formed substantially in the shape of a wedge substantially from its longitudinally central portion to its lower end, and holes 136 and 138 are formed therein.
As a result, an attempt is thereby made to make the outer fixed frame member 132 lightweight.
Supporting bolts 146, 148, and 150 having external threads 152 formed at only their tip portions are inserted in supporting holes 140 and 142 which are formed substantially in a vehicle vertical direction center of the outer fixed frame member 132 at vehicle front and rear side positions thereof, and in a supporting hole 144 which is formed at a lower end of the outer fixed frame member 132, in such a manner as to be inserted from the vehicle transverse direction outer side toward the inner side (in the leftward direction in the plane of the drawing in Fig.
10). Further, an inner fixed frame member 154 is secured to the external threads 152 of the supporting bolts 146, 148, and 150 by means of nuts 156 in such a manner as to become parallel with the outer fixed frame member 132. Thus, a fixed frame 158 having a function similar to that of the fixed frame 28 in accordance with the first embodiment is constituted by the outer fixed frame member 132, the supporting bolts 146, 148, and 150, and the inner fixed frame member 154.
An engaging member 160 is fixed to an upper end of the inner fixed frame member 154 by means of a bolt. The engaging member 160 is engaged with the drum brake 36 for braking the driving wheel or the vehicle bod~7, and renders the fixed frame 158 unswingable with respect to the vehicle body.
A pair of torsion bushes 162, which serve as a rotation controlling means and are formed integrally with a swingable frame 168 (which will be described later) at widthwise opposite side positions of the swingable frame 168, are secured to a portion of the supporting bolt 150 located between the outer fixed frame member 132 and the inner fixed frame member 154 (i.e., a portion where the external thread 152 is not formed). As also shown in Fig. 12, each torsion bush 162 is comprised of rubber 164 formed in a substantially hollow cylindrical shape and an outer cylinder 166 secured to an outer periphery of the rubber 164. The supporting bolt 150 is inserted in the hollow portion of the rubber 164 and is secured thereto.
When the supporting bolt 150 and the outer cylinders 166 relatively rotate in the circumferential directions (i.e., undergo twistins), shearing forces in opposite directions respectively act in the circumferential directions on the inner peripheral surface and outer peripheral surface of the rubber 164. Here, the rubber 164 has an elastic characteristic which is shown by a curve L1 in Fig. 13. (In Fig. 13, the abscissa shows the angle of displacement between the inner peripheral surface and the outer peripheral surface, while the ordinate shows the elastic force of the rubber 164, as being "+" in a case where the outer peripheral surface has rotated clockwise in Fig. 10 with respect to the inner peripheral surface, and as being "-" in a case where it has rotated counterclockwise, respectively.) Namely, the greater the relative rotational difference between the inner peripheral surface and the outer peripheral surface of the rubber 164, the greater the elastic force acting nonlinearly in the direction in which this rotational difference is overcome. For this reason, with respect to the relative rotation of the supporting bolt 150 and the outer cylinders 166, the greater this rotational difference, the greater resistance acts, so that the rotation is suppressed. (It should be noted that, in Fig.
13, the relationship between the amount of torsion in a case where a bearing is used and frictional resistance with respect to this torsion is shown by a straight line L2. As can be appreciated from this straight line L2, in the case of the bearing, the frictional resistance of the bearing with respect to this torsion is fixed irrespective of a change in the amount of torsion.) In addition, due to the internal resistance of the rubber 164, the rubber 164 has an attenuating component shown by a shaded portion D in Fig. 13. When relative rotation at a high angular velocity has occurred between the inner peripheral surface and the outer peripheral surface of the rubber, a large resistance acts with respect to this rotation due to this attenuating component, thereby suppressing the rotation.
The swingable frame 168 formed integrally with the pair of torsion bushes 162 is disposed between the torsion bushes 162, and the supporting bolt 150 is inserted in an insertion hole 170 formed in the swingable frame 168. Accordingly, the swingable frame 168 is swingably pivotally supported by the fixed frame 158 by means of the supporting bolt 150 and the torsion bushes 162. The large swinging motion at a high angular velocity of the swingable frame 168 about the supporting bolt 150 is suppressed by the elasticity of the rubber 164.
The swingable frame 168 in a side view is formed to be substantially elongated, and its upper surface is gradually inclined downward and tapered substantially from a vehicle longitudinal direction center toward a front end. In addition, the swingable frame 168 is bent obtusely upward at a position substantially intermediate between its center and its rear end.
As shown in Fig. 11, a shaft hole 171 is formed in the thicknesswise direction (i.e., in the left-and-right direction in Fig. 11) in the rear end of the swingable frame 168, and a supporting shaft 174 is inserted in the shaft hole 171 via a bearing 172. A pair of disk-shaped mounting plate portions 176 are formed at opposite ends of the supporting shaft 174, and a pair of metallic wheels 180 are respectively mounted on the mounting plate portions 176 by bolts 178.
Each wheel 180 is integrally formed of a disk 182 formed in the shape of a disk, a hollow cylindrical rim 184 extending from an outer periphery of the disk 182 toward both sides in the thicknesswise direction of the disk 182, and an annular guide disk 186 extending radially outward from a swingable frame-side end of the rim 184. A plurality (four in this embodiment) of mounting holes are formed in the disk 182, and the wheel 180 is mounted on the mounting plate portion 176 by inserting the bolts 178 into the mounting holes, respectively.
A pair of tires 188 serving as the rear rolling wheels are each mounted around an outer periphery of the rim 184 coaxially with the wheel 180, and the tire 188 and the wheel 180 rotate as a unit. Each tire 188 is formed of rubber, -its interior is inflated with air into the shape of a bag, and it is formed in an annular shape as a whole. The outer periphery of the tire 188 abuts against the inner periphery of the crawler 26 for substantially forming an isosceles triangle around which the crawler 26 is wound, and supports the load from the road surface.
The guide disk 186 is formed with a smaller diameter than that of the tire 188, and a predetermined gap which is shorter than the height of the protrusion 38 is formed between the guide disk 186 and the inner surface of the crawler 26. The axial lengths of the supporting shaft 174 and the rim 184 are determined such that a predetermined gap will be produced also between the guide disk 186 and the protrusion 38 of the crawler 26. Accordingly, the two guide disks 186 are disposed in face-to-face relation to each other with a predetermined interval with the protrusion 38, and are located on the widthwise opposite end sides of the protrusion 38. As a result, during the normal traveling, the guide disk 186 does not come into contact with the inner peripheral surface and the protrusion 38 of the crawler 26, but depending on the road condition and the like, when the crawler 26 undergoes relative movement with respect to the tire 188 in the axial direction of the supporting shaft 174, the protrusion 38 comes into contact with the guide disk 186, thereby restricting the relative movement within a fixed range.
A projecting shaft 190 is provided at a front end portion (i.e., a vehicle front side end portion) of the swingable frame 168 in such a manner as to project outwardly in the thickness direction (toward this side in the plane of the drawing in Fig. 9). This projecting shaft 190 is inserted in a shaft hole 194 formed at a lower end of a supporting arm 192, so that the supporting arm 192 is rotatable.
The supporting arm 192 in a side view is formed substantially in the shape of an isosceles triangle, and the front rolling wheels constituted by a pair of tires 196 are pivotally supported at its front end portion (i.e., a vehicle front side end portion) by a pivotally supporting structure similar to the pivotally supporting structure of the rear rolling wheels. Namely, as shown in Fig. 14, a supporting shaft 174 is rotatably inserted in the shaft hole 170, which is formed in the thicknesswise direction in the front end of the supporting arm 192, via the bearing 172.
The disk 182 of each wheel 180 is mounted on the mounting plate portion 176, which is provided at opposite ends of the supporting shaft 174, by means of the bolts 178. Further, the tire 196 similar to the tire 188 is coaxially mounted around the rim 184 of the wheel 180, thereby constituting the front rolling wheel. The outer periphery of the tire 196 abuts against the inner periphery of the crawler 26 for substantially forming the isosceles triangle around which the crawler 26 is wound, and supports the load from the road surface.
The guide disk 186 of the wheel 180 of the front rolling wheel is also formed with a smaller diameter than that of the tire 196 in the same way as the wheel 180 of the rear rolling wheel, and a predetermined gap which is shorter than the height of the protrusion 38 is formed between the guide disk 186 and the inner surface of the crawler 26.
Also, the axial lengths of the supporting shaft 174 and the rim 184 are determined such that a predetermined gap will be produced also between the guide disk 186 and the protrusion 38 of the crawler 26. When the crawler 26 undergoes relative movement with respect to the tire 196 in the axial direction depending on the road condition and the like, the protrusion 38 comes into contact with the guide disk 186, thereby restricting the relative movement of the crawler 26 with respect to the tire 196 within a fixed range.
A supporting plate 198 is provided in such a manner as to project upward from an upper surface of the longitudinally intermediate portion of the swingable frame 168. An internally threaded hole 200 is formed in the supporting plate 198 along the longitudinal direction of the -vehicle, and an adjusting bolt 202 is inserted in the internally threaded hole 200 from the vehicle rear side toward the front side. As a result, the adjusting bolt 202 is movable in the transverse direction of the vehicle. In addition, this movement toward the front side is restricted as a nut 204 serving as a double nut threadedly engaged with the adjusting bolt 202 abuts against the supporting plate lg8 .
A pin 205 is provided at a distal end of the adjusting bolt 202 in such a manner as to project substantially horizontally in its radially outward direction. A pressing plate 206 is pivotally supported by the pin 205. A front surface 206A of the pressing plate 206 is in plane contact with a rear surface 192A of the supporting arm 192, and maintains the supporting arm 192 in a predetermined position against the clockwise rotating force, shown in Fig. 9, to which the supporting arm 192 is subjected from the elastically depressed tires 196 with the crawler 26 of a predetermined length wound therearound. Then, as shown by the two-dotted dash lines in Fig. 9, when the adjusting bolt 202 is rotated to move the supporting arm 192 in the longitudinal direction of the vehicle, the supporting arm 192 rotates about the projecting shaft l90, with the result that the position of the tires 196 changes (in Fig. 9, the tires 196 are moved in the rearward direction of the vehicle by moving the supporting arm 192 in the rearward direction of the vehicle). Consequently, a predetermined winding length adjusted to the crawler 26 is formed by the driving wheel 18, the tires 188 (rear rolling wheels), and the tires 196 (front rolling wheels). Thus, by setting the amount of depression of the tires 196 to a fixed level, it is possible to make fine adjustment of the tension of the crawler 26, so that the crawler 26 can be wound with a predetermined tension. Incidentally, the supporting plate 198, the adjusting bolt 202, the nut 204, and the pressing plate 206 constitutes a tension adjusting means.
In addition, since the swingable frame 168 and the supporting arm 192 are arranged as described above, in the same way as in the first embodiment, the swinging center axis (supporting bolt 150) of the swingable frame 168 is disposed in a region below a segment P" which connects the rolling center axes (vehicle front and rear side shafts 174) of the tires 188 and 196. Further, a segment R" which connects the supporting bolt 150 and the front and rear shafts 174 is substantially horizontal in a side view. More specifically, the supporting bolt 150 is offset downward by a predetermined distance from the segment P" which connects the front and rear shafts 174.
A collar 208 formed of a resin into a hollow cylindrical shape and serving as a swinging-angle restricting member is fitted around a central portion (a portion where the external thread 152 is not formed) of the supporting bolt 146 on the vehicle front side in such a manner as to be disposed coaxially with the supporting bolt 146 and rotatably therewith. When the swingable frame 168 is swung clockwise in Fig. 9 about the supporting bolt 150 against the elastic force of the rubber 164 of the torsion bushes 162 and the resisting force of a damper member 212 which will be described later, the tires 196 are brought into contact with the collar 208 after the swingable frame 168 has swung by a fixed angle, thereby restricting the swinging motion. Since the tires 196 are made of rubber which is elastically deformable, even if the tires 196 are forcibly brought into contact with the collar 208, the tires 196 undergo elastic deformation, thereby dampening the impact. For this reason, it is unnecessary to rigidly form the collar 208 and the supporting bolt 146 by taking this impact into consideration, and an input of a strong impact against the fixed frame 158 is reduced, thereby improving the durability of the fixed frame 158. In addition, the impact sound at a time when the tires 196 are brought into contact with the collar 208 is also alleviated.
Since the collar 208 is rotatable, when the rotating tires 196 are brought into contact with the collar 208, the collar 208 also rotates due to the force of friction with the tires 196. As a result, since the tires 196 and the collar 208 do not rub against each other, the wear and the damage of the tires 196 are prevented. In addition, frictional sound does not occur, either.
A hollow cylindrical collar 210 formed of a resin is also fitted coaxially and rotatably around a central portion (a portion where the external thread 152 is not formed) of the supporting bolt 148 on the vehicle rear side. This collar 210 is split into two parts at its axial center, and a tubular portion 214 of the damper member 212 serving as a swinging suppressing means is rotatably fitted around a portion of the supporting bolt 148 between the split portions of the collar 210.
As also shown in Fig. 15, the damper member 212 is comprised of a piston rod 216 projecting radially outward from the tubular portion 214 and a cylinder 218 into which the piston rod 216 is inserted. A viscous fluid is sealed in the cylinder 218, and the axial movement of the piston rod 216 receives a resisting force due to the viscous resistance of this viscous fluid. In addition, a distal end of the cylinder 218 is fixed to an upper surface of the swingable frame 168. Accordingly, the damper member 212 extends between the fixed frame 158 and the swingable frame 168.

When the swingable frame 168 tends to swing clockwise or counterclockwise in Fig. 9 about the supporting bolt 150 against the elastic force of the rubber 164 of the torsion bushes 162, this swinging motion is suppressed by the viscous resistance of the viscous fluid in the cylinder 218 of the damper member 212. When the swingable frame 168 ~-swings counterclockwise by a fixed angle about the supporting bolt 150 against the elastic force of the rubber 164 and the resisting force of the viscous fluid, the tires 188 are brought into contact with the collar 210, thereby restricting the swinging motion. Even if the tires 188 are forcibly brought into contact with the collar 210, the tires 188 undergo elastic deformation, thereby dampening the impact. For this reason, it is unnecessary to rigidly form the collar 210 and the supporting bolt 146 by taking this impact into consideration, and an input of a strong impact against the fixed frame 158 is reduced, thereby improving the durability of the fixed frame 158. In addition, the impact sound at a time when the tires 188 are brought into contact with the collar 210 is also alleviated. When the rotating tires 188 are brought into contact with the collar 210, the collar 210 also rotates due to the force of friction with the tires 188. As a result, since the tires 188 and the collar 210 do not rub against each other, the CA 02214474 1997-09-ll wear and the damage of the tires 188 are prevented. In addition, frictional sound does not occur, either.
Next, a description will be given of the operation in accordance with this embodiment.
As shown in Fig. 9, the crawler 26 in a side view is wound into the shape of an isosceles triangle around the driving wheel 18, the tires 196 serving as the front rolling wheels, and the tires 188 serving as the rear rolling wheels. Here, by rotating the adjusting bolt to change the position of the tires 196, a predetermined winding length adjusted to the crawler 26 is formed by the driving wheel 18, the tires 196, and the tires 188, whereby the fine adjustment of the tension of the crawler 26 can be made.
That is, even if variations have occurred in the amount of elastic deformation of the rubber-made tires 196 and 188 due to variations in the actual length of the crawler 26, and the winding length of the crawler 26 (i.e., the winding length of the crawler 26 which is formed by the driving wheel 18, the tires 196, and the tires 188) has changed, the changing of the position of the tires 196 makes it possible to fix the amount of elastic deformation of the tires 196 and 188 and allow the winding length o~ the crawler 26 to agree with the actual length of the crawler 26, thereby making it possible to wind the crawler 26 with appropriate tension.

When the crawler 26 circulates upon receiving the driving force from the driving wheel 18, the crawler vehicle (see Fig. 3) travels. When the crawler vehicle travels on a road surface having irregularities, since the swingable frame 168 swings by using the supporting bolt 150 as the swinging center axis as shown in Fig. 16 or 17, the area of contact of the crawler 26 with the road surface increases, so that stable traveling can be maintained. Since the supporting bolt 150 which is the swinging center axis of the swingable frame 168 is located below the drive shaft 32, even in a case where the crawler units 130 are mounted in ordinary tire installation spaces, it is possible to provide a large installation area for the crawlers 26 without causing the crawlers 26 and the tires 196 and 188 to interfere with vehicle body-side component members.
Moreover, it is unnecessary to provide stoppers and the like for preventing the interference with the vehicle body.
Furthermore, since the supporting bolt 150 is disposed in a region below the segment P" which connects the rolling center axes (supporting shafts 174) of the tires 196 and 188, in a case where a load oriented from the front side toward the rear side is inputted to the vehicle front side supporting shaft 174 when riding over a bump on the road surface, a component force for displacing that support shaft 174 rearwardly upward occurs. On the other hand, in a case -where a load oriented from the rear side toward the front side is inputted to the vehicle rear side supporting shaft 174, a component force for displacing that support shaft 174 forwardly upward occurs. As a result, it is possible to eliminate the amount of forward or rearward projection of the tires 196 and 188 and the crawler 26 when the swingable frame 268 has swung.
Here, if the front and rear rolling wheels are formed of a material which is not elastically deformable, such as a metal, when the swingable frame 168 has swung in the above-described manner, and the shape of the crawler has assumed that of a triangle excluding an isosceles triangle as shown in Fig. 16 or 17, the winding length of the crawler 26 becomes shorter than the actual length of the crawler 26.
Accordingly, there is a possibility that, due to the slackening of the crawler 26, the teeth of the driving wheel 18 may become disengaged from the recessed portion of the crawler 26, and the crawler 26 may be disengaged from the crawler unit 130. However, with the crawler unit in accordance with this embodiment, since the front rolling wheels are constituted by the tires 196 and the rear rolling wheels by the tires 188, as the tires 196 and 188 undergo elastic deformation (more specifically, as the depressions are recovered), it is possible to absorb the change in the winding length of the crawler 26 and cause the winding length to agree with the actual length of the crawler 26.
For this reason, the crawler 26 is wound with appropriate tension, so that the teeth of the driving wheel 18 are prevented from becoming disengaged from the recessed portion of the crawler 26, and the crawler 26 is prevented from becoming disengaged from the crawler unit 130. In addition, by merely providing the arrangement in which the front rolling wheels are constituted by the tires 196 and the rear rolling wheels by the tires 188, it is possible to demonstrate the above-described operation (the absorption of the change in the winding length of the crawler 26 due to the swinging motion of the swingable frame 168), so that the number of parts used does not increase, and the structure does not become complex.
The swinging motion of the swingable frame 168 is suppressed by the elastic force of the rubber 164 constituting the torsion bushes 162 and the resisting force of the viscous fluid constituting the damper member 212. In particular, since the rubber 164 has an elastic characteristic in which its elastic force becomes large nonlinearly, as shown by the curve Ll in Fig. 13, large swinging motion of the swingable frame 168 can be suppressed. In addition, since the rubber 164 has the attenuating component D shown in Fig. 13, the swinging motion at a high angular velocity of the swingable frame 168 can be suppressed.
Further, in the case where the front rolling wheels are constituted by the tires 196 and the rear rolling wheels by the tires 188 as in the crawler unit 130 in accordance with this embodiment, since the elastic constants of the tires 196 and 188 are low, a spring-mass system in which the tires 196 and 188 act as springs is constituted by the tires 196 and 188 and the swingable frame 168. For this reason, when the crawler unit 130 passes irregularities on the road surface or when the vehicle accelerates or decelerates, the swingable frame 168 tends to vibrate with low frequencies having a resonance point. Even in this case, however, the damper member 212 suppresses the vibrations, so that the vibrations settle down in a short period of time.
Therefore, the vibration of the swingable frame 168 and the swaying of the overall vehicle due to this vibration can be suppressed.
In addition, since the swingable frame 168 is pivotally supported by the fixed frame 158 by using the torsion bushes 162 to disuse the bearing, the supporting structure of the swingable frame 168 is simplified. Moreover, since it is unnecessary to provide a hermetic seal which is generally provided in the case where the bearing is used, the structure is further simplified, thereby making it possible to reduce the manufacturing cost. Since the bearing is not used, foreign substances such as water, sand, and the like do not enter the bearing, so that the reliability and durability of the crawler unit 130 improves.
In the case where the swingable frame 168 has swung clockwise by a large degree, the tires 196 come into contact with the collar 208 as shown in Fig. 16, so that further swinging motion is prevented. Since the tires 196 are made of rubber, even if the tires 196 are forcibly brought into contact with the collar 208, the tires 196 undergo elastic deformation to alleviate the impact, so that an input of a strong impact against the fixed frame 158 is reduced.
Consequently, the durability of the fixed frame 158 improves, and the impact sound is also alleviated. It is unnecessary to rigidly form the fixed frame 158 by taking the input of this impact into consideration.
On the other hand, in the case where the swingable frame 168 has swung further counterclockwise by a large degree, the tires 188 come into contact with the collar 210, so that further swinging motion is prevented. Since the tires 188 are made of rubber, the impact can be alleviated, so that an input of a strong impact against the fixed frame 158 is reduced. Consequently, the durability of the fixed frame 158 improves, and the impact sound is also alleviated.

In the case where the crawler unit 130 has impulsively hit against a bump on the road surface, the tires 196 undergo elastic deformation to absorb this load, so that the load acting on the vehicle body becomes small. For this reason, it becomes unnecessary to increase the strength of the vehicle body by taking a large load into consideration.
Also, the riding comfort improves.
When a force acts on the crawler 26 in its widthwise direction (in the axial direction of the drive shaft 32), the crawler 26 undergoes relative movement with respect to the tires 196 and 188, but since the guide disk 186 abuts against the protrusion 38, this movement is restricted.
Consequently, since the tires 196 and 188 are prevented from riding over the protrusion 38, it is possible to prevent the damage, lateral offset, and disengagement of the crawler 26.
It should be noted that although, with the crawler unit 130 in accordance with the third embodiment, the arrangement provided is such that both the torsion bushes 162 and the damper member 212 are provided, either one of them may be provided insofar as it is capable of suppressing the large swinging motion and fast swinging motion of the swingable frame 168.
In addition, the tires 196 constituting the front rolling wheels and the tires 188 constituting the rear rolling wheels need not be the above-described pneumatic tires, and if the tires are elastically deformable and are formed in an annular shape, the material and the structure are not particularly restricted. For instance, it is possible to use all rubber tires which are not formed in the shape of a bag and their interiors are also formed of rubber. In addition, either the front rolling wheels or the rear rolling wheels are formed of elastically deformable rubber and are formed in an annular shape, such rolling wheels undergo elastic deformation during the swinging of the swingable frame 168, and the winding length of the crawler 26 can be made to agree with the actual length of the crawler 26.
Further, the collars 208 and 210 may not necessarily be fitted around the supporting bolts 146 and 148, and suffice if they are attached at positions where they do not swing with the swingable frame 168 even if the swingable frame 168 has swung. For example, shaft members are provided so as to project directly from the vehicle body outwardly in the transverse direction of the vehicle, the collars 208 and 210 are rotatably mounted on the shaft members, such that the collars 208 and 210 come into contact with the tires 196 and 188 during the swinging of the swingable frame 168, thereby restricting the swinging motion. In addition, in order to restrict the swinging angle of the swingable frame 168 within a fixed range, the rotatable collars 208 and 210 may not necessarily be provided as the swinging-angle restricting members, and it is possible to use unrotatable members (e.g., rod members, blocks, etc.).
In addition, in the above-described embodiments, insofar as the arrangement is provided such that the bottom portion 28A, 72A, or the supporting bolt 150 serving as the swinging center axis in a side view is disposed in a region below the segment P, P', or P", which connects the front rolling shaft 46 (in the third embodiment, the supporting shaft 174 of the vehicle front side tires 196) of the front rolling wheels 20 and the rear rolling shaft 48 (in the third embodiment, the supporting shaft 174 of the vehicle rear side tires 188) of the rear rolling wheels 22 (i.e., the arrangement in which the segment R, R', or R", which connects the three axes, i.e., the front rolling shaft 46 (or the tires 196), the rear rolling shaft 48 (or the tires 188), and the swinging center axis (the bottom portion 28A, 72A, or the supporting bolt 150) of the swingable frame 30, 76, or 168, is accommodated between the segment P, P', or P"
and the bottom portion 26A of the crawler 26, 72A, or the supporting bolt 150), it is possible to adopt all such arrangements. Parenthetically speaking, although the relationship of layout of the respective shafts should be essentially arranged as described above, even if an arrangement is adopted such that the swinging center axis is actually located slightly above the segment P, P', or P", it is conceivably possible to obtain the advantage of reducing the amount of projection as compared with the conventional structure. Hence, the arrangement includes that extent in the present invention.
In addition, the rubber members 31 in accordance with the first embodiment may be provided on the crawler unit 70 in accordance with the second embodiment or on the crawler unit 130 in accordance with the third embodiment. In particular, in the case where the rubber members 31 are provided on the crawler unit 130 in accordance with the third embodiment, the tires 196 come into contact with the collar 210, and the upper surface of the swingable frame 168 comes into contact with the rubber member 31. Hence, even if the swingable frame 168 has forcibly swung, the angle of this swinging can be reliably restricted to a fixed range.

Claims

1. A crawler vehicle comprising:
a driving wheel fixed to a drive shaft which is rotatively driven by receiving a driving force, said driving wheel being adapted to rotate with said drive shaft;
a front rolling wheel and a rear rolling wheel which are arranged at positions lower than said driving wheel in a longitudinal direction of a vehicle, respectively;
a crawler wound around said driving wheel, said front rolling wheel, and said rear rolling wheel, and adapted to move in a winding direction as said driving wheel rotates;
a fixed frame supported by a vehicle body in a state of being unrotatable about said drive shaft, said fixed frame being adapted to pivotally support said drive shaft; and a swingable frame for interconnecting said front rolling wheel and said rear rolling wheel and for pivotally supporting said front rolling wheel and said rear rolling wheel, said swingable frame being connected swingably to said fixed frame such that a swinging center axis of said swingable frame is located below said drive shaft.

2. A crawler vehicle according to claim 1, wherein the swinging center axis of said swingable frame in a side view is disposed in a region below a segment connecting a rolling center axis of said front rolling wheel and a rolling center axis of said rear rolling wheel.

3. A crawler vehicle according to claim 1, further comprising:
an intermediate rolling shaft disposed between said front rolling wheel and said rear rolling wheel such that a position of a rolling center of said intermediate rolling wheel and a position of a swinging center of said swingable frame coincide with each other.

4. A crawler vehicle according to claim 1, wherein said fixed frame is provided in such a manner as to be supported by said drive shaft on both sides of said driving wheel in a thicknesswise direction thereof.

5. A crawler vehicle according to claim 1, wherein at least one of said front rolling wheel and said rear rolling wheel is formed in an annular shape permitting elastic deformation in a radial direction.

6. A crawler vehicle according to claim 5, further comprising:
a restricting member for restricting a swinging angle of said swingable frame within a fixed range by coming into contact with at least one of said front rolling wheel and said rear rolling wheel formed in the annular shape permitting elastic deformation.

7. A crawler vehicle according to claim 6, wherein said restricting member is a rotary member disposed rotatably about a shaft parallel with a center of rotation of the contacting one of said front rolling wheel and said rear rolling wheel.

8. A crawler vehicle according to claim 1, further comprising:
a contacting member provided on said fixed frame and adapted to restrict a swinging angle of said swingable frame within a fixed range by coming into contact with said swingable frame.

9. A crawler vehicle according to claim 1, further comprising:
rotation controlling means formed integrally with said swingable frame and adapted to control relative rotation of said swingably rotating shaft of said swingable frame and said swingable frame.

10. A crawler vehicle according to claim 1, further comprising:
swinging-motion suppressing means provided in such a manner as to be connected to said fixed frame and said swingable frame and adapted to suppress the swinging motion of said swingable frame.

11. A crawler vehicle according to claim 5, further comprising:
tension adjusting means provided on said swingable frame and adapted to adjust the tension of said crawler by pressing one of said front rolling wheel and said rear rolling wheel.

12. A crawler vehicle comprising:
a driving wheel fixed to a drive shaft which is rotatively driven by receiving a driving force, said driving wheel being adapted to rotate with said drive shaft;
a front rolling wheel and a rear rolling wheel which are arranged at positions lower than said driving wheel in a longitudinal direction of a vehicle, respectively;
a crawler wound around said driving wheel, said front rolling wheel, and said rear rolling wheel, and adapted to move in a winding direction as said driving wheel rotates;
a fixed frame supported by a vehicle body in a state of being unrotatable about said drive shaft, said fixed frame being adapted to pivotally support said drive shaft;
a swingable frame for interconnecting said front rolling wheel and said rear rolling wheel and for pivotally supporting said front rolling wheel and said rear rolling wheel, said swingable frame being connected swingably to said fixed frame such that a swinging center axis of said swingable frame is located below said drive shaft, wherein the swinging center axis of said swingable frame in a side view is disposed in a region below a segment connecting a rolling center axis of said front rolling wheel and a rolling center axis of said rear rolling wheel; and an intermediate rolling shaft disposed between said front rolling wheel and said rear rolling wheel such that a position of a rolling center of said intermediate rolling wheel and a position of a swinging center of said swingable frame coincide with each other.

13. A crawler vehicle according to claim 12, wherein said fixed frame is provided in such a manner as to be supported by said drive shaft on both sides of said driving wheel in a thicknesswise direction thereof.

14. A crawler vehicle according to claim 12, further comprising:
a contacting member provided on said fixed frame and adapted to restrict a swinging angle of said swingable frame within a fixed range by coming into contact with said swingable frame.

15. A crawler vehicle according to claim 12, wherein said intermediate rolling wheel is provided such that its rolling center axis and the swinging center axis of said swingable frame become identical.

16. A crawler vehicle comprising:
a driving wheel fixed to a drive shaft which is rotatively driven by receiving a driving force, said driving wheel being adapted to rotate with said drive shaft;
a front rolling wheel and a rear rolling wheel which are arranged at positions lower than said driving wheel in a longitudinal direction of a vehicle, respectively, at least one of said front rolling wheel and said rear rolling wheel being formed in an annular shape permitting elastic deformation in a radial direction;
a crawler wound around said driving wheel, said front rolling wheel, and said rear rolling wheel, and adapted to move in a winding direction as said driving wheel rotates;
a fixed frame supported by a vehicle body in a state of being unrotatable about said drive shaft, said fixed frame being adapted to pivotally support said drive shaft; and a swingable frame for interconnecting said front rolling wheel and said rear rolling wheel and for pivotally supporting said front rolling wheel and said rear rolling wheel, said swingable frame being connected swingably to said fixed frame such that a swinging center axis of said swingable frame is located below said drive shaft, wherein the swinging center axis of said swingable frame in a side view is disposed in a region below a segment connecting a rolling center axis of said front rolling wheel and a rolling center axis of said rear rolling wheel.

17. A crawler vehicle according to claim 16, wherein said fixed frame is provided in such a manner as to be supported by said drive shaft on both sides of said driving wheel in a thicknesswise direction thereof.

18. A crawler vehicle according to claim 16, further comprising:
a restricting member for restricting a swinging angle of said swingable frame within a fixed range by coming into contact with at least one of said front rolling wheel and said rear rolling wheel formed in the annular shape permitting elastic deformation.

19. A crawler vehicle according to claim 18, wherein said restricting member is a rotary member disposed rotatably about a shaft parallel with a center of rotation of the contacting one of said front rolling wheel and said rear rolling wheel.

20. A crawler vehicle according to claim 16, further comprising:
a torsion bush formed integrally with said swingable frame and adapted to control relative rotation of said swingably rotating shaft of said swingable frame and said swingable frame.

21. A crawler vehicle according to claim 20, further comprising:
a damper member provided in such a manner as to be connected to said fixed frame and said swingable frame and adapted to suppress the swinging motion of said swingable frame.

22. A crawler vehicle according to claim 16, further comprising:
tension adjusting means provided on said swingable frame and adapted to adjust the tension of said crawler by pressing one of said front rolling wheel and said rear rolling wheel.