Abstract:
A suspension device for motor driven vehicles such as snowmobiles comprises a pair of slide rails which are resiliently suspended under the vehicle body to ensure engagement of the ground-engaging portion of a flexible endless track with the ground, the endless track being driven by a drive sprocket wheel journalled on the front portion of the vehicle body and stretched at its rear portion over rear idler wheels journalled on the rear portions of the slide rails. The resiliency of the suspension device is adjusted to prevent skidding of the rear portion of the endless track.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a suspension device for motor driven vehicles such as snowmobiles or tractors having an endless track driven by power taken from the vehicle engine by means of a sprocket wheel located on the front portion of the vehicle body, and more particularly to an improved suspension device of a type including a pair of slide rails which are resiliently suspended under the vehicle body to ensure good engagement of the lower or ground-touching face of the endless track with the ground and journal at the rear ends thereof a supporting shaft of idler wheels for the endless track located on the rear portion of the vehicle body. 
     SUMMARY OF THE INVENTION 
     The prime object of the present invention is to provide a suspension device for a snowmobile, wherein a pair of slide rails suspended under the body of the snowmobile are well prevented from skidding at the rear portion of an endless track when the snowmobile makes turns at various speeds under various road conditions. 
     Another object of the present invention is to provide a suspension device for a snowmobile, having the above-mentioned characteristics, wherein the suspension characteristics at the front portion of the endless track can easily be adjusted to maintain the pleasant and safe riding of the snowmobile under various road conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features that are considered to be characteristic of the present invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its construction and its mode of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the Figures. 
     In the drawings: 
     FIG. 1 is a schematic side view of a suspension device for a small snowmobile in accordance with the present invention; 
     FIG. 2 is a cross-sectional plan view taken on line 2 -- 2 of FIG. 1, with the body broken away for convenience of illustration; 
     FIG. 3 is an enlarged vertical cross-sectional view taken on line 3 -- 3 of FIG. 1; 
     FIG. 4 is an enlarged side view taken from line 4 -- 4 of FIG. 3; 
     FIG. 5 is a vertical cross-sectional side view taken on line 5 -- 5 of FIG. 6, showing an actual application of the suspension device in accordance with the present invention; 
     FIG. 6 is a plan view of the suspension device shown in FIG. 5, with the body portion broken away for convenience of illustration; and 
     FIG. 7 is an enlarged cross-sectional view taken on line 7 -- 7 of FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, particularly to FIGS. 1 and 2, an endless track 10 is stretched over a pair of front wheels 12, 12 located on the front portion of the vehicle body B and a pair of idler wheels 14, 14 located on the rear portion of the vehicle body B. The front wheels 12, 12 are secured on a drive shaft 11 journalled on the front portion of the vehicle body B and the rear idler wheels 14, 14 are secured on an idler shaft 13 journalled on the rear ends of a pair of slide rails 16, 16 which are provided longitudinally along the endless track 10. The drive shaft 11 is driven by the power taken from the vehicle engine by way of a drive sprocket wheel 15 secured at the center thereof. The slide rails 16, 16 are resiliently suspended under the vehicle body B by means of a suspension device 20 in accordance with the present invention. 
     The suspension device 20 comprises a pair of front arms 21, 21 journalled on the vehicle body B at the front ends thereof, a pair of rear arms 22, 22 swingably journalled on the vehicle body B, a pair of coiled springs 23, 23 interposed between the rear extensions of the front arms 21, 21 and the front extensions of the rear arms 22, 22 and a pair of torsion springs 24, 24 to normally bias the front arms 21, 21 downwardly. The slide rails 16, 16 are swingably connected to the intermediate portions of the front arms 21, 21 respectively at their substantial central portions. The slide rails 16, 16 are further connected swingably and telescopically to the rear ends of the rear arms 22, 22 at the rear portions thereof to prevent transverse movements of the rear portions of the slide rails 16. The swinging movements of the rear arms 22, 22 are restricted in the vertical direction. The coiled springs 23, 23 are to resiliently bias the front arms 21, 21 downwardly and forwardly and to bias the rear ends of the rear arms 22, 22 rearwardly and downwardly. Further referring to FIGS. 3 and 4, the coiled springs 23, 23 are forward-or-aft displaceably connected to the rear extensions of the front arms 21, 21 respectively at their lower ends and to the front extensions of the rear arms 22, 22 respectively at their upper ends thereby to adjust the biasing forces of the coiled springs 23, 23 respectively. 
     The operation of the above-constructed embodiment of the present invention is described hereinafter in detail. In the case to run the snowmobile under rough road conditions, the pleasant riding of the vehicle is secured by maintaining spring constant against pitching of the front ground-engaging portion of the endless track 10 to be lower than spring constant at the rear ground-engaging portion of the endless track 10. This is carried out by displacing forwardly the lower mounting positions of the coiled springs 23, 23 or by displacing rearwardly the swinging fulcrum of the front arms 21, 21. In this instance, the endless track 10 is well prevented from skidding at the rear portion thereof at turns of the snowmobile. 
     In high speed travelling of the snowmobile under regular road conditions, the lower mounting positions of the coiled springs 23, 23 are displaced rearwardly or the swinging fulcrum of the front arms 21, 21 are displaced forwardly to maintain the spring constant against pitching of the front ground-engaging portion of the endless track 10 to be higher than the spring constant at the rear ground-engaging portions of the endless track 10. This fully effects the driving power of the engine of the snowmobile for its high speed operation. In this instance, as in the case of the rough road running, the rear portions of the slide rails 16, 16 are well supported by the rear ends of the rear arms 22, 22 thereby to prevent the rear portion of the endless track 10 from skidding in high speed turns of the snowmobile. 
     In the above embodiment, the pair of coiled spring 23, 23 are adapted to give vertical urging force to the rear and front extensions respectively of the front and rear arms 21, 21 and 22, 22. These coil springs 23 may be assembled together with conventional oil dampers to ensure the pleasant riding of the snowmobile. 
     FIGS. 5 through 7 illustrate an actual application of the present invention, wherein the slide rails 16 and 16 are integrally connected in parallel to each other by way of transverse tubular connecting bars 31, 32 and a pivot shaft 33. The connecting tubular bar 31 is connected at its both ends with the front portions of the slide rails 16, 16 and connected also at its central portion by means of a connecting band 25 to an upper supporting shaft 34 journalled on the vehicle body B. The connecting tubular bar 32 and the pivot shaft 33 are integrally connected at the both ends thereof with the substantial central portions of the slide rails 16, 16 by way of a pair of brackets 35, 35 secured on the respective slide rails 16. The tubular bar 32 journalls a pair of bogie wheels 19, 19 through a shaft 19a provided therethrough. 
     In this application, the front arms 21, 21 are integrally connected to each other with a transverse tubular bar 36 and journalled at their both ends on the upper and lower supporting shafts 34 and 33 by way of tubular shafts 34a and 33a respectively. The rear extensions of the front arms 21, 21 are composed of a pair of U-shaped brackets 37, 37 secured on the tubular shaft 33a, and the front extensions of the rear arms 22, 22 are composed of a pair of U-shaped brackets 38, 38 secured on a transverse tubular shaft 39a which is journalled on a supporting shaft 39 mounted on the vehicle body B to support the rear arms 22, 22. The coiled springs 23, 23 are assembled together with respective oil dampers 23a, 23a which are respectively pivoted on the upper brackets 38 and the lower brackets 37 at the both ends thereof. 
     Although certain specific embodiments of the invention have been shown and described, it is obvious that many modifications thereof are possible. The invention, therefore, is not intended to be restricted to the exact showing of the drawings and description thereof, but is considered to include reasonable and obvious equivalents.