Snowmobile Skid Frame Assembly

Abstract

A skid frame for a snowmobile is disclosed including a generally planar skid surface extending between front and rear idler wheels. The front and rear idler wheel are offset from one another and define a longitudinal direction. A track encircles the skid frame having the skid surface positioned over a center of the track such that a major longitudinally extending portion of the track that is coextensive with the skid surface has first and second unsupported lateral portions on either side of the skid surface. The first and second unsupported lateral portions extend in the horizontal direction at least 25 percent of a width of the track. A suspension arm member may mount the skid rail and include mount portions for mounting to a tunnel and spanning a distance at least twice the width of the longitudinal beam.

What is claimed: 
     
         1 . A track system for a vehicle, the track system comprising:
 a skid frame assembly that includes a skid rail having a hollow portion, a front idler wheel, and a rear idler wheel, wherein the skid rail extends in a longitudinal direction and includes a wear strip, the wear strip extending along at least a portion of a bottom surface of the skid rail; and   a track encircling the skid frame assembly, the track having an inner slide surface and an outer surface that engages with the ground, wherein the track is pivotable relative to the skid rail about at least one longitudinally extending roll axis.   
     
     
         2 . The track system of  claim 1 , wherein an orientation of the track relative to the skid rail is defined by an uphill angle and a downhill angle, wherein the uphill angle is defined between the bottom surface of the skid rail and the inner slide surface of the track on a uphill side of the vehicle, wherein the downhill angle is defined between the bottom surface of the skid rail and the inner slide surface of the track on a downhill side of the vehicle. 
     
     
         3 . The track system of  claim 2 , wherein the track is substantially rigid in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is within ten degrees of the downhill angle. 
     
     
         4 . The track system of  claim 2 , wherein the track is substantially rigid in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is within five degrees of the downhill angle. 
     
     
         5 . The track system of  claim 2 , wherein the track is flexible in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is greater than the downhill angle. 
     
     
         6 . The track system of  claim 1 , wherein first and second portions of the track extend unsupported on either side of the wear strip in a horizontal direction perpendicular to the longitudinal direction. 
     
     
         7 . The track system of  claim 6 , wherein the first and second unsupported portions of the track extend from an edge of the wear strip to an outermost edge of the track and having an extent in the horizontal direction of at least 25 percent of a width of the track, wherein the first and second unsupported portions extend longitudinally from the front idler wheel to the rear idler wheel. 
     
     
         8 . The track system of  claim 1 , wherein the at least one longitudinally extending roll axis includes a first longitudinally extending roll axis and a second longitudinally extending roll axis. 
     
     
         9 . The track system of  claim 8 , wherein the first longitudinally extending roll axis and the second longitudinally extending roll axis are offset in a horizontal direction from a longitudinally extending centerline axis. 
     
     
         10 . A tracked vehicle comprising:
 a chassis;   at least one ski steerably secured to the chassis;   a skid frame assembly mounted to the chassis that includes a front idler wheel, a rear idler wheel, and a skid surface that extends in a longitudinal direction;   a track encircling the skid frame assembly, the skid surface positioned over the track and wherein the track has first and second unsupported lateral portions each extending in a horizontal direction transverse to the longitudinal direction from an edge of the skid surface to an outermost edge of the track, wherein the first and second unsupported lateral portions extends longitudinally from the front idler wheel to the rear idler wheel, and wherein an orientation of the track relative to the skid surface varies to maintain contact between the track and ground surface.   
     
     
         11 . The tracked vehicle of  claim 10 , wherein the orientation of the track relative to the skid surface is defined by an uphill angle and a downhill angle, wherein the uphill angle is defined between the skid surface and a slide surface of the track on a uphill side of the tracked vehicle, wherein the downhill angle is defined between the skid surface and the slide surface of the track on a downhill side of the tracked vehicle. 
     
     
         12 . The tracked vehicle of  claim 11 , wherein the track is substantially rigid in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is within ten degrees of the downhill angle. 
     
     
         13 . The tracked vehicle of  claim 11 , wherein the track is substantially rigid in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is within five degrees of the downhill angle. 
     
     
         14 . The tracked vehicle of  claim 11 , wherein the track is flexible in a horizontal direction perpendicular to the longitudinal direction, and wherein the uphill angle is greater than the downhill angle. 
     
     
         15 . The tracked vehicle of  claim 10 , wherein the first and second unsupported lateral portions of the track have an extent in the horizontal direction of at least 25 percent of a width of the track. 
     
     
         16 . A tracked vehicle comprising:
 a chassis;   at least one ski steerably secured to the chassis;   a skid frame assembly secured to the chassis, the skid frame assembly including a skid rail having a hollow portion, a front idler wheel, and a rear idler wheel, wherein the skid rail extends in a longitudinal direction and includes a wear strip, the wear strip extending along at least a portion of a bottom surface of the skid rail; and   a track encircling the skid frame assembly, the track having an inner slide surface and an outer surface that engages with the ground, wherein the track is pivotable relative to the skid rail about at least one longitudinally extending roll axis.   
     
     
         17 . The tracked vehicle of  claim 16 , wherein the at least one longitudinally extending roll axis includes a first longitudinally extending roll axis offset in a horizontal direction from a longitudinally extending centerline axis and a second longitudinally extending roll axis offset in the opposite horizontal direction from the longitudinally extending centerline axis. 
     
     
         18 . The tracked vehicle of  claim 16 , wherein first and second portions of the track extend unsupported on either side of the skid rail in a horizontal direction perpendicular to the longitudinal direction. 
     
     
         19 . The tracked vehicle of  claim 18 , wherein the first and second unsupported portions of the track extend from an edge of the wear strip to an outermost edge of the track and having an extent in the horizontal direction of at least 25 percent of a width of the track, wherein the first and second unsupported portions extend longitudinally from the front idler wheel to the rear idler wheel. 
     
     
         20 . The tracked vehicle of  claim 16 , wherein the track is substantially rigid in the horizontal direction.