Motor vehicles – Including one or more ski-like or runner members – With at least one surface-engaging propulsion element
Reexamination Certificate
2000-07-11
2001-11-27
Johnson, Brian L. (Department: 3618)
Motor vehicles
Including one or more ski-like or runner members
With at least one surface-engaging propulsion element
C305S127000, C180S190000
Reexamination Certificate
active
06321864
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a track suspension for a track-propelled snow vehicle or other track-propelled land vehicle, and more specifically to a mechanism that controls the weighting distribution of the track upon the surface of the snow or ground while allowing a limited angular range of longitudinal incline and decline of the ground contacting run of the track relative to the vehicle chassis.
DISCUSSION OF RELATED ART
Two types of personal motorized snow vehicles utilize rear suspension apparati for mounting an endless-loop track for propulsion of the snow vehicle and for supporting and cushioning the snow vehicle chassis upon the ground-contacting run of the track, namely, the well-known snowmobile and the less well-known snow cycle. The snow cycle is very similar to the snowmobile, but generally has only one steerable ski, and is leaned or banked in turning like a motorcycle or bicycle.
Snowmobile track suspensions have traditionally been heavy due to the number of structural components and the number of shock absorbers (typically two or more) used in these suspensions. The shock absorbers typically each include both a hydraulic dashpot-type damper mechanism and a coil spring surrounding the damper body, and are quite heavy. Most of these types of snowmobile track suspensions include separate forward and rearward swingarms. The forward swingarm is typically connected pivotally at a forward upper end to the vehicle chassis, and connected pivotally at a rearward lower end to a track carriage. The track carriage typically includes a pair of slide rails mounting track slides and having multiple sets of idler wheels journaled on cross-shafts with the cross-shafts attached at their ends to the slide rails. The track slides and idler wheels of the track carriage slide and roll, respectively, upon the interior of the lower run of the track to support the snowmobile upon the track. The rearward swingarm connects pivotally at its forward end to the rearward-extending portion of the snowmobile chassis called the track tunnel and a lower rearward pivot on the rearward portion of the track carriage. The rearward swingarm typically includes a telescoping mechanism that allows the separation between the forward and rearward pivots of the rearward swingarm to vary between a minimum compressed length and a maximum extended length. This telescoping relationship between the vehicle chassis and the rearward portion of the track carriage allows the track carriage to incline or decline longitudinally to a limited degree relative to the vehicle chassis to allow the track to bear uniformly on uneven snow surfaces. The degree of telescoping of the rearward swingarm is limited to prevent too severe of incline or decline angles that would overly stretch or slacken the track or would adversely affect propulsion or braking of the snowmobile. These track suspensions typically deploy one shock absorber in conjunction with the forward swingarm to support and cushion the vehicle chassis on the forward portion of the track carriage. A second shock absorber is deployed in conjunction with the rear swingarm to support and cushion the vehicle chassis on the rearward portion of the track carriage. One type of structure used to form the telescoping function of the rear swingarm is a pivot and slide-block combination where the lower swingarm mounts pivotally to a block that slides in a slot on each of the slide rails. Examples of track suspensions that use this type of structure are described in U.S. Pat. No. 5,265,692 (Mallette) and U.S. Pat. No. 5,881,834 (Karpik). Another structure employed to provide the telescoping function is a short pivot arm that attaches pivotally between the track carriage and the lower end of the rearward swingarm to form a knuckle-type pivot joint between the short pivot arm and the swingarm. Track suspensions using this type of structure are described in U.S. Pat. No. 5,730,242 (Furusawa) and U.S. Pat. No. 5,692,579 (Peppel et. al.). In the track suspension described in the Peppel et al. patent, the telescoping range of this rear swingarm structure is limited using mechanical stops that limit the angular swing of the short pivot arm. This limits the longitudinal inclination and declination of the track carriage relative to the vehicle chassis to the desired range. Furusawa employs separate telescoping members with stop bumpers to limit the telescoping range of the rearward swingarm structure. One of the primary reasons for limiting the track carriage inclination and declination in snowmobile track suspensions is to limit the variability in the path-length of the endless-loop track, thereby limiting the amount of track stretching and slacking that result when the track rails decline and incline.
The Mallete, Karpic, and Peppel track suspensions described in the patents listed above have structural geometries that result in regressive actuation of the shock absorbers. By definition, regressive actuation of the shock absorber occurs when incremental compressive displacements of the track suspension result in proportionally smaller incremental compressions of the shock absorber when the track suspension is more heavily loaded and compressed as compared to when the track suspension is less heavily loaded and compressed. Such regressive shock absorber actuation is less desirable than a linear or progressive shock absorber actuation since it provides less resistance to suspension “bottoming” and requires the suspension to be set more stiffly to avoid bottoming, thereby sacrificing ride comfort.
The track suspension described in the Furusawa patent deploys a complex bell crank and connecting rod linkage mechanism to provide progressive actuation of the rear swingarm shock absorber and spring. The actuation of the front swingarm shock absorber, however, is regressive. While progressive actuation of the rear shock absorber results in a track suspension that offers improved resistance to bottoming along with a plusher ride, this suspension has many pivoting joints and structural members, making it heavy, complex and difficult to maintain.
A single swingarm track suspension is described in U.S. Pat. No. 5,860,486 (Boivin & Boivin). This track suspension employs a tension-only member in parallelogram configuration with the single swingarm, snowmobile tunnel and track carriage to limit the range of allowable track carriage inclination relative to the vehicle chassis. The track carriage declination is limited to an acceptable amount by a mechanism that comprises a bell crank, connecting rod and tension strap connecting to the forward portion of the track carriage. While this suspension has fewer structural members and pivots, it also suffers from regressive actuation of the shock absorbers.
Snow cycle track suspensions tend to be one of two predominant types, the first of which is very similar to snowmobile track suspensions. Snow cycles of this type typically use the same general type of clutches and power trains as snowmobiles, and so these snow cycles are quite heavy, typically weighing well over 300 pounds. A snow cycle using a snowmobile style of track suspension is described in U.S. Pat. No. 5,904,217 (Yamamoto & Kouchi). This snow cycle track suspension is a two swingarm design using a slide block & slot type pivot as the lower pivot connection between the rear swingarm and the track carriage for limiting the range of track carriage inclination and declination. This track suspension also suffers from regressive shock absorber actuation, but deploys a physically separate suspension spring with nearly linear actuation as the suspension is compressed.
A second type of snow cycle track suspension is found on snow cycles whose designs are based on off-road motorcycles and motor scooters. These track suspensions most often have shorter tracks that circulate in fixed paths around track carriages. Their snow cycle bodies are supported and cushioned upon their track carriages using shock absorber mechanisms that are deployed external to their track loops. Examples of such tr
Johnson Brian L.
Ormiston & McKinney PLLC
Yeagley Daniel
LandOfFree
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