Patent ID: 7229140

Claim:
A track tensioning device for an endless track on a vehicle having a track frame, said track tensioning device comprising a roller to engage an interior surface of a track, a track tensioner arm supporting the roller, the track tensioner arm including a tubular slide housing, a spring assembly within the tubular slide housing for urging the roller to provide tension in the track comprising first and second compression springs mounted to be loaded in series, the springs being of substantially different spring rates, a first of the springs having a lower spring rate than a second of the springs, a support on the track frame for slidably guiding the tubular housing, a base plate fixed to an end of the tubular housing adjacent the roller, a slide plate slidably mounted in the tubular housing, the second spring being positioned in the tubular housing between the base plate and the slide plate, a force reaction wall mounted on the track frame spaced from an end of the tubular housing opposite from the base plate, the first spring being mounted between the slide plate and the force reaction wall to react spring force to the force reaction wall, a mechanical stop engaging the slide plate as the first spring is compressed by loads on the track tension arm as the slide housing is forced toward the force reaction wall, to prevent loading the first spring more than a selected amount, and thereafter the second spring being compressed between the end plate and the slide plate by increased loads on the track tensioner arm to resist movement of the roller and the slide housing toward the force reaction wall caused by tension in the track.