Endless track tension release mechanism

Claim 1

A tensioning device for use in a track-propelled vehicle having a frame and an endless track looped around at least one driving sprocket and one idler wheel secured to said frame for maintaining the track under proper tension as a result of transient conditions of overtension in the track comprising a first cylinder and a piston which constitute a piston and cylinder unit defining a main expansible hydraulic working chamber, at least one of said piston and cylinder members of the unit being a movable member which is movable relative to the other member, the movable member having one end connected to the axis of the idler wheel and the other end hydraulically actuatable in said main working chamber, the other member of the unit being connected to the frame, a hydraulic accumulator supported by said frame and including first and second opposed abutment members fixed to the frame, an accumulator expansible hydraulic working chamber having a second cylinder movable between said abutment members, a prestressed spring having one extremity in abutment with the first abutment member and the other extremity in abutment with the second cylinder and urging the same against the second abutment member; a piston fixed to the frame and extending from the second abutment member towards the first abutment member within the second cylinder, the sides of the piston being sealingly engaged with the walls of the second cylinder such that the said accumulator working chamber is formed between an end of the second cylinder and the end of the fixed piston closest to the first abutment member, an axial passage through the fixed piston placing the main and accumulator working chambers into fluid communication with each other, and hydraulic conduit means connecting the main working chamber with the accumulator working chamber and allowing a transfer of fluid into the accumulator working chamber when the force exerted on the movable member by the idler wheel axle exceeds a predetermined value, said hydraulic conduit means including a pair of parallel fluid lines, one-way valve means in each of said fluid lines, the valve means in a first of said parallel fluid lines being openable toward the accumulator working chamber after a given pressure has been exerted thereagainst to transfer fluid from the main working chamber to the accumulator working chamber to compress said prestressed spring; and the one-way valve means in the other of said parallel fluid lines being openable from the accumulator working chamber to the main working chamber to allow the passage of said fluid in its fluid line when the transient condition of overtension in the track is terminated to return said fluid to the main working chamber.