Working machines such as excavators are known and include two tracks laterally spaced from each other. The tracks are attached to a chassis upon which a body is rotatably mounted about a generally vertical axis. The body includes a working implement such as a loading arm. At an end of the loading arm is a bucket. The excavator can move a load (such as earth) by rotating the body about a generally vertical axis. As the body rotates with a full bucket then the centre of gravity of the vehicle as a whole moves as the loading arm swings. Additionally, in some excavators the loading arm may swing about a king post relative to the body about a vertical axis.
Some excavators have the track set at a fixed distance apart which is relatively large distance. Accordingly, if a load is picked up with the arm pointing forwards, i.e. parallel to the tracks, and that load is then swung sideways as the body is rotated 90 degrees, then the centre of the gravity of the machine will move towards that track which is located between the bucket and the rotational axis of the body. The spacing of the track is designed so that the machine is stable under these circumstances.
Other excavators, typically small excavators, have the ability to vary the distance between the two tracks. Thus, for access purposes to gain access through narrow gates and the like, and for example when the excavator is loaded onto a relatively narrow transportation trailer, the tracks can be positioned in a retracted position where they are relatively close together. When the excavator is required to carry out work, such as moving loads, then the tracks are extended to a deployed (or extended) position where they are positioned further apart in the retracted position. This gives the excavator more lateral stability.
Some excavators with variable track have a first track assembly mounted on two laterally extending beams and a second track assembly mounted on a further two laterally extending beams. Each pair of beams is slideably mounted in the chassis. The track assembly and associated beam can be extended away from the chassis to a deployed position and can be moved towards the chassis in a retracted position. In the deployed position the beams act as cantilevers and therefore must have a certain overlap with the chassis so as to ensure mechanical integrity. Because of this overlap, when the tracks are in their retracted position the left hand end of the beams of the right hand track is close to the inside edge of the left hand track and vice versa. This limits the amount of extension each beam can achieve relative to the chassis.
Furthermore, the tracks are moved apart and together by a hydraulic actuator which is attached to the inside of each track assembly. The spacing apart of the tracks in the retracted position limits the length of the hydraulic actuator which in turn limits the amount by which the tracks can be extended.
An object of the present invention is to provide a working machine with improved track extension/retraction abilities.