US Patent 7614465 Sub-frames for a working vehicle

A working machine having a main frame structure which includes a pair of endless tracks. Each track is entrained about track supporting devices mounted by a track sub-frame. The sub-frame includes inner and outer members interconnected by cross members. The inner and outer members are arranged side by side. At least one upper track support device is mounted between the inner and outer members at or adjacent upper edges thereof. At least one lower track supporting device is mounted to extend between the inner and outer members at or adjacent lower edges thereof. The inner and outer members and cross members of at least one of the track sub-frames is provided by a monolithic casting.