Skid steer loader machines are manufactured to provide a compact work machine that is maneuverable and durable in various applications. Skid steer loader machines are propelled by independently driven wheels on opposite sides of the vehicle that can be driven at different speeds and in different directions. Some skid steer loader machines use a loader body or lower frame assembly, in conjunction with a subframe or upper frame assembly, to define a main frame assembly for the loader machine. The lower frame assembly typically includes axle openings within which axles are disposed. The main frame may be assembled in a variety of ways to provide effective serviceability and durability.
Tracked skid steer loader machines or multi-terrain loader machines utilize an endless track undercarriage in place of the independently driven wheels to provide greater traction in mud, snow, ice and the like. An all-terrain vehicle is disclosed in U.S. Pat. No. 3,728,909 issued on Apr. 24, 1973 to Herbert A. Jesperson that is designed for high capability of travel over difficult and rough ground contours, conditions and textures. In particular, the Jesperson patent includes a body that has a center section with a bottom wall and front and rear walls extending from the bottom wall. Opposing side walls extending from the bottom wall and from the front and rear walls generally complete the center section. Located transversely on the underside of the bottom wall are a plurality of spaced parallel downwardly open channels which are formed in the continuous bottom wall surface. The channels cooperate with the track suspension group to permit modular assembly while, at the same time, affording maximum vertical clearance under the bottom wall and between the tracks, consistent with maintaining water-tight integrity of the body and maximum depth to afford sufficient space in the center section for the power group and the user's legs. In this regard, the track suspension group includes a frame having a plurality of structural cross members which are respectively and individually located in the respective downwardly open channels. The cross members are connected to the body by means in the form of plates which are welded to the cross members and adapted to span the ends of the channels and contact the exterior surface of the side margins around the channel ends. Screws or bolts are used to attach the plates to the side walls of the body. Although the open channels provide vertical clearance and depth, axial loads from the upper portion of the machine are directed on the screws or bolts attaching the cross members with the body. Therefore, such screws or bolts are likely to incur shear or torsional stresses that may damage or destroy the screws or bolts and, thereby, weaken the assembly. Further, the depth utilized to mount the cross members is not sufficient to lower the center of gravity of the machine to a maximum level.
The present invention is directed to overcoming the problems, as set forth above, by providing a structural design that enables a multi-terrain loader machine to be modularly assembled by mounting a solitary lower frame assembly or a fully assembled main frame to a pre-assembled undercarriage in a manner that distributes axial loading on the undercarriage.