INCREASE TRACTION WITH HYDRAULIC ASSIST DRIVE

A two-wheel assist hydrostatic drive add-on unit for combines and tractors over 75kW (100 hp) is described and evaluated. The add-on unit manufactured by Mud-Hog Drive Systems consists of two hydraulic motors, two Torque-Hubs, and associated controls, providing four-wheel drive advantages to a vehicle. The Mud-Hog units were designed to replace the original steerable wheels at the rear of the combine in order to increase total vehicle traction without unduly taxing the existing hydrostatic drive circuit; to allow vehicle movement through its normal range of operating speeds, including on-road travel; to utilize the existing power steering system; to allow variable spacing of all the wheels; to avoid excessive tire wear and wheel "spin-outs"; to provide easy on-off control from the operator's station under all situations; and to limit the time required for field installation to no more than one day. The objectives were met and confirmed with field observation. The units have proved beneficial to farmers by increasing their vehicle's tractive effort capacity in adverse soil conditions. A computer program model was developed to estimate the amount of increased drawbar pull for a front wheel assist drive unit on a tractor operating on various soil conditions. Although the model could not be verified in all conditions with actual field data, the predictive performance appears to agree with results of field experience.