One of the major areas of tracked tractor design is steerability. Tracked vehicles generally present more turning resistance than wheeled ones, which means that more power is spent to overcome this greater resistance. Mechanical systems simulation has shown to be an important tool for solution of vehicle dynamics analysis problems. Its use has reduced cost and time spent in the solution of such problems. The objective of this research was to develop a 3-D parametric model to simulate the rubber-tracked tractor steerability. The computer program Automatic Dynamic Analysis of Mechanical Systems (ADAMS) was used. The model was composed of the following submodels: a) engine; b) power transmission system; c) differential system; d) hydraulic steering system; and e) soil/track interface. To validate the model, tests were done on a concrete pad, on firm soil and on tilled soil. Different loads were applied to the drawbar, different track widths were used, and different paths over the field were tested. The tests included the use.of a fixed and a swing drawbar. The rubber-tracked tractor used in the tests was a Challenger 75 made by Caterpillar. The parameter used to evaluate the tractor performance was the turning path of the tractor. Furthermore the developed model predicted the speed and torque of the engine and drive wheels. These parameters were evaluated during the field tests. The errors obtained by comparing the simulated results to the experimental data were below 10 percent, which is considered to be satisfactory for engineering application. The drawbar load showed to be the most important factor affecting the steering performance of the tractor. The turning radius increased 22% when fixed drawbar were used instead of a swing drawbar.
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