Stability criteria for tractor-implement operation on slopes

Mathematical models of tractor-implement combinations were developed to predict their stability on slopes. A procedure based on three criteria was then developed to assess the stability of both tractor-trailed implement combinations and tractor-mounted implement combinations. The three criteria were "sideslip criterion" which determines the slope angle-heading angle combination at which uncontrollable slip sets in; "overturning criterion" which determines the slope angle-heading angle combinations at which partial and total stability limits are reached, i.e. slope angle-heading angle combinations at which the vertical load on one or two tyres will be zero; and the "general criterion", which results directly from regulations in many countries that require tractor-implement combinations to have at least 20% of their total weight on the front axle at all times. This criterion extended this requirement to the effect that at least 20% of the total weight must be available on each side of the combination at all times. The application of these criteria gave stability regions for a given combination. Simultaneous application of the criteria gave optimum parameters which would maximize these stability regions. Simulation results showed that for better, stability of tractor-implement combinations, the implement centre of gravity should be behind its axle. Other results showed that tractors in combination with mounted implements like sprayers, spreaders etc., would be more stable if the implements were designed so that their centres of gravity move forward as emptying progresses. (C) 1998 ISTVS. All rights reserved.