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A torque management model (TMM) focused on the close matching of driving requirements and operating conditions for electric tractors was developed. The TMM used the accelerator pedal output signal to establish the torque demand to adapt for two conditions – field traction and road driving. Further, the TMM uses the limitations of a time-based torque ramp, maximum motor torque at the current speed, and battery state of charge. To verify the performance of the TMM, a tractor control unit (TCU) to support the TMM was designed, and a test bench comprising both driving and loading devices was built. The bench provided the TMM/TCU with the necessary operating states needed as inputs to determine the torque demand. Experiments were performed under five specific manoeuvring cases. The test results showed that the TMM was capable of accurately converting pedal manipulations into torque demands both in the field traction and road driving conditions. The torque changes during testing were properly smoothed by limiting the rising and falling time of the target torque, which was favourable for eliminating impacts due to torque fluctuations. Overloading operations that would occur in case of excessive torque request were avoided by the torque capacity limitation both in the field traction and road acceleration tests. When the bus voltage was deliberately adjusted below the alarm threshold, the TMM could scale down the torque demand in real time according to the deviation between the actual voltage and the threshold, and therefore, it always kept the voltage above the safe level.

Statistics show that lateral overturns are the most frequent fatal accidents involving tractors. There is thus much research interest in improving tractor lateral stability. Previous research has discovered the effects of various factors on tractor dynamic responses. While these factors have been analysed separately, their relative significance with respect to other factors remain uncertain. Furthermore, the practical limits of what operators can do have not been considered. The present study assumed a possible case that a tractor operator has several spare tyres of different types and service condition. Additionally, the ballast weight, track width, and implement position can usually be controlled before operation. A scale model tractor was thus developed allowing changes to these factors. The model tractor was designated to pass over typical farming road surfaces. Moreover, the tractor lateral stability was evaluated in terms of the roll angle, lateral-load transfer ratio, and Phase I overturn index. Employing the Taguchi method, we arranged experiments and assessed the applicability of the three kinds of indexes regarding tractor Phase I overturn. Results revealed that the roll angle did not well reflect the initiations of overturns. Compared with the lateral-load transfer ratio, the Phase I overturn index had more convincing factorial effects on tractor stability. Further investigation of the suggested tractor configuration supported this conclusion by comparing predicted and experimental results. In practical cases, this approach may provide a reference for engineers to help operators improve driving safety with limited spare parts.

Tractor overturns are serious potential hazards for operators. While rollover protective structures (ROPS) protect operators passively, greater protection can be achieved through theoretical prediction of a potential overturn. Given effective warning, an operator can act to correct a tractor's motion when a tyre is about to lose contact with the ground. Such a loss of contact is associated with the initiation of a Phase I tractor overturn. However, it remains unclear how the initiation of tractor overturn is influenced by certain factors. Furthermore, the current mathematical models for tractors should be further extended for general utilisation. This study was conducted to develop stability indicators based on a more general model for dynamic Phase I tractor overturn. We considered practical tractor configurations and motion characteristics in a three-dimensional (3D) reference frame in formulating the mathematical model. Tractor stability indicators for overturn and sideslip were derived from force calculations. A parametric study was conducted using an example tractor. The tractor speed and slope angle were found to affect the overturning stability significantly. The coefficient of maximum static friction was found to be the main factor contributing to tractor sideslip. Critical tractor speeds for various ground conditions were identified by considering the zero values of the tractor stability indicators. The critical tractor speed was determined as a function of the maximum static friction and the slope angle. By providing a display device based on ergonomics principles, the results of this study can be further implemented in the form of guidance to operators.

A dynamic three-dimensional model was constructed for a half-track tractor that considers its bounce, pitch, and roll motions in order to clarify the tractor’s vibration characteristics. Driving experiments were conducted in which the tractor was driven on a solid asphalt road surface in order to investigate its vibration characteristics and to verify the validity of an analysis based on motion equations that were formulated from the proposed dynamic model. The experiments were conducted with a half-track tractor apparatus equipped with twelve accelerometers for the measurement of 6 DOF of acceleration of the tractor’s centre of gravity. The discrete time series of the measured data was resolved and reconstructed by wavelet analysis. The model was verified using the fixed lug phase difference between the left and the right crawler systems for each combination of three location arrangements of the track rollers and seven levels of tractor speed. Results showed that the acceleration of the centre of gravity for the bounce, pitch, and roll motions was at a minimum when the track rollers were set equidistant from one another. The acceleration caused by the bounce and pitch motions decreased with an increase in the lug phase difference, while the acceleration caused by the roll motion increased with an increase in the lug phase difference. The results further suggested that the proposed three-dimensional dynamic model could be improved by incorporating into it the lug phase differences that change during actual tractor driving, instead of a constant lug phase difference.