Mechanism and performance test of pivot turning system with single driving for rice combine harvester

Combine harvester is one of important tools for rice harvest. Combine harvester is apt to work in the field of high moisture other than wheeled vehicle. So for the sake of steady running, rubber tracked vehicles are commonly applied in harvesters against the characteristics of high moisture and low carrying capacity of paddy soil. Because the combine harvester has large touching surface with soil, the pressure between the earth and track will decline enormously compared with the wheeled vehicle, which can’t work steady due to the sinkage of its wheels. But the long track will cause big turning resistance. In China, the unilateral shift is broadly applied in the medium or small-size tracked vehicles. But this steering ways will often bring accumulation of soil, especially during turning angle with 90, which will cause hard turning, so it has to turn a little degree each time, and repeat some times to achieve turning. In order to overcome this problem, a new kind of combine harvester steering mechanism was developed in the paper, which contains a pivot turn steering mechanism powered by one-side tractive force using a tracked vehicle chassis attached to the stripping harvester. This machine can realize spin turning at any radius, so it is more flexible in paddy field.In order to obtain the turning resistance parameters and test the turning performance under different working conditions, the straight-line driving and pivot turning experiments were carried out under three different working conditions—solid, hard and paddy fields. The compactness and moisture of the fields were measured. The output shaft torque under each working condition was obtained through the strain test method. The results showed that:1) The driving wheel torque remained the same in the same kind of ground condition no matter straight forward or backward, which indicated no difference between the front or rear wheel driving. 2) The driving wheel torque was relatively small in straight forward or backward under different ground conditions. The torque shoot up under pivot turning especially in the paddy field, which indicated that the friction resistance and side bulldozing resistance between track and the ground increased sharply under pivot turning condition. The driving wheel torque of a pivot turning was 4.5 times of a straight driving under solid or hard ground conditions. But the driving wheel torque of a pivot turning was up to 6 times of a straight forward driving in paddy field.Besides, detailed tests were carried out in paddy field after rice harvest. The left and right output shaft torque in counterclockwise turning, the velocity in straight-line driving and the angular velocity in turning were measured. The results showed that: 1) Left and right output shaft torque increased with the decrease of turning radius. 2) Maximum output shaft torque appeared in pivot turning (the turning radius was 0). In the meantime, the left and right output shaft torques were roughly equal, which were about 2 278 N•m on average. 3) The turning resistance for spin turning was not less than that of the expected pivot turning, but it was dramatically larger at the 0-radius turning. However, the operation of pivot turning was flexible, the angular velocity was approximately 0.619 rad/s, i.e. a 360° turning only need 10 s. Generally just 90 ° turning needed in practical working, so the turnaround time was short, which can effectively improve the work efficiency and need less turning area. 4) The regression equation was obtained between the right and left output shaft torque and the turning radius based on the data, which can serve as the empirical formula to predict the left and right output shaft torque under different turning radius.Theoretical analysis and test results prove that the turning mechanism has the characteristics of short turnaround time, less turning area, and so on, which can improve the overall efficiency of the crawler combine harvester. The empirical formula and the turning resistance torque parameters obtained under different ground conditions and different turning radius can lay a foundation for the later study.