Formerly, torsional vibration of crankshaft in off-highway diesel engine (agricultural machinery) were given little attention at their developmental stages, however with increasing agricultural activities, numerous torsional vibration problems have been noted to occur in agricultural machinery, especially in their diesel engines. This results in engine vibration, crankshaft failure and undesirable engine noise. In this paper, a six-cylinder four-stroke inline diesel engine's crankshaft model was developed using AVL Excite Designer. After experimentally validating the model, it was used to numerically determine the torsional vibrations of a crankshaft. For the reduction of torsional vibration, two methods of crankshaft improvements were proposed based on simulation results. The first method, is to decrease the inertia of the crank pulley while the second, involves the replacement of the crank pulley with a torsional vibration damper. To ensure minimal engine alterations and cost effectiveness, the second improvement method was adopted for improving torsional vibration. Afterwards, engine radiating noise and surface vibration measurements were conducted to ensure that the required limits were achieved by the improved engine. The simulation, experiment and the improvement process of the crankshaft torsional vibration are documented further in this research. These improvements have applicable values in the developmental or quality enhancement stage of diesel engines used in agricultural machinery.

This study compared the NOx emissions of a nonroad compression ignition engine using pilot injection and a NH 3 -SCR system and revealed their effects on NOx reduction. Furthermore, the interaction of pilot injection and the NH 3 -SCR system on NOx reduction was also studied by simultaneously using the two technologies under broad engine operating conditions. The pilot-main interval and the rate of pilot-to-main injection used in this study are in the range of 2∼8 CA and 9.5∼58.5%, respectively. Results showed that alteration in the pilot-main injection interval and the pilot-injection fuel amount under low load conditions was prone to lead to more variation in NOx emissions in comparison with that under high-load conditions. Relative to the pilot-main injection interval, the pilot-injection fuel amount played a more important role in the NOx emission. Lower NOx emissions could be achieved when using a smaller pilot-injection amount. However, excessively advanced pilot injection and a larger pilot-injection amount would increase the NOx emissions. Under a lower engine load, the effect of pilot injection on NOx reduction enhanced, whereas the effect of the NH 3 -SCR system diminished. Over broad operating conditions, the NOx reduction percentage by pilot injection coupled with the SCR system was lower than the total reduction degree when separately using pilot injection and the SCR system.

Obstacle avoidance operations of tractors can cause parts of land to be unavailable for planting crops, which represents a reduction in land utilization. However, land utilization is significant to the increase in agricultural productivity. Traditional obstacle avoidance path planning methods mostly focus on automatic tractor navigation with small errors, ignoring the decrease in land utilization due to obstacle avoidance operations. To address the problem, this paper proposed an obstacle avoidance path planning method based on the Genetic Algorithm (GA) and Bezier curve. In this paper, a third-order Bezier curve was used to plot the obstacle avoidance path, and the range of control points for the third-order Bezier curve was determined according to the global path and the location of the obstacle. To target the navigation error and land utilization problems, GA was used to search for the optimal point from the selection range of the control point under multiple constraints for automatic tractor navigation such as the obstacle collision avoidance, the minimum turning radius, and the maximum turning angle. Finally, the optimal obstacle avoidance path was determined based on the selected control points to minimize the navigation error and maximize land utilization. The algorithm proposed in this paper was compared with existing methods and the results showed that it has generally favorable performance on obstacle avoidance path planning.

The rubber bushing of screw drilling tool is the weak part of motor in drilling work. It is divided into conventional stator rubber bushing and equal wall thickness rubber bushing. The main material is NBR. With the help of large-scale finite element analysis software ABAQUS, based on the known nonlinear characteristics of rubber materials and the constitutive model of rubber materials, the influence of internal pressure on the rubber bushing of screw drilling tools and the influence of different Poisson's ratio on the rubber bushing of screw drilling tools are obtained. In order to guide the use of the screw drill and the preparation of NBR under relevant conditions..

The vibration tests were carried out using a 162kW wheeled tractor to evaluate the Whole-body vibration while the tractor working in the field, driving on concrete road and in-parking state. The tractor ride comfort was analyzed using the joint weighted acceleration of seat surface vibration from 1 to 80 Hz as the evaluation indicator, according to ISO2631 standard suggestions. During field work, the combined acceleration of the driver’s whole body vibration is 1.39, and the subjective feeling is extremely uncomfortable. Based on the multi-body dynamics analysis software, a tractor dynamics simulation model including the seat, cab mounts, chassis, tyre and road coupling system was established. By changing the model parameters, the influence of the tractor driver’s whole body vibration under the condition of the artificial test track was further analyzed. The analysis shows that the factors that have a greater impact on the driver’s whole body vibration when driving on the artificial runway are the vertical stiffness of the tyre, the vertical stiffness of the seat suspension, and the damping coefficient of the tyre.