The rolling resistance of a four-wheel drive tractor is mainly due to the deformation of the tire and the soil. Under the heavy pressure of the four-wheel drive tractor, the tire is flattened and the soil is compacted. During the rolling process of the wheel, the various parts of the tire that contact the ground in the circumferential direction are then flattened and deformed, and the soil pressure in front of the wheel is downward, and the soil is deformed downward to form wheel ruts, that is, rolling resistance prevents the wheel from rolling forward. There are many factors that affect rolling resistance, mainly related to factors such as ground firmness and the degree of moisture in the vertical load. For the same four-wheel drive tractor, if the ground conditions are different, its rolling resistance is also different. For example, the rolling resistance is small when driving on asphalt cement or dry and hard ground, and the traction of the four-wheel drive tractor is large. Under the same use conditions, if the weight added to the tire is large, the deformation of the soil in the vertical direction is also large, and the rolling resistance is also large. Generally speaking, reducing the deformation of the tire itself and the deformation of the soil in the vertical direction is conducive to reducing rolling resistance. If the four-wheel drive tractor runs on soft ground, using low-pressure tires and increasing the tire support area can reduce the deformation of the soil in the vertical direction, reduce rolling resistance, and thus improve traction. Since four-wheel drive tractors are mainly used for field operations and run on soft ground to reduce the deformation of soil in the vertical direction, the four-wheel drive tractors generally use lower pressure tires, and the widened tires are also used for the same reason. In our operation, we should pay attention to the difference between low-pressure tires, widened tires and high-pressure tires in use.
Traction resistance is the resistance overcome by the tractor to drive the agricultural machinery to work, which is equal to the traction of the tractor through the agricultural machinery through the connecting device. Since traction is equal to drive minus rolling resistance, increasing driving force and reducing rolling resistance are effective measures to improve traction. It is the horizontal reaction force of the road to the drive wheel. Therefore, the driving torque Mk of the internal combustion engine is transmitted to the drive wheel through the transmission system, indicating that the driving force Pk of the tractor is also large. But since Mk is determined by the power of the internal combustion engine, Pk will also be limited by the power of the internal combustion engine. At the same time, Pk is limited by soil conditions and cannot be increased indefinitely, because when the soil reaction force, that is, the driving force Pk, increases to a certain extent, the soil will be damaged, the driving wheel will slip severely, and the driving force Pk can no longer be increased. We call the maximum force that the soil can exert on the driving wheel "adhesion". It can be seen that the maximum value of the driving force Pk is not only limited by the speed of the internal combustion engine, but also by the adhesion of the soil, and it is impossible to increase it indefinitely. It reflects the ability of the driver to generate a large driving force between the driver and the soil. There are many factors that affect adhesion, mainly related to ground conditions, tire pressure, size, pattern, and the size of the vertical load borne by the tire. For tractors, under certain soil conditions, reducing tire pressure within a certain range, increasing tire support area, improving wheel grip on the soil, and increasing wheel adhesion weight are all conducive to improving tractor adhesion. Low-pressure tires are widely used on tractors. Some tractors use widened tires and high-pattern tires, and add counterweights to the tractor drive wheels. This is to increase the adhesion of the tractor, improve the traction capacity of the tractor, and take measures. However, it should be pointed out that adding counterweights to the drive wheels can increase adhesion, but it will also increase the deformation of the soil in the vertical direction and increase rolling resistance. Therefore, whether to add counterweights depends on the specific use and the overall effect.
