1. Rolling resistance. The rolling resistance of the tractor is mainly caused by the deformation of the tire and soil. Under the action of the tractor's weight, the tire is flattened and the soil is compacted. In the rolling process of the wheel, the parts of the tire in contact with the ground along the direction around the circle are flattened and deformed, and the high soil in front of the wheel is pressed down to deform the soil and form wheel ruts, that is, the rolling resistance that prevents the wheel from rolling forward. There are many factors affecting rolling resistance, which are mainly related to the firmness of the ground and the size of the vertical load on the degree of moisture. For the same tractor, if the ground conditions are different, its rolling resistance is different, such as in asphalt and cement or dry ground driving rolling resistance is small, tractor traction is large, in the same use conditions, if added to the weight of the tire, the greater the soil deformation in the vertical direction, the greater the rolling resistance. 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 tractor is driving on soft ground, the use of low pressure tires, increase the tire bearing area, can reduce the soil deformation in the vertical direction, reduce the rolling resistance, so as to improve the traction. Because the tractor is mainly used for field operations, mostly driving on soft ground, in order to reduce the soil deformation in the vertical direction, so the tractor generally uses the lowest pressure tire, using the widened tire is 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.

2. Traction resistance. Traction resistance is the resistance that the tractor drives the agricultural machinery and tools to overcome. It is equal to the traction force transmitted by the tractor through the connecting device to the agricultural machinery and tools. Since traction is equal to drive minus rolling resistance, increasing driving force and reducing rolling resistance are effective measures to improve traction.

3. Driving force. It is the horizontal reaction of the road against the driving wheel. Therefore, the size of the driving torque Mk transmitted by the internal combustion engine to the driving wheel through the transmission system indicates that the tractor's driving force Pk is also larger. But since Mk is determined by the power of the internal combustion engine, Pk is also limited by the power of the internal combustion engine. At the same time Pk is limited by soil conditions, can not be infinite increase, because when the soil reaction force that driving force Pk increased to a certain extent, the soil is destroyed, the driving wheel is seriously skidded, driving force Pk can not be increased. We call the maximum force the soil can exert on the driving wheel "adhesion". Thus, in addition to the internal combustion engine rate limit, the maximum driving force Pk is also limited by soil adhesion, and cannot be infinite increase. The adhesion reflects the ability of the driver to produce the maximum driving force between the soil and the driver. There are many factors affecting the adhesion, mainly related to the ground conditions, tire pressure, size, pattern and the size of the vertical load acting on the tire. For the tractor, under certain soil conditions, in a certain range to reduce the tire pressure, increase the tire bearing area, improve the wheel to the soil gripping ability, increase the wheel adhesion weight, etc., are conducive to improving the tractor adhesion. Now tractors generally use low pressure tires, some tractors use widened tires and high pattern tires and add counterweight iron on the tractor driving wheel, are in order to increase the adhesion of the tractor, improve the traction capacity of the tractor and take measures. But it should be pointed out that the driving wheel with counterweight iron, although it can increase adhesion, but also increase the soil deformation in the vertical direction, increase the rolling resistance, so whether to add counterweight iron, but also depending on the specific use conditions, balance the overall effect of trade-off. The maximum adhesion ability and skid resistance between the tractor driving wheel and the ground is called the adhesion performance of the tractor. If the adhesion performance is good and the skidding is light, the driving torque can be fully utilized, and the ability of the internal combustion engine can be fully played. The tractor appears strong when working. If the adhesion performance is poor and the skidding is serious, the driving torque can not be fully utilized, the ability of the internal combustion engine can not be fully played, the tractor is not strong when working, or the tractor is not strong. Driving wheel serious skid, will reduce the speed of the tractor driving, production and economic decline, but also accelerate the wear of the driving wheel tire, in addition to the structure of the soil will be destroyed.

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