Tractor Driving Principle And Influencing Factors

Driving principle
The driving wheel can drive by the power of the internal combustion engine through the transmission system, so that the driving wheel obtains the driving torque Mk. The driving wheel that obtains the driving torque then applies a small, backward horizontal force (tangential force) to the ground through the tire pattern and tire surface, and the ground applies a horizontal force Pk of equal magnitude and opposite direction to the driving force. This Pk force is the driving force (also called propulsion force) that pushes the tractor forward. When the driving force Pk is sufficient to overcome the forward rolling resistance of the front and rear wheels and the traction resistance of the agricultural implements, the tractor will move forward. If the driving wheel is lifted off the ground, that is, the driving force Pk is equal to zero, the driving wheel can only idle in place and the tractor cannot drive; if the sum of the rolling resistance and the traction resistance is greater than the driving force Pk, the tractor cannot drive. It can be seen that the driving of a wheeled tractor is achieved by the interaction between the driving torque driving wheel and the ground, and the driving force must be greater than the sum of the rolling resistance and the traction resistance.
Influencing factors
1. Rolling resistance. The rolling resistance of the tractor is mainly caused by the deformation of the tires and the soil. Under the weight of the tractor, the tires are flattened and the soil is compacted. During the rolling process, the parts of the tire that are in contact with the ground along the circumference of the wheel are successively flattened and deformed, and the soil in front of the wheel is pressed down to deform the soil and form wheel tracks, which generates rolling resistance that hinders the wheel from rolling forward. There are many factors that affect rolling resistance, mainly related to factors such as the solidity of the ground and the size of the vertical load on the wetness. For the same tractor, if the ground conditions are different, its rolling resistance is also different. For example, if the rolling resistance is small when driving on asphalt and cement or dry and hard ground, the tractor has greater traction. Under the same conditions of use, if the weight added to the tire is greater, the soil deformation in the vertical direction is greater, and the rolling resistance is also greater. 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, 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 tractors are mainly used for field operations and are mostly driven on soft ground, in order to reduce the deformation of the soil in the vertical direction, the lowest pressure tires are generally used for tractors. The same is true for using widened tires. 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 has to overcome when driving agricultural machinery to operate. It is equal to the traction force transmitted to the agricultural machinery by the tractor 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.
3. Driving force. It is the horizontal reaction force of the road to the drive wheel. Therefore, the size of the driving torque Mk transmitted to the drive wheel by the internal combustion engine through the transmission system indicates that the driving force Pk of the tractor is also greater. However, 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 and cannot be increased indefinitely, because when the reaction force of the soil, that is, the driving force Pk, increases to a certain extent, the soil is destroyed, the drive wheel slips severely, and the driving force Pk can no longer be increased. We call the maximum reaction force that the soil can produce on the drive wheel "adhesion". It can be seen that the maximum value of the driving force Pk is not only limited by the internal combustion engine, but also by the soil adhesion, and cannot be increased indefinitely.
Adhesion reflects the ability to generate the maximum driving force between the drive and the soil. There are many factors that affect adhesion, mainly related to the ground conditions, tire pressure, size, pattern and the size of the vertical load acting on the tire. For tractors, under certain soil conditions, reducing tire pressure within a certain range, increasing tire support area, improving the wheel's grip on the soil, and increasing the wheel's adhesion weight are all conducive to improving the tractor's adhesion. Low-pressure tires are generally used on tractors. Some tractors use widened tires and high-pattern tires, as well as adding counterweights to the tractor's drive wheels. These are all measures taken to increase the tractor's adhesion and improve the tractor's traction capacity. However, it should be pointed out that adding counterweights to the drive wheels can increase adhesion, but it also increases the deformation of the soil in the vertical direction and increases rolling resistance. Therefore, whether to add counterweights depends on the specific conditions of use and weighs the overall effect. The maximum adhesion and anti-skidding ability between the tractor's driving wheels and the ground are called the tractor's adhesion performance. If the adhesion performance is good and the slippage is light, the driving torque can be fully utilized, the capacity of the internal combustion engine can be fully utilized, and the tractor will appear to be powerful when working. If the adhesion performance is poor and the slippage is serious, the driving torque cannot be fully utilized, the capacity of the internal combustion engine cannot be fully utilized, and the tractor will appear to be unable to exert its strength when working, or the tractor will not be very powerful. Severe slippage of the driving wheel will reduce the tractor's driving speed, reduce production and economy, and accelerate the wear of the driving wheel tires. In addition, the structure of the soil will also be destroyed.