Driving principle

The driving force is generated by the internal combustion engine, which, through the transmission system, applies a driving torque Mk to the drive wheels. These drive wheels, in turn, exert a small, rearward horizontal force (tangential force) on the ground through the tire tread pattern and tire surface. The ground, in response, exerts a horizontal force Pk that is equal in magnitude and opposite in direction to the driving force. This force Pk is the driving force that propels the tractor forward (also known as thrust). 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 attached agricultural tools, the tractor moves forward. If the drive wheels are lifted off the ground, meaning the driving force Pk equals zero, the drive wheels can only spin in place, and the tractor cannot move. Similarly, if the sum of rolling resistance and traction resistance exceeds the driving force Pk, the tractor cannot move. Thus, the movement of wheeled tractors is achieved through the interaction between the driving torque applied to the drive wheels and the ground, and the driving force must exceed the sum of rolling resistance and traction resistance.

influencing factors

1. Rolling resistance. The rolling resistance of a tractor is primarily caused by the deformation of tires and soil. Under the weight of the tractor, the tires are compressed and the soil is compacted. During the rolling process, various parts of the tire that are in contact with the ground along the circumferential direction undergo compression deformation, and the soil above the front of the tire is pressed down, causing soil deformation and forming wheel tracks, which generates rolling resistance that hinders the forward rolling of the wheel. Many factors affect rolling resistance, primarily related to the firmness and wetness of the ground, as well as the vertical load on the ground. For the same tractor, rolling resistance varies depending on ground conditions. For example, when driving on asphalt, cement, or dry hard ground, rolling resistance is low, and the tractor's traction is high. Under the same conditions, if the weight on the tires is greater, the soil deformation in the vertical direction will be greater, and rolling resistance will also be greater. Generally speaking, reducing the deformation of the tires themselves and the deformation of the soil in the vertical direction is beneficial for reducing rolling resistance. If the tractor is driving on soft ground, using low-pressure tires and increasing the tire support area can reduce soil deformation in the vertical direction and lower rolling resistance, thereby improving traction. Since tractors are mainly used for field work and often drive on soft ground, to reduce soil deformation in the vertical direction, they generally use very low-pressure tires. The same principle applies to wider tires. In our operations, we should pay attention to the differences in use between low-pressure tires, wider tires, and high-pressure tires.

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

3. Driving force. It refers to the horizontal reaction force of the road surface on the driving wheel. Therefore, the magnitude of the driving torque Mk transmitted from the internal combustion engine to the driving wheel 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 also limited by soil conditions and cannot be infinitely increased, because when the reaction force of the soil, that is, the driving force Pk, increases to a certain extent, the soil is damaged, the driving wheel slips severely, and the driving force Pk cannot be further increased. We refer to the maximum reaction force that the soil can exert on the driving wheel as "adhesion". It can be seen that the maximum value of the driving force Pk is limited not only by the power of the internal combustion engine but also by the soil adhesion, and cannot be infinitely increased.

Adhesion reflects the ability to generate significant driving force between the drive and the soil. There are many factors that affect adhesion, primarily related to ground conditions, tire pressure, size, tread pattern, and the magnitude of the vertical load acting on the tire. For tractors, under certain soil conditions, reducing tire pressure, increasing tire support area, improving the wheel's grip on the soil, and increasing the wheel's adhesive weight within a certain range are all beneficial to improving the tractor's adhesion. Low-pressure tires are commonly used on tractors, and some tractors adopt widened tires and high-tread tires, as well as adding counterweights to the tractor's drive wheels, all as measures to increase the tractor's adhesion and improve its traction capability. However, it should be noted that adding counterweights to the drive wheels, although increasing adhesion, also increases soil deformation in the vertical direction and rolling resistance. Therefore, whether to add counterweights depends on specific usage conditions and a trade-off between overall effects.

The strong adhesion and resistance to slipping between the tractor's drive wheels and the ground are referred to as the tractor's adhesion performance. If the adhesion performance is good and the slipping is light, the drive torque can be fully utilized, and the internal combustion engine's capacity can also be fully utilized, making the tractor powerful during operation. If the adhesion performance is poor and the slipping is severe, the drive torque cannot be fully utilized, and the internal combustion engine's capacity cannot be fully utilized, making the tractor appear to lack power during operation, or in other words, the tractor does not have much power. Severe slipping of the drive wheels will reduce the tractor's driving speed, decrease production and economy, and also accelerate the wear of the drive wheel tires. In addition, the structure of the soil will be damaged.