Tractors can run by the power of internal combustion engine through the transmission system, so that the driving wheels can get the driving torque MK. The driving wheels with driving torque will give the ground a small backward horizontal force (tangential force) through the tire tread and tire surface, and the ground will face the horizontal reaction Pk with the same driving force and opposite direction. This Pk reaction force is the driving force to push the tractor forward (also called feed propulsion). When the driving force Pk is enough to overcome the forward rolling resistance of the front and rear wheels and the traction resistance of the farm tools, the tractor will travel forward. If the driving wheel is 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 run; If the sum of rolling resistance and traction resistance is greater than the driving force Pk, the tractor can't run either. It can be seen that the driving of wheeled tractor is realized by the interaction between driving torque and the ground, and the driving force is greater than the sum of rolling resistance and traction resistance.

Let's analyze the main factors that affect tractor driving.

Main factors affecting tractor driving

(1) Rolling resistance The rolling resistance of tractors is mainly caused by the deformation of tires and soil. Under the weight of the tractor, the tires were squashed and the soil was compacted. During the rolling process of the wheel, rolling deformation occurs at all parts where the tire contacts the ground along the circumferential direction, and the front part of the wheel is pressed down to the soil, so that the soil is deformed to form ruts, that is, rolling resistance is generated to prevent the wheel from rolling forward. There are many factors that affect the rolling resistance, mainly related to the vertical load such as the firmness and humidity of the ground. For the same tractor, the rolling resistance will be different if the ground conditions are different. For example, when driving on asphalt cement or hard ground, if the rolling resistance is small, the tractor traction will be large. Under the same service conditions, the greater the weight added to the tire, the greater the vertical deformation of the soil and the greater the rolling resistance. Generally speaking, reducing the deformation of the tire itself and the vertical deformation of the soil is conducive to reducing the rolling resistance. If the tractor runs on soft ground, using low-pressure tires and increasing the supporting area of tires can reduce the vertical deformation of soil, reduce rolling resistance and improve traction. Because tractors are mainly used for field work and mostly run on soft ground, in order to reduce the deformation of soil in the vertical direction, it is the same for tractors to use the lowest pressure tires and widen the tires. In our business, we should pay attention to the differences in the use of low-pressure tires, widened tires and high-pressure tires.

(2) Traction resistance Traction resistance is the resistance that the tractor drives the agricultural machinery to work, which is equal to the traction that the tractor transmits to the agricultural machinery through the connecting device. Since traction is equal to driving 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 surface to the driving wheel. Therefore, the magnitude of the driving torque Mk transmitted by the internal combustion engine to the driving wheels 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 internal combustion engine, Pk is also limited by the power of 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 is destroyed and the driving wheel slips seriously, and the driving force Pk cannot be increased any more. We call the maximum reaction force that the soil can produce to the driving wheel "adhesion". It can be seen that the maximum driving force Pk is not only limited by the internal combustion engine rate, but also by the soil adhesion, and cannot be increased indefinitely.

Other factors

Adhesion reflects the ability to generate the maximum driving force between driving force and soil. There are many factors affecting adhesion, mainly related to ground conditions, tire pressure, size, pattern and vertical load acting on the tire. For tractors, under certain soil conditions, reducing tire pressure, increasing tire support area, improving the grip of wheels on soil and increasing additional weight are all conducive to improving tractor adhesion. Low-pressure tires are widely used in tractors. Some tractors use widened tires and high-tread tires, and add counterweight iron to the driving wheels. These are all measures to increase tractor adhesion and improve tractor traction capacity. However, it should be pointed out that adding counterweight iron to the driving wheel can increase the adhesion, but at the same time it also increases the deformation of soil in the vertical direction and increases the rolling resistance. Therefore, whether to add counterweight iron depends on the specific use conditions and overall effect.