1. Rolling resistance. The rolling resistance of the tractor is mainly caused by the deformation of the tire and the soil. Under the weight of the tractor, the tire is flattened and the soil is compacted. When the wheel is rolling, the parts of the tire that are in contact with the ground in the direction of the circle are successively squashed and deformed, and the soil above the wheel is pressed down to deform the soil and form a rut, which prevents the wheel from moving forward. Rolling resistance of rolling. There are many factors affecting rolling resistance, mainly related to factors such as the firmness of the ground and the size of the vertical load on the wet degree. 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 on dry hard ground, the tractor traction will be large. Under the same conditions of use, if the tire is added to the tire The greater the weight, 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 is running on soft ground, using low-pressure tires and increasing the tire support area, the vertical deformation of the soil can be reduced, rolling resistance can be reduced, and traction can be improved. Since tractors are mainly used for field operations, they often run on soft ground. In order to reduce the vertical deformation of the soil, the lowest pressure tires generally used by tractors are the same with widened tires. In our operations, we should pay attention to the difference in the use of low-pressure tires, widened tires and high-pressure tires.
2. Traction resistance. The traction resistance is the resistance that the tractor must overcome when driving the agricultural machinery to perform operations. It 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 force of the road surface to the driving wheels. Therefore, the magnitude of the driving torque Mk transmitted from 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 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 increase indefinitely, because when the reaction force of the soil, that is, the driving force Pk, increases to a certain level, the soil is destroyed, the driving wheel is severely slipped, and the driving force Pk cannot be increased. We call the maximum reaction force that the soil can produce against the driving wheel "adhesion." It can be seen that the maximum value of driving force Pk is not only limited by the rate of the internal combustion engine, but also limited by soil adhesion, and cannot be increased indefinitely.
Adhesion reflects the ability of the driver and the soil to generate the maximum driving force. There are many factors that affect the 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 the tire pressure within a certain range, increasing the tire supporting area, improving the wheel’s ability to grip the soil, increasing the attachment weight of the wheels, etc., are all conducive to improving the attachment of the tractor. Focus on low-pressure tires commonly used on tractors. Some tractors use widened tires and high-pattern tires, as well as adding counterweight irons to the tractor driving wheels. These are measures to increase the tractor’s adhesion and improve the tractor’s traction capacity. . However, it should be pointed out that adding counterweight iron to the driving wheel can increase adhesion, but it also increases soil deformation in the vertical direction and increases rolling resistance. Therefore, whether to add counterweight iron depends on the specific conditions of use and weighs the total The effect is selected.
The maximum adhesion between the tractor's driving wheels and the ground and the ability to resist skidding are called the adhesion performance of the tractor. If the adhesion performance is good and the slip is lighter, the driving torque can be fully utilized, the ability of the internal combustion engine can also be fully utilized, and the tractor will appear vigorous when working. If the adhesion performance is poor and the skidding is serious, the driving torque cannot be fully utilized, the ability of the internal combustion engine cannot be fully utilized, and the tractor will appear to be unable to perform vigorously when working, or the tractor is not very powerful. Severe slippage of the driving wheels will reduce the tractor's running speed, reduce production and economy, and accelerate the wear of the driving wheels and tires. In addition, the structure of the soil will also be destroyed.
The driving ability depends on the power of the internal combustion engine through the transmission system, so that the driving wheel obtains the driving torque Mk, and the driving wheel obtains the driving torque to give the ground a small backward horizontal force (tangent force) through the tire pattern and tire surface. The horizontal force Pk with the same driving force and opposite direction is applied. This Pk force is the driving force that pushes the tractor forward (also called the propulsion force). 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 tools, the tractor will move forward. If the driving wheel is set off the ground, that is, the driving force Pk is equal to zero, the driving wheel can only idle on the spot, and the tractor cannot travel; if the sum of rolling resistance and traction resistance is greater than the driving force Pk, the tractor cannot travel. It can be seen that the driving of a wheeled tractor is realized by the interaction between the driving torque driving wheels and the ground, and the driving force is greater than the sum of rolling resistance and traction resistance.
