1. Rolling resistance.
The rolling resistance of a 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.
As the wheel rolls, the parts of the tire that contact the ground along its circumference are flattened and deformed, pressing down the soil in front of the wheel and creating ruts, thus generating rolling resistance that hinders the wheel's forward movement. Many factors influence rolling resistance, primarily the firmness and moisture of the ground, and the magnitude of the vertical load. For the same tractor, rolling resistance varies depending on ground conditions. For example, rolling resistance is low on asphalt, cement, or hard, dry surfaces, resulting in higher tractor traction. Under the same operating conditions, greater weight on the tires leads to greater vertical soil deformation, increasing rolling resistance. Generally, reducing tire deformation and vertical soil deformation helps reduce rolling resistance. When a tractor travels on soft ground, using low-pressure tires and increasing the tire's contact area reduces vertical soil deformation, lowers rolling resistance, and increases traction. Since tractors are primarily used for fieldwork and often travel on soft ground, low-pressure tires are generally used to minimize vertical soil deformation; the same principle applies to using wider tires. In our operations, we should pay attention to the differences in the use of low-pressure tires, wide tires, and high-pressure tires.
2. Traction Resistance.
Traction resistance is the resistance that a tractor must overcome to drive agricultural implements. It is equal to the traction force transmitted from the tractor to the implements through the connecting device. Since traction force equals the driving force minus rolling resistance, increasing the driving force and reducing rolling resistance are effective measures to improve traction.
3. Driving Force.
This is the horizontal reaction force of the road surface on the drive wheels. Therefore, the magnitude of the driving torque Mk transmitted from the internal combustion engine to the drive wheels through the transmission system indicates the greater the driving force Pk of the tractor. However, since Mk is determined by the power of the internal combustion engine, Pk is also limited by the engine's power. Simultaneously, Pk is also limited by soil conditions and cannot increase indefinitely. When the soil reaction force, i.e., the driving force Pk, increases to a certain level, the soil is damaged, the drive wheels slip severely, and the driving force Pk cannot increase further. We call the maximum reaction force that the soil can generate on the drive wheels "adhesion." Thus, the maximum value of the driving force Pk is limited not only by the internal combustion engine power but also by the soil adhesion, and cannot increase indefinitely.
Adhesion reflects the ability of the tractor to generate a large driving force between itself and the soil. Many factors affect adhesion, mainly related to ground conditions, tire pressure, size, tread pattern, and the magnitude of the vertical load acting on the tires. For tractors, under certain soil conditions, reducing tire pressure, increasing tire bearing area, improving wheel grip, and increasing wheel weight all contribute to improving tractor traction within a certain range. Low-pressure tires are commonly used on tractors, and some tractors employ wider tires, higher tread depth tires, and additional weights on the drive wheels-all measures taken to increase tractor traction and improve its pulling power. However, it should be noted that while adding weights to the drive wheels increases traction, it also increases soil deformation in the vertical direction, increasing rolling resistance. Therefore, whether or not to add weights depends on the specific operating conditions and requires a trade-off based on the overall effect.
The traction and anti-slip ability of a tractor's drive wheels between themselves and the ground is called its traction performance. Good traction and minimal slippage allow for full utilization of drive torque and the internal combustion engine's capabilities, making the tractor feel powerful during operation. Conversely, poor traction and severe slippage prevent the full utilization of drive torque and the internal combustion engine's capabilities, resulting in a tractor that feels powerless or lacks power. Severe drive wheel slippage reduces tractor speed, decreases productivity and economy, accelerates tire wear, and damages soil structure.
