# The Current Development Status of Agricultural Machinery
## 2 Power System of Agricultural Machinery Chassis
### Mechanical Power System  
The power transmission topology of a mechanical chassis follows the conventional internal-combustion-engine-driven architecture. A fuel-powered engine serves as the primary power source, while a clutch enables controlled coupling and disengagement of the power flow. The generated torque is sequentially transmitted through the gear transmission system, universal drive shaft, and drive axle assembly. Following this, the main reducer amplifies the torque and redirects the power flow direction, after which the differential distributes torque to the individual wheels. Finally, the half-shafts deliver rotational power to the drive wheel assemblies. The working principle is illustrated in Figure 2. This transmission design demonstrates high mechanical efficiency and strong terrain adaptability, which has established it as the dominant configuration in tractor applications [22; 23; 24]. It is particularly well suited for medium- to low-complexity hilly terrains with inclines below 25\({}^{\circ}\). Western nations, capitalizing on their advantageous geographical conditions and advanced industrial technological heritage, have conducted earlier and more mature research into tractor chassis designed for hilly and mountainous terrains. The Terratrac series of mountain tractors manufactured by Switzerland's Aebi Company (Figure 3) feature a low-profile, wide-body design with a low center of gravity and agile steering, providing exceptional stability and traction adhesion in complex terrains such as hilly and mountainous regions. Figure 4 illustrates the MACH4 tractor developed by Karola AG [25], which utilizes a four-wheel drive system integrated with a quad-track chassis to achieve superior stability performance. Traditional mechanical power systems exhibit commendable obstacle navigation capability, traction performance, and slope stability. However, they are inherently constrained by high energy consumption, low transmission efficiency, complex operational procedures,  
Figure 3: Aebi Terratrac Series Mountain Tractors (Switzerland). Figure 2: Mechanical powertrain architecture. and inadequate load adaptability. These limitations become especially critical under abrupt slope change conditions, where inertial load impacts on the transmission system often lead to power interruptions and component fatigue failure, thereby intensifying energy efficiency degradation. [PERSON] et al. (2016) proposed an integrated control algorithm that incorporates engine-transmission efficiency characteristics. Through experimental validation, they identified an optimal operational line that significantly enhanced overall system efficiency. Nevertheless, this approach did not account for the time-varying influence of dynamic load impacts on transmission efficiency, which restricts its effectiveness in real-world applications. To address the issues of low accuracy and high noise levels in hydro-mechanical continuously variable transmission (HMCVT) efficiency prediction, [PERSON] et al. (2017) introduced a hybrid methodology combining variational mode decomposition (VMD), particle swarm optimization (PSO), and backpropagation neural networks. Despite its advantages, this method fails to differentiate between meaningful signals induced by load fluctuations and random noise. This limitation underscores the need to integrate chassis dynamics models--such as Bekker's equation--to reconstruct temporal load characteristics for more accurate efficiency modeling. [PERSON] et al. (2018) introduced an innovative design methodology for power-chained hydro-mechanical continuously variable transmission (PCHMCVT) systems, with the key advancement being the deep integration of chassis dynamics modeling into transmission system optimization. The study developed a tractor dynamics model based on traction force equilibrium equations to quantitatively assess the influence of rolling resistance, grade resistance, acceleration resistance, and tillage resistance on transmission loading.