Trucks carry loads of various weights and require high power. Due to its distinctive characteristics from ordinary passenger cars, Fuel economy and dynamic performance are very important when designing.

The transmission is a very important factor in determining the dynamic performance of a vehicle among various parts of a vehicle, and has a great influence on improving the performance of the vehicle. Therefore transmission design must be considered very important. Design of gears are very complex process that requires consideration of tooth shape, vibration, deformation, and stress. Based on the development know-how, it is difficult to predict the vulnerability for various development requirements in the design by simple experience. Therefore, it is difficult to design an optimal design that satisfies requirements such as weight reduction and compactness.

The existing transmission development process does not go through systematic verification of the basic design due to cost and time issues. This development process leads to numerous failures in the parts development and prototype development stages.

In addition, these failure factors are directly related to the loss of the company, and considerable difficulties arise in securing the required performance established in the system concept design stage. Currently, transmission development companies stays at the low level of simply benchmarking products of advanced overseas companies, and they are having a lot of difficulties in securing their own technology.

In this study, firstly, the factors affecting the power performance from the perspective of a rotating body in an automobile powertrain are investigated. By calculating the mass moment of inertia of the powertrain for each 12-speed, the gears that affect fuel economy are identified. And these use as a basis for the design of weight reduction of gears and shafts.

Secondly, based on the basic design, a systematic design verification using CAE (Computer Aided Engineering) is performed to derive an optimized original design through structural analysis, life analysis, and optimization analysis of major components in the transmission

Thirdly, a performance tests are carried out by mounting the transmission manufactured based on the design plan to secure the reliability of the optimal design.

Lastly, assume that the power source was changed from the existing internal combustion engine power source to an electric motor, the performance of the existing internal combustion engine commercial vehicle and the transmission mounted electric drive (TMED) commercial vehicle are compared.