Automotive Transmissions

Since the small torque range of the automobile engine cannot adapt to the requirements of automobile driving under various road conditions, the transmission that can change the speed ratio and drive torque is adopted in the automotive drivetrain to make the torque and speed output by the engine and other power systems vary in a considerable range.

Despite the rapid development of automatic transmission technology, the traditional engine-matched manual transmission (MT) will continue to play an important role for some time to come, mainly because of its low cost, high efficiency and reliable operation. At present, 5 speed MT is mainly used in China, and some cars start to carry 6 speed MT, covering SUV, middle-sized and compact vehicles. The 6 speed MT will gradually become the mainstream. ZF and BMW are developing the 7 speed MT.

Automatic transmission (AT), as the earliest AT, mainly consists of the hydraulic torque converter, planetary gear train and shift control system. Its variable speed and variable torque function is mainly accomplished through different gear combinations and hydraulic transfer.

The continuously variable transmission (CVT) is a transmission which is driven by a non-geared drive mechanism and can continuously change the gear ratio.

The dual clutch transmission (DCT) is different from other automatic transmissions in that it uses two clutches to control the clutch actuator and the gear selecting and shift actuator to achieve gear shift without power interruption. The DCT mainly includes dual clutch system, shaft-tooth system, control system, gear shift actuating system, clutch actuating system, cooling and lubrication system, parking system and other modules.

Automatic transmission control is an important technology in modern automobile and also the basic function of intelligent vehicles. With the development of the automobile industry, people put forward higher and higher requirements for the convenience and comfort of automotive controllability, and the increase of non-professional drivers has made the automatic transmission that can facilitate driving and reduce the labor intensity of drivers have a broad market.

The hybrid electric vehicle is a hybrid vehicle powered by two or more energy converters. Depending on the hybrid energy, the hybrid power can be divided into engine (gasoline or diesel) + motor, engine (gasoline or diesel) + hydraulic system, engine (gasoline or diesel) + mechanical system and so on. At present, the most common hybrid electric vehicle is of the “gasoline engine + motor” form.

Transmission is an important part of powertrain. In the transmission design, in addition to the transmission type, basic performance characteristics and purpose, this chapter mainly introduces the gear design, bearing selection and design, case design, parking mechanism design, synchronizer design, seal selection and transmission ventilation design and transmission test. The design of hydraulic torque converter and planetary gear train will be introduced in corresponding sections.

With the development of automobile transmission technology, higher performance requirements have been put forward for the transmission fluid. In particular, with the continuous improvement of fuel economy, the transmission fluid tends to develop towards low viscosity.

The hydraulic torque converter is located at the most significant end of the AT and is mounted on the engine flywheel, acting like a clutch with MT. It is a vane transmission with the liquid as the medium. When the hydraulic torque converter is working, the interaction between the active wheel blade and working liquid is used to realize the interconversion of mechanical energy and liquid energy (that is, the impeller continuously absorbs the power the internal combustion engine and transfers it to the turbine), and the transmitted torque is changed through the change of the liquid moment of momentum. With the ability to continuously change the speed and torque, it is a continuously variable transmission (CVT) most successfully used in the vehicles, fundamentally simplifies the manipulation; makes the vehicle start smoothly, accelerate quickly and gently with excellent vibration damping performance, thus prolonging the life of the powertrain and improving the ride comfort, average vehicle speed and driving safety; during stall, it has the maximum torque ratio, which prevents engine flame-out and more importantly, greatly improves the vehicle passability.

With the development of automatic transmission technology, noise reduction and efficiency improvement have become important issues in the field of automotive technology. In AT, the planetary gear train, which can obtain a large gear ratio and meet the requirements of miniaturization and lightweight, has been widely applied, which puts forward higher requirements for the noise and efficiency of the planetary gear train.

The AT electronic control system, as the brain of the AT, is mainly to communicate with other VOBCs through various sensors to obtain real-time transmission, engine and vehicle operating state, achieve accurate shift control and clutch control according to the vehicle speed, accelerator pedal and other signals, free the driver from the heavy manual shift and achieve good driving comfort and better fuel economy.

The automotive vibration and noise is an important factor that affects the ride comfort. The automotive vibration and noise is complex and difficult to analyze, but can be represented by the basic mass spring model in most of the phenomena. It is very important to understand the automotive vibration and noise by means of mass spring model.