Abstract
Much progress has been made in the development of automotive transmissions over the past 20 years, e.g., an increased speed number, expanded ratio spread and improved efficiency and shift quality. Automotive transmissions are moving toward electrification in response to stringent legislation on emissions and the pressing demand for better fuel economy. This paper reviews progress in automotive transmission technology. Assisted by computer-aided programs, new transmission schemes are constantly being developed. We therefore first introduce the synthesis of the transmission scheme and parameter optimization. We then discuss the progress in the transmission technology of a conventional internal combustion engine vehicle in terms of new layouts; improved efficiency; noise, vibration and harshness technology; and the shifting strategy and control technology. As the major development trend, transmission electrification is subsequently discussed; this discussion includes the configuration design, energy management strategy, hybrid mode shifting control, single-speed and multi-speed electric vehicle transmission and distributed electric drive. Finally, a summary and outlook are presented for conventional automotive transmissions, hybrid transmissions and electric vehicle transmissions.
Highlights
With pressing demands to reduce emissions and improve fuel economy, automotive transmissions have evolved over the past 20 years while rapidly progressing toward electrification
This review focuses on the progress of automatic transmission (AT), dual-clutch transmission (DCT) and continuously variable transmission (CVT) because they largely account for the development of transmission technology in the past 20 years and have gradually replaced manual transmission (MT) and automated manual transmission (AMT) in passenger cars
The results indicate that the optimal engine-start control strategy should choose a proper torque reserve and a corresponding clutch pressure that balances the engine-start time and torque responsiveness depending on the vehicle state and driver input
Summary
With pressing demands to reduce emissions and improve fuel economy, automotive transmissions have evolved over the past 20 years while rapidly progressing toward electrification. With the integration of the electric motor (EM) into conventional ATs, DCTs and CVTs are examples of transmission electrification and are normally realized by adding a hybrid module or replacing the launching element with a hybrid module. Such add-on solutions have excellent inheritance because most parts can be shared between conventional transmissions and hybrid transmissions, which facilitates modular design and manufacture. As for electric vehicles (EVs), single-speed gearboxes are most commonly used today It is not necessary for an EV to have a complex multi-speed transmission owing to the torque and efficiency characteristics of the EM.
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