The most common transmission systems that have been used for the automotive industry are manual transmission, automatic transmission, semi-automatic transmission, and continuously-variable transmission (CVT).
The first transmission invented was the manual transmission system. The driver needs to disengage the clutch (see Figure 4) to disconnect the power from the engine first, select the target gear, and engage the clutch again to perform the gear change. This will challenge a new driver. It always takes time for a new driver to get used to this skill.
An automatic transmission uses a fluid-coupling torque converter to replace the clutch to avoid engaging/disengaging clutch during gear change. A completed gear set, called planetary gears, is used to perform gear ratio change instead of selecting gear manually. With the invention of the automatic transmission, a driver no longer needs to worry about gear selection during driving. It makes driving a car much easier, especially for a disabled or new driver. However, the indirect gear contact of the torque converter causes power loss during power transmission, and the complicated planetary gear structure makes the transmission heavy and easily broken.
A semi-automatic transmission tries to combine the advantages of the manual and automatic transmission systems, but avoid their disadvantages. However, the complicated design of the semi-automatic transmission is still under development, and the price is not cheap. It is only used for some luxury or sports cars currently.
CVT has been used for low-powered machinery like scooters for a long time due to its highly efficient gear change. However, it is a challenge to install it on high power machinery because of the strength of the driving belt. With the progress of materials technology, engineers have been successfully installed it on automobiles, making the power transmission efficient.
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