A brief guide on auto transmission gear parts

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The automatic transmission is also called as auto shifting or self- shifting. Auto transmission gear parts and their operation can be elaborated as below:

  1. Hydraulic automatic transmission: This system is hydraulically operated using a fluid coupling or torque converter and a set of planetary gear sets to provide a range of gear ratios.
  • Torque converter: These are like fluid coupling, hydraulically connecting the engine to the transmission. The fluid coupling works well when both the impeller and turbine are rotating at similar speeds, but it is very inefficient at initial acceleration where rotational speeds are very different.
  • Planetary gears train: This portion of the transmission system constitutes of planetary gear sets as well as clutches and bands. As well, these provide various gear ratios, altering the speed of rotation of the output shaft depending on which planetary gears are locked.
  • Hydraulic controls: Depending on the vehicles running condition, oil pumps control various clutches and bands using special transmission fluid.
  • Continuously variable transmission: It is a different type of automatic transmission called as continuously variable transmission or CVT, which can smoothly and steplessly alter its gear ratio by varying the diameter of a pair of belt or chain – linked pulleys, wheels or cones.

E – CVT: Some of the world-class hybrid car makers like Toyota, Lexus and Ford have an electronically controlled continuously variable transmission. In this exercise, the transmission has fixed gears, but the ratio of wheel speed to engine speed can be continuously varied by controlling the speed of the third input to a differential using motor – generators.

  • Dual – clutch transmissions: These are the modern type of semi–automatic transmission and electrohydraulic manual transmission. It uses two separate clutches for odd and even gear sets. It can be even described as two separate manual transmissions contained within one housing and working as one unit.
  • Automated manual transmission: This setup of gear system is also known as semi-automatic transmission. This system utilizes a regular clutch and gear setup but automates the action by the use of sensors, actuators, processors, and pneumatics.
  • Manual controls: It is an automated gear system but has the mode in which the driver has full control of ratios change (either by moving the selector or through the use of buttons or paddles), completely overriding the automated function of the hydraulic controller.
  • Manufacturer – specific modes: These modes are like the customized transmission modes. These depend on the manufacturer. These transmission types are not that prevalent in the market.


Automated transmission systems are easy to use for the driver but it is mechanically a complicated system. The fuel consumption is more in this mode of transmission systems compare to the manual transmission. A detailed narration of the auto transmission system explained above may ease you to make the choice.

References: https://en.wikipedia.org/wiki/Automatic_transmission

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