Breakdown of Transmission Types

Out of all of the systems controlling your car, one of the most important is the transmission. This mechanism transmits the power from the engine to the wheels.

To better understand how a transmission works, first you need to understand a few key terms.

Transmission Gear

Transmission gear refers to the set of toothed wheels that function together to alter or determine the relationship between the speed of the wheels and the engine speed of the vehicle. This term also describes the ratio of the gears selected by the driver on the output and input shafts.

 Gear Ratio

The gear ratio refers to the ratio at which the output and input gears rotate (i.e. 3:4 ratio).


A clutch is a mechanism for connecting and then disconnecting the engine from the transmission system of the vehicle.

 Shift Lever

The shift lever refers to the control lever first used by the driver to manage the gear range of the transmission.


An H-Pattern is used to describe the arrangement of gears designated on the knob of the shift lever, which is where the placement falls in a parallel row series.

Once you understand the terminology, then it is easier to grasp the function and mechanics of a transmission.

Types of Transmissions

Cars are manufactured with a variety of transmission types. These types include:

  • Manual Transmission (MT)
  • Dual-clutch Transmission (DCT)
  • Automatic Transmission (AT)
  • Semi-Automatic Transmission (SAT)
  • Continuously Variable Transmission (CVT)

The automatic transmission is by far the most popular variety, but the manual transmission with its simpler function and construction is also an old-time favorite.

Manual Transmission

A manual transmission includes a set of gears and a pair of shafts, the output shafts and input shafts. During an engagement, the gears on one shaft mesh with the other gears on the other. The overall gear ratio results between the engaged gear on the output shaft and the selected gear on the input shaft. Overall, the manual transmission is fully operated by the driver without any computer controls which makes it the most exciting for an auto enthusiast.

 Dual-Clutch Transmission

The function of the dual-clutch transmission is almost the same as a manual transmission, but the difference lies in the control system. The dual-clutch transmission features a computer control. As it bridges the gap between automatic and manual transmissions, then it is becoming widely popular among customers. The biggest advantages of the dual-clutch transmission are its fuel economy, ease of operation, and shift times.

Automatic Transmission

The automatic transmission is the most popular type of transmission. One of the main differences between a manual transmission and an automatic transmission is that the automatic transmission doesn’t have a clutch. The automatic transmission uses a torque converter to couple or decouple the gear set with the engine.

The automatic transmission can be further sub-categorized into the semi-automatic transmission and continuously variable transmission.

Semi-Automatic Transmission

A semi-automatic transmission is a system that uses electronic processors, actuators, and sensors for gearshifts on the driver’s command. With the semi-automatic transmission in use, there isn’t any need to use a clutch pedal for changing gear. In this system, electronic equipment actuates the clutch, synchronizing the torque and timing required for smooth and quick gearshifts. Semi-automatic transmissions are popular in many vehicles.

Continuously Variable Transmission

A continuously variable transmission, or a single-speed transmission, is a type of automatic transmission that can move seamlessly through gear ratios falling between a minimum and maximum value. It is one of the best features of the CVT, as other mechanical transmissions offer a finite number of gear ratios. It is because of its flexibility that the input shaft then maintains a consistent angular velocity.

How a Transmission Works

When the driver shifts to select gears in the manual transmission, then the shifter engages a linkage which controls the gears movement along the input shaft. On moving the lever, backward or forward, the driver selects between the two gears given on a linkage. Note that the car with four gears uses two gear links while the model with five speeds uses three gear links. By moving the shift lever right and left, the driver makes changes between the linkages.

First, the driver disconnects the engine from the transmission’s input shaft by pushing the clutch pedal. When he does, then it engages the gear in the manual transmission. The disconnection frees the input shaft gears to move. Then, the gears on the shaft are engaged when the engine sends torque through it. Once the clutch disconnects the power to the transmission from the engine, then the driver chooses the appropriate gear while releasing the clutch which re-engages the power of the engine to the input shaft. Finally, this process propels the vehicle using the chosen gear ratio.

Automatic Transmissions

As in the manual transmission, the mechanics of the automatic transmission use one concentric shaft.  The gears on this shaft work as the ratio of output to input gear speed changes. The process involves engagement of one gear with another. Here, a complex hydraulics system is present which controls the mechanism and not a shift lever. This system includes a set of planetary gears, engaged at a given time. An electronic control unit programmed to suit the engine, which in turn, controls this hydraulic control system.

The gear sets are connected by a series of internal clutches to the motor’s input. These move as the hydraulic system moves and determine the gear ratio of the output to the drive shaft.

The functioning of a semi-automatic transmission and continuously variable transmissions is far better than that of traditional automatic transmissions. As mentioned earlier, with semi-automatic transmissions there isn’t any need for shifting the gears manually, as the transmission’s computer handles the job. Semi-automatics retain a clutch like a manual transmission controlled by electro-hydraulic systems.

Dual Clutch Transmissions

The dual-clutch transmission uses two different clutches, each at even and odd gear sets. It almost seems like two manual gearboxes placed into a single housing. Typically, the dual clutch transmissions operate in the same way as a standard automatic transmission with no clutch pedal and a PRND gear selector. They may also function like an automatic transmission, where the gears can be shifted automatically via a separate gate or paddle shifters on the gear selector.

Several components work together to move your vehicle. If any one of them is out of alignment, then the car won’t travel. Getting the clutch and gears to operate smoothly can be difficult, but with proper maintenance, your transmission should hold up. First, check your transmission fluid when you change your oil. Then, take your car to a transmission shop if you feel it shifting hard or there is a lack of power. The transmission is an extremely important system within any vehicle.



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