Thanks to the continuous development of the automobile, today you can choose your favorite from a wide range of transmission types when buying a car. The semi-automatic transmission is always a source of confusion. Is it an automatic transmission or not?
Clutch and converter
With a conventional manual transmission, you separate the engine from the transmission by means of a clutch. You have to operate these with your foot via the clutch pedal. In a semi-automatic or automatic transmission, the clutch pedal is not present. Does this mean that the two shift systems do not require a clutch??
At automatic transmission if this is indeed the case. Instead of a clutch between the engine and the transmission there is a torque converter. This transmits the torque from the engine to the lamina clutches in the automatic transmission. In addition, the torque in the torque converter is amplified to allow starting or acceleration. The automatic transmission contains planetary wheels that are braked or accelerated by means of brake bands and laminae clutches. This is how manufacturers realize up to nine gear ratios in a very small space.
The semi-automatic transmissions on the other hand, hardly differs from a manual transmission. a conventional dry clutch is attached to the flywheel, which is located between the engine and the gearbox. This transfers the torque from the engine to the input shaft of the manual transmission. The engine can be separated from the transmission via the diaphragm springs on the clutch housing. During a gearshift, individual gears are firmly connected to the input or output shaft. As with a manual transmission, up to six different gear ratios are possible.
The clutch process
But the semi-automatic transmission is not a manual transmission. With a manual transmission, you take over the shifting process completely yourself. On the other hand, the semi-automatic transmission takes over the clutch process for you. While you initiate the gear change with the help of a shift lever or paddles, an electrohydraulic system separates the engine from the transmission.
This is done via a sensor located in the gearshift lever or in the gearshift paddles. If the sensor detects that you want to change gears, it immediately sends an electrical signal to the transmission control unit. The control unit then forwards a command to the actuator. In a semi-automatic transmission, this is a hydraulic pump or electric motor. A release mechanism disengages the clutch and separates the engine from the transmission.
The gear change
After the engine is disconnected from the transmission, the transmission gears are load-free and the gear change takes place. The transmission control unit sends electrical signals to the actuators in the transmission. These are connected to the gearshift forks and thus adjust the gearshift sleeves as desired. The gearshift sleeves detach the gears from the transmission shaft or connect them firmly to it. This enables a new transmission ratio and the clutch is engaged again.
More popular alternative
The semi-automatic transmission differs from the automatic transmission in the way it shifts gears and in the way it is constructed. For this reason it cannot be named as such. With an automatic transmission, gear changes can also be barely noticeable. Semi-automatic transmissions, on the other hand, take longer to change gears, making them less comfortable for the driver.
This is why manufacturers are increasingly using dual-clutch transmissions today. These are based on the principle of the semi-automatic transmission, but have two clutches. One clutch engages the even gears and the other engages the odd gears. While one clutch is engaged, the other is disengaged and its gears are load-free.
This means that the next gear can already be shifted on this transmission shaft. As soon as a gear change is desired, only the clutch has to be engaged. This enables faster gear changes, better exhaust emission values and a more comfortable driving experience. The dual-clutch transmission is therefore also the more popular alternative to an automatic or manual transmission.