The sizes and radii of the two clutches are different. Clutch 2 with a smaller radius is included in clutch 1. The two clutches are inlaid with each other in the installation position relationship, which is very compact and basically the same size and volume as the clutches of other types of gearboxes.
We know that the transmission route of power in the transmission is: input shaft -> gear -> output shaft. We regard a group of input shaft gears and a group of output shaft gears as sub-transmission 1, then the other group is sub-transmission 2. The ingenious design of the dual clutch trans is that the input shaft 1 is inserted into the hollow input shaft 2, which meshes with the gears of the output shaft 1 and the output shaft 2 respectively, and transmits power.
The reason why twin clutch is favored is that twin clutch has a natural advantage, which is unmatched by other types of automatic transmissions. This advantage is high transmission efficiency, fast shifting speed. Why? We will explain one by one:
(1) High transmission efficiency
Among all transmission modes, the transmission efficiency of gear transmission is the highest, which can reach more than 95%. The dual clutch trans is all geared during power transfer, while the automatic transmission has a torque converter in place of the clutch. The torque converter relies on hydraulic pressure to transmit power, and the power loss is relatively large. We can simply think that the transmission efficiency of twin clutch transmission can reach 95%, while the transmission efficiency of automatic transmission is about 80%, which is why matching twin clutch transmission models are more fuel-efficient.
(2) Fast speed
Because the two clutches of the dual clutch actuator work continuously and alternately, when one is working and the other is in a pre-working state, it only takes about 0.5 seconds for each shift, which greatly improves the shifting speed. At the same time, because the shifting speed is increased, the power interruption time of the vehicle is very short, and it is difficult for the driver to feel the change of the gear position, so the smoothness of the shifting of the vehicle is also improved.
The twin clutch transmission is divided into a dry double clutch box and a wet double clutch transmission. The structure of the two is basically the same, but the difference lies in the cooling method. The dry dual clutch trans is air-cooled, while the wet double clutch transmission is cooled by oil and air.
The first thing to know is that dry clutches use the friction between the clutch plates to transmit torque, and the friction of the clutch plates pressing against each other can generate a lot of heat. If the clutch heat dissipation effect is not good, the high temperature will scorch the clutch friction plate, causing the friction force of the clutch plate to decrease or even disappear, thereby slipping. The power of the engine cannot be transmitted to the drive shaft through the gearbox, which will cause the power of the vehicle to be reduced or even interrupted. This is the often-heard twin clutch overheating failure.
This weakness of the dry twin clutch makes it unable to withstand and transmit large torques. In a congested road section, the clutch is always in a semi-linked state, and the clutch friction plates are continuously working, so such road conditions are more likely to cause the dual clutch to overheat and fail. The wet clutch is different. The cooling method of oil cooling and air cooling speeds up the heat dissipation and can always keep the clutch working within a safe temperature range. Therefore, the reliability of the wet double clutch transmission is better, and it can transmit more torque. In the next few years, the application market of the wet twin clutch should be further expanded. At present, many brands are matching the wet dual clutch transmission in the planned models.
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