AT automatic gearbox principle


Talk to the working principle of the AT automatic gearbox today.

Let's talk about a small story here. Although the structure of the manual gearbox is closest to the double clutch DCT gearbox. However, the first paragraph can automatically shift, and the gearbox without the clutch pedal is an AT automatic transmission. This is also the origin of this noun.


↑ HYDRA-MATIC automatic gearbox is used in Cadillac's model (from General Motors)

Although I have introduced two automatic gearboxes in 1908, a two-stop automatic transmission is introduced, but the truly commercial commercial for AT automatic transmission from General Motors is a HYDRA-MATIC automatic transmission developed by the World War II tank M24. The gearbox was successfully applied in Cadillac in 1947 after the war. It is possible to automatically shift from a big selling point for high-end models without stepping away. The HYDRA-MATIC automatic transmission has also laid the prototype of modern AT automatic gearbox.


 ↑ 1947 General Group Hydra-Matic Automatic Transmission (from General Motors)

AT automatic gearbox contains two major feature parts

Liquid coupler

2. Planetary gear set

Hydraulic Coupler


↑ ↑ Structure of the hydraulic coupler (from mass self-study textbook SSP)

The AT automatic gearbox can replace people to complete shifts and steps, the process can be said that the greatest hero is a hydraulic coupler. It is like two opposing electric fans. After the side is turned, the air flow will drive the other side to follow the rotation. This power transmission method that allows the speed difference is perfectly solved how the speed of speed synchronization is perfect after the shift. Under the incorrect conditions of early electric control technology, the Liquid coupler helped the AT automatic transmission to successfully bypass the largest technical difficulty. At the same time, the new advantage of the AT automatic gearbox is also introduced. That is, the larger the speed difference, the greater the torque. Make the AT automatic gearbox to provide very large start torque when the vehicle starts.

Planetary gear set


↑ Planet gear set dismantling photos (from mass self-study textbook SSP)

The manual gearbox and dual-clutch DCT gear sets that are parallel with a parallel multi-axis. The choice of different gear is complete through the dog teeth clutch DOG-CLUTCH. In order to avoid actuators with higher electronically controlled precision, the AT automatic gearbox is introduced into the planetary gear set. The largest feature of the planetary gear set is that the input shaft and the output shaft are coaxial. The corresponding multi-chip clutch having a lower electronically controlled requirement is used as an actuator.


↑ Planetary gear set structure diagram, left ordinary, right double small gear type (from mass self-study textbook SSP)

The planetary gear set is like today's sun with the planet system of the Earth. The central axis is a sun gear, and the outside is surrounded by planetary gears. In order to fix the planetary gears around the sun, the planet carrier is used as a bracket to carry planetary gears, and one is shaft power transmission. The outermost ring of the planetary gear is the internal gear (also known as the ring gear). In order to improve the power transmission capacity, some planetary gear sets are deformed into two sets of pinion mutual transmission power. A group of contact with the sun is in contact with the other group. It is called a double small gear planetary gear set.


↑ Multi-film Actuator Structure Schematic (from BOSCH Textbook)

In order to make a plurality of different gears in the planetary gear set, the plurality of clutches are here as an actuator. The rotation of the sun gear, the planet carrier and the inner ring gear is controlled by the clutch or stopping the formation of different teeth. When the plurality of clutch is used to lock (axis and transmission housing stationary), it is referred to as a brake BRAKE. The shaft is called clutch CLUTCH when the shaft is rotated with another axis.


↑ Composite planet gear set structure diagram, left partner, right in the right sun (from Bosch textbook)

At the same time, in order to simplify the structure of the gearbox in the expanded gear combination. The former people came up the method of composite planetary gear sets. The composite planetary gear set is a means of consolidation, and a plurality of planetary gear sets are manufactured in one mechanism. Commonly used shared sun gears, there are two sets of planetary gears (planet carriers) and internal ring gears, respectively. And a common interior ring gear, and there are two sets of planetary gears (planet carriers) and sun round programs.

AT automatic gearbox video

3. Example analysis


↑ Volkswagen 6-speed transverse AT automatic gearbox, left schematic, right structure diagram (from mass self-study textbook SSP)

Since the mass sales in China is huge, we analyze the structure as an example of 6-speed transverse AT transmission used by the public. From left to right, the hydraulic coupler is connected to the engine. Then it is close to the oil pump. The power is then transmitted to the first planetary gear set. As mentioned previously, it consists of the solar wheel S1, the planetary gear P1, the planet carrier PT1, and the inner gear H1. The right side of the gearbox is a set of composite planetary gear sets. Two planetary gear sets shared inner ring gear H2, and there are two planetary gears P2 / P3, the planet carrier PT2 and the sun gear S2 / S3. Both the brake B1 / B2 and the clutch K1 / K2 / K3 composed of different multi-chip clutches combine 6 front gear / 1 reversing.

4. Tiptronic gearbox control strategy


↑ Tiptronic power transmission strategy flow chart (from Bosch textbook)

Everyone understands a lot of knowledge of the Volkswagen AT gearbox begins with a name Tiptronic. In fact, this name is not a mechanical structure, but a gearbox control strategy. It originated from Porsche on the control strategy of the sports car AT gearbox application. Its feature is to give an AT automatic gearbox different driving mode and manual addition and subtraction. Under the premise of collecting the vehicle status (throttle, engine speed, speed, speed, acceleration), the uppermost shift policy matches the shift characteristic curve in accordance with the shift mode. The second floor is shorter transient response in the vehicle status (overlying or snow). The most underlying can be responded to the hand-moving unit according to the engine speed limit.

The above, the principle of the AT automatic transmission is introduced. It is the earliest automatic gearbox type. And as always provide a comfortable and smooth shift experience. Matching with big displacement engine is also perfect. However, it is also working to meet fuel consumption requirements. I hope this brief introduction to understand the AT automatic gearbox help.

Reference and extended reading:

Bosch textbook - Bosch Traditional Power Transmission System and Hybrid Drive System