How automatic transmission works?
The automatic transmission works start from the Torque converter. The torque converter continues the engine speed to the transmission input shaft by utilizing hydraulic pressure from the transmission oil called Automatic Transmission Fluid (ATF).
The torque converter will make the transmission input shaft rotate along with the engine speed. The transmission input shaft will be connected to other automatic transmission components such as clutch and brake components, planetary gear, and the final drive gear.
From the torque converter to the final drive gear, all of these components work mechanically and hydraulically. The clutch and brake components work mechanically and hydraulically. They work based on the hydraulic pressure supplied by the hydraulic control unit.
The hydraulic control unit has an electrical control and operation fully controlled by the Transmission Control Module (TCM). Yes, the Automatic Transmission Fluid (ATF) in the automatic transmission is regulated by the TCM by utilizing the opening and closing of the channel on the solenoid valve and the AT accumulator.
In addition, the TCM has also programmed the level of forwarding acceleration and reverse acceleration, known as the shift pattern. The shift pattern is formed based on the driving position on the transmission lever, the size of the gas pedal opening (throttle valve), and the output shaft rotation speed (rpm).
Based on the driving position on the transmission lever and the engine speed, the TCM will automatically change the acceleration level of the automatic transmission by activating the solenoid on the hydraulic control unit.
As a result, the ATF oil pressure in the hydraulic control unit will also be channelled to the clutch and brake components, forming a certain working combination. The combination of work between the clutch and brake on this automatic transmission will affect the gear ratio that occurs in the planetary gear component.
The planetary gear can obtain the speed and torque of each gear as in manual transmissions such as for 1st gear, 2nd gear, 3rd, etc. Also, the gear ratio for 1st gear is always greater than the gear ratio of the highest gear.
In addition, the working combination of this planetary gear unit can also change the direction of rotation of the output shaft so that the car can move backwards. Here's how automatic transmission works based on the position on the gearshift lever.
When the car is in the N (Neutral), P (Park) position
When the car is in the N (neutral) and P (Park) positions, all components in the automatic transmission will be in the idle position (rotating but not moving the vehicle). This idle position has been determined by the TCM so that no clutch and brake components work.
So, each of the mechanical components of the transmission, such as the torque converter, clutch and brake, planetary gear, the final drive gear is not connected to the engine rotation.
In addition, the hydraulic pressure in the hydraulic control unit will only flow to lubricate the moving mechanical components (no pressure activates the clutch and brake). With this condition, the car will not go even if we fully press the gas pedal.
Read Also:- Components of automatic transmission planetary gear type
- What does a torque converter do
- How a torque converter works
When the car is in the forward acceleration (D,2, L) position
When the car is in the forward acceleration position (the gearshift lever is in position D, 2, or L), the engine speed will connect to the input shaft of the automatic transmission. This condition also creates a rotation that can produce a rate of acceleration. Two main things will influence the rate of forwarding acceleration, the rotational speed of the transmission output shaft and the degree of opening of the throttle valve.
Both of these things will affect the shift pattern that occurs. For example, when in Drive position (D), when the gas pedal opening is about 15% and the output shaft rotation is 800 rpm, the transmission gear position is in 1st gear.
If the gas pedal pressure increases to 50% and the output shaft rotation increase to 4000 rpm, the transmission gear position will automatically move from 1 to 2, 2 to 3, to 4th gear by adjusting the solenoid and accumulator work on the hydraulic control unit. Take a look at the example of gear movement in the shift pattern table below.
In the picture above, the Upshift process applies, which automatically raises the acceleration gear to a higher level.
It also applies when the gas pedal is released suddenly at high speed. There will be an automatic downshift by the shift pattern stored in the automatic transmission computer memory. The decrease in acceleration gear on an automatic transmission is often called Downshift.
When the car is in Reverse (R) position
When the car is in the reverse position, the transmission computer will instruct the hydraulic control unit to adjust the clutch and brake to get the reverse gear combination on the planetary gear.
Yes, the combination of the clutch and brake on the automatic transmission can produce the best rotation direction for the planetary gear. Thus, the ratio and direction of rotation of the final drive gear can be reversed so that the car can move backwards.
That's the article about how the planetary gear type automatic transmission works on cars that you can convey. Hopefully, it can be helpful.