What Is An Automatic Transmission System? How It Works

Just like the manual transmission, an automatic transmission is used in an internal combustion engine. Their major purpose is to convert the engine power to the wheels. An automatic transmission system is also known as an auto, self-shifting transmission, or n-speed automatic. The n represents its number of forwarding gear ratios. This type of transmission is abbreviated as AT.

In this reading, we’ll explore what an automatic transmission is, its diagram, parts, types, and how it works.

Let’s get started!

What is Automatic Transmission?

The automatic transmission system is a type of motor vehicle transmission that changes the gear ratio automatically. The gear change occurs as the vehicle moves. Drivers have no business with the gear engagement as it is manually done in manual transmission.

The hydraulic planetary automatic transmission is the most popular in automobiles. However, larger devices are used for heavy-duty commercial and industrial vehicles as well as equipment.

Additionally, some other automated transmissions include continuously variable transmission (CVT) and automated manual transmissions. They also use the traditional torque converter hydraulic automatic transmission. This is the reason why they are classified as types of automatic transmission.

Related: What Is A Transmission System? Its Diagram, Parts, and Types

Diagram of Automatic Transmission

Automatic Transmission System

Parts Of An Automatic Transmission

To control the flow of power, choose the right gear ratios, and keep the car running smoothly in different weather and terrains, all these parts work with one another. Automatic transmissions are able to offer the convenience and efficiency that they do due to the precise coordination of these components:

Torque Converter

An automatic transmission would be incomplete without the torque converter. There are two primary components found inside the torque converter. These components are the impeller and the turbine. The engine transfers power to the gearbox by turning the impeller, which in turn powers the turbine. A lock-up clutch is an efficiency-enhancing feature of the torque converter that allows for a direct mechanical connection when cruising.

Oil Pump

The oil pump in an automatic transmission pumps the transmission fluid throughout the system. It provides the cooling and lubricating fluid that the torque converter, clutches, and other parts need. The gearbox would overheat and wear more quickly if fluid wasn’t circulated properly.

Planetary Gear Set

The automatic transmission’s core component is the planetary gear set. It comprises a sun gear, a planet carrier with multiple planet gears, and a ring gear. The gearbox may achieve varied gear ratios by engaging different combinations of these gears, enabling the vehicle to smoothly shift gears and travel forward or backward.

Clutch Packs

The clutch packs, also referred to as friction discs or plates, of a planetary gear set are responsible for engaging and disengaging various components. Hydraulic pressure causes clutch packs to grip together, allowing certain gears to engage and transmit power. The selection of gears depends on the varying pressure applied to the different clutch packs.

Band Brake

Certain automatic transmissions use band brakes to hold or apply resistance to particular parts. They work by wrapping around a drum attached to a specific gear or shaft and being activated hydraulically to control gear engagement.

Valve Body

In an automatic transmission, the valve body serves as the control center. As the transmission fluid flows through it, different valves and channels control the engagement of clutch packs and bands. The vehicle’s computer (ECU) sends signals to the valve body, which changes the hydraulic pressure to make shifting gears smooth and easy.

Output Shaft

The output shaft transfers torque from the gearbox to the wheels of the vehicle. It transfers the engine’s rotational force to move the vehicle forward or backward through the planetary gear set.

Oil Pan

In the transmission, the oil pan is a reservoir that stores transmission fluid at the bottom. It also houses the transmission filter, which is responsible for the removal of contaminants from the fluid. Periodic maintenance entails the replacement of the filter and the replenishment of the transmission fluid through the removal of the oil pan.

Types of Automatic Transmission

Below are the various types of automatic transmissions seen in modern and older vehicles:

Traditional Automatic Transmission

The traditional automatic transmission is the most common, known as torque converter automatic. It is widely used among all kinds of automated transmission. A hydraulic fluid coupling or a torque converter is used to perform its operation.

These gears’ changing operation is achieved with a clutch in manual transmissions. An ECU (Engine Control Unit) is used to allow smooth and precise engine control of the vehicle. It is directly connected to the transmission mechanism.

Dual-Clutch Transmission (DCT)

The dual-clutch transmissions are a combination of automatic and manual transmissions. A torque converter is eliminated, but two separate shafts with clutches are used for changing gears. One shaft is for odd-numbered gears, while the other is for even-numbered gears.

Engaging higher and lower gears can be smooth but get noisy and rough shifting if wear occurs. In the dual-clutch transmission, drivers do not need to change gearbox fluid. The clutches are dry and wear out their fractional quality eventually.

Automated-Manual Transmission

The automated manual types are also known as semi-automatic transmissions. It works with a clutch and gear configuration. However, it makes use of sensors, actuators, and processors. Vehicles with such transmissions are known to have jerky engine performance. It runs at low speeds at hard acceleration, but it’s highly economical in terms of fuel mileage.

Continuously Variable Transmission (CVT)

The CVT types of transmission use belts or pulleys instead of traditional steel gears. Seamless gear shifting is obtained due to the engine speed, or RPM. Maximum efficiency and continuous acceleration are accurate in this transmission. But the engine can be so noisy.

Tiptronic Transmission

The Tiptronic transmission is used on high-performance and sports vehicles. It is also called “manumatic.”. Porsche was a pioneer of this transmission in the 1990s. It works similarly to a manual gearbox, but it uses a torque converter instead of a clutch pedal. This transmission gives a chance for automatic shifting of the gears, and drivers can override the automatic mode’s manual selection of gears. Tiptronic transmissions are designed with a built-in safety device that prevents the gearbox from being damaged. It is achieved with over-revving when downshifting.

Direct Shift Gearbox (DSG)

A direct-shift gearbox is similar to the dual-clutch setup. It also uses two clutches, which disengage alternately when changing gears. Faster shifting and seamless acceleration are obtained with this transmission. Its modern version offers fuel efficiency that exceeds that of manual gearboxes. Unlike the DCT, direct shift gearboxes are wet transmissions. Fluids are regularly changed, which must lead to vehicle service or maintenance.

How Automatic Transmission Works

When the engine is spinning slowly, very little torque is transmitted through a fluid and turbine inside the torque converter. And when the engine is spinning quickly, all of the engine’s torque is transferred to the transmission.

The torque converter is the reason why cars with automatic transmissions move slowly forward when idling and in the drive. A small amount of the engine’s torque is supplied to the transmission’s input shaft.

The torque converter handles the connection of the transmission’s input from the engine. the gears inside the transmission are engaged without the driver’s direct instruction. The transmission uses a single concentric shaft with a set of gears inside and around each other in a planetary arrangement, including a sun gear.

A planet carrier holds multiple planet gears and rings gears. The planetary gear set functions by changing the rate of input to output gear speeds through the engagement of one gear to another. The range of available ratios depends on which is engaged.

Furthermore, there is a complete hydraulic system or control system that engages the set of planetary gears at a given time. An electronic control unit is in charge of controlling this hydraulic control system.

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