What Is Automatic Transmission and How Does it Work?

A “transmission” is simply the name given to the device that connects the engine to the wheels. It is a device designed for cars that changes the gear size in the car to more efficiently use engine power. In simple terms, it allows us to convert the engine power output to the wheels.

A car transmission consists of gears that are used to transfer the rotational motion of one shaft to another. They come in two main types, automatic transmissions, and manual transmissions.

Why do Automobiles Need Transmissions?

You don’t need to be a technological genius to understand why a car needs an engine. It provides the motive force to move the vehicle. And it is also pretty evident that it is critical to get the motive force from the engine to the wheels to drive the car.

The system that does that is called the transmission. But there’s more to it than a simple mechanical hookup between the engine and drive wheels.

An internal combustion engine creates power and torque in a very narrow operating range. This necessitates that the car has gears that enable the engine to operate in its range as the vehicle accelerates, reaches a constant cruising speed, and decelerates. Without that, a car’s speed potential would be extremely limited.

In an internal combustion engine car with a manual transmission, the driver changes the gears. A reasonably straightforward mechanical arrangement enables the driver to use a shift lever to choose the individual gear from among a selection of gears appropriate for the immediate driving situation.

Manual shifting between gears requires the frequent disconnection of the engine from and reconnection to the driving mechanism—the propellor shaft and half-shafts that go to the drive wheels—during any drive.

The mechanical clutch is the means of disconnection and reconnection. It is foot-operated using the car’s clutch pedal. Changing gears requires dexterity and footwork. Though doing it well can be fun, it also takes effort.

What is Automatic Transmission?

An “automatic transmission” is one where the driver doesn’t have to shift gears manually. Automatic car transmissions are different from conventional manual transmissions. Both are used in automobiles; however, there are some key differences between the two.

Automatic transmissions use hydraulic fluid to engage the correct gear and maintain optimal RPM. They are found in most modern vehicles today.

Manual transmissions are still very popular because they offer better fuel economy and superior control. However, many people prefer the convenience of automatic transmissions over manual ones.

Automatic Transmission Diagram

Parts of Automatic Transmission

Let’s take a look different parts of an Automatic Transmission:

• Transmission Casing.
• Torque Converter.
• Pump (aka impeller).
• Turbine.
• Stator (aka Reactor).
• Torque converter clutch.
• Planetary Gears.
• Brake Bands and Clutches.

#1. Torque Converter.

The torque converter sits between the engine and transmission. It looks like a donut and is located in the large opening of the bell housing of the gearbox. This has two main functions in relation to the transmission of torque:

• Transfers power from the engine to the transmission input shaft
• Multiplies engine torque output

It performs these two functions thanks to hydraulic power provided by the transmission fluid inside your transmission.

#2. Torque converter clutch.

To avoid this loss of energy, most modern torque converters have a torque converter clutch attached to the turbine.

When the car reaches a certain speed (usually 45-50 mph), the torque converter clutch engages, causing the turbine to spin at the same speed as the pump. A computer controls when the converter clutch is engaged.

#3. Planetary Gears.

On an automatic transmission, gear ratios increase and decrease automatically. And this can happen thanks to the ingenious design of planetary gear.

A planetary gear consists of three components:

• A sun gears. Sits at the center of the planetary gear set.
• The planet gears/pinions and their carrier. Three or four smaller gears surround the sun gear and are in constant mesh with the sun gear. The planet gears (or pinions) are mounted and supported by the carrier. Each one of the planet gears spins on their own separate shafts that are connected to the carrier. Planet gears not only spin, but they also orbit the sun gear.
• The ring gears. The ring gear is the outer gear and has internal teeth. The ring gear surrounds the rest of the gear set, and its teeth are in constant mesh with the planet gears.

#4. Brake Bands.

Brake bands are made of metal that is lined with organic friction material. The brake bands can be tightened to keep the ring or sun gear stationary or loosened to allow them to rotate.

Whether a brake band tightens or loosens is controlled by a hydraulic system.

#5. Oil Pump.

The pump looks like a fan. It has a series of blades extending from its center. The pump is mounted directly on the torque converter housing, which in turn is bolted directly to the engine flywheel.

As a result, the pump rotates at the same speed as the engine’s crankshaft. The pump “pumps” transmission oil from the center to the outside.

How does an Automatic Transmission Work?

When you drive a vehicle with an automatic transmission, putting the car in Drive activates the system. By pushing on the accelerator pedal, the engine’s crankshaft begins rotating more rapidly and this, in turn, leads to more pressure within the torque converter.

As the car moves forward, the transmission’s hydraulics and electronics sense its speed in relation to engine speed, and the transmission changes gears automatically in response.

In the classic automatic transmission, hydraulics within the transmission sense those speed changes. Those hydraulics then activate other hydraulics to change gears in the planetary gear set.

Today, electronics supplement that sensing process and the automatic transmission works in concert with the car’s other systems.

So, the next time you drive your car, you should be aware that millions of calculations go into the gear that your transmission chose at that moment. Your car is doing a lot of work every second to make driving much easier for you.

Gears of an Automatic Transmission

The gears of an automatic transmission include the following:

When you switch your vehicle to drive mode, switch on all available forward gears. This means that the transmission can move between its entire gear range if necessary. Six-speed automatic transmissions are the most common number of gears, but older vehicles and entry-level compacts may still have four or five automatic transmissions.

Third gear either blocks the transmission in third gear or limits it to first, second and third gear ratios. This provides the power and traction needed to either go uphill or downhill, or to pull a boat, RV, or trailer. When the engine reaches a certain number of revolutions per minute (RPM), most vehicles automatically shift into third gear to prevent damage to the engine.

The second gear either blocks the transmission in second gear or limits it to the first and second gear ratios. This equipment is ideal for riding uphill and downhill in slippery conditions, as well as riding in ice, snow and other poor weather conditions.

First gear is used when you want to lock the transmission in first gear. However, some vehicles automatically turn this gear off to protect the engine at a certain speed. Like second and third gear, this gear is best for towing, going up or down hills, and when driving in slippery, icy conditions.

What are the types of automatic transmission?

Some of the most commonly used gearboxes in this category include:

• Automated Manual Transmission (AMT),
• Continuously Variable Transmission (CVT),
• Dual-Clutch Transmission (DCT) and
• Intelligent Manual Transmission (iMT)

#1. Automated Manual Transmission – AMT.

Automated Manual Transmission or AMT is an automatic transmission that uses an actuator and an onboard computer to determine which gear to shift at which engine speed. With AMTs there is a selector stick which you will have to use to select the drive mode.

Once engaged, sit back, relax and drive, the AMT will push the clutch and shift gears for you. The AMT is fairly smooth, however, you might feel a slight jerk when the gears change automatically during up and downshifting.

The AMT is an affordable transmission system and can be found on cars like Tata Nexon, Maruti Suzuki Wagon R, Hyundai Grand i10 Nios and many others.

Advantages

• Driving Comfort – The gears are being automatically changed without your intervention.
• Efficiency – Since the onboard computer predicts the accurate time for the gear change as per engine speed, you get good fuel economy.
• Manual Mode – Some AMTs also have a manual mode, so when required you can always use it if you feel that driving is becoming too easy. Unlike the manual transmission you just need to nudge the gear lever up and down to upshift or downshift, all without a clutch.

#2. Continuously Variable Transmission – CVT.

Continuously Variable Transmission or CVT is a newer type of automatic transmission. In this kind of transmission gear ratios change continuously depending on the speed of the car.

This is done by two conical pulleys that are connected by a belt that changes diameters by moving together or apart depending on the gear ratio required by speed, weight, incline, and decline.

CVT is very efficient as it tries to maintain constant engine revolutions per minute (RPM) while the vehicle moves at varying speeds.

Advantages

• Very Efficient – CVT tries to maintain constant engine speed this in turn gives better fuel efficiency.
• Smooth Ride Quality – Due to constant engine speed CVT gives a ride quality that is smooth and pleasing.

#3. Dual Clutch Transmission/Direct Shift Gearbox – DCT/DSG.

Direct Shift Gearbox or Dual Clutch Transmission uses two clutches to change gears automatically. Gears placed in odd and even groups of 1 3 5 and  2 4 6 are operated by two separate clutches.

This gear arrangement prevents power loss from occurring unlike AMT and manual transmission as the gears are already engaged and ready to be deployed as soon as one gear rev is achieved.

A DSG/DCT Transmission gives smooth and efficient performance and can be seen on high end cars.

Advantages

• Faster Shifting – The arrangement of gears in a DSG transmission allows superfast and smooth shifting of gears.
• Better Mileage – Fast and accurate shifting of gears results in better mileage.

#4. Intelligent Manual Transmission – iMT.

Intelligent Manual Transmission is Hyundai’s latest offering in automatic transmission. iMT unlike other transmissions, does involve manual shifting of gears albeit without a clutch.

An actuator engages the clutch upon feedback from sensors when the gear stick is moved. Just like manual transmission, the driver is in control of gear shifts, and fuel economy.

Advantages

• Efficient – Since the clutch control is automated, there is no compromise on fuel efficiency.
• Low cost – iMT is cheaper than most automatic transmissions in the market.

Advantages of Automatic Transmission

• Ease of Use. Automatic transmissions are known for their user-friendly nature. With no need for manual gear shifting, drivers can focus more on the road, making them an excellent choice for those who prefer a less involved driving experience.
• Convenience in Traffic. Stop-and-go traffic can be a hassle with a manual transmission, requiring constant shifting between gears. Automatic transmissions excel in such conditions, offering seamless transitions between gears without driver intervention.
• Reduced Learning Curve. Learning to drive with an automatic transmission is generally simpler than mastering a manual gearbox. This makes automatics an attractive option for new drivers or those who prefer a more straightforward learning process.
• Growing Technological Advancements. Modern automatic transmissions often have advanced features such as adaptive shifting, hill start assist, and sport mode. These technologies contribute to a more refined and customizable driving experience.
• Resale Value. Automatic transmissions have become the norm in many markets, potentially increasing the resale value of your vehicle. This is particularly true in regions where automatics are more popular or preferred.

Disadvantages of Automatic Transmission

• Cost and Maintenance. Automatic transmissions are generally more expensive to manufacture and repair than manual transmissions. Additionally, maintenance costs can be higher, making them potentially costlier over the vehicle’s lifetime.
• Fuel Efficiency. Traditionally, manual transmissions were considered more fuel-efficient than automatics. While technological advancements have narrowed this gap, some drivers still prefer manuals for their perceived better fuel economy.
• Less Control for Enthusiasts. Driving enthusiasts often appreciate the control and engagement of a manual gearbox. Automatic transmissions, while convenient, may not provide the same level of involvement for those who enjoy the act of shifting gears themselves.
• Towing Capacity. In certain scenarios, manual transmissions offer better towing capabilities. If towing heavy loads is a regular part of your driving needs, a manual transmission might be a more suitable choice.
• Initial Cost. Vehicles equipped with automatic transmissions tend to have a higher initial cost than their manual counterparts. This upfront expense might be a consideration for budget-conscious buyers.

FAQs.