Automatic Transmission, How it works?

Summary

This video script delves into the intricate workings of automatic transmissions, focusing on the planetary gear set as the core mechanism. It explains how different speeds are applied to the sun and ring gears to achieve various gear ratios, utilizing clutch packs for power transmission. The script also covers the function of the transmission control unit and the torque converter, providing a comprehensive yet simplified explanation of high-performance automatic transmission systems.

Takeaways

• 🏎️ Automatic transmissions are popular in high-performance automobiles for their ease and reliability.
• 🌟 The working principles of automatic transmissions are based on the planetary gear set, which is a complex mechanism.
• 📚 Planetary gear sets consist of two inputs (ring and sun gears) and one output (planet carrier).
• 🔄 Different speeds applied to the inputs result in various output speeds, which is the core of automatic transmission operation.
• 🔄🔄 The ring and sun gears can rotate at the same speed, or in opposite directions, affecting the gear ratio and direction of the vehicle.
• 🌀 The speed variation is achieved by engaging a few clutch packs, which transmit different rotation speeds to the gears.
• 🔧 In an automatic transmission, there is no direct connection between the input and output shafts; an intermediate shaft and clutch packs are used for power transmission.
• 🛠️ Clutch packs lock the hub to the case, creating the simplest form of automatic transmission.
• 🔄 Applying different clutch packs to the planetary gear sets allows for achieving various gear ratios, including 1st, 2nd, and higher gears.
• 🔄🔄🔄 The combination of applying C1 and C4, for example, results in a higher output speed, demonstrating the gearing process for higher gears.
• 🔄🔄🔄🔄 A direct drive, like 4th gear, is achieved when the sun and ring gears rotate at the input shaft speed, facilitated by specific clutch pack applications.
• 🔄🔄🔄🔄🔄 The 3rd planetary gear set is used to achieve additional gear ratios, with the sun gear always connected to the input shaft.
• 🔄🔄🔄🔄🔄🔄 The reverse gear is achieved by applying the ring gear clutch, causing the sun gear to rotate in the opposite direction.
• 🤖 A transmission control unit decides when to apply which clutch pack, automating the gear shifting process.
• 🔄⚙️ A torque converter is necessary in automatic transmissions to isolate the engine rotation from the transmission when brakes are applied, using fluid coupling.

Q & A

What is the primary advantage of automatic transmissions in high-performance automobiles?

The primary advantage is that they offer easy and reliable driving with the ability to transmit different rotation speeds through a complex mechanism.

Which company's automatic transmission is used as an example in the video?

Allison Transmission is used as the example to explain the working principles of automatic transmissions.

What are the basic components of a planetary gear set?

A planetary gear set consists of a sun gear, a ring gear, and a planet carrier, which serve as two inputs and one output, respectively.

How does the output speed of a planetary gear set change when different speeds are applied to the inputs?

The output speed changes based on the rotation speed of the sun and ring gears. For instance, if the sun gear is rotating and the ring gear is stationary, the carrier spins, and if both gears rotate at the same speed, the mechanism moves as a single unit.

What is the role of clutch packs in an automatic transmission?

Clutch packs are used to transmit power by locking the hub to the case when pressed together, allowing for different speed variations to be achieved in the transmission.

How does the application of the 1st clutch pack affect the input and intermediate shafts?

Applying the 1st clutch pack connects the input shaft to the intermediate shaft, enabling power transmission between them.

What happens when both the 1st and 2nd clutch packs are applied together in an automatic transmission?

When both clutch packs are applied, the input shaft turns the sun gear, and since the ring gear is stationary, the output shaft rotates at almost one third of the input speed, achieving the 1st gear.

How is the 2nd gear achieved in an automatic transmission?

2nd gear is achieved by applying both C1 and C4 clutch packs, which causes the ring gear of the output set to turn, increasing the speed of the output planet carrier.

What is the purpose of the hollow shaft connected to the planet carrier?

The hollow shaft can be directly connected to the input shaft with a rotating clutch module, allowing for a direct drive in certain gear ratios, such as 4th gear.

How does the application of C1 and C2 clutch packs help achieve 6th gear?

Applying C1 and C2 connects the sun and ring gears directly to the input shaft, providing a high overdrive ratio at the output by giving the input rotation to the carrier while keeping the ring gear stationary.

What is the function of a torque converter in automatic transmissions?

A torque converter is necessary to isolate the engine's rotation from the transmission when the transmission is in gear and brakes are applied, using fluid coupling to accomplish this.

Outlines

00:00

🚗 Principles of Automatic Transmission

This paragraph delves into the inner workings of automatic transmissions, focusing on the planetary gear set as the core component. The video will simplify the complex mechanism using an example from Allison Transmission. It explains the basic parts of a planetary gear set, including the sun and ring gears, and the planet carrier that serves as the output. The paragraph illustrates how different speeds are applied to the inputs to achieve various output speeds, including reverse gear. The automatic transmission's ability to vary speed through engaging clutch packs is highlighted, setting the stage for a deeper exploration of how Allison's automatic transmission operates.

05:00

🔧 Gear Ratios and Clutch Packs in Automatic Transmissions

The second paragraph continues the exploration of automatic transmissions, detailing how gear ratios are achieved through the application of clutch packs. It explains the process of engaging the 1st and 2nd gear using specific clutch packs, and how the input and output shafts are connected through an intermediate shaft. The paragraph further explains the concept of direct drive in 4th gear, achieved by connecting the planet carrier to the input shaft. It also discusses the use of additional planetary gear sets to achieve higher gear ratios and overdrive, and the role of the transmission control unit in deciding clutch pack application. The paragraph concludes with the necessity of a torque converter in automatic transmissions for engine isolation during braking, and mentions a 2D animation as a visual aid for understanding the system.

Keywords

💡Automatic Transmission

Automatic transmission refers to a type of gearbox that automatically changes gear ratios without the need for manual intervention from the driver. In the video's context, it is the central theme, explaining how this system works using the Allison Transmission as an example. The script describes how automatic transmissions provide easy and reliable driving by using a complex mechanism that simplifies the process of gear shifting.

💡Planetary Gear Set

A planetary gear set is a set of gears that consists of a sun gear, planet gears, and a ring gear, all of which rotate around a common axis. The video script explains that automatic transmissions operate based on these sets, with two inputs and one output, and the output rotation is derived from the planet carrier. The concept is fundamental to understanding the automatic transmission's operation.

💡Input and Output Shafts

In the context of the video, the input and output shafts are key components of the automatic transmission. The input shaft connects to the engine, while the output shaft delivers power to the wheels. The script mentions that there is no direct connection between these shafts; instead, an intermediate shaft and clutch packs are used to transmit power, which is essential for the gear-changing process.

💡Clutch Packs

Clutch packs are components in automatic transmissions that, when engaged, lock together to connect different parts of the transmission system. The script illustrates how clutch packs are used to achieve different gear ratios by connecting the input shaft to the intermediate shaft or making the ring gear stationary, which is crucial for understanding the gear-shifting process.

💡Gear Ratios

Gear ratios are the relationship between the number of teeth on the input gear and the output gear, which determines the speed and torque output of the vehicle. The video script explains how different gear ratios are achieved by engaging various clutch packs, which is essential for the vehicle's performance in different driving conditions.

💡Torque Converter

A torque converter is a fluid coupling device that transfers power from the engine to the automatic transmission. The script mentions its necessity in automatic transmissions, especially when the vehicle is in gear and brakes are applied, to isolate the engine's rotation from the transmission, ensuring smooth operation.

💡Ring Gear

The ring gear is the outermost gear in a planetary gear set. In the video script, it is described as one of the two inputs of the planetary gear set, and its stationary or rotating state, depending on the clutch pack engagement, affects the output speed and the gear ratio achieved.

💡Sun Gear

The sun gear is the central gear in a planetary gear set, around which the planet gears orbit. The script explains how the rotation of the sun gear, either in the same or opposite direction, can result in different gear ratios or even reverse gear, highlighting its importance in the automatic transmission's functionality.

💡Planet Carrier

The planet carrier is the component that holds the planet gears in a planetary gear set and is connected to the output of the automatic transmission. The video script describes how the rotation of the planet carrier, influenced by the input speeds to the ring and sun gears, determines the output speed.

💡Reverse Gear

Reverse gear is a gear setting that allows the vehicle to move in the opposite direction of the normal driving direction. The script explains that in an automatic transmission, turning the sun gear in the opposite direction while the ring gear is stationary results in a reverse gear, demonstrating the versatility of the system.

💡Transmission Control Unit (TCU)

The transmission control unit is an electronic device that manages the operation of the automatic transmission by deciding when to apply which clutch pack. The script mentions that unlike manual transmissions, a TCU is necessary for automatic transmissions to ensure smooth and efficient gear changes.

Highlights

Automatic transmissions are popular for high-performance automobiles due to their ease and reliability.

The video explores the working principles of an automatic transmission developed by Allison Transmission.

Planetary gear sets are the basis of automatic transmission, with two inputs and one output.

The output rotation in automatic transmission is derived from the planet carrier.

Different speeds applied to the inputs affect the output speed in various ways.

When the ring gear is stationary and the sun gear rotates, the carrier spins.

Both ring and sun gears rotating at the same speed moves the mechanism as a single unit.

Turning the sun gear in the opposite direction enables reverse gear operation.

Speed variation in automatic transmission is achieved by engaging a few clutch packs.

An intermediate shaft and clutch packs transmit power between input and output shafts.

Pressing clutch packs together locks the hub to the case, forming a basic automatic transmission.

1st gear is achieved by applying both 1st clutch pack and making the ring gear stationary.

Additional gear ratios are achieved using another planetary gear set with specific clutch applications.

4th gear is achieved with a direct drive setup, connecting the sun and ring gears to the input shaft.

6th gear is achieved by removing C1 and applying C4, providing a high overdrive ratio.

A 3rd planetary gear set is necessary for the remaining gear ratios, with its sun gear always connected to the input shaft.

Reverse gear is achieved by applying the ring gear clutch C5, causing the sun gear to rotate in the opposite direction.

A transmission control unit decides when to apply which clutch pack for optimal gear selection.

A torque converter is essential in automatic transmissions to isolate engine rotation when brakes are applied.

A 2D animation provides a clear understanding of the automatic transmission system.

Transcripts

When it comes to high-performance automobiles, automatic transmission are

the popular option for easy and reliable driving.

In this video we will explore the working principles of this complex mechanism

in a simple and logical way.

We'll use an automatic transmission developed by Allison Transmission for this purpose.

Automatic transmissions work based on the planetary gear set.

In order to understand this process, let's take a look at the basic parts of planetary gear sets.

Planetary gear sets have two input and one output.

In automatic transmission the output rotation is drawn from the planet carrier.

The two inputs are connected to the ring and sun gears.

Now let's see what happens to the output speed when we apply different speeds to the inputs.

Here the ring gear is stationary and rotation is given exclusive to the sun gear.

This will cause the carrier to spin as you can see here.

The ring gear is also rotating.

The ring and sun gears rotate at the same speed.

In this case the whole mechanism moves as a single unit.

The ring gear speed is increased further.

Turning the sun gear in the opposite direction will result in a reverse gear.

So the operation of automatic transmission

is all about transmitting different rotation speeds

into the ring and sun gears.

The beauty of automatic transmission is that this speed variation

can be transmitted simply by engaging few clutch packs.

In the coming sessions we well see how this is achieved in Allison.

In an automatic transmission there is no direct connection

between the input and the output shafts,

rather there is an intermediate shaft between the two.

In addition to clutch packs are used for transmitting power.

Pressing the clutch packs together will lock the hub to the case.

This is the simplest form of automatic transmission.

With this in mind, let's see how 1st gear works.

If 1st clutch pack is applied

the input shaft will connect to the intermediate shaft.

On the other hand, if 2nd clutch pack is applied,

the ring gear will connect to the case

which will make the gear become stationary.

In order to achieve 1st gear

just apply both the clutch packs together.

You can note that the input shaft will turn the sun gear.

Since the ring gear is stationary

the output shaft will rotate as shown

with almost one third of the input speed.

To achieve additional gear ratios at another planetary gear set.

It is clear that apply C1 will always rotate the both of sun gears at the input shaft speed.

If we apply C4 as well the planet carrier of the 2nd set will turn.

But here is the tricky part:

this planet carrier is permanently linked to the ring gear of the 1st set.

So, when C1 and C4 are applied together, the ring gear of the output set will turn.

Thus, at the output set the situation is similar to that at 1st gear

except that here the ring gear will rotate as well.

This means that the speed of the output planet carrier will increase.

This is 2nd gear of the transmission.

The planet carrier is also fitted with a hollow shaft.

The shaft can be directly connected to the input shaft with the help of a rotating clutch module.

Take a moment to observe and understand this arrangement -

the rest of the process will be easy.

With this setup we can achieve 4th gear with a direct drive.

We know: in order to get a direct drive

the ring and sun gears of the output set should rotate at the speed of input shaft.

If we apply C1 and C2, this is what happens:

The sun and ring gears will be directly connected to the input shaft.

In order to achieve 6th gear just remove C1 and apply C4.

Here at 2nd set the input rotation is given to the carrier and the ring gear is stationary.

This combination gives a very high rotational speed to the sun gear.

Thus, we can achieve a high over drive ratio at the output.

3rd planetary gear set is required to get the remaining gear ratios.

The sun gear of this set is always connected to the input shaft as shown here.

And here again the output of the set is connected to the input of the adjacent set.

This means that applying C3 will always turn the ring gear of 2nd set.

For the remaining gear ratios C3 is always applied.

For 3rd gear just apply C1 as well.

For 5th gear remove C1 and apply C2.

In order to go in reverse apply the ring gear clutch C5 as well.

Since the planet gear of 2nd set cannot revolve,

they will spin as shown here.

This will eventually lead to the reverse rotation of the sun gear.

Consequently, the final output will be a rotation in the opposite direction.

A transmission control unit will decide when to apply which clutch pack.

Unlike manual transmissions a torque converter is needed in the automatic transmissions.

When the transmission is in gear and we apply the brakes

we have to isolate the rotation of the engine

from the transmission.

With a fluid coupling the torque converter will help accomplish this.

A 2D animation will also give you a good idea of the automatic transmission system.

Thank you!

Subtitles are written by @IEEE_English