These animation, video, text & picture examples explain the principles of your car's automatic transmission and how it works using by a Ravigneaux planetary gear set.
All Pictures taken from How Automatic Transmissions Work! (Animation).
How Automatic Transmissions Work! (Animation) Youtube Video
Transmissions are very complex components and are a mystery to many who don’t have mechanical knowledge of motorized vehicles. For you to understand how automatic transmissions work you will first need to know the answers to the following questions: How does an automatic transmission know when to shift gears on time? Why does the engine keep running even when the car is not moving? What is a transmission? & What does a transmission do? All, the answers are listed here in this article. For such a vital component, most people who own and operate vehicles do not know enough about their automatic transmissions to know when they may have a problem or what they should do once their experiencing transmission problems. This article is to bring clarity to the realm of automatic transmissions for those who would like to know more about how automatic transmissions work. Let's first take a look at what transmissions do.
What is an automatic transmission
Automatic transmissions are devices that are connected to the backside of your engine that send power from the engine through the transmission to drive the wheels. A car engine usually runs best at specific RPMs (Revolutions Per Minute) and it's the job of the transmission to make sure the power from the engine gets delivered to the wheels while staying within that specific RPM range. They do this by using multiple gear combinations. In 1st gear, your engine turns really fast in relation to driving the wheels, as opposed to 4th, 5th or 6th gear (depending on your type of transmission) where your engine is turning much slower, even when speeds excess of 65mph. Transmissions also have neutral positions that disconnect the drive wheels from and the engine. Reverse position cause the wheels to turn in an opposite direction allowing you to back your car up. The last position is the park position. In park position there is a latch that is inserted into the output shaft. This latch locks the drive wheels and keeps them from moving, preventing it from rolling away.
There are 2 Different types of automatic transmissions, front wheel drive and rear wheel drive.
- Rear wheel drive cars have the transmission mounted to the back of the engine, usually located under a hump in the floorboard. Drive shaft's connect the transmission's rear to the final drive which is used to send drive power to the wheels. The power flow on rear wheel drive cars is very simple, it moves straight forward from the engine, to the torque converter (How Torque Converters Work), then through the drive shaft and transmission before it reaches the final drive where it splits and gets sent to the rear wheels.
- Front wheel drive cars have theirs transmissions combined with the final drive typically referred to as a transaxle. Front wheel drive engines are typically mounted sideways in the automobile with the transaxle under it, on the side of the engine. Front axles are joined together with the transaxle and give power to the 2 front wheels. Power flow from the engine, to the torque converter, to a chain that pushes the power through a one hundred and eighty degree turn to the transmission that is on the side of the engine. After that, the power is then routed through the trans to the final drive where it gets split and sent the front wheels.
What Does A Transmission Do?In cars, what transmissions do is convert speed and torque along the drive train. The sole purpose is to maximize the efficiency of your engine to achieve lower fuel consumption while at the same time giving you the most amount of torque possible. Basically, your transmission keeps your cars performance in check and makes your wheels turn. If you didn't have your transmission, your car would not be able to drive or fuction properly. Your transmission is what converts the engines power to turn the wheels at a controlled rate for the best fuel economy.
Automatic transmissions are comprised of so many components that it is either incomprehensible or very intimidating for people to wrap their heads around. Transmissions, at first, may seem like an esoteric force is behind their operation and functionality, but it all does all make sense once broken down and simplified. We are going to go over common torque converter based transmission systems.
You will find the main connection between the engine and your vehicles automatic transmission housed in a casing called ‘bell housing’, bell housing houses the torque converter and takes the place of a clutch that would be used with manual transmissions. The torque converter acts as a liaison between you engine and the wheels of your vehicle by controlling the torque output according to the state of the transmission in real time. The transmission controls the gear ratios with planetary gear sets, which dictate when the car shifts from one gear to another. We will break down both the torque converter components, the planetary gear sets and how they all work together to drive your wheels.
1) Torque converters and multi-plate clutches
2) Multi-plate brakes, band brakes
3) Ravigneaux Planetary gear sets
4) Large and small sun gears
5) Planet Carriers and Planets
6) Ring gears
7) High Gear ratios
Today, automatic transmissions are comprised of torque converters, several multi-plate breaks, multi-plate clutches and band breaks. The first topic we will cover is torque converters and multi-plate clutches.
Torque Converters and Multi-Plate Clutches
(Picture of Torque Converter & Multi-Plate Clutches)
The torque converter is connected to you’re the engine’s flex plate, which maintains a working relationship between the torque converter and the crankshaft. This enables the torque converter to connect and disconnect the engine’s power that is being sent to the drive train. (How To Choose The Correct Torqe Converter for your Automatic Transmission)
Does an automatic transmission have a Clutch?
Yes, an automatic transmissions have multi-plate clutches. In an automatic transmission car, the clutches will adjust their selves according to the speed that the vehicle is traveling. Therefore, automatic transmissions will never be as fast as a racing car that uses manual clutch.
The torque converters main components are the impeller, stator, turbine, as well as a lock up clutch. The impeller is connected to the vehicles engine as it is part of the housing for the torque converter and it is responsible for driving the turbine. The turbine, which connects to the input shaft of the transmission, is effected by the rotation of the impeller so it can exert various forces on a fluid, which will, in turn, cause the turbine to rotate and send torque to the transmission. Transmission fluid is sent between the impeller and turbine in a perpetual loop.
In between the turbine and the impeller sits the stator. The stator’s purpose to redirect the returning transmission fluid as it is returning to the impeller from the turbine, which creates more torque output. This is accomplished by directing most of the high velocity fluid toward the impeller which aides it’s movement and increases torque. This process is why they are called torque converters.
The stator is a clutch that only rotates in one direction in alignment with the turbine and impeller. The stator cannot move independently of the impeller. The stator isn’t always providing a boost to the vehicle’s torque, it does so when the vehicle is slowing down (like when brakes are applied) or when the vehicle is accelerating. When driving at a sustained speed the stator does not provide extra torque. Another component found with some torque converters are lock-up clutches that lock the housing of the torque converter to the turbine ensuring a mechanical connection between the turbine and the impeller. This ensures that no torque is lost in transit due to fluid couplings. In the next top we explore the ravigneaux planetary gear set.
Ravigneaux Planetary Gear SetA Ravigneaux planetary gear set is used to give more forward gear ratios than a single planetary gear set.
(Picture of Ravigneaux gear set)
The planetary gear systems in a transmission are literally modeled after the solar system we live in. You have the sun gear in the center, planet gears that ‘orbit’ the sun gear, the planet carrier which connects all of the planet gears along with a ring gear that can interface and mesh with the planet gears. The logic behind this kind of system is being able to control, stop and activate certain components with brakes and various clutches. This allows for a greater degree of control over the entire vehicle and it’s movement by being able to alter the input and output to the transmission. This process effectively give you control over the gear ratios.
A Ravigneaux gear set is a double planetary gear set. It is composed of a small sun gear that meshes with three gears that surround it kind of like planets.
(Picture of Ravigneaux Gear set with titles)
Many modern day automatic transmissions utilize what is called a Ravigneaux compound planetary gear set. This gear set is unique because it has two sun gears, one large and one small, along with two sets of planets, one inner, one outer and one planet carrier. It’s basically two systems combined into one.
The shaft of the of the large sun goes through the hollow shaft of the small sun. The other planets couple together with the large sun, the planets of the small sun and the ring gear.
(Picture of Ring Gear)
All of the planets of the automatic transmission contain a single planet carrier. With these kind of automatic transmission, high hear ratios can be achieved by connecting and locking components.
(Picture of Planet Carrier)
Next up is "how your automatic transmission's 1st thru 5th gear operates".
How Automatic Transmission First thru Fifth Gear Components Work
Gear ratios depend on if certain components are fixed or not. If the ring gear is in a fixed position, for example, the gear ratio is going to be much shorter than if, say, the sun gear was in a fixed position instead. The role of clutches and brakes is to move the gears. The transmission fluid pressure is what causes the clutches and brakes to activate within the planetary gear set system. A gear pump, usually a gerotor pump, that spins and meshes with its housing to create ‘chambers’ that can fluctuate in volume. When volume raises to a certain threshold, the increase creates a vacuum which is the inlet for the pump. Once the volume levels lower, the meshing gears pump the fluid as it is compressed through the pump exit. Gear changes are signaled by a hydraulic unit which can also lock the torque converter.
How Your Transmission's 1st Gear Works
(Picture of 1st Gear Transmission)
In 1st first gear, the small suns is usually driven by the torque converter, which is driven by the automobile engine. The planet carrier is made to hold still by a one way clutch or a multi-plate break so it cannot rotate. The ring gear is connected to the output that are used to drive the wheels of the car.
How Your Transmission's 2nd Gear Works
(Picture of 2nd Gear Transmission)
The planetary is no longer a fixed member of the system in 2nd gear. Now, it can rotate freely, however, the large sun is held stationary, so the large sun cannot rotate, but once again the small sun is the input of the system that drives the ring gear.
How Your Transmission's 3rd Gear Works
(Picture of 3rd Gear Transmission)
In 3rd gear, the gear ratio: 1 is accomplished by locking all of the rolling polls of the planetary gear set. Now, the entire planetary gear set is rotating.
How Your Transmission's 4th Gear Works
(Picture of 4th Gear Transmission)
The planet carrier is the input in 4th gear. The large sun holds stationary allowing for the ring gear to drive the wheels of the car.
How Your Transmission's Reverse Gear Works
(Picture of Reverse Gear Transmission)
In reverse gear the large sun is used as the input as in 1st gear. The planet carrier is held stationary by a breaking unit, the ring gear is the output .
Now, let's take a quick look at how to change gears using multi-plate clutches. Both clutch baskets are connected to and driven by the engine.
(Picture of Multi-Plate Clutches)
When one of the multi-plate clutch is engaged the mechanical energy provided by the engine is transmitted to the corresponding gear.
(Picture of Multi-Plate Clutches Engaged)
Why Does a Transmission Slip and what does it do when its going out or low on fluid?
The reason why transmissions slip or is go out because of worn gears or low fluid pressure. You planetary gear set can become worn overtime. This wear and tear makes it harder for the transmission to shift properly. Your engine will tend to over rev and cause erratic or random shifting. Also, your transmission fluid is what is used to apply pressure to certain components to get them moving. IF you fluid is low, your transmission cannot apply all of the pressure needed to control those components and get your wheel moving.
Click here to find out how manual transmissions work.
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Automatic transmissions work well but tend to break down over time, its alway wise to have a certified auto repair company diagnose and fix your transmission problems for you. Also, if you are in need of auto glass replacement, auto body repair, RV Insurance, car ignition services, car key creation or car lockout services click here.