The Review Of How An Automatic Transmission Works

The Review Of How An Automatic Transmission Works

Want to know the most typically front wheel drive transmissions with complicated mechanical components? An automatic transmission contains a mechanical system, an electrical system, a hydraulic system and a computer control that work together in perfect harmony. Its components include seals, gaskets, torque converter, planetary gear sets, an oil pump, clutches, bands, a modulator and a throttle cable. In this article, we are going to discuss how an automated transmission works.

How Does An Automatic Transmission Works?

Ever wonder how a transmission shifts gears? Why doesn’t the engine die when you stop? Automated transmissions are pretty much black magic. They are very difficult to comprehend because of the sheer number of moving parts they have. We are going to simplify it a bit to know the basic understanding of how it performs in a torque converter based system.

The engine connects to the transmission at bell housing which contains your torque converter for an automated transmission equipped vehicles unlike on manual cars. Your torque converter connects the engine to the transmission and the driven wheels. Your transmission has planetary gear sets in charge of producing different gear ratios. Let’s explain more about torque converters of your vehicle and the planetary gear sets to understand how your automated transmission systems work.

Torque converter

First, your engine’s flex plate is connected to your torque converter. So as your crankshaft rotates, your torque converter also rotates. The main goal of your torque converter is providing a means of connecting and disconnecting the power of your engine to your driven load. Your torque converter then takes place of the clutch on a conventional manual transmission.

How does a torque converter work? Check out, to know the basic principle behind a fluid coupling. Then, continue reading to see the difference between a torque converter and a standard fluid coupling.

The components of torque converter include an impeller, a turbine, a stator and a lock-up clutch. An impeller is part of torque converter housing connected to the engine. It drives your turbine via viscous forces. And the turbine is connected to the input shaft of your transmisssion. The engine turns on the impeller to impart forces on the fluid, which rotates the turbine to send your torque to transmission. The transmission fluid flows to the turbine via a loop placed between the impeller to work against the rotation of your impeller and against the engine.

The stator is placed between your impeller and turbine to reduce churn losses and maximize the output of torque by directing the fluid to the impeller when it returns from the turbine. The main purpose of this is to ensure the majority of the velocity it has is directed to the impeller to help the impeller move, thus adding to the torque produced by your motor. The stator sits on a one-way clutch and can rotate in one direction only when your turbine and impeller move at the same speed.

In addition, stators provide more torque when you are at stall or accelerating, but not when highway cruising. Some torque converters have a lock-up clutch to use the torque converter housing to lock the turbines to mechanically connect your turbine and your impeller. Replacing the fluid coupling with a mechanical connection is to ensure all the torque of the engine is transmitted to your transmission input shaft.

Planetary Gears (An Epicyclic Gear Set)

Now that we’ve explained how the engine sends power to the transmission, let’s now figure out how it changes the gears. The function of a compound planetary gear set is to change gears on a conventional transmission. Now let’s look at a basic planetary gear set and understand it.

An epicyclic gear set has a sun gear in the center, planet gears rotating around the sun gear, a planet carrier connecting the planet gears, and a ring gear on the outside which meshes with the planet gears. The basic idea behind a planetary gear set is using the clutches and brakes to stop some components form moving.

Preventing certain components from moving can change the input and output of the system, and thus change the gear ratio. Look at it this way: a planetary gear set enables you to alter the gear ratios engaging different gears that are already engaged. What you have to do is just to use the clutches and brakes to change which component rotate and which ones remain stationary.

The fixed component will determine the final gear ratio. For instance, if your gear ring is fixed, your gear ratio will much shorter than if your sun gear is fixed. What you lock determines the different gear ratios you will get. To get a 1:1 gear ratio, you just lock the components together to make the crankshaft spins at a similar speed as the transmission output shaft.

How Do The Brakes And Clutches Move To Alter Your Gears?

Well, the torque converter also drives the transmission fluid pump. The fluid pressure activates the clutches and brakes in the planetary gear set. The pump is always a gear pump to mean a rotor spins in a pump housing as it meshes with the housing to create chambers changing in volume. When volume increases, a vacuum is created at the pump inlet. And when the volume decreases, the fluid gets compressed or pumped as the gears mesh at the pump exit. The hydraulic control unit sends hydraulic signals to alter the gears and to lock the torque converter via the band brakes and clutches. Check out, to see the gear pump picture.

Latest modern automatic transmissions use a Ravigneaux compound planetary gear set with two small sun gears (small and large), two planet sets (inner and outer) and just one planet carrier.

In summary……

Well, now you are fully informed on how an automatic transmission works. It’s a closed system, so it doesn’t need a lot of work for maintenance. But still, you have to look for leaks, check your dipstick, achieve a complete stop before shifting and regularly change your transmission fluid. Check out, and for more article on the transmission ins and outs, both the manual transmission and automated.

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