What Is Transmission?- Types And How Does It Work

What is a Transmission?

A transmission is a machine in a power transmission system, which provides controlled application of power. Often the term 5-speed transmission refers simply to the gearbox, that uses gears and gear trains to provide speed and torque block conversions from a rotating power source to another device.

The term transmission properly refers to the whole drivetrain, including clutch, gearbox, prop shaft, differential, and final drive shafts. In America, the term is sometimes used in casual speech to refer more specifically to the gearbox alone, and detailed usage differs.

The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and where different rotational speeds and torques are adapted.

Often, a transmission has multiple gear ratios with the ability to switch between them as the speed varies. This switching may be done manually or automatically. Directional control may also be provided. Single-ratio transmissions also exist, which simply change the speed and torque of motor output.

In motor vehicles, the transmission generally is connected to the engine crankshaft via a flywheel or clutch or fluid coupling, partly because internal combustion engines cannot run below a particular speed.

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The output of the transmission is transmitted via the driveshaft to one or more differentials, which drive the wheels. While a differential may also provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds as it changes the direction of rotation.

Transmission Diagram

Automatic Transmission Diagram
Transmission Diagram

What does a transmission do?

A car transmission is one of the most important components of a vehicle. It’s what moves the power from the engine to the wheels.

There are a variety of car transmissions. Some are automatic, while manual transmissions in stick-shift cars require the driver to complete extra steps for the vehicle to operate effectively. Where is a transmission in a car located? Typically, a transmission is mounted onto the chassis of a vehicle in the front.

If you’ve wondered about how a transmission works, the process varies depending on the type of transmission. Whatever type of transmission it is, the answer to what does a transmission do is to enable the gear ratio between the drive wheels and engine to adjust as the car slows down and speeds up.

When a vehicle is stopped, the transmission disconnects the engine from the drive wheels so that the engine can keep idling when the wheels aren’t in motion. Transmissions also enable quick acceleration from a stop and enable the engine to run more slowly to cut down on wear while the vehicle is driving at consistent speeds.

How does a transmission work?

Regardless of whether your vehicle has a manual or automatic transmission, all car gearboxes work in essentially the same way. The only difference is whether the driver must manually push the clutch to disconnect the engine and transmission and move the car into a new gear level.

  • A gear lever selects and moves gears to connect with one another. The driver operates the gear lever using the clutch control/pedal (if manual). Otherwise, this is performed automatically.
  • When engaged, a clutch or gear lever maneuvers “collar” plates (also called clutch plates) into place to connect to larger gears, which are themselves connected to your car’s differential.
  • As the gear lever moves, different gears may be connected at different times. This alters which sets of gears turn and the power ratio delivered from the engine to wheels.

Ever wondered why your car’s engine might make a horrible sound if you engage the clutch incorrectly? It’s not because the gear teeth are mismatched, as is commonly believed.

In modern transmissions, gear teeth are positioned to be fully engaged at all times – even gears that aren’t technically in play (a state called “freewheeling”).

Instead, that awful grinding sound occurs when the collar plate’s “dog teeth” (connecting notches) don’t match up with the right holes in the side of transmission gear.

How does a manual transmission work?

With a manual transmission, the driver has to select the proper gear and engage or disengage the clutch. The transmission uses a flywheel, pressure plate, and clutch to engage and disengage the engine from the transmission.

The flywheel and pressure plate are connected to the engine. The clutch is sandwiched between them and is splined to the transmission input shaft. The term “push in the clutch” means to release the pressure plate, which disengages the clutch from the engine. Every time you make a shift, you have to push in the clutch first.

How does an automatic transmission work?

The main automatic vs. manual transmission difference is that with an automatic transmission, the process that powers a manual transmission happens within the transmission itself. Automatic transmissions typically don’t use clutches. Instead, the automatic transmission relies on a torque converter to change gears.

Types of Transmission

There are four Types of Car Transmissions

  • Manual transmission.
  • Automatic transmission.
  • Continuously variable transmission (CVT)
  • Semi-automatic and dual-clutch transmissions.

1. Manual transmission

The simplest and oldest type of transmission still in use is the trusty manual. This gearbox uses a friction clutch modulated by the driver’s foot to connect the engine’s rotational energy to the transmission’s input shaft. From there, a fixed set of gears are engaged using a synchro and gear-selector fork connected to the shifter operated by the driver’s right hand (or left, in certain countries).

It’s gone by a variety of names over the years, manual, stick shift, standard, three, four, five, or six-speed, but whatever you call it, there’s no denying that the trusty manual is an endangered species, at least in the U.S. Fewer and fewer new car models are offering a row-it-yourself gearbox and an ever-increasing percentage of the driving public doesn’t seem to know how to use one.

In spite of the grim outlook for its future, the manual has a lot of advantages over the newer and more complicated options. The stick shift’s simplicity means that it’s less likely to need expensive repairs than any other transmission type, and if it does have a problem, it’s likely to be cheaper and easier to fix.

For decades, the standard was the only choice when it came to performance and virtually every race and sports car on the planet was equipped with one. In recent years, though, the manual has been eclipsed by the Dual-Clutch or semi-auto transmission in most high-end performance cars.

However, it still offers better performance than most automatics and virtually all CVT transmissions. And fuel economy is a similar story. Up until recently, drivers who chose to shift their own gears enjoyed demonstrably better fuel economy than those who didn’t. Automatics, with their ever-increasing gear count, have now substantially narrowed the gap.

Aside from its inherent simplicity, performance, and fuel economy, perhaps the most compelling case for the venerable stick shift is the driving experience itself. For true driving enthusiasts, nothing can beat the feeling of a perfectly timed shift on a good old manual.

2. Automatic transmission

The automatic is by far the most common transmission on the road today. It uses a highly-complex torque converter to transmit the engine’s rotational energy, while gear shifts are controlled by the vehicle’s computer and accomplished with a planetary gear set and a series of clutches and brakes.

Though the behind-the-scenes action is quite complicated, all the driver has to do is select from the familiar P-R-N-D-L choices on the gear selector. The advantage is, of course, a simplified driving experience and a gentle learning curve.

The trade-off for the driving simplicity is mechanical complexity, which makes the automatic more prone to failure and pricier to fix.

Though most automatics can’t match a manual transmission for performance or fuel economy, modern examples are much closer than previous generations. Some late-model cars are equipped with transmissions boasting eight or even nine forward gears.

3. Continuously variable transmission (CVT)

The CVT offers a similar driving experience to an automatic but operates using a completely different mechanism. In fact, the CVT doesn’t have gears at all instead, it uses a system of belts and pulleys to produce an infinite range of ratios.

The car’s computer decides how to adjust the pulleys to create the optimal ratio for the particular driving situation. This creates the CVT’s primary advantage: fuel economy. No other transmission type can offer more MPGs than a CVT (yet).

Since they’re not as complicated as automatics, CVTs are less prone to failure and costly repairs (though not as much so as manuals). Their biggest drawback may be a subjective one — the driving experience. Since there are no gearshifts, just smooth and seamless acceleration, CVTs may leave a true driving enthusiast feeling like he or she is operating an appliance instead of driving a car.

4. Semi-automatic and dual-clutch transmissions

Think of it as a hybrid between a fully automatic and manual transmission. A semi-automatic uses a similar mechanical layout to a conventional transmission but uses a system of pneumatics and actuators to change gears.

In a Dual-Clutch Transmission (DCT), there are separate clutches for both odd and even gears, which allows for incredibly fast shifts. These gearboxes can generally be operated in a fully automatic mode, or manually shifted via paddles on the steering wheel.

Semi-Auto and DCT transmissions offer cutting-edge performance with lightning-fast gear changes that a pure manual just can’t match. Currently, these gearboxes are mainly found on race and high-end sports cars, and are, therefore, quite expensive. This disadvantage is magnified by their extreme complexity, which leads to more frequent and costly repairs.