What is Transmission in a Car?
A car transmission is the gearbox of a vehicle. It’s roughly analogous to the gear shifter and chain system that bicycles use.
These components are always mounted directly on the engine to allow the attached belt and gear system to effectively convert the combustion power generated by the engine into physical momentum.
Remember how a car engine works:
- Fuel (gasoline) is ignited in the combustion chamber of your vehicle’s engine.
- When the fuel ignites, the expanding gas and heat from the miniature explosion pushes a series of pistons into your engine’s cylinders.
- When the pistons are pushed, they move up and down, turning your engine’s crankshaft.
- The crankshaft then turns the drive wheels of your car. This mechanism converts explosive energy into mechanical energy.
So, where does transmission come into play? Without a transmission, the explosive power of a typical car’s internal combustion engine would simply be too high for starting or stopping your car or when you need to drive relatively slowly.
A typical car transmission consists of five to six sets of gears and a series of gear trains (essentially belts or chains running around the outside of two or more gears) — which allow a driver to control how much power is delivered to the car without changing how fast the engine is running.
Put another way, a car transmission helps ensure your engine is turning at the correct speed without overspeeding or under speeding for your needs. It also ensures your wheels are getting the right amount of power. Without a transmission, any car would be difficult to start and stop and totally unreliable.
A transmission changes gears depending on car speed and how far down you push the pedal of your car so that the engine’s RPM or “revolutions per minute” are kept appropriately low.
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 does 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?
The transmission works by transmitting the power that comes from the engine to the wheels along the driveshaft and axle allowing you to drive the car. It does all of this by using gears and gear ratios that are selected either automatically or manually by the driver.
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 the 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 most common type of automatic transmission uses hydraulic power to shift gears. The torque converter connects the engine to the transmission and uses pressurized fluid to transfer power to the gears. This apparatus replaces a manual friction clutch and lets the vehicle come to a complete stop without stalling.
The main automatic vs. manual transmission difference is that with an automatic transmission, the process that powers a manual transmission happen 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 Transmissions
Cars are continuously evolving, improving, and becoming more efficient. That goes for the transmission as well.
There are four Types of Transmissions:
- Manual transmission.
- Automatic transmission.
- Continuously variable transmission (CVT)
- Semi-automatic and dual-clutch transmissions.
1. Manual Transmissions
The manual transmission is the original type of transmission. It’s also called the standard transmission, but there’s a good chance you’ll know it as the stick shift. This type of transmission has the driver using a clutch to control the torque transfer from the engine to the transmission, manually shifting between gears as necessary.
Mechanically, manual transmissions are the simplest type of transmission and often last longer than other types, simply put, there’s less that can go wrong. The only major disadvantage to a manual transmission is the learning curve; these types of vehicles require more concentration and maneuvering than other transmissions.
MORE: What is Manual Transmission?
2. Automatic Transmissions
Yes, manual transmissions are mechanically simpler, but with the caveat of being harder to operate. If a driver doesn’t have the time to take on the extra work that comes with driving a stick shift, then they’re best suited for choosing to drive an automatic transmission vehicle.
This type of transmission automatically changes gears as the vehicle moves, leaving the driver to focus more on the road, rather than shifting the clutch. Once a car is in drive, its computer takes over the transmission, shifting between gears as necessary while the car accelerates and decelerates.
You’ve probably heard the sound of your engine getting higher, but then the sound drops as you continue to accelerate; that’s your car moving from a lower to a higher gear. Most automatic transmissions have between five and ten gears and the more gears your transmission has, the better it will perform at different speeds.
A transmission with more gears means a vehicle has a wider range of speeds where it will perform optimally and lead to better overall fuel economy. While easier to use, automatic transmissions have more complex parts and are therefore more prone to failures. And automatic transmission repair or replacement can get very expensive.
MORE: What is Automatic Transmission?
3. CVT Transmissions (Continuous Variable Transmission)
The more gears a transmission has, the better it will operate over a wide range of speeds. But what’s the limit when it comes to the number of gears a transmission can have? Thanks to the continuous variable transmission (CVT), there is a continuous or limitless amount.
It’s also known as the shiftless transmission and, unlike other types, the CVT transmission doesn’t use gears as a means for producing varying speeds, but instead relies on a belt-driven design of two rubber or metal pulleys.
The two pulleys work in sync, mimicking the effect produced when gears of different diameters are engaged. The pulleys’ ability to increase and decrease their effective diameters allows the CVT transmission to move fluidly through a limitless range of effective gears.
The CVT transmission isn’t new; it’s been around for decades, rising in popularity among Japanese and European manufacturers in the mid-2000s. If you’re looking for a car with a CVT transmission, you’ll need to do some research.
Most new cars will state the type of transmission they have on the window sticker. If you’re buying a pre-owned car, some online research will help to determine the type of transmission a certain make and model has installed.
Although CVT transmissions offer a limitless range of gears and superior fuel economy, they do have their limits. This type of transmission is not suited for off-road environments, due to its limited torque-handling ability. Another drawback is that CVT transmissions cannot provide engine braking.
Because of their complexity, these transmissions routinely require more maintenance and repairs can be costly. Over time, the belts can break down due to excessive wear and stretching. When you’re searching for a shop to work on your transmission, be sure to check if they’re able to work on CVT transmissions—going to a dealer facility is a good option as well, though it will be expensive.
MORE: What is CVT Transmission?
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.