Do Automatic Cars Have a Clutch?
Ellie Dyer-Brown, 10 months ago
5 min read
- Clutch
- Car ownership
FixMyCar explains how an automatic transmission works and whether it has a clutch.
Automatic cars are a bit like Marmite - you either love or hate them. Since most vehicles in the UK are manual, some people consider automatic transmissions boring and claim they take the fun out of driving. For others, their ease of use is welcome.
While many drivers have an opinion about automatic cars, few understand exactly how they work. After all, you don’t need to understand the mechanics of a car’s transmission to drive it, though this knowledge may come in handy if you ever need to diagnose a fault.
Whether you’ve got a burning question about automatic cars - such as whether they have a clutch - or you’re just a little curious, this guide contains all the information you need.
Contents
Do automatic cars have a clutch?
What's the difference between a manual and automatic transmission?
How does an automatic transmission work?
Different types of automatic gearboxes
Advantages of automatic gearboxes
Do automatic cars have a clutch?
Automatic cars don’t have a clutch pedal or traditional gearstick. Instead, they have a gear shifter, allowing you to switch between neutral, park, reverse and drive.
However, while they don’t have a clutch pedal, some automatic vehicles still use a clutch. The difference is that the clutch operates without assistance from the driver, changing gears automatically.
What’s the difference between a manual and automatic transmission?
Automatic transmissions change gears automatically, so you never have to think about which gear to use. In contrast, in manual transmissions, you choose the gears yourself and shift using a clutch pedal.
The other key difference to be aware of is how the gears operate. In manual vehicles, the transmission locks and unlocks different gears to the output shaft, achieving various gear ratios. In automatics, the same set of gears creates all the gear ratios, which is made possible by the planetary gearset.
How does an automatic transmission work?
There are several variations of automatic transmission, each working slightly differently. We’ll cover these shortly. The most common automatic transmission configuration uses planetary gearsets operated by hydraulics.
What is the planetary gearset?
The planetary gearset is roughly the size of a melon and creates all the gear ratios the transmission can produce. There are two planetary gearsets in an automatic transmission folded into one component.
Each gearset contains:
The sun gear
The ring gear
The planet gears
Each component can be an output, an input or held stationary; combining them in different roles creates different gear ratios. A gear ratio is the ratio of the rotations of a driver gear to the rotations of a driven gear; a lower ratio provides a higher top speed.
Putting the car in drive
As previously mentioned, you can’t select a gear in automatic cars - instead, to move forward, you put the vehicle into ‘drive’. Then, when you push the accelerator, the crankshaft (a shaft that converts the linear force of the pistons into rotational force) starts rotating more rapidly, creating more pressure in the torque converter.
The torque converter connects the prime mover to the automatic gear train, which drives the load.
As the car moves, the transmission’s electronics and hydraulics sense its speed compared to the engine speed, and the transmission automatically changes gears in response.
In older automatic systems, hydraulics were exclusively used to sense speed changes, activating other hydraulics to change gear in the planetary gearset. However, modern transmissions use electronics to aid the sensing process.
Different types of automatic gearboxes
Here are some automatic gearbox types you should be aware of.
1. Continuously Variable Transmissions (CVTs)
CVTs (sometimes called shiftless transmissions) are often found in hybrid cars because they have a belt that acts as a single-gear ration. They are relatively simple, compact and don’t have a clutch.
Within a CVT, you will find two cone-shaped pulleys and a V-shaped drive belt connecting them. One pulley is attached to the wheels, and the other to the engine. When you accelerate, the engine revs, and the cone moves according to the required power. The other cone adjusts to maintain the same tension, determining how fast the car accelerates.
CVTs are efficient and reliable, providing a smoother drive because the car doesn’t skip through gears. However, acceleration is slow compared to other automatic gearboxes.
2. Dual-Clutch Transmissions (DCTs)
A dual-clutch automatic is similar to a conventional automatic but uses two independent, automatically-operated clutches instead of a torque converter. One clutch handles the odd-numbered gears, and the other is responsible for the even numbers.
DCTs are advantageous because they offer improved fuel efficiency, more horsepower and faster gear shifts, but they can also be jerky and are expensive to replace.
3. Conventional Automatic Transmissions
As discussed earlier in this guide, conventional automatic cars use a torque converter instead of a clutch. They are more refined than other types of automatic transmission but use more fuel than a manual car would.
4. Direct-Shift Gearboxes (DSG)
A DSG gearbox uses a pair of electronically controlled clutches that the car can engage and disengage automatically. Several manufacturers use this transmission type in the Volkswagen Group, including SEAT, Skoda and Audi.
One clutch transmits the engine’s power to the car’s wheels via the gearbox. Simultaneously, the onboard computer predicts the required gear and uses the second clutch to prepare it. When the computer wants to change the gear, it disengages one clutch and engages the other.
DSGs are popular because they are more fuel-efficient than traditional automatic transmissions and offer faster shifting, though they are expensive to repair when they go wrong. They need servicing approximately every 40,000 miles.
Learn more about how DSGs work in this guide.
5. Automated Manual Gearboxes
Automated manual gearboxes operate similarly to a traditional manual. The difference is that they select gears automatically, and a computer rather than a pedal operates the clutch. They are often jerky.
Advantages of automatic gearboxes
Some advantages of using a car with an automatic gearbox are laid out below.
Learning to drive in an automatic allows you to focus on road position and speed
Automatic cars are simpler to drive
Better in traffic - no need to change gears manually every time you stop, start or change speed
Slightly safer to operate because you can keep both hands on the wheel
More power
Faster shifting
Disadvantages of automatic gearboxes
Consider the following disadvantages.
Automatic cars are more expensive
Boring to drive compared to a manual
Require more frequent and expensive maintenance
Offer the driver less control
More complex to repair
Some automatics can’t be towed with wheels on the ground
What are semi automatic cars?
A semi-automatic car contains a combination of a manual and automatic gearbox. It uses a set of actuators and a hydraulic motor to replace the gear lever and clutch pedal, and a control unit is responsible for the engine torque and speed. You can switch between manual and automatic controls, allowing you to enjoy the best of both worlds.
When you want to change gears in manual mode, you either push a lever on the gearstick or use steering wheel paddles, depending on how the car is designed. There’s no need to use a clutch.
Pros and cons of semi-automatic cars
Pros
Often more fuel efficient than fully automatic cars
Choose between manual or automatic modes
Usually less expensive to maintain and repair than fully automatic transmissions
Cons
More expensive to buy and maintain than manual transmissions
Learning curve for drivers who are used to fully-automatic cars
Jerky gear shifts are common
Not as widely available as manual and automatic cars
Are all electric cars automatic?
All electric cars are automatic because they are powered by an electric motor, which means their power and speed remain constant without requiring a change of gears. However, there are crucial differences between EVs and traditional automatic cars.
In a car with an automatic gearbox, there is a series of forward gear ratios that are automatically selected by the vehicle to optimise the transmission of engine power to the wheels.
Contrastingly, EVs don’t use a gearbox. Instead, they are driven by one or two motors, with the amount of electricity sent to those motors determining the car's speed.
Since the motor spins too fast to drive the wheels directly, the rotational force is sent to a reduction gear first, where it is reduced. Unlike the numerous gears in a combustion engine, the reduction gear is a single-speed unit.
Some high-performance EVs, like the Porsche Taycan, have a two-speed reduction gearbox to optimise motor and battery efficiency.
Looking for repairs or maintenance for your automatic car? Whatever you need, FixMyCar can help you find the right garage at the right price.
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