Once upon a time, drivers simply had the choice between manual or automatic gearboxes. Now for anyone who wants to let the car’s electronic brain take the strain, there are a variety of different self-shifting gearboxes available.
Thanks to advances in technology, automatic gearboxes have become far more efficient. And as they can accommodate more ratios – some have 10 speeds – they help drivers to save fuel too.
Here we explain the difference between the four main types of automatic gearbox and look at the advantages and disadvantages of each.
What it is: Rather than employing a clutch, the engine is connected to the gearbox using a thing called a torque converter. This uses hydraulic fluid to transmit drive between the engine and gearbox. It means you simply slot the gearlever into ‘D’, press the accelerator and the gearbox does the rest, changing gear when its electronics say it’s appropriate.
Advantages: Although not as smooth as a direct shift gearbox, you get a more seamless change than an automated manual. Also, the fundamentals behind an automatic gearbox have been in use for more than 70 years. This is proven technology and as long as they’re serviced at the prescribed intervals, they should be reliable.
Disadvantages: An automatic gearbox tends not to be as fuel efficient as a manual or a direct shift gearbox.
Also known as: Dual clutch, twin clutch, dual shaft, DSG
What it is: The direct shift gearbox is effectively two gearboxes with two clutches: one for odd numbered gears; one for even numbers. These are packaged as one (above). When you select first gear as you accelerate, the ‘second’ gearbox primes second. Then when its electronic brain says it’s time to change gear, rather than moving up a cog in the traditional way, it simply swaps input shafts. If you’re still accelerating, ‘gearbox one’ then gets third gear ready for the change up.
Advantages: As swapping shafts is quicker than engaging and disengaging clutches and changing cogs, you get almost seamless gear changes. Most direct shift systems can change gear quicker than a human with a clutch. Gearboxes like this are also more efficient than a regular automatic.
Disadvantages: Low speed manoeuvring in first gear can be slightly jerky in some cars. It’s also quite a new system and on some cars they’ve proved unreliable in older models.
Continuously Variable Transmission
Also known as: CVT, E-CVT, Multitronic
What it is: Instead of cogs to regulate engine speed, the CVT uses cones. One cone is attached to the engine, the other to the wheels (via drive shafts). These cones have a belt running between them. As the engine speed increases, a computer controls tells the cones to move closer or further away from each other. This increases and decreases the angle of the belt, altering the gearing.
Advantages: In many ways this is the most efficient system for regulating engine speed because it doesn’t involve gears. Instead, the gearing can be constantly adjusted to suit the driving conditions and engine speed.
Disadvantages: Acceleration can be noisy because the sound of the engine stays at a constant pitch, rather like a car with a slipping clutch.
Also known as: Robotised manual, clutchless manual, semi-automatic
What it is: Imagine a regular manual gearbox. It has gears and a clutch. However, rather than the driver operating the clutch, in an automated manual, the car’s electronic brain does it. So when it changes gear, the car engages the clutch, moves the gear then disengages the clutch. All the driver does is accelerate or brake.
Advantages: The automated manual gearbox is very simple to drive because it has just accelerator and brake pedals like a conventional auto.
Disadvantages: The engine’s electronics must oversee quite a complicated process. And frequently the result is a slow, jerky gear change as they juggle their various tasks.
If you want the car to do the gear changing for you, you’re not short of options. For keen drivers, the direct shift gearbox is the way to go. A CVT simply won’t be engaging enough and an automated manual will change gear too slowly. For regular drivers, the traditional auto is probably the best bet. It’s pretty bullet proof and does exactly what it says on the tin with none of the disadvantages of a CVT or automated manual.