When automatic gearboxes first became widely available in the middle of the last century, they were very much the preserve of luxury motoring. They were a labour-saving device that contributed to a smoother driving experience, but they were heavy, expensive and less fuel-efficient than conventional manual gearboxes.
Although automatic transmission systems were refined over the years, the manual gearbox with a physical clutch pedal held on to the majority of car sales for a long time. In fact, as late as 2010, four-fifths of all cars sold in the UK were fitted with a manual gearbox rather than an automatic.
Yet technology marches on. New innovations, including different types of automatic gearbox – such as dual-clutch transmissions, improved CVTs and robotised manuals – have broadened the abilities of non-manual transmissions. They're no longer purely the preserve of luxury cars, while efficiency improvements mean that automatics are now often greener, with lower emissions, and more fuel-efficient than their manual equivalents.
In 2020, sales of automatic cars overtook sales of manual models for the first time, with 56% of all cars sold being automatics. For some manufacturers, that proportion is much higher – 90% of Volvos sold in the UK are automatic, while across Europe, 83% of Mercedes’ car sales are autos.
With the increasing ubiquity of hybrid and electric drivetrains – and with electric vehicles (EVs) often not needing a multi-ratio transmission at all – it’s hard to see a future for the traditional manual, other than as a niche piece of retro technology.
But what are the different types of automatic gearbox and how do they work? Read on to find out.
Torque Converter Automatic Gearboxes
The torque converter is one of the original types of automatic gearbox. In this sort of automatic transmission, the torque converter is the piece of equipment that transmits the power from the engine to the gearbox, and then on to the driven wheels.
Unlike a mechanical clutch, which creates a physical connection to transmit power (or, strictly speaking, torque), a torque converter uses hydraulic fluid to get drive from the engine through the gearbox to the wheels. This thick, spinning fluid ‘connection’ is why torque converter automatics are able to change gears so smoothly, and why torque converter automatics are sometimes referred to as ‘slush boxes’.
The downside of a torque converter automatic is that it’s an inefficient way of transferring power, so tends to be less fuel-efficient than other types of gearbox. The design can also mean gearchanges can feel a little sluggish. However, the length of time this technology has been around means engineers have had plenty of time to finesse the concept, so modern versions are both more efficient and more effective than their older equivalents. Many versions even allow you to select gear ratios manually – albeit electronically rather than physically.
Overall, a torque converter is still one of the most common types of auto gearbox. You’ll find eight-speed torque converter autos in many cars, including the Peugeot 2008, Volvo XC40 and BMW 3 Series. Mercedes-Benz, meanwhile, uses a nine-speed auto in the C-Class and E-Class (among others) and Ford even fits a 10-speed auto (developed jointly with General Motors) in the Mustang sports coupe and Ford Ranger pick-up.
Dual-Clutch Gearboxes
As you’ll no doubt guess from the name of this type of gearbox, a dual-clutch system uses two clutches, so unlike in a torque converter, there is a physical mechanical connection between the gearbox and the engine.
The advantage of using two clutches is that the gearbox uses one clutch on the gear cog you’re currently in, but is able to prepare the gear it ‘thinks’ you’re going to use next with the other clutch, enabling near-instantaneous changes. In simple terms, if you’re accelerating in third gear, it will line up fourth for you in advance, whereas if you’re braking in third gear it will prepare to shift down into second gear.
Most cars equipped with dual-clutch gearboxes allow you to change gears yourself (should you wish to) via paddle shifters on the steering wheel or steering column, and via a push-pull action on the gear selector lever itself. It’s worth noting that not all dual-clutch cars come with steering wheel mounted paddle shifters as standard.
The advantages of a dual-clutch gearbox is that they are more efficient and deliver quicker gearchanges than conventional torque converter automatic gearboxes, making them suitable both for performance cars and for models focused on maximum fuel economy.
The downside is that they can be a bit jerky to change gear, especially at low speeds. Perhaps more significantly, due to their mechanical complexity, older models can be unreliable – and maintenance and gearbox repairs can be costly.
Volkswagen and sister brand Audi were the pioneers of dual-clutch gearboxes in road cars in the early 2000s, and today the VW Group brands are still big advocates of this gearbox technology. Models that use DSG gearboxes (as Volkswagen calls dual-clutch transmissions) include the Polo, Golf and Tiguan, as well as multiple Seat, Skoda and Audi Models.
Because of the fast responses of a dual-clutch gearbox set-up, performance cars such as the BMW M4 (DCT) or Porsche 911 (PDK) also use dual-clutch transmissions.
Other manufacturers where you’ll find twin-clutch gearboxes include Ford, Hyundai, Kia and Mercedes-Benz.
Robotised Manual Gearboxes
The robotised manual gearbox – also known as a semi-automatic gearbox or automated manual gearbox – has been around for many decades, but it was popularised in the 1990s, with Alfa Romeo, Renault, Saab and Vauxhall all offering versions of a gearbox with an automated clutch rather than a traditional pedal.
Broadly speaking, there are two types of automated manual gearbox: ones that are sequential, and ones that follow an H-pattern shift (just like a normal manual). Sequential versions often have a fully automated self-shifting functionality as well as paddle shifters or buttons on the steering wheel, while H-pattern versions tend to be more like a manual car – albeit one with only two foot pedals as opposed to three.
In the 1990s and early 2000s, high-end performance cars used sequential automated manual transmissions. Notable among these were Ferrari, which launched its ‘F1’ paddle-shift system in the 355, and BMW, which used a system it branded ‘SMG’ in the M3 and M5 in the 2000s. The problem with these gearbox systems, particularly in performance-car applications, was that the shifts tended to be jerky and the gearboxes were quite prone to failure if not used gently.
The trick with these types of gearbox, particularly the ones with a full self-shifting function, is to learn to ‘predict’ when the shift will happen, and lift off the accelerator at these points. That puts less load through the system and will ensure it lasts longer, as well as delivering a smoother gearshift.
Notable recent uses of the robotised manual shift include the EGC/EGS system found in some Peugeot and Citroen models (such as the Citroen C4 mk1, the Peugeot 207 and the mk1 Peugeot 208), though it has been superceded by a more conventional automatic in the most recent models.
As for the H-pattern automated manual shifter, the Hyundai Tucson and i20 feature a six-speed version of this type of gearbox, where the clutch is operated electronically rather than via a conventional clutch pedal.
CVT Gearboxes
CVT is short for continuously variable transmission, and it’s one of the stranger ways of transmitting power to your car’s wheels. Instead of a series of fixed-ratio cogs, CVTs feature a pair of pulleys shaped like cones (narrow at on end and wide at the other). One is connected to the engine, and the other to the driveshaft to the wheels, and are connected to one another by a belt.
As you accelerate or decelerate the belt moves up and down the pulleys, effectively constantly varying the diameter of the pulley and thus altering the gear ratio.
The advantage to this is that the engine is constantly kept in its most efficient power band, with infinitely adjustable ratios, so it won’t drop out of its optimum operating point as would happen when you change to a higher gear in a car with fixed ratios, for example.
This makes for smooth power delivery, but often a slightly odd sound experience, with the engine effectively being held at constant revs. This can make CVTs quite a noisy experience, especially in smaller-engined cars that need to be revved more to get the best from them.
Cars with CVT gearboxes include the Toyota Prius and C-HR, Honda C-RV and Honda Jazz, and the Subaru Forester.
Single-Speed Gearboxes
Electric motors have two key advantages over an internal combustion engine: they produce all their torque from zero revs, and they can spin much faster than petrol engines – easily up to 20,000 rpm.
As a result of this, most electric cars don’t require multi-ratio gearboxes, since all the torque – or twisting force – necessary to get the wheels going is available as soon as you press the accelerator pedal, and the wide available rev band mean that an electric car can go from zero to its maximum speed without the need to change gear.
This is in contrast to petrol and diesel engines, which develop power and torque in a more narrow band, so require multiple gear ratios to help get the best from the engine.
The gear ratio manufacturers choose for this single speed transmission is important, though. Too high, and you’ll get a good top speed but poor acceleration, while gearing that’s too low will give you explosive acceleration but a limited top speed. This is why some high-performance electric cars – such as the Porsche Taycan and Audi E-tron GT – use a two-speed gearbox, as this permits a balance between good acceleration and a longer, more efficient second gear for high-speed cruising.
Most electric cars, though, such as the VW ID3 and ID.4 or the Nissan Leaf, use a single-speed automatic gearbox as they just don’t need the extra ratios. An added benefit of this is that they are both cheaper to maintain and cheaper to produce in the first place.