Small Autos – the Background

A little history, and the options available now

new Ford Fiesta with automatic transmission

new Ford Fiesta with automatic transmission

If you spend most of your time grinding your way around town in the usual stop-start manner you'll know that this is just the sort of environment that cries out for a small car with an auto gearbox. And yet, even until the last decade or so, the automatic gearbox has very much been the preserve of the luxury car.

There are three reasons: it's a costly piece of kit, it's bulky and it tends to absorb valuable engine power, or at least that was the case with traditional torque converter (fluid coupling) transmissions.

On a small, inexpensive car, the last thing you need is an expensive optional extra robbing it of its already modest power output.

Technology, however, has come on apace in recent years. As such there's been something of a resurgence in the world of the small auto. Now buyers looking at models from the mainstream makers have a choice.

More efficient engines

It's all largely down to more efficient engines boasting improved fuel economy and, crucially, more horsepower than a decade a go. Where once a supermini might have had around 65bhp, a similar car today could have around 100bhp. Factor in a little more torque to help boost acceleration and you've got yourself a better platform with which to use a conventional auto gearbox. And those gearboxes have got smaller, lighter and more efficient.

What's on offer?

The days of pottering around in three-speed auto Minis are long gone. Yes the conventional auto remains, but you're now treated to several more forward gears. And there's even the prospect of doing it yourself. The trend for sequential operation is growing – the push-pull element of the gearlever can add fun to the driving experience.

The same is true of the F1-style paddles often located behind the steering column.

Paddles

Although sometimes dismissed as a gimmick, paddles can help make progress more predictable if your gearbox has a habit of 'holding on' to a gear for too long. Screaming around town in second is not good for fuel economy and refinement, making a quick flick of a paddle is a useful way of boosting economy and reducing excessive wear and tear.

Continuously variable

Screaming used to be a regular activity for cars equipped with continuously variable transmissions (CVTs). Serious enthusiasts will probably remember DAF's attempts with its Variomatic technology from the 1950s. Early drawbacks included a clunky operation and the hefty weight of the gearbox – hardly ideal when fitted to a small car – plus the prospect of engines revving hard but not delivering sufficient forward motion.

Bosch manufacture CVT push belts

Bosch manufactures CVT push belts

Since then Ford and Fiat took the plunge with the Fiesta and Uno respectively, although early results weren't terribly impressive. They have since been joined by the likes of Honda, Mercedes, Mini and Audi in the quest for better performance, economy and driver convenience. And with economy a major factor for cars with hybrid powertrains, the CVT gearbox comes into its own.

How does CVT work?

In essence, a CVT gearbox employs two pulleys and a belt. With one pulley fixed, by way of clever engineering, the other pulley varies its diameter and hence the overall gear ratio. The belt rides up and down this 'gradient' just like a bicycle chain on a set of gears. The only limitation is an engine's torque figure. Only Audi has managed to successfully combine CVT with big, torquey engines, although this isn't a major consideration in the supermini arena.

Smaller, lighter gearboxes, plus more powerful engines, have conspired to make the CVT route a more desirable one for makers and buyers alike. Promises of improved fuel economy are becoming a reality, while refinement and ease of use are also important plus points. Because there's no traditional gearchange as such, there's no 'step', which means smoother progress during acceleration.

Manufacturers, in a bid to boost driving appeal, sometimes engineer faux-stepped gearchanges, and combine this feature with steering wheel-mounted controls. Honda's Jazz is an obvious example.

Bosch manufactures CVT push belts - the central component of a CVT - and in 2013 claimed that a quarter of automatic transmissions will soon feature CVT.

Honda Jazz CVT

Honda Jazz CVT

Something more conventional

If you want the experience of a manual gearbox but without the hassle of using a clutch pedal, the other major development has been in automating conventional manual gearboxes.  Offerings include SensoDrive (Citroen), Durashift EST (Ford), iShift (Honda), Quickshift (Renault), Multimode MMT (Toyota) , Easytronic (Volvo), and ASG (VW).

In simple terms, clever hydraulics or electric motors operate the clutch and gear-change mechanism for you. Early efforts delivered decidedly jerky results unless you were smooth with throttle inputs. Some critics maintain nothing much has changed, but the key is to not treat these gearboxes as regular automatic units. To facilitate a smooth change you do need to lift off the throttle a little, like you would with a normal manual gearbox. And this is the problem: if it's supposed to be automatic in operation, why do you have to change your driving habits?

Initially such technology was fitted to sporty models as a way of connecting a car firm's motorsport aspirations with performance driving. The combination of a sequential-style gear lever and steering wheel-mounted paddles certainly helped, and it's been improvements in electronics that have helped smooth out most of the early problems.

However, in a curious twist, such technology is being promoted as more of a convenience feature. With gear levers in this case nothing more than glorified electronic switches, car makers realise they can put them anywhere, thus freeing up space between the front seats of a people carrier for example.

Gearlevers as electric switches? F1-style paddles? Shouldn't an automatic gearbox be all about convenience and ease of use? Well yes, it should, and if you just want a car that allows you to get in and go then you probably need one of the latest twin-clutch automatics.  These are capable of delivering seamless automatic changes but can also be operated manually if you later crave greater involvement.

Twin clutch automatic gearboxes

For the most refined, seamless gear changes you need look no further than state-of-the-art twin clutch automatics such as  PowerShift (Ford/Volvo), PDK (Porsche), DSG - Direct Shift Gearbox (VW Group), DCT (BMW), DCS (Peugeot/Citroen) , and TCT (Alfa Romeo).

Volkswagen Polo DSG

Volkswagen Polo DSG

Here two clutches are connected to what amounts to two separate gearboxes, one for the odd-numbered gears and the other for the evens. As one gear is engaged the electronic control system preselects the next so that changing gear is a simple and virtually seamless matter of shifting from one clutch to the other by hydraulic control.

Future fantastic?

That's all very well for the present, but the leaps made in refining all the major gearbox options have happened in only the last few years. With that in mind, you'd expect progress to race along. In fact, save for anything radical coming along, it's unlikely that much will change dramatically until new propulsion units appear.

Talking of which, the new crop of electric vehicles do away with conventional gearboxes altogether and feature simple ‘one gear’ transmission and to select reverse the engine just rotates the other way.  There will of course be a rev limiter to stop you doing 100mph in reverse!

For cars with conventional combustion engines, look out for increased refinement, more diesel automatics and more gears added to regular auto gearboxes as part of refinement and efficiency drives. Lexus is already up to eight cogs on its LS 460 and it's only a matter of time before that filters down to humbler motors.

(6 February 2014)