by David Finlay (23 Nov 00)

Although the Netherlands is heavily involved in the motor industry in other ways, such as being a European outpost of various Japanese manufacturers, it has never made a serious effort at becoming a car-producing nation. Yet the Dutch (who, it's as well to remember, had one of the leading European scientific communities centuries ago when the church was stifling progress in neighbouring countries) did come up with an automotive innovation which is becoming increasingly common.

If the name DAF means anything to you, it's probably in connection with truck manufacturers Leyland-DAF, now LDV. But thirty years ago the Van Doorne company was building cars which, though small, slow and not especially popular, were unique in that they had neither manual nor conventional gearboxes, but instead used continuously variable transmission (CVT).

DAF was eventually bought over by Volvo, which briefly continued to produce the DAF 66 as the Volvo 66, still with the same transmission, and also introduced CVT to its own 340 series cars. When that idea was abandoned, CVT went into hibernation, but over the last few years it has made a comeback - updated, certainly, but still using the same basic principle . . .

. . . which is this. Instead of using sets of gears or a torque convertor, the engine's power is transferred to the wheels via a system which includes a large belt (originally rubber, but now a complex arrangement of steel segments). This belt is V-shaped, and the space between the two halves of the pulley in which it sits is adjustable, which makes the effective width of the belt variable and thereby alters the gear ratio.

Broadly speaking, the space in the pulley is determined by engine load, and this is what distinguishes the CVT from any other commercially used system. Instead of driving through a gear ratio which is fixed (as in a manual) or smudged around a pre-determined figure by the torque convertor (as in an automatic), the engine gets to choose the ideal ratio for the job in hand, as dictated by the amount of throttle the driver uses.

The Aural Illusion

This has strange aural consequences. If you decide to overtake another vehicle in a car with manual transmission, you will tend to apply most throttle early in the manoeuvre, and then subconsciously back off as you reach an appropriate speed. The engine note will continue to rise, since you are still accelerating, even at a reduced rate, and that feels perfectly natural.

If your car has CVT, as soon as you back off the revs will drop, since the engine now needs to do less work to achieve the smaller level of acceleration. The first time you try this it's easy to imagine that the car is suddenly slowing down, even though the countryside is still whizzing past at an increasing rate. If there happens to be a lorry coming the other way, this can be most disconcerting, though you do get used to it eventually.

In terms of power loss, a CVT is less efficient than a manual, but slightly better than a conventional auto because there are fewer moving parts. Where CVTs score over the other systems is in the fact that they are always in the correct ratio, so the engine is always working at its best for the required circumstances.

This has led several people to consider the use of CVTs in motorsport, though one attempt to introduce it into Grand Prix racing was squelched by the FIA's decision to specify a permitted number of gear ratios in Formula 1. It's almost impossible to quantify how many gear ratios a CVT has - within the boundaries of its highest and lowest gearing it can be said that there is an infinite number of ratios to choose from - so development was immediately abandoned as being totally pointless. Looking at this from a slightly cynical perspective, the fact that CVTs were effectively banned from motorsport suggests that they could actually have worked pretty well, and that modified versions might by now have been appearing in high-performance road cars.

Instead, CVTs are now increasingly being used as alternatives to conventional automatics, most notably by Nissan and Fiat. Although they are fairly complex to build, they are ridiculously easy to use. If you want to go forwards, you put the gearlever into the forward position. If you want to go backwards, you put that lever into that slot. (This is literally the only choice a DAF driver had, though more modern cars have extra luxuries such as neutral, park and low-ratio hold.) When you want some action, you press the throttle, and off you go.

Magnetic Attraction

There is no clutch in the normal sense, but the system has to engage somehow, and most modern cars use a brilliant system of magnetised metal filings. When you are sitting at idle these just float around aimlessly, but when the call comes they are brought to order by an electric charge which collects them into a solid block through which drive is transferred from the engine to the wheels. From the driver's point of view the operation is practically seamless.

The CVT's ease of use makes it ideal for people who might otherwise consider an automatic car. We've been driving a Nissan Almera Tino CVT recently, and within a few miles it's easy to forget that it has any kind of transmission at all. Other automatics change gear with varying degrees of smoothness, but the Tino constantly blends through a range of thousands of ratios without the driver ever being really aware of it. Throttle response is not immediate, because the system has to react to the change of load when the driver suddenly requires more power, but this is no more of a problem than it is with normal automatics.

Recently, though, the potential of CVTs to add a performance element to a car has been taken up through the use of ratio holds. The same unit used in the Tino also appears in a version of the Primera, which uses six ratio holds to give the effect of a sequential six-speed gearbox. Fiat has gone a step further and used not only a sequential six-speed but even a sequential seven-speed in versions of the Punto we tried earlier this year.

Purists say that these ratio holds negate the whole purpose of a CVT, and this is a fair point. On the other hand, the seven-speed Punto in particular was magnificent fun. Its official acceleration figures are not as good as they are in the equivalent manual, but Fiat people say that in real life they reckon it is actually quicker. A really good standing start involves a certain amount of wheelspin, which a CVT does not allow, but once it is moving it is always at the ideal engine speed and should therefore perform better.

We've all heard silly manufacturer claims before, but that's one we would enjoy testing, in the confident expectation that it would be fulfilled.

There's no sign that CVTs, in their current form at least, will revolutionise the motor industry's thinking on the subject of transmissions. On the other hand, this is a very intriguing line of development which deserves to put that unsatisfactory lump, the conventional automatic, into the history books. The full potential of the Van Doorne invention may yet be realised to an extent that the long-ago owner of one of those curious DAFs would never have imagined.

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