Driving force

When Torotrak offered the first test drives of its infinitely variable transmission, David Fowler was at the wheel.

I’d seen pictures of the Ford Expedition. It seemed to have the shape and proportion of a typical 4×4, nothing out of the ordinary.

What I was unprepared for was its sheer bulk.It’s about twice the size of a Ford Explorer, and even makes a Range Rover appear small. But despite its appearance it is two-wheel drive and corners like a barge.

For some reason, though, Americans love these things, and their closely related pick-up truck variants. Ford, GM and Chrysler sell about seven million annually, accounting for about half the total US vehicle market. They’re gas guzzlers: the Expedition comes with a 5.4-litre V8 engine, and some models go up to seven litres – which is a clue to why transmission developer Torotrak has chosen them as its target market.

Practically all these pick-ups and large MPVs come with automatic transmissions, so it’s a big market. For now they count as light commercial vehicles for the purpose of average fuel consumption rules for US fleet vehicles, so they have to meet less stringent fuel consumption targets than cars. But environmental lobbyists want the regs tightening.

Enter Torotrak, whose infinitely variable transmission promises a fuel economy gain of 20 per cent over a conventional automatic.

A lot has been written about Torotrak and its long road towards convincing big car manufacturers that its transmission can work. Until now, though, no one outside car executives and development engineers has had a chance to try it out.

But because Torotrak paid for the development of its latest series 3 transmission itself, whereas previous phases were joint efforts with car makers, it’s no longer bound by confidentiality agreements. Which is how The Engineer came to be driving a left-hand drive US-spec behemoth around Lancashire roads near Torotrak’s base in Leyland.

The key target of the series 3 development programme, says business development director Geoff Soar, was to demonstrate the system’s fuel economy gains as well as durability and driveability. If the IVT is to be accepted in the market, it mustn’t draw attention to itself. In other words, it’s got to be at least as smooth as a normal auto and similar driving characteristics.

Torotrak depends on integrated software control of the transmission and engine, and its engineers have spent a lot of time in phase 3 writing software to give it the right characteristics: building in things like creep, a characteristic of auto transmissions that will hold the car without brakes on slight uphill gradients, or allow it to inch forward when manoeuvring, with no throttle input.

The fuel economy gain was successfully demonstrated on the standard US test cycle: we’re now about to find out about the driveability. The Expedition we’re driving is standard except for the transmission itself, a new engine management chip and a drive-by-wire throttle (a key ingredient of the Torotrak system).

Creep is quickly demonstrated, holding the Expedition on a six per cent gradient at the adjacent Leyland Technical Centre test track.

On the open road the car accelerates as smoothly as a normal auto, but without the gear changes. Get on a stretch of motorway and you notice how low the engine revs are at cruising speeds. The IVT’s spread of ratios goes right up to a high overdrive, whereby the engine is only turning at around 1,200rpm at 80mph. The transmission is torque rather than ratio controlled, and to maintain cruising speed you don’t need much torque.

Accelerate and the car responds quickly. It avoids the quirk of the traditional belt drive CVT, in which, on acceleration, the engine revs rise dramatically and stay there, while the actual speed builds much more slowly. Again, through suitable software strategy, Torotrak engineers have largely eliminated this phenomenon, producing an effect more like the kickdown in a conventional auto box.

Torotrak can also do a few tricks conventional autos can’t. The powertrain management system is programmed not to let the engine rev beyond maximum power, because there’s no real point. This removes the need for a separate rev limiter, though the Expedition’s engine does have one.

The really clever thing, though, is descending steep hills. Land Rover has a system for controlling speed down steep gradients using a combination of the engine management system to limit the throttle setting and the anti-lock braking system to slow its 4x4s to a set speed without the wheels locking. The IVT has it built in. It features a ‘geared neutral’, meaning that the engine is always connected to the wheels even when the car is stationary, avoiding the need for the customary torque converter. It also means that, going downhill, you can put the car in reverse and use the engine to act in opposition to the weight of the car pulling it down the hill.

You stop at the top of the steep gradient, and – a bit counter-intuitively – engage reverse. Release the brake and the car rolls downhill. At this point a car with a torque converter and reverse engaged would stall. Depress the throttle. Oddly, the revs rise a bit, while the car slows down. Keep pressing the throttle and it stops, then reverses back up the hill if you want.

On production models principal engineer Pasco De Palma envisages, you’d probably have a button marked ‘hill descent’ so drivers don’t think of it as engaging reverse, but it would work just the same.

Overall it’s an impressive package. There are a couple of glitches: the pump that circulates oil round the transmission, basically an unmodified power steering pump, is noisy; and occasionally you feel a slight clunk as the clutches that switch between the transmission’s high and low ranges engage and disengage, though this is supposed to happen at a synchronous speed. But these are the sort of thing you’d expect on a prototype and more development should iron them out.

Torotrak is working on manufacturing the transmission with Japan’s biggest gearbox supplier Aisin, and awaiting Ford’s verdict on an Expedition it has been evaluating over the past few months. Torotrak believes that once the IVT gets out into the market it will gain wide acceptance: it’s just securing that vital first foothold.

On this showing, it’s hard not to agree. It’s just a pity IVT’s improved fuel economy is likely to find its first application in rescuing US gas guzzlers. Then again, if Americans can’t be persuaded to collect their shopping in anything other than a light truck then maybe making their fuel consumption a bit less profligate is better than nothing.

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