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A car version of Ford's long-awaited continuously variable transmission is now in production, and judging by our test drive it will revolutionise the urban delivery scene.
• Ford has finally announced the production version of its long-awaited CTX continuously-variable transmission, or CVT. The CTX is initially being built by its design parent, Van Doorne's Transrnissie, for both Ford and Fiat, but in strictly limited numbers_ This means that, in Ford's case, the transmission will be available only on 1.1 litre Fiesta hatchbacks, and the total number built this year will only be some 15,000. Numbers will rise next year when Ford's Bordeaux gearbox plant will take over manufacture for both Ford and Fiat.
In the long term, then, this conceptually simple transmission will become widely available. It will certainly be fitted to the petrol-eng;ined Fiesta van before long, and when stronger versions become available it will be fitted to both the Escort van and the Fiesta diesel, so it was well worth trying out this new transmission before it becomes available for commercial vehicles.
The CTX is a comprehensively redeveloped extension of the old Daf belt driven automatic as still used in some small Volvo cars. In this new guise it uses one belt instead of two, and multi-plate, engine-oil-pressure engaged clutches for forward and reverse instead of a single centrifugal unit.
The new belt is the heart of the unit. It is based on two steel bands, each consisting of 10 x 0.2mm-thick strips. These bands carry 320 steel blocks which butt against each other to allow the belt to transmit power by compression instead of the usual tension.
This belt is fitted between two split pulleys with conical faces: moving the pulley halves apart reduces their effective diameter; moving them together increases it, thus altering the gearing of the unit steplessly.
This belt variator is connected to an epicyclic geartrain and the two forward/ reverse clutches. Control of the unit is by hydraulic pressure, generated by an integral oil pump running at engine speed. Control inputs are simply of direction (from the selector lever), throttle position, engine speed and output speed. The two latter inputs are from pitot heads inside the casing. The transmission runs on Ford's standard own-brand automatic transmission fluid.
The total ratio spread of the belt variator is 5.85:1, compared with the 4.74:1 of the normal Fiesta five-speed manual gearbox. The larger spread allows both lower and higher gearing than the five-speeder gives. At the tail of the gearbox there is a further set of reduction gears to give the correct speed before drive goes to the 3.84:1 final drive.
The CTX is rather more bulky than the conventional Ford transverse gearbox and weighs some 10kg more. A unit with more capacity than the current one, which is limited to 120Nm of torque, would weigh still more. The price penalty is a significant 2673 over the four-speed Fiesta, and 2573 more than for the fivespeed. According to Ford the fuel economy of a CTX Fiesta is only marginally worse than that of the fivespeed model: the difference is negligible on the open road, and only 12% on the EEC urban fuel consumption cycle.
DRIVING
Driving the CTX-equipped Fiesta makes a fascinating contrast to both conventional planetary automatics and to the Perburytype Leyland CVT. It is, not surprisingly, closest in feel to the old belt-drive Dafs in style, but is so much more refined as to be a totally different transmission.
The driver is faced with a conventional floor-mounted selector, marked out in what used to be the standard way before transmission manufacturers started offering sophisticated over-rides and the Like. There are just five positions, for Park, Reverse, Neutral, Drive and Lock, and there are simple detents to divide them: there are no interlocks to prevent movement between positions. All the other controls are standard, except that the brake pedal is doubled in width so that left-foot braking is made easy. Starting off from rest is unusual. The wet clutch engages very smoothly as engine revs are increased, but there is none of the initial urge which is imparted by the usual torque convertor. Because there is no fluid coupling, the rather dodgy — but useful — technique of holding the car on the brake to build revs up for a fast getaway is not practical in this case.
Once the vehicle is underway, pickup to around 50Icm/h is surprisingly quick and enables the Fiesta to keep up with much more powerful manual-gearbox vehicles. If full throttle is used the revs climb immediately to some 4,900rpm and will stay there while road speed builds up to about 115km/h. Only beyond that level will the engine speed rise in line with road speed, until a claimed road speed of some 135km/h is reached, with the engine The eerie part of the transmission's performance is the way that it gears itself up as soon as engine load is eased even fractionally. Thus, if the driver is extremely careful, the throttle can be eased back so that road speed is maintained at an indicated 1151un/h with about 2,800rpm showing. The converse of this is that even a slight extra pressure on the throttle will send the engine speed soaring up towards the 4,900rpm normal upper limit. This makes the vehicle's behaviour on motorways rather restless: it would be much nicer to be able to engage a positive 'top gear' lockup as on many planetary gearboxes, or to have a control which reduces the gearbox's sensitivity to throttle position for motorway running. As increased throttle pressure will always make the transmission change down, there is no need for a separate 'kickdown' mode.
SLOWING DOWN
Slowing down is also unusual. Initially road and engine speeds drop roughly in parallel, until the engine is turning at some 1,600rpm. As road speed drops further the transmission progressively gears itself down to leave the engine speed contstant, until it is in 'bottom' where the road speed is around 151an/h at 1,600rpm. The engine and road speeds are then effectively locked together, so that there is marked engine braking down to the clutch release point at around 70Orpm.
The 'L' position gives some of the benefits of the usual lock-down control on an automatic, but in this case it only prevents the transmission from changing up, rather than physically engaging a lower gear. This means that theoretically 1' can be selected at any speed: this generally holds true in practice, but on one occasion we were able to fool the transmission by selecting 'L' after the car had been coasting for some distance at a high road speed with low engine revs. This gave an instant rise to very high revs and a chirp from the lefthand front wheel as the transmission tried to find a low gear. We are assured that this is an unusual, if not unique, fault on the vehicle concerned: certainly we were unable to trigger it again.
The 1' position does give quite good retardation: its effect is similar to that of an exhaust brake applied in a middle gear on a conventional truck, in that it prevents acceleration down a hill rather than noticeably slowing the vehicle. It is of at least equal use climbing hills, when a momentary lift-off – for instance when entering a corner in 'D' – lets the transmission change up. That results in the vehicle running wide instead of tightening its line as a front-wheel-drive vehicle will usually do.
The CTX seems otherwise quite viceless. There is a slight whine discernable on the over-run between 80 and 50km/h, but otherwise it is completely unobtrusive.
It is, quite simply, the most impressive and smoothest automatic transmission we have tried, and will doubtless revolutionise urban delivery vehicles when it becomes available in them.
by Allan Winn