The automatic car has been a firm favourite of car buyers in Malaysia, and for good reason. Unless you live in the kampung, you will be faced with traffic jams. Even Kangar, Perlis, has jams when Hari Raya comes around. It used to be that the only option when buying an auto was the ubiquitous fluid transmission, with its torque converters, solenoids and numerous clutch packs, but nowadays, there is the choice of continuously variable transmission, or CVT.
CVT has been around a long time. It is mostly used in small capacity scooters and is the most common transmission for them. CVT doesn’t have fixed gear ratios like a manual gearbox or an automatic transmission. Most manual gearboxes will allow up to six speeds, or more commonly five speeds, while an auto has four or five speeds.
CVT does away with gears entirely. Instead of gears, there are two pulleys connected by a belt. How it works is that the two variable-diameter pulleys, each shaped like a pair of opposing cones, are connected by a metal belt or chain running between them. One pulley is connected to the engine (input shaft) and the other to the drive wheels (output shaft). The halves of each pulley (the opposing cones) are movable; as the pulley halves come closer together, the belt is forced to ride higher on the pulley, effectively making the pulley’s diameter larger.
Changing the diameter of the pulleys varies the transmission’s ratio quite in the same way that a bicycle routes its chain over larger or smaller gears to change the ratio. Making the input pulley smaller and the output pulley larger gives a low ratio (a large number of engine revolutions producing a small number of output revolutions) for better low-speed acceleration. As the car accelerates, the pulleys vary their diameter to lower the engine speed as actual speed rises. The effect is that the transmission is changing gear all the time. That is the fundamental principle of CVT.
What CVT does is make the engine “hold” in a certain sweet spot while the gears “change” as the relative sizes of the two pulleys change. The result is a smoother, more efficient and quicker drive than a normal automatic. Engines do not develop constant power at all speeds. At a certain engine speed, torque and horsepower or fuel efficiency are at their highest. CVT can vary the engine speed as needed to access maximum power as well as maximum fuel efficiency. This trick allows CVT to provide quicker acceleration than a conventional automatic or manual transmission while delivering superior fuel economy.
However, there is a downside. Energy losses due to friction are greater with a CVT, about five to 15 per cent, depending on the type, compared with two to five per cent in a manual gearbox. However, the fact CVT allows the engine to remain in its optimum rev band more than compensates for the efficiency loss.
Another downside is that the normal sound of a car accelerating is quite distinct in a CVT car. The revs will build quickly, while the car accelerates at a slower rate and continues accelerating when the engine reaches its sweet spot. This actually feels like a burnt clutch in a normal manual transmission and is disconcerting for anyone not used to it.
Some manufacturers build in pre-set points where the two pulleys will be of certain relative sizes, just like normal gears. CVT will “pause” at those fixed pulley sizes and “changes gear” to the next preset. It almost feels natural, although it is nothing more than software settings in the gearbox computer. Modes can be built-in, where “Economy” can be six presets, while “Sport” is eight presets. You could easily put 16 speeds if you want to.
CVT transmissions can’t handle as much power and torque as conventional transmissions. That’s why you don’t see them on high-performance sedans or big heavy trucks. An average sized SUV is about the limit for current designs, but the technology is sure to advance due to the acceptance of this new automatic transmission.
A CVT-equipped car will normally be more fuel efficient than a normal auto, particularly for stop/start traffic or during constant speed changes. It is also smoother and quieter than manuals or autos. If you can live with the scooter-like feel, then a CVT could well be the perfect choice.