San Diego — Sitting in the parking lot of the Le Meridien Hotel on Coronado Island, the tiny car looks perfectly normal, but the driver immediately knows that something is different when the car is shifted into gear. Unlike a typical automatic transmission, the subcompact Subaru Justy doesn't move when it's shifted into ``drive''; it sits there, without the familiar slow forward ``creep.'' But when the driver puts a foot on the gas, the Justy comes to life, accelerating with unusual pep, far more than one would expect from such a small car equipped with a conventional automatic.
On the road, the driver notices other differences. For one thing, there is no ``shift shock,'' the sudden jumpy shudder one feels when a normal transmission goes from one gear to another.
And a glance at the tachometer reveals the most startling deviation of all: As the Justy accelerates from 30 to 55 miles an hour to enter the freeway, the engine maintains a steady speed of about 3,500 revolutions per minute (r.p.m.). When the driver steps on the gas, the tach will surge momentarily, but as the car begins to accelerate, the engine speed remains stable.
For Subaru, all this represents a technological coup with its entry-level Justy. The model has become the first car on the American roadway to offer an electronic, continuously variable transmission, also known as an ECVT, or just CVT.
The company hopes it will help win customers who want an automatic transmission but don't want to give up the faster acceleration they get from a standard, or ``stick,'' shift.
Like a conventional automatic - which uses hydraulic systems to shift gears without the driver's doing it - the ECVT doesn't really shift gears at all.
``A continuously variable transmission is to a regular automatic transmission what a dimmer switch is to a three-way bulb,'' explains Alex Fedorak, Subaru's director of technical training and development.
The basic concept of the CVT is surprisingly simple. At its heart are three basic parts: two pulleys and a metallic belt. One of the pulleys is connected to the engine, the other to the shaft driving the wheels. The belt connects the two pulleys.
Each of the input and output pulleys is split in half, and their insides are like double cones (see illustration). At different speeds, hydraulic pressures regulating the two pulleys change, and the halves widen, so the interior profile on which the metal belt rides becomes larger or smaller.
At low speeds, the input or primary pulley has a small diameter, and it drives a large-diameter secondary, or output, pulley, which provides a low gear ratio. As the car speeds up, the diameter of the primary pulley gets larger while the secondary pulley gets smaller, yielding a higher, though continuously variable, gear ratio - hence the name.
In theory, at least, the CVT has several advantages over a conventional automatic transmission: For small cars such as the Justy, it is incredibly compact and lightweight. Subaru officials claim that their ECVT delivers the fuel economy and ease of use of an automatic, but with the performance closer to that of a car with a stick shift.
That is essential, insists Tom Gibson, president of Subaru of America, because one of the major objections about many small cars is weak performance, particularly when equipped with an automatic.
``The ECVT helps us in the overall market, especially with the female market, because [women] are inclined to drive automatics,'' Mr. Gibson says.
Though Subaru is the first automaker to bring a continuously variable transmission to market in the United States, the CVT concept is not so very new. Originally Dutch-designed, it first appeared in 1959 on the Daf (now Volvo).
There have been countless technical developments since then, and several other automakers are using or developing CVTs of their own design. The Ford Motor Company offers a version in its Fiesta, sold only in Europe. The Ford transmission is also used by Fiat, though the Italian automaker recently announced plans to start using the same CVT found in the Justy, which is built by Fuji Heavy Industries of Japan, the company that builds cars for Subaru.
Though Ford has reportedly been considering a CVT for one of the cars it sells in the US, Ford spokesman Paul Preuss says that is ``not even being talked about. It's way, way off in the future.''
Similarly, General Motors Corporation spokesman Mark Cocroft says that while GM is continuing to research continuously variable transmission designs, it has delayed introducing its own version in Europe, where one had been planned.
There are several reasons that Ford, GM, and other automakers have taken a go-slow approach. For one thing, there is what Mr. Preuss describes as the ``squishy'' ride of the CVT. Some consumers have complained about the way the engine revs up and then stabilizes before the car actually gets up to speed.
According to Mr. Cocroft, however, ``the biggest challenge is the durability of the belt'' between the two pulleys.
Initially, CVT belts were made of rubberized materials, just like the fan belts found in conventional automobiles. The Subaru/Fuji belt is made of a series of tightly linked metal segments wrapped around flexible metal bands.
Subaru's Mr. Fedorak says he has been surprised at the durability of that design. ``We wanted to get a few broken belts from Japan [where the ECVT has been on the market for over a year] to show our mechanics what to look for, but Fuji says so far they haven't had any break.''
For the time being, CVTs will be limited to just small cars, typically with engines of less than 1.6 liters displacement. With current designs, a continuously variable transmission would have to quadruple in size to handle an engine twice as large - the size of today's typical V-6, for example. That would do away with many of the size and fuel economy benefits, according to Subaru engineers.