Fiat researches a stepless transmission as a gas saver
Turin, Italy — The car looks like any other Fiat on the road. Yet it is one of 100 or more Ritmo 75s (Strada in the US) with what engineers call a continuously variable transmission.
In other words, instead of the usual three-step automatic transmission of most cars, the stepless-type has an almost infinite number of transmission ratios in an attempt to increase the gasoline mileage in a car.
"The increase in fuel mileage is in the area of 10 to 15 percent over the usual automatic transmission," contends Dr. Paolo Scolari, director of product engineering for Fiat. "It will be about the same as a manual transmission or maybe a little better," he adds.
Instead of putting the lever into "D," or drive -- as is the case with a normal automatic transmission -- I moved it into "SD" . . . and away I go. To get more pickup -- for passing another vehicle, for example -- I throw the lever to the left. After passing, I move it back to the right.
At least 100 cars now are in the hands of Italian motorists, including taxi drivers, who have agreed to go along with the test.
Whether the stepless transmission will ever go into production, of course, no one really knows. Fiat engineers seem very buoyant on its future and predict the system will actually be on the road in volume in the next three or four years. Other automobile companies, both in Europe and the US, aren't so sure.
"We are still investigating the concept," asserts Dr. Wolfgang Lincke, research and development chief for Volkswagenwerk AG, "but it is very probable we will never use it."
There are just too many problems, including gearbox friction loss, engine noise, and the behavoir of the car under way, he reports. Still, a university group in West Germany now developing a car under contract with the West German government will have an electronically controlled stepless mechanical transmission, according to Dr. Lincke.
Nonetheless, the system "still has a long way to go," in the view of the R&D director for VW.
Backing up Dr. Lincke's assessment is Vw's Dr. Ulrich W. Seifert, who told the Automotive News World Congress in Detroit last July: "Even though some progress has been made, the present efficiency of such transmissions is still so low that some of the gains are eliminated on the engine side."
Fiat is developing the stepless concept in tandem with Borg-Warner in the US and the Dutch firm of Van Doorne Transmissie.
Van Doorne had provided an earlier version of the system to DAF, the Dutch vehiclemaker, which later sold its auto operation to Volvo while International Harvester took over the trucks.
The Fiat system uses a steel belt, unlike the earlier DAF system which relied on a rubber belt.
Durability was never a problem even with the DAF system, however. "The DAF had good durability," notes Dr. Lincke of VW, adding: "I don't see any problem with durability in principle. However, to pin-point the weak points of any new systems, and then improve the design, takes time."
The Fiat system uses two variable-diameter pulleys with a steel belt between them. From the starting of a vehicle to top speed, the diameter of the pulleys varies from one extreme value to the other, therefore bringing about a continuous variation in the transmission ratio.
The steel belt is the most interesting structural feature of the transmission , according to Fiat.
It consists of a series of high-resistance steel blocks strung on a steel band. There are, in fact, several concentric bands with a thickness of around one-tenth of a millimeter.
Each belt has some 300 blocks, each having a trapezoidal shape so as to ensure that they fit correctly into the slots of the pulleys.
The centrifugal clutch in the current version of the system may be a problem, admits Mr. Scolari of Fiat. However, the Italian carmaker is planning to switch to another clutch system which will improve the operation of any future cars with this type transmission.
Too, future versions of the car will be designed for low-rpm city-type driving, thus improving the behavoir of the car in making tight corners, parking , and the like.
If the system does indeed go into production, it will be available for cars with engines up to 2 liters, according to Mr. Scolari.
The stepless transmission is just one system which European carmakers are evaluating in an effort to sharply increase the mpg under all types of driving conditions on the road.
Together, they should significantly reduce the fuel consumption of the "cars of tomorrow.