CONTINOUS VARIABLE TRANSMISSION (CVT) TRANSMISSION

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In the car, with the purpose of creating a new and efficient transmission for performance and also for the fuel efficiency they are several transmission that had been created. From the manual transmission to the Dual Clutch transmission they are several of them created and been upgraded to serve the car lovers better. One such transmission is the Continous Variable Transmission or in short called as CVT. CVT is a transmission that will change seamlessly through a continuous range of a gear ratio and the CVT does not require a clutch like the DSG. Simply it is a transmission that does not have a fixed gear speed.This is far different than the conventional transmission that had a fixed gear numbers or ratio.

It is a belt driven design and due to the nature of this design, it can produce a higher RPM that can achieve peak efficiency. This CVT design surprisingly started in 1490 by Leonardo Da Vinci who had imagined the concept of steps less drive. This is one of his many futuristic design imaginations that exceeded his time. With the design imagined by Leonardo Da Vinci, Milton Reeve the pioneer of American automobile industries had made Leonardo Da Vinci design to reality when he had invented the CVT for his saw milling and applied to his first car in 1897. Although Milton had fixed CVT in his car, in Europe in 1886 the first patent for the friction based belt CVT were filed by Daimer and Benz in that year and in 1935 the US patent for the toroidal CVT was filed.

leonardo-da-vinci
Leonardo Da Vinci, the creator of the Monalisa portraits

Although in the earlier stages the European and American had invented and filed for a patent for CVT but it was the Japanese manufacturer who had fall in love with CVT. It started from the Subaru who had fixed a CVT electronically in their model Justy. And with this in 1989, Subaru become the first car in the US to offer the CVT transmission. Until today, Subaru continues to be loyal to the CVT transmission as all their models from Legacy, Forester, Impreza and much more had been fixed with CVT gearbox.

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The first car model in the US to have the CVT transmission, Subaru Justy 1989 model

Toyota, Nissan, and Honda too fixed CVT in their flagship like Camry, Teana, and Accord respectively. Each called the CVT in a different name where Nissan called it as Xtronic CVT and Toyota as e-CVT. For now, only the Japanese model had fixed the CVT in the model while the European and American preferred the manual torque converter, DSG, and ZF transmission.

They are several types of CVT transmission and the first one is Variable Diameter Pulley(VDP). In this type of transmission, they are 2 V-belt pulleys that are split perpendicular for them to rotate with another V-belt running between them. The gear ratio will be changed by moving 2 sheaves at 1 pull close together and 2 sheaves of another pulley further apart.

vdp
The layout on the VDP types CVT works

The next one is Toroidal CVT. In this CVT, it is made up of the disc and a roller that transmits power between the disc. They are 2 disc where one is the input and another is the output. The gear ratio will change when the roller moved along the axis of the near-conical part changing the angle that will cause the roller to the near-conical part that provides the ratio.

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The layout of the Toroidal CVT

Another type of CVT is called as Magnetic CVT or M-CVT. It was developed in 2006 at the University of Sheffield and it had a variable magnetic transmission which gives an electronically controllable gear ratio.

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The M-CVT design

And finally, they are another type called as Planetary or e-CVT. The gear ratio in this of CVT is shifted by tilting the axes of spheres in a continuous fashion to provide different contract radius which in turn drive the input and output disc. In this type of CVT, they are multiple levels called as a planet to transfer the torque through multiple fluid paths.

e-cvt
The e-CVT design

They are several reasons on why the Japanese automobile manufacturer like the CVT transmission and the first of it is it improves the fuel efficiency of the car. Since the CVT change the gear ratio based on the driving style and does not have the fixed gear it will positively maximize the fuel economy.

It also provides a smoother ride where since it does not have a fixed gear ratio, the car will not provide the feel of gear changes or jerking that is associated with the gear change hence it will provide a smoother ride.

CVT is one of the most improved transmission with many of Japanese manufacturer had invested millions of yen in R & D for the CVT transmission and in the future, the CVT will be expected to be better than the current model.

Although the CVT had several pros, they are some cons that make the European and American manufacturer to discontinued the CVT in their model. Compared to a conventional transmission, the CVT is costlier to maintain. For some transmission, the gear oil need to be changed for 40,000km or 60,000 km depends on the transmission manufacturers, the CVT transmission oil needs to be changed on every 20,000km and in some case any small malfunction will lead the whole transmission to be repaired with can cost a buck for the owners.

Since the CVT eliminate the feel of the gear changes, it does not provide the thrill and excitement the car lovers love when they rev the car hard.

The next problem is CVT unable to withstand high horsepower. Unlike the ZF transmission and DSG the CVT is not fixed in the high-performance car due to this characteristic and this is one of the reasons on why the European and American manufacturer does not fix CVT in their car.

The CVT transmission, however, will not be eliminated altogether due to the advantages that CVT have to compare to the traditional transmission especially on the smoother ride and the fuel efficiency. However, until any improvement or any breakthrough had been made, the CVT is unable to be fixed on the high performance or high horsepower cars.

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