EnginePulley

Transmission Mechanism for CVTCVT is the mechanism that can deliver the power of the engine efficiently to the tires through pulleys, one for the engine (left) and one for the tires (right). The pulleys are set up between two plates. As the plates get closer or further away from each other, the diameter of the front and back pulley parts in contact with the belt changes. CVT shifts gears (transmission) through this change in diameter, in other words, by the transmission gear ratio changing.

Seamless Driving and Improved Fuel Efficiency!

CVT Evolution Part 1

Three types of automatic transmissionImagine you are riding a bicycle with gears.

When starting off or on a slope, you switch down to a low

gear and then it will be easier to pedal. But when your speed

increases or when you're going down a hill, you will get the

feeling that you are pedaling more than necessary if you stay

in the low gear.

So you go up a gear or two, and then you zip along.

Well, an automobile transmission is fundamentally the same

idea. In the same way that the strength of a human body has

limits, so too is it hard to greatly change the torque in an

engine. And that's where gears come in. By using the high

gears and low gears at different times, you can move

forward smoothly without needing to change the amount of

effort you put into pedaling – or, in case of a car, the amount

of power from the engine.

With a car, a driver selects a low gear (i.e. first or second)

when starting off from a traffic signal or going up a hill. And

then, as the car picks up speed, the drive will shift up to

fourth or fifth gear.

In Japan, over 90% of vehicles have automatic transmissions

(often called just “automatic” ) that can change gears by

itself. We can classify automatic transmission systems into

three main types. The first is the conventional automatic

transmission (AT). Then there is the dual clutch transmission

(DCT), and last but not least, continuously variable

transmission (CVT).

Of the three, CVT is uniqueTransmission, including the formerly mainstream manual

transmission, selects the combination of gears from many

types and then shifts gear. However, CVT sets the

transmission gear ratio freely with the pulley and the belt.

This is why CVT is known as “stepless” transmission.

How does it work?　Okay, let's go back to your bicycle. Think about how you

switch gears on a bike? Changing gear changes the size

correlation (i.e. transmission gear ratio) of the front and back

wheels. Well, CVT uses a pulley and belt. As in the diagram

below, by changing the width of two pulleys it becomes

possible to change transmission gear ratio.

The advantage of CVT is that it can choose the optimum

transmission gear ratio. For example, there are times with AT

and DCT when the gear that is optimum for the vehicle's

speed is actually between fourth or fifth gear. The “gear” that

would really give the best driving results would be “4.25” or

“2.16,” but the number of gears is limited, so the system has

to compromise.

CVT doesn ' t have to compromise . I t 's a “stepless”

transmission where you can set the transmission gear ratio

freely, meaning the car can always drive in the gear ratio that

is most efficient. It can be used when driving at a set speed,

as well as for continuous optimal transmission gear ratio

during acceleration.

Due to this, fuel efficiency also improves. Another benefit is a

smooth ride without the jerk you can get from shifting gears.

CVT is transmission with great potential, achieving a powerful

driving experience that is smooth and with superb fuel

efficiency.

CVT Pulley MechanismAs the engine (input) pulley width increases and the tire (output) pulley width decreases, the engine pulley becomes smaller than the tire pulley for the diameter of the part where the pulley and belt are in contact. This is the state of being in low gear, such as first gear for AT. Vice versa, as the engine pulley width decreases and the tire pulley width increases, the diameter of the part where belt and pulley are in contact grows larger for the engine pulley than the tire pulley, which is the state of being in high gear (fifth or sixth for AT). One of CVT’ s fortes is that pulley width can be continuously changed, allowing the system to change transmission gear ratio smoothly and without steps.

High Speed

Tire Pulley

EnginePulley

EnginePulley

Tire Pulley

Low Speed

What is CVT? A subtle usage of pulleys and belt