Today I want to finish off our look at CVT transmission. Let`s go step-by-step to understand how it works:
- CVT transmission working principle;
- How reliable is CVT transmission?
- How to know if CVT transmission is bad?
- Advantages and disadvantages of CVT transmission.
Last time we can see many vehicles with CVT transmissions. The most popular CVT is v belt CVT, so I`ll tell you about its working principle.
On the shaft, which is connected to the motor shaft, there is a drive pulley made of two halves. The halves can move along the shaft (the axis of their rotation). A similar (consisting of two halves) pulley is located on another shaft connected to the car wheel drives. This pulley is called the driven pulley. Between themselves, the driving and driven disks are connected by a belt, wedge-shaped in cross-section.
At low engine speeds, the halves of the drive pulley are moved apart and the belt is “failed” towards the axis of rotation, and on the driven pulley, the opposite is true: the belt is “squeezed out” as far as possible from the axis of rotation.
Thus, due to the observation at the point of contact with the appearance of halves of the pulleys, a belt drive occurs, schematically shown in the following figure.
How CVT works (schematically)
That is, the drive shaft is, as it were, similar to a gear of a small diameter, and the driven shaft is to a large diameter. Accordingly, at low speeds, the angular velocity of the driving pulley is significantly higher than that of the driven pulley, to which the maximum traction force (and minimum angular velocity) is transmitted.
The halves of the drive pulley are shifted by the end force, which, depending on the design of the CVT, is formed by inertial forces (from rollers inside one half of the pulley moving due to centrifugal forces) or by hydraulics receiving commands from the electronic control unit (modern systems).
At high speeds, the deal is reversed: the “gear” of the drive pulley becomes large in diameter (the belt is squeezed out to the periphery of the pulley), while the halves of the driven pulley move apart and the belt “falls through” to the center (“gear” of small diameter). The friction required to change the distance between the halves of the driven pulley and the tension of the belt is provided by a spring.
