Continuous Variable Transmission (CVT)

What is a CVT
How the CVT works
Summary


 What is a CVT (Continuously Variable Transmission)?

A CVT is a transmission that can change without steps, eliminating the need for gear changes.

Before we examine how the CVT works, let’s take a look at its merits.

 

 

 

 

 

 

If a bicycle were equipped with a continuously variable transmission, it would maintain just the right pedal weight for minimum exertion, whether starting off, cruising, or climbing a hill.

The reason:
In a CVT, the drive gear ratio can be continuously changed to maintain the right pedal weight for the driving conditions. This eliminates  the need to shift up and down between 1st gear, 2nd gear, 3rd gear, and so on.

When this principle is applied to an automobile:

 

 

 

 

The engine continually maintains a low-load rpm during acceleration.

Conclusion

The CVT allows the engine to continuously maintain the optimum speed for low-road operation.

This results in powerful performance combined with superior fuel economy.


 How the CVT works

The Honda CVT combines a drive belt with variable-diameter pulleys to transmit power with a continuously variable ratio.

 



Honda Insight Front

 

 

 Summary

 

What

CVT is a user and environmentally friendly automatic type transmission. While the concept of a CVT transmission is as old as the motor car itself, it has taken Honda to re-engineer the idea to suit the demands of the 21st Century, including full grade logic electronic control with drive and sport modes.

Where

CVT is available in the Honda Civic, Honda Jazz Hybrid, Honda Insight and Honda CRZ replacing the conventional 'automatic' transmission. CVT fully complements these low emission engines.

The transmission automatically selects a gear which is nearest to the current road speed

Why

Why CVT?

'Conventional' automatic transmissions have a series of fixed gear ratios. The transmission automatically selects a gear which is nearest to the current road speed and throttle position. However, ideal gear matching is not often accomplished. In addition, most automatic transmissions use a 'torque converter' to connect to the engine. Even if this is fitted with a 'lock up clutch' only an average of 90% engine power efficiency is achieved.

There are no fixed gear ratios with the CVT technology. Nor does it have a power-robbing torque converter. As its name suggests, it is seamless in operation, ranging from rest to full speed on one smooth jet-like operation.

By continuously matching the ideal ratio to engine performance, the engine can be operated in a highly-efficient manner in D range, or take advantage of S range for brisker performance or off-road conditions.

the transmission computer provides the right balance of oil pressure to each drum

How

Technically, in a CVT conventional gears are replaced by two variable size drums and a steel drive belt. The flexible steel belt runs in a groove formed between the sides of each drum. The diameter of each drum is controlled by the transmission computer, applying or reducing oil pressure to the movable part of each drum.

The drive pulley has low oil applied, and has expanded to allow the belt to run in a small diameter. In turn, the driven pulley has high oil pressure applied, forcing the belt outward around a larger diameter. This condition results in the driving pulley turning over four resolutions to the driven pulleys once. This is a low ratio (1st gear).

In its highest ratio ('top gear'), high oil pressure is applied to the drive pulley and removed from the driven pulley. The drum diameters are now reversed so the driven pulley is turning faster than the driving pulley.

In between these two positions, lowest to highest ratios, the transmission computer provides the right balance of oil pressure to each drum. This achieves the correct ratio to suit the prevailing road conditions and accelerator position. Drive mode selected etc.