Traction Drives

Among all other speed changing mechanisms, the most simplest type of mechanism is the Traction Drive. These drives are the most frequent choice for many drive systems due to their simplicity and having the ability to adjust the speed smoothly and in excellent way. For more than 100 of years, these drives have been used in industrial services. In the recent period, these drives are considered as rivals of the best gears and the best gear belts, because these contain best quality traction fluids and super quality bearing steels which are highly fatigue resistant. Two conical shape, rotating rollers are used in a common type of Traction drive. These rollers are used in transferring torque between themselves through the adhesive metallic sheet of a thin film of special lubricants. In another basic type of Traction Drive, pivotal traction rollers are used. These rollers in this type of Traction Drive, come in between an output disc and an output disc.

Functional Principles of Traction Drives
This Drive is a kind of fixed-ratio mechanical adjustable speed drive. There are two types of mechanical adjustable speed drive. Along with variable pitch drive, this is the second type of it. Through metal rollers running, These Drive transmits power against the mating metal rollers. The ratio between the input and output speed is controlled to keep to remain constant by moving the rollers and thus changing the diameters of the contact path. Also, different shape of rollers and mechanical designs have also been used for the same purpose. The shapes of the rollers may be either cylindrical, conical, rings, discs, toroids or spherical. With the help of rotational radius of the driven roller on the driven member, the speed ratio is being determined by these drives. To maximize the efficiency of these drives as well as their life, the roller's normal load to the torque should be adjusted. For this adjustment, a torque responsive roller loading mechanism is applied in these Drives. The performance of these Drive in adjusting the mechanical speed with high effectiveness, depends upon following thing: the friction that is generated between specially shaped output & input plates and the speed adjustment mechanism.

Types of Traction Drives

Limitations of Basic Traction Drives
The limitation of these two basic types of Drives is their low potential to resist the high throughput power and the torque impetuses which are common in the automotive drive-trains. Another shortcoming of these basic Traction Drives is their low durability. This low durability arises from the high surface weary stresses generate in the elements of the Traction Drive. Although, the fluid/lubricant technology is improving day by day, but still it is the major source of concern for these drives. The third type of problem which is found in these Drive is: the rotating components in these drives are bulky. This reduces the speed of rotation of these components along with the desired acceleration rate. This in effect, increase the emissions of the vehicles.

Configurations of Traction Drives
There is a great possibility that the configurations of these drives may differ from each another. But, most of the design differentiations lie in their respective power transferring speed to the outer members. Some examples are:

Applications of Traction drives
In the power transmission industry, it was believed that these Drives would not make any noticeable impact. The reason was that, most of the experts did not believe that two smooth rollers of a Traction Drive could transmit force through a fluid. But, today, with the changing advance technology, people start to believe that traction drives can do this thing. Therefore, in the engineering industry, these drives have made an intense popularity. These drives are used in various applications in the engineering industry, especially when it is the requirements of high efficiency and sound operations. These drives are also widely used in engineering industry, when it is concerned to speed control, bringing compactness and consistency in performances. The inherent accuracy of these drives is proved by the micrometer speed-setting dials which are fitted on these drives. Such speed setting dials also provide extra torque even at low speed.

In the planetary vehicles, these drives have proved themselves as the best alternatives of the gear drives. Contact geometry can be formed in the low wear to the solid lubricants through these drive rollers which are present in these drives. In contrast, in other traditional drives, to bring smooth torque at low speed, additional components are required in these.