When creating machines and mechanisms, the most common task facing designers is the transmission of torque from one part to another. It is solved in various ways. Toothed gears, linear belts and even electromagnetic fields set the wheels in motion, and in each case the application of one method or another is motivated by technical requirements. Friction gear is used when a smooth change in speed is required.
When there were no gears
The word frictio in Latin means "friction". Until a gear was invented , the friction gear was the main means of communicating torque. Moreover, already in antiquity, mechanics revealed the dependence of the angular velocity on the ratio of the diameters of the driving and driven rollers, learning how to accelerate or slow down the operation of mills or water pressure stations. This invention is applied today.
Smooth acceleration - merit clutch
A serious engineering study of this unit began at the end of the 19th century, the need for it arose during the rapid development of mechanical engineering, and especially with the advent of the first cars. The transmission, built on gears, could not withstand sharply changing loads when moving from one speed to another, gears broke, and a complex and expensive repair was required. Disc friction transmission provided soft contact between the engine shaft and the universal joint, giving time for a smooth change in speed, which greatly increased the reliability of vehicles.
Application in radio engineering
And in other mechanical systems, when smooth acceleration or braking is required, mechanical engineers use this important element. The design of any tape recorder certainly includes special oncoming disks to change the angular speed of the winding unit, because the more the receiving coil is wound, the more it should spin more slowly. Friction transmission provides a change in the number of revolutions per unit time: at the beginning of playing a cartridge or reel, the receiving unit spins quickly, and at the end - slowly.
Variety of shapes
There is much in common between the gear train and the clutch. Firstly, the ratio of wheel diameters in both cases forms a gear ratio. Secondly, the directions of motion of the receiving and output shafts can have a diverse spatial orientation, from parallel to perpendicular. When experimenting with the first samples of railway transport, they even tried to create a “rail-wheel” gear pair, but soon they abandoned this idea, making it smooth, with the possibility of slipping and a smooth increase in friction. Types of friction gears correspond to types of gear kinematic schemes, they are conical, cylindrical and disk (frontal). The smooth shape of the contacting surfaces creates conditions for solving more complex technical problems when spherical or torus geometry of parts is required, for example, with a variable vector of the driven shaft. At the same time, the task posed affects the choice of a particular kinematics method. Cylindrical friction gear is used for parallel transmission, and bevel for perpendicular.
disadvantages
Despite the ancient age of the invention, this method of transmitting rotational mechanical torque is widely used in modern technology. But he also has drawbacks. Clutch discs and brake pads periodically require replacement on all cars - from the luxurious Bentley to the modest Lada.
The main efforts of material technologists engaged in frictions are aimed at increasing the service life of the contacting surfaces, because they constantly rub against each other, and therefore wear out.