Friction gear: when you need smoothness


When creating machines and mechanisms most oftenthe challenge facing designers is to transfer the torque from one part to the other. It is solved in various ways. Toothed gears, running belts and even electromagnetic fields drive the wheels, and in each case the use of one or another method is motivated by technical requirements. Frictional gear is used when a smooth change in speed is required.

friction gear

When there were no cog wheels

The word frictio in Latin means "friction". Until the cogwheel was invented, the friction gear was the main means of communicating the torque. In this case, in ancient times, mechanics discovered the dependence of the angular velocity on the ratio of the diameters of the master and the driven rollers, having learned to accelerate or slow down the work of mills or water-power stations. This invention is still used today.

Smooth acceleration is the merit of a clutch

Serious engineering study of this unitbegan in the late XIX century, the need for it arose during the rapid development of machine building, and especially with the advent of the first cars. The transmission, built on cogwheels, did not withstand the sharply changing loads during the transition from one speed to another, the gears broke, complicated and expensive repairs were required. The disc friction transmission provided a soft contact between the motor shaft and the cardan, 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 requiredsmooth acceleration or deceleration, mechanical engineers apply this important element. The design of any tape recorder necessarily includes special counter discs for changing the angular velocity of the reeling unit, because the more the receiving coil is wound up, the more slowly it should spin. Frictional transmission provides a change in the number of revolutions per unit of time: at the beginning of the playback of the cassette or coil, the receiving unit spins quickly, and at the end - slowly.

cylindrical friction gear

Variety of forms

Between the gear and the clutch there are manycommon. First, 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 varied spatial orientation, from parallel to perpendicular. When experimenting with the first samples of the railway transport, they tried even to create a gear pair "rail-wheel", but soon this idea was abandoned, making it smooth, with the possibility of slipping and a smooth increase in friction. The types of frictional gears correspond to the 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 modified vector of the driven shaft. At the same time, the chosen task is influenced by the choice of one or another method of kinematics. Cylindrical friction gear serves for parallel transmission, and conical - for perpendicular.

types of friction gears


Despite the ancient age of the invention, thisThe method of transferring rotational mechanical moment is widely used in modern technology. But he also has disadvantages. Disc clutch and brake pads periodically require replacement on all cars - from the chic "Bentley" to the modest "Lada".

The main efforts of technologists-materials scientists,engaged in friction, are aimed at increasing the service life of contacting surfaces, because they are constantly rubbing against each other, and therefore wear out.

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