Gear transmissions have been used by mankind for a long time, this method of communicating rotational energy is the most common in mechanics.
These mechanisms transfer motion from one shaft to another, usually with a change in the frequency of revolutions per unit of time. The means of engagement and the direct elements of communication of movement are either wheels or rails with recesses and protrusions of a special shape cut into their working surfaces.
Of the two round elements interacting in the transmission, one of the larger diameter is called a wheel, and the second is called a gear, although, in essence, they are both gears.
Depending on whether the task of increasing the speed of rotation or, conversely, reducing it, is set in the gearbox, either a wheel or a gear is leading.
Modern construction materials make it possible to create gears capable of successfully transforming power up to 36 million watts.
Requirements for mechanisms are different, so the variety of gearing shapes is very large. The axes of rotation can be parallel, crossing or intersecting, depending on this, there are cylindrical, helical,worm or bevel gears. A feature of the latter is the ability to impart rotation to a shaft located at right angles to the drive axle. This possibility is often needed in a variety of mechanisms, for example, the transfer of mechanical energy from the cardan shaft of a car to the drive wheels is carried out precisely according to such a kinematic scheme.
Most often, bevel gears have straight, radially cut (tangential) teeth. If the driving and driven axles do not intersect, then such a gearbox is called hypoid. The use of such mechanisms in the design of the rear axle is caused by the desire of developers to lower the overall center of gravity of the car to give it greater stability.
In addition to spur gears, other gears are used, for example, with spiral cutting.
In addition, bevel gears make it possible to communicate rotation not only at a straight line, but also at almost any other angle, obtuse or sharp.
The manufacturing technology of bevel gears is about the same as that of cylindrical gears, but the workpiece has a rather complex shape. It consists, as it were, of two truncated cones with a common large base on the same axis. The generatrices of the cones are at right angles. The tooth profile is clearly visible from the non-working side of the bevel wheel, while the width of the tooth decreases from the periphery to the center. The material of manufacture is special steel, resistant to wear and veryfirm.
The cutting profile is an involute line, this shape provides the smoothest rotation, uniform wear and maximum distribution of mechanical stress at the moment of contact between the teeth.
Gears with a variable profile shape along the length are difficult to manufacture, and CNC machines are used to obtain them.
