Many moving mechanisms are designed in such a way that the transfer of energy directly from the drive unit to the actuator is impossible. In some situations, the engine and the driven device are structurally located far and offset from each other. In other cases, energy must first be converted: to reduce or increase the engine speed, change the direction of rotation, or turn the rotational motion into translational.
Then some intermediate mechanisms are required to transmit or convert this energy. One of the main elements used for this purpose is gears. They are used wherever considerable effort is required to be transferred while maintaining the compactness of the device and long service life — be it a car gearbox, fishing rod reel or hydroelectric turbine.
What are the transfers
There are many varieties of gears. They are classified according to the following criteria:
- direction of motion transmission - cylindrical, worm, conical;
- side of the wheel on which the teeth are cut - internal or external gearing;
- teeth direction - straight, oblique, chevron;
- the shape of the teeth is cycloid and involute transmission, Novikov gearing.
Cycloid gearing
This technology was patented in 1931 by a German engineer Lorenz Braren. Unfortunately, it has significant drawbacks.
- Difficulty in manufacturing - each wheel is cut by a separate gear-cutting tool.
- Extremely high sensitivity to changes in center distance. In other words, this type of engagement requires the highest accuracy in production and installation, and in the case of the slightest mechanical damage, it fails.
- Difficulties in repair due to the lack of standardization of such gears.
The advantage of this transmission is a significant reduction in stress at the contact point of the teeth due to their round shape, due to which greater durability of the parts is achieved.
As a result of this, the cycloidal compound has found its application in a rather narrow field of industry - in the manufacture of watches and other precision instruments, some types of compressors and pumps.
Involute type
This type of tooth design was proposed by the famous mechanic and mathematician Leonard Euler in 1760 and was most widely used in industry.
In a gear pair, a part with a smaller diameter is usually called a gear, and with a larger one, a wheel. In an involute joint, the teeth have a profile with convex faces. It is the same for both the gear and the wheel. This implies the main economic benefit of involute engagement: the low complexity of manufacturing parts while maintaining sufficient accuracy and, consequently, high productivity. For the manufacture of such wheels does not require complex equipment, their quality is easy to control.
This compound has another indisputable advantage associated with the presence of the human factor in production: involute teeth are insensitive to changes in the center distance if their engagement is not interrupted. Simply put, such wheels "allow" some inaccuracies in both manufacturing and installation without much loss in performance.
Also, involute engagement provides the gears with a long service life due to the fact that the tooth surfaces with a convex shape roll along each other. Due to this, the friction of surfaces is significantly reduced, that is, wear of parts is minimized.
Creating a Novikov program
Sometimes it is necessary to transmit a very high torque and at the same time not to go beyond a certain framework of dimensions and mass of the mechanism. Under these conditions, the involute connection may not be reliable enough - due to the high contact stresses at the point of contact of the teeth, they can quickly fail.
This is where the so-called helical gearing comes to the rescue. It was developed in 1954 by a Soviet engineer and inventor M.L. Novikov. He came to this decision by examining the problems that arose when designing heavy, but relatively slow machines, such as tractors and tanks.
This technique has a large mass, which requires the transmission of the appropriate torque from the engine through the transmission to the wheels or track rollers. Involute teeth do not always cope with this task.
What are the benefits of opening ...
A connection was created in which the gear teeth and wheels are convex and concave in shape, respectively. Due to this, a significant increase in the contact surface of the teeth was achieved, since the gear teeth and the troughs between them at the wheel have very close radii.
Thus, the voltage at the point of contact was reduced. This allowed, depending on specific circumstances, either to significantly reduce the size of the mechanism while maintaining the transmitted power, or while maintaining the available dimensions and weight, to significantly increase the load on the connection without fear of an early breakdown.
... and its flaws
In contrast to the involute joint, where two convex surfaces are in contact, in the gears with Novikov gearing, the convex and concave parts form almost a single unit when connected. Because of this, the friction between the teeth increases significantly, affecting their durability. Although in the case of slow-moving machines, for which the circular screw connection was originally developed, this factor is not so important.
In addition, this design, similarly to cycloid engagement, places high demands on the quality of workmanship and thoroughness of assembly, since a violation of the center distance can lead to catastrophic consequences.
Prior to Novikov, numerous attempts had already been made to improve the design of the gearing, but only he managed to develop a viable technology. After some improvements, it was introduced in many industries.
Improvement of the invention
In total, there are two types of Novikov links:
- with one line of touch (can be polar and polar);
- with two lines of touch (pre-polar).
In the first type, the gear teeth and wheels have the same curvature along the entire contour. With a polar connection, the profile of the drive wheel is made convex, and the profile of the driven wheel is concave. With the pre-polar, on the contrary. This compound was directly developed by Mikhail Novikov, who received the Lenin Prize for this.
However, it soon became clear that the manufacture of gears of this type is technologically quite difficult. Since the wheels are not the same, but have different cutting teeth, for the manufacture of a pair of wheels requires two different pieces of equipment, which is not very economical.
Research has begun in this direction. Their result was the development of pre-polar engagement, in which the teeth at the wheel and gear are the same, but have a convex contour closer to the top and concave closer to the base, with a smooth transition between them. This not only achieved the unification of the production of parts, but also found that such gears have a much greater load-bearing capacity than connections with one line of engagement.
Distribution of the new development
Being originally developed for heavy, including military equipment, Mikhail Novikov's gear transmission scheme began to spread rapidly in many industries. The first in the territory of the former Soviet Union the production of products using new technology was launched by the Lugansk Engineering Plant in Ukraine.
At present, gearboxes based on this transmission in Russia are manufactured by: ZAREM OJSC (Maykop gear factory), Scientific and Technical Center Reducer (St. Petersburg), Reducer OJSC (Izhevsk) and many others.
Foreign countries are also actively interested in this development. Japan is developing on its implementation in the automotive industry, and England and the United States also do not stand aside. The invention of the Soviet scientist may well set off to conquer the Universe: international organizations are funding research on the use of Novikov gearing in space shuttles, probes, and other equipment.
Scope Technology
The bulk of this development is implemented in the following areas:
- traction drives of various heavy machines - trolley buses, buses, trams, helicopters);
- rocking machines and other equipment of the oil industry;
- coal mining equipment;
- crane gears for lifting and moving.
There are also special bearings created using Novikov gear, which have three times the carrying capacity than usual.
Production of Novikov gears and regulatory documents
A special tooling was developed for cutting teeth in the manufacture of Novikov gear - cutter. This tool has a rather high cost, since high requirements are applied to the precision of gear manufacturing. A slight deviation - and that ideal harmony of the contact contours, which ensures a high service life of the gears and the transmitted power, will no longer be observed.
Since the quality of both the teeth themselves and the cutters for their cutting are particularly high demands, separate state standards have been developed to control their manufacture. For Novikov’s gearing, GOST 17744-72, for gear-cutting tools, GOST 16771-81.
The new tooth manufacturing principle, developed by M. L. Novikov, gained recognition not only in the territory of the former USSR, but also in many other countries.