Noise in the gearbox with helical steel gears. Protection from noise and ultrasound. Methods for dealing with noise. Howling when reversing

Gears are often the main source of vibration and noise in a variety of machines. As gear speeds increase, the problem of reducing vibration and noise becomes increasingly important. Noise level is one of the most important performance indicators of gears and gearboxes.

The noise level of gears is determined by the accuracy of gearing, inertial and rigidity parameters of the system. Meshing errors are the causative agents of forced vibrations, and the inertial and rigidity parameters determine the natural vibrations of the system.

Typically, the actual dimensions of the main pitches of the driving and driven wheels are different. This causes the mating teeth to impact as they engage. As a result, an oscillatory process occurs. The impact force is directly dependent on the magnitude of the engagement error, which is determined by the difference in the main pitches of the driving and driven wheels and their peripheral speed. As the shaft rotation speed increases, the noise intensity increases accordingly.

The optimal noise level corresponds not to zero, but to some positive value of the difference in the main steps, determined by the amount of elastic deformation of the teeth. Another cause of vibration and noise of gears is an instantaneous change in the rigidity of the gearing during the transition from a double-pair tooth engagement to a single-pair one, as well as an instantaneous change in the direction of the friction force acting between the working profiles of the teeth in the meshing strip.

Rice. 38. Various shapes of the contact patch of gear pairs

Errors in the profile of the teeth that arise during the cutting process, as well as the cutting of the profile of the teeth as a result of discontinuity in the cutting process, cause shock pulses.

Improper fastening of the tool and workpiece when cutting teeth also causes cyclic errors in gears, and consequently, intense noise and vibration. For example, the non-perpendicularity of the ends relative to the axis of the workpiece when it is fixed on the table of a gear cutting machine causes a deviation of the geometric axis of the cut workpiece relative to the axis of rotation of the table, resulting in an error in the direction of the teeth. This error causes an unsatisfactory shape of the contact patch (contact area) between the mating teeth, which contributes to increased noise and vibration.

In Fig. Figure 38 shows various shapes of the contact spots of gear pairs. With the contact patch shape shown in Fig. 38, a, the gear train produces a rustling or slight low-pitched hum; such teeth can be considered suitable.

With the spot shape shown in Fig. 38, b, a rustling sound is heard without load, and a howl is heard under load; these teeth are useless. The defects and teeth with the shapes of the contact spots shown in Fig. are also represented. 38, c and d. Without load they make a small knock, and under load - a howl and a frequent intermittent knock, in the other - a frequent intermittent knock without a load and a howl under load.

The occurrence of increased noise is caused by errors in boring the base holes in the gear housing. When gears are carefully manufactured, misalignment of the shafts on which they are mounted can lead to results similar to those obtained from errors in the gears themselves.

Reducing vibration and noise of gears can be achieved in the following ways.

Rice. 39 . Tooth shape:

a - ordinary; b - barrel-shaped

The first method is to change the shape of the teeth (Fig. 39). If they are given a barrel shape, then as a result of improving contact between the teeth and reducing the influence of tooth misalignment, the noise of the interacting gears will decrease by 3-4 dB.

Another way to reduce vibration and noise is to flank the tooth profiles to compensate for errors in the manufacture and installation of gears, as well as to reduce the effect of tooth deformation when they operate under load.

The vibration and noise characteristics of gears are improved as a result of the introduction of the teeth shaving operation, which increases the smoothness of the engagement. Some reduction in vibration and noise can be achieved by using a finishing operation - grinding in the teeth using special laps.

One of the factors that determines the ability of a gear drive system to dampen vibrations is the material of the wheel. By replacing at least one wheel in a gear pair with one made of plastic, you can achieve a significant effect in reducing noise levels. Research has established that the noise of plastic gears at all speed modes and loads is lower than the noise of steel wheels, and the most effective noise reduction is achieved in high-speed transmissions, at resonant modes and at increased loads.

Knowing from formulas (12) and (15) what the sound pressure level at the design point depends on, the following methods can be used to reduce noise:

1) reduction of noise at the source;

2) change in the direction of radiation;

3) rational planning of enterprises and workshops, acoustic treatment of premises;

4) reduction of noise along the path of its propagation. Reducing noise at the source. Fighting noise with

reducing it at the source (decreasing Lp) is the most rational.

The noise of mechanisms arises due to elastic vibrations of both the entire machine as a whole and its individual parts. The reasons for the occurrence of these vibrations are mechanical, aerodynamic and electrical phenomena determined by the design and nature of the mechanism’s operation, as well as technological inaccuracies made during its manufacture and, finally, operating conditions. In this regard, noise of mechanical, aerodynamic and electromagnetic origin is distinguished.

Mechanical noise. The factors causing noise of mechanical origin are the following: inertial disturbing forces arising from the movement of mechanism parts with variable accelerations; collision of parts at joints due to inevitable gaps; friction in the joints of machine parts; impact processes (forging, stamping), etc.

The main sources of noise, the origin of which is not directly related to the technological operations performed by the machine, are primarily rolling bearings and gear drives, as well as unbalanced rotating parts.

The frequencies of oscillations, and therefore the noise created

imbalance, multiples of n/60 (n - rotation speed, rpm).

The noise spectrum of ball bearings occupies a wide frequency band. Sound power P depends on the rotation speed of the machine:

An increase in the rotation speed of rolling bearings from px to p2 (rpm) leads to an increase in noise by the amount ΔL (dB):

Gears are sources of noise over a wide frequency range. The main causes of noise are the deformation of the mating teeth under the influence of the transmitted load and dynamic processes in the meshing caused by inaccuracies in the manufacture of wheels. The noise is discrete in nature.

Gear noise increases with increasing wheel speeds and load.

Reduction of mechanical noise can be achieved by improving technological processes and equipment, replacing outdated processes and equipment with new ones. For example, the introduction of automatic welding instead of manual welding eliminates the formation of spatter on the metal, which eliminates the noisy operation of cleaning the weld. The use of milling tractors for processing metal edges for welding instead of pneumatic chisels makes this process much less noisy.

Often, increased noise levels are a consequence of malfunction or wear of mechanisms, and in this case, timely repairs can reduce the noise.

It should be noted that carrying out many measures to combat vibrations (see Chapter 4) simultaneously reduces noise. To reduce mechanical noise it is necessary:

replace impact processes and mechanisms with impactless ones; for example, use hydraulically driven equipment in the technological cycle instead of equipment with crank or eccentric drives;

replace stamping with pressing, riveting with welding, trimming with cutting, etc.;

replace the reciprocating movement of parts with a uniform rotational movement;

use helical and chevron gears instead of spur gears, and also increase the classes of processing accuracy and surface cleanliness of gears; Thus, eliminating errors in gear meshing results in a noise reduction of 5-10 dB, replacing spur gears with herringbone gears - by 5 dB;

if possible, replace gear and chain drives with V-belt and toothed belt drives; for example, replacing a gear drive with a V-belt reduces noise by 10-15 dB;

replace, whenever possible, rolling bearings with plain bearings; such a replacement reduces noise by 10-15 dB;

if possible, replace metal parts with parts made of plastic and other “silent” materials, or alternate impacting and rubbing metal parts with parts made of “silent” materials, for example, use textolite or nylon gears paired with steel ones; Thus, replacing one of the steel gears (in a pair) with a nylon gear reduces noise by 10-12 dB;

the use of plastics in the manufacture of housing parts gives good results. For example, replacing steel gearbox covers with plastic ones leads to a noise reduction by 2-6 dB at medium frequencies and by 7-15 dB at high frequencies;

when choosing a metal for the manufacture of parts, it is necessary to take into account that the internal friction in different metals is not the same, and therefore the “sonority” is different, for example, ordinary carbon steel and alloy steel are more “sonorous” than cast iron; After hardening, manganese alloys with 15-20% copper and magnesium alloys have greater friction; parts made from them sound dull and weaken when struck; chrome plating of steel parts, such as turbine blades, reduces their “sonority”; when the temperature of metals increases by 100-150 ° C, they become less sonorous;

more widely use forced lubrication of rubbing surfaces in joints, which also reduces their wear;

apply balancing of rotating machine elements;

use gasket materials and elastic inserts in connections to eliminate or reduce the transmission of vibrations from one part or part of the unit to another; Thus, when straightening metal sheets, the anvil must be installed on a gasket made of damping material.

Installing soft pads in places where parts fall from a conveyor or are dropped from machines or rolling mills can significantly reduce noise.

For bar automatic machines and turret machines, the source of noise is the pipes in which the bar material rotates. To reduce this noise, various designs of low-noise pipes are used: double-walled pipes with rubber laid between them, pipes with an outer surface wrapped in rubber, etc.

To reduce the noise that occurs during the operation of tumbling drums, crushers, ball mills and other devices, the outer walls of the drum are lined with sheet rubber, asbestos cardboard or other similar damping materials.

Aerodynamic noise. Aerodynamic processes play a big role in modern technology. As a rule, any flow of gas or liquid is accompanied by noise, and therefore issues of combating aerodynamic noise have to be encountered very often. These noises are the main component of the noise of fans, blowers, compressors, gas turbines, steam and air exhausts, internal combustion engines, pumps, etc.

Sources of aerohydrodynamic noise include: vortex processes in the flow of the working medium; vibrations of the environment4 caused by the rotation of the impellers; pressure pulsations of the working environment; vibrations of the medium caused by the heterogeneity of the flow entering the wheel blades. In hydraulic mechanisms, cavitation processes are also added to these noise sources.

When a body moves in an air or gaseous environment, when a medium flow blows over the body near the surface of the body, vortices are formed that periodically break away from it (Fig. 43, a). The compression and rarefaction vortices that arise during the breakdown of the medium propagate in the form of a sound wave. This sound is called vortex.

The frequency of the vortex sound (Hz) is expressed by the formula

f=Sh(v/D)

where Sh is the Strouhal number, determined experimentally; v—flow velocity, m/s; D is the projection of the width of the frontal surface of the body onto a plane perpendicular to v; for a sphere and a cylinder, the value D is their diameters.

Vortex noise when flowing around bodies of complex shape has a continuous spectrum.

Eddy noise sound power (W)

where k is a coefficient depending on the shape of the body and the flow regime; cx is the drag coefficient.

From this it can be seen that in order to reduce vortex noise it is necessary, first of all, to reduce the flow speeds and improve the aerodynamics of the bodies.

Rice. 43. Aerodynamic noise:

a - vortex; b — noise from flow inhomogeneity; c — jet noise; 1 - obstacle; 2—velocity field in absolute motion; 3 - the same in relative motion; 4 — wheel blade; 5 - direction of rotation

For hydraulic machines with rotating impellers (fans, turbines, pumps, etc.), noise from non-uniform flow occurs.

Flow inhomogeneity at the inlet or outlet of the wheel, arising due to poorly streamlined structural parts or guide vanes, leads to unsteady flow around the wheel blades and stationary elements located near the wheel and, as a consequence, to noise from the inhomogeneity (noise from obstacles in the flow, blade, siren noise).

Noise generation from flow inhomogeneity, as well as vortex noise, is caused by pressure pulsations on obstacles and blades (Fig. 43, b).

In relative motion, the speed at the entrance to the wheel is equal to the geometric sum of the speed in absolute motion and the peripheral speed. When a blade hits the aerodynamic shadow of an obstacle (a depression in the absolute velocity profile), the relative speed changes in magnitude and direction and entails a change in the angle of attack, and, consequently, the vector of force acting on the blade, which causes the appearance of a sound pulse. _ The sound power of noise from flow inhomogeneity is also determined by expression (15), since the nature of both noises is the same.

Lykov A.V., Lakhin A.M.The paper examines the issues of reducing noise in the operation of gears. An analysis of the causes of noise and vibration in the operation of gears has been carried out, and the main design and technological methods for its reduction have been determined.

Key words:

gear transmission, noise, wear.

Introduction

One of the most important performance indicators of gears is the noise of their operation. To the greatest extent, increased noise of gears is typical for high-speed and heavily loaded gears, and this indicator in most cases also characterizes the reliability and durability of a mechanism with gears.

Main content and results of the work

The noise level of gears depends on many factors, the main ones being the accuracy of the gearing, as well as the inertial and rigidity parameters of the system. Meshing errors are the causative agents of forced vibrations, and the inertial and rigidity parameters determine the natural vibrations of the system.

Due to the difference in the actual steps of the driving and driven wheels, impacts of the mating teeth occur at the moment they engage. This causes an oscillatory process. The impact force is directly dependent on the difference in engagement steps and peripheral speed. Therefore, as the rotation speed of shafts with gears increases, the noise intensity also increases.

Another cause of vibration and noise of gears is the instantaneous change in the rigidity of the gearing during the transition from a double-pair tooth engagement to a single-pair one, as well as an instantaneous change in the friction force acting between the working profiles of the teeth in the engagement pole. This causes vibration to spread from the gears to all parts of the gear mechanism and generate sound waves.

When considering various shapes of the tooth contact patch, the following characteristic cases can be identified (Fig. 1).

Figure 1 - Shapes of the contact patch of pairs of teeth

With the shape of the contact patch shown in Fig. 1, a, the gear train produces a quiet rustling and low hum, which practically increases with increasing peripheral speed. In this case, the load is distributed evenly over the teeth, and the transmission is considered suitable. With the shape of the contact patch (Fig. 1, b), a rustling noise is heard without load, and a howling noise is heard under load, increasing with increasing peripheral speed. Gears with the contact patch shape shown in Fig. 1,c, when operating without load, they emit a small knock, which develops into a howl and frequent intermittent knocking. In the case (Fig. 1, d), the transmission emits a frequent intermittent knock that develops into a howl.

As can be seen from the shapes of the contact patch, noise is also caused by errors in the processing of the base holes of the gear housing, which causes distortions of the shafts and bearings during installation of the gear. This causes results similar to circumferential pitch and tooth direction errors.

Based on the causes of noise in the operation of gears, it is possible to determine the main ways to reduce it, among which we will highlight constructive and technological methods.

Constructive methods include methods related to improving the design of gears, which make it possible to eliminate shock and vibration when pairs of teeth engage.

To improve the smooth operation of the gear train, it is advisable to use helical, chevron and curved tooth wheels instead of straight teeth. Such gears allow each tooth to engage not immediately along its entire length, usually with an impact, but gradually, smoothly, causing elastic microdeformations of tooth sections, compensating for errors in the circumferential pitch and direction of the tooth. The transition from a straight tooth to a helical or curved tooth shape can reduce the noise level by 10-12 dB.

If the gear design for some reason does not allow the use of an oblique or curved tooth shape, noise reduction can be achieved by modifying the tooth shape. Here two methods can be distinguished: longitudinal modification and modification of the tooth profile shape. Longitudinal modification consists of a smooth change in the cross-sectional dimensions of a tooth along its length, and most often comes down to the use of barrel-shaped teeth. In such gears, the tooth width decreases from the middle to the edges of the ring gear. This makes it possible to reduce the influence of tooth misalignment due to non-parallelism of the shaft axes and tooth direction errors, while the gear noise is reduced by 3-4 dB.

Modification of the shape of an involute tooth profile most often comes down to flanking the head and stem of the tooth - the targeted removal of part of the tooth profile for a more uniform arrangement of teeth on the wheel and reducing errors in the main pitch. This makes it possible to simplify the installation of gears in the transmission and reduce the effect of tooth deformation when operating under load. As a result of flanking, tooth contact outside the meshing line is replaced by theoretically correct contact along the meshing line, as a result of which the tooth contact patch increases and the gear noise level decreases.

It is also known that one of the factors determining the ability of a gear to dampen vibrations is the material of the wheel. By replacing at least one transmission gear with a plastic wheel, the noise level can be significantly reduced, which is most achieved for high-speed transmissions, in resonant operating modes, and also under increased loads. The noise of non-power transmissions can be significantly reduced by using steels with low surface hardness, metal powders, etc. A good combination in a gear transmission is the use of a gear made of high-hardness steel and ground teeth with a wheel made of softer steel and shaving teeth.

For quieter and smoother operation of the gear transmission under constant loading conditions, a minimum gear module should be specified. This increases the axial and axial overlap ratios, improving smooth operation and reducing vibration in the meshing. At the same time, due to the reduction in the cross-section of the base of the tooth engaged in engagement, the level of permissible loads on the tooth decreases. To compensate for this disadvantage, it is necessary to increase the pitch diameter, the width of the ring gear, the use of multi-pair gearing, etc.

Gear noise can also be reduced by providing a whole number tooth overlap ratio. Tests have shown that an overlap ratio of 2.0 provides the quietest transmission operation.

Gear noise is affected by the load on the teeth. As the load factor increases, the dynamic load in the meshing decreases. At the same time, elastic deformations in the meshing increase, compensating for inevitable tooth pitch errors, the smoothness of the transmission increases and the noise level decreases.

In addition, noise is affected by the design and material of the gear housing, which should prevent the spread of sound into the environment. As a rule, cast housings dampen vibrations better than welded ones. The quality of a lubricant is also determined by its ability to dampen vibrations. More viscous lubricants provide quieter operation, but at the same time reduce gear efficiency. The type of gear shaft bearings also affects the noise level of the transmission. Rolling bearings, working with an oil film at high speeds, ensure quieter operation of the gear transmission, while having, however, significantly higher friction losses compared to rolling bearings. Therefore, rolling bearings are recommended for use in high-speed transmissions.

Among the technological methods for reducing noise in the operation of gears, we will consider the main technological operations of finishing teeth. As discussed previously, the main influence on gear noise is the accuracy and quality of the tooth surfaces. Reducing gear noise for non-hardened gears can most effectively be achieved by shaving. At the same time, errors in circumferential pitch, tooth direction and tooth profile deviations are significantly reduced. For hardened gears, the most effective and efficient method of noise control is gear honing, which reduces transmission noise by 2-4 dB. Gear grinding provides the highest accuracy of the ring gear parameters and the lowest transmission noise level. However, this method is the least productive.

Conclusions

In general, the study established that the main source of noise in the operation of gears is shock and vibration resulting from the inaccuracy of gear elements. We identified the main design and technological methods for reducing noise in the operation of gears.

List of used literature

1. Kudryavtsev V. N. Gear transmissions. - M.: Mashgis, 1957. - 263 s.
2. Kosarev O.I. Methods for reducing excitation and vibration in spur gearing. / O. I. Kosarev // Bulletin of mechanical engineering. - 2001. - No. 4. pp. 8-14.
3. Rudnitsky V. N. Influence of geometric parameters of gears on noise in gears / V. N. Rudnitsky. Sat. Art. Contribution of scientists and specialists to the national economy / BGITA - Bryansk, 2001. - pp. 125-128.

The article describes a simulation technology whose purpose is to eliminate noise generated by power transmission gears. This is a rather unpleasant noise with a predominance of high frequencies, resulting from rotational deviations (transmission errors) due to tooth shape and manufacturing defects. To reduce transmission error, it is necessary to determine a suitable tooth profile, taking into account the influence of several factors.

This gearbox simulation technology has been used in product design since 2012. The example shows the reduction of transmission error and gear noise by optimizing the tooth profile using the presented simulation technology.

1. Introduction

As a component manufacturer within the Yanmar group of companies, Kanzaki Kokyukoki Mfg. Co.,Ltd. designs, manufactures and markets hydraulic equipment and various transmissions. The company has extensive experience and proprietary technologies in a wide range of design and manufacturing areas, especially gears, which are the main components of kinematic systems. In addition, in recent years, the trend towards increasing the speed and comfort of vehicles makes it imperative to reduce gear noise, which is very difficult to achieve using traditional technologies. This article describes a simulation technology for gear noise reduction that Kanzaki Kokyukoki Mfg. is currently working on.

2. Types of gear noise

Gear noise in transmissions is usually divided into 2 types: squealing and crackling (see Table 1). Whistling is a thin, high-frequency noise primarily caused by small errors in gear tooth profile and rigidity. Crackling is the sound of the side surfaces of gear teeth touching, the main sources of which are fluctuations in the load acting on the gears and the gaps between the side surfaces of the teeth (side gaps). In the products of Kanzaki Kokyukoki Mfg. The main problem is often squealing, so the company focuses on determining the appropriate tooth profile during the design, construction, and quality control stages of the manufactured gears.

3. Mechanism of squealing

The cause of squealing is a phenomenon in which vibration caused by small rotational deviations due to tooth profile errors or manufacturing defects is transmitted through the gear shaft bearings to the housing, resulting in vibration of the housing surface (see Fig. 1).

These rotational deviations occur due to errors in the angle of rotation of the teeth as they mesh, which is called transmission error.

The causes of transmission error, in turn, can be divided into geometric factors and tooth stiffness factors. If geometric factors are present (see Fig. 2), deviation from the ideal involute mesh occurs due to an installation error or shaft misalignment, which leads to a lag or advance in the angle of rotation of the driven gear. In addition, deviations in the angle of rotation arise due to the unevenness of the side surfaces of the teeth.

In the presence of factors associated with tooth stiffness (see Fig. 3), the meshing stiffness changes depending on how many teeth are in contact at a given time, resulting in deviations in the rotation angle of the driven gear.

In other words, geometric factors and tooth stiffness factors act together to influence transmission error and thereby create an exciting force. Therefore, when designing a low noise gear, these factors must be taken into account to select a suitable tooth profile.

4. How to reduce transmission error

As stated above, several factors must be considered to reduce transmission error in gears.
In Fig. Figure 4 shows the relationship between torque and transmission error for a helical gear with an ideal involute profile (unmodified) and another gear with a specially modified tooth profile. Here, to change the tooth profile, a deviation from the ideal involute profile is specially introduced, as shown in Fig. 4 (right). An unmodified gear with a smaller profile error has optimal performance in terms of transmission error fluctuations at low load torque, while a gear with a modified profile performs better when the load torque is above a certain value. This shows how variations in gear error can be minimized by changing the tooth profile to match the load on the gear.

In order to predict the influence of various phenomena on the gear in the kinematic system and take it into account at the design stage, Kanzaki Kokyukoki Mfg. has developed a modeling technology that it has been using in product design since 2012 (see Fig. 5). Using tooth profile data for different gear types as input, the technology can evaluate parameters such as load capacity and transmission error under real operating conditions by analyzing the deformation of the gear shaft and bearings.

5. An example of the application of technology in product design

The example below shows a reduction in transmission error in a utility vehicle gearbox. In this case, the goal is to reduce transmission error by analyzing the possible change in the three-dimensional tooth profile of the bevel gear at the initial design stage, taking into account tooth profile deviations resulting from deformation of the shaft, bearings and other components, as shown in Fig. 6.

To confirm the performance improvements of the improved tooth profile, the tooth profiles, transmission errors and mesh noise of the production gear and its improved variant were measured.
The results for the transmission error are presented in Fig. 7. The measurements are shown on the left, and the results of the analysis of these measurements with tracking of the meshing order are shown on the right. The meshing order comparison results demonstrate that the improved gear has a smaller transmission error deviation.
The results of meshing noise measurements presented in Fig. 8 show a significant reduction in noise in the improved gear at second and third order meshing frequencies.

6. Conclusion

The article describes the modeling technology developed by Kanzaki Kokyukoki Mfg, part of the group of companies. to reduce gear noise. This technology is used in new designs where it helps predict performance during the design stage. In the future, it is expected that this simulation technology will continue to contribute to the development of better solutions for customers by reducing the size and increasing the power output and reliability of products.

Why do the gear wheels still rattle? The obvious answer: “because they are curves.” Obvious, but not sufficient. A gear is a rather complex part and its geometry is described by many parameters, all of which have different effects on transmission noise. Depending on the circumstances, in each particular case, some errors may affect the noise more, others less.

The basic concept in this matter is kinematic transmission error or gear. According to GOST 1643-81 (Appendix 1 clause 1).

Kinematic transmission error F i - the difference between the actual and nominal (calculated) angle of rotation of the driven transmission gear.

Let's say the transmission consists of a gear z 1 =20 and a wheel z 2 =40, i.e. gear ratio u = 2. If the gears are made with perfect precision, then when the gear is rotated by one angular step of 360° / 20 = 18°, the wheel will rotate through an angle of 18° / 2 = 9°. If the gear is rotated by two angular steps of 36°, the wheel will rotate by 18°, and so on. These are the nominal (calculated) rotation angles and for ideal gears they are connected by a gear ratio. At any angle of rotation of the gear, the wheel will turn at an angle 2 times smaller.

wheel angle = gear angle / u

But in reality, nothing is perfect. All details have some errors. Therefore, in fact, the driven wheel will rotate at an angle different from the nominal (calculated) one and the error can be expressed as follows:

Fi= wheel rotation angle - gear rotation angle / u

Those. In reality, the gear ratio is not constant, which means that the speed of rotation of the driven wheel will fluctuate. And in the spectrum of these vibrations there may be frequencies with a fairly high amplitude. These vibrations may cause noise.

Manufacturing of highly precise gears. Turetsky I.Yu., Lyubimkov L.N., Chernov B.V.

Why does kinematic error occur?

The reasons can be very different:

meshing geometry: interference or non-optimal overlap occurs. These errors can occur both at the gear calculation stage and during manufacturing (for example, the use of the wrong tool).
Wheel manufacturing errors distorting the tooth profile (involute) and the uniformity of the teeth (pitch errors)
errors in assembly and associated parts (housing, shafts, bearings)
thermal deformations and tooth deformations under load distorting the tooth profile

vertical axis - kinematic error taking into account tooth rigidity under different loads.

horizontal axis - wheel rotation angle

The noise level measured by acoustic methods will depend on the entire structure as a whole - not only on the gears, but also on the bearings, housing, fastening of the gearbox housing, the nature of the load, etc.

Schematically, the physical essence of the phenomenon can be expressed as follows:

geometric wheel errors

kinematic transmission error

mass, moment of inertia, stiffness and damping

Vibrations in gearing

Forces acting on bearings

Mass, rigidity and damping of body parts

Body vibrations

Fastening the gearbox housing

Vibration of the whole machine

There is currently no single generally accepted calculation method that would take into account the influence of all errors on noise. Calculations are based either on empirical dependencies or on some models with assumptions.

Why does a spur gear make noise, but a helical gear does not?

A frequently encountered principle: “if the gear is noisy, then it needs to be replaced with a helical one”. This is due, first of all, to the fact that overlap angle in helical gearing, more than in spur gearing.

Overlap angle- the angle of rotation of the transmission gear from the position where the teeth engage in engagement until they disengage.

The overlap is estimated by the overlap coefficient - the ratio of the overlap angle to the angular pitch of the wheel.

If the overlap ratio = 1, then each tooth disengages exactly at the moment when the next tooth engages.
If the overlap ratio< 1, то между выходом из зацепления одного зуба и входом в зацепления следующего зуба контакт между колёсам разрывается.
If the overlap coefficient is > 1, then at any given time two or more teeth are in mesh. The more teeth are in mesh at the same time, the less tension in the mesh and the less deformation of the teeth and the influence of profile errors is smoothed out and averaged.

Replacing straight-toothed wheels with helical ones is not a panacea. In real conditions, it is necessary to evaluate different options. Overall, reducing noise by increasing the accuracy of spur gears or some other measures may be more effective than simply replacing them with helical gears.

How to measure kinematic error?

In the form as described at the beginning, measuring the kinematic error is a rather expensive matter. To do this, it is necessary to be able to install angle sensors of appropriate accuracy on the gear and wheel. Or you need a special device and a reference gear. These methods are good for mass or large-scale production. At the same time, the measurement of the kinematic error itself provides little information about its source. Kinematic error is a complex indicator and consists of various errors that arise in different operations.

For small batches and single production, it is often advisable to carry out control using several individual parameters, which together allow one to evaluate the kinematic accuracy: