How to write an overview of gears

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According to historical records, gears were used in ancient China as early as 400~200 BC. The bronze gear unearthed in Shanxi Province, China is the oldest gear found so far. As a mechanical device reflecting the achievements of ancient science and technology, the South Guide Car is a gear mechanism. At the end of 17, people began to study the shape of gear teeth that can transmit motion correctly. 18th century, after industrial revolution in europe, gear transmission was widely used. Firstly, cycloidal gear was developed, and then involute gear was developed. Until the beginning of the 20th century, involute gears played a dominant role in the application.

As early as 1694, French scholar Philip? De? Los Angeles? Hire first proposed that involute can be used as tooth profile curve. 1733, Frenchman m Camus proposed that the common normal of gear tooth contact point must pass through the node on the center line. When the auxiliary instantaneous centerline rolls along the instantaneous centerline (pitch circle) of the big wheel and the small wheel respectively, the two tooth profile curves formed by the auxiliary tooth profiles fixedly connected with the auxiliary instantaneous centerline on the big wheel and the small wheel are conjugated with each other, which is Camus's theorem. It considers the meshing state of two tooth surfaces; The modern concept of contact point trajectory is clearly established. 1765, L. Euler of Switzerland put forward the mathematical basis for the analytical study of involute tooth profile, and expounded the relationship between the curvature radius and the curvature center position of a pair of meshing gear tooth profile curves. Later, Savari further improved this method and became the present Eu-let-Savary equation. Roteft promotes the application of involute tooth profile? WUlls, who proposed that involute gears have the advantage of constant angular velocity ratio when the center distance changes. 1873, German engineer Hoppe put forward the involute tooth profile of gears with different numbers of teeth when the pressure angle changes, which laid the ideological foundation for modern modified gears.

At the end of 19, the principle of generating tooth cutting and the appearance of special machine tools and tools using this principle made involute tooth profile show great advantages after gears were equipped with more complete tools. When cutting teeth, as long as the gear cutter is slightly moved from the normal meshing position, the corresponding modified gear can be cut on the machine tool with the standard cutter. During the period of 1908, MAAG of Switzerland studied the modification method and manufactured the generating gear shaper. Later, British BSS, American AGMA and German DIN successively put forward various calculation methods of gear modification.

In order to improve the service life of power transmission gear and reduce its size, in addition to improving the material, heat treatment and structure, arc tooth profile gear is also developed. 1907, Frank, England? Humphris first published the circular tooth profile. 1926, Eruest, a native of Switzerland? Wildhaber obtained the patent of normal circular arc bevel gear. 1955, M.L. Novikov of the Soviet Union completed the practical research of circular-arc gears and won the Lenin Medal. 1970, R.M.Studer, an engineer of Rolh—Royce Company in England, obtained the patent of double circular arc gear in the United States. People pay more and more attention to this kind of gear and play an important role in production.

Gear is a kind of toothed mechanical parts that can mesh with each other, which is widely used in mechanical transmission and the whole mechanical field. Modern gear technology has reached: the gear module is 0.004 ~100 mm; Gear diameters range from 1mm to150m; Transmission power can reach hundreds of thousands of kilowatts; The rotating speed can reach hundreds of thousands of revolutions per minute; The maximum circumferential speed is 300m/s.

The application of gears in transmission appeared very early. More than 300 years BC, the ancient Greek philosopher Aristotle expounded the problem of transmitting rotary motion with bronze or cast iron gears in Mechanical Problems. The South Compass invented by China in ancient times has used a whole set of gear trains. However, were ancient gears made of wood or gold? It is cast, which can only transmit the rotary motion between shafts, and cannot guarantee the stability of transmission, and the bearing capacity of gears is also very small.

With the development of production, the stability of gear operation has been paid attention to. 1674, the Danish astronomer Romer first proposed using epicycloid as the tooth profile curve to get a smooth running gear.

/kloc-during the industrial revolution in the 0 th and 8 th centuries, gear technology developed rapidly, and people did a lot of research on gears. 1733, the French mathematician Camille published the basic law of tooth profile meshing; 1765, the Swiss mathematician Euler suggested using involute as the tooth profile curve.

/kloc-gear hobbing machine and gear shaper appeared in the 0/9th century, which solved the problem of mass production of high-precision gears. 1900, Pfeiffer installed a differential device on the gear hobbing machine, which can process helical gears on the gear hobbing machine. Since then, hobbing machines have become popular, and gear generation method has an overwhelming advantage, and involute gears have become the most widely used gears.

1899, Lasher first realized the scheme of modifying gears. The modified gear can not only avoid undercutting, but also match the center distance and improve the bearing capacity of the gear. 1923, Wilder Haber of the United States first proposed the circular-arc tooth profile gear. 1955, Sunovikov made an in-depth study on circular-arc gear, and circular-arc gear was applied to production. This kind of gear has high bearing capacity and high efficiency, but it is not as easy to manufacture as involute gear and needs further improvement.

Gears are generally composed of teeth, tooth grooves, end faces, normal faces, tooth top circles, tooth root circles, base circles and indexing circles.

Gear teeth are called teeth for short, on the gear? Convex parts for meshing, which are generally arranged radially, and the teeth on the paired gears are in contact with each other, so that the gears continuously mesh and run; Cogging is the space between two adjacent teeth on the gear; Is the end face on the cylindrical gear or the cylindrical worm? The plane perpendicular to the gear or worm shaft; Normal plane refers to the plane perpendicular to the tooth line of gear teeth; Tooth tip circle refers to the circle where the tooth tip is located; Tooth root circle refers to the circle where the groove bottom is located; The base circle is the circle in which the generatrix of involute makes pure rolling; Split circle? Is the reference circle for calculating the geometric dimensions of gears in the end face.

Gears can be classified according to tooth profile, gear shape, tooth line shape, surface where gear teeth are located and manufacturing method.

The tooth profile of gear includes tooth profile curve, pressure angle, tooth height and displacement. Involute gears are easier to manufacture, so among the gears used in modern times? Involute gears account for an absolute majority, while cycloidal gears and circular arc gears are seldom used.

In terms of pressure angle, the bearing capacity of small pressure angle gear is small; The gear with large pressure angle has high bearing capacity, but it increases the bearing load under the same transmission torque, so it is only used in special circumstances. The tooth height of gears has been standardized, and the standard tooth height is generally adopted. Modified gears have many advantages and have been used in various mechanical equipment.

In addition, gears can be divided into cylindrical gears, bevel gears, non-circular gears, racks, worms and worm wheels according to their shapes. ; According to the shape of tooth line, it is divided into spur gear, helical gear, herringbone gear and curved gear; According to the surface of gear teeth, it is divided into external gear and internal gear; According to the manufacturing method, it can be divided into casting gear, cutting gear, rolling gear and sintering gear.

The manufacturing materials and heat treatment process of gears have great influence on the bearing capacity, size and weight of gears. Carbon steel was used for gears before 1950s, alloy steel was used in 1960s, and surface hardened steel was used in 1970s. By hardness? Tooth surface can be divided into soft tooth surface and hard tooth surface.

The gear with soft tooth surface has lower bearing capacity, but it is easier to manufacture and has good running-in. It is mostly used in general machinery and small batch production without strict restrictions on the size and weight of the transmission. Because the small wheel bears a heavy burden in the paired gears, the tooth surface hardness of the small wheel is generally higher than that of the big wheel in order to make the working life of the big and small gears roughly equal. .

The hard tooth surface gear has high bearing capacity, which is after the gear is finely cut. And then quenching, surface quenching or carburizing quenching to improve the hardness. However, in the process of heat treatment, the gear will inevitably deform, so do you need to grind, grind or finish cut after heat treatment? In order to eliminate the error caused by deformation and improve the accuracy of gears.

The steels commonly used in manufacturing gears are quenched and tempered steel, hardened steel, carburized and hardened steel and nitrided steel. The strength of cast steel is slightly lower than that of forged steel, and it is often used for larger gears. Gray cast iron has poor mechanical properties and can be used for light load open gear transmission. Can nodular cast iron partially replace steel as gear? ; Plastic gears are mostly used in places with light load and low noise requirements, and the matching gears are generally steel gears with good thermal conductivity.

In the future, gears are developing in the direction of heavy load, high speed, high precision and high efficiency, striving for small size, light weight, long service life, economy and reliability.

The development of gear theory and manufacturing technology will further study the mechanism of gear tooth damage, which is the basis for establishing a reliable strength calculation method and the theoretical basis for improving gear bearing capacity and prolonging gear life. Develop a new tooth profile represented by circular arc tooth profile; Research on new gear materials and new gear manufacturing technology:? The elastic deformation, manufacturing and installation errors and temperature field distribution of gear are studied, and the gear teeth are modified to improve the stability of gear operation and increase the contact area of gear teeth when fully loaded, thus improving the bearing capacity of gear.

What are friction, lubrication theory and lubrication technology? The basic work in gear research is to study the theory of elastohydrodynamic lubrication, popularize synthetic lubricating oil and add extreme pressure additives to the oil, which can not only improve the bearing capacity of the tooth surface, but also improve the transmission efficiency.

Types of gear mechanism:

1, classified by transmission ratio?

Fixed transmission ratio? ——? Circular gear mechanism (cylinder, cone)?

Variable transmission ratio? ——? Non-circular gear mechanism (elliptical gear)?

2, according to the relative position of the axle classification?

Plane gear mechanism?

Straight cylindrical gear drive?

External meshing gear transmission?

Internal meshing gear transmission?

Rack and pinion drive?

Helical cylindrical gear drive?

Herringbone gear drive?

Spatial gear mechanism?

Bevel gear drive

Staggered shaft helical gear drive?

Worm gear and worm drive

Gear technology:

Bevel gear?

Semi-finished gear?

Spiral gear?

Internal gear?

Spur gear?

worm wheel

Main parameters of helical cylindrical gear

Spiral angle: β? & gt？ 0 is left-handed and vice versa.

Pitch: pn? =? Ptcosβ, subscript n and t represent normal and end face respectively.

Modulus: mn =? mtcosβ

Tooth width:

Diameter of dividing circle: d? =? mtz

Center distance: a= 1/2*m(z 1+z2)

Correct meshing condition: m 1? =? m2，α 1？ =? α2,β 1? =? β2

Coincidentally:

Equivalent number of teeth:

Simple diagnosis method of gear vibration

The purpose of simple diagnosis is to quickly judge whether the gear is in normal working condition, and further diagnose and analyze the gear in abnormal working condition or take other measures. Of course, in many cases, according to the simple analysis of vibration, some obvious faults can also be diagnosed.

Simple diagnosis of gears includes noise diagnosis, vibration level diagnosis and shock pulse (SPM) diagnosis, among which vibration level diagnosis is the most commonly used.

Vibration leveling diagnosis method is a diagnostic method to judge whether the gear is in normal working condition by using the vibration intensity of the gear. According to the different judgment indexes and standards, it can be divided into absolute value judgment method and relative value judgment method.

1. absolute value determination method

Absolute value judgment method is to directly evaluate the running state with the amplitude value measured at the same measuring point on the gearbox as the index.

In order to identify the gear state by absolute value judgment method, corresponding judgment standards must be formulated according to different gearboxes and different use requirements.

The main basis for determining the absolute value of gear is as follows:

1) theoretical research on abnormal vibration phenomenon;

(2) Vibration phenomenon analysis based on experiments;

(3) Statistical evaluation of measurement data;

(4) Refer to relevant standards at home and abroad.

In fact, there is no absolute value criterion that can be applied to all gears. When the size and type of gears are different, the judgment criteria will naturally be different.

When judging broadband vibration according to measured parameters, the standard value must change according to frequency. When the frequency is below 1kHz, the vibration is judged by the speed; If the frequency is above 1kHz, the vibration can be judged by the acceleration. The actual standard depends on the specific situation.

2. Phase value judgment method

In practical application, for gears whose absolute value judgment standard has not been worked out, we can make full use of the data measured in the field to make statistical average and formulate appropriate relative judgment standard, which is called relative value judgment method.

The relative judgment standard requires that the amplitude measured in the same part of the gearbox at different times be compared with the amplitude in the normal state, and when the measured value is compared with the normal value to a certain extent, it is judged as a certain state. For example, the relative value judgment standard stipulates that when the actual value reaches 1.6~2 times of the normal value, attention should be paid, and when it reaches 2.56~4 times, it means danger. Whether it is classified by 1.6 times or by 2 times depends on the use requirements of the gearbox. Roughing equipment (such as mining machinery) usually uses higher multiple classification.

In practice, in order to achieve the best results, the above two methods can be used for comparison and comprehensive evaluation.

[Edit this paragraph] Gear-main terms

Tooth-each convex part of a gear for meshing. Generally speaking, these convex parts are arranged radially. The teeth on the paired gears contact each other, which causes the gears to mesh continuously. ?

Cogging-the space between two adjacent teeth on a gear. ?

Gear face-the plane perpendicular to the cylindrical gear or worm shaft. ?

Normal plane-On a gear, the normal plane refers to the plane perpendicular to the tooth line of the gear. ?

Tooth tip circle-the circle where the tooth tip is located. ?

Tooth root circle-the circle where the groove bottom is located. ?

Base circle-the circle on which the generatrix forming involute performs pure rolling. ?

Dividing circle-the reference circle for calculating the geometric dimensions of the face gear. For spur gears, the modulus and pressure angle on the indexing circle are standard values. ?

Tooth flank-the flank of a gear tooth between the cylindrical surface of the tooth top and the cylindrical surface of the tooth root. ?

Tooth Profile-Tooth surface profile cut by a specific curved surface (the plane of cylindrical gear). ?

Tooth line-the intersection line between the tooth surface and the indexing cylindrical surface. ?

End tooth pitch pt- the length of indexing arc between two adjacent end tooth profiles on the same side. ?

Modulus m- quotient obtained by dividing the pitch by π, in millimeters. ?

Diameter pitch p- reciprocal of modulus, in inches. ?

Tooth thickness s? —— Indexing arc length between tooth profiles on both sides of a gear tooth on the end face. ?

Groove width e? —— Length of indexing arc between tooth profiles on both sides of a tooth slot on the end face. ?

Height of the tooth tip hι- the radial distance between the tooth tip circle and the indexing circle. ?

Tooth root height HF- radial distance between indexing circle and tooth root circle. ?

Full tooth height h—— the radial distance between the tooth top circle and the tooth root circle. ?

Tooth width b—— the dimension of gear teeth along the axial direction. ?

Face pressure angle? ɑt——？ The acute angle between the radial line intersecting the indexing circle through the tooth profile of the end face and the tangent line of the tooth profile passing through this point. ?

Reference frame (standard? Rack): Only the dimensions such as base circle, tooth profile, full tooth height, tooth crown height and tooth thickness meet the standard spur gear specifications, and the rack cut according to its standard gear specifications is called reference rack.

Reference pitch circle (standard? Pitch? Circle): the reference circle used to determine the size of each part of the gear. For what? Number of teeth x modulus?

Reference pitch line (standard? Pitch? Line): The specific pitch line on the rack or the tooth thickness measured along this line is half of the pitch.

Action pitch circle (action? Pitch? Circle): When a pair of spur gears are engaged, each has a tangent to make a rolling circle.

Reference pitch (standard? Pitch): If the selected standard pitch is taken as the reference, it is equal to the reference rack pitch.

Pitch (pitch? Circle): The track left on the meshing contact point of two gears is called pitch circle.

Pitch (pitch? Diameter): pitch circle diameter.

Effective tooth height (working? Depth): the crown height of a pair of spur gears. Also known as working tooth height.

Appendix: Radius difference between top circle and pitch circle.

Backlash: The gap between tooth surfaces when two teeth bite.

Clearance: the clearance between the top circle of one gear tooth and the bottom of the other gear tooth when two teeth mesh.

Nodes (pitch? Point): the point where a pair of gears meet and are tangent to the pitch circle.

Pitch: the arc distance of the corresponding point between two adjacent teeth.

Normal pitch (normal? Pitch: the pitch of involute gear, measured along the same vertical line of a specific section.

Introduction of plastic gears;

With the development of science, gears have gradually changed from metal gears to plastic gears. Because plastic gears are more lubricated and wear-resistant. ? It can reduce noise, cost and friction.