What Is a Cogwheel?

Gear is a kind of transmission component, which is divided into spur, helical and bevel according to different shapes. The gear foundation contains the basic parameters of the gear and the laws it follows.

Gear foundation

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Gear is a kind of transmission component, which is divided into spur, helical and bevel according to different shapes. The gear foundation contains the basic parameters of the gear and the laws it follows.
Tooth shape and
Single head and double head
When a pair of gears mesh, the gap between the tooth surfaces.
Backlash is a parameter required for smooth running of gear meshing.
bending
Center distance refers to the distance between the axes of a pair of gears.
The center distance has an effect on the backlash.
The larger the center distance, the larger the backlash.
How much should the center distance of the spur gear be allowed?
Generally, the tolerance of the reference value is close to 0.
Intersecting shaft gear (bevel gear) and staggered shaft gear (staggered shaft)
The axial distance from the cone vertex of the bevel gear to the positioning surface (the mounting reference surface).
The assembly distance is an important dimension that affects gear tooth contact and backlash.
Tip: In English, the assembly distance is called Locating distance (Mounting distance).
What is the dimensional tolerance of "assembly distance"?
In order to obtain proper backlash and gear tooth contact, the tolerance should be as close to 0 as possible.
For the tolerance of the reference size (tolerance is approximately 0), js7 to js9 are recommended.
How to find DP (
Along
To avoid tooth top interference during gear meshing, consciously trim the tooth shape near the tooth top.
The purpose of tooth shape modification is to smooth the meshing of the gear teeth, which is similar to the drum shape machining in the tooth shape direction.
The chamfering process is performed at the same time as the gear teeth are processed.
Its advantages are:
1. Prevent burrs and the like generated during cutting.
2. Prevent bumps that are easy to occur during use and transportation.
[Note] Tooth top = the intersection of the tooth surface and the tooth top surface.
1. What is the basic law of tooth profile meshing and what is the basic law of tooth profile meshing with a fixed gear ratio? What is the role of the basic law of tooth meshing?
Answer: A pair of gears meshes and drives, the tooth profile contacts at any point, and the transmission ratio is equal to the inverse ratio of two line segments divided by the common normal of the contact point. This law is called the basic law of tooth profile meshing. If the common normals of all the contact points of the tooth profile cross the centerline at a fixed point, then it is the basic law of tooth profile of constant gear ratio.
Effect; the requirement of the tooth profile curve is determined by whether the transmission ratio is constant.
2. What are nodes, nodes, and circles? What is a gear called a node's trajectory on a gear?
Answer: The intersection of the common normal of the tooth profile contact point and the concentric line is called a node. The trajectory of the node on the gear during the meshing process of a pair of teeth is called a pitch line. Gears with pitch circles are circular gears, otherwise they are non-circular gears.
3. What is a conjugate tooth gallery?
Answer: A pair of tooth profiles that meet the basic law of tooth profile meshing is called a conjugate tooth profile.
4. How is the involute formed? What is its nature?
Answer: The occurrence line rolls purely on the base circle. The trajectory of any point on the occurrence line is called the involute.
Properties: (1) The length of the straight line where the line rolls over is equal to the length of the arc over the base circle.
(2) The normal of any point on the involute line must be tangent to the base circle.
(3) The smaller the radius of curvature of the point that is closer to the base circle on the involute line, the larger the curvature radius on the contrary, the straighter the involute line.
(4) The distances of the normal directions of two involutes on the same base circle are equal.
(5) The shape of the involute depends on the size of the base circle. When the spread angle is the same, the smaller the base circle, the larger the curvature of the involute, the larger the base circle, the smaller the curvature, and the infinite the base circle becomes. straight line.
(6) There is no involute in the base circle.
5. Please write the involute polar coordinate equation.
Answer: rk = rb / cos k k = inv k = tgk-k
6. What is the reason why the involute tooth profile meets the basic law of tooth profile meshing?
Answer; (1) From the nature of the involute, the normal of any point of the involute must be tangent to the base circle
(2) There is only one internal tangent line on the same side of the two circles, and the common normal of the involute contact point of the two-wheel tooth profile must be tangent to the two base circles, so there is only one node, that is,
i12 = 1 / 2 = O2P / O1P = r2 / r1 = rb2 / rb1 = constant
7. What is a mesh line?
Answer: The trajectory of the contact points of the two wheel profiles.
8. What are the characteristics of involute tooth profile meshing and why?
Answer: (1) The transmission ratio is constant, because i12 = 1 / 2 = r2 / r1 , because there is only one internal tangent line on the same side of the two base circles, and it is the common normal line and meshing line of the contact points of the two tooth profiles, There is only one intersection point with the connecting line. Therefore, the transmission ratio is constant.
(2) The center distance is separable and the rotation ratio does not change, because i12 = 1 / 2 = rb2 / rb1, so the transmission ratio is determined after the processing of a pair of gears, regardless of the center distance.
(3) The direction of the positive pressure between the tooth profiles is unchanged, because the direction of the normal pressure between the tooth profiles is along the common normal direction of the contact point, which is also the common tangent line on the same side of the two base circles, and there is only one. The pressure direction does not change.
(4) The meshing angle changes with the center distance, because a COS = aCOS .
(5) Four lines in one. 1. The meshing line is the internal tangent line on the same side of the two base circles. 2. It is the common normal line of the contact points of the tooth profile. 3. The trajectory of the contact point is the meshing line. The line of pressure is the sum of the radius of curvature of the contact point.
9. What are modulo and indexing circles?
Answer: m = p / is the modulus, and the circle where m and are the standard values is called the index circle.
10. What is the pitch, tooth thickness and alveolar width?
Answer: The arc length between two adjacent teeth on the same side on a circumference is called the perimeter. The arc length occupied by tooth thickness is called tooth
Thick, the arc length occupied by the cogging is called the cogging width.
11. What is a standard gear?
Answer: m, , h * a, c * are standard values, and s = e = p / 2 gears.
12. What are the characteristics of the rack?
Answer: (1) The straight line sections parallel to the tooth tip line are equal, and their modulus and pressure angle are standard values.
(2) The straight line of the parallel tooth tip line with the groove width equal to the tooth thickness is called the center line, which is the reference line for determining the rack size.
13. What is the theoretical mesh line, actual mesh line and tooth profile working section?
A: Theoretical meshing line: the internal tangent line on the same side of the two base circles is theoretically the trajectory of the meshing point of the tooth profile, two tangent points
Is the engagement limit point.
Actual meshing line: the line segment between the intersection of the two tooth tips and the theoretical meshing line.
Tooth profile working section: The part of tooth profile participating in meshing in gear transmission.
14. What are the correct meshing conditions and continuous meshing transmission conditions for involute spur gears?
Answer: Correct meshing conditions: m1 = m2 = m 1 = 2 =
Continuous meshing conditions: = B1B2 / Pb 1
15. What is the significance of coincidence? What is the degree of coincidence related to?
Answer: The degree of coincidence indicates the number of pairs of meshing on the meshing line at the same time during a pair of gear transmissions. The degree of coincidence is an important indicator of the bearing capacity of the gear and the stability of the gear. The degree of coincidence is independent of m and increases with the increase of Z1 and Z2. The larger , the smaller , and change with the center distance. , The larger a, the larger , and the smaller .
16. What is the standard installation center distance of the standard gear. What are the characteristics of a standard installation?
Answer: The center distance of the standard gear installed according to the backlash is called the standard installation center distance of the standard gear, and the center distance of the standard gear installed according to the standard top clearance is also called the standard installation center distance.
For standard installation, a = a , r = r , a = r1 + r2
17. What is the non-standard installation center distance? What are the characteristics of non-standard installations?
Answer: A pair of gears with meshing transmission, the installation where the pitch circle and the index circle do not coincide is called non-standard installation, and its center distance is called non-standard installation center distance.
Features r r , a a , a = r1 + r2 = (r1 + r2) cos / cos ie a a r1 r1 r2 r2 c c
There are gaps on the tooth side, which produces impact, reduces the degree of coincidence, and has poor stability.
18. What are the characteristics of gear and rack meshing transmission?
Answer: (1) The position of the mesh line does not change due to the change in the relative position between the gear and the rack. It is always a fixed straight line that is tangent to the base circle and perpendicular to the straight tooth profile of the rack.
(2) r = r = = rack tooth profile angle
19. What are the characteristics of standard rack tools for processing standard gears?
Answer: The indexing circle of the wheel blank is purely tangent to the center line of the rack cutter. The number of teeth of the processed gear is guaranteed by the moving speed of the tool and the angular velocity of the wheel blank to ensure that V cutter = r blank.
20. What is the undercut phenomenon of the involute tooth profile? What is the reason?
Answer: Fan gear is used to process gears. When the processed involute tooth profile is cut again, it is called undercut phenomenon.
Reason: The intersection point of the tool tip line and the mesh line exceeds the meshing limit point of the cut gear, and the tool tip line exceeds
The reason for the over-engagement limit point is that the number of teeth of the gear to be processed is too small, the pressure angle is too small, and the coefficient of tooth height is too large.
21. How to determine the minimum number of teeth for standard external gears that do not undercut?
Answer: Determined by Zmin = 2h * a / sin2.
22. What is a shift gear?
Answer: Gears whose indexing tooth thickness is not equal to the cogging width and gears whose tooth top height is not standard are called shift gears. Gears in which the center line of the rack cutter during processing is not tangent to the index circle of the gear being processed are called shift gears.
23. What is the displacement amount and displacement coefficient and the minimum displacement coefficient?
Answer: Displacement: The vertical distance that the center line of the tool is translated by the position of the processing standard gear.
Coefficient of displacement: The coefficient required to express the amount of displacement in standard modulus.
Minimum displacement coefficient: The minimum displacement coefficient required for machining involute gears without undercutting.
xmin = h * a (Zmin-Z) / Zmin
24. Compared with standard gears, which dimensions are the same as the number of gears, which dimensions have changed and which dimensions do not change, why?
Answer: The number of teeth, the modulus, the pressure angle, the index circle, the base circle, the index circle, the total tooth height are unchanged, the tooth top circle, the tooth root circle, the index circle tooth thickness, and the alveolar width have changed.
Reason: The standard gear cutter is used to process the displacement gear, and the processing method is unchanged, that is, the correct meshing conditions are unchanged, so the indexing circle modulus and pressure angle are not changed. Therefore, it can be known from the formula that the index circle and the base circle are unchanged, and then the calculation of the root height, top height, root circle, and tooth circle is based on the index circle. When machining the index gear, the centerline of the standard tool is From the index circle, the root height becomes smaller and the root circle becomes larger. If you want to ensure that the total tooth height remains the same, the tooth tip height becomes larger. The tooth tip circle becomes larger because the tool moves outside the gear index circle. The tooth thickness of the tool becomes smaller, that is, the tooth groove being processed becomes smaller, and the tooth thickness becomes thicker because the indexing circumferential joint is unchanged.
25. How is the tooth profile of a helical involute spiral surface formed?
Answer: When the involute generating surface rolls purely on the base cylinder, a line at the b angle with the base circle generatrix is formed on the generating surface, and its trajectory forms the involute spiral surface of the helical gear teeth.
26. Are the spiral angles of the spirals of the coaxial cylindrical surfaces where the helical gear profile is located the same? Why?
Answer: The helix angle is different, because the helix angle i is determined by the lead L and the diameter di of the cylinder. The lead is the same, but the diameter of each circle is different, so the helix angle is different. The relationship is: tgi = L / di
27. What are the characteristics of helical gear meshing?
Answer: (l) The tooth profiles of the two wheels start to contact from the point, and the contact line changes from short to long, and then becomes shorter until the point touches, and then disengages, unlike the spur gear transmission, which suddenly contacts and suddenly disengages along the entire tooth width. Engage, but gradually enter the mesh and gradually disengage, so the impact is small, the noise is small, and the transmission is stable.
(2) Large coincidence = +
28. Which is the standard parameter surface of the helical gear and which surface is the standard involute? Explain the reason.
Answer: The normal surface is the standard parameter surface. In theory, the end surface is a standard involute, because the formation of the involute is a pure rolling of the generating surface on the base cylindrical surface, and the trajectory of the oblique straight line on the generating surface is an involute. From a machining point of view, the normal surface is a standard involute, because the helical gear tooth profile is a standard tool for processing spur gears. The cutting movement direction is along the helical line, and the tool surface is at its normal surface. Therefore, the normal surface is Standard Zhejiang Kai line.
29. What is the relationship between the end face of a helical gear and the geometric parameters of the normal surface, why is the end face parameter required?
Answer: mn = mt cos, tgn = tgt cosb, h * at = h * ancos, c * t = c * ancos
Because the geometric dimensions are end faces dt, dbt, dat, dft, pt, pbt.
30. What are the correct meshing conditions and continuous transmission conditions for a pair of helical gears?
Answer: Correct meshing conditions: mn1 = mn2 = m n1 = n2 =
External engagement 1 =-2 Internal engagement 1 = 2
Continuous transmission conditions: = + 1
31. What are the equivalent gears and equivalent teeth of a helical gear? What is the use of equivalent teeth?
Answer: A spur gear that is equivalent to the helical gear's normal tooth profile is called the equivalent gear of a helical gear. The number of teeth of an equivalent gear is called the number of equivalent teeth. The number of equivalent teeth is an important basis for selecting the tooth profile of the gear by copying the gear. The number of equivalent teeth is also the main basis for the strength design of the gear.
32. What are the characteristics of the worm gear?
Answer: (1) Transfer the motion and power between the interlaced axes of space, that is, the space mechanism.
(2) When the worm gear and worm gear mesh, in theory, the tooth profile contact is point contact, but the worm gear is added by the hob of the worm meshed with the worm gear, which is actually a space curve contact.
(3) The transmission ratio of the worm and worm gear is calculated using the number of worm heads (lines).
(4) The indexing circle diameter of the worm is not the number of heads multiplied by the modulus but the characteristic coefficient multiplied by the modulus, that is, d1 = qm
(5) The center distance of the worm gear is also used in the calculation of the characteristic coefficient.
a = m q + Z2 / 2
(6) A large transmission ratio can be obtained, and the worm gear is self-locking when active.
33. Which is the standard parameter surface of the worm gear? What are the conditions to achieve correct meshing?
Answer: (1) is the main section, that is, the section parallel to the end surface of the worm gear passing through the axis of the worm is called the main section.
(2) Correct meshing conditions: ma1 = mt2 = m a1 = t2 = 1 + 2 = 900
34. Why is the characteristic coefficient q of the worm determined as a standard value?
Answer: (1) It is conducive to the standardization of worms and reduces the number of worms.
(2) The number of worm hobs for machining worm gears is reduced.
35. How to determine the steering when the worm gear is engaged?
Answer: First determine the direction of rotation of the worm or worm gear: put the axis of the worm or worm up, the right side of the helix is right-handed, and the left side is left-handed. Then determine the steering: Right-handed use the right-hand rule, the active worm is right-handed and the four fingers of the right hand are used to hold the worm along the direction of the worm.
36. What are the characteristics of a spur gear mechanism?
Answer: (1) Transfer motion and power between two intersecting axes. (2) The gear distribution on the cone shrinks from large to small. (3) The large end face is a standard parameter face. (4) The tooth profile curve is a spherical involute.
37. What are the correct meshing conditions for a spur bevel gear?
Answer: m1 = m2 = m, 1 = 2 = R1 = R2 (R is the cone distance)
38. What is the back cone, equivalent gear, and equivalent teeth of a bevel gear?
Answer: A cone that is tangent to the indexing circle on the large end spherical surface of the bevel gear is called the back cone of the bevel gear. The sector formed by the projection of the large end surface of the bevel gear and the parallel conical generatrix on the back cone is called the sector gear. A spur gear with a tooth shape corresponding to the large end face of a bevel gear is called an equivalent gear of a bevel gear, and its number of teeth is called an equivalent number of teeth.
39. What is the use of equivalent gears and equivalent teeth?
Answer: A pair of bevel gear equivalent gears is used to study the meshing principle of the bevel gears, such as coincidence and correct meshing conditions. A single equivalent gear is used to calculate the minimum number of teeth that are not undercut and to use the profiling method to process a bevel gear Select the tool number and calculate the bending strength of the bevel gear.

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