A method for trimming the tooth profile of an involute worm

Abstract

The present invention provides a method for trimming the tooth profile of an involute worm, wherein the normal module of the worm is m1, the axial module is m2, the number of heads is z, the axial pressure angle is a°, the major diameter is φº, the pitch circle diameter is φ¹, and the minor diameter is φ². The method comprises the following steps: 1) determining a trimming starting point on the tooth profile of the worm gear tooth, and determining a trimming end point on the tooth top; 2) drawing an arc line on the gear tooth portion between the trimming starting point and the end point, and the radius of the arc line is: m1-f (normal module margin); 3) trimming the gear tooth profile based on the arc line. The above technical scheme can extend the effective meshing length of the worm wheel and the worm to the available length, so that the meshing in and out are instantly and smoothly transferred, and the impact vibration and abnormal noise are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical processing, and in particular to a method for trimming the tooth profile of an involute worm. Background Art

[0002] The processing of worm wheels and worms in automotive power steering (EPS) has always attracted much attention, and its processing quality and consistency affect the brand and price of the entire column. The quality of the meshing of worm wheels and worms determines the smoothness, reliability, vibration and abnormal noise of the transmission, which directly affects the comfort and satisfaction of car buyers with the car. There is a clear difference between worm wheel and worm transmission and gear transmission. It not only has radial movement but also axial movement. Radial impact and meshing, axial extrusion and friction are important reasons for abnormal noise. The requirements of various automobile manufacturers for EPS are becoming more and more humane and strict. Improving the processing quality of worm wheels and worms, ensuring smooth transfer of worm wheels and worms, stable transmission, uniform and gentle power assistance, safety and reliability, is the only way to upgrade.

[0003] The worm gear tooth profile is milled by a hob in the form of a "ZI" spiral line, and the trajectory of each point on the meshing surface of the worm is developed in the form of an involute. Therefore, the detected charts are all involute-type lower quasars "︶". The depth of this concave arc refers to the arc between the root, drum, and top of the tooth on the full tooth depth.

[0004] The processing of the worm gear tooth profile is done by grinding the profile made by the diamond pen on the grinding wheel. In fact, the tooth profile is divided into several sections (mostly 5-7 sections) throughout the whole process. The curve is folded by multiple oblique straight lines. The distortion is less in the middle of the tooth profile with smaller curvature, and the distortion is the largest at the point where the top curvature is the largest. A raised point called a notch will be formed at the joint of the straight lines, which is the origin of the impact. The more notches there are and the higher the notch protrusions are, the higher the impact rate will be, the greater the impact force, the more vibrations will be, and the louder the abnormal noise will be.

[0005] Therefore, the dressing of worm tooth profile has attracted more and more attention, but the traditional grinding wheel dressing method is the straight line dressing method (modifying into a triangle, trapezoid or square tooth shape according to the pressure angle), and the tooth top rounding is only a conceptual or habitual deburring and rounding effect, without any deep meaning. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for trimming the tooth profile of an involute worm, extending the effective meshing length of the worm wheel and the worm to the available length, making the meshing in and out of the meshing transition instantaneously and smoothly, and reducing impact vibration and abnormal noise.

[0007] In order to solve the above technical problems, the present invention adopts the following technical scheme: a method for trimming the tooth profile of an involute worm, wherein the normal module of the worm is m1, the axial module is m2, the number of heads is z, the axial pressure angle is a°, the major diameter is φº, the pitch circle diameter is φ¹, and the minor diameter is φ², and the method comprises the following steps: 1) determining a trimming starting point on the tooth profile of the worm gear tooth and determining a trimming end point on the tooth top; 2) drawing an arc line on the gear tooth portion between the trimming starting point and the end point, and the radius of the arc line is: m1-f (normal module-margin); 3) trimming the gear tooth profile based on the arc line.

[0008] In step 1), the diameter of the starting point of the modification is (the diameter of the starting point of the worm engagement + the actual engagement depth of the worm).

[0009] The calculation formula for the diameter of the worm's starting meshing point is: H = worm pitch circle diameter - actual worm meshing depth / 2, that is: H = φ¹-K / 2; the calculation formula for the actual worm meshing depth is: K = (worm major diameter - worm minor diameter) / 2 - 1 / 4 of the sum of the major and minor diameters R of the worm and worm wheel and the difference between the center distance, that is: K = (φº-φ²) / 2-[(φº+φ²+ψº+ψ²) / 4-L], where ψº and ψ² are the major and minor diameters of the worm wheel tooth type, and L is the center distance of the worm gear meshing.

[0010] In step 1), the end point of the modification is determined in the following way: draw an oblique line from the starting point of the modification to the central axis of the worm, the angle between the oblique line and the central axis of the worm is equal to the axial pressure angle a° of the worm, and draw a circle with the starting point of the modification as the center and m1-f (normal module-margin) as the radius, which intersects at the oblique line point N, and then draw a circle with point N as the center and m1-f (normal module-margin) as the radius, which intersects at the starting point of the modification and the tooth top point G on the tooth profile. Point G is the end point of the modification.

[0011] The beneficial effects of the present invention are as follows: A. By determining the trimming arc line, the tooth top of the worm, especially the notch near the diameter of the starting meshing point and the ending meshing point, can be trimmed, so that the contact moment of the turbine worm changes from impact to extrusion, from vibration to push-slip, and from edges to smoothness, thereby alleviating the impact, vibration and abnormal noise occurring during the transmission process; B. After trimming according to the smooth curved surface of the arc line, the meshing and pushing-slipping time of the worm wheel and worm and the length of the meshing line (extending the available length) can be extended, thereby reducing the impact and abnormal noise during meshing; C. By lowering the height of the notch protrusion in the starting meshing area and lengthening the contact curve, the impact force can be dispersed and released, thereby reducing the vibration intensity and the decibel of abnormal noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the gear structure of the TDF99 worm in an embodiment of the present invention. DETAILED DESCRIPTION

[0013] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0014] It should be noted in advance that, in the present invention, unless otherwise clearly specified and limited, the first feature being "above", "above" and "above" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature includes the first feature being directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature. The terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0015] An embodiment of the present invention provides a method for trimming the tooth profile of an involute worm, wherein the normal module of the worm is m1, the axial module is m2, the number of heads is z, the axial pressure angle is a°, the major diameter is φº, the pitch circle diameter is φ¹, and the minor diameter is φ². The method comprises the following steps: 1) determining a trimming starting point on the tooth profile of the worm gear tooth, the diameter of the trimming starting point is (the diameter of the worm starting engagement point + the actual meshing depth of the worm), and then determining a trimming end point on the tooth top based on the diameter of the trimming starting point; 2) drawing an arc line on the gear tooth portion between the trimming starting point and the end point, the radius of the arc line is: m1-f (normal module-margin); 3) trimming the gear tooth profile based on the arc line.

[0016] In step 1), the calculation formula for the diameter of the worm's starting meshing point is: H = worm pitch circle diameter - actual worm meshing depth / 2, that is: H = φ¹-K / 2; the calculation formula for the actual worm meshing depth is: K = (worm major diameter - worm minor diameter) / 2-1 / 4 of the sum of the major and minor diameters R of the worm and worm wheel and the difference between the center distance, that is: K= (φº-φ²) / 2-[(φº+φ²+ψº+ψ²) / 4-L], where ψº and ψ² are the major and minor diameters of the worm wheel tooth type, and L is the center distance of the worm gear meshing.

[0017] In step 1), the end point of the modification is determined in the following way: draw an oblique line from the starting point of the modification to the central axis of the worm, the angle between the oblique line and the central axis of the worm is equal to the axial pressure angle a° of the worm, and draw a circle with the starting point of the modification as the center and m1-f (normal module-margin) as the radius, which intersects at the oblique line point N, and then draw a circle with point N as the center and m1-f (normal module-margin) as the radius, which intersects at the starting point of the modification and the tooth top point G on the tooth profile. Point G is the end point of the modification.

[0018] The present invention is further described below by taking the TDF99 worm wheel and worm as an example.

[0019] Worm parameters: Worm type ZI, normal module 2.25, axial module 2.394, number of threads 2, normal pressure angle 13°39′32″, axial pressure angle 14.5°, rotation direction right, helix angle 20°, center distance 51.

[0020] Worm gear parameters: transmission type ZI type, normal module 2.25, axial module 2.394, number of threads 2, normal pressure angle 13°39′32″, axial pressure angle 14.5°, helix angle 20°, rotation direction right, number of worm gear teeth 37, displacement coefficient 0.052, center distance 51.

[0021] Worm dimensions: major diameter φ17, sub-circle diameter φ13.157, minor diameter φ8, normal tooth thickness 2.266.

[0022] Worm gear dimensions: major diameter φ92.67, circular diameter φ88.593, minor diameter φ83.575, axial tooth thickness 5.11.

[0023] 1. According to the calculation formula of the actual engagement depth of the worm: K = (worm major diameter - worm minor diameter) / 2 - 1 / 4 of the sum of the major and minor diameters R of the worm and worm wheel and the difference between the center distance, that is: K = (φº-φ²) / 2 - [(φº+φ²+ψº+ψ²) / 4-L], then substitute the relevant parameters of the TDF99 worm wheel and worm into it: K = (17-8) / 2 - [51- (17+8+92.67+83.575) / 4] = 3.811, and finally the actual engagement depth of the worm is 3.811mm.

[0024] 2. According to the calculation formula of the diameter of the starting meshing point of the worm: H = worm pitch circle diameter - actual meshing depth of the worm / 2, that is: H = φ¹-K / 2; then substitute the relevant parameters of the TDF99 worm wheel and worm into it: H = 13.157-3.811 / 2 = 11.247, and finally the diameter of the starting meshing point of the worm is 11.247mm.

[0025] 3. The diameter of the starting point of the modification is (the diameter of the starting point of the worm engagement + the actual engagement depth of the worm), that is, 11.247+3.811=15.058mm.

[0026] 4. Figure 1 The figure shows the gear tooth structure of the TDF99 worm. The gear tooth has an original tooth profile curve. The common tangent point in the figure is located at the outer diameter of the tooth profile of 15.058mm, which is the starting point of the modification. A slash line is drawn from the common tangent point to the central axis of the worm. The angle between the slash line and the central axis of the worm is equal to the axial pressure angle of the worm, 14.5°. A circle is drawn with the common tangent point as the center and m1-f (2.25-0.225=2.025) as the radius, intersecting at the slash line point N. Then, a circle is drawn with point N as the center and m1-f (2.25-0.225=2.025) as the radius, intersecting at the common tangent point on the tooth profile and the tooth top point G. The G point is the modification end point. The arc line between the common tangent point and point G is the modified tooth profile curve. Then, the tooth top is modified according to the modified tooth profile curve. The part between the original tooth profile curve and the modified tooth profile curve is the tooth top modification amount.

[0027] It should be noted that the coordinate values ​​(φ values) of the meshing points of any worm gear and worm are not representative values ​​of the meshing width or contact width area. They are related to the meshing center distance, the diameters of the two meshing circles, and the distance of advance or lag. In specific operations, the starting point of the worm tooth top rounding should be below the dividing circle of the starting meshing point of the worm wheel and worm plus the actual meshing depth. The arc radius of the modified tooth profile curve is 2.025. This value is an approximate value and can be slightly adjusted upward or downward as needed. As long as the force is extended, dispersed, and smoothly elongated backward when the worm is meshed and impacted, the impact can be changed to extrusion to relieve the force; when the worm is meshed and suspended, the corresponding worm wheel profile must have a delayed transition contact surface, so that the degree of abnormal noise can be reduced. Countless practices have proved that completely ideal tooth profiles are not necessarily very good when meshing, and the tooth profile modified by the present invention has achieved very good results.

[0028] The above is only the preferred implementation of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as the preferred embodiment as above, it is not used to limit the product form and style of the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments with equivalent changes without departing from the scope of the technical solution of the present invention. However, all contents that do not depart from the technical solution of the present invention still fall within the patent scope of the technical solution of the present invention.

Claims

1. A method for trimming the tooth profile of an involute worm, wherein the worm has a normal modulus of m1, an axial modulus of m2, a number of starts of z, a margin of f, an axial pressure angle of a°, a major diameter of φº, a pitch circle diameter of φ¹, and a minor diameter of φ², wherein: The method comprises the following steps: 1) Determine a modification starting point on the tooth profile of the worm gear tooth. The diameter of the modification starting point is: the diameter of the worm starting engagement point + the actual meshing depth of the worm; determine a modification end point on the tooth top; the modification end point is determined in the following way: draw an oblique line from the modification starting point to the central axis of the worm, the angle between the oblique line and the central axis of the worm is equal to the axial pressure angle a° of the worm, draw a circle with the modification starting point as the center and m1-f as the radius, intersecting at the oblique line point N, and then draw a circle with point N as the center and m1-f as the radius, intersecting at the modification starting point on the tooth profile and the tooth top point G, and the point G is the modification end point; 2) Draw an arc line on the gear tooth part between the starting point and the end point of the modification. The radius of the arc line is: m1-f; 3) Use the arc line as a reference to adjust the gear tooth profile.

2. The method for trimming the involute worm gear tooth profile according to claim 1, characterized in that: The calculation formula for the diameter of the worm's starting meshing point is: H = worm pitch circle diameter - actual worm meshing depth / 2, that is: H = φ¹-K / 2; the calculation formula for the actual worm meshing depth is: K = (worm major diameter - worm minor diameter) / 2 - 1 / 4 of the sum of the major and minor diameters of the worm and worm wheel and the difference between the center distance, that is: K = (φº-φ²) / 2-[(φº+φ²+ψº+ψ²) / 4-L], where ψº and ψ² are the major and minor diameters of the worm wheel tooth type, and L is the meshing center distance of the worm wheel.

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