Gear manufacturing method
A two-stage grinding process randomizes undulation patterns on gear tooth surfaces by altering the depth of cut and feed rate, effectively reducing non-integer order gear noise and enhancing gear performance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2023-08-17
- Publication Date
- 2026-06-23
AI Technical Summary
Existing gear machining methods form periodic undulations on tooth surfaces, leading to prominent non-integer order gear noise, which are difficult to eliminate.
A two-stage grinding process is employed, where a second grinding operation with a different depth of cut and feed rate is performed after a first grinding operation, randomizing the undulation pattern by reducing the periodicity of undulations on the tooth surface.
The method effectively reduces gear noise by dispersing non-integer order gear noise into multiple orders, making it less noticeable, while maintaining efficient processing and cost-effectiveness.
Smart Images
Figure 0007878219000001 
Figure 0007878219000002 
Figure 0007878219000003
Abstract
Description
Technical Field
[0001] The present invention relates to a method for machining gears, and particularly to a method for grinding or polishing tooth surfaces.
Background Art
[0002] In order to reduce gear noise, grinding or polishing the tooth surface of gears has been widely performed conventionally. However, inevitable irregularities (undulations, or sometimes called undulation marks) remain on the tooth surface. If the irregularities are periodic or regular, the noise caused by the irregularities becomes prominent and the gear noise may increase. Patent Document 1 describes a machining method for changing the feed rate of a tool for machining the tooth surface so that the intervals of scratches corresponding to such irregularities are irregular in the direction along the tooth surface. The change in the feed rate is said to be in a form of change represented by a sine wave function, a step function, a ramp function, or the like. According to the machining method described in Patent Document 1, by changing the feed rate of the tool (relative feed rate with respect to the workpiece) to be represented by, for example, a sine wave, the intervals of fine scratches in grinding become irregular along the width direction of the tooth surface.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] The scratches described in Patent Document 1 are, at a microscopic level, irregularities, or undulations (or undulation lines), on the tooth surface, which are formed by the contact of the tool with the tooth surface. This can be described as a shape in which the tool's trajectory is transferred to the tooth surface. Since the tool is fed at a speed that changes as expressed by a predetermined function, in the machining method described in Patent Document 1, irregularities (scratches) that change periodically according to the function that determines the tool's feed rate are formed on the tooth surface. For example, in parts where the feed rate based on the adopted function is high, the height of the undulations formed on the tooth surface is high, and in subsequent parts where the feed rate is slow, the height of the undulations on the tooth surface is low. Therefore, the shape formed on the tooth surface is equivalent to that formed when machining is performed at a constant feed rate, although the pitch or period of the undulations differs, in that it is a periodically repeating irregular shape. As described above, the machining method described in Patent Document 1 is a method of transferring the so-called trajectory of a tool with a controlled feed rate to the tooth surface. Therefore, it is difficult to eliminate the periodicity of the fine irregularities (scratches) formed on the tooth surface, and there is still room for improvement in obtaining gears with low gear noise (especially non-integer order gear noise that does not depend on the number of teeth).
[0005] This invention was made in view of the above-mentioned technical problems, and aims to provide a machining method for obtaining gears that reduce gear noise (especially non-integer gear noise) by eliminating or reducing the periodicity of the tooth surface undulation. [Means for solving the problem]
[0006] To achieve the above objective, the present invention provides a gear machining method comprising grinding a gear tooth surface by feeding a grinding tool, which rotates about a central axis, along the tooth surface of the gear in a direction perpendicular to the central axis, characterized in that, after performing a first grinding operation by moving the grinding tool along the tooth surface with a predetermined first depth of cut and a first feed rate, a second grinding operation is performed by moving the grinding tool along the tooth surface that has been ground in the first operation with a second depth of cut less than or equal to the first depth of cut and a second feed rate that is deviated by a predetermined amount from the first feed rate. [Effects of the Invention]
[0007] According to the present invention, a second grinding process is performed on the tooth surface in addition to the first grinding process. Since the depth of cut in the second grinding process is less than or equal to the depth of cut in the first grinding process, the portion of the undulations on the tooth surface that protrudes above the tooth surface is ground down by the second grinding process. That is, at least one of the tops or protruding ends of the undulations is ground down, reducing their height. Furthermore, the feed rate of the grinding tool in the second grinding process is shifted by a predetermined amount from the feed rate in the first grinding process. Therefore, the period or pitch of the undulations that are expected to occur when the second grinding process is performed is shifted from the period or pitch of the undulations that occur in the first grinding process. Therefore, the peaks or protruding ends of the undulations created in the first grinding process are irregularly mixed together in the second grinding process, with some being heavily ground, some not ground at all, and some being moderately ground, resulting in varying degrees of processing. In other words, the periodicity of the undulations on the tooth surface is almost eliminated, resulting in so-called randomization. Even if gear noise occurs on the tooth surface of the gear obtained in this way, no particular non-integer order gear noise is noticeable, and the gear noise is dispersed into multiple non-integer order gear noises of different orders. As a result, a gear can be obtained in which the gear noise does not feel unnatural, or at least feels very unnatural. [Brief explanation of the drawing]
[0008] [Figure 1] This is a process diagram illustrating the processing sequence or process in an embodiment of the present invention. [Figure 2] (a) is a schematic diagram of a grinding wheel used in an embodiment of the present invention, and (b) is a line diagram illustrating the grinding state by the grinding wheel. [Figure 3] This diagram shows the measured cross-sectional shape of the undulations obtained during the precision grinding process. [Figure 4] This is a schematic diagram illustrating the undulation. [Figure 5]This diagram shows the cross-sectional shape of the undulations that are expected to occur during additional processing. [Figure 6] This diagram shows the cross-sectional shape of the undulation caused by the additional processing. [Figure 7] This diagram shows the measurement results of non-integer order gear noise. (a) shows the measurement results of non-integer order gear noise for a gear using a conventional method without additional machining, and (b) shows the measurement results of non-integer order gear noise for a gear using the method of the present invention with additional machining. [Modes for carrying out the invention]
[0009] Next, the present invention will be described based on the embodiments shown in the figures. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the present invention.
[0010] The present invention relates to a machining method that eliminates or reduces the periodicity of undulations (fine irregularities) on a tooth surface generated during the precision grinding process as a finishing process for tooth surfaces by removing a portion of the undulations through additional machining. In other words, rather than imparting non-periodicity to the behavior of the grinding tool during the finishing grinding process, this method is characterized by eliminating or reducing the periodicity of the undulations on the tooth surface by applying a grinding process with a different periodicity to the periodic undulations.
[0011] Therefore, the machining method as an embodiment of the present invention is characterized by a finishing process called a precision polishing process, in which additional machining is performed after the precision polishing process, or at least two precision polishing processes are performed. Such finishing processes can be performed, for example, in creative grinding using a multi-start threaded grinding wheel. Figure 1 shows an example of the machining process according to the machining method of the present invention, indicated by the trajectory of the grinding wheel. The grinding wheel is fed in a predetermined direction relative to the workpiece to perform rough machining, and thereafter, the grinding wheel is fed in the opposite direction to the previous one to perform a precision polishing process (corresponding to the first grinding process in the embodiment of the present invention). After that, the grinding wheel is fed in the opposite direction to the precision polishing process to perform additional machining (or a second precision polishing process, corresponding to the second grinding process in the embodiment of the present invention).
[0012] Figure 2 schematically shows an example of grinding a tooth surface 2 after rough grinding using a grinding wheel 1 having five spiral grooves. The grinding wheel 1 rotates counterclockwise in Figure 2 around a central axis perpendicular to the plane of the paper in Figure 2(a). Figure 2(a) shows the depths of the spiral grooves g1, g2, g3, g4, and g5. The grinding wheel 1 grinds the tooth surface 2 by rotating in contact with it. Therefore, the amount of downward movement or pressure in Figure 2(a) is the depth of cut, and the amount of movement along the tooth surface 2 and perpendicular to the central axis of rotation (to the right in Figure 2(a)) is the feed rate.
[0013] In the example shown in Figure 2(a), the first groove g1 has the largest depth of cut, followed by the second groove g2 and the fifth groove g5, and then the third groove g3 and the fourth groove g4 have the smallest depths of cut. Also, the amount of movement (feed rate) during one rotation of the grinding wheel 1 is set to be somewhat smaller than the circumference (outer length) of the grinding wheel 1. Therefore, during the grinding process by the first groove g1, the amount of cut by the second groove g2 and the third groove g3 is smaller than the amount of cut by the first groove g1, resulting in a cut corresponding to the trajectory of the first groove g1, as shown in Figure 2(b). Due to the feed rate during one rotation of the grinding wheel 1, the third groove g3 comes into contact with the tooth surface 2, but because the amount of cut by the third groove g3 is small, the first groove g1 remains in contact with the tooth surface 2, and subsequently the fifth groove g5 comes into contact with (is pressed against) the tooth surface 2, resulting in a cut by the fifth groove g5.
[0014] During the process of cutting by the fifth groove g5, cutting by the first groove g1 occurs. However, because the amount of cutting by the first groove g1 is large, the fourth groove g4 does not come into contact with the tooth surface 2, and no cutting occurs by the fourth groove g4. As a result, an uneven shape, or undulation, is formed on the tooth surface 2, with so-called recesses cut by the first groove g1 and so-called protrusions cut by the fifth groove g5 and the second groove g2 between them.
[0015] Figure 3 shows the shape of the undulation W obtained in the actual precision grinding process, with the vertical axis representing the undulation height and the horizontal axis representing the position along the tooth surface (the feed direction of the grinding wheel 1). A schematic representation of this is shown in Figure 4, which represents an undulation W where the irregularities repeat periodically in the feed direction. In Figure 4, the spacing (pitch) of the undulation W is indicated by the symbol P, which in the example shown in Figure 2 above is represented by the product of the number of grooves J in the grinding wheel 1 and the feed amount F per revolution. Also in Figure 4, the height (or depth) of the undulation W is indicated by the symbol H, which in the example shown in Figure 2 above corresponds to the amount of cut by the first groove g1.
[0016] In the finishing process alone or in the finishing process for the first finishing, the waviness W schematically shown in FIG. 4 is formed on the tooth surface 2. Therefore, if the gear as it is is used in a predetermined transmission mechanism, fluctuations in the periodic rotation amount or torque due to the waviness W occur, which become non-integer vibrations or noises (gear noises). In the processing method as an embodiment of the present invention, the convex portions of the waviness W generated in the first finishing process, as schematically shown in FIG. 4, are irregularly removed within at least a predetermined range, such as within the tooth width range or within the range mainly involved in torque transmission on the tooth surface 2. A secondary processing or second finishing process (hereinafter, these are collectively referred to as secondary processing) is performed.
[0017] The secondary processing in the embodiment of the present invention is a grinding process using the grinding wheel 1 used in the immediately preceding finishing process, and it is preferably performed continuously with the first finishing process. Since a rotary tool such as a multi-threaded grinding wheel 1 is used, the secondary processing becomes a grinding process that generates waviness. However, by making the depth of cut and the feed amount in the secondary processing different from those in the first finishing process, the waviness W generated in the preceding first finishing process can be made irregular without periodicity.
[0018] Specifically, the depth of cut in the secondary processing is made smaller than the depth of cut in the first finishing process. For example, the distance between the center of the grinding wheel 1 and the center of the workpiece (the gear to be ground) is made slightly smaller than the distance in the first finishing process. Therefore, in the secondary processing, the grinding wheel 1 does not contact the bottom portion of the concave portion in the waviness W generated in the preceding first finishing process and does not process that portion, and only the convex portion is processed and partially removed. In other words, the amount of reduction in the depth of cut in the secondary processing is an amount smaller than the height H of the already formed waviness W (0 ≤ reduction amount < H).
[0019] Also, the feed amount in the additional machining is an amount slightly deviated from the feed amount F in the first lapping process described above, and is the actual feed amount or the feed control amount of the grinding wheel 1. Here, the "slightly deviated amount" means that the ratio of the feed amount in the additional machining to the feed amount F in the first lapping process is not an integer, or is not an amount that becomes "1 / integer". Therefore, the feed amount in the additional machining may be smaller than the feed amount F in the first lapping process, but in terms of the machining efficiency or machining speed of the gear, it is preferable that the feed amount (feed speed) in the additional machining is larger than the feed amount F (feed speed) in the first lapping process.
[0020] As described above, since the additional machining is a grinding process that feeds and moves the rotating grinding wheel, it is a process that generates waviness. The waviness W' that is assumed to occur in the additional machining is schematically shown by a solid line in FIG. 5. The example shown here is an example in which the feed amount is made larger than the feed amount in the first lapping process, and the waviness has a pitch P' larger than the pitch P of the waviness W (dashed line in FIG. 5) that already exists on the tooth surface 2. And since the depth of cut in the additional machining is smaller than the depth of cut in the first lapping process, the waviness W' due to the additional machining does not interfere with the bottom of the waviness W in the first lapping process, and the waviness W' in the additional machining interferes with the convex portion in the first lapping process, and becomes a waviness obtained by grinding or removing the convex portion. In addition, depending on the difference in the pitches P and P' of the respective wavinesses W and W', the grinding amounts of the convex portions of the waviness W in the first lapping process vary, and there are mixed convex portions that are largely ground, convex portions with a small grinding amount, and convex portions that are not ground, and they are arranged irregularly.
[0021] Figure 6 schematically shows the undulation W0 that occurs on the tooth surface 2 after additional machining. The shape shown here is the shape after a portion of the protrusions of the undulation W from the first precision grinding process has been removed by the additional machining. In other words, it is the shape obtained by connecting the lower line of the dashed undulation W and the solid undulation W' shown in Figure 5. As described above, the depth of cut and feed rate of the grinding wheel 1 in the additional machining process are different from those in the first precision grinding process, resulting in uneven height H0 and pitch P0 of the resulting undulation W0. That is, the so-called periodicity is lost.
[0022] As described above, according to the processing method in the embodiment of the present invention, the pitch P0 and height H0 of the undulation W0 on the tooth surface are randomized. As a result, even if non-integer order gear noise is generated when the tooth surfaces come into contact and transmit torque, no particular non-integer order gear noise becomes prominent, and the vibration or noise is distributed among multiple non-integer order gear noises. Figures 7(a) and 7(b) show a simplified representation of the measurement results of non-integer order gear noise obtained in experiments conducted by the inventors. Figure 7(a) shows the measurement results of non-integer order gear noise for a gear that has undergone only the first precision grinding process and no additional processing, and Figure 7(b) shows the measurement results of non-integer order gear noise for a gear that has undergone additional processing. In these figures, the upward-sloping solid line represents non-integer order gear noise, and the thicker the line, the higher the sound pressure level.
[0023] As shown in Figure 7(a), in gears that do not undergo additional machining, a specific non-integer order gear noise Na becomes large, which is considered unusual. In contrast, as shown in Figure 7(b), in gears that undergo the additional machining described above in addition to the first precision grinding process, multiple non-integer order gear noises Nb, Nc, and Nd are observed to be generated, and no specific non-integer order gear noise becomes particularly large, while the sound pressure levels of all of them are relatively low. Therefore, these multiple non-integer order gear noises are easily blended with so-called background noise, and for example, when such gears are used in the transmission mechanism of a vehicle (such as a BEV, HEV, or PHEV vehicle), even at low vehicle speeds where the overall noise of the vehicle is low, the non-integer order gear noise generated by the gears is not particularly noticeable. In other words, according to the method of the present invention, gears with reduced gear noise (especially non-integer order gear noise) can be obtained. Moreover, since the additional machining can be performed using the grinding wheel used in the previous precision grinding process, processing costs can be suppressed and efficient processing can be performed.
[0024] It should be noted that the present invention is not limited to the embodiments described above, and can be applied to form grinding as well as to creative grinding. Furthermore, the grinding wheel (grinding tool) used in the present invention may be a tool other than a multi-start threaded grinding wheel. [Explanation of symbols]
[0025] 1 whetstone 2 Tooth surface F feed amount H,H0 swell height J Number of articles P,P0 pitch W, W', W0 Wavy pattern g1, g2, g3, g4, g5 (spiral grooves of the grinding wheel)
Claims
[Claim 1] A gear machining method comprising grinding a gear tooth surface by feeding a grinding tool, which rotates about a central axis, along the tooth surface of the gear in a direction perpendicular to the central axis, After performing a first grinding operation by moving the grinding tool along the tooth surface with a predetermined first depth of cut and a first feed rate, The second grinding operation is performed by moving the grinding tool along the tooth surface that has undergone the first grinding operation, using a second depth of cut less than or equal to the first depth of cut and a second feed rate that is shifted by a predetermined amount from the first feed rate. A gear machining method characterized by the following.