Machining method of gear

Abstract

To provide a machining method of a gear which obtains a gear reducing non-integer order gear noise due to waviness of tooth surface.SOLUTION: There is provided a machining method of a gear in which a griding tool rotating around a center axis is transferred along a tooth surface of the gear in a direction orthogonal to the center axis to grind the tooth surface. The machining method of the gear includes: performing a first griding which moves the griding tool along the tooth surface at a predetermined first cutting quantity and at a predetermined first feed rate; and performing a second griding machining which moves, along the tooth surface where the first griding is performed, the griding tool at a second cutting quantity that is the first cutting quantity or less and at a second feed rate deviated from the first feed rate by a predetermined quantity.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for machining gears, and more particularly to a method for grinding or polishing the tooth flanks. [Background technology]

[0002] In the past, gear tooth surfaces have been widely ground or polished to reduce gear noise. However, unavoidable irregularities (sometimes called humming or humming) remain on the tooth surface, and if the irregularities are periodic or regular, the sound (noise) caused by the irregularities may be noticeable, resulting in increased gear noise. Patent Document 1 describes a machining method in which the feed rate of a tool used to machine the tooth surface is changed in order to make the intervals between scratches corresponding to such irregularities irregular in the direction along the tooth surface. The change in the feed rate is said to be a change mode expressed by a sine wave function, a step function, a ramp function, or the like. According to the machining method described in Patent Document 1, the feed rate of the tool (the feed rate relative to the workpiece) is changed so as to be expressed by, for example, a sine wave, so that the intervals between fine grinding scratches become irregular along the width direction of the tooth surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-335061 A Summary of the Invention [Problem to be solved by the invention]

[0004] The scratches described in Patent Document 1 are, microscopically, unevenness on the tooth surface, i.e., undulations (or wavy lines), which are formed by the contact of a tool with the tooth surface. This can be said to be a shape in which the trajectory of the tool is transferred to the tooth surface. The tool is fed at a speed that changes as expressed by a predetermined function, so in the machining method described in Patent Document 1, unevenness (scratches) that change periodically according to the function that determines the feed speed of the tool are formed on the tooth surface. For example, in a portion where the feed speed based on the adopted function is fast, the height of the undulations formed on the tooth surface is high, and in the subsequent portion where the feed speed is slow, the height of the undulations on the tooth surface is low. Therefore, the shape formed on the tooth surface is the same as that formed when machining is performed at a constant feed speed, in that the pitch or period of the undulations is different, but it is the same in that it is a periodically repeating uneven shape. As described above, the machining method described in Patent Document 1 is a method in which the so-called trajectory of a tool with a controlled feed speed is transferred onto the tooth surface, making it difficult to eliminate the periodicity of fine irregularities (scratches) formed on the tooth surface, and there is still room for improvement in terms of obtaining gears with low gear noise (especially non-integer gear noise whose order is independent of the number of teeth).

[0005] The present invention has been made in light of the above-mentioned technical problems, and has as its object to provide a processing method for obtaining gears with reduced gear noise (particularly non-integer gear noise) by eliminating or reducing the periodicity of the waviness on the tooth surface. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a gear machining method in which a grinding tool rotating about a central axis is fed along a tooth flank of a gear in a direction perpendicular to the central axis to grind the tooth flank, characterized in that a first grinding process is performed by moving the grinding tool along the tooth flank at a predetermined first depth of cut and a first feed speed, and then a second grinding process is performed by moving the grinding tool along the tooth flank where the first grinding process has been performed at a second depth of cut that is less than the first depth of cut and at a second feed speed that is deviated by a predetermined amount from the first feed speed. Effect of the Invention

[0007] According to the present invention, in addition to the first grinding process, the second grinding process is performed on the tooth surface. Since the cutting depth of the second grinding process is equal to or less than that of the first grinding process, the protruding portion of the waviness generated on the tooth surface by the first grinding process is ground by the second grinding process. That is, at least one of the apex or protruding end of the waviness is ground to reduce its height. In addition, the feed rate of the grinding tool in the second grinding process is deviated by a predetermined amount from the feed rate in the first grinding process. Therefore, the period or pitch of the waviness that is expected to be generated when the second grinding process is performed is deviated from the period or pitch of the waviness generated by the first grinding process. Therefore, the apex or protruding end of the waviness generated in the first grinding process is ground heavily, not ground at all, or ground moderately in the second grinding process, resulting in an irregular mixture of waviness with different degrees of processing in the second grinding process. In other words, the periodicity of the waviness generated on the tooth surface is almost eliminated, so to speak, randomized. Even if gear noise occurs on the tooth surface of the gear obtained in this way, a specific non-integer gear noise will not be noticeable, and the gear noise will be dispersed into multiple non-integer gear noises of different orders, resulting in a gear with no or little discomfort in the gear noise. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a process diagram for explaining a processing order or a processing process in the embodiment of the present invention. [Diagram 2] FIG. 2A is a schematic diagram of a grindstone used in an embodiment of the present invention, and FIG. 2B is a diagram illustrating the state of grinding by the grindstone. [Diagram 3] FIG. 4 is a diagram showing the cross-sectional shape of the ripples obtained in the precision grinding process, as measured. [Figure 4] FIG. 2 is a diagram showing the undulations in a schematic manner. [Diagram 5]FIG. 13 is a diagram showing a cross-sectional shape of a waviness that is expected to occur by additional machining. [Figure 6] FIG. 13 is a diagram showing a cross-sectional shape of a waviness resulting from additional machining. [Figure 7] 1A is a graph showing measurement results of non-integer order gear noise for a gear produced by a conventional method without additional machining, and FIG. 1B is a graph showing measurement results of non-integer order gear noise for a gear produced by the method of the present invention with additional machining. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Next, the present invention will be described based on the embodiment shown in the drawings. Note that the embodiment described below is merely one example of a specific embodiment of the present invention, and is not intended to limit the present invention.

[0010] The present invention is a processing method for eliminating or reducing the periodicity of waviness (fine irregularities) on a tooth surface that occurs in a precision grinding process as a finish process for the tooth surface by removing part of the waviness through additional processing. In other words, the method is characterized in that, rather than imparting non-periodicity to the behavior of the grinding tool in the finish grinding process, the periodic waviness on the tooth surface is eliminated or reduced by superimposing a grinding process with a different periodicity on the periodic waviness.

[0011] Therefore, the processing method according to the embodiment of the present invention is characterized by a precision polishing process (precise grinding process) which is a finishing process, and additional processing is performed after the precision grinding process, or at least two precision grinding processes are performed. As an example, such finishing can be performed in a generating grinding process using a grinding wheel with a multiple-threaded thread. FIG. 1 shows an example of a processing process according to the processing method of the present invention by the trajectory of the grinding wheel, in which the grinding wheel is fed in a specified direction relative to the workpiece to perform rough cutting, and then the grinding wheel is fed in the opposite direction to the previous direction to perform a precision grinding 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 grinding process to perform additional processing (or a second precision grinding process, which corresponds to the second grinding process in the embodiment of the present invention).

[0012] Figure 2 shows a schematic example of grinding a tooth flank 2 after rough cutting using a grindstone 1 with five spiral grooves, with the grindstone 1 rotating (spinning) in the counterclockwise direction in Figure 2 around a central axis perpendicular to the paper surface of Figure 2(a). The depths of the spiral grooves g1, g2, g3, g4, and g5 are shown in Figure 2(a). The grindstone 1 grinds the tooth flank 2 by rotating in contact with the tooth flank 2, so the amount of downward movement or pressure in Figure 2(a) is the cutting amount, and the amount of movement along the tooth flank 2 and in a direction perpendicular to the axis of rotation (to the right in Figure 2(a)) is the feed amount.

[0013] In the example shown in FIG. 2(a), the first groove g1 has the largest amount of cut, followed by the second groove g2 and the fifth groove g5, and the third groove g3 and the fourth groove g4 has the smallest amount of cut. The amount of movement (feed) during one rotation of the grinding wheel 1 is set to be slightly smaller than the circumferential length (length of the outer periphery) of the grinding wheel 1. Therefore, during the grinding process using 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, so that a cut is generated according to the trajectory of the first groove g1, as shown in FIG. 2(b). The third groove g3 faces the tooth surface 2 due to the feed during one rotation of the grinding wheel 1, 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 then the fifth groove g5 comes into contact (presses) with the tooth surface 2, and a cut is generated by the fifth groove g5.

[0014] In the process of cutting by the fifth groove g5, a cut is made by the first groove g1. Since the amount of cutting by the first groove g1 is large, the fourth groove g4 does not come into contact with the tooth flank 2 and no cut is made by the fourth groove g4. As a result, an uneven shape, i.e., a waviness, is formed on the tooth flank 2, with so-called convex portions cut small by the fifth groove g5 and the second groove g2 between so-called concave portions cut large by the first groove g1.

[0015] In Fig. 3, the shape of the ripples W obtained in an actual precision grinding process is shown with the vertical axis representing the ripple height and the horizontal axis representing the position along the tooth surface (the feed direction of the grinding wheel 1). This is shown diagrammatically in Fig. 4, where the ripples W are formed by cyclically repeating concaves and convexes in the feed direction. In Fig. 4, the spacing (pitch) of the ripples W is indicated by the symbol P, which in the example shown in Fig. 2 above is represented by the product of the number of grooves J in the grinding wheel 1 and the feed amount F per rotation. Also in Fig. 4, the height (or depth) of the ripples W is indicated by the symbol H, which in the example shown in Fig. 2 above corresponds to the amount of cut by the first groove g1.

[0016] In the precision grinding process alone, or in the precision grinding process for the first finish, a waviness W, as shown diagrammatically in Fig. 4, is formed on the tooth flank 2. Therefore, if a gear is used in a given power transmission mechanism as is, the waviness W causes periodic fluctuations in the amount of rotation or torque, which results in non-integer vibration or noise (gear noise). In the processing method according to the embodiment of the present invention, an additional process or a second precision grinding process (hereinafter collectively referred to as additional process) is carried out to irregularly remove the protruding portions of the waviness W generated in the first precision grinding process, as diagrammatically shown in Fig. 4, at least within a given range, such as within the range of the face width or within the range of the tooth flank 2 that is mainly involved in torque transmission.

[0017] The additional machining in the embodiment of the present invention is a grinding process using the grindstone 1 used in the immediately preceding precision grinding process, and is preferably performed consecutively to the first precision grinding process. Since a rotating tool such as a grindstone 1 with a multiple thread shape is used, the additional machining is a grinding process that generates wavy lines, but by making the cutting depth and feed amount in the additional machining different from those in the first precision grinding process, the wavy lines W generated in the preceding first precision grinding process can be made irregular and non-periodic.

[0018] Specifically, the amount of cut in the additional processing is made smaller than the amount of cut in the first precision grinding process. For example, the distance between the center of the grinding wheel 1 and the center of the workpiece (the gear that is the object to be ground) is made slightly smaller than the distance in the first precision grinding process. Therefore, in the additional processing, the grinding wheel 1 does not come into contact with the bottom parts of the recesses in the waviness W that occurred in the preceding first precision grinding process, and does not process these parts, but processes only the protruding parts, thereby partially removing them. In other words, the reduction in the amount of cut in the additional processing is an amount smaller than the height H of the waviness W that has already been formed (0≦reduction amount <H)である。

[0019] The feed amount in the additional machining is an amount that deviates slightly from the feed amount F in the first precision grinding process described above, and is the actual feed amount or feed control amount of the grinding wheel 1. Here, "amount that deviates slightly" means that the ratio of the feed amount in the additional machining to the feed amount F in the first precision grinding process is not an integer, or is not "1 / integer." Therefore, the feed amount in the additional machining may be smaller than the feed amount F in the first precision grinding process, but in terms of gear machining efficiency or machining speed, it is preferable that the feed amount (feed rate) in the additional machining is larger than the feed amount F (feed rate) in the first precision grinding process.

[0020] As described above, the additional machining is a grinding process in which a rotating grindstone is fed and moved, and therefore is a process that creates a waviness. The waviness W' that is expected to be created by the additional machining is shown in solid line in Figure 5. The example shown here is an example in which the feed rate is larger than the feed rate in the first precision grinding process, and the waviness has a pitch P' that is larger than the pitch P of the waviness W (broken line in Figure 5) already created on the tooth surface 2. Since the cutting depth in the additional machining is smaller than the cutting depth in the first precision grinding process, the waviness W' by the additional machining does not interfere with the bottom of the waviness W in the first precision grinding process, but the waviness W' by the additional machining interferes with the convex portion in the first precision grinding process, and the waviness is obtained by grinding or removing the convex portion. Depending on the differences in the pitches P, P' of each rib W, W', the amount of grinding of the convex portions of the ribs W in the first precision grinding process will vary, and convex portions that are ground away significantly, convex portions that are ground away only slightly, and convex portions that are not ground at all will be mixed and arranged irregularly.

[0021] FIG. 6 shows a schematic diagram of the waviness W0 on the tooth surface 2 after additional machining. The shape shown here is the shape of the waviness W produced by the first precision grinding process after some of the protruding parts have been removed by additional machining. In other words, it is the shape obtained by connecting the lower lines of the waviness W shown by the broken line and the waviness W' shown by the solid line in FIG. 5. As described above, the cutting depth and feed amount of the grinding wheel 1 in the additional machining are made different from those in the first precision grinding process, so that the height H0 and pitch P0 of the obtained waviness W0 are not uniform. In other words, the so-called periodicity is lost.

[0022] In this way, according to the processing method of the embodiment of the present invention, the pitch P0 and height H0 of the swell W0 on the tooth surface are randomized. As a result, even if non-integer gear noise that is not related to the number of teeth occurs when the tooth surfaces contact each other to transmit torque, a specific non-integer gear noise does not become prominent, and the vibration or noise is dispersed into multiple non-integer gear noises. Figures 7(a) and (b) show simplified measurements of non-integer gear noise obtained in an experiment conducted by the present inventors. Figure 7(a) shows the measurement results of non-integer gear noise for a gear that has been subjected to only the first precision grinding process and has not been subjected to additional machining, and Figure 7(b) shows the measurement results of non-integer gear noise for a gear that has also been subjected to additional machining. In these figures, the solid line sloping upward to the right indicates the non-integer gear noise, and the thicker the line, the higher the sound pressure level.

[0023] As shown in FIG. 7(a), in the gear that is not subjected to additional machining, the specific non-integer gear noise Na becomes large, which causes an unnatural feeling. In contrast, as shown in FIG. 7(b), in the gear that has been subjected to the above-mentioned additional machining in addition to the first precision grinding process, it can be seen that multiple non-integer gear noises Nb, Nc, and Nd are generated, and the specific non-integer gear noises are not particularly large, and the sound pressure levels of all of them are relatively low. Therefore, these multiple non-integer gear noises are easily blended into so-called background noise, and when the gear is used in the transmission mechanism of a vehicle (such as a BEV vehicle, HEV vehicle, or PHEV vehicle), the non-integer gear noise generated by the gear does not cause an unnatural feeling even at a low vehicle speed where the noise of the entire vehicle is low. In other words, according to the method of the present invention, it is possible to obtain a gear with reduced gear noise (particularly non-integer gear noise). Moreover, since the additional machining can be performed using the grindstone used in the previous precision grinding process, the machining cost can be suppressed and the machining can be performed efficiently.

[0024] The present invention is not limited to the above-described embodiment, and can be applied to form grinding as well as generating grinding. The grinding wheel (grinding tool) used in the present invention may be a tool other than a multiple-threaded grinding wheel. [Explanation of symbols]

[0025] 1. Grindstone 2 Tooth surface F Feed rate H,H0 Swell height J Number of articles P,P0 pitch W, W', W0 Wavy g1, g2, g3, g4, g5 (grinding wheel) spiral grooves

Claims

[Claim 1] A method for grinding a gear by feeding a grinding tool rotating about a central axis along a tooth surface of a gear in a direction perpendicular to the central axis, the method comprising the steps of: a first grinding process is performed by moving the grinding tool along the tooth surface at a first predetermined cutting depth and a first feed rate, A second grinding process is performed by moving the grinding tool along the tooth surface on which the first grinding process has been performed, at a second cutting depth equal to or less than the first cutting depth and at a second feed speed deviating from the first feed speed by a predetermined amount. A gear machining method comprising the steps of:

Images