Gear and grinding method

Abstract

The present invention provides a gear that can reduce gear noise by dispersing excitation energy, and a method for grinding the gear therefor. [Solution] A gear having a grinding tooth surface with a plurality of main recesses along the tooth height direction and a plurality of main protrusions between the main recesses, wherein a plurality of sub-protrusions that demarcate a plurality of sub-recesses shallower than the main recesses are formed at the top of the main protrusions at intervals in the tooth width direction. The feed rate during grinding is changed and the feed rate during grinding is determined based on the DFT analysis results of the tooth surface undulation shape of the obtained gear.

Description

Technical Field

[0001] The present invention relates to a gear and a method for grinding its tooth surface, and particularly to a gear obtained by grinding the tooth surface with a helical grinding wheel and a method for grinding the tooth surface with a helical grinding wheel.

Background Art

[0002] In a gear device, when teeth mesh with each other to transmit torque, meshing noise (gear noise) inevitably occurs. One of the causes of gear noise is known to be irregularities such as fine machining marks or streaks formed on the tooth surface. Conventionally, various attempts have been made to improve the irregularities on the tooth surface in order to reduce gear noise. For example, in Patent Document 1, when a grinding wheel is fed in the axial direction or the tooth width direction of a gear to grind the tooth surface, a method is described in which the feed rate of the grinding wheel is changed along the stroke length along the width of the surface of the tooth. According to this processing method, the interval of fine scratches caused by grinding becomes irregular along the width of the surface of the tooth, and as a result, it is said that a gear with low gear noise can be obtained.

[0003] Further, in Patent Document 2, a processing method is described in which, in order to reduce the height of undulations formed on the grinding surface, the feed amount during spark-out grinding is shifted in phase each time by an amount equal to the amount divided by the number of spark-out grinding times.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Gear noise occurs when teeth mesh and slide relative to each other along their tooth surfaces, due to the repeated forces that separate and bring together the tooth surfaces caused by irregularities on the tooth surfaces. Therefore, for example, if the height of the protrusions on the tooth surface is high, the force pushing the tooth surfaces apart becomes larger, which is likely to increase gear noise. According to the gear or tooth surface grinding method described in Patent Document 1, the so-called irregularities such as scratches caused by grinding become irregular, but if the height of the irregularly occurring protrusions is high, the excitation force generated at that point becomes large, so the gear noise may not necessarily be reduced.

[0006] Furthermore, the machining method described in Patent Document 2 is a method in which spark-out grinding is performed on the surface after grinding by applying feed to the grinding wheel, and it cannot be applied to machining gears using a screw-shaped grinding wheel, or it is difficult to apply it to grinding the tooth surface of gears due to increased man-hours and costs. In addition, the machining method in Patent Document 2 is a method that reduces the so-called height of the irregularities, so the repetition of the irregularities remains. For this reason, when the torque transmitted by the gear is large or the rotational speed is high, it may not necessarily reduce gear noise.

[0007] This invention has been made in view of the above technical problems, and aims to provide a gear that can reduce gear noise by dispersing excitation energy, and a method for grinding the gear therefor. [Means for solving the problem]

[0008] To achieve the above objective, the gear of the present invention is a gear in which a plurality of main recessed portions and a plurality of main convex portions between the main recessed portions are formed on the ground tooth surface, wherein a plurality of sub-convex portions that demarcate a plurality of sub-recessed portions shallower than the main recessed portions are formed at intervals in the tooth width direction of the gear at the top of the main convex portions.

[0009] In the gear of the present invention, the width of the portion where the plurality of sub-recessed grooves are provided may be half or more of the width of the main protruding groove and less than the width of the main protruding groove.

[0010] In the gear of the present invention, the spacing between the sub-ridges in the tooth width direction may be equal.

[0011] The present invention provides a method for grinding gears, wherein a plurality of threaded grinding wheels are rotated and relatively fed in the tooth width direction of the tooth surface to grind the tooth surface, thereby forming a plurality of recessed portions and a plurality of raised portions that demarcate the recessed portions on the tooth surface, characterized in that a predetermined thread on the grinding wheel forms a plurality of main recessed portions and main raised portions that are the portions between the main recessed portions on the tooth surface, and a plurality of sub-recessed portions that are shallower than the main recessed portions and a plurality of sub-raised portions that demarcate the sub-recessed portions are formed at intervals in the tooth width direction on the top of the main raised portions by other threads adjacent to the predetermined thread, and the relative feed speed of the grinding wheel in the tooth width direction is set to a speed at which the intervals between the sub-recessed portions are equal to perform the grinding of the tooth surface.

[0012] In the method of the present invention, the feed rate may be set to a speed at which the width of the locations where the plurality of sub-recessed grooves are provided is at least half the width of the main protruding groove and less than the width of the main protruding groove.

[0013] Furthermore, the present invention is a method for grinding gears in which a plurality of screw-shaped grinding wheels are rotated and relatively fed in the tooth width direction of the tooth surface to grind the tooth surface, thereby forming a plurality of recessed portions and a plurality of raised portions that demarcate the recessed portions on the tooth surface, wherein a predetermined screw thread on the grinding wheel forms a plurality of main recessed portions and main raised portions that are the portions between the main recessed portions, and a plurality of sub-recessed portions that are shallower than the main recessed portions and a plurality of sub-raised portions that demarcate the sub-recessed portions are formed at intervals in the tooth width direction on the top of the main raised portions by other screw threads adjacent to the predetermined screw thread, and grinding is attempted by setting the relative feed speed of the grinding wheel in the tooth width direction to a predetermined speed, and the amplitude of meshing that occurs in the resulting gear is determined, and the feed speed is determined based on the amplitude.

[0014] In the method of the present invention, the grinding trial may be performed multiple times by changing the feed rate, and the feed rate that produces the smallest amplitude among the amplitudes obtained from the multiple trials may be set as the feed rate for grinding the tooth surface. [Effects of the Invention]

[0015] According to the present invention, the tooth surface is formed by a plurality of main recessed and main protruding portions arranged in parallel at predetermined intervals, and a plurality of sub-recessed portions formed in parallel at the top of each main protruding portion, with the sub-recessed portions being shallower than the main recessed portions. Therefore, the excitation energy caused by the so-called irregularities on the tooth surface when the gears mesh and transmit torque is dispersed by the main protruding portions and the plurality of sub-recessed portions relative to one main protruding portion, resulting in a reduction in the peak value of so-called gear noise. In other words, a gear with low gear noise can be obtained. Furthermore, according to the grinding method of the present invention, the feed rate during grinding only needs to be maintained at the feed rate with the smallest peak value of gear noise obtained through trials, thus simplifying the grinding operation. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic perspective view showing the process of grinding gears using a screw grinding wheel. [Figure 2] This is a partial perspective view schematically showing the uneven shape that occurs on the tooth surface. [Figure 3] These are schematic cross-sectional diagrams showing the uneven shape due to differences in feed rate; (a) is a cross-sectional diagram when the feed rate is slow, and (b) is a cross-sectional diagram when the feed rate is fast. [Figure 4] Figure 3 shows a diagram illustrating the results of DFT analysis on the tooth surface of a gear with an uneven shape, where (a) shows the results of DFT analysis on the gear with an uneven shape shown in Figure 3(a), and (b) shows the results of DFT analysis on the gear with an uneven shape shown in Figure 3(b). [Figure 5] This is a process diagram illustrating the grinding method according to the present invention. [Modes for carrying out the invention]

[0017] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0018] The gear 1 according to the present invention may be an appropriate gear such as a spur gear, a helical gear, an external gear, or an internal gear, and is a gear formed by grinding the tooth surface. The grinding is performed using a plurality of screw-shaped grinding wheels. The state of the grinding is schematically shown in FIG. 1. The grinding wheel 2 is formed into a cylinder as a whole with a plurality of screw threads 3 spirally formed on the outer peripheral surface, and is held by a rotating shaft (not shown) with the central axis horizontal. On the other hand, the gear 1 is held by another rotating shaft, which is a so-called vertical axis, with the rotation central axis directed in the vertical direction. Either one of the gear 1 and the grinding wheel 2 is movable so as to approach and separate from the other, and is also relatively movable in the vertical direction. Then, the screw thread 3 of the grinding wheel 2 and the tooth 4 of the gear 1 are meshed, and in this state, the grinding wheel 2 and the gear 1 are rotated synchronously, so that the screw thread 3 rubs against the tooth surface to perform grinding. Further, since the screw thread 3 is spiral, the teeth 4 are sequentially meshed with the screw thread 3 of the grinding wheel 2 and are ground. Further, in order to perform grinding over the entire width direction of the tooth, either one of the gear 1 and the grinding wheel 2 is reciprocated relatively in the vertical direction (the width direction of the gear 1) with respect to the other. This relative movement in this direction is referred to as feed.

[0019] Therefore, the grinding of the tooth surface is performed by the sequential and repeated contact of the plurality of screw threads 3, resulting in so-called intermittent grinding. Therefore, inevitably, unevenness is formed on the tooth surface. The state is schematically shown in FIG. 2. Since the grinding wheel 2 rotates about the horizontal axis and the grinding wheel 2 and the gear 1 move relatively in the vertical direction, the unevenness of the tooth surface is formed by a plurality of concave strip portions (concave groove portions) 5 substantially along the tooth flank direction and arranged in the width direction, and a plurality of convex strip portions 6 partitioning these concave strip portions 5. Here, the width direction intersecting these concave strip portions 5 and convex strip portions 6 is the relative movement direction between the gear 1 and the grinding wheel 2, that is, the feed direction. The depth and height of the unevenness in the embodiment described here are about several μm, and the width is about several mm.

[0020] Such concavities and convexities are caused by the rotation of the grinding wheel 2 and the intermittent contact of each thread 3 thereof with the tooth surface. In that case, there occurs runout of the grinding wheel 2 with respect to the gear 1 due to a slight deviation of the rotation axis of the grinding wheel 2, a dimensional error of the grinding wheel 2, or vibration or the like. The runout means, for example, with respect to a predetermined thread (assumed to be the first thread) where the grinding depth is the deepest, other threads (assuming three threads as an example, the second thread and the third thread) adjacent to the first thread retreat in a direction away from the gear 1 and are in a state of grinding shallowly. As a result, a plurality of shallow concave strip portions are machined between the deep concave strip portions 5.

[0021] The concavo-convex shape in which the concave strip portion 5 or the convex strip portion 6 overlaps is shown in schematic cross-sectional views in FIGS. 3(a) and (b). FIG. 3(a) shows the concavo-convex shape obtained when the feed rate is relatively slow, and FIG. 3(b) shows the concavo-convex shape obtained when the feed rate is faster than that in the case of FIG. 3(a). The example shown here is an example when grinding with a three-thread grinding wheel. When the concave strip portion 5a formed by the aforementioned first thread 3a is the deepest and this is taken as the main concave strip portion 5a, the main concave strip portions 5a are formed at a predetermined interval (pitch) according to the feed rate. Therefore, the portion between these main concave strip portions 5a is the main convex strip portion 6a that is convex on the tooth surface, and the interval (pitch) of the main concave strip portions 5a is the width of the main convex strip portion 6a.

[0022] While the first thread 3a is grinding the tooth surface, the aforementioned second thread 3b and third thread 3c contact the tooth surface and perform grinding, but the grinding depth is shallower than that by the first thread 3a. Therefore, the second thread 3b and the third thread 3c grind the top of the main convex strip portion 6a described above. The shallow concave strip portions formed at the top of the main convex strip portion 6a in this way are the sub-concave strip portions 5b, and these sub-concave strip portions 5b are equidistant from each other and are shifted by one-third (1 / 3) each with respect to the interval (pitch) of the main concave strip portions 5a in the case of a three-thread grinding wheel. The portion between the sub-concave strip portions 5b formed in this way and the portion partitioning the sub-concave strip portions 5b become the sub-convex strip portion 6b.

[0023] As the grinding wheel 2 rotates and is fed in the width direction of the gear 1, the distance between the concave ridges 5 and the convex ridges 6 increases with increasing feed rate. That is, when the feed rate is relatively slow, as shown in Figure 3(a), the width of the main convex ridge 6a narrows, and the sub-concave ridges 5b and sub-convex ridges 6b formed at its tops come closer together. In a typical example, the tip edges of the second thread ridge 3b and the third thread ridge 3c (the bottom of the sub-concave ridge 5b) separate from the main convex ridge 6a. As a result, the top of the main convex ridge 6a is ground as a slope that becomes part of the sub-concave ridge 5b, and no so-called recessed area is created. Therefore, the sub-concave ridge 5b becomes more like a flat or inclined surface than a recess, and the main convex ridge 6a becomes a convex part with a gently sloping, pointed top or a narrow, flat shape. In other words, the irregularities on the tooth surface are essentially formed by the main recessed portion 5a and the main raised portion 6a.

[0024] In contrast, when the feed rate is increased, as shown in Figure 3(b), the width of the main protruding ridge 6a increases, and sub-recessed ridges 5b are formed at its top, with wider spacing between them and wider openings. In the case of a three-ridge grinding wheel, three sub-protruding ridges 6b demarcate these sub-recessed ridges 5b, and these ridges are formed at equal intervals. Furthermore, the depth of the sub-recessed ridges 5b is greater compared to when the feed rate is slow. That is, the bottom of each sub-recessed ridge 5b (the part where the tangency is horizontal) is formed at the top of the main protruding ridge 6a. The height of the sub-protruding ridges 6b is measured from the deepest part (bottom) of the main recessed ridge 5a, and the height of the sub-protruding ridges 6b does not particularly differ between the slow and fast feed rates. Therefore, when the feed rate is increased, the resulting uneven shape on the tooth surface is such that multiple shallow secondary recesses 5b are formed at the top of the wide main protrusions 6a; in other words, smaller irregularities (irregularities with small recess depths and small protrusion heights) are formed and mixed in between larger irregularities, and this pattern repeats.

[0025] Here, the depth of the recess is the dimension from the bottom of the recessed area on the tooth thickness side to the tip (apex) of the surface that smoothly continues from that bottom, and this corresponds to the height of the convex portion. Furthermore, since the depth of these recesses and the height of the convex portions affect the vibration or noise generated by the sliding contact between the tooth surfaces, the depth of the recesses and the height of the convex portions can be defined according to the direction of sliding contact. For example, in the example shown in Figure 3(b), if the sliding contact direction is from left to right, the height of the left secondary convex portion 6b is the height from the bottom of the main recessed portion 5a, making it the highest, while the heights of the other secondary convex portions 6b are the heights from the bottom of the secondary recessed portion 5b, making them lower.

[0026] Gear noise is generated by the irregularities (or machined grooves) on the tooth surface described above, which act as excitation sources. Therefore, the undulation shape of the tooth surface was analyzed using Discrete Fourier Transform (DFT) for gears with the irregular shape shown in Figure 3(a), i.e., gears ground at a slow feed rate, and gears with the irregular shape shown in Figure 3(b), i.e., gears ground at a fast feed rate. Similar results can be obtained by DFT analysis of the vibration of the gears when rotated at a predetermined rotational speed and transmitted torque. Examples of such analysis results are shown in Figures 4(a) and (b).

[0027] Figure 4(a) shows the analysis results for a gear ground to achieve the uneven shape shown in Figure 3(a) above by slowing down the feed rate, where the amplitude of the first-order vibration is extremely large compared to the amplitudes of vibrations of other orders. In contrast, Figure 4(b) shows the analysis results for a gear ground to achieve the uneven shape shown in Figure 3(b) above by increasing the feed rate, where the amplitude of the first-order vibration is about the same as, or even smaller than, the amplitude of the second-order vibration.

[0028] From this analysis, it can be seen that in gears whose tooth surfaces are ground to create the uneven shape shown in Figure 3(a), the excitation energy is concentrated, causing vibration and resulting in increased noise (gear noise) due to primary vibration. In contrast, in gears whose tooth surfaces are ground to create the uneven shape shown in Figure 3(b), the excitation energy is dispersed by the secondary recessed portion 5b and the resulting secondary protrusion 6b formed at the top of the main protrusion portion 6a, causing vibration. Even if some noise (gear noise) from secondary vibration is generated in addition to noise (gear noise) from primary vibration, the amplitude of this vibration is small, resulting in overall gear noise being lower than that of gears where the feed rate during grinding is slowed. Furthermore, gears that exhibit such gear noise reduction effects are those in which the width of the portion of the main protruding portion 6a where the secondary recessed portion 5b is provided is less than the width of the main protruding portion 6a (the spacing between the main recessed portions 5a), and the tooth surface has irregularities (i.e., ground grooves or undulations on the tooth surface) that are more than half the width of the main protruding portion 6a.

[0029] The grinding method according to the present invention is a method for obtaining a gear that can reduce gear noise by dispersing the above-mentioned excitation energy. The grinding wheel used is a multi-threaded threaded grinding wheel. As explained with reference to Figure 1, the grinding wheel is rotated about a horizontal axis, and the gear is held so as to be rotatable about an axis along the vertical direction. The threads of the grinding wheel are engaged with the teeth of the gear and rotated, and the grinding wheel and the gear are moved relative to each other in the vertical direction. In the grinding method according to the present invention, a trial is performed to determine the feed rate. Figure 5 shows the work process in a block diagram. In the example shown in Figure 5, an example is shown in which a grinding trial T is performed by changing the feed rate to three types: "low," "medium," and "high."

[0030] As mentioned above, when the feed rate is slow, the spacing between the main recessed parts 5a becomes narrower, and the width of the main convex parts 6a decreases, and the same applies to the secondary recessed parts 5b and secondary convex parts 6b. Therefore, the secondary recessed parts 5b and secondary convex parts 6b are not clearly formed at the top of the main convex parts 6a, and in effect, the irregularities on the tooth surface are formed only by the main recessed parts 5a and main convex parts 6a. Conversely, the faster the feed rate, the wider the spacing between the main recessed parts 5a becomes, and the wider the width of the main convex parts 6a, and the same applies to the secondary recessed parts 5b and secondary convex parts 6b, and therefore the secondary recessed parts 5b and secondary convex parts 6b formed at the top of the main convex parts 6a become clearer.

[0031] The undulation shape (concave and convex shape) of the tooth surface of the gear that has been ground in trial T is analyzed by discrete Fourier transform (DFT) A. Alternatively, the gear obtained in trial T may be incorporated into an appropriate gear mechanism and rotated, and the vibration in that case may be analyzed by DFT. As explained with reference to Figure 4, the amplitude of a predetermined order changes according to the feed rate, and the faster the feed rate at a predetermined rotational speed, the more the excitation energy is dispersed and the lower the amplitude peak becomes. In other words, a gear with less gear noise is produced. In the method of the present invention, the feed rate D is determined based on the results of the DFT analysis A of the gear obtained in trial T. Specifically, the feed rate used when grinding a gear with a small amplitude peak is adopted. The convex and convex shape that occurs on the tooth surface when grinding at the feed rate determined in this way is almost the same as the convex and convex shape shown in Figure 3(b) above, that is, a shape in which multiple sub-concave parts 5b and sub-convex parts 6b are formed at the top of the main convex part 6a. In other words, the resulting surface has a textured shape in which smaller irregularities caused by the secondary recessed sections 5b and secondary raised sections 6b are interspersed within larger irregularities caused by the main recessed sections 5a and main raised sections 6a.

[0032] It should be noted that the present invention is not limited to the embodiments described above, and the grinding according to the present invention may be performed as one step in the manufacturing process, or as a separate step from the manufacturing process. [Explanation of Symbols]

[0033] 1 gear 2 whetstones 3a, 3b, 3c threaded strips 4 teeth 5 Concave section 5a Main groove 5b Sub-concave part 6. Convex part 6a Main protruding section 6b Sub-convex part A DFT analysis D. Determination of feed rate T trial

Claims

1. A gear having a ground tooth surface formed with a plurality of main recesses along the tooth height direction and a plurality of main protrusions between the main recesses, Multiple sub-protrusions, which delineate multiple sub-recesses that are shallower than the main recess, are formed at intervals in the tooth width direction of the gear at the top of the main protrusion, and these sub-protrusions are formed at intervals in the tooth width direction of the gear. A gear characterized by the following features.

2. The gear according to claim 1, The width of the area where multiple sub-recessed grooves are provided is at least half the width of the main protruding groove and less than the width of the main protruding groove. A gear characterized by the following features.

3. A gear according to claim 1 or 2, The spacing of the aforementioned sub-ridges in the tooth width direction is equal. A gear characterized by the following features.

4. A gear grinding method comprising grinding the tooth surface by rotating and relatively feeding multiple threaded grinding wheels in the tooth width direction of the tooth surface, thereby forming multiple recessed portions and multiple raised portions that demarcate the recessed portions on the tooth surface, The predetermined threads in the grinding wheel form a plurality of main recessed portions along the tooth height direction of the tooth surface and main convex portions which are the portions between the main recessed portions, and Multiple sub-recesses and multiple sub-protrusions that demarcate the sub-recesses are formed at the top of the main protrusion, with spacing in the tooth width direction, by other threads adjacent to the predetermined thread. The tooth surface is ground by setting the relative feed rate of the grinding wheel in the tooth width direction to a speed at which the intervals between the sub-recesses become equal. A gear grinding method characterized by the following features.

5. A method for grinding gears according to claim 4, The feed rate is set to a speed such that the width of the area where the multiple sub-recesses are provided is at least half the width of the main protrusion and less than the width of the main protrusion. A gear grinding method characterized by the following features.

6. A gear grinding method comprising grinding the tooth surface by rotating and relatively feeding multiple threaded grinding wheels in the tooth width direction of the tooth surface, thereby forming multiple recessed portions and multiple raised portions that demarcate the recessed portions on the tooth surface, The predetermined threads in the grinding wheel form a plurality of main recessed portions along the tooth height direction of the tooth surface and main convex portions which are the portions between the main recessed portions, and Multiple sub-recesses and multiple sub-protrusions that demarcate the sub-recesses are formed at the top of the main protrusion, with spacing in the tooth width direction, by other threads adjacent to the predetermined thread. The relative feed rate of the grinding wheel in the tooth width direction is set to a predetermined speed, and grinding is attempted. The amplitude of the meshing that occurs in the resulting gear is then determined. The feed rate is determined based on the amplitude. A gear grinding method characterized by the following features.

7. A method for grinding gears according to claim 6, The aforementioned feed rate is changed, and the grinding trial is performed multiple times. The feed rate that yields the smallest amplitude among the multiple trials mentioned above is determined as the feed rate for grinding the tooth surface. A gear grinding method characterized by the following features.

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