Gear pair

Abstract

This gear pair comprises a first gear and a second gear. The first gear has a first available tooth surface and the second gear has a second available tooth surface, which can be brought into contact with each other. The first available tooth surface has an arithmetic average roughness Ra1 of 0.05-0.50 μm, and the second available tooth surface has an arithmetic average roughness Ra2 of 0.01-0.15 μm. The arithmetic average roughness Ra1 is greater than the arithmetic average roughness Ra2. With regard to the first available tooth surface, as per a load curve of a contour curve, the ratio of a cutting level difference Rδc (1-60%) to a cutting level difference Rδc (1-98%) is 0.15-0.30.

Description

Gear Pair

[0001] The present disclosure relates to gear pairs.

[0002] When gear pairs rotate at high speeds, the lubricant loses its agitation, causing its temperature to rise and its viscosity to decrease. To achieve better fuel economy, the use of low-viscosity lubricants for the gears of automobiles and industrial machinery has become more common in recent years. When the viscosity of the lubricant decreases, the coefficient of friction between the meshing tooth surfaces of the gear pairs increases in poorly lubricated conditions, where the oil film thickness on the gear tooth surfaces is thin. Therefore, when gear pairs are used in poorly lubricated conditions, this can increase friction loss and reduce transmission efficiency.

[0003] It is known that smoothing the tooth flanks of gear pairs reduces the coefficient of friction between the mating tooth flanks when used under poor lubrication conditions. However, under certain conditions, smoothing the tooth flanks reduces the ability of the tooth flanks to retain lubricant, which can actually increase the coefficient of friction between the mating tooth flanks of the gear pair.

[0004] Patent Document 1 discloses a gear train that includes a pair of meshing gears having a predetermined Vickers hardness and a predetermined peak height, and that has high meshing transmission efficiency during initial operation and completes break-in quickly. Figures 3 and 4 of Patent Document 1 show, by means of a tooth surface roughness curve and a load curve, that one gear of the pair of meshing gears has smoother tooth surface characteristics than the other gear.

[0005] Patent Document 2 discloses gears that have a predetermined protruding valley depth of the plateau portion and a predetermined area occupied by recesses in the plateau portion, and that can widen the operating region where the coefficient of friction between a pair of meshing tooth flanks is small. Figure 5 of Patent Document 1 shows, using a load curve of the tooth surface roughness curve, that the tooth surface of the third drive gear has larger irregularities than the tooth surface of the third driven gear.

[0006] Patent Document 3 discloses gears with excellent spalling resistance obtained from gear steel having a predetermined chemical composition. Figures 10 and 11 of Patent Document 3 show surface roughness curves and relative load curves for gears of examples and comparative examples.

[0007] JP 2014-137082 A JP 2013-083322 A JP 2010-185123 A

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide a gear pair in which the coefficient of friction between the meshing tooth flanks is reduced.

[0009] The gear pair of the present disclosure comprises a first gear and a second gear, wherein the first gear comprises: a plurality of first tooth crests; a plurality of first tooth roots; a first tooth flank located between the first tooth crests and the first tooth roots and facing a first side in the circumferential direction of the first gear; and a second tooth flank located between the first tooth crests and the first tooth roots and facing a second side in the circumferential direction of the first gear, wherein the first tooth flank comprises: a first usable tooth flank adjacent to the first tooth crests; and a first fillet located radially inward of the first gear from the first usable tooth flank and adjacent to the first tooth root, and wherein the second gear comprises: a plurality of second tooth crests; a plurality of second tooth roots. the second gear has a third tooth flank located between the second tooth crest and the second tooth root and facing a third side in the circumferential direction of the second gear; and a fourth tooth flank located between the second tooth crest and the second tooth root and facing a fourth side in the circumferential direction of the second gear, the third tooth flank having: a second usable tooth flank adjacent to the second tooth crest; and a second fillet located radially inward of the second gear from the second usable tooth flank and adjacent to the second tooth root; the first usable tooth flank and the second usable tooth flank are contactable; the arithmetic mean roughness Ra1 of the first usable tooth flank is 0.05 μm or more and 0.50 μm or less; and the arithmetic mean roughness Ra2 of the second usable tooth flank is 0.01 μm or more and 0.15 μm or less; The arithmetic mean roughness Ra1 is greater than the arithmetic mean roughness Ra2, and the first usable tooth surface has, with respect to a cut level difference Rδc of the profile curve and a load length ratio Rmr(c) in a load curve of the profile curve, a ratio of a cut level difference Rδc(1%-60%) of a cut level c1% at a load length ratio Rmr(1%) and a cut level c60% at a load length ratio Rmr(60%) to a cut level difference Rδc(1%-98%) of a cut level c1% at a load length ratio Rmr(1%) and a cut level c98% at a load length ratio Rmr(98%) is 0.15 or more and 0.30 or less.

[0010] The gear pairs of the present disclosure have a reduced coefficient of friction between the mating tooth flanks.

[0011] 1 is a cross-sectional schematic diagram of a gear pair according to an embodiment of the present disclosure; 2 is an enlarged schematic diagram of the meshing region of the gear pair shown in FIG. 1; 3 is an explanatory diagram showing the relationship between the profile shear level difference Rδc and the load length ratio Rmr(c) in the load curve of the profile curve of the usable tooth flank; 4 is a graph showing the relationship between the friction coefficient ratio between the flat surface of the disk and the surface of the ball, and the shear level difference Rδc (1%-60%) / shear level difference Rδc (1%-98%) of the flat surface of the disk, for the flat surface of the disk and the ball used in an MTM traction tester simulating gear pairs No. 1 to No. 10; and 5 is a load curve for the flat surface of each disk of No. 4, No. 5, and No. 10.

[0012] <Outline of Embodiments of the Invention of the Present Disclosure> Below, outlines of embodiments of the invention of the present disclosure will be listed and described. (1) A gear pair according to the present disclosure is a gear pair comprising a first gear and a second gear, wherein the first gear comprises: a plurality of first tooth crests; a plurality of first tooth roots; a first tooth flank located between the first tooth crests and the first tooth roots and facing a first circumferential side of the first gear; and a second tooth flank located between the first tooth crests and the first tooth roots and facing a second circumferential side of the first gear, wherein the first tooth flank comprises: a first usable tooth flank adjacent to the first tooth crests; and a first fillet located radially inward of the first gear from the first usable tooth flank and adjacent to the first tooth root; and wherein the second gear comprises: a plurality of second tooth crests; a plurality of second tooth roots. the second gear has a third tooth flank located between the second tooth crest and the second tooth root and facing a third side in the circumferential direction of the second gear; and a fourth tooth flank located between the second tooth crest and the second tooth root and facing a fourth side in the circumferential direction of the second gear, the third tooth flank having: a second usable tooth flank adjacent to the second tooth crest; and a second fillet located radially inward of the second gear from the second usable tooth flank and adjacent to the second tooth root; the first usable tooth flank and the second usable tooth flank are contactable; the arithmetic mean roughness Ra1 of the first usable tooth flank is 0.05 μm or more and 0.50 μm or less; and the arithmetic mean roughness Ra2 of the second usable tooth flank is 0.01 μm or more and 0.15 μm or less; The arithmetic mean roughness Ra1 is greater than the arithmetic mean roughness Ra2, and the first usable tooth surface has, with respect to a cut level difference Rδc of the profile curve and a load length ratio Rmr(c) in a load curve of the profile curve, a ratio of a cut level difference Rδc(1%-60%) of a cut level c1% at a load length ratio Rmr(1%) and a cut level c60% at a load length ratio Rmr(60%) to a cut level difference Rδc(1%-98%) of a cut level c1% at a load length ratio Rmr(1%) and a cut level c98% at a load length ratio Rmr(98%) is 0.15 or more and 0.30 or less.

[0013] According to the gear pair (1), the coefficient of friction between the meshing tooth surfaces is reduced.

[0014] (2) In the gear pair of the above (1), the first usable tooth surface and the second usable tooth surface are preferably made of steel.

[0015] (3) In the gear pair of the preferred (2) above, the first usable tooth surface and the second usable tooth surface each have a hardness of HV 500 or more and HV 860 or less.

[0016] (4) In a preferred gear pair according to any one of (1) to (3) above, the arithmetic mean roughness Ra1 is greater than the arithmetic mean roughness Ra2 by 0.05 μm or more and 0.35 μm or less.

[0017] (5) In a preferred gear pair according to any one of (1) to (4) above, the first usable tooth surface has a cutting level difference Rδc (1%-98%) of 1.20 μm or more and 2.10 μm or less, and a cutting level difference Rδc (1%-60%) of 0.10 μm or more and 0.50 μm or less.

[0018] According to the gear pairs (2) to (5), the coefficient of friction between the meshing tooth surfaces is further reduced.

[0019] <Details of the Embodiments of the Invention of the Present Disclosure> Hereinafter, embodiments of the present disclosure will be described. Note that in this disclosure, the embodiments of the invention are to be considered as illustrative in all respects and not restrictive. The scope of the rights of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0020] [Overall Configuration of Gear Pair] The overall configuration of a gear pair 1 according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional schematic view of the gear pair 1. Figure 2 is an enlarged schematic view of the meshing region of the gear pair 1 shown in Figure 1. Gear terminology is described in accordance with JIS B 0102:2013.

[0021] The gear pair 1 shown in FIG. 1 is a parallel-axis gear pair. The gear pair 1 is also an external gear pair. The gear pair 1 includes a first gear 10 and a first shaft 30, which is the rotation axis of the first gear 10, and a second gear 20 and a second shaft 40, which is the rotation axis of the second gear 20. The first gear 10 has a plurality of first teeth 11 and a plurality of first tooth roots 12 located between adjacent first teeth 11. The second gear 20 has a plurality of second teeth 21 and a plurality of second tooth roots 22 located between adjacent second teeth 21. Both the first gear 10 and the second gear 20 in the gear pair 1 are spur gears.

[0022] Two arrows in Fig. 1 indicate the rotation direction FRD of the first gear 10 and the rotation direction SRD of the second gear 20, respectively. Two double-headed arrows in Figs. 1 and 2 indicate the circumferential direction FCD of the first gear 10 and the circumferential direction SCD of the second gear 20. FIS indicates a first side of the circumferential direction FCD. SES indicates a second side of the circumferential direction FCD opposite the first side FIS. THS indicates a third side of the circumferential direction SCD. FOS indicates a fourth side of the circumferential direction SCD opposite the third side THS.

[0023] As shown in Fig. 2, the first tooth 11 has a first tooth crest 110, a first tooth flank 111, and a second tooth flank 112. The first tooth flank 111 and the second tooth flank 112 are located between the first tooth crest 110 and the first tooth root 12. The first tooth flank 111 is one of the two tooth flanks of the first tooth 11 that is located on a first side FIS in the circumferential direction FCD of the first gear 10 from the first tooth crest 110. The second tooth flank 112 is one of the two tooth flanks of the first tooth 11 that is located on a second side SES in the circumferential direction FCD of the first gear 10 from the first tooth crest 110.

[0024] The second tooth 21 has a second tooth crest 210, a third tooth flank 211, and a fourth tooth flank 212. The third tooth flank 211 and the fourth tooth flank 212 are located between the second tooth crest 210 and the second tooth root 22. The third tooth flank 211 is one of the two tooth flanks of the second tooth 21 that is located on a third side THS in the circumferential direction SCD of the second gear 20 from the second tooth crest 210. The fourth tooth flank 212 is one of the two tooth flanks of the second tooth 21 that is located on a fourth side FOS in the circumferential direction SCD of the second gear 20 from the second tooth crest 210.

[0025] The first tooth flank 111 has a first usable tooth surface 111a adjacent to the first tooth crest 110. The first tooth surface 111 also has a first fillet 111b located radially inward of the first gear 10 from the first usable tooth surface 111a and adjacent to the first tooth root 12.

[0026] The second tooth flank 211 has a second usable tooth surface 211a adjacent to the second tooth crest 210. The second tooth surface 211 also has a second fillet 211b located radially inward of the second gear 20 from the second usable tooth surface 211a and adjacent to the second tooth root 22.

[0027] In the gear pair 1, the first gear 10 is a drive gear, and the second gear 20 is a driven gear. The first usable tooth surface 111a and the second usable tooth surface 211a are configured to be able to come into contact as meshing tooth surfaces. The rotational force of the first gear 10 in the rotation direction FRD is transmitted to the second gear 20 by the first usable tooth surface 111a coming into contact with the second usable tooth surface 211a. As a result, the second gear 20 rotates in the rotation direction SRD.

[0028] [Regarding the usable tooth surfaces] The arithmetic mean roughness Ra1 of the first usable tooth surface 111a is 0.05 μm or more and 0.50 μm or less. The arithmetic mean roughness Ra2 of the second usable tooth surface 211a is 0.01 μm or more and 0.15 μm or less. In addition, in the gear pair 1, the arithmetic mean roughness Ra1 is configured to be larger than the arithmetic mean roughness Ra2. This reduces the coefficient of friction between the meshing tooth surfaces of the gear pair 1. The arithmetic mean roughness (Ra) is obtained in accordance with JIS B 0601:2013.

[0029] The first usable tooth surface 111a is configured so that the cutting level difference Rδc of the profile curve and the load length ratio Rmr(c) in the load curve of the profile curve satisfy the following formula (I): Cutting level difference Rδc (1%-60%) / Cutting level difference Rδc (1%-98%)≦0.30 Formula (I) In this embodiment, a roughness curve is applied as the profile curve. The roughness curve is created based on the measurement results obtained by using a known stylus or laser probe measuring instrument.

[0030] In formula (I), the cut level difference Rδc(1%-98%) is the difference between the cut level c1% at the load length ratio Rmr(1%) and the cut level c98% at the load length ratio Rmr(98%). The cut level difference Rδc(1%-60%) is the difference between the cut level c1% at the load length ratio Rmr(1%) and the cut level c60% at the load length ratio Rmr(60%).

[0031] That is, the first usable tooth surface 111a is configured so that the ratio of the cut level difference Rδc (1%-60%) of the cut level c1% at the load length ratio Rmr (1%) and the cut level c60% at the load length ratio Rmr (60%) to the cut level difference Rδc (1%-98%) of the cut level c1% at the load length ratio Rmr (1%) and the cut level c98% at the load length ratio Rmr (98%) is 0.30 or less. The cut level c, the cut level difference Rδc, and the load length ratio Rmr(c) are obtained in accordance with JIS B 0601:2013.

[0032] 3A and 3B are explanatory diagrams showing the relationship between the profile cutting level difference Rδc and the load length ratio Rmr(c) in the profile load curve of a usable tooth surface. Fig. 3A is a schematic diagram of the profile PA and load curve of a usable tooth surface where the difference between the peaks and valleys is large and the peaks and valleys are approximately uniform. Fig. 3B is a schematic diagram of the profile PB and load curve of a usable tooth surface where the difference between the peaks and valleys is small and the peaks and valleys are approximately uniform. Fig. 3C is a schematic diagram of the profile PC and load curve of a usable tooth surface where approximately 70% of the usable tooth surface has a region with a small difference between the peaks and valleys, and the remaining approximately 30% has a region with a large proportion of deep valleys.

[0033] In FIG. 3(a), A-Rδc(1%-60%) and A-Rδc(1%-98%) respectively indicate the cut level difference Rδc(1%-60%) and cut level difference Rδc(1%-98%) of the profile curve PA. In FIG. 3(b), B-Rδc(1%-60%) and B-Rδc(1%-98%) respectively indicate the cut level difference Rδc(1%-60%) and cut level difference Rδc(1%-98%) of the profile curve PB. In FIG. 3(c), C-Rδc(1%-60%) and C-Rδc(1%-98%) respectively indicate the cut level difference Rδc(1%-60%) and cut level difference Rδc(1%-98%) of the profile curve PC.

[0034] As shown in Figures 3(a) and 3(b), the smaller the difference between the peaks and valleys of the profile curve of the usable tooth surface, the smaller the cutting level difference Rδc (0%-100%) in the load curve. In other words, the smoother the usable tooth surface, the gentler the slope of the load curve. Here, smoothing the usable tooth surface uniformly reduces the difference between the peaks and valleys. Therefore, the proportion of deep valleys present on the usable tooth surface also decreases. As a result, in the load curves of Figures 3(a) and 3(b), the ratio of A-Rδc (1%-60%) to A-Rδc (1%-98%) and the ratio of B-Rδc (1%-60%) to B-Rδc (1%-98%) are both 0.40 or greater.

[0035] The first usable tooth flank 111a has a load curve with a profile curve PC shown in Figure 3(c). Approximately 70% of the first usable tooth flank 111a is an area with a small difference between peaks and valleys. Furthermore, approximately 30% of the first usable tooth flank 111a is an area with a large proportion of deep valleys. Therefore, the load curve PC of the first usable tooth flank 111a has a gentle slope from the load length ratio Rmr (0%) to the load length ratio Rmr (70%). On the other hand, the load curve PC of the first usable tooth flank 111a has a steep slope from the load length ratio Rmr (70%) to the load length ratio Rmr (100%). That is, in the load curve of the first usable tooth surface 111a shown in FIG. 3(c), the ratio of C-Rδc (1%-60%) to C-Rδc (1%-98%) is 0.15 or more and 0.30 or less.

[0036] As the first gear 10 and the second gear 20 rotate, the first usable tooth flank 111a and the second usable tooth flank 211a come into contact with each other. A load is generated at the contact portion between the first usable tooth flank 111a and the second usable tooth flank 211a. Therefore, if the first usable tooth flank 111a is rough, the coefficient of friction at the contact portion increases. Furthermore, if the proportion of deep valleys present on the first usable tooth flank 111a is small, the ability of the first usable tooth flank 111a to retain lubricant decreases, and the coefficient of friction at the contact portion increases. Furthermore, if the roughness of the portion of the first usable tooth flank 111a excluding the deep valleys is too small, the amount of lubricant that can be retained in this portion becomes too small.

[0037] In the first usable tooth surface 111a, the shear level difference Rδc (1%-60%) from the load length ratio Rmr (1%) to the load length ratio Rmr (60%), which shares the load on the contact portion, is configured to be small. Furthermore, in the first usable tooth surface 111a, the shear level difference Rδc (1%-98%) from the load length ratio Rmr (1%) to the load length ratio Rmr (98%), which ensures the lubricant retention capacity, is configured to be large.

[0038] Here, in the minute regions where the load length ratio is less than 1% and where the roughness peaks are locally high, deformation occurs due to contact between the meshing tooth flanks during rotation immediately after assembly of the gear pair, eliminating the localized roughness. Furthermore, even if the roughness valleys in the small regions where the load length ratio is greater than 98% are extremely deep, the lubricant storage performance does not improve significantly. Therefore, by focusing on the ratio of the shear level difference Rδc (1%-60%) to the shear level difference Rδc (1%-98%) of the first usable tooth flank 111a, which does not include the minute regions, and setting this ratio to 0.15 or more and 0.30 or less, the coefficient of friction between the meshing tooth flanks of the gear pair 1 is reduced.

[0039] The first usable tooth flank 111a and the second usable tooth flank 211a can be processed by a known method used in processing mating tooth flanks. Examples of known methods include shot peening, laser processing, and etching. By appropriately using the known methods, the arithmetic mean roughness Ra of the first usable tooth flank 111a and the second usable tooth flank 211a and the ratio of the cutting level difference Rδc (1%-60%) to the cutting level difference Rδc (1%-98%) of the first usable tooth flank 111a can be adjusted.

[0040] The first usable tooth surface 111a and the second usable tooth surface 211a can be made of a known metal material used for gears. Examples of known metal materials include iron, steel, and aluminum. In the gear pair 1, the first usable tooth surface 111a and the second usable tooth surface 211a are preferably made of steel. More preferably, the first usable tooth surface 111a and the second usable tooth surface 211a each have a hardness of HV 500 or more and HV 860 or less. This suppresses deformation of the meshing tooth surfaces during contact. Therefore, the coefficient of friction between the meshing tooth surfaces of the gear pair 1 is maintained small.

[0041] A preferred ratio of the cutting level difference Rδc (1%-60%) to the cutting level difference Rδc (1%-98%) of the first usable tooth flank 111a is 0.15 or greater. That is, a preferred first usable tooth flank 111a is configured so that the cutting level difference Rδc of the profile curve and the load length ratio Rmr(c) in the load curve of the profile curve satisfy the following formula (II): 0.15≦cutting level difference Rδc (1%-60%) / cutting level difference Rδc (1%-98%)≦0.30 ... formula (II) When the first usable tooth flank 111a satisfies formula (II), local contact that occurs at high peak heights of the roughness is alleviated, the lubricant retention capacity in deep valley depths of the roughness is ensured, and the load generated at the usable tooth flank is shared and borne by the usable tooth flank. Therefore, power can be transmitted by the gear pair 1, and the coefficient of friction between the meshing tooth surfaces of the gear pair 1 is further reduced.

[0042] It is preferable that the shear level difference Rδc (1%-98%) of the first usable tooth surface 111a is 1.20 μm or more and 2.10 μm or less, and the shear level difference Rδc (1%-60%) is 0.10 μm or more and 0.50 μm or less. This ensures a well-balanced shear level difference Rδc between the meshing tooth surfaces of the gear pair 1 in the area that shares the load on the contact area and the area that ensures the ability to retain lubricant. This further reduces the coefficient of friction between the meshing tooth surfaces of the gear pair 1.

[0043] [Others] The gear pair 1 in the above embodiment is a parallel-axis gear pair, but the gear pair of the present invention is not limited to a parallel-axis gear pair. The gear pair of the present invention can also be, for example, an intersecting-axis gear pair or an intersecting gear pair. Also, the gear pair 1 in the above embodiment is an external gear pair, but the gear pair of the present invention is not limited to an external gear pair. The gear pair of the present invention can also be an internal gear pair.

[0044] Although the first gear 10 and the second gear 20 in the above embodiment are both spur gears, the gears applicable to the gear pair of the present invention are not limited to spur gears. The gears of the present invention can also be, for example, straight bevel gears, helical gears, double helical gears, spiral bevel gears, or helical bevel gears.

[0045] The gear pair 1 in the above embodiment is configured such that the first gear 10, which is the driving gear, rotates in the rotation direction FRD, thereby rotating the second gear 20, which is the driven gear, in the rotation direction SRD, but the gear pair of the present invention is not limited to the above configuration.

[0046] For example, the gear pair of the present invention may be configured so that the first gear 10, which is the drive gear, rotates in the direction opposite to the rotational direction FRD. In this case, the rotational force of the first gear 10 is transmitted to the second gear 20 by contact of the usable tooth surface of the second tooth flank 112 (hereinafter referred to as the "third usable tooth surface") with the usable tooth surface of the fourth tooth flank 212 (hereinafter referred to as the "fourth usable tooth surface"). This causes the second gear 20 to rotate in the direction opposite to the rotational direction SRD. In this case, the third usable tooth surface functions in the same way as the first usable tooth surface 111a in the gear pair 1. Furthermore, the fourth usable tooth surface functions in the same way as the second usable tooth surface 211a in the gear pair 1. Therefore, by configuring the arithmetic mean roughness Ra of the third usable tooth surface and the ratio of the cutting level difference Rδc (1%-60%) to the cutting level difference Rδc (1%-98%) to be similar to those of the first usable tooth surface 111a, and configuring the arithmetic mean roughness Ra of the fourth usable tooth surface to be similar to that of the second usable tooth surface 211a, the coefficient of friction between the mating tooth surfaces is reduced.

[0047] The gear pair of the present invention can also be configured such that the second gear 20 rotates in the rotation direction SRD as a drive gear. In this case, the fourth usable tooth flank functions similarly to the first usable tooth flank 111a in gear pair 1. The third usable tooth flank functions similarly to the second usable tooth flank 211a in gear pair 1. Therefore, by configuring the arithmetic mean roughness Ra of the fourth usable tooth flank and the ratio of the cutting level difference Rδc (1%-60%) to the cutting level difference Rδc (1%-98%) similarly to the first usable tooth flank 111a in gear pair 1, and configuring the arithmetic mean roughness Ra of the third usable tooth flank similarly to the second usable tooth flank 211a in gear pair 1, the coefficient of friction between the meshing tooth flanks is reduced.

[0048] Furthermore, the gear pair of the present invention can be configured such that the second gear 20 rotates as a drive gear in the direction opposite to the rotation direction SRD. In this case, the second usable tooth flank 211a functions similarly to the first usable tooth flank 111a in the gear pair 1. The first usable tooth flank 111a also functions similarly to the second usable tooth flank 211a in the gear pair 1. Therefore, by configuring the second usable tooth flank 211a similarly to the first usable tooth flank 111a in the gear pair 1, and by configuring the first usable tooth flank 111a similarly to the second usable tooth flank 211a in the gear pair 1, the coefficient of friction between the meshing tooth flanks is reduced.

[0049] Next, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.

[0050] In this example, as a test simulating a gear pair, the friction coefficients between the flat surface of disks having surfaces No. 1 to No. 10 described below and the ball were measured using an MTM traction tester (manufactured by PCS Instruments). The flat surface of the disk was treated as one surface of a drive gear or a driven gear, and the desired surface texture was created. The surface of the ball was treated as the other surface of a drive gear or a driven gear, and the desired surface texture was created. In addition, the friction coefficient ratio between the flat surface of each disk and the surface of the ball was evaluated based on the measurement result of the friction coefficient between the flat surface of disk No. 4 and the surface of the ball.

[0051] (Test Method) The disks are manufactured to ASTM 52100 (equivalent to JIS SUJ2), and the surface that comes into contact with the ball is flat. The balls are 3 / 4 inch and manufactured to ASTM 52100 (equivalent to JIS SUJ2). All were heated to 820°C to 840°C, rapidly cooled, quenched, and tempered. The surface hardness of all disks is 650HV to 750HV.

[0052] Furthermore, the surface of the ball and the flat surface of the disk were prepared by polishing to the arithmetic mean roughness Ra and cutting level difference Rδc shown in Table 1.

[0053] The tangential velocity of the disc at the contact point between the ball and the flat surface of the disc was 0.2 m / s. The contact surface pressure of the ball against the flat surface of the disc was 1300 MPa. The MTM traction tester was placed in a test room with an ambient temperature of 25°C, and the friction coefficient was measured with the lubricant temperature adjusted to 50°C. The tangential velocity of the ball was made faster and slower than the tangential velocity of the disc to simulate the contact state between the drive gear and the driven gear. The average friction coefficient was calculated for the state where the tangential velocity of the ball was 0.19 m / s and the tangential velocity of the disc was 0.21 m / s, and the state where the tangential velocity of the ball was 0.21 m / s and the tangential velocity of the disc was 0.19 m / s.

[0054] (Load Curve and Arithmetic Average Roughness Ra) The surface texture of the flat surfaces of the disks No. 1 to No. 10 and the surface of the ball was measured using a laser microscope OLS4100 (manufactured by Olympus Corporation (now Evident Co., Ltd.)). Roughness curves were created based on the measurement results. Based on the created roughness curves, load curves and arithmetic average roughness Ra were obtained in accordance with JIS B 0601:2013.

[0055] (Friction Coefficient Ratio) Using an MTM traction tester, the coefficient of friction between the surface of each ball and the flat surface of the disc was measured at the tangential velocity of the ball and the tangential velocity of the flat surface of the disc for No. 1 to No. 10. The friction coefficient ratios shown in Table 1 were calculated by dividing the measured coefficient of friction between the surface of each ball and the flat surface of the disc by the coefficient of friction between the surface of No. 4 ball and the flat surface of the disc.

[0056] Table 1 shows, for each of balls No. 1 to No. 10 and discs, the friction coefficient ratio between the surface of each ball and the flat surface of the disc, the arithmetic mean roughness Ra of the ball surface and the flat surface of the disc, as well as the cut level difference Rδc (1%-60%), the cut level difference Rδc (1%-98%), and the cut level difference Rδc (1%-60%) / cut level difference Rδc (1%-98%) of the ball surface.

[0057] In Table 1, the surface texture of the disk plane corresponds to the usable tooth surface of one of the drive gear and the driven gear. The surface texture of the ball corresponds to the usable tooth surface of the other of the drive gear and the driven gear. Rδc1-60 and Rδc1-98 indicate the cutting level difference Rδc (1%-60%) and the cutting level difference Rδc (1%-98%), respectively.

[0058] Fig. 4 is a graph showing the relationship between the friction coefficient ratio between the flat surface of each disk and the surface of the ball and the cutting level difference Rδc (1%-60%) / cutting level difference Rδc (1%-98%) of the flat surface of the disk shown in Table 1. Fig. 5 shows the load curves of the flat surfaces of each of disks No. 4, No. 5, and No. 10.

[0059] Table 1 shows that the ratios of the coefficients of friction between the flat surface of disk No. 5, No. 6, No. 9, and No. 10 and the surface of the ball are lower than the ratio of the coefficient of friction between the flat surface of disk No. 4 and the surface of the ball. On the other hand, Table 1 shows that the ratios of the coefficients of friction between the flat surface of disk No. 1, No. 2, No. 3, No. 7, and No. 8 and the surface of the ball are higher than the ratio of the coefficient of friction between the flat surface of disk No. 4 and the surface of the ball.

[0060] Table 1 shows that the arithmetic mean roughness Ra of the flat surface of each of the disks No. 5, No. 6, No. 9, and No. 10 is greater than the arithmetic mean roughness Ra of the surface of each of the balls. Table 1 also shows that the arithmetic mean roughness Ra of the flat surface of each of the disks No. 5, No. 6, No. 9, and No. 10 is 0.07 μm or more and 0.43 μm or less, and the arithmetic mean roughness Ra of the surface of each of the balls is 0.02 μm or more and 0.03 μm or less. As described above, the results of this test simulating a gear pair experimentally suggested that the coefficient of friction between the meshing tooth surfaces is reduced in a gear pair in which the arithmetic mean roughness Ra of the usable tooth surface of one of the drive gear and the driven gear is 0.05 μm or more and 0.50 μm or less, and the arithmetic mean roughness Ra of the usable tooth surface of the other of the drive gear and the driven gear is 0.01 μm or more and 0.15 μm or less, and the arithmetic mean roughness Ra of the usable tooth surface of one of the drive gear and the driven gear is greater than the arithmetic mean roughness Ra of the usable tooth surface of the other of the drive gear and the driven gear.

[0061] Table 1 shows that the arithmetic mean roughness Ra of the flat surface of disk No. 4 is lower than the arithmetic mean roughness Ra of the flat surface of disk No. 5. Table 1 also shows that the arithmetic mean roughness Ra of the flat surface of disk No. 4 is the same as the arithmetic mean roughness Ra of the flat surface of disk No. 10, and is the lowest among the combinations of flat disk surfaces and ball surfaces. Meanwhile, Table 1 also shows that the flat surfaces of disk No. 5 and disk No. 10 both have lower friction coefficient ratios than the flat surface of disk No. 4. In other words, this example experimentally demonstrated that adjusting the arithmetic mean roughness Ra of the mating tooth flanks alone may not be enough to sufficiently reduce the coefficient of friction between the mating tooth flanks.

[0062] As is clear from Figure 5, the load curve of the flat surface of disk No. 4 in Figure 5(a) has a smaller proportion of deep valleys between the load length ratio Rmr (60%) and the load length ratio Rmr (98%) than the load curves of the flat surfaces of disks No. 5 in Figure 5(b) and No. 10 in Figure 5(c). Therefore, as shown in Table 1, the cut level difference Rδc (1%-60%) / cut level difference Rδc (1%-98%) of No. 4 is larger than the cut level difference Rδc (1%-60%) / cut level difference Rδc (1%-98%) of No. 5 and No. 10.

[0063] 4 also shows that the cut level difference Rδc(1%-60%) / cut level difference Rδc(1%-98%) for the flat surfaces of disks No. 5, No. 6, No. 9, and No. 10, which have lower friction coefficient ratios than the combination of the flat surface of disk No. 4 and the surface of the ball, are all smaller than the cut level difference Rδc(1%-60%) / cut level difference Rδc(1%-98%) for the flat surface of disk No. 4. Furthermore, Table 1 shows that the cut level difference Rδc(1%-60%) / cut level difference Rδc(1%-98%) for the flat surfaces of disks No. 5, No. 6, No. 9, and No. 10 are 0.21 or more and 0.28 or less. As described above, the results of this test simulating a gear pair experimentally suggested that the coefficient of friction between the meshing tooth flanks is reduced in gear pairs where the cut level difference Rδc (1%-60%) / cut level difference Rδc (1%-98%) on the usable tooth flanks of one of the drive gear and driven gear of the gear pair is 0.30 or less, particularly in the range of 0.15 to 0.30.

[0064] 1 Gear pair 10 First gear 11 First tooth 110 First tooth crest 111 First tooth flank 111a First usable tooth flank 111b First fillet 112 Second tooth flank 12 First tooth root 20 Second gear 21 Second tooth 210 Second crest 211 Third tooth flank 211a Second usable tooth flank 211b Second fillet 212 Fourth tooth flank 22 Second tooth root 30 First shaft 40 Second shaft FRD Rotation direction of first gear SRD Rotation direction of second gear FCD Circumferential direction of first gear SRD Circumferential direction of second gear FIS First side SES Second side THS Third side FOS Fourth side

Claims

1. A pair of gears including a first gear and a second gear, wherein the first gear includes: - tops of a plurality of first teeth; - bottoms of the plurality of first teeth; - a first tooth surface located between the tops of the first teeth and the bottoms of the first teeth and facing a first side in the circumferential direction of the first gear; and - a second tooth surface located between the tops of the first teeth and the bottoms of the first teeth and facing a second side in the circumferential direction of the first gear. The first tooth surface includes: - a first available tooth surface adjacent to the top of the first tooth; and - a first fillet located radially inward of the first available tooth surface with respect to the first gear and adjacent to the bottom of the first tooth. The second gear includes: - tops of a plurality of second teeth; - bottoms of the plurality of second teeth; - a third tooth surface located between the tops of the second teeth and the bottoms of the second teeth and facing a third side in the circumferential direction of the second gear; and - a fourth tooth surface located between the tops of the second teeth and the bottoms of the second teeth and facing a fourth side in the circumferential direction of the second gear. The third tooth surface includes: - a second available tooth surface adjacent to the top of the second tooth; and - a second fillet located radially inward of the second available tooth surface with respect to the second gear and adjacent to the bottom of the second tooth. The first available tooth surface and the second available tooth surface are capable of being in contact with each other. The arithmetic mean roughness Ra1 of the first available tooth surface is 0.05 μm or more and 0.50 μm or less. The arithmetic mean roughness Ra2 of the second available tooth surface is 0.01 μm or more and 0.15 μm or less. The arithmetic mean roughness Ra1 is greater than the arithmetic mean roughness Ra2. For the first available tooth surface, with respect to the cut-off level difference Rδc and the load length ratio Rmr(c) in the load curve of the profile curve, the ratio of the cut-off level difference Rδc(1%-60%) between the cut-off level c1% at the load length ratio Rmr(1%) and the cut-off level c60% at the load length ratio Rmr(60%) to the cut-off level difference Rδc(1%-98%) between the cut-off level c1% at the load length ratio Rmr(1%) and the cut-off level c98% at the load length ratio Rmr(98%) is 0.15 or more and 0.30 or less. A pair of gears.

2. The pair of gears according to claim 1, wherein the first available tooth surface and the second available tooth surface are each made of steel.

3. The gear pair according to claim 2, wherein the first available tooth surface and the second available tooth surface each have a hardness of HV500 or more and HV860 or less.

4. The gear pair according to claim 1, wherein the arithmetic mean roughness Ra1 is 0.05 μm or more and 0.35 μm or less greater than the arithmetic mean roughness Ra2.

5. The gear pair according to claim 1, wherein the cutting level difference Rδc(1% - 98%) of the first available tooth surface is 1.20 μm or more and 2.10 μm or less, and the cutting level difference Rδc(1% - 60%) is 0.10 μm or more and 0.50 μm or less.

Images