Gear pair

Abstract

Provided is a gear pair that comprises a first gear and a second gear. A first usable flank of the first gear and a second usable flank of the second gear can contact each other. The first usable flank has a surface texture at which the core roughness depth (first Rk) of the first usable flank and the reduced valley depth (first Rvk) of the first usable flank as found from a material ratio curve for a first profile of the first usable flank are 0.030–0.060 μm and 0.015–0.030 μm, respectively, and the second usable flank has a surface texture at which the core roughness depth (second Rk) of the second usable flank and the ratio (second Rvk / second Rk) of the reduced valley depth (second Rvk) of the second usable flank to the core roughness depth (second Rk) of the second usable flank as found from a material ratio curve for a second profile of the second usable flank are 0.080–0.240 μm and 2.20–3.00, respectively.

Description

Gear pair

[0001] The present disclosure relates to a gear pair.

[0002] In recent years, low-viscosity oil has been used for lubricating gear pairs for the purpose of achieving lower fuel consumption in automobiles. When a gear pair is operated at a high rotational speed, the temperature rises along with an increase in stirring loss of the lubricating oil, which reduces the viscosity of the lubricating oil that lubricates the tooth flanks. If the viscosity of the lubricating oil decreases excessively, the oil film formed on the tooth flanks becomes thinner, friction loss increases, and transmission efficiency decreases. The aforementioned increase in friction loss and decrease in transmission efficiency can be suppressed by reducing the friction coefficient between the meshing tooth flanks of the gear pair. Therefore, there is a demand for reducing the friction coefficient between the meshing tooth flanks of gear pairs used at high rotational speeds.

[0003] Patent Document 1 discloses a surface-hardened gear having a steel material with a predetermined composition as a base material, wherein Rpk and Rk respectively represent the peak protrusion height (μm) and the core level difference (μm) in the load-bearing surface roughness curve along the load movement direction of the gear surface, and the surface roughness along the load movement direction of the gear surface satisfies "0.2 μm ≦ Rpk + 0.5Rk ≦ 0.8 μm". The gear disclosed is surface-hardened and has high pitting strength even when not subjected to solid lubrication treatment such as molybdenum disulfide coating.

[0004] Patent Document 2 discloses a gear train in which the peak protrusion height Rpk of the tooth flank of one gear is smaller than the peak protrusion height Rpk of the tooth flank of the other gear and is 0.1 μm or less, and the valley protrusion depth Rvk of the tooth flank of the one gear is smaller than the valley protrusion depth Rvk of the tooth flank of the other gear. The gear train disclosed has high meshing transmission efficiency during initial operation and completes running-in at an early stage.

[0005] Japanese Patent Application Laid-Open No. 2006-225741, Japanese Patent Application Laid-Open No. 2014-137082

[0006] An object of the present invention is to provide a gear pair in which the friction coefficient between meshing tooth flanks is reduced.

[0007] 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 vertices, a plurality of first tooth roots, a first tooth surface located between the first tooth vertices and the first tooth roots and facing a first side in the circumferential direction of the first gear, and a third tooth surface located between the first tooth vertices and the first tooth roots and facing a third side in the circumferential direction of the first gear, wherein the first tooth surface comprises a first usable tooth surface adjacent to the first tooth vertices, and a first fillet tooth located radially inward from the first usable tooth surface and adjacent to the first tooth root, and the second gear comprises a plurality of second tooth vertices, a plurality of second tooth roots, The gear comprises: a second tooth surface located between the apex and the root of the second tooth and facing the second side in the circumferential direction of the second gear; and a fourth tooth surface located between the apex and the root of the second tooth and facing the fourth side in the circumferential direction of the second gear, wherein the second tooth surface comprises: a second usable tooth surface adjacent to the apex of the second tooth; and a second fillet located radially inward from the second usable tooth surface and adjacent to the root of the second tooth, wherein the first usable tooth surface and the second usable tooth surface are contactable, and the first usable tooth surface has a level difference (first Rk) of the core portion of the first usable tooth surface determined from the load curve of the first contour surface of the first usable tooth surface of the first usable tooth surface of 0.030 μm or more and 0.060 μm or less. The first usable tooth surface has a surface characteristic in which the depth of the protruding valley (first Rvk) is 0.015 μm or more and 0.030 μm or less, and the second usable tooth surface has a surface characteristic in which the level difference of the core portion of the second usable tooth surface (second Rk), determined from the load curve of the second contour curve of the second usable tooth surface, is 0.080 μm or more and 0.240 μm or less, and the ratio of the depth of the protruding valley (second Rvk) of the second usable tooth surface to the level difference of the core portion (second Rk) of the second usable tooth surface (second Rvk / Rk) is 2.20 or more and 3.00 or less.

[0008] The gear pair of this disclosure is a gear pair in which the coefficient of friction between the meshing tooth surfaces is reduced.

[0009] Figure 1 is a schematic cross-sectional view of a gear pair according to one embodiment of the present disclosure. Figure 2 is an enlarged schematic view of the meshing region of the gear pair shown in Figure 1. Figure 3 is a schematic diagram of an MTM traction testing machine.

[0010] <Outline of Embodiments of the Invention Disclosed> Below, an outline of embodiments of the invention disclosed will be listed and explained. (1) 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 vertices, a plurality of first tooth roots, a first tooth surface located between the first tooth vertices and the first tooth roots and facing a first side in the circumferential direction of the first gear, and a third tooth surface located between the first tooth vertices and the first tooth roots and facing a third side in the circumferential direction of the first gear, wherein the first tooth surface comprises a first usable tooth surface adjacent to the first tooth vertices, and a first fillet tooth located radially inward from the first usable tooth surface and adjacent to the first tooth root, and the second gear comprises a plurality of second tooth vertices, a plurality of second tooth roots, The gear comprises: a second tooth surface located between the apex and the root of the second tooth and facing the second side in the circumferential direction of the second gear; and a fourth tooth surface located between the apex and the root of the second tooth and facing the fourth side in the circumferential direction of the second gear, wherein the second tooth surface comprises: a second usable tooth surface adjacent to the apex of the second tooth; and a second fillet located radially inward from the second usable tooth surface and adjacent to the root of the second tooth, wherein the first usable tooth surface and the second usable tooth surface are contactable, and the first usable tooth surface, as determined from the load curve of the first contour curve of the first usable tooth surface, has a level difference (first Rk) of the core portion of the first usable tooth surface of 0.030 μm or more and 0.060 μm or less. The first usable tooth surface has a surface characteristic in which the depth of the protruding valley (first Rvk) is 0.015 μm or more and 0.030 μm or less, and the second usable tooth surface has a surface characteristic in which the level difference of the core portion of the second usable tooth surface (second Rk), determined from the load curve of the second contour curve of the second usable tooth surface, is 0.080 μm or more and 0.240 μm or less, and the ratio of the depth of the protruding valley (second Rvk) of the second usable tooth surface to the level difference of the core portion (second Rk) of the second usable tooth surface (second Rvk / Rk) is 2.20 or more and 3.00 or less.

[0011] According to the gear pair described in (1) above, the coefficient of friction between the meshing tooth surfaces is reduced.

[0012] (2) A preferred gear pair according to (1) is one in which the first Rk is 0.040 μm or more and 0.050 μm or less, the first Rvk is 0.020 μm or more and 0.025 μm or less, the second Rk is 0.090 μm or more and 0.235 μm or less, and the second Rvk / Rk is 2.40 or more and 2.90 or less.

[0013] (3) A preferred gear pair according to (1) or (2) above has a ratio of the first Rvk to the first Rk (first Rvk / Rk) of 0.40 or more and 0.50 or less, a projection peak height of the second usable tooth surface (second Rpk) determined from the load curve of the second contour surface of the second usable tooth surface of 0.050 μm or more and 0.150 μm or less, and a projection valley depth of the second usable tooth surface (second Rvk) of 0.200 μm or more and 0.700 μm or less.

[0014] (4) In any of the gear pairs described in (1) to (3) above, the first usable tooth surface and the second usable tooth surface are made of steel.

[0015] (5) A preferred gear pair of any of the above (1) to (4) is one in which the first usable tooth surface and the second usable tooth surface each have a hardness of HV500 or more and HV860 or less.

[0016] According to the gear pairs described in (2) to (5) above, the coefficient of friction between the meshing tooth surfaces is further reduced.

[0017] (6) A preferred gear pair of any of the above (1) to (5) is one in which the first gear is an external gear and the second gear is an external gear.

[0018] As with the gear pair described in (6) above, the present invention can be applied to an external gear pair.

[0019] <Details of Embodiments of the Invention in This Disclosure> Embodiments of the invention in this disclosure are described below. It should be understood that the embodiments of the invention in this disclosure are illustrative and not restrictive in all respects. The scope of the invention is defined by the claims and is intended to include all modifications within the meaning and scope of equivalence to the claims.

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

[0021] The gear pair 1 shown in Figure 1 is a parallel-axis gear pair. Furthermore, gear pair 1 is an external gear pair. Gear pair 1 comprises a first gear 10 and a first shaft 30 which is the axis of rotation of the first gear 10, and a second gear 20 and a second shaft 40 which is the axis of rotation of the second gear 20. The first gear 10 is a small gear, and the second gear 20 is a large gear. 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 gear pair 1 are spur gears.

[0022] In Figure 1, the two arrows indicate the rotational direction FRD of the first gear 10 and the rotational direction SRD of the second gear 20, respectively. In Figures 1 and 2, the two double arrows indicate the circumferential direction FCD of the first gear 10 and the circumferential direction SCD of the second gear 20. FIS indicates the first side of the circumferential direction FCD. THS indicates the third side of the circumferential direction FCD, opposite to the first side FIS. SES indicates the second side of the circumferential direction SCD. FOS indicates the fourth side of the circumferential direction SCD, opposite to the second side SES.

[0023] As shown in Figure 2, the first tooth 11 comprises a first tooth apex 110, a first tooth surface 111, and a third tooth surface 112. The first tooth surface 111 and the third tooth surface 112 are located between the first tooth apex 110 and the first tooth root 12. The first tooth surface 111 is the tooth surface of the first tooth 11 that is located on the first side FIS of the circumferential FCD of the first gear 10, from the first tooth apex 110. The third tooth surface 112 is the tooth surface of the first tooth 11 that is located on the third side THS of the circumferential FCD of the first gear 10, from the first tooth apex 110.

[0024] The second tooth 21 comprises a apex 210, a second tooth surface 211, and a fourth tooth surface 212. The second tooth surface 211 and the fourth tooth surface 212 are located between the apex 210 and the root 22 of the second tooth. The second tooth surface 211 is the tooth surface of the second tooth 21 that is located on the second side SES of the circumferential SCD of the second gear 20, from the apex 210 of the second tooth. The fourth tooth surface 212 is the tooth surface of the second tooth 21 that is located on the fourth side FOS of the circumferential SCD of the second gear 20, from the apex 210 of the second tooth.

[0025] The first tooth surface 111 includes a first usable tooth surface 111a adjacent to the apex 110 of the first tooth. The first tooth surface 111 also includes a first fillet tooth surface 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 third tooth surface 112 includes a third usable tooth surface 112a adjacent to the apex 110 of the first tooth. The third tooth surface 112 also includes a third fillet tooth surface 112b located radially inward of the first gear 10 from the third usable tooth surface 112a and adjacent to the root 12 of the first tooth.

[0027] The second tooth surface 211 includes a second usable tooth surface 211a adjacent to the apex 210 of the second tooth. The second tooth surface 211 also includes a second fillet tooth surface 211b located radially inward of the second gear 20 from the second usable tooth surface 211a and adjacent to the root 22 of the second tooth.

[0028] The fourth tooth surface 212 includes a fourth usable tooth surface 212a adjacent to the apex 210 of the second tooth. The second tooth surface 212 also includes a fourth fillet tooth surface 212b located radially inward of the second gear 20 from the fourth usable tooth surface 212a and adjacent to the root 22 of the second tooth.

[0029] In the gear pair 1, the first gear 10 is a driving 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 in contact as meshing tooth surfaces. The rotational force of the first gear 10 in the rotational direction FRD is transmitted to the second gear 20 by the contact of the first usable tooth surface 111a with the second usable tooth surface 211a. As a result, the second gear 20 rotates in the rotational direction SRD.

[0030] [Regarding the usable tooth surface] In embodiments of this disclosure, the surface properties of the usable tooth surface are obtained in accordance with JIS B 0671-2:2002, with respect to the core roughness depth (Rk), reduced peak height (Rpk), and reduced valley depth (Rvk), which are determined from the load curve of the contour surface. The ratio of the valley depth (Rvk) of the usable tooth surface to the core roughness depth (Rk) of the usable tooth surface (Rvk / Rk) is obtained by dividing Rvk by Rk.

[0031] The level difference of the core portion of the first usable tooth surface 111a (hereinafter sometimes referred to as "first Rk"), determined from the load curve of the first contour curve of the first usable tooth surface 111a, is 0.030 μm or more and 0.060 μm or less, preferably 0.040 μm or more and 0.050 μm or less. The level difference of the core portion of the second usable tooth surface 211a (hereinafter sometimes referred to as "second Rk"), determined from the load curve of the second contour curve of the second usable tooth surface 211a, is 0.080 μm or more and 0.240 μm or less, preferably 0.090 μm or more and 0.235 μm or less.

[0032] The depth of the protruding valley of the first usable tooth surface 111a (hereinafter sometimes referred to as "first Rvk"), which is determined from the load curve of the first contour curve of the first usable tooth surface 111a, is 0.015 μm or more and 0.030 μm or less, preferably 0.020 μm or more and 0.025 μm or less.

[0033] The ratio of the second Rvk to the second Rk (hereinafter sometimes referred to as "second Rvk / Rk") is 2.20 or more and 3.00 or less, preferably 2.40 or more and 2.90 or less.

[0034] A gear pair 1 having a combination of a first Rk, a first Rvk, a second Rk, and a second Rvk / Rk having the above-mentioned numerical range reduces the coefficient of friction between the meshing tooth surfaces. In particular, gear pairs having i) a combination in which the first Rk is 0.045 μm or more and 0.050 μm or less, the first Rvk is 0.020 μm or more and 0.025 μm or less, the second Rk is 0.230 or more and 0.235 or less, and the second Rvk / Rk is 2.80 or more and 2.90 or less (hereinafter sometimes referred to as the "first combination"), or ii) a combination in which the first Rk is 0.040 μm or more and 0.045 μm or less, the first Rvk is 0.020 μm or more and 0.025 μm or less, the second Rk is 0.090 μm or more and 0.095 μm or less, and the second Rvk / Rk is 2.40 or more and 2.50 or less (hereinafter sometimes referred to as the "second combination") have a further reduction in the coefficient of friction between the meshing tooth surfaces.

[0035] The ratio of the first Rvk to the first Rk (hereinafter sometimes referred to as "first Rvk / Rk") is preferably 0.40 or more and 0.50 or less. Furthermore, the height of the protruding peak of the second usable tooth surface 211a (hereinafter sometimes referred to as "second Rpk"), which is determined from the load curve of the second contour curve of the second usable tooth surface 211a, is preferably 0.050 μm or more and 0.150 μm or less. In addition, the depth of the protruding valley of the second usable tooth surface 211a (hereinafter sometimes referred to as "second Rvk"), which is determined from the load curve of the second contour curve of the second usable tooth surface 211a, is preferably 0.200 μm or more and 0.700 μm or less.

[0036] In addition to the combinations of a first Rk, a first Rvk, a second Rk, and a second Rvk / Rk having the above-mentioned numerical ranges, a gear pair 1 further having combinations of a first Rvk / Rk, a second Rvk, and a second Rpk having the above-mentioned numerical ranges further reduces the coefficient of friction between the meshing tooth surfaces. In particular, a gear pair having the following combinations in addition to the first combination described above: iii) a combination in which the first Rvk / Rk is 0.45 or more and 0.50 or less, the second Rpk is 0.100 μm or more and 0.150 μm or less, and the second Rvk is 0.600 μm or more and 0.700 μm or less (hereinafter sometimes referred to as the "third combination"), or iv) a combination in addition to the second combination described above: a first Rvk / Rk is 0.45 or more and 0.50 or less, the second Rpk is 0.050 μm or more and 0.100 μm or less, and the second Rvk is 0.200 μm or more and 0.300 μm or less (hereinafter sometimes referred to as the "fourth combination"), has a further reduction in the coefficient of friction between the meshing tooth surfaces.

[0037] The first usable tooth surface 111a and the second usable tooth surface 211a can be machined using known methods used for machining meshing tooth surfaces. Examples of known methods include shot peening, laser processing, and etching. By appropriately using the above known methods, the level difference Rk of the core portion, the height Rpk of the protruding peaks, and the depth Rvk of the protruding valleys, which are determined from the load curves of the respective contour surfaces of the first usable tooth surface 111a and the second usable tooth surface 211a, can be adjusted.

[0038] The first usable tooth surface 111a and the second usable tooth surface 211a can be made of a known metallic material used as a gear material. Examples of known metallic materials include iron, steel, and aluminum. In the gear pair 1, the preferred first usable tooth surface 111a and the second usable tooth surface 211a are made of steel. More preferably, the first usable tooth surface 111a and the second usable tooth surface 211a each have a hardness of HV500 or more and HV860 or less. This suppresses deformation of the surface properties of the meshing tooth surfaces when in contact. Therefore, when rotational force is transmitted from the first gear 10 to the second gear 20, the coefficient of friction between the meshing tooth surfaces of the gear pair 1 is maintained at a low level.

[0039] [Other] In the above embodiment, gear pair 1 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, a cross-axis gear pair or a misaligned gear pair. Also, in the above embodiment, gear pair 1 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.

[0040] Although the first gear 10 and the second gear 20 in the above embodiment are both spur gears, the gears applied 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, spiral bevel gears, or spiral bevel gears.

[0041] In the above embodiment, the gear pair 1 is configured such that the first gear 10, which is the driving gear, rotates in the rotational direction FRD, causing the second gear 20, which is the driven gear, to rotate in the rotational direction SRD. However, the gear pair of the present invention is not limited to the above configuration.

[0042] In the above embodiment, the gear pair 1 is configured such that the first gear 10 is a small gear and the second gear 20 is a large gear. However, it is also possible to configure the gear so that the first gear 10 is a large gear and the second gear 20 is a small gear. The large gear may also be provided with a first usable tooth surface 111a and the small gear may be provided with a second usable tooth surface 211a.

[0043] For example, the gear pair of the present invention may be configured such that the first gear 10, which is a drive gear, rotates in a direction opposite to the rotation direction FRD. In this case, the rotational force of the first gear 10 is transmitted to the second gear 20 by the contact of the third available tooth surface 112a of the third tooth surface 112 with the fourth available tooth surface 212a of the fourth tooth surface 212. Accordingly, the second gear 20 rotates in a direction opposite to the rotation direction SRD. In this case, the third available tooth surface 112a functions in the same manner as the first available tooth surface 111a in the gear pair 1. Further, the fourth available tooth surface 212a functions in the same manner as the second available tooth surface 211a in the gear pair 1. Therefore, by configuring the surface properties of the third available tooth surface 112a to be the same as one of the surface properties of the first available tooth surface 111a in the above-described gear pair 1 and the surface properties of the second available tooth surface 211a in the above-described gear pair 1, and configuring the surface properties of the fourth available tooth surface 212a to be the same as the other of the surface properties of the first available tooth surface 111a in the above-described gear pair 1 and the surface properties of the second available tooth surface 211a in the above-described gear pair 1, the friction coefficient between meshing tooth surfaces is reduced.

[0044] Further, the gear pair of the present invention may be configured such that the second gear 20 serves as a drive gear and rotates in the rotation direction SRD. In this case, the fourth available tooth surface 212a functions in the same manner as the first available tooth surface 111a in the gear pair 1. Further, the third available tooth surface 112a functions in the same manner as the second available tooth surface 211a in the gear pair 1. Therefore, by configuring the surface properties of the fourth available tooth surface 212a to be the same as one of the surface properties of the first available tooth surface 111a in the above-described gear pair 1 and the surface properties of the second available tooth surface 211a in the above-described gear pair 1, and configuring the surface properties of the third available tooth surface 112a to be the same as the other of the surface properties of the first available tooth surface 111a in the above-described gear pair 1 and the surface properties of the second available tooth surface 211a in the above-described gear pair 1, the friction coefficient between meshing tooth surfaces is reduced.

[0045] Furthermore, the gear pair of the present invention can also be configured such that the second gear 20 rotates in the opposite direction to the rotational direction SRD as a drive gear. In this case, the second usable tooth surface 211a functions in the same way as the first usable tooth surface 111a in the gear pair 1. Also, the first usable tooth surface 111a functions in the same way as the second usable tooth surface 211a in the gear pair 1. Therefore, by configuring the surface properties of the second usable tooth surface 211a in the same way as one of the surface properties of the first usable tooth surface 111a in the gear pair 1 and the surface properties of the second usable tooth surface 211a in the gear pair 1, and configuring the surface properties of the first usable tooth surface 111a in the same way as the other of the surface properties of the first usable tooth surface 111a in the gear pair 1 and the surface properties of the second usable tooth surface 211a in the gear pair 1, the coefficient of friction between the meshing tooth surfaces is reduced. In this case, the gear pair 1 is configured such that the first gear 10 is a small gear and the second gear 20 is a large gear. However, it is also possible to configure it so that the first gear 10 is a large gear and the second gear 20 is a small gear. It is also possible to configure it so that the large gear has a first usable tooth surface 111a and the small gear has a second usable tooth surface 211a.

[0046] Next, the invention of this disclosure will be described in more detail based on examples. However, the invention of this disclosure is not limited to the examples.

[0047] In this embodiment, as a test simulating a gear pair, the coefficient of friction between a ball and a disc having the surface properties No. 1 to No. 14 described later was measured using an MTM traction tester (manufactured by PCS Instruments). Figure 3 is a schematic diagram of the MTM traction tester. The MTM traction tester 50 shown in Figure 3 comprises a ball 51, a disc 52, a lubricating oil reservoir 53, and a heater 54.

[0048] The ball 51 is 3 / 4 inch, and is made of ASTM 52100 (equivalent to JIS SUJ2). The disk 52 is made of ASTM 52100 (equivalent to JIS SUJ2), and the surface in contact with the ball 51 is a flat surface. Both the ball 51 and the disk 52 are heated at 820°C to 840°C, quenched by rapid cooling, and tempered. Also, both the ball 51 and the disk 52 have a surface hardness of 650HV to 750HV. The ball 51 and the disk 52 are each configured to be rotatable by independent servo motors (not shown).

[0049] As shown in Figure 3, the disk 52 is rotatably supported in a state in contact with the ball 51 inside a lubricating oil reservoir 53 in which lubricating oil LUO is stored. The lubricating oil LUO is placed in the lubricating oil reservoir 53 up to a position where the contact surface between the ball 51 and the disk 52 is immersed in the lubricating oil LUO. The lubricating oil reservoir 53 is provided with a heater 54. The temperature of the lubricating oil LUO stored in the lubricating oil reservoir 53 is adjusted by the heater 54. The lubricating oil LUO used in the present embodiment is TOYOTA AUTO FLUID WS (manufactured by Toyota Motor Corporation).

[0050] In the present embodiment, the coefficient of friction was measured by regarding the surface of the ball 51 as a first available tooth flank and the surface of the disk 52 as a second available tooth flank. Specifically, under the conditions of a tangential velocity difference of 0.15 m / s of the disk 52 at the contact surface between the ball 51 and the disk 52, a contact surface pressure of 1300 MPa of the ball 51 against the disk 52, and a lubricating oil temperature of 50°C, the contact state between a driving gear and a driven gear was simulated by making the tangential velocity of the ball 51 faster and slower than the tangential velocity of the disk 52. The coefficient of friction is the average of the coefficient of friction in a state where the tangential velocity of the ball 51 is 0.225 m / s and the tangential velocity of the disk 52 is 0.375 m / s, and the coefficient of friction in a state where the tangential velocity of the ball 51 is 0.375 m / s and the tangential velocity of the disk 52 is 0.225 m / s.

[0051] Table 1 shows the measurement results of the coefficient of friction between the ball 51 and the disc 52 having surface properties No. 1 to No. 14. In Table 1, the first Rk, the first Rvk, and the first Rvk / Rk represent the level difference of the core portion (Rk), the depth of the protruding valley (Rvk), and the ratio of the depth of the protruding valley (Rvk) to the level difference of the core portion (Rk) (Rvk / Rk), respectively, of the surface of the ball 51 corresponding to the first usable tooth surface. The second Rk, the second Rpk, the second Rvk, and the second Rvk / Rk represent the level difference of the core portion (Rk), the height of the protruding peak (Rpk), the depth of the protruding valley (Rvk), and the ratio of the depth of the protruding valley (Rvk) to the level difference of the core portion (Rvk) (Rvk / Rk), respectively, of the surface of the disc 52 corresponding to the second usable tooth surface.

[0052] The surfaces of the ball 51 and the disk 52 were prepared to the surface characteristics shown in Table 1 by polishing. The surface characteristics of the ball 51 and the disk 52 were obtained in accordance with JIS B 0671-2:2002 based on measurement results using a laser microscope OLS4100 (manufactured by Olympus Corporation (now Evident Corporation)).

[0053]

[0054] Table 1 shows that the coefficient of friction between the ball 51 and the disc 52 having surface properties No. 1 and No. 2 is lower than the coefficient of friction between the ball 51 and the disc 52 having surface properties No. 3 to No. 14. Both No. 1 and No. 2 have surface properties where the first Rk is 0.030 μm or more and 0.060 μm or less, the first Rvk is 0.015 μm or more and 0.030 μm or less, the second Rk is 0.080 μm or more and 0.240 μm or less, and the second Rvk / Rk is 2.20 or more and 3.00 or less. On the other hand, the second Rvk / Rk of No. 3 to No. 14 is all less than 2.20. Also, No. 5, No. 6, No. 8, No. 11, No. The first Rk of No. 13 and No. 14 both exceed 0.060 μm. Furthermore, the first Rvk of No. 8, No. 11, No. 13, and No. 14 all exceed 0.030 μm. In addition, the second Rk of No. 3, No. 5, No. 11, No. 12, No. 13, and No. 14 all exceed 0.240 μm.

[0055] It is known that smoothing the tooth surfaces reduces the coefficient of friction between the meshing tooth surfaces of a gear pair. Smoothing the meshing tooth surfaces of a gear pair reduces the unevenness of the tooth surfaces. A reduction in the unevenness of the tooth surfaces can be expected to reduce friction between the meshing tooth surfaces of a gear pair. Therefore, according to conventional technical concepts, the smaller the level difference of the core portion (Rk), the height of the protruding peak (Rpk), and the depth of the protruding valley (Rvk) between the first usable tooth surface and the second usable tooth surface, the lower the coefficient of friction will be.

[0056] Here, No. 4, No. 7, No. 9, and No. 10 all have surface properties such that the first Rk is 0.030 μm or more and 0.060 μm or less, the first Rvk is 0.015 μm or more and 0.030 μm or less, and the second Rk is 0.080 μm or more and 0.240 μm or less. Also, the second Rpk of No. 4, No. 7, No. 9, and No. 10 is all smaller than the second Rpk of No. 1. Furthermore, the second Rvk of No. 4, No. 7, No. 9, and No. 10 is all smaller than the second Rvk of No. 1 and No. 2. That is, No. 4, No. 7, No. 9, and No. A ball 51 having surface texture No. 10 is as smooth as a ball 51 having surface texture No. 1, while a disc 52 having surface textures No. 4, No. 7, No. 9, and No. 10 is at least smoother than a disc 52 having surface texture No. 1. Therefore, according to the conventional technology described above, the coefficient of friction between a ball 51 and a disc 52 having surface textures No. 4, No. 7, No. 9, and No. 10 is expected to be at least lower than the coefficient of friction between a ball 51 and a disc 52 having surface texture No. 1. However, contrary to the expectation based on the conventional technology described above, the coefficient of friction between a ball 51 and a disc 52 having surface texture No. 1 is lower than that between a ball 51 and a disc 52 having surface textures No. 4, No. 7, No. 9, and No. It was experimentally proven that the coefficient of friction between the ball 51 and the disc 52, which have 10 surface properties, is reduced.

[0057] Therefore, the experimental results shown in Table 1 experimentally suggest that a gear pair having a first usable tooth surface with a first Rk of 0.030 μm or more and 0.060 μm or less, preferably 0.040 μm or more and 0.050 μm or less, and a first Rvk of 0.015 μm or more and 0.030 μm or less, preferably 0.020 μm or more and 0.025 μm or less, and a second usable tooth surface that contacts the first usable tooth surface with a second Rk of 0.080 μm or more and 0.240 μm or less, preferably 0.090 μm or more and 0.235 μm or less, and a second Rvk / Rk of 2.20 or more and 3.00 or less, preferably 2.40 or more and 2.90 or less, reduces the coefficient of friction between the meshing tooth surfaces. Furthermore, in addition to the above-mentioned conditions for the first Rk and first Rvk, a gear pair having a first usable tooth surface with a first Rvk / Rk of 0.40 or more and 0.50 or less, and a second gear having a second usable tooth surface in contact with the first usable tooth surface, with a second Rpk of 0.050 μm or more and 0.150 μm or less, and a second Rvk of 0.200 μm or more and 0.700 μm or less, was experimentally suggested to further reduce the coefficient of friction between the meshing tooth surfaces. In addition, it was experimentally suggested that a gear pair having the above-mentioned combinations from the first to the fourth combinations further reduces the coefficient of friction between the meshing tooth surfaces.

[0058] 1 Gear pair 10 First gear 11 First tooth 110 Top of first tooth 111 First tooth surface 111a First usable tooth surface 111b First fillet 112 Second tooth surface 112a Third usable tooth surface 112b Third fillet 12 First tooth root 20 Second gear 21 Second tooth 210 Second top 211 Third tooth surface 211a Second usable tooth surface 211b Second fillet 212 Fourth tooth surface 212a Fourth usable tooth surface 212b Fourth fillet 22 Second tooth root 30 First shaft 40 Second shaft 50 MTM traction tester 51 Ball 52 Disc 53 Lubricating oil reservoir 54 Heater FRD: Rotation direction of the first gear; SRD: Rotation direction of the second gear; FCD: Circumferential direction of the first gear; SRD: Circumferential direction of the second gear; FIS: First side; SES: Second side; THS: Third side; FOS: Fourth side; LUO: Lubricating oil

Claims

1. A gear pair comprising a first gear and a second gear, wherein the first gear comprises a plurality of first tooth vertices, a plurality of first tooth roots, a first tooth surface located between the first tooth vertices and the first tooth roots and facing a first side in the circumferential direction of the first gear, and a third tooth surface located between the first tooth vertices and the first tooth roots and facing a third side in the circumferential direction of the first gear, wherein the first tooth surface comprises a first usable tooth surface adjacent to the first tooth vertices, and a first fillet tooth located radially inward from the first usable tooth surface and adjacent to the first tooth root, and the second gear comprises a plurality of second tooth vertices, a plurality of second tooth roots, The gear comprises: a second tooth surface located between the apex and the root of the second tooth and facing the second side in the circumferential direction of the second gear; and a fourth tooth surface located between the apex and the root of the second tooth and facing the fourth side in the circumferential direction of the second gear, wherein the second tooth surface comprises: a second usable tooth surface adjacent to the apex of the second tooth; and a second fillet located radially inward from the second usable tooth surface and adjacent to the root of the second tooth, wherein the first usable tooth surface and the second usable tooth surface are contactable, and the first usable tooth surface has a level difference (first Rk) of the core portion of the first usable tooth surface determined from the load curve of the first contour surface of the first usable tooth surface of the first usable tooth surface of 0.030 μm or more and 0.060 μm or less. A gear pair having a surface texture in which the depth of the protruding valley (first Rvk) of the first usable tooth surface is 0.015 μm or more and 0.030 μm or less, and the second usable tooth surface has a surface texture in which the level difference of the core portion of the second usable tooth surface (second Rk), determined from the load curve of the second contour curve of the second usable tooth surface, is 0.080 μm or more and 0.240 μm or less, and the ratio of the depth of the protruding valley (second Rvk) of the second usable tooth surface to the level difference of the core portion (second Rk) of the second usable tooth surface (second Rvk / Rk) is 2.20 or more and 3.00 or less.

2. The gear pair according to claim 1, wherein the first Rk is 0.040 μm or more and 0.050 μm or less, the first Rvk is 0.020 μm or more and 0.025 μm or less, the second Rk is 0.090 μm or more and 0.235 μm or less, and the second Rvk / Rk is 2.40 or more and 2.90 or less.

3. The gear pair according to claim 2, wherein the ratio of the first Rvk to the first Rk (first Rvk / Rk) is 0.40 or more and 0.50 or less, the height of the protruding peak of the second usable tooth surface (second Rpk), determined from the load curve of the second contour surface, is 0.050 μm or more and 0.150 μm or less, and the depth of the protruding valley of the second usable tooth surface (second Rvk) is 0.200 μm or more and 0.700 μm or less.

4. The gear pair according to any one of claims 1 to 3, wherein the first usable tooth surface and the second usable tooth surface are each made of steel.

5. The gear pair according to claim 4, wherein the first usable tooth surface and the second usable tooth surface each have a hardness of HV500 or more and HV860 or less.

6. The gear pair according to any one of claims 1 to 3, wherein the first gear is an external gear and the second gear is an external gear.

7. The gear pair according to claim 4, wherein the first gear is an external gear and the second gear is an external gear.

8. The gear pair according to claim 5, wherein the first gear is an external gear and the second gear is an external gear.

Images