Method for manufacturing gear device, and gear device

Abstract

To provide a gear device capable of suppressing generation of stick slip and generation of frictional sound.SOLUTION: A method of manufacturing a gear device including a gear pair having a first gear made of steel and a second gear made of resin and meshing with the first gear, and grease containing a base oil and a thickener, the thickener being diurea, the grease having an unworked penetration of 165 or more and 215 or less, the grease adhering to a first available tooth surface of the first gear and a second available tooth surface of the second gear, the method comprising: Applying a heating treatment to the gear pair to which the pre-heating grease has adhered after the pre-heating grease has adhered to the first available tooth surface of the first gear and the second available tooth surface of the second gear, wherein a worked penetration of the pre-heating grease is 260 or more and 315 or less, an unworked penetration of the pre-heating grease is 220 or more and 300 or less, and in the heating treatment, the gear pair to which the pre-heating grease has adhered is left to stand at a temperature of 90 °C or more and 130 °C or less for 10 hours or more and 30 hours or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a gear device, and to a gear device. [Background technology]

[0002] An electric power steering device is configured such that, when a driver rotates a steering member such as a steering wheel, the output rotation of an electric motor for assisting steering force is controlled in accordance with the steering torque applied to the steering member, and the rotational force of this electric motor is transmitted to the steering mechanism via a reducer, thereby assisting the operation of the steering mechanism in accordance with the rotational operation of the steering member.

[0003] The speed reducer is a type of gear device, and typically includes a metal worm and a resin worm wheel that mesh with each other, and a housing to house them in. The housing is filled with grease to lubricate the meshing portion between the worm and the worm wheel (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-122659 Summary of the Invention

[0005] A method for manufacturing a gear device according to one aspect of the present disclosure includes: a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; Equipped with the first gear is made of steel; the second gear is made of resin, The thickener is diurea, The unmixed penetration of the grease is 165 or more and 215 or less, A method for manufacturing a gear device in which the grease is applied to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear, the method comprising: a step of applying pre-heated grease to the first usable tooth surface of the first gear and the second usable tooth surface of the second gear, and then subjecting the gear pair to a heat treatment; The worked penetration of the grease before heating is 260 or more and 315 or less, The unmixed penetration of the grease before heating is 220 or more and 300 or less, In the heat treatment, the gear pair to which the pre-heated grease is attached is left standing at a temperature of 90° C. or higher and 130° C. or lower for 10 hours or higher and 30 hours or lower.

[0006] A gear device according to one aspect of the present disclosure includes: a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; A gear train comprising: the first gear is made of steel; the second gear is made of resin, The thickener is diurea, the grease adheres to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear; The unmixed penetration of the grease is 165 or more and 215 or less. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a configuration of a power steering device. [Figure 2] 2 is a partial cross-sectional view showing a reducer provided in the power steering device of FIG. 1. [Figure 3] FIG. 1 is a diagram illustrating a reciprocating sliding friction and wear tester. [Figure 4] 1 is a graph showing the relationship between the number of cycles and acceleration measured in a reciprocating sliding friction and wear test. [Figure 5] 1 is a photograph showing the evaluation results of grease A. [Figure 6] 10 is a photograph showing the evaluation results of grease C. DETAILED DESCRIPTION OF THE INVENTION

[0008] <Problems to be Solved by the Invention of the Present Disclosure> In a reducer provided in a power steering device, stick-slip occurs at the meshing portion between the worm and the worm wheel, and abnormal noise due to stick-slip is a problem. As explained above, the meshing portion between the worm and the worm wheel is lubricated with grease, but if the grease is removed from the sliding surfaces and becomes scarce, the worm and the worm wheel come into direct contact, causing stick-slip and abnormal noise.

[0009] One possible solution to the above problem is to reduce the consistency of the grease, thereby making it more difficult for the grease to escape from the sliding surfaces, thereby suppressing the occurrence of stick-slip and other problems. However, if the consistency of the grease is reduced, it becomes difficult to seal the grease into the reducer when manufacturing the reducer, and the grease is not sufficiently supplied to the meshing portion between the worm and the worm wheel. In the manufactured reducer, the sliding surfaces of the meshing portion may not be sufficiently lubricated with grease. Furthermore, sealing the grease takes time and effort, which can increase the cycle time during manufacturing.

[0010] <Effects of the Invention of the Present Disclosure> According to the invention of the present disclosure, a gear device can be provided in which low-viscosity grease is supplied to the meshing portion of the gear pair, making it difficult for the grease to escape from the sliding surfaces of the meshing portion, and thereby suppressing the occurrence of stick-slip and friction noise over a long period of time.

[0011] <Summary of the embodiments of the present disclosure> Below, an outline of the embodiments of the present disclosure will be listed and described. (1) The manufacturing method of the gear device of the present disclosure includes: a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; Equipped with the first gear is made of steel; the second gear is made of resin, The thickener is diurea, The unmixed penetration of the grease is 165 or more and 215 or less, A method for manufacturing a gear device in which the grease is applied to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear, the method comprising: a step of applying pre-heated grease to the first usable tooth surface of the first gear and the second usable tooth surface of the second gear, and then subjecting the gear pair to a heat treatment; The worked penetration of the grease before heating is 260 or more and 315 or less, The unmixed penetration of the grease before heating is 220 or more and 300 or less, In the heat treatment, the gear pair to which the pre-heated grease is attached is left standing at a temperature of 90° C. or higher and 130° C. or lower for 10 hours or higher and 30 hours or lower.

[0012] According to the above-described method for manufacturing a gear device, it is possible to provide a gear device in which low-consistency grease is applied to the first usable tooth surface of the first gear and the second usable tooth surface of the second gear. The above manufacturing method allows for smooth supply of green material, so the cycle time does not increase compared to manufacturing a gear device lubricated with high-consistency grease.

[0013] (2) In the method for producing a gear device according to (1) above, the heat treatment is preferably carried out in a state where the gear pair to which the pre-heated grease is attached is placed in the internal space of a container.

[0014] (3) The gear device of the present disclosure is a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; A gear train comprising: the first gear is made of steel; the second gear is made of resin, The thickener is diurea, the grease adheres to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear; The unmixed penetration of the grease is 165 or more and 215 or less.

[0015] In the above gear device, the grease adhering to the first usable tooth flank of the first gear and the second usable tooth flank of the second gear is a hard grease with an unmixed penetration of 165 to 215, which is difficult to remove from the sliding surfaces of the meshing portions of the gear pair. As a result, the above gear device is able to suppress the occurrence of stick-slip and friction noise over a long period of time.

[0016] <Details of the embodiment of the present disclosure> Hereinafter, embodiments of the present disclosure will be described. It should be noted that in this disclosure, the embodiments of the invention should be considered to be illustrative in all respects and not restrictive. The scope of the rights of the present disclosure is defined by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0017] As an example of an embodiment of a gear device and a manufacturing method thereof according to the present disclosure, a reducer provided in a column-type electric power steering device and a manufacturing method thereof will be described below. In this reducer, the worm corresponds to the first gear and the worm wheel corresponds to the second gear.

[0018] Fig. 1 is a schematic diagram showing the configuration of a column-type electric power steering device equipped with a reducer according to an embodiment of the present disclosure, and Fig. 2 is a partial cross-sectional view showing the reducer equipped in the column-type electric power steering device of Fig. 1. This column type electric power steering device P is a column type electric power steering device in which a steering member 1 and wheels 2 are mechanically connected.

[0019] The steering member 1 is connected to a steering shaft 3 so as to be rotatable together with the steering shaft 3, and a pinion gear 4 is provided at the tip of the steering shaft 3. The pinion gear 4 meshes with a rack gear 6 provided on a rack shaft 5 extending in the left-right direction of the vehicle. Tie rods 7 are connected to both ends of the rack shaft 5. Each tie rod 7 is connected to a wheel 2 via a corresponding knuckle arm (not shown).

[0020] When the steering shaft 3 is rotated by rotating the steering member 1, the rotational motion of the steering shaft 3 is converted by the pinion gear 4 and the rack gear 6 into linear motion of the rack gear 6 along the left-right direction of the vehicle. By rotating the steering member 1, the wheels 2 are steered in the desired direction.

[0021] The steering shaft 3 includes a cylindrical first steering shaft 8 connected to the steering member 1 and a second steering shaft 9 connected to the pinion gear 4. The first steering shaft 8 and the second steering shaft 9 are connected to each other on the same axis via a torsion bar 10. A torque sensor 11 is disposed adjacent to the torsion bar 10. The torque sensor 11 detects the steering torque applied to the steering member 1 by the driver. The torque detection result of the torque sensor 11 is transmitted to a control unit 12. Based on the transmitted torque detection result, the control unit 12 controls the voltage applied to a steering-assist electric motor 14 via a driver 13. The rotation of a rotary shaft 21 (see FIG. 2) of the electric motor 14 is transmitted to the second steering shaft 9 via a reducer 20 (described later) to assist the driver's steering.

[0022] The reducer 20 reduces the rotation of the rotary shaft 21 of the electric motor 14 and transmits it to the second steering shaft 9. As shown in Fig. 2, the reducer 20 includes a worm shaft 22 driven by a rotating shaft 21 of the electric motor 14, and a worm wheel 23 driven by the worm shaft 22. The worm shaft 22 is disposed coaxially with the rotating shaft 21 and is rotatable integrally therewith. The worm shaft 22 is made of steel, such as S43C or SCM420. The worm wheel 23 is disposed to mesh with a worm 24 provided near the axial middle of the worm shaft 22, and is engaged with the second steering shaft 9 and is rotatable integrally therewith. The worm shaft 22 and the worm wheel 23 constituting the reducer 20 are accommodated in an aluminum housing 15 together with rolling bearings, which will be described later.

[0023] The worm shaft 22 is connected to the rotating shaft 21 of the electric motor 14 via a spline joint 25. This spline joint 25 is composed of a spline shaft 26 and a boss 27. The spline shaft 26 is formed on the motor-side end 22a of the worm shaft 22, and has multiple keyways on the outer peripheral surface of the motor-side end 22a. The boss 27 is a cylindrical body that is connected to the rotating shaft 21 of the electric motor 14 so as to be rotatable together with it, and has ridges on its inner peripheral surface. The ridges fit into the keyways of the spline shaft 26.

[0024] The worm shaft 22 is rotatably supported near both ends by rolling bearings 30, 40, each consisting of a ball bearing. More specifically, the worm shaft 22 is supported near its motor-side end by a first rolling bearing 30. An inner ring 32 of the first rolling bearing 30 is fitted into a corresponding necked portion of the worm shaft 22, and an outer ring 33 of the first rolling bearing 30 is held in a bearing retaining hole 31 in the housing 15. The outer ring 33 of the first rolling bearing 30 is fixed to the bearing retaining hole 31 in the housing 15 by means of a screw or the like so that it is substantially immovable when the worm shaft 22 rotates. Meanwhile, the worm shaft 22 is supported near its anti-motor end 22b by a second rolling bearing 40. The inner ring 42 of the second rolling bearing 40 is fitted into a corresponding necked portion of the worm shaft 22, and the outer ring 43 of the second rolling bearing 40 is held in a bearing retaining hole 41 of the housing 15. Unlike the outer ring 33 of the first rolling bearing 30, the outer ring 43 of the second rolling bearing 40 is disposed in the bearing retaining hole 41 of the housing 15 with a small gap remaining between it and the inner surface of the bearing retaining hole 41 so that it can move when the worm shaft 22 rotates. The outer ring 33 of the first rolling bearing 30 is urged toward the second rolling bearing 40 by a screw member 34 for adjusting the preload. After the preload has been adjusted, the screw member 34 is fixed with a lock nut 35.

[0025] The worm wheel 23 is made of a core 23a and a toothed portion 23b. The core 23a is annular. The core 23a is connected to the second steering shaft 9 so as to be rotatable integrally therewith. The toothed portion 23b is disposed on the outer periphery of the core 23a. The toothed portion 23b is made of synthetic resin. Teeth are provided on the outer periphery of the toothed portion 23b. The teeth of the toothed portion 23b are provided to mesh with the worm 24. The synthetic resin used as the material for the toothed portion 23b is, for example, polyamide such as polyamide 6 (PA6), polyamide 66 (PA66), or polyamide 46 (PA46).

[0026] Grease G is sealed inside the housing 15. The grease G is a lubricant for suppressing wear at the meshing portion between the worm 24 and the worm wheel 23. The grease G is attached to at least the usable tooth surface of the worm 24 and the usable tooth surface of the tooth portion 23b of the worm wheel 23. The grease G may be filled throughout the housing 15.

[0027] Grease G contains a base oil and a thickener. The thickener is diurea. Grease G is a urea-based grease. Examples of the base oil include mineral oil, ether oil such as alkyl diphenyl ether (ADE), ester oil, poly-α-olefin (PAO), polyalkylene glycol, fluorine oil, silicone oil, etc. Among these, the preferred base oil is poly-α-olefin (PAO). The preferred kinematic viscosity (40°C) of the base oil is 48mm 2 The kinematic viscosity of the base oil is, for example, a value in accordance with JIS K 2283.

[0028] The diurea is preferably a diurea represented by the following formula (1). R 1 -NHCONH-R 2 -NHCONH-R 3 ···(1) (In formula (1), R 1 and R 3 are independent of each other, -C n H 2n+1 (n is an integer of 8 to 18), or an alkyl group represented by R 4 -C6H 10 -(R 4 is hydrogen, a 2-methyl group, a 3-methyl group, or a 4-methyl group), and R 2 is -(CH2)6-, -C6H3(CH3)-, or -C6H4-CH2-C6H4-. In the above formula (1), R 2 When R is —C6H3(CH3)—, the phenylene group is preferably bonded at the 2,4 or 2,6 positions with the methyl group at the 1 position.2 When is -C6H4-CH2-C6H4-, both phenylene groups are preferably bonded at the para position.

[0029] The diurea represented by the above formula (1) is a product formed by the reaction of an amine compound with a diisocyanate compound. The amine compound is an aliphatic amine and / or an alicyclic amine. The aliphatic amine is, for example, an aliphatic amine having 8 to 18 carbon atoms, and specific examples of the aliphatic amine include octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, and oleylamine. Specific examples of the alicyclic amine include cyclohexylamine, 1-amino-2-methylcyclohexane, 1-amino-3-methylcyclohexane, and 1-amino-4-methylcyclohexane.

[0030] The grease G may contain additives in addition to the base oil and the thickener. Examples of the additives include antioxidants, rust inhibitors, extreme pressure agents, oiliness agents, anti-wear agents, dyes, color stabilizers, thickeners, structure stabilizers, metal deactivators, and viscosity index improvers.

[0031] The unmixed penetration of the grease G is 165 or more and 215 or less. This grease G is harder than the grease sealed in conventional reducers. Therefore, even when the worm 24 and the tooth portion 23b of the worm wheel 23 slide against each other, the grease G is less likely to escape from the meshing portion (sliding surface) between them. Grease G having an unworked penetration of less than 165 is difficult to prepare. On the other hand, if the unmixed penetration of the grease G exceeds 215, the grease G is likely to escape from the meshing portion between the worm 24 and the tooth portion 23b of the worm wheel 23. Therefore, it is difficult for the grease G to remain attached to the usable tooth surfaces of the worm 24 and the usable tooth surfaces of the tooth portion 23b of the worm wheel 23.

[0032] In the presently disclosed invention, the worked penetration and unworked penetration of the grease are both measured by a method conforming to "7. Penetration test method" of JIS K 2220 (2013).

[0033] Next, a method for manufacturing the reducer 20 will be described. (1) First, a reducer 20' that is not filled with grease and grease G' are prepared. The reducer 20' has the same configuration as the reducer 20, except that the grease G is not filled. Grease G' is a urea-based grease. Grease G' contains the same base oil, thickener, and additives as Grease G in the same proportions as Grease G. Grease G' has a different unmixed consistency from Grease G. When grease G' is heated, hydrogen bonds are formed between the thickener molecules, causing the consistency to decrease and becoming grease G. Grease G' before being heated is also called pre-heated grease.

[0034] The worked penetration of grease G' is 260 or more and 315 or less. The unworked penetration of grease G' is 220 or more and 300 or less. When the worked penetration of the grease G' is within the above range, it is easy to seal the grease G' inside the reducer 20', and the grease G' easily adheres to the usable tooth surfaces of the worm 24 and the usable tooth surfaces of the tooth portion 23b of the worm wheel 23. Therefore, the grease G' is smoothly supplied into the reducer 20', and an increase in the cycle time for manufacturing the reducer 20 can be avoided.

[0035] Since the unmixed penetration of grease G' is within the above range, after grease G' is sealed inside reducer 20', the reducer 20' containing grease G' is subjected to a heat treatment under specified conditions, so that grease G' is suitable for becoming grease G having an unmixed penetration of 165 or more and 215 or less.

[0036] Grease G' can be produced by a conventionally known method for producing urea-based grease. Specifically, grease G' is, for example, (a) preparing a base oil containing an amine compound and a base oil containing a diisocyanate compound; (b) A step of adding dropwise one base oil to another base oil and mixing the two to react the amine compound with the diisocyanate compound to generate diurea as a thickener in the base oil; and (c) adding additives as needed; It is manufactured through the following process.

[0037] (2) Next, the grease G' (pre-heated grease) is sealed in the housing 15 of the reducer 20', and the grease G' adheres to the usable tooth surface of the worm 24 and the usable tooth surface of the tooth portion 23b of the worm wheel 23. Thereafter, the reducer 20' filled with the grease G' is subjected to a heat treatment.

[0038] The heat treatment is carried out by leaving the reducer 20' filled with the grease G' for 10 to 30 hours in an environment at a temperature of 90 to 130° C. As a result, the grease G' changes into the grease G having an unmixed penetration of 165 to 215. By carrying out this heat treatment, hydrogen bonds are formed between the molecules of the thickener diurea, and as a result, grease G' becomes grease G, which has a low immiscible consistency and is hard. The heating conditions are adjusted within the above ranges, taking into consideration the unmixed penetration of the grease before heating (grease G') and the unmixed penetration of grease G.

[0039] If the heating temperature during the heat treatment is less than 90°C, the unmixed penetration of the grease G may not decrease to the above range. On the other hand, if the heating temperature exceeds 130°C, deterioration of the grease G may be accelerated, resulting in a loss of lubrication. This may also accelerate deterioration of the synthetic resin from which the worm wheel is made.

[0040] If the heating time is less than 10 hours during the heat treatment, the unmixed penetration of the grease G may not decrease to the above range. On the other hand, if the heating time exceeds 30 hours, the deterioration of the grease G may be accelerated, resulting in a loss of lubrication. This may also accelerate the deterioration of the synthetic resin from which the worm wheel is made.

[0041] By going through these steps, a reducer 20 is manufactured in which grease G having an unmixed penetration of 165 or more and 215 or less is adhered to the usable tooth surface of the worm 24 and the usable tooth surface of the tooth portion 23b of the worm wheel 23.

[0042] The performance of the grease produced under the conditions of the manufacturing method of this embodiment was evaluated. The evaluation method and evaluation results are shown below. In this evaluation, the sliding performance of three types of grease was compared.

[0043] In this evaluation, first, the following greases A and B were prepared. Both grease A and grease B are urea-based greases. Grease A: Kyodo Yushi, thickener: aliphatic diurea, base oil: PAO8 (worked penetration (60W): 392, unworked penetration: 379) Grease B: Kyodo Yushi, thickener: aliphatic diurea, base oil: PAO8 (worked penetration (60W): 263, unworked penetration: 240)

[0044] Next, grease B was subjected to a heat treatment at 100°C for 20 hours to change into grease C. The resulting grease C had a worked penetration (60W) of 227 and an unworked penetration of 188.

[0045] Greases A to C were subjected to a reciprocating sliding friction and wear test. This test was carried out using a reciprocating sliding friction and wear tester (manufactured by IS Giken Co., Ltd.) under the following conditions. FIG. 3 is a diagram illustrating a reciprocating sliding friction and wear tester 100. As shown in FIG.

[0046] This testing machine 100 has a steel plate 101 and a movable arm 103 to the tip of which a sliding member 102 is fixed. This movable arm 103 is configured to be able to move back and forth while pressing the sliding member 102 against the steel plate 101 with a predetermined surface pressure. In the testing machine 100, the steel plate 100 is made of S43C (unheat-treated, HV200). The sliding member 102 is made of resin, and is made of polyamide 6 (MC901, manufactured by Mitsubishi Chemical Advanced Materials Corporation). Furthermore, in this testing machine 100, an acceleration sensor 105 is attached to the movable arm 103.

[0047] In this evaluation, one of greases A to C was applied to the upper surface of the steel plate 101 to a thickness of 1 to 2 μm, and the sliding member 102 was moved back and forth in the left and right direction (see the double-headed arrows in FIG. 3 ) with the movable arm 103 pressing the sliding member 102 against the steel plate 101 so that the steel plate 101 and the sliding member 102 came into contact with each other via the grease. One reciprocation constitutes one cycle. The sliding conditions are: Sliding speed: 2mm / s ·Return travel distance: 20mm Load: 30N (surface pressure: 1.5MPa) Test temperature: 90℃ Number of cycles: 600 cycles (cyc) is.

[0048] In this evaluation, the acceleration of the movable arm 103 is measured using the acceleration sensor 105, and the acceleration (m / s 2 The maximum value of acceleration was calculated. The results are shown in Figure 4. Figure 4 is a graph showing the relationship between the number of cycles and acceleration measured in a reciprocating sliding friction and wear test, with the horizontal axis representing the number of cycles and the vertical axis representing the maximum acceleration value in one cycle.

[0049] Furthermore, in the evaluation of Grease A and Grease C, the state of remaining grease at the turning points of the reciprocating movement on the steel plate 101 was observed at the end of 10 cycles, 100 cycles, and 200 cycles. The results are shown in FIGS. Fig. 5 is an observation photograph of grease A, and Fig. 6 is an observation photograph of grease C. The grease remaining on the steel plate 101 is observed as a convex arc on the left side of the figure. Comparing Figs. 5 and 6, it can be seen that more grease C (Fig. 6) remains on the steel plate than grease A (Fig. 5).

[0050] From these results, it can be seen that the gear device according to the embodiment of the presently disclosed invention can maintain grease adhered to the meshing portions of the gear pair (the usable tooth surfaces of the first gear and the usable tooth surfaces of the second gear) for a long period of time.

[0051] While the speed reducer provided in a column-type electric power steering device has been described as a specific example of a gear device according to an embodiment of the present disclosure, the specific example of the gear device may also be a speed reducer provided in a dual-pinion type electric power steering device. [Explanation of symbols]

[0052] 1 Steering member 2 wheels 3 Steering shaft 4 pinion gear 5 rack axis 8 First steering shaft 9 Second steering shaft 10 Torsion Bar 14 Electric motor 15 Housing 20 Reducer 21 Rotation axis 22 Worm shaft 23 Worm Wheel 24 Warm 25 spline joint 30 Rolling bearing (first rolling bearing) 31 Bearing retaining hole 32 Inner circle 33 Outer ring 40 Rolling bearing (second rolling bearing) 41 Bearing retaining hole 42 Inner circle 43 Outer ring 100 Reciprocating sliding friction and wear tester P Power steering device Grease

Claims

1. a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; Equipped with the first gear is made of steel; the second gear is made of resin, the thickener is diurea, The unmixed penetration of the grease is 165 or more and 215 or less, A method for manufacturing a gear device in which the grease is applied to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear, the method comprising: a step of applying pre-heated grease to the first usable tooth surface of the first gear and the second usable tooth surface of the second gear, and then subjecting the gear pair to a heat treatment; The worked penetration of the grease before heating is 260 or more and 315 or less, The unmixed penetration of the grease before heating is 220 or more and 300 or less, The method for manufacturing a gear device, wherein the heat treatment comprises leaving the gear pair having the pre-heated grease attached thereto at a temperature of 90°C or higher and 130°C or lower for 10 hours or higher and 30 hours or lower.

2. The method for manufacturing a gear device according to claim 1 , wherein the heat treatment is performed in a state where the gear pair to which the pre-heated grease is attached is placed in an internal space of a container.

3. a gear pair including a first gear and a second gear meshing with the first gear; a grease containing a base oil and a thickener; A gear train comprising: the first gear is made of steel; the second gear is made of resin, the thickener is diurea, the grease adheres to a first usable tooth surface of the first gear and a second usable tooth surface of the second gear; A gear device, wherein the unmixed penetration of the grease is 165 or more and 215 or less.

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