JP2015187480A - Gear wheel mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gear wheel mechanism that can suppress uneven wear of a coating layer formed at a surface of a base material.SOLUTION: In the gear wheel mechanism that includes a first gear wheel and a second gear wheel meshing with the first gear wheel and rotating at a rotation number different from that of the first gear wheel, where the surface of the base material forming a tooth of each of the gear wheels is coated with a material with a predetermined hardness, surface hardness of a first coating layer coating the surface of the base material 5 in a gear wheel that rotates at a smaller rotation number of the first gear wheel and the second gear wheel is formed so as to be lowered from the addendum toward the dedendum thereof, while surface hardness of a second coating layer coating the surface of the base material 5 in a gear wheel that rotates at a larger rotation number of the first gear wheel and the second gear wheel is formed so as to be lowered from the dedendum toward the addendum thereof.

Description

  The present invention relates to a gear mechanism in which teeth having a coating layer mesh with each other to transmit torque.

  In Patent Document 1, an incompletely hardened layer inevitably generated by heat treatment of a tooth surface is peeled off by spraying a high-hardness granular material, and shot peening is performed on the tooth surface from which the incompletely hardened layer has been peeled off. A gear configured to impart compressive residual stress by processing is described. In addition, the gear mechanism described in Patent Document 2 selects a gear on which a large torque acts due to torsional vibration or torque fluctuation from among a plurality of gears, and carburizes or shot peening only the gear. Further, it is configured to improve the hardness of the tooth surface as compared with other gears by performing a surface hardening process such as nitriding or induction hardening.

JP 2002-166366 A JP 2007-100894 A

  By the way, as for the gears meshing with each other, the oil film thickness interposed between the tooth surfaces in meshing contact with each other increases as the average tooth surface speed at the portion where these gears mesh with each other increases. In addition, the gears that mesh with each other change the friction coefficient at the time of torque transmission according to the ratio of transmitting torque through metal contact and the ratio of transmitting torque through an oil film interposed between the tooth surfaces of the gears. . Specifically, the friction coefficient during torque transmission decreases as the ratio of torque transmission through the oil film increases. Therefore, when the meshing position is changed and the average tooth surface speed is changed, the friction coefficient at the time of torque transmission is changed. Therefore, the manner of wear differs depending on the meshing position, and the tooth surface may be unevenly worn.

  The present invention has been made against the background described above, and an object of the present invention is to provide a gear mechanism that can suppress uneven wear of a coating layer formed on the surface of a base material.

  To achieve the above object, the invention of claim 1 includes a first gear and a second gear that meshes with the first gear and rotates at a rotational speed different from the rotational speed of the first gear, In the gear mechanism in which the surface of the base material forming the teeth of each gear is coated with a material having a predetermined hardness, the surface of the base material in the gear rotating at a low rotational speed of the first gear and the second gear. In the gear that is formed so that the hardness of the surface of the first coating layer that covers the surface decreases from the tooth tip toward the tooth base, and rotates at a high rotational speed of the first gear and the second gear. It is characterized in that the hardness of the surface of the second coating layer covering the surface of the base material is formed so that the hardness decreases from the tooth base toward the tooth tip.

  According to the present invention, two gears having different rotational speeds mesh with each other to transmit torque. In such a gear mechanism in which two gears having different rotational speeds mesh with each other and transmit torque, when the tooth root side of the gear rotating at a low rotational speed meshes and transmits torque, the tooth surface and the other tooth surface are transmitted to each other. The oil film thickness interposed between the two tooth surfaces becomes thicker than the oil film thickness interposed between the tooth surface and the other tooth surface when the tooth tip side of the gear rotating at a low rotational speed meshes and transmits torque. . In addition, when the tooth tips in a gear rotating at a high rotational speed mesh with each other to transmit torque, the oil film thickness interposed between the tooth surface and the other tooth surface is the tooth in the gear rotating at a high rotational speed. When the original side meshes and transmits torque, it becomes thicker than the oil film thickness interposed between the tooth surface and the other tooth surface. Therefore, the hardness of the surface of the first coating layer covering the surface of the base material in the gear rotating at a low rotational speed is formed so that the hardness decreases from the tooth tip to the tooth root, and the gear rotates at a high rotational speed. By forming the hardness of the surface of the second coating layer covering the surface of the base material in the gear so that the hardness decreases from the tooth root toward the tooth tip, the wear amount between the tooth tip and the tooth root in each gear is reduced. Different things, that is, uneven wear can be suppressed.

It is sectional drawing for demonstrating the structure of the coating layer in this invention. It is a figure for demonstrating the change of an average tooth surface speed. It is a figure for demonstrating distribution of oil film thickness.

  The gear mechanism that is the subject of this invention is used as a speed-up gear or a speed reducer so that the rotation speed on the input side is changed and output, and the rotation speeds of the driving gear and the driven gear are different. It is a gear mechanism that can be used for vehicles and various industrial machines. The gear is generally a helical gear, but may be a gear having another structure such as a spur gear. In the following description, a gear mechanism using a gear formed of a metal material will be described as an example. In general, a gear formed of a metal material is formed from a raw material through a process such as rolling, turning, and gear cutting, and a rough shape is formed and then the teeth are ground. Further, in order to improve the strength of the tooth surface, compressive residual stress is applied by shot peening or the like in which fine particles are sprayed on the tooth surface. In such a shot peening process, since the surface roughness of the tooth surface becomes rough by spraying fine particles on the tooth surface, a coating layer of a material having low hardness is formed on the surface of the ground base material. In addition, when forming a coating layer of a high hardness material on the surface of the base material according to the load acting on the tooth surface, or a coating layer of a high hardness material on the surface of the base material according to the meshing loss of the tooth surface Sometimes it forms. Therefore, the coating layer in this invention should just coat | cover the surface of a base material, and does not limit whether the hardness is higher than the hardness of a base material.

この式で、ｈｃは油膜厚さ、Ｅは歯車を形成する材料の弾性定数、ｕは平均歯面速度（＝（ｕ_１＋ｕ_２）／２）、Ｒｘは接触部における互いに直交する一方の主曲率面の半径をそれぞれＲ_ｘ１、Ｒ_ｘ２とした場合に（Ｒ_ｘ１ ^−１＋Ｒ_ｘ２ ^−１）^−１で表される値、Ｒｙは他方の主曲率面の半径をそれぞれＲ_ｙ１、Ｒ_ｙ２とした場合に（Ｒ_ｙ１ ^−１＋Ｒ_ｙ２ ^−１）^−１で表される値、η_０は大気圧でのオイル粘度、αはオイルの粘度−圧力係数であって一般的な鉱油では「２０Ｇｐａ^−１」程度である。また、ｕ_１は一方の歯車における噛み合い部の歯面速度（周速）、ｕ_２は他方の歯車における噛み合い部の歯面速度（周速）である。したがって、潤滑油の粘度や歯車の諸元は固定値であるため、平均歯面速度ｕが増大すると、油膜厚さｈｃが増大する。 The gear mechanism formed as described above normally transmits power while lubricating oil is supplied to the meshing portion between the driving gear and the driven gear. In other words, power is transmitted with the lubricating oil interposed in the meshing portion. The thickness of the lubricating oil (hereinafter referred to as oil film thickness) varies according to the average value (hereinafter referred to as average tooth surface speed) of the peripheral speeds of the meshing portions that mesh with each other and transmit power. Specifically, it can be calculated by the following Chittenden film thickness calculation formula.

In this equation, hc is the oil film thickness, E is the elastic constant of the material forming the gear, u is the average tooth surface speed (= (u ₁ + u ₂ ) / 2), and Rx is one of the main parts orthogonal to each other at the contact portion. When the radius of the curvature surface is R _x1 and R _x2 , respectively, the value represented by (R _x1 ⁻¹ + R _x2 ⁻¹ ) ⁻¹ , Ry is the radius of the other main curvature surface, R _y1 and R _y2 , respectively. (R _y1 ⁻¹ + R _y2 ⁻¹ ) ⁻¹ , η ₀ is the oil viscosity at atmospheric pressure, α is the viscosity-pressure coefficient of the oil, and “20 Gpa ^{− About 1} ". U ₁ is the tooth surface speed (peripheral speed) of the meshing portion of one gear, and u ₂ is the tooth surface speed (peripheral speed) of the meshing portion of the other gear. Therefore, since the viscosity of the lubricating oil and the specifications of the gear are fixed values, the oil film thickness hc increases as the average tooth surface speed u increases.

  As described above, the gear mechanism that is the subject of the present invention is such that the rotational speeds of the drive side gear and the driven side gear are different. Therefore, when the gears transmit power on the pitch circle, more specifically, when the gears transmit power on the line connecting the rotation center of the driving gear and the rotation center of the driven gear. And the average tooth surface speed u is different from when the power is transmitted other than the pitch circle. FIG. 2 shows changes in the average tooth surface speed u when the position where the power is transmitted between the gears is away from the pitch circle. The horizontal axis in FIG. 2 indicates the distance between the pitch circle and the meshing position where power is transmitted, the direction closer to the rotation center of the driving gear is indicated by “−”, and the driven gear is The one near the center of rotation is indicated by “+”. Further, when the gear mechanism functions as a speed increaser, in other words, the change in the average tooth surface speed u when the rotational speed of the driven gear is faster than the rotational speed of the driving gear is shown by a solid line, and the gear mechanism is a speed reducer In other words, the change in the average tooth surface speed u when the rotational speed of the driven gear is slower than the rotational speed of the driving gear is indicated by a one-dot chain line. In the following description, a case where the gear mechanism functions as a speed increaser will be described as an example.

  As shown in FIG. 2, when the gear mechanism functions as a speed-up gear, when the teeth mesh with each other near the center of rotation of the driving gear and transmit power, the power is transmitted on the pitch circle. When the average tooth surface speed u is higher than when the gear is engaged and the teeth are meshed at a position close to the rotation center of the driven gear to transmit power, the power is transmitted on the pitch circle. The average tooth surface speed u is slow. That is, the average tooth surface speed u at the start of engagement between the teeth of the driving gear and the teeth of the driven gear is high, and the average tooth surface speed u decreases as the gear rotates by transmitting power, and the engagement ends. The average tooth surface speed u of the position is the slowest. This is because the drive-side gear is formed larger than the driven-side gear, and the rate of change of the tooth surface speed at the meshing position due to the change in radius from the rotation center to the meshing position due to the meshing position changing is different. It is.

  That is, when the gear mechanism functions as a speed increaser, when the tooth base side of the driving gear and the tooth tip side of the driven gear mesh with each other, the average tooth surface speed u is high, and the tooth in the driving gear is high. When the front side and the tooth base side of the driven gear are engaged with each other, the average tooth surface speed u is decreased.

  As described above, when the average tooth surface speed u changes, the oil film thickness hc at the tooth meshing position changes. Therefore, in the case of a gear mechanism that functions as a speed increaser, as shown in FIG. 3, the average tooth surface speed u at the start of meshing is faster than the average tooth surface speed u on the pitch circle, as shown in FIG. In addition, the oil film thickness hc is larger than the oil film thickness hc on the pitch circle. On the other hand, since the average tooth surface speed u at the position where the meshing is finished is slower than the average tooth surface speed u on the pitch circle, the oil film thickness hc is thin as shown in FIG. FIG. 3 schematically shows changes in the oil film thickness hc. The horizontal axis represents the same as the horizontal axis shown in FIG. 2, and the vertical axis represents the oil film thickness hc. .

On the other hand, the friction coefficient μ at the entire meshing position is determined by the ratio of the portion that handles the load with the oil film and the portion that handles the load with the tooth surface (metal). Specifically, it is calculated | required by the formula shown below.
μ = (1−α) μ _L + αμ _S

Incidentally, mu _L is the coefficient of friction of the oil film sharing parts, mu _S friction coefficient of the metal sharing parts, alpha is the ratio of the metal division portion, the alpha is known that can be expressed in the following equation.
α = A · log (ΣR / hc)
A is a constant, for example “0.5”. Further, h is the oil film thickness, and ΣR is the height of the surface irregularities, that is, the tooth surface roughness. Therefore, when the oil film thickness hc is changed, the ratio α that is responsible for the load on the tooth surface is changed, and eventually, the friction coefficient μ at the entire meshing position is changed.

  Therefore, the gear mechanism according to the present invention is configured to change the hardness of the surface of the coating layer covering the surface of the base material from the tooth tip side toward the tooth base side. Specifically, when the rotational speed of the driven side gear is higher than the rotational speed of the drive side gear, that is, when the gear is configured to function as a speed increaser, The hardness is made lower than the hardness on the tooth tip side, and the hardness on the tooth tip side in the driven gear is made lower than the hardness on the tooth root side. Further, when the rotational speed of the driven gear is lower than the rotational speed of the driving gear, that is, when the gear is configured to function as a speed reducer, the hardness of the tooth tip side of the driving gear is set to the tooth base. The hardness on the driven side gear is set to be lower than the hardness on the tooth tip side. That is, among the gears that mesh with each other and transmit torque, the gear that rotates at a relatively high rotational speed is configured such that the surface hardness decreases from the tooth base side to the tooth tip side, The gear that rotates at a low rotational speed is configured such that the surface hardness decreases from the tooth tip side to the tooth base side.

  Specifically, the hardness of the surface of the coating layer is continuously changed so that the change rate of the oil film thickness hc in the toothpaste direction matches the change rate of the hardness, or a predetermined length as shown in FIG. Every time, the surface hardness of the coating layer is changed stepwise. FIG. 1 shows a cross-sectional view of the drive side gear in a gear mechanism that functions as a speed increasing stage, with the left side in FIG. 1 showing the tooth tip side and the right side showing the tooth base side. In the following description, the first coating layer 1, the second coating layer 2, the third coating layer 3, and the fourth coating layer 4 are described in order from the left side in FIG. Therefore, in the example shown in FIG. 1, the surface hardness decreases in the order of the first coating layer 1, the second coating layer 2, the third coating layer 3, and the fourth coating layer 4.

  As described above, by changing the hardness of the surface of the coating layer according to the oil film thickness hc that can be obtained based on the average tooth surface speed u, it is possible to suppress the change in the manner of wear at each meshing position. Can do. As a result, it is possible to prevent the tooth surface from being unevenly worn and to suppress the generation of abnormal noise during torque transmission.

  In addition, the hardness of the base material 5 is generally uniform. Therefore, in order to improve the adhesion between the coating layers 1, 2, 3, 4 and the base material 5, the coating layers 1, 2, 3, 4 shown in FIG. It is configured. Specifically, when the surface hardness of each coating layer 1, 2, 3, 4 is formed to be lower than the surface hardness of the base material 5, each coating layer 1, 2, 3, 4 4 is formed so that the hardness increases toward the surface side of the base material 5 in the thickness direction, and the difference between the hardness of the portion adhering to the surface of the base material 5 and the hardness of the base material 5 is reduced. Has been. As described above, when forming coating layers having different hardnesses in the thickness direction, elements having different hardnesses may be attached by a conventionally known physical vapor deposition method (PVD method).

  Next, a method for forming the coating layer shown in FIG. 1 will be described. First, as described above, the tooth surface (the surface of the base material 5) is ground, and the distribution of the oil film thickness hc obtained based on the average tooth surface speed u is calculated. Next, the coating layers 1, 2, 3, 4 are formed on the surface of the base material 5 based on the calculated oil film thickness hc. When the coating layers 1, 2, 3, 4 are formed in this way, first, the surfaces other than the surface of the base material 5 on which any one coating layer 1 (2, 3, 4) is formed are masked. The layer 1 (2, 3, 4) is formed, and then the coating layer 1 (2, 2, 4) other than the surface of the base material 5 on which the other coating layer 2 (1, 3, 4) is formed is formed. The surface of 3, 4) is masked to form another coating layer 2 (1, 3, 4). Thus, each coating layer 1, 2, 3, 4 is formed in order. Then, after each coating layer 1, 2, 3, 4 is formed, shot peening is performed in order to improve the tooth surface strength. That is, compressive residual stress is applied to the tooth surface.

  As described above, each of the coating layers 1, 2, 3, and 4 is configured such that the hardness changes in the thickness direction, and by reducing the difference in hardness between the base material 5 and a portion attached to the base material 5, When the load acts on the tooth surface, the difference in the amount of bending deformation that occurs between the base material 5 and the portions of the coating layers 1, 2, 3, and 4 that adhere to the base material 5 can be reduced. Therefore, it can suppress that each coating layer 1, 2, 3, 4 peels from the base material 5. FIG. In other words, peel resistance can be improved.

  1, 2, 3, 4 ... coating layer, 5 ... base material.

Claims (1)

A first gear and a second gear that meshes with the first gear and rotates at a rotational speed different from the rotational speed of the first gear, and the surface of the base material forming the teeth of each gear has a predetermined hardness In the gear mechanism coated with the material of
The hardness of the surface of the first coating layer covering the surface of the base material in the gear rotating at a low rotational speed of the first gear and the second gear is such that the hardness decreases from the tooth tip toward the tooth root. Formed into
The hardness of the surface of the second coating layer that covers the surface of the base material in the gear rotating at a high rotational speed of the first gear and the second gear is such that the hardness decreases from the tooth base toward the tooth tip. A gear mechanism characterized in that it is formed.

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