JP2014105725A - Gear mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gear mechanism which can suppress or prevent the generation of noise accompanied by a change of an engagement position of teeth and an increase of a power loss.SOLUTION: In the gear mechanism having a first gear and a second gear which is engaged with the first gear and rotates at the number of revolutions different from that of the first gear, the surface roughness of at least one of the first gear and the second gear in a position in which an average tooth face speed of a tooth face speed of the first gear and a tooth face speed of the second gear in an engagement part in which the first gear and the second gear are engaged with each other becomes low is made smaller than the surface roughness of at least one of the first gear and the second gear in a position in which the average gear face speed becomes high.

Description

  The present invention relates to a gear mechanism that transmits torque by meshing teeth with each other and rotates, and has a rotation speed ratio corresponding to the number of teeth, and particularly relates to the surface properties of the tooth surface.

  When power is transmitted by gears meshing with each other, power loss occurs due to inevitable slipping on the tooth surface. Therefore, conventionally, various attempts have been made to reduce the coefficient of friction on the tooth surface and maintain the tooth surface strength. In order to reduce the coefficient of friction on the tooth surface, it is necessary to reduce the roughness of the tooth surface to reduce so-called metal contact and to securely hold the oil film by the lubricating oil. In the present invention, a plateau-like tooth surface having a skewness Rsk of the tooth surface roughness curve of “−5” or more and “−0.2” or less is formed. This is a structure to improve the strength against damage such as pitching and scoring, and since the tooth surface is plateau-like, it improves both the characteristics of metal contact reduction and lubricating oil retention. It is said that the friction coefficient can be reduced. Further, in the gear manufacturing method described in Patent Document 1, the maximum roughness Rmax of the tooth surface before polishing is set to 5 μm or less, and the average roughness Ra is set to 0.5 μm, and this is set according to the roughness. Therefore, the thickness is removed by 0.2 to 2 times the maximum roughness Rmax.

JP-A-7-293668

  As described in Patent Document 1, if the tooth surface has a plateau shape in which the skewness Rsk of the roughness curve is in the above-mentioned range of negative values, the number of sharp protrusions is reduced and the friction coefficient is reduced. Is advantageous. However, as described in Patent Document 1, the maximum roughness Rmax and the arithmetic average roughness Ra are increased before polishing, and the thickness removed by polishing is maximized as described in Patent Document 1. If the plateau is formed by chemical polishing or electropolishing with a roughness Rmax of 0.2 to 2 times, the sharp projections are first polished and removed, but then the corners of the gear teeth have priority. Since the entire surface is gradually polished while being polished, the tooth surface shape may deviate from the expected shape. If the tooth surface shape changes, there is a possibility that the tooth contact deteriorates and abnormal noise is generated.

  In addition, since the oil film thickness of the meshing portion in the gear mechanism changes according to the average tooth surface speed of the driving gear and the driven gear, in the case of a gear mechanism used for decelerating or increasing the speed, As the meshing position of the gears changes, the oil film thickness also changes. Furthermore, the coefficient of friction of the entire meshing portion of the gear mechanism varies depending on the ratio of the portion responsible for the load in the oil film and the portion responsible for the load in the tooth surface, and the ratio depends on the oil film thickness and the roughness of the tooth surface. Will change accordingly. For this reason, the oil film thickness at the meshing portion is constantly changed according to the situation in which the gear mechanism is used, and the ratio of the portion that bears the load on the tooth surface that changes according to the oil film thickness is constantly changed.

  Therefore, as described in Patent Document 1, the maximum roughness Rmax and the arithmetic average roughness Ra are increased before polishing, and the thickness removed by polishing is set to 0.2 to 2 times the maximum roughness Rmax. If a plateau is formed by polishing or electropolishing, the sharp protrusions are first polished and dissolved and removed, but then the corners of the gear teeth and the metal structures that are easy to dissolve on the tooth surfaces are polished. Therefore, there is a possibility that the load that bears the load on the tooth surface at the meshing portion may locally increase, resulting in an increase in power loss due to an increase in the friction coefficient or a decrease in the strength of the tooth surface. There is a possibility of sneaking. In addition, in the removal method of processing the entire tooth surface other than dissolution removal for the purpose of removing the protrusions to the same roughness, the tooth surface shape is expected from the shape that was planned as the removal amount of the protrusions increased. There is a possibility that it will change, and there is a possibility that the load that the tooth surface bears on the meshing portion will locally increase. As a result, an increase in power loss due to an increase in the coefficient of friction occurs, and the strength of the tooth surface decreases.

  The present invention has been made paying attention to the above technical problem, and can suppress or prevent the generation of abnormal noise, the increase in power loss, or the decrease in the strength of the tooth surface due to the change in the meshing position of the teeth. An object of the present invention is to provide a gear mechanism.

  In order 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, at a position where an average tooth surface speed between the tooth surface speed of the first gear and the tooth surface speed of the second gear becomes small at a meshing portion where the first gear and the second gear mesh with each other. The surface roughness of at least one of the first gear and the second gear is at least one of the first gear and the second gear at a position where the average tooth surface speed is increased. It is configured to be smaller than the surface roughness of one tooth surface.

  Further, in the invention of claim 2, in the invention of claim 1, the surface roughness on the tooth tip side of the gear having the longer distance from the rotation center to the pitch circle in the first gear and the second gear is A gear mechanism characterized in that the distance from the rotation center to the pitch circle is smaller than the surface roughness on the tooth base side of the longer gear.

  Furthermore, the invention of claim 3 is the surface of the tooth root side of the gear having the shorter distance from the rotation center to the pitch circle in the first gear and the second gear in the invention of claim 1 or claim 2, respectively. The gear mechanism is characterized in that the roughness is smaller than the surface roughness on the tooth tip side of the gear having the shorter distance from the rotation center to the pitch circle.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, at least one tooth of the first gear and the second gear at a position where the average tooth surface speed becomes small. The gear mechanism is characterized in that only the surface is polished.

  According to the present invention, the surface roughness of the tooth surface where the average tooth surface speed decreases in the meshing portion of the meshing gears is smaller than the surface roughness of the tooth surface where the average tooth surface speed increases. . Therefore, the ratio of the portion responsible for the load on the tooth surface that changes according to the average tooth surface speed and the portion responsible for the load on the oil film does not change. As a result, it is possible to suppress or prevent the friction coefficient at the meshing portion from changing due to the change in the average tooth surface speed. In addition, since it is possible to suppress or prevent a situation in which the tooth surface where the average tooth surface speed increases becomes excessively polished, the time required for polishing can be shortened, and the teeth associated with polishing can be reduced. Changes in the surface shape can be suppressed or prevented. As a result, it is possible to suppress or prevent the generation of abnormal noise, an increase in power loss, or a decrease in tooth surface strength due to changes in the tooth surface shape.

  In addition, by polishing only the tooth surface at the position where the average tooth surface speed becomes small, the range to be polished can be narrowed, the time required for polishing can be further shortened, and the change in the tooth surface shape It is possible to further suppress or prevent generation of abnormal noise, increase in power loss, or decrease in tooth surface strength.

It is a schematic diagram for demonstrating the relationship with the roughness of a tooth surface, the thickness of an oil film, and the ratio of a metal share part. It is a schematic diagram for demonstrating the average tooth surface speed which changes with the change of a meshing position. It is a schematic diagram for demonstrating the oil film thickness which changes with the change of a meshing position.

  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. Gears made of metallic materials are basically made from raw materials through rolling, turning, gear cutting, and other roughing processes, and then the teeth are ground and subjected to appropriate surface treatment. Manufactured by polishing. The polishing method may be a conventionally known appropriate method such as chemical polishing, electrolytic polishing, or resin polishing using a resin.

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、ｕ_２は他方の歯車における噛み合い部の歯面速度である。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 of a metal material as described above normally transmits power while supplying lubricating oil 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 tooth surface speed 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 of the meshing portion of one gear, and u ₂ is the tooth surface 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, in other words, when the gears transmit power on the line connecting the rotation center of the driving gear and the rotation center of the driven gear, The average tooth surface speed u is different from that when power is transmitted in a shape other than a circle. FIG. 2 shows a change 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 higher than the rotational speed of the driving gear is indicated 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 beginning of meshing 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, so that the meshing is performed. The average tooth surface speed u at the end 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, the average tooth surface speed u is high when meshing on the tooth base side of the driving gear, in other words, meshing on the tooth tip side of the driven gear. When meshing on the tooth tip side of the driving gear, in other words, when meshing on the tooth root side of the driven gear, the average tooth surface speed u becomes slow.

  As described above, when the average tooth surface speed u changes, the oil film thickness 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. The oil film thickness becomes thicker than the oil film thickness on the pitch circle. On the other hand, since the average tooth surface speed u at the position where the meshing is completed is slower than the average tooth surface speed u on the pitch circle, the oil film thickness becomes thin as shown in FIG. In addition, the horizontal axis in FIG. 3 is described similarly to the horizontal axis shown in FIG. 2, and the vertical axis indicates the oil film thickness.

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 / h)
A is a constant, for example “0.5”. Further, h is the oil film thickness, and ΣR is the height of the unevenness on the surface, that is, the roughness of the tooth surface, and these relationships are schematically shown in FIG. Therefore, when the oil film thickness h changes, the ratio α that bears the load on the tooth surface changes, and eventually the friction coefficient μ at the entire meshing position changes.

  Therefore, the gear mechanism according to the present invention determines the tooth surface roughness ΣR according to the oil film thickness h that changes based on the average tooth surface speed u, and polishes the tooth surface so as to have the roughness ΣR. Is formed. Specifically, in the case of a gear mechanism that functions as a speed increaser, when meshing on the tooth base side of the drive side gear, the average tooth surface speed u is faster than when meshing on the pitch circle, and the oil film Since the thickness h is increased and, as a result, the ratio α of the portion responsible for the load on the tooth surface is decreased, the surface roughness ΣR on the tooth base side can be increased. On the other hand, when meshing on the tooth tip side of the drive side gear, the average tooth surface speed u is slower than when meshing on the pitch circle, and the oil film thickness h is reduced. Since the ratio α of the portion responsible for the load increases, the surface on the tooth tip side is smoothed. In other words, the surface roughness on the tooth tip side of the driving gear is made smaller than the surface roughness on the tooth base side. Alternatively, only the tooth tip side of the driving gear may be polished to reduce the surface roughness on the tooth tip side.

なお、面性状としては、最大高さ粗さＲｚや二乗平均平方根粗さＲｑあるいは突出山部高さＲｐｋなどの表面粗さを表す種々の指標である。 That is, the surface properties of the tooth surface are defined so as to satisfy the following expression.

The surface properties are various indexes representing surface roughness such as the maximum height roughness Rz, the root mean square roughness Rq, or the protruding peak height Rpk.

  By changing the surface properties of the tooth tip side and the tooth root side in this way, the friction coefficient μ at the entire meshing position does not change due to a change in the meshing position. Moreover, since the range which grind | polishes a tooth surface can be narrowed, while the time which the grinding | polishing requires can be shortened, the change of the shape of the tooth surface by grind | polishing can be suppressed or prevented. Therefore, it is possible to suppress or prevent generation of abnormal noise, increase in power loss, or reduction in tooth surface strength due to the change in tooth surface shape.

  Further, the first gear and the second gear at a position where the average tooth surface speed of the tooth surface speed of the first gear and the tooth surface speed of the second gear becomes small at the meshing portion where the first gear and the second gear mesh with each other. It is preferable to grind only the tooth surfaces of the two gears. In that case, the tooth surfaces of the first gear and the second gear at the position where the average tooth surface speed is increased need not be ground. The required time can be further shortened, and the generation of abnormal noise, an increase in power loss, and a reduction in tooth surface strength due to changes in the tooth surface shape can be further suppressed.

  The gear mechanism according to the present invention is not limited to functioning as a speed increaser as in the above-described example, but may function as a speed reducer. In that case, the surface roughness on the tooth base side of the driving gear may be made smaller than the surface roughness on the tooth tip side. In addition to the driving gear, the surface roughness of the tooth surface of the driven gear may be different between the tooth tip side and the tooth base side. That is, when the gear mechanism functions as a speed increaser, the surface roughness on the tooth base side of the driven gear may be made smaller than the surface roughness on the tooth tip side, and when the gear mechanism functions as a speed reducer. The surface roughness on the tooth tip side of the driven gear may be made smaller than the surface roughness on the tooth root side.

  Further, the gear mechanism transmits the power by meshing the driving side gear and the driven side gear, so that the surface roughness of both tooth surfaces is changed without changing the surface roughness of only one gear as described above. You may comprise so that roughness may be changed. That is, when the gear mechanism functions as a speed increaser, the surface roughness on the tooth tip side of the driving gear is made smaller than the surface roughness on the tooth root side, and the surface roughness on the tooth root side of the driven gear is reduced. The surface roughness on the tooth side may be smaller than the surface roughness on the tooth tip side. When functioning as a speed reducer, the surface roughness on the tooth base side of the driving gear is made smaller than the surface roughness on the tooth tip side, and the tooth tip of the driven gear is The surface roughness on the side may be made smaller than the surface roughness on the tooth base side.

Claims (4)

In a gear mechanism comprising 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 meshing portion where the first gear and the second gear mesh with each other, the first tooth surface speed at the position where the average tooth surface speed between the tooth surface speed of the first gear and the tooth surface speed of the second gear becomes small. The surface roughness of at least one tooth surface of the gear and the second gear is determined based on at least one tooth surface of the first gear and the second gear at a position where the average tooth surface speed is increased. A gear mechanism characterized by being configured to be smaller than the surface roughness of the gear.   The surface roughness of the tooth tip side of the gear having the longer distance from the rotation center to the pitch circle in the first gear and the second gear is the tooth of the gear having the longer distance from the rotation center to the pitch circle. The gear mechanism according to claim 1, wherein the gear mechanism is configured to be smaller than the surface roughness of the original side.   The surface roughness on the tooth base side of the gear having the shorter distance from the rotation center to the pitch circle in the first gear and the second gear is the tooth of the gear having the shorter distance from the rotation center to the pitch circle. The gear mechanism according to claim 1, wherein the gear mechanism is configured to be smaller than the surface roughness of the front side.   4. At least one tooth surface of the first gear and the second gear at a position where the average tooth surface speed becomes small is polished. The gear mechanism described.

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