gear

Abstract

To reduce friction in meshing slide parts of gears to improve wear resistance.SOLUTION: A plurality of grooves 13 extending in a direction perpendicular to a sliding direction of a tooth surface 12 is provided side by side in a streak-like unevenness processing region 14 of the tooth surface 12, and the arithmetic mean roughness of the streak-like unevenness processing region 14 is within a range of 0.01 μm or more and 0.4 μm or less.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0001] The present invention relates to a gear having rolling and sliding during meshing between tooth surfaces.

Background Art

[0002] Patent Document 1 discloses a gear provided with a linear groove extending in the tooth width direction on the tooth tip side of the contact surface where the tooth surfaces of two gears constituting a gear pair come into contact with each other.

[0003] Patent Document 2 discloses a gear structure in which the tooth surface of one gear of a gear pair includes a meshing region that comes into contact with the tooth surface of the other gear when meshing with the other gear and a non-meshing region that does not come into contact with the other gear even when meshing with the other gear, and a groove extending in a direction intersecting the meshing progress direction of the gear pair is provided in the non-meshing region of the tooth surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When transmitting torque from a driving gear to a driven gear in a pair of gears, rolling and sliding due to the tooth root of the driving gear and the tooth tip of the driven gear, rolling on the pitch circle of the tooth surfaces of the driving gear and the driven gear, and rolling and sliding due to the tooth tip of the driving gear and the tooth root of the driven gear occur sequentially and continuously. When the friction of the meshing sliding portion that meshes and slides between the tooth surfaces increases, there is a possibility of a decrease in the power transmission efficiency due to frictional loss and seizure of the gear, and there is also a possibility of a decrease in the wear resistance of the gear.

[0006] The gear invention disclosed in Patent Document 1 aims to reduce friction on the sliding surfaces by supplying lubricating oil accumulated in the grooves to the sliding surfaces during sliding between the tooth surfaces. However, even if grooves are provided on the tooth tip side of the contact surfaces where the tooth surfaces come into contact, the lubricating oil will flow out of the system when the parts of the contact surfaces without grooves come into contact and slide against each other. Therefore, there is doubt as to whether an oil film can be formed on the meshing sliding parts of the gears as intended, and there is room for further consideration regarding the optimization of the grooves.

[0007] The gear structure invention disclosed in Patent Document 2 aims to reduce friction in the meshing region by supplying lubricating oil, which is blocked by grooves in the non-meshing region, to the meshing region, thereby forming an oil film in the meshing region. However, it is unlikely that lubricating oil would flow from grooves in the non-meshing region into the meshing region, where two narrow, closed surfaces are in contact. Furthermore, since the non-meshing region is an open system, lubricating oil pushed out of the system due to sliding is not blocked by grooves, and no hydraulic pressure is generated, so it is thought to flow out of the system. Therefore, it is unlikely that grooves in the non-meshing region contribute to the formation of an oil film in the meshing region.

[0008] Therefore, the present invention aims to improve wear resistance by reducing friction in the meshing sliding parts of gears. [Means for solving the problem]

[0009] The gear according to the present invention is A gear in which, when a gear pair rotates, rolling and sliding occurs sequentially at the tooth tips, rolling on the pitch circle, and rolling and sliding at the tooth roots, Multiple grooves extending in a direction perpendicular to the sliding direction of the tooth surface are arranged in a striated uneven surface area of ​​the tooth surface, and the arithmetic mean roughness of the striated uneven surface area is in the range of 0.01 μm to 0.4 μm.

[0010] Gear according to the present invention teeth, The aforementioned grooved and uneven processing region is provided from the tooth tip to a position halfway down the tooth height on the tooth surface. It is characterized by the following.

[0011] In one embodiment of the gear according to the present invention, the plurality of grooves may be provided in a straight line across the entire width of the tooth. [Effects of the Invention]

[0012] The present invention can reduce friction in the meshing sliding portion of a gear and improve wear resistance.

Brief Description of the Drawings

[0013] [Figure 1] It is a side view showing a state in which the gears of the present embodiment are meshed to form a gear pair. [Figure 2] It is a perspective view of the gear of the embodiment of the present invention. [Figure 3] It is a view showing the side surface of the teeth of the gear of the present embodiment. [Figure 4] It is a view showing the tooth surface of the gear of the present embodiment. [Figure 5] It is a schematic view of a testing machine used in an evaluation test of surface properties effective for reducing the friction coefficient. [Figure 6] It is a view showing the outer peripheral surface of test piece A used in the evaluation test. [Figure 7] It is a view showing the outer peripheral surface of test piece B used in the evaluation test. [Figure 8] It is a view showing the outer peripheral surface of test piece C used in the evaluation test. [Figure 9] It is a view showing the outer peripheral surface of test piece D used in the evaluation test. [Figure 10] It is a view showing the measurement results of the friction coefficients of test pieces A to D. [Figure 11] It is a view showing the measurement results of the wear depth of the mating material of test pieces A to D [Figure 12] [[ID=*45]]It is a table showing a list of set values used in the calculation of the influence of the arithmetic mean roughness on the friction coefficient. [Figure 13] It is a view showing the result of calculating the friction coefficient at a sliding speed of 0.5 m per second. [Figure 14] It is a view showing the result of calculating the friction coefficient at a sliding speed of 1 m per second. [Figure 15] It is a view showing the result of calculating the friction coefficient at a sliding speed of 2 m per second.

Modes for Carrying Out the Invention

[0014] FIG. 1 is a side view showing a state in which two gears 10 are meshed to form a gear pair. The gear 10 is used, for example, in a drive system unit for an automobile. In this gear pair, the lower gear 10 is used as a driving gear 10a that rotates counterclockwise, and the upper gear 10 is used as a driven gear 10b that rotates clockwise. In region A1, rolling-sliding occurs between the tooth root of the driving gear 10a and the tooth tip of the driven gear 10b. In region A2, rolling occurs on the pitch circle between the tooth surface 12 of the driving gear 10a and the tooth surface 12 of the driven gear 10b. In region A3, rolling-sliding occurs between the tooth tip of the driving gear 10a and the tooth root of the driven gear 10b. The rolling-sliding by the tooth tip, the rolling on the pitch circle, and the rolling-sliding by the tooth root occur sequentially and continuously.

[0015] FIG. 2 is a perspective view of the gear 10. As shown in FIG. 2, the gear 10 is a spur gear provided with teeth 1. FIG. 3 is a view showing the side surface 11 of the tooth 1. FIG. 4 is a view showing the tooth surface 12 of the tooth 1.

[0016] In the gear 10, a rib-shaped concavo-convex machining region 14 is provided in a range from the tooth tip of the tooth surface 12 to a position half of the tooth height. In the rib-shaped concavo-convex machining region 14, a plurality of grooves 13 extending linearly in the tooth width direction are arranged side by side from the tooth tip to the tooth root. That is, the grooves 13 are provided so as to extend in a direction perpendicular to the sliding direction of the tooth surface 12 in the rolling-sliding occurring in region A1 and the sliding direction of the tooth surface 12 in the rolling-sliding occurring in region A3. The grooves 13 are preferably provided over the entire width of the tooth width. Further, the grooves 13 have a triangular cross-sectional shape. However, the grooves 13 may have a cross-sectional shape other than a triangle, such as a quadrangle or a semi-circle. The arithmetic mean roughness of the rib-shaped concavo-convex machining region 14 provided with the grooves 13 is preferably within a range of 0.01 μm or more and 0.4 μm or less.

[0017] In the meshing of the drive gear 10a and driven gear 10b in Figure 1, the proportion of sliding increases compared to rolling as you approach the tooth tip or tooth root in the tooth height direction from the pitch circle on the tooth surface 12. Therefore, frictional loss due to rolling and sliding is large near the tooth tip and tooth root, making seizure and wear more likely. The meshing with a high proportion of sliding is near the tooth tip and tooth root in regions A1 and A3 of Figure 1. Therefore, by providing grooves 13 in the grooved uneven machining region 14, which is at least near the tooth tip, frictional loss can be effectively reduced and seizure and wear can be suppressed.

[0018] An evaluation test was conducted using a block-on-ring testing machine (model: LFW-1) to assess the surface properties effective in reducing the coefficient of friction. Figure 5 shows a schematic configuration of the testing machine 20 used in the evaluation test. As shown in Figure 5, a block test piece 22 made of SCM420 carburized material was placed on a ring test piece 21 made of carburized material, and the evaluation test was conducted by rotating the ring test piece 21 while a load was applied from above the block test piece 22. In the evaluation test, the lower part of the ring test piece 21 was immersed in lubricating oil 23. By rotating the ring test piece 21, the lubricating oil 23 attached to the outer surface of the ring test piece 21 rotated together with the ring test piece 21, supplying lubricating oil 23 to the sliding surface between the ring test piece 21 and the block test piece 22. The lubricating oil 23 used was commercially available ATF (Toyota genuine auto fluid WS) used in the transaxles of hybrid vehicles. The oil temperature during the test was 80°C.

[0019] The sliding speed of the outer surface of the ring test piece 21 due to rotation was 0.9 m / s. For the first 5 minutes of the test, a load of 444 N was applied from above the block test piece 22 to allow the sliding surface to settle in, and the ring was slid. After 5 minutes, the load was increased to the target load of 1177 N, and the ring was slid for 25 minutes, during which the coefficient of friction and the wear depth of the block test piece 22 were measured. Calculated using Hertz's maximum pressure, the maximum surface pressure with a load of 1177 N applied from above the block test piece 22 was approximately 0.6 GPa.

[0020] As shown in Figures 6 to 9, the measurement results were compared using four types of test pieces A to D as ring test pieces 21. In test piece A, as shown in Figure 6, a groove 13 extending perpendicular to the sliding direction was provided on the outer surface of the ring test piece 21. In test piece B, as shown in Figure 7, a groove 13 extending at a 45-degree angle to the sliding direction was provided on the outer surface of the ring test piece 21. In test piece C, as shown in Figure 8, a groove 13 extending parallel to the sliding direction was provided on the outer surface of the ring test piece 21. In test piece D, as shown in Figure 9, a textured surface created by shot blasting was provided on the outer surface of the ring test piece 21.

[0021] Figure 10 shows the measurement results of the coefficient of friction for test specimens A to D. Compared with test specimens B to D, the coefficient of friction of test specimen A was particularly low. The coefficient of friction of test specimen A was less than half that of test specimen C.

[0022] Figure 11 shows the results of measuring the wear depth of block specimen 22 for specimens A to D. The wear depth measured using specimen A was the smallest. The wear depth measured using specimen A was less than one-tenth of the wear depth measured using specimen C.

[0023] The reason why the coefficient of friction of test piece A was reduced and the wear depth of block test piece 22 was minimized is thought to be that by providing grooves 13 that extend in a direction perpendicular to the sliding direction between ring test piece 21 and block test piece 22, the lubricating oil 23 was blocked on the sliding surface, generating hydraulic pressure and forming a thick oil film.

[0024] As described above, by providing multiple grooves 13 extending in a direction perpendicular to the sliding direction of the tooth surface 12 in the groove-like uneven processing region 14 near the tooth tip of the tooth surface 12, it is possible to reduce friction between tooth surfaces and improve wear resistance.

[0025] Furthermore, a computational model was used to investigate the influence of the direction of the grooves 13 relative to the sliding direction of the tooth surface 12 of the gear 10 and the arithmetic mean roughness of the groove-like uneven surface area 14 on the coefficient of friction. The computational model applied was the known oil film pressure analysis (Patir-Cheng mean flow model) and solid contact analysis (Matsumoto's equation based on the ratio of roughness to oil film thickness). If the oil film pressure is p(x, y), the contact area is S, and the resultant oil film force is Fo, then the following equation 1 holds according to the Patir-Cheng mean flow model.

[0026]

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[0027] Let Rz1 and Rz2 be the maximum height roughness of the two contacting surfaces, ho be the minimum oil film thickness, D be the ratio of oil film thickness to surface roughness, α be the proportion of solid contact in the contact area, F be the applied load, and Fc be the resultant contact force. Then, according to Matsumoto's equations based on the ratio of roughness to oil film thickness, the following equations 2, 3, and 4 hold true.

[0028]

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[0029]

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[0030]

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[0031] The additional load F can be calculated using the following equation 5. The coefficient of friction between the two surfaces was calculated by determining the viscous friction force and boundary friction force from the viscosity of the lubricating oil and the coefficient of boundary friction, and then dividing their sum by the additional load F.

[0032]

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[0033] Figure 12 shows a list of calculation conditions set to simulate the state of the tooth surface during meshing in the calculation of the effect of arithmetic mean roughness on the coefficient of friction. Assuming low to medium loads where reducing gear meshing friction (transmission loss) is a challenge, the maximum surface pressure was set to 0.44 to 0.98 GPa and the sliding speed to a maximum of 2 m / s. The relationship between the arithmetic mean roughness Rq and the coefficient of friction of parallel groove machined surfaces and orthogonal groove machined surfaces was calculated at a maximum surface pressure of 0.98 GPa and sliding speeds of 0.5 m / s, 1 m / s, and 2 m / s. A parallel groove machined surface is a machined surface with grooves arranged in a direction parallel to the sliding direction, as shown in Figure 8. An orthogonal groove machined surface is a machined surface with multiple grooves arranged in a direction perpendicular to the sliding direction, as shown in Figure 6.

[0034] Figure 13 shows the results calculated under the conditions of a maximum surface pressure of 0.98 GPa and a sliding speed of 0.5 m / s. Figure 14 shows the results calculated under the conditions of a maximum surface pressure of 0.98 GPa and a sliding speed of 1 m / s. Figure 15 shows the results calculated under the conditions of a maximum surface pressure of 0.98 GPa and a sliding speed of 2 m / s. As shown in Figures 13 to 15, it can be seen that, at a maximum surface pressure of 0.98 GPa, the coefficient of friction can be lowered compared to a parallel groove machined surface by setting the arithmetic mean roughness of the orthogonal groove machined surface to a range of 0.01 μm to 0.4 μm, regardless of the sliding speed conditions of 0.5 m / s, 1 m / s, and 2 m / s. [Explanation of symbols]

[0035] 1 tooth, 10 gear, 10a drive gear, 10b driven gear, 11 side view, 12 tooth surface, 13 groove, 14 grooved surface area, 20 testing machine, 21 ring test piece, 22 block test piece, 23 lubricating oil.

Claims

1. A gear in which, when a gear pair is formed and rotates, rolling and sliding by the tooth tips, rolling on the pitch circle, and rolling and sliding by the tooth roots occur sequentially and continuously, Multiple grooves extending in a direction perpendicular to the sliding direction of the tooth surface are arranged in a line within the grooved surface area of ​​the tooth surface. The arithmetic mean roughness of the aforementioned striated uneven surface area is in the range of 0.01 μm or more and 0.4 μm or less. The gear is characterized in that the grooved and uneven processing region is provided on the tooth surface from the tooth tip to a position half the tooth height.

2. The gear according to claim 1, The gear is characterized in that the plurality of grooves are provided in a straight line across the entire width of the tooth.

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