JP7487077B2 - Gear Manufacturing Method - Google Patents

Description

The present invention relates to a gear with grooves formed on the tooth surface, a gear device using the gear, and a gear manufacturing method for forming grooves on the tooth surface of a gear.

In industrial gear devices, there is a demand for smaller gears to reduce the size and cost of the gear device. However, simply making the gears smaller increases the contact stress on the tooth surfaces during power transmission, which can damage the tooth surfaces and cause vibrations and noise in the gear device, or even cause the gear device to lose its functionality.

The allowable contact stress of gears is determined not only by the material conditions (hardness distribution, material cleanliness, etc.) but also by the lubrication conditions between the tooth surfaces. The former material conditions are determined by the material selection and hardening conditions. This invention focuses on the latter lubrication conditions.

In gear devices, a sliding velocity occurs at the contact points between the tooth flanks, so it is common to form an oil film between the tooth flanks. It is known that the thicker the oil film, the more metal contact between the tooth flanks can be avoided and the allowable contact stress can be improved. To form a thick oil film between the tooth flanks, a structure that retains more lubricating oil must be provided at the contact points. As a structure for retaining lubricating oil, for example, a gear with an oil groove formed in the contact direction (tooth height direction in the case of spur gears) has been proposed (Non-Patent Document 1). However, with gear grinding machines that are widely used in gear manufacturing, it is not possible to form an oil groove in the contact direction, and sufficient retention of lubricating oil cannot be expected.

Although the purpose is different from that of Non-Patent Document 1, the manufacturing method of Patent Document 1 is known as a gear processing method that forms grooves on the tooth surface in the direction of travel. The abstract of this document states, "This application discloses a gear device that includes a plurality of spur gears formed as involute gears and an input gear that meshes with the plurality of spur gears and rotates the plurality of spur gears synchronously. Each of the plurality of spur gears has a tooth surface on which grinding marks extending in the tooth profile direction are formed." Also, paragraphs 0082 and 0083 state, "The operator sprays free abrasive grains from the nozzle 141. As a result, the free abrasive grains are supplied to the meshing portion between the first involute gear 150 and the second involute gear 160." and "Since the free abrasive grains are interposed between the tooth surface of the first involute gear 150 and the tooth surface of the second involute gear 160, grinding marks extending in the tooth profile direction are efficiently formed on the tooth surfaces of the first involute gear 150 and the second involute gear 160." That is, according to Patent Document 1, noise generated from the meshing portion is reduced by supplying free abrasive grains to the tooth surface and forming grinding marks that extend in the tooth profile direction (the direction in which the tooth surface advances).

JP 2017-214941 A

Japan Science and Technology Publishing Company, Akira Yoshida, Rolling fatigue life and surface pressure strength for tribo-design

As mentioned above, the surface durability of gears can be improved by thickening the oil film between the tooth surfaces of the gear device. For this purpose, it is effective to provide grooves on the tooth surfaces of the gears to retain the lubricating oil, but with the gear manufacturing methods of Non-Patent Document 1 and Patent Document 1, grooves can only be provided in one direction on the tooth surfaces, making it difficult to retain a sufficient amount of lubricating oil on the tooth surfaces.

The present invention aims to provide a gear manufacturing method that processes and forms a number of grooves on the gear tooth surface that can adequately retain lubricating oil by scanning a rotating tool in the contact advancement direction of the gear to process and form grooves in a first direction, while simultaneously processing and forming grooves in a second direction perpendicular to the first groove, and to provide gears manufactured by this manufacturing method.

A gear manufacturing method for machining and forming a plurality of progression direction grooves on the tooth surface by repeating a first step of machining and forming a progression direction groove on the tooth surface by scanning the rotating tool in the progression direction while in contact with the gear, and a second step of moving the rotating tool to an area without the progression direction groove by scanning the rotating tool in a direction perpendicular to the progression direction without contacting the gear, characterized in that in the first step, when the rotating tool machines and forms the progression direction groove, an orthogonal direction groove perpendicular to the progression direction groove is machined and formed.

According to the gear manufacturing method of the present invention, when a rotating tool is scanned in the contact advancement direction of the gear to machine and form grooves in a first direction, grooves in a second direction perpendicular to the first groove are also machined at the same time, so that a number of grooves that can adequately retain lubricating oil can be machined and formed on the gear tooth surface.

Furthermore, with gears manufactured using the gear manufacturing method of the present invention, sufficient lubricating oil can be retained on the tooth surface even when the gear is miniaturized, improving tooth surface durability and enabling the gear device to be miniaturized and have a longer life.

Other issues, configurations, and advantages will become clearer in the following examples.

FIG. 1 is a perspective view showing a gear device according to a first embodiment of the present invention; FIG. 1 is a perspective view showing a tooth surface of a gear according to a first embodiment; FIG. 1 is a conceptual diagram showing a gear manufacturing method according to a second embodiment of the present invention; FIG. 11 is an auxiliary view showing a gear manufacturing method according to a second embodiment of the present invention. Conceptual diagram showing the oil groove machining method of Example 2

The following describes an embodiment of the present invention with reference to the drawings.

First, the gear device 10 and gears 11 and 12 according to the first embodiment of the present invention will be described with reference to Figures 1 and 2.

Figure 1 is a perspective view showing an example of a gear device 10 of this embodiment. The gear device 10 shown here is a device that transmits power from one rotating shaft to the other rotating shaft by meshing spur gears 11 and 12, one of which is a drive gear and the other a driven gear. Note that in Figure 1, a single gear pair is shown as an example of the minimum necessary configuration for the sake of simplicity of explanation, but in an actual gear device 10, multiple gear pairs or different types of gears may be used.

High contact stress and slippage occur on the sliding surface 1a of the tooth flank 1 of each gear, causing damage to the gear material due to rolling fatigue. One currently thought mechanism for damage to the tooth flank 1 is the phenomenon in which protrusions of a size similar to the surface roughness of the tooth flank 1 come into contact with protrusions on the mating tooth flank, becoming the starting point for tooth flank damage. On the other hand, to take into account the slippage of the tooth flanks, an oil film is formed between the tooth flanks, preventing the tooth flanks from coming into direct solid contact with each other. Therefore, increasing the thickness of the oil film between the tooth flanks improves the tooth surface durability.

To thicken the oil film between the tooth surfaces, an oil groove 2 may be formed on the tooth surface so that the lubricating oil does not escape from the contact area between the tooth surfaces. In this embodiment, as shown in FIG. 2, an oil groove (hereinafter referred to as "progression groove 2a") in the contact progression direction of the tooth surface (tooth depth direction in the case of spur gears) and an oil groove (hereinafter referred to as "orthogonal groove 2b") in the direction perpendicular to the contact progression direction (tooth trace direction in the case of spur gears) are formed on the tooth surface of each gear. In FIG. 2, the progression groove 2a and the orthogonal groove 2b are formed on the entire surface of the tooth surface, but it is not necessary to form these grooves on the entire surface. For example, the progression groove 2a and the orthogonal groove 2b may be formed only on the sliding surface 1a where the gears actually contact each other when the gear device 10 is in operation. Also, FIG. 2 shows an example of a spur gear, but the same configuration can be used for helical gears and bevel gears.

When the gear device 10 is in operation, the lubricating oil becomes highly pressurized at the contact points of the gear pair and tries to escape in the contact progression direction of the tooth surface 1 (tooth height direction) or in the perpendicular direction (tooth trace direction). However, since the tooth surface 1 of this embodiment has a progression direction groove 2a, the lubricating oil remains in the progression direction groove 2a when the gear pair rotates, and the movement of the lubricating oil in the tooth trace direction is suppressed. The lubricating oil that moves in the tooth height direction within the progression direction groove 2a is reused to form an oil film at the next meshing. In addition, since the perpendicular direction groove 2b is provided within the progression direction groove 2a, the amount of lubricating oil that moves in the tooth height direction within the progression direction groove 2a can be minimized.

In order to properly maintain the thickness of the oil film between the tooth surfaces of each gear, it is necessary to allow some movement of the lubricant in the contact advance direction (tooth height direction) while more strictly suppressing movement in the perpendicular direction (tooth trace direction). For this reason, in this embodiment, the depth of the advance direction groove 2a formed in the contact advance direction (tooth height direction) is made deeper than the depth of the perpendicular direction groove 2b formed in the perpendicular direction (tooth trace direction). With this structure, when the gear device 10 is in operation, the lubricant in the contact part of the gear pair is suppressed from moving in the perpendicular direction (tooth trace direction) to the contact advance direction (tooth height direction), so that it is possible to avoid the situation where the lubricant escapes outside the tooth surface 1, and the thickness of the oil film between the tooth surfaces can be properly maintained.

According to the present embodiment described above, by forming an oil groove in the contact advance direction and an oil groove in the direction perpendicular to the contact direction on the tooth surface of the gear, a sufficient amount of lubricating oil can be retained on the tooth surface, and a sufficiently thick oil film can be formed on the contact portion of the gear pair while the gear device is in operation. This makes it possible to improve the tooth surface durability while the gear device is in operation.

Next, a specific method for machining the tooth surface 1 of Example 1 will be described with reference to Figures 3 and 4. Note that overlapping explanations of points common to Example 1 will be omitted.

In this embodiment, a machining center is used to machine and form the oil groove 2. A machining center is a machine tool that can freely control the tool path P of a rotating tool 20 rotated at high speed to machine any surface shape. In this embodiment, the machining marks from the cutting and grinding processes that machine the tooth surface 1 to the designed surface roughness (usually several tens of μm or less) are used as the oil groove 2, thereby eliminating the machining process just for machining the oil groove 2 and shortening the machining time, but a separate process for machining and forming the oil groove 2 may also be provided after machining the tooth surface 1 to the designed surface roughness.

Figure 3 is a perspective view showing the process in which a rotating tool 20 of a machining center processes the surface of tooth surface 1 to the designed surface roughness. As shown here, the rotating tool 20, which rotates at high speed in the r direction, scans along a tool path P from the base to the tip of the tooth, allowing cutters 21 arranged on the circumference of the rotating tool 20 to remove excess metal from the surface of tooth surface 1 and form a progression direction groove 2a.

Specifically, first, the rotating tool 20 rotating at high speed is scanned along the tool path _P1 while being in contact with the tooth surface 1 at the left end of the tooth surface 1. As a result, a first progression direction groove 2a parallel to the contact progression direction (tooth height direction in the case of a spur gear) is machined and formed at the left end of the tooth surface 1. After machining the tool path _P1 , the rotating tool 20 rotating at high speed is moved to a location shifted in the tooth trace direction from the tool path _P1 without contacting the tooth surface 1, and then scanned along the tool path _P2 at that location while being in contact with the tooth surface 1. As a result, a second progression direction groove 2a is machined and formed next to the first progression direction groove 2a. Then, by repeating this, progression direction grooves 2a can be formed over the entire surface of the tooth surface 1.

<Details of the Progressive Direction Groove 2a>
Here, the positional relationship of the progression direction grooves 2a formed by an arbitrary n-th tool path _Pn and an (n+1)-th tool path Pn ₊₁ will be described with reference to the cross-sectional view of FIG.

Figure 4 is a cross-sectional view in the normal direction of the tool path P, showing the position and size of the advancement direction groove 2a formed by each tool path P. In this figure, the outer diameter of the cutter 21 of the rotating tool 20 is D, the tool path interval is x, and the depth of the advancement direction groove 2a is δ. The relationship between these is expressed by the following equation 1.

Since the rotary tool diameter D is known and the depth δ of the groove 2a in the advance direction should be equal to or less than the designated value δ ₀ of the surface roughness of the tooth surface 1, the tool path interval x is determined by the following equation 2.

To form a sufficient number of forward grooves 2a on the tooth surface 1, this process should be performed on the entire tooth contact area, which is the contact area of the gear, or on the entire tooth surface.

<Details of orthogonal groove 2b>
3 and 4, when the progression direction grooves 2a are machined and formed using a machining center, periodic grooves (orthogonal direction grooves 2b) are formed inside the progression direction grooves 2a due to the influence of core runout, unbalanced vibration, or outer diameter error of the cutter 21 of the rotating tool 20. The principle of how the orthogonal direction grooves 2b are formed will be described with reference to FIG.

Fig. 5 is an enlarged plan view showing a part of the progress direction groove 2a formed when the rotating tool 20 is scanned along the tool path _Pn and the tool path _Pn+1 shown in Fig. 3. When the progress direction groove 2a is formed by applying the above-mentioned machining method, an orthogonal direction groove 2b perpendicular to the tool path _Pn and the tool path _Pn+1 is formed inside the progress direction groove 2a due to core runout of the rotating tool 20 or the like.

The orthogonal grooves 2b are formed due to periodic fluctuations in the tip of the cutter 21 caused by core wobble of the rotating tool 20, etc., so if the scanning speed of the rotating tool 20 along the tool path P is constant, the arrangement of each orthogonal groove 2b will be periodic. In addition, since the magnitude of core wobble of the rotating tool 20 is smaller than the diameter D of the rotating tool 20, the depth of the advancement direction groove 2a is deeper than the depth of the orthogonal direction groove 2b, and the width of the advancement direction groove 2a is wider than the width of the orthogonal direction groove 2b.

Gears manufactured using the gear manufacturing method of this embodiment allow sufficient lubricating oil to remain on the tooth surface 1, even when the gear is miniaturized, improving the tooth surface durability and enabling the gear device 10 to be miniaturized and have a longer life.

Next, we will explain the third embodiment of the present invention. Note that we will not repeat the explanation of the points in common with the above embodiments.

In the above embodiment, spur gears are used as specific examples of gears, but the present invention may be applied to other types of gears. For example, bevel gears and spiral bevel gears, which are types of gears, are used on large ships and the like, and there is a need for small-scale production. Gears produced in small quantities are often processed using a machining center, but if the rotating tool 20 is scanned along a path perpendicular to the normally used contact advance direction, a scale pattern is generated on the tooth surface 1, which causes pitting. Therefore, in this embodiment, the scanning direction of the rotating tool 20 is set to the contact advance direction of the gear, thereby intentionally generating oil grooves that contribute to improving the tooth surface durability. In this way, this proposal is particularly effective in processing bevel gears.

REFERENCE SIGNS LIST 1 tooth surface 1a sliding surface 2 oil groove 2a groove in forward direction 2b groove in perpendicular direction 10 gear device 11, 12 gear 20 rotary tool 21 cutter

Claims (3)

a first step of machining and forming a groove in the tooth surface in a progression direction by scanning a rotary tool in contact with the tooth surface in a progression direction;
a second step of moving the rotating tool to a region where there is no groove in the direction of travel by scanning the rotating tool in a direction perpendicular to the direction of travel without contacting the gear;
a gear manufacturing method for machining and forming a plurality of the progression direction grooves on the tooth surface by repeating the steps of:
a gear manufacturing method comprising the steps of: forming a groove in a direction perpendicular to the groove in the first step of machining the groove in the ... 2. The method for producing a gear according to claim 1 ,
a gear manufacturing method according to claim 1, wherein the orthogonal grooves are periodic grooves that are machined and formed due to the influence of core runout, unbalanced vibration, or external shape error of the rotating tool when the rotating tool is scanned in the traveling direction. 3. The gear manufacturing method according to claim 2 ,
The gear manufacturing method according to claim 1, wherein the groove in the forward direction is deeper than the groove in the perpendicular direction.

Images