Gear Machining Method

Abstract

To provide a gear processing method that can improve a meshing ratio other than an initial stage of meshing while avoiding trochoidal interference at the initial stage of meshing.SOLUTION: A gear processing method comprises: tooth flank corner part processing processes ST3, ST14 in which a tooth flank corner part D, b, that is at least one of a tooth tip and tooth trace directional end or a tooth root and tooth trace directional end, is scraped away from a prescribed tooth flank shape by performing gear skiving that adds bias correction to standard processing conditions; and standard tooth flank processing processes ST4, ST13 which are performed in a previous process or a post-process of the tooth flank corner part processing processes ST3, ST14, and in which parts other than tooth flank corner parts D, b are processed into the prescribed tooth flank shape by performing tooth flank processing according to standard processing conditions.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to a gear machining method. [Background technology]

[0002] Trochoidal interference is known to be one of the causes of damage to gears. Trochoidal interference is a phenomenon in which the tips of the teeth of a driven gear bite into the root of the teeth of a driving gear at the beginning of meshing due to deformation of the teeth caused by the load when the gears are driven or errors during assembly. To avoid this type of interference, it is known to perform semi-topping, in which the tips of the teeth in the entire tooth trace direction (tooth width direction) are chamfered.

[0003] Patent Document 1 also describes that in addition to semi-topping, the following tooth flank modifications are performed in gear skiving to adjust the meshing state of the gear teeth. The tooth flank modifications include, for example, crowning modification, bias modification, helix angle modification, pressure angle modification, and tooth profile roundness modification. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-11011 A Summary of the Invention [Problem to be solved by the invention]

[0005] When semi-topping is applied, the amount of tooth addendum available for meshing is reduced, and the meshing ratio is reduced. Therefore, large semi-topping cannot be applied. If the semi-topping is made small, the trochoid interference cannot be sufficiently reduced.

[0006] In addition, in gears with a helix angle, such as helical gears, the line of contact between the drive gear and driven gear at the time of meshing is inclined with respect to the tooth trace direction. Therefore, by applying semi-topping to the entire area of ​​the tooth tip in the tooth trace direction, the meshing ratio decreases even in periods other than the early stage of meshing (middle and late stages of meshing). The decrease in the meshing ratio increases the surface pressure.

[0007] Therefore, it is necessary to modify the tooth surface so as to avoid trochoid interference in the initial stage of meshing while preventing a decrease in the contact ratio in other stages of meshing. It is not easy to improve the contact ratio while avoiding trochoid interference in the initial stage of meshing only by applying crowning modification or bias modification.

[0008] The present invention has been made in view of the above background, and aims to provide a gear cutting method capable of improving the contact ratio during periods other than the initial period of meshing while avoiding trochoid interference during the initial period of meshing. [Means for solving the problem]

[0009] One aspect of the present invention is A gear machining method for machining a gear tooth surface on a workpiece, comprising the steps of: a tooth flank corner processing step of performing a gear skiving process with bias modification applied to a reference processing condition to perform a process of cutting off at least one of a tooth flank corner portion, which is a tooth tip and an end portion in the tooth trace direction, or a tooth base and an end portion in the tooth trace direction, with respect to a predetermined tooth flank shape; a reference tooth flank machining step which is carried out before or after the tooth flank corner machining step, and which machines a portion other than the tooth flank corner into the predetermined tooth flank shape by performing gear machining under the reference machining conditions; The present invention relates to a gear machining method comprising the steps of: Effect of the Invention

[0010] Bias modification is a modification method that changes the tooth flank shape before modification to a twisted flank shape. In other words, bias modification is a modification method that changes the tooth profile shape so that the pressure angle gradually changes as you move in the tooth trace direction. Therefore, when bias modification is applied and the entire tooth flank is machined, one pair of corners out of the four corners that make up the tooth flank will be cut off relatively deeply, and the remaining pair of corners will be cut off relatively shallowly.

[0011] Therefore, in the tooth flank angle processing step, a bias modification is applied to process the tooth flank angle, which is at least one of the tooth tip and end in the tooth trace direction, or the tooth base and end in the tooth trace direction. Meanwhile, in the reference tooth flank processing step, a specified tooth flank shape is processed under reference processing conditions. In other words, on the tooth flank of the gear after processing is completed, the tooth flank angle is the portion processed in the tooth flank angle processing step, and the portion other than the tooth flank angle is the portion processed in the reference tooth flank processing step.

[0012] In this way, multiple machining steps are used, including a machining step with bias modification applied to the standard machining conditions and a machining step under the standard machining conditions. Therefore, only the tooth flank corners can be machined deeper than other parts. Gears machined in this way can improve the meshing ratio except for the initial meshing stage while avoiding trochoid interference at the initial meshing stage. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of a gear machining device. [Diagram 2] This is a view of the workpiece and the tool viewed from a direction perpendicular to the rotation axis of the workpiece in the XZ plane. The dashed line showing the tool indicates the position after the workpiece has been subjected to gear machining. [Diagram 3] This is a view of the workpiece and the tool from the Y direction. The dashed line showing the tool indicates the position after gear machining has been performed on the workpiece. [Figure 4] This shows the meshing portion between the drive gear and the driven gear where trochoid interference occurs. [Diagram 5] In a gear having a helix angle, the teeth of the driven gear are shown, and the line that simultaneously contacts the drive gear during meshing is shown by a dashed line, and the white arrow indicates the direction of movement of the contact line as meshing progresses. [Figure 6] FIG. 4 is a diagram illustrating a pressure angle. [Figure 7] FIG. 13 is a diagram illustrating bias correction. [Figure 8] This is a coordinate system that represents the specified tooth flank shape of a gear on a plane of the tooth profile direction (radial direction) and the tooth trace direction (tooth width direction) on the vertical axis H0, and shows a permuted coordinate system in which the vertical axis represents the amount of deviation (modification amount) from the specified tooth flank shape. [Figure 9] The target shape of one tooth of the driven gear is shown. [Figure 10] The target shape of one tooth of the driven gear is shown in a permuted coordinate system. [Figure 11] FIG. 11 is a diagram in which the permuted coordinate system shown in FIG. 10 is flipped 180°, and shows the tooth flank angle portion to be modified on the near side. [Figure 12] 1 is a flowchart showing a gear machining method. [Figure 13] In a permuted coordinate system, the tooth flank shape after the reference rough machining process two cycles before the finish machining process is shown. [Figure 14] In a permuted coordinate system, the tooth flank shape after the rough machining process one cycle before the finish machining process is shown. [Figure 15] This is a view of the tooth flank shape after the rough modification process, as viewed from the tooth profile direction (radial direction) of the permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. [Figure 16] This is a diagram of the tooth flank shape after the rough modification process, as viewed from the tooth trace direction (tooth width direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. [Figure 17] The tooth flank shape after the finishing process is shown in a permuted coordinate system. [Figure 18] This is a view of the tooth flank shape after the finishing process, as viewed from the tooth profile direction (radial direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. [Figure 19]This is a diagram of the tooth flank shape after the finish machining process, as viewed from the tooth trace direction (tooth width direction) of a permuted coordinate system. The oblique lines indicate the surface that is visible on the near side. [Figure 20] 1 shows a calculation diagram for determining machining conditions in a rough machining process in a permuted coordinate system. [Figure 21] 10 is a flowchart showing another example of a gear machining method. [Figure 22] The target shape of one tooth of the drive gear is shown. [Figure 23] The target shape of one tooth of the drive gear is shown in a permuted coordinate system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (1. Configuration of gear machining device 1) The gear machining device 1 will be described with reference to Fig. 1. The gear machining device 1 is a device that generates a tooth profile on the workpiece W by using the gear skiving cutter T by moving the gear skiving cutter T and the workpiece W relatively while rotating them.

[0015] In this embodiment, the gear machining device 1 is a general-purpose machine tool, for example, a machining center. The machining center is configured to be tool replaceable, and can perform machining according to the attached tool. For example, the replaceable gear machining tool is a gear skiving cutter T, as well as a hob cutter, a shaper cutter, etc. By replacing it with a hob cutter or a shaper cutter, the gear machining device 1 becomes a device that processes a tooth profile on the workpiece W by hobbing or shaping.

[0016] Moreover, examples of replaceable tools other than those for gear machining include end mills, milling tools, drills, turning tools, threading tools, grinding tools, etc. Note that a tool exchange device and a tool magazine for storing tools are not shown in FIG.

[0017] In this embodiment, the machining center serving as the gear machining device 1 is basically a horizontal machining center. However, the gear machining device 1 can also be configured in other ways, such as a vertical machining center.

[0018] As shown in Fig. 1, the gear machining device 1 has, for example, three mutually orthogonal linear axes (X-axis, Y-axis, Z-axis) as drive axes. Here, the direction of the rotation axis of the gear skiving cutter T (equal to the rotation axis of the tool spindle) is defined as the Z-axis direction, and two axes perpendicular to the Z-axis direction are defined as the X-axis and Y-axis. In Fig. 1, the horizontal direction is the X-axis direction, and the vertical direction is the Y-axis direction.

[0019] Furthermore, the gear machining device 1 has one rotation axis (B axis) as a drive axis for changing the relative posture between the gear skiving cutter T and the workpiece W. In this embodiment, the B axis is a rotation axis whose center of rotation is the Y axis direction. The gear machining device 1 also has a Ct axis as a rotation axis for rotating the gear skiving cutter T, and a Cw axis as a rotation axis for rotating the workpiece W.

[0020] In the gear machining device 1, the configuration for relatively moving the gear skiving cutter T and the workpiece W can be appropriately selected. For example, the gear machining device 1 may have an A-axis with the X-axis direction as the center of rotation instead of the B-axis. In the following, an example will be given of the gear machining device 1 in which the gear skiving cutter T can be linearly moved in the Y-axis and Z-axis directions, the workpiece W can be linearly moved in the X-axis direction, and the workpiece W can be rotated about the B-axis.

[0021] The gear machining apparatus 1 includes a bed 10, a workpiece holding device 20, a tool holding device 30, and a control device 40. The bed 10 is placed on an installation surface and formed into a shape corresponding to the shapes of the workpiece holding device 20, the tool holding device 30, and their movement mechanisms. In this embodiment, the bed 10 is, for example, rectangular. An X-axis guide rail 11 and a Z-axis guide rail 12 are formed on the upper surface of the bed 10.

[0022] The workpiece holding device 20 allows the workpiece W to move linearly in the X-axis direction and rotate about the B-axis and Cw-axis relative to the bed 10. The workpiece holding device 20 mainly includes an X-axis moving table 21, a B-axis rotating table 22, and a workpiece spindle device 23.

[0023] The X-axis moving table 21 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) to move in the X-axis direction while being guided by the X-axis guide rail 11 of the bed 10. The B-axis rotating table 22 is placed on the upper surface of the X-axis moving table 21 and moves in the X-axis direction together with the X-axis moving table 21. The B-axis rotating table 22 is also provided rotatably on the B-axis relative to the X-axis moving table 21. A rotating motor (not shown) is housed in the B-axis rotating table 22, and the B-axis rotating table 22 can rotate on the B-axis by driving the rotating motor.

[0024] The workpiece spindle device 23 is provided on the B-axis rotating table 22, and rotates about the B-axis integrally with the B-axis rotating table 22. The workpiece spindle device 23 supports the workpiece W. A rotary motor (not shown) is housed in the workpiece spindle device 23, and the workpiece spindle device 23 is capable of rotating the workpiece W about the Cw-axis by being driven by the rotary motor. In this way, the workpiece holding device 20 enables the workpiece W to move in the X-axis direction relative to the bed 10, and to rotate about the B-axis and the Cw-axis.

[0025] The tool holding device 30 mainly includes a column 31, a saddle 32, and a tool spindle device 3. The column 31 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) to move in the Z-axis direction while being guided by the Z-axis guide rail 12 of the bed 10. A Y-axis guide rail 31a is formed on a surface (left surface in FIG. 1) of the column 31 that extends in the vertical direction. The saddle 32 is driven by a driving device such as a linear motor or a ball screw mechanism (not shown) to move in the Y-axis direction while being guided by the Y-axis guide rail 31a of the column 31.

[0026] The tool spindle device 33 is provided on the saddle 32 and moves in the Y-axis direction integrally with the saddle 32. The tool spindle device 33 supports the gear skiving cutter T. A rotary motor (not shown) is housed in the tool spindle device 33, and the tool spindle device 33 is capable of rotating the gear skiving cutter T about the Ct axis by driving the rotary motor. In this way, the tool holding device 30 holds the gear skiving cutter T so that it can move in the Y-axis and Z-axis directions relative to the bed 10 and can rotate about the Ct axis.

[0027] The control device 40 includes a calculation device and a storage device, and controls each driving device by executing a machining program.

[0028] (2. Gear skiving processing explanation) The state in which a tooth profile is generated on a workpiece W by the gear skiving cutter T will be described with reference to Figs. 2 and 3.

[0029] In gear skiving, the rotation axis At of the gear skiving cutter T is set at an intersection angle θ with an axis parallel to the rotation axis Aw of the workpiece W. The rotation axis At of the gear skiving cutter T and the rotation axis Aw of the workpiece W are parallel to the XZ plane. The center-to-center distance between the rotation axis At of the gear skiving cutter T and the rotation axis Aw of the workpiece W, i.e., the distance in the Y-axis direction, is Da (hereinafter referred to as the "axis distance").

[0030] The workpiece W is rotated around the rotation axis Aw (Cw axis), and the gear skiving cutter T is rotated around the rotation axis At (Ct axis). While synchronizing the rotation of the workpiece W and the rotation of the gear skiving cutter T, the gear skiving cutter T is moved relative to the workpiece W in the direction of the rotation axis Aw of the workpiece W, thereby generating a gear tooth profile on the workpiece W. In gear skiving, each tooth groove portion of the workpiece W is machined only once by the gear skiving cutter T while the workpiece W rotates once.

[0031] (3. Explanation of Trochoid Interference) Trochoidal interference will be described with reference to Fig. 4. As shown in Fig. 4, the driving gear G1 and the driven gear G2 are in mesh with each other to transmit power. At the beginning of the meshing between the driving gear G1 and the driven gear G2, the tooth tip of the driven gear G2 bites into the tooth base of the driving gear at the Pa portion. This phenomenon is called trochoidal interference.

[0032] Also, referring to Fig. 5, a description will be given of the change over time in the contact line between the drive gear G1 and the tooth flank of the driven gear G2 when the drive gear G1 and the driven gear G2 are gears having a helix angle. As shown by the dashed line in Fig. 5, the contact line (meshing line) between the drive gear G1 and the tooth flank of the driven gear G2 is inclined with respect to the tooth trace direction. In detail, first, the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the tooth flank of the driven gear G2, meshes, and then the contact line (meshing line) moves toward the tooth flank corner B, which is the tooth base and the other end in the tooth trace direction.

[0033] That is, in gears having a helix angle, trochoid interference can occur at tooth flank corner D of the driven gear G2. In the driving gear G1, it can occur at a tooth flank corner (not shown) that corresponds to tooth flank corner D of the driven gear G2 and is the tooth root and the end in the tooth trace direction. Gears having a helix angle include, for example, helical gears, double helical gears, and spiral bevel gears.

[0034] (4. Tooth surface modification method) The pressure angle will be explained with reference to Fig. 6. The pressure angle δ is the angle between a radial line passing through a certain point on the tooth flank of Gear G and a tangent to the tooth profile. In Fig. 6, the tooth flank is an involute tooth flank, and the pressure angle δ indicates the pressure angle at the reference pitch point of the involute tooth flank. Pressure angle modification, which is one of the tooth flank modification methods, is a method of modifying the pressure angle δ. For example, pressure angle modification means modifying the pressure angle δ at the center of the tooth trace direction of Gear G.

[0035] As one of the tooth flank modification methods, bias modification will be described with reference to FIG. 7. Bias modification is a method of continuously changing the pressure angle in the tooth trace direction to give the tooth flank a twist. For example, at the other end in the tooth trace direction (other end in the tooth width direction) which is the left front side of FIG. 7, the pressure angle is modified so that the tooth flank angle A at the tooth tip moves to the outside of the tooth flank (right side in FIG. 7), while the tooth flank angle B at the tooth base moves to the inside of the tooth flank (left side in FIG. 7). On the other hand, at one end in the tooth trace direction (one end in the tooth width direction) which is the right rear side of FIG. 7, the pressure angle is modified so that the tooth flank angle D at the tooth tip moves to the inside of the tooth flank (left side in FIG. 7), while the tooth flank angle C at the tooth base moves to the outside of the tooth flank (right side in FIG. 7).

[0036] In Fig. 7, the portion where the modification amount of the pressure angle, which changes continuously in bias modification, becomes 0 is the center portion in the tooth trace direction. However, the portion where the modification amount of the pressure angle, which changes continuously in bias modification, becomes 0 can also be located at a position shifted from the center portion in the tooth trace direction.

[0037] For example, when the modification amount of the pressure angle δ at the center in the tooth trace direction is set to 0, the modification amount of the pressure angle at one end in the tooth trace direction and the modification amount of the pressure angle at the other end in the tooth trace direction will have opposite positive and negative signs, but the absolute values ​​will not match. However, when a modification amount of the pressure angle δ is applied to the center in the tooth trace direction, the modification amount of the pressure angle at one end in the tooth trace direction and the modification amount of the pressure angle at the other end in the tooth trace direction will have opposite positive and negative signs, but the absolute values ​​will not match.

[0038] The bias modification and pressure angle modification can be realized by changing the intersecting angle θ, the axis distance Da, the position in the X-axis direction, the rotation axis Ct of the gear skiving cutter T, the rotation axis Cw of the workpiece W, etc. For example, this is a known technique from JP 2021-11011 A. The same applies to tooth surface modification methods other than bias modification and pressure angle modification, such as crowning modification.

[0039] (5. Explanation of permuted coordinate system) A permuted coordinate system as a coordinate system for easily grasping the tooth flank shape of a gear will be described with reference to Fig. 8. As shown on the left side of Fig. 8, the predetermined tooth flank shape of a gear G is, for example, an involute tooth flank shape or a shape obtained by applying a modification process such as crowning to an involute tooth flank. Since the predetermined tooth flank shape such as an involute tooth flank shape is a three-dimensional curved surface, it is not possible to visually grasp the amount of tooth flank modification.

[0040] In order to visually grasp the tooth flank shape of the gear G, particularly the amount of tooth flank modification, a permuted coordinate system as shown on the right side of FIG. 8 is used. The permuted coordinate system is a coordinate system that expresses a predetermined tooth flank shape of the gear G on a plane of the tooth profile direction (radial direction) and the tooth trace direction (tooth width direction) at a reference value H0 on the vertical axis. The vertical axis in the permuted coordinate system indicates the deviation amount (modification amount) from the predetermined tooth flank shape. A value larger than the reference value H0 indicates a deviation value in the shallower direction, and a value smaller than the reference value H0 indicates a deviation value in the deeper direction. When the tooth flank of the gear G has a predetermined tooth flank shape, the four tooth flank corners A, B, C, and D on the tooth flank shown on the left side of FIG. 8 are located at the corners of a rectangle on a plane whose vertical axis corresponds to the reference value H0, as shown on the right side of FIG. 8.

[0041] (6. Target tooth surface shape of driven gear G2) The target tooth flank shape of the driven gear G2 will be described with reference to Fig. 9 to Fig. 11. Fig. 9 shows the target tooth flank shape of the driven gear G2 in an actual three-dimensional coordinate system, and Fig. 10 and Fig. 11 show the tooth flank of the driven gear G2 in a permuted coordinate system.

[0042] The target tooth flank shape of the driven gear G2 is a shape for reducing the above-mentioned trochoid interference. Specifically, as shown in Fig. 9, the target tooth flank shape of the driven gear G2 is a shape in which a tooth flank corner D, which is the tooth tip and one end in the tooth trace direction, is cut off, and the portion other than the tooth flank corner D is expressed by a predetermined tooth flank shape.

[0043] For example, when the specified tooth flank shape is an involute shape, the portions other than the tooth flank corner D are formed in an involute shape. On the other hand, the tooth flank corner D is cut away from the involute shape, which is the specified tooth flank shape. In other words, only the tooth flank corner D is formed into a shape that has been chamfered with respect to the specified tooth flank shape. As shown in FIG. 9, the tooth flank corner D has a triangular shape. Note that the tooth flank corner D is not a flat surface, but a curved surface that is slightly convexly curved.

[0044] Here, the predetermined tooth flank shape is not limited to an involute shape, but may be a shape in which a predetermined tooth flank modification is applied to an involute shape. For example, the predetermined tooth flank shape may be a shape in which a tooth flank modification such as crowning is applied to an involute shape.

[0045] 10 and 11, in the permuted coordinate system, the portions other than tooth flank corner D have a predetermined tooth flank shape and are therefore represented by a plane whose vertical axis is the reference value H0. In other words, the portions other than tooth flank corner D are formed on a plane that passes through corner points A0, B0, and C0 corresponding to the tooth flank corners A, B, and C, respectively.

[0046] The tooth flank corner D has a shape that is cut away like a chamfer from the specified tooth flank shape. Therefore, the vertical axis of the tooth flank corner D indicates a value smaller than the reference value H0. The corner point D1 of the tooth flank corner D indicates the smallest value on the vertical axis. As shown in Fig. 10 and Fig. 11, the tooth flank corner D has a shape with a triangular outline and is shown as a slightly curved surface. Note that since the tooth flank corner D is located on the rear side in Fig. 10, Fig. 11 is shown in a permuted coordinate system rotated so that the tooth flank corner D is located on the front side.

[0047] (7. Gear Machining Method) A gear machining method for machining the tooth flank of a gear G on a workpiece W by gear skiving will be described with reference to Fig. 12 to Fig. 19. Here, the case of machining the tooth flank of a driven gear G2 will be described.

[0048] The gear machining method is performed by causing a control device 40 (shown in FIG. 1) constituting the gear machining apparatus 1 to execute a machining program, thereby operating each driving device constituting the gear machining apparatus 1. In this embodiment, the cutting from the material shape of the workpiece W to the finishing tooth surface of the driven gear G2 is performed in multiple steps.

[0049] First, the control device 40 performs a reference rough machining process ST1 in which gear skiving is performed under reference machining conditions. The reference machining conditions are machining conditions for machining the tooth flank of the gear G into a predetermined reference rough tooth flank shape. The predetermined reference rough tooth flank shape is, for example, an involute shape. That is, in the reference rough machining process ST1, the entire tooth flank is rough-machined, so that the tooth flank is machined into a predetermined reference rough tooth flank shape, for example, an involute shape.

[0050] The predetermined reference rough tooth flank shape corresponds to the predetermined tooth flank shape in the target tooth flank shape of the driven gear G2 described above. However, since the cutting depths of the two are different, the predetermined reference rough tooth flank shape and the predetermined tooth flank shape in the target tooth flank shape do not match.

[0051] The tooth flank of the driven gear G2 after the standard rough machining process ST1 is machined in a permuted coordinate system as shown in Fig. 13. Since the entire tooth flank is formed into a predetermined standard rough tooth flank shape, the vertical axis is expressed in a plane having a reference value H2 in the permuted coordinate system. In other words, in the permuted coordinate system, the tooth flank of the driven gear G2 after the standard rough machining process ST1 is formed into a plane passing through the corner points A2, B2, C2, and D2 corresponding to the tooth flank corners A, B, C, and D, respectively.

[0052] 12, the control device 40 judges whether the currently performed reference rough machining step ST1 is two cycles before the finish machining step (judgment step ST2). If it is not two cycles before the finish machining step (ST2: No), the control device 40 adds a cutting amount and executes the reference rough machining step ST1 again until it reaches two cycles before the finish machining step.

[0053] When the reference rough machining step ST1 that has been performed reaches two cycles before the finish machining step (ST2: Yes), the control device 40 performs a modification rough machining step ST3 in which gear skiving is performed under modification rough machining conditions. The modification rough machining conditions are machining conditions in which at least bias modification is applied to the reference machining conditions as shown in FIG. 7. In this embodiment, the modification rough machining conditions are machining conditions in which bias modification is applied to the reference machining conditions as shown in FIG. 7, and pressure angle modification is applied at the center in the tooth trace direction as shown in FIG. 6. The pressure angle modification amount is δ.

[0054] The tooth flank of the driven gear G2 after the modification rough machining step ST3 is machined in the permuted coordinate system as shown in Figs. 14 to 16. The reference value H1 in the modification rough machining step ST3 is a value obtained by adding a predetermined rough cutting amount Db to the reference value H2 in the immediately preceding standard rough machining step ST1. In other words, if machined under standard machining conditions, the tooth flank is machined to a plane having the reference value H1 in the permuted coordinate system. The tentative standard machining conditions here are machining conditions obtained by adding a cutting amount to the standard machining conditions in the standard rough machining step ST1, and are machining conditions for machining the tooth flank into a tooth flank shape (virtual standard tooth flank shape) corresponding to a predetermined standard rough tooth flank shape.

[0055] However, in the modification rough machining step ST3, at least a bias modification is applied to the reference machining conditions, and further a pressure angle modification is applied. Therefore, the tooth flank machined in the modification rough machining step ST3 has a surface shape that deviates from the plane passing through the reference value H1 (the virtual reference tooth flank shape in the modification rough machining step ST3).

[0056] In this embodiment, a predetermined rough cutting depth Db is set so that the corner point C1 corresponding to the tooth flank corner C coincides with the reference value H1. Therefore, the corner point C1 corresponding to the tooth flank corner C coincides with the corner point C10 located on the virtual reference tooth flank shape. The tooth flank corners B and D are machined to be deeply cut away with respect to the virtual reference tooth flank shape. Therefore, the corner points B1 and D1 corresponding to the tooth flank corners B and D are located in the negative direction (downward in FIG. 14) of the corner points B10 and D10 located on the virtual reference tooth flank shape.

[0057] In this embodiment, the corner point A1 corresponding to the tooth flank corner A is also set to coincide with the reference value H1. Therefore, the corner point A1 corresponding to the tooth flank corner A coincides with the corner point A10 located on the virtual reference tooth flank shape. However, the corner point A1 corresponding to the tooth flank corner A may be set so as not to coincide with the reference value H1.

[0058] By performing the rough modification process ST3 as described above, the entire tooth surface of the driven gear G2 is machined. In detail, in the rough modification process ST3, machining is performed by at least a predetermined rough cutting depth Db.

[0059] Here, in the rough modification process ST3, the pressure angle modification amount at the center in the tooth trace direction is set to δ, as shown in Fig. 14. This allows the absolute value of the pressure angle at one end in the tooth trace direction to be different from the absolute value of the pressure angle at the other end in the tooth trace direction. In particular, the corner point D1 corresponding to the tooth flank corner D can be cut deeper than the corner point B1 corresponding to the tooth flank corner B.

[0060] More specifically, the distance (modification amount) between corner point D1 corresponding to tooth flank corner D and corner point D10 located on the virtual reference tooth flank shape is set to a value larger than a predetermined finish cutting-in amount Dc described later. On the other hand, the distance (modification amount) between corner point B1 corresponding to tooth flank corner B and corner point B10 located on the virtual reference tooth flank shape is set to a value smaller than a predetermined finish cutting-in amount Dc described later. In this way, the modification rough machining process ST3 is called a tooth flank corner machining process because it is a process in which the tooth flank corner D is cut off to a larger extent than other parts.

[0061] 12, the control device 40 executes a finishing process ST4 (reference tooth surface machining process) following the rough modification process ST3 (tooth surface corner machining process). In the finishing process ST4, gear skiving is performed under reference machining conditions.

[0062] The tooth flank of the driven gear G2 after the finish machining step ST4 is machined in the permuted coordinate system as shown in Figs. 17 to 19. The reference value H0 in the finish machining step ST4 is a value obtained by adding a predetermined finish cutting-in amount Dc to the reference value H1 in the immediately preceding modification rough machining step ST3. That is, in the finish machining step ST4, the tooth flank is machined to a plane having the reference value H0 in the permuted coordinate system. The reference machining conditions here are machining conditions obtained by adding a cutting-in amount to the reference machining conditions in the reference rough machining step ST1, and are machining conditions for machining the tooth flank into a predetermined tooth flank shape (finish tooth flank shape).

[0063] However, as described above, in the rough modification process ST3, the distance (modification amount) between the corner point D1 corresponding to the tooth flank corner D and the corner point D10 located on the virtual reference tooth flank shape is set to a value larger than a predetermined finish cutting-in amount Dc described later. In other words, the tooth flank corner D is located at a position deeper than the position corresponding to the finish cutting-in amount Dc. On the other hand, the parts other than the tooth flank corner D are located at positions shallower than the positions corresponding to the finish cutting-in amount Dc.

[0064] Therefore, in the finishing process ST4, the portions other than the tooth flank corner D are machined into a predetermined tooth flank shape. On the other hand, in the finishing process ST4, the tooth flank corner D is not machined. That is, the tooth flank corner D remains as the surface machined in the rough modification process ST3.

[0065] (8. Method for determining machining conditions in rough machining process ST3) A method for determining the machining conditions in the rough trimming process ST3 will be described with reference to FIGS.

[0066] 14 and 17, the corner point C1 corresponding to the tooth flank corner C in the rough modification process ST3 coincides with the reference value H1. The tooth flank machined in the rough modification process ST3 is located on the plane corresponding to the reference value H1 or at a position deeper than the plane corresponding to the reference value H1 in the permuted coordinate system.

[0067] 14 and 17, the tooth flank is twisted over the entire length S3 in the tooth trace direction because bias modification is applied in the rough modification process ST3. As shown in Fig. 14, the length from one end face in the tooth trace direction to position P1 in the tooth trace direction where the pressure angle modification amount becomes 0 is defined as S2. Here, because pressure angle modification is applied at the center in the tooth trace direction, the position where the pressure angle modification amount becomes 0 is located at a position shifted from the center in the tooth trace direction. In this embodiment, length S2 is longer than half of the entire length in the tooth trace direction.

[0068] 17, the distance (modification amount) between corner point D1 corresponding to tooth flank corner D and corner point D10 located on the virtual reference tooth flank shape is set to a value larger than a predetermined finish cutting depth Dc in the finish processing step ST4. Therefore, in the finish processing step ST4, the area other than tooth flank corner D is machined, and tooth flank corner D remains as a triangular chamfer. The length of the modification area of ​​tooth flank corner D in the tooth profile direction is R1, and the length of the modification area of ​​tooth flank corner D in the tooth trace direction is S1.

[0069] The tooth flank shape in the rough modification process ST3 is a very complicated three-dimensional shape because bias modification is applied. However, if such a complicated three-dimensional shape is used, it is not easy to design the tooth flank shape. Therefore, as shown in Figure 20, the range (S2) from one end in the tooth flank direction to the position where the pressure angle modification amount becomes 0 in the tooth flank direction and the range (R2) of the entire length in the tooth profile direction is defined as a virtual shape as shown below.

[0070] A reference plane is generated that passes through the corner point C1 corresponding to the tooth flank corner C to be machined in the rough modification machining process ST3. The reference plane is a plane that passes through points C1, P2, P3, and P4 and has the same vertical axis value. Point P2 coincides with point D10 shown in Figure 14. Point P3 has a different value from point P1 shown in Figures 14 and 17. However, point P3 may also coincide with point P1.

[0071] Next, a triangular plane with points C1, P3, and D1 as vertices is generated. The triangular plane is the shaded area in Fig. 20. In other words, the triangular plane is a plane including tooth flank corner D, and is a truncated triangular plane obtained by cutting off vertex P2 of a tooth portion composed of three surfaces, namely, the tooth flank of the driven gear G2 (upper surface in Fig. 20), the tooth end surface on one side in the tooth trace direction (left front surface in Fig. 20), and the tooth tip surface (right front surface in Fig. 20). In other words, the tooth flank corner D included in a part of the shaded area is approximated as a truncated triangular plane obtained by cutting off vertex P2 of a tooth portion composed of three surfaces, namely, the tooth flank of the driven gear G2 (upper surface in Fig. 20), the tooth end surface on one side in the tooth trace direction (left front surface in Fig. 20), and the tooth tip surface (right front surface in Fig. 20).

[0072] The pressure angle modification amount at one tooth end face in the tooth trace direction is defined as α. The distance between the corner point C0 corresponding to the tooth flank corner C in the finishing process ST4 and the corner point C1 corresponding to the tooth flank corner C in the rough modification process ST3 is defined as β. In other words, the distance β coincides with the predetermined finish cutting depth Dc in the finishing process ST4. Moreover, in the final shape of the tooth flank, the maximum modification amount in the tooth thickness direction at the tooth flank corner D is defined as γ.

[0073] The pressure angle modification amount α at one tooth end face in the tooth trace direction is determined so as to satisfy the formulas (1), (2), and (3). α = β + γ (1) α / R2=γ / R1 (2) α / S2=γ / S1 (3) α: Pressure angle modification amount at the tooth end face β: Distance in the tooth thickness direction between the end point on the truncated triangular plane opposite the tooth flank corner and the specified tooth flank shape γ: Maximum modification amount in the tooth thickness direction at the tooth flank angle R1: Length in the tooth profile direction in the modification area of ​​the tooth flank corner R2: Evaluation range in the tooth profile direction (distance between the tooth tip and the tooth base side tooth profile reference surface) S1: Length in the tooth trace direction in the tooth flank corner modification area S2: Length from the tooth end face to the position in the tooth trace direction where the pressure angle modification amount becomes 0

[0074] Here, the predetermined finishing cutting depth β in the finishing process ST4 is determined within the range of "0<β<maximum modification amount of α". The maximum modification amount of α is the maximum value of the modification amount that can be imparted to the tooth flank corner D in the rough modification process ST3.

[0075] (9. Effects of gear processing method) As described above, the tooth flank corner D is machined in the rough modification process ST3, and the portions other than the tooth flank corner D are machined in the finish processing process ST4. The bias modification in the rough modification process ST3 is a modification method that changes the tooth flank shape before modification to a twisted surface shape. In other words, bias modification is a modification method that changes the tooth profile shape so that the pressure angle gradually changes as it progresses in the tooth trace direction. Therefore, when the entire tooth flank is machined by applying bias modification, one pair of corners out of the four corners that make up the tooth flank is cut off relatively deeply, and the remaining pair of corners is cut off relatively shallowly.

[0076] Therefore, in the rough modification process ST3 (tooth flank corner processing process), a bias modification is applied to process the tooth flank corner D located at the tooth tip and one end in the tooth trace direction of the driven gear G2 deeply. Meanwhile, in the finish processing process ST4 (reference tooth flank processing process), a predetermined tooth flank shape is processed under reference processing conditions. In other words, on the tooth flank of the driven gear G2 after processing is completed, the tooth flank corner D is the portion processed in the rough modification process ST3, and the portion other than the tooth flank corner D is the portion processed in the finish processing process.

[0077] In this way, multiple machining steps are used, including a machining step in which bias modification is applied to the standard machining conditions and a machining step under the standard machining conditions. Therefore, in the driven gear G2, only the tooth flank corner portion D can be machined deeper than other portions. The driven gear G2 machined in this way can improve the meshing ratio except for the initial meshing period while avoiding trochoid interference at the initial meshing period.

[0078] In addition, the finishing process ST4 is performed as a process subsequent to the rough modification process ST3. As a result, the rough modification process ST3 processes the tooth flank corner D and also processes the areas other than the tooth flank corner D. The finishing process is performed subsequent to the rough modification process ST3, and processes the areas other than the tooth flank corner D in the rough modification process ST3. In other words, the rough modification process ST3 functions as one of the normal rough machining processes, and there is no need to add a special machining process for machining the tooth flank corner D.

[0079] Here, the driving gear G1 and the driven gear G2 are gears having a helix angle. When the driven gear G2 is the processing target, the rough modification process ST3 processes the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the driven gear G2. In particular, in gears having a helix angle, it is possible to avoid trochoid interference at the tooth flank corner D of the driven gear G2 and improve the meshing ratio except at the initial stage of meshing.

[0080] In the rough modification process ST3, in order to apply a bias modification, when the tooth flank corner portion D is machined deeper than the reference value H1, there is a possibility that the diagonally located tooth flank corner portion B will also be machined deeper than the reference value H1.

[0081] However, in the modification rough machining step ST3, bias modification is applied to the reference machining conditions, and pressure angle modification is applied to the center of the tooth trace direction. By doing so, the modification amount at the tooth flank corner D, which is the tooth tip and one end in the tooth trace direction of the driven gear G2, is relatively large, and the modification amount at the tooth flank corner B, which is the tooth root and the other end in the tooth trace direction, is relatively small.

[0082] That is, the tooth flank corner D, which is the tip and one end in the tooth trace direction of the driven gear G2 processed in the rough modification process ST3, is a portion that is not processed in the finish processing process ST4. On the other hand, the tooth flank corner B, which is the root and the other end in the tooth trace direction of the driven gear G2 processed in the rough modification process ST3, is a portion that is processed in the finish processing process ST4.

[0083] In this way, by applying not only bias modification but also pressure angle modification to the center in the tooth trace direction in the rough modification process ST3, the final tooth flank shape has only the tooth flank corner D machined in the rough modification process ST3, and the other parts have surfaces machined in the finish processing process ST4. Therefore, in a gear having a helix angle, it is possible to avoid trochoid interference at the tooth flank corner D of the driven gear G2 and improve the meshing ratio except at the initial stage of meshing.

[0084] In addition, the standard rough machining process ST1, the rough correction machining process ST3, and the finishing machining process ST4 all use gear skiving to machine the tooth surface. Therefore, gears can be machined without changing tools. In addition, machining can be performed in a series of machining operations.

[0085] (10. Other examples of gear machining methods) Another example of the gear machining method will be described with reference to Fig. 21. In the above, the finishing process ST4 is performed after the rough modification process ST3 (tooth flank corner machining process). In this example, the finishing process ST13 is performed before the tooth flank corner machining process ST14.

[0086] The control device 40 performs the standard rough machining step ST11. The standard rough machining step ST11 is the same as the standard rough machining step ST1 described above. Next, the control device 40 judges whether the standard rough machining step ST11 performed this time is one cycle before the finish machining step (judgment step ST12). If it is not one cycle before the finish machining step (ST12: No), the control device 40 performs the standard rough machining step ST11 again until it reaches one cycle before the finish machining step.

[0087] When the performed reference rough machining step ST11 reaches one cycle before the finish machining step (ST12: Yes), the control device 40 performs the finish machining step ST13. The finish machining step ST13 is performed under the same machining conditions as the finish machining step ST4 in the above embodiment. That is, in the finish machining step ST13, the entire tooth surface is machined, and the tooth surface is formed into a predetermined tooth surface shape.

[0088] Next, the tooth flank corner processing step ST14 is performed. The tooth flank corner processing step ST14 is performed under the same processing conditions as the above-mentioned rough modification processing step ST3. That is, the tooth flank corner processing step ST14 processes the tooth flank corner D. However, the tooth flank corner processing step ST14 does not process any part other than the tooth flank corner D.

[0089] In this way, even if the finishing process ST13 is performed as a process preceding the tooth flank corner processing process ST14, it is possible to ultimately form a shape in which only the tooth flank corner D is machined away. As a result, it is possible to avoid trochoid interference at the tooth flank corner D of the driven gear G2 and improve the meshing ratio except for the initial stage of meshing.

[0090] (11. Target tooth surface shape of driving gear G1) The above description is for the driven gear G2. The same can be applied to the drive gear G1. However, the part where trochoid interference occurs is the tooth tip in the driven gear G2, whereas it is the tooth base in the drive gear G1. Therefore, a shape equivalent to the tooth flank corner D of the tooth flank of the driven gear G2 is formed on the tooth base side of the tooth flank of the drive gear G1.

[0091] The target tooth flank shape of the driving gear G1 in this case will be described with reference to Figures 22 and 23. Figure 22 shows the target tooth flank shape of the driving gear G1 in an actual three-dimensional coordinate system, and Figure 23 shows the tooth flank of the driving gear G1 in a permuted coordinate system.

[0092] The target tooth flank shape of the driving gear G1 is a shape in which the tooth flank corner b, which is the tooth root and one end in the tooth trace direction, is cut away in order to reduce the above-mentioned trochoidal interference, and the portion other than the tooth flank corner b is expressed by a predetermined tooth flank shape. In Figures 22 and 23, the tooth flank of the driving gear G1 has tooth flank corners a, b, c, and d, and the corner points corresponding to the tooth flank corners a, b, c, and d are a0, b1, c0, and d0, respectively.

[0093] The gear cutting method for the driven gear G2 described above can be applied to the tooth surface of the driving gear G1 in the same manner. Specifically, the gear cutting method shown in Fig. 12 and the gear cutting method shown in Fig. 21 can be applied.

[0094] Regarding the method of determining the machining conditions in the tooth flank corner machining steps ST3 and ST14, in the driven gear G2, the tooth flank corner D is approximated as a truncated triangular plane in which the apex of the tooth portion consisting of the three surfaces of the tooth flank, tooth end surface, and tooth tip surface is cut off. In the driving gear G1, the tooth flank corner b can be approximated as a truncated triangular plane in which the apex of the tooth portion consisting of the three surfaces of the tooth flank, tooth end surface, and tooth profile reference surface on the tooth bottom side is cut off. The tooth profile reference surface is a virtual surface that corresponds to the back side of the tooth tip surface in the tooth portion.

[0095] In this way, the trochoidal interference can be reduced by machining the drive gear G1 to have the tooth flank corner b cut off to a specified tooth flank shape. Moreover, by machining both the drive gear G1 and the driven gear G2 as described above, the trochoidal interference can be reduced more reliably.

[0096] (12. Others) In the above embodiment, the standard rough machining step ST1, the rough modification machining step ST3, and the finishing machining step ST4 are all performed by performing gear skiving to machine the tooth surface. In addition, for example, the standard rough machining step ST1 and the rough modification machining step ST3 may apply gear skiving, and the finishing machining step ST4 may apply other gear machining methods such as hobbing with a hob cutter or shaping with a shaper cutter. Also, the standard rough machining step ST1 may apply hobbing or shaping, and the rough modification machining step ST3 and the finishing machining step ST4 may apply gear skiving. Also, a heat treatment step such as quenching may be performed after the rough modification machining step ST3, and the finishing machining step ST4 may be performed after the heat treatment step.

[0097] In the rough modification process ST3 and tooth flank corner processing process ST14, bias modification was applied to the entire tooth flank. Alternatively, bias modification can be applied only to the portion including tooth flank corners D and b in the tooth trace direction, and the remaining portions in the tooth trace direction (portions close to tooth flank corners A and B, and portions close to tooth flank corners c and d) can be processed without bias modification. In other words, halfway through the tooth trace direction in one processing feed operation, a state in which bias modification is applied and a state in which bias modification is not applied are switched.

[0098] For example, in the case of driven gear G2, when starting machining from tooth flank corners A and B in the tooth trace direction, bias modification is not applied at first, and bias modification is applied halfway in the tooth trace direction until machining reaches tooth flank corners C and D. In addition, in the case of driven gear G2, when starting machining from tooth flank corners C and D in the tooth trace direction, bias modification is applied at first, and machining is continued until tooth flank corners A and B without bias modification halfway in the tooth trace direction.

[0099] For example, in the case of the drive gear G1, when starting machining from the tooth flank corners c and d in the tooth trace direction, bias modification is not applied at first, and bias modification is applied halfway in the tooth trace direction until machining reaches the tooth flank corners a and b. Also, in the case of the drive gear G1, when starting machining from the tooth flank corners a and b in the tooth trace direction, bias modification is applied at first, and machining is continued until machining reaches the tooth flank corners c and d without bias modification halfway in the tooth trace direction. [Explanation of symbols]

[0100] W Workpiece G, G1, G2 Gears ST3, ST14 Tooth flank corner machining process ST4, ST13 Standard tooth surface machining process D, b Tooth flank angle

Claims

1. A gear machining method for machining a gear tooth surface on a workpiece, comprising the steps of: a tooth flank corner processing step of performing a gear skiving process with bias modification applied to a reference processing condition to perform a process of cutting off at least one of a tooth flank corner portion, which is a tooth tip and an end portion in a tooth trace direction, or a tooth base and an end portion in a tooth trace direction, with respect to a predetermined tooth flank shape; a reference tooth flank machining step which is carried out before or after the tooth flank corner machining step, and which machines a portion other than the tooth flank corner into the predetermined tooth flank shape by performing gear machining under the reference machining conditions; A gear machining method comprising:

2. the tooth flank corner processing step processes the tooth flank corner and also processes a portion other than the tooth flank corner, 2. The gear machining method according to claim 1, wherein the reference tooth flank machining step is performed after the tooth flank corner machining step, as a finish machining step for machining a portion other than the tooth flank corner in the tooth flank corner machining step.

3. 3. The gear machining method according to claim 1, wherein the reference tooth flank machining step performs gear skiving under the reference machining conditions to machine a portion other than the tooth flank corner portion into the predetermined tooth flank shape.

4. The gear to be machined is a driven gear having a helix angle, 4. The gear machining method according to claim 1, wherein the tooth flank corner machining step machines a tooth flank corner that is a tooth tip and one end in a tooth trace direction of the driven gear.

5. 5. A gear machining method according to claim 4, wherein the tooth flank angle machining step applies the bias modification with respect to the reference machining conditions and also applies a pressure angle modification at a central portion in the tooth trace direction to make the modification amount at the tooth tip and one end in the tooth trace direction relatively large and the modification amount at the tooth base and the other end in the tooth trace direction relatively small, thereby machining the tooth tip and one end in the tooth trace direction of the driven gear.

6. The gear to be machined is a drive gear having a helix angle, 4. The gear machining method according to claim 1, wherein the tooth flank corner machining step machines a tooth flank corner that is at a root and one end in a tooth trace direction of the drive gear.

7. 7. A gear machining method according to claim 6, wherein the tooth flank angle machining step applies the bias modification with respect to the reference machining conditions and also applies a pressure angle modification at a central portion in the tooth trace direction to make the modification amount at the tooth base and one end in the tooth trace direction relatively large and the modification amount at the tooth tip and the other end in the tooth trace direction relatively small, thereby machining the tooth base and one end in the tooth trace direction of the drive gear.

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