Worm shaft, worm reduction gear and manufacturing process of a worm shaft
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- KYB CORP
- Filing Date
- 2020-03-03
- Publication Date
- 2026-07-30
AI Technical Summary
The existing manufacturing process for worm shafts in worm gear reducers results in increased costs due to the formation of burrs during the processing of tapered portions, necessitating additional efforts to remove them.
The worm shaft is designed with a configuration that includes a tapered portion with a gradually increasing diameter, a main body portion, and a gear portion positioned radially outer to the rotation axis, minimizing the formation of burrs and reducing manufacturing costs by simplifying the processing steps.
This design effectively suppresses burr formation, thereby reducing manufacturing costs and ensuring proper assembly and operation of the worm shaft without amplifying gearing noise.
Abstract
Description
Technical area
[0001] The present invention relates to a worm shaft, a worm reduction gear and a manufacturing method for the worm shaft. State of the art
[0002] A worm gear reduction unit comprising a worm shaft connected to an electric motor, a worm wheel engaging with the worm shaft, and a pair of bearings rotatably supporting the worm shaft is known (see JP 2017 - 211 000 A). On the end face of a worm shaft 18, as described in patent literature 1, a stepped positioning section 42 is formed such that it comes into contact with one of the end faces of an inner ring 40 of a bearing 34 (see Fig. 2 in JP 2017 - 211 000 A). Summary of the invention
[0003] The stepped positioning section 42 of the worm shaft 18 described in JP 2017-211000A is shaped such that it has a diameter smaller than the outer diameter of a gear section 18c, so that the worm shaft 18 does not come into contact with an outer ring 43 of the bearing 34. A cylindrical column section and a tapered section connecting the cylindrical column section and the gear section 18c are formed between the stepped positioning section 42 and the gear section 18c.
[0004] In such a worm gear reduction mechanism, the worm shaft is assembled by inserting it axially from an opening in the housing while engaged with the worm gear. This adjusts the length of the gear section of the worm shaft to the length required for assembly. Therefore, depending on the specific worm gear reduction mechanism, there may be a case where the gear section extends to the tapered section at one end of the worm shaft.
[0005] However, in a case where the gear section is formed up to the tapered section, there is a risk of burrs forming in the tapered section. If burrs form, there is a risk of increased manufacturing costs, as machining to remove them is required, thus incurring additional manufacturing effort.
[0006] It is an object of the present invention to reduce the manufacturing costs of a worm shaft.
[0007] According to one aspect of the present invention, a worm shaft is freely rotatable by a pair of bearings at a tip end and a base end of the worm shaft, wherein the worm shaft has a gear section that engages with a worm wheel, the worm shaft comprising: an insertion section formed at the tip end, wherein the insertion section is inserted into the bearing; a wall surface formed such that it is radially directed outwards from an end section of the insertion section; a tapered section formed such that a diameter gradually increases from the wall surface towards the base end;and a main body section configured to extend from the tapered section towards the base end face, the gear section being configured on the main body section and the tapered section such that a lower web of the gear section is positioned on the radially outer side of a line extending parallel to a rotational center axis of the worm shaft and passing through a boundary between the wall surface and the tapered section. List of characters Fig. Figure 1 is a configuration diagram of a power steering system with a worm gear reduction unit according to an embodiment of the present invention. Fig. Figure 2 is a cross-sectional view of the power steering system with worm gear reduction according to the present invention. Fig. Figure 3 is a flowchart showing a manufacturing process for a worm shaft. Fig. Figure 4 is a side view of a material of the worm shaft. Fig. Figure 5 is a side view of the material with a tapered section and shows a tool used for gear machining of the material, using two-point catenary lines. Fig. Figure 6 is a side view of the worm shaft. Fig. Figure 7 is an enlarged view showing an enlarged end section of the worm shaft according to this embodiment and a worm shaft according to a comparative example of this embodiment using two-point catenary lines. Description of the embodiments
[0008] A power steering system with a worm gear reduction unit according to an embodiment of the present invention is described with reference to the drawings. The power steering system is a device mounted on a vehicle to assist a steering force exerted by a driver on a steering wheel.
[0009] As in the Fig. 1 and Fig. Figure 2 shows a power steering system 10 equipped with a worm gear 100 and an electric motor 7 serving as the drive source. The worm gear 100 comprises a worm shaft 2, which is connected to an output shaft 7a of the electric motor 7 and rotates when the electric motor 7 is driven, a worm wheel 1, which engages with a gear section 129 of the worm shaft 2, and a gearbox housing 3, which accommodates the worm shaft 2 and the worm wheel 1. The worm shaft 2 and the output shaft 7a of the electric motor 7 are coupled by a shaft coupling 19, which allows for misalignment.
[0010] A steering shaft 20 is connected to a steering wheel 16, and the steering shaft 20 is rotated by the rotation of the steering wheel 16. The steering shaft 20 is provided with an input shaft 21, which is connected to the steering wheel 16, an output shaft 22, which is connected to a rack and pinion shaft 8, and a torsion bar 23, which connects the input shaft 21 and the output shaft 22. The worm gear 1 is mounted on the output shaft 22.
[0011] The power steering device 10 further comprises: a torque sensor 24, which detects a steering torque applied to the torsion bar 23 by a relative rotation between the input shaft 21 and the output shaft 22 caused by steering input from the driver; and a controller 25, which controls the drive of the electric motor 7 based on the steering torque detected by the torque sensor 24. The torque delivered by the electric motor 7 is transmitted by the worm shaft 2 to the worm gear 1 and applied as auxiliary torque to the output shaft 22. As previously described, the power steering device 10 assists the driver's steering input by controlling the drive of the electric motor 7 through the controller 25 based on the results detected by the torque sensor 24.
[0012] With the worm gear 100, the rotation of the worm shaft 2 is slowed down and transmitted to the worm wheel 1 when the worm shaft 2 is rotated by the drive of the electric motor 7. In this configuration, the torque of the electric motor 7 is transmitted via the output shaft 22, on which the worm wheel 1 is located, to the rack shaft 8, which controls the gears 6.
[0013] As in Fig. As shown in Figure 2, the worm shaft 2 is housed in the metallic gearbox housing 3, and the electric motor 7 is attached to the gearbox housing 3. The worm shaft 2 is formed with a gear section 129 which meshes with a gear section 119 of the worm wheel 1. The gearbox housing 3 has an opening section 3c at a position corresponding to the gear section 129, and the gear section 129 of the worm shaft 2 and the gear section 119 of the worm wheel 1 mesh through the opening section 3c.
[0014] The worm gear 100 comprises: a first bearing 4, which supports the base end (the side of the electric motor 7) of the worm shaft 2 so that it can rotate freely; a second bearing 11, which supports the tip end (the side opposite the electric motor 7) of the worm shaft 2 so that it can rotate freely; and a coil spring 12, which acts as a preload element, biasing the worm shaft 2 via the second bearing 11 in the direction of the worm wheel 1. In other words, the worm shaft 2 is supported by a pair of bearings (the first bearing 4 and the second bearing 11) so that it can rotate freely in the gear housing 3. The direction of rotation along a rotational center axis 90 of the worm shaft 2 (see figure) is described below. Fig. 6) simply referred to as the axial direction, and a radiation direction centered on the rotational center axis 90 of the worm shaft 2 is referred to as the radial direction.
[0015] The first bearing 4 is a deep groove ball bearing in which the balls serving as rolling elements are inserted between an annular outer ring and an annular inner ring. The outer ring of the first bearing 4 is arranged axially between a stepped section 3a formed in the gearbox housing 3 and a lock nut 5 fastened in the gearbox housing 3. The inner ring of the first bearing 4 is arranged axially between a stepped section 2b of the worm shaft 2 and a worm-side joint 9 of the shaft coupling 19, which is connected to the worm shaft 2.
[0016] The second bearing 11 is a deep groove ball bearing in which the balls 143, serving as rolling elements, are arranged between an annular outer ring 141 and an annular inner ring 142. The second bearing 11 is mounted in a lower part of the gearbox housing 3.
[0017] The worm shaft 2 comprises: a column-shaped cylindrical insertion section 111, which is formed at the head end of the worm shaft 2 and which is inserted into the inner ring 142 of the second bearing 11; a wall surface 121, which is designed such that it is vertically radially oriented outwards from a base end section of the cylindrical insertion section 111 and which can come into contact with the inner ring 142 of the second bearing 11; a tapered section 112, which is designed such that its diameter gradually increases from the wall surface 121 towards the base end of the worm shaft 2 (towards the right in the figure); and a main body section 113, which extends from the tapered section 112 towards the base end of the worm shaft 2 (towards the right in the figure).
[0018] A flange section 17 with a flat end face 17a is formed on an outer circumferential surface of the gearbox housing 3 such that it projects outwards. The flange section 17 is provided with a through-hole 13 that opens to face an outer circumferential surface of the second bearing 11. A portion of the opening of the through-hole 13, which opens into the end face 17a of the flange section 17, is closed by a plug 14.
[0019] The coil spring 12 is inserted into the through-hole 13 in a state where it is compressed between a pointed end face of the plug 14 and the outer circumferential surface of the second bearing 11. The coil spring 12 presses the second bearing 11 in the direction that reduces the gap between the gear section 129 of the worm shaft 2 and the gear section 119 of the worm wheel 1; in other words, in the direction in which the worm shaft 2 engages with the worm wheel 1.
[0020] An inner circumferential surface 3b of the gear housing 3, surrounding the outer circumferential surface of the second bearing 11, is shaped as an elongated hole with a pair of parallel flat surface sections, allowing the second bearing 11 to move towards the worm gear 1 due to the preload force exerted by the coil spring 12. The inner circumferential surface 3b can have any shape, as long as the second bearing 11 can move within it. For example, the inner circumferential surface 3b can be in the form of a circular hole with an inner diameter larger than the outer diameter of the second bearing 11, and the pair of parallel flat surface sections is not required.
[0021] Initially, once the worm shaft 2 is fully assembled in the gearbox housing 3, the second bearing 11 is preloaded towards the worm gear side 1 by the preload force exerted by the coil spring 12, thus creating a state in which there is no play (gap) between the worm shaft 2 and the worm gear 1. In this state, the worm shaft 2 is inclined about the first bearing 4, which serves as the pivot point, by the preload force exerted by the coil spring 12.
[0022] In the power steering system 10, the gear section 129 of the worm shaft 2 and the gear section 119 of the worm wheel 1 are subject to progressive wear during continuous use. In this embodiment, even as the wear of the gear sections 119 and 129 progresses, the second bearing 11 in the elongated hole of the gearbox housing 3 is moved by the preload force exerted by the coil spring 12, thereby reducing the backlash between the gear section 129 of the worm shaft 2 and the gear section 119 of the worm wheel 1. Thus, in the worm reduction gear 100 according to this embodiment, even when the worm reduction gear 100 is in continuous use and the wear of the gear sections 119 and 129 progresses, the gear noise caused between the gear section 129 of the worm shaft 2 and the gear section 119 of the worm wheel 1 is suppressed.
[0023] In the worm shaft 2 according to this embodiment, the gear section 129 is configured on the main body section 113 and the tapered section 112 such that a lower web 129a of the same is positioned on the radially outer side of the line SL, which extends parallel to the rotational center axis 90 of the worm shaft 2 and passes through the boundary between the wall surface 121 and the tapered section 112. Furthermore, the gear section 129 is shaped such that the end section of the lower web 129a of the gear section 129 is positioned axially on an outer circumferential surface of the tapered section 112, that is, on a section between an outer circumferential edge of the wall surface 121 and an outer circumferential edge of the main body section 113.As previously described, by forming the gear section 129 not only on the main body section 113 but also on the tapered section 112, it is possible to ensure the length of the gear section 129 while suppressing the wavelength of the worm shaft 2. In the case above, where the gear section 129 is formed only on the main body section 113 but not on the tapered section 112, there is a risk that the length of the gear section 129 will be insufficient.
[0024] In the worm gear 100 according to this embodiment, the worm shaft 2 is inserted through the opening section of the gearbox 3 along the axial direction of the gearbox 3 after the worm wheel 1 has been mounted on the gearbox housing 3, while engaged with the worm wheel 1. If the length of the gear section 129 is insufficient, there is a risk that the worm shaft 2 will collide with the worm wheel 1 during assembly, preventing proper installation. Therefore, the length of the gear section 129 of the worm shaft 2 must be adjusted to a length that allows for the installation of the worm shaft 2.
[0025] By making the wavelength of the worm shaft 2 sufficiently long, it is possible to ensure the length of the gear section 129, even in a case where the gear section 129 is formed only on the main body section 113. In this case, however, the position of the second bearing 11 is different from that in Fig. The position shown in Figure 2 is shifted to the left (towards the underside of the gearbox housing 3). In other words, the distance between the first bearing 4 and the second bearing 11 increases. As a result, the movable amount of the second bearing 11, which is preloaded by the coil spring 12, increases, and there is a risk of amplifying the gear noise caused between the gear section 129 of the worm shaft 2 and the gear section 119 of the worm gear 1.
[0026] In contrast, in this embodiment, the gear section 129 is formed not only on the main body section 113 but also on the tapered section 112. This makes it possible to ensure a gear section 129 with a length sufficient to allow the worm shaft 2 to be mounted without increasing its length. Therefore, this embodiment minimizes the increase in the moving portion of the second bearing 11 and suppresses gear noise.
[0027] The wall surface 121 is a stepped surface located between the outer circumferential surface of the inlet section 111 and the outer circumferential surface of the tapered section 112, and is annular in shape. In this embodiment, the outer diameter of the main body section 113 is larger than the inner diameter of the outer ring 141. Therefore, if the outer diameter of the wall surface 121 is equal to the outer diameter of the main body section 113, there is a risk that the wall surface 121 will come into contact with the outer ring 141. In this embodiment, the outer diameter of the annular wall surface 121 is larger than the inner diameter of the inner ring 142 and smaller than the inner diameter of the outer ring 141. In other words, the outer diameter of the wall surface 121 is adjusted to the outer diameter, thus enabling the wall surface 121 to come into contact only with the inner ring 142 of the second bearing 11.
[0028] In this embodiment, the wall surface 121 is in contact with the inner ring 142 of the second bearing 11 when the worm gear 100 is in operation. However, when the worm gear 100 is in operation, the wall surface 121 does not need to be in contact with the inner ring 142 of the second bearing 11. It is sufficient for the worm gear 100 to be configured such that the wall surface 121 comes into contact with the second bearing 11 when the second bearing 11 is displaced, and the movement of the wall surface 121 can be restricted.
[0029] Next, an example of a manufacturing process for the worm shaft 2 is described. As in Fig. As shown in Figure 3, the manufacturing process of the worm shaft 2 comprises a preparation step S110, a step to form a tapered section S120, a step to form a gear section S130, and a finishing step S140. As shown in the figure, in the manufacturing process of the worm shaft 2, the preparation step S110, the step to form the tapered section S120, the step to form the gear section S130, and the finishing step S140 are carried out in this order.
[0030] In preparation step S110, as in Fig. As shown in Figure 4, a rod-shaped material 102A is produced. The material 102A has a small-diameter cylindrical column section 111A with a cylindrical column shape, formed at a tip end section of the material 102A, and a large-diameter cylindrical column section 113A with a cylindrical column shape, extending axially from the small-diameter cylindrical column section 111A. The outer diameter of the large-diameter cylindrical column section 113A is larger than the outer diameter of the small-diameter cylindrical column section 111A.
[0031] In step S120 for forming a tapered section, a lathe chuck is used to support the base end of the rod-shaped material 102A, and machining is performed on the rod-shaped material 102A using a cutting tool, thereby forming a tapered section 112B at a tip end section of the large-diameter cylindrical column section 113A (see Fig. 5).
[0032] As in Fig. As shown in Figure 5, by performing step S120 of forming the tapered section, a material 102B is formed with the tapered section 112B. Here, the tapered section 112B has a truncated conical shape and corresponds to part of the tapered section 112 of the previously described worm shaft 2 before the formation of the gear section. A large-diameter cylindrical column section 113B extending from the tapered section 112B has a cylindrical column shape and corresponds to part of the main body section 113 of the previously described worm shaft 2 before the formation of the gear section.
[0033] The following describes an inclination angle θ of an outer circumferential surface of the tapered section 112B (112). The inclination angle θ of the outer circumferential surface of the tapered section 112B (112) refers to an inclination angle with respect to the rotational center axis 90 of the worm shaft 2.
[0034] It was experimentally determined that if the angle of inclination θ of the outer circumferential surface of the tapered section 112B (112) is greater than 45 degrees, burrs tend to form in step S130 of the gear section forming process described below. Therefore, it is advantageous to set the angle of inclination θ of the outer circumferential surface of the tapered section 112B (112) to 45 degrees or less. If the angle of inclination θ of the outer circumferential surface of the tapered section 112B (112) is equal to or less than 45 degrees, it is possible to effectively suppress the formation of burrs in step S130 of the gear section forming process described below.
[0035] On the other hand, if the inclination angle θ of the outer circumferential surface of the tapered section 112B (112) is less than 30 degrees, there is a risk that a sufficient length for an effective thread section (effective length) of the gear section 129 engaging with the gear section 119 of the worm gear 1 cannot be guaranteed. In a case where the wavelength of the worm shaft 2 is made longer to ensure the effective length, the amount of movement of the second bearing 11 increases, as previously described, and there is a risk of increased gear noise. Furthermore, there is a risk that the worm reduction gear 100 will become larger if the wavelength of the worm shaft 2 is increased. Therefore, it is preferable to set the inclination angle θ of the outer circumferential surface of the tapered section 112B (112) to an angle of 30 degrees or more.In this way it is possible to shorten the wavelength of the worm shaft 2, reduce the gear noise and decrease the size of the worm reduction gear 100.
[0036] As previously described, it is advantageous that the angle of inclination θ of the outer circumferential surface of the tapered section 112B (112) is set to an angle of 30 degrees up to and including 45 degrees. Furthermore, it is more preferred that the outer circumferential surface of the tapered section 112B (112) is shaped such that the angle of inclination θ has 35 degrees up to and including 40 degrees.
[0037] In step S130 for forming the gear section, the gear section 129 is formed on the large-diameter cylindrical column section 113B (the main body section 113), which extends from the tapered section 112B (112) and the tapered section 112B (112) formed in step S120 for forming the tapered section (see Fig. 6) In this embodiment, the gear section 129 is formed by performing a gear machining operation on the rod-shaped material 102B with the tapered section 112B (112) using a gear machining device, such as a worm grinding machine, etc. As schematically shown by two-point chain lines in Fig. As shown in Figure 5, the gear machining device has a single toothed tool 190 in which a blade is formed for roughing on an outer circumference of a disc.
[0038] During gear machining, the material 102B is cut by the tool 190, which is rotated at high speed. In addition, the material 102B is rotated at a low speed around the central axis of rotation 90 and moved at a low speed along the central axis of rotation 90. In this way, the helical gear section 129 (see Fig. 6) formed. The gear section 129 is shaped such that its lower web diameter is larger than the outer diameter of the annular wall surface 121. The gear machining is performed in a region of predetermined width L1 from a gear start point P1 on the base end face (the right face in the figure) of material 102B to a gear end point P2 on the tip end face (the left face in the figure) of material 102B. The gear start point P1 is the position where the gear machining performed by the tool 190 begins, and the gear end point P2 is the position where the gear machining performed by the tool 190 ends. As shown in the figure, the gear end point P2 is defined on the tapered section 112B (112).
[0039] As in Fig. As shown in Figure 6, in the finishing step S140, finishing is carried out over a predetermined width L2 within an area to form gear sections with the predetermined width L1. In this embodiment, the finishing is carried out such that only the gear section 129 formed on the main body section 113 is completed. During the finishing, the gear section 129 is completed by machining the gear section 129 with the predetermined width L2 on the main body section 113 using a tool with a cutting edge.
[0040] Instead of machining, a rolling process can be carried out using a rolling device (not shown) equipped with a pair of rolling jaws. In rolling, the gear section 129 is finished by clamping the material between the pair of rolling jaws, each of which has a finishing blade on an outer circumference, and by deforming the material by rotating the pair of rolling jaws. The gear section (a threaded section) with the predetermined width L2, on which the finishing is carried out, forms the effective threaded section that engages with the gear section 119 of the worm gear 1.
[0041] The operational advantages achieved through this embodiment are described in comparison with a comparative example of this embodiment. Fig. Figure 7 is an enlarged view showing a magnified end section of the worm shaft 2. Fig. 7 the end section of the worm shaft 2 according to this embodiment is represented by a solid line, and the end section of a worm shaft according to the comparative example of this embodiment is represented by a two-point catenary line.
[0042] As in Fig. As shown in Figure 7, a cylindrical column section 915 is formed in the worm shaft according to the comparative example of this embodiment between the inlet section 111 and a tapered section 912. The distance from the wall surface 121 to the main body section 113 is the same in this embodiment as the distance from the wall surface 121 to the main body section 113 in the comparative example.
[0043] In the comparative example of this embodiment, the wall surface 121 is thus located further away from the tapered section 912 by a distance corresponding to the length of the cylindrical column section 915 in the axial direction. In contrast, in the worm shaft 2 according to this embodiment, the wall surface 121 is directly connected to the outer circumferential surface of the conical section 112.
[0044] Thus, the inclination angle θ of the outer circumferential surface of the conical section 112 of this embodiment is smaller than the inclination angle α of an outer circumferential surface of the tapered section 912 of the comparative example. Since, in the comparative example, the inclination angle α of the outer circumferential surface of the tapered section 912 is greater than 45 degrees and the teeth become pointed near a gear endpoint of the gear machining, there is a risk of burrs forming near the gear endpoint. In contrast, in this embodiment, since the inclination angle θ of the outer circumferential surface of the tapered section 112 is designed to be smaller than the inclination angle α of the outer circumferential surface of the tapered section 912 of the comparative example (for example, the inclination angle θ is about 35 degrees), the teeth are prevented from becoming pointed near the gear endpoint P2, and tooth stiffness is ensured.Thus, in this embodiment, the formation of burrs near the gear endpoint P2 is suppressed. In other words, according to this embodiment, it is possible to suppress the formation of burrs without increasing the wavelength compared to the reference example.
[0045] Furthermore, in a case where the lower web 129a is positioned on the radially inner side of the line SL, which extends parallel to the rotational center axis 90 of the worm shaft 2 and passes through the boundary between the wall surface 121 and the tapered section 112, and in a case where an end section of the lower web 129a is positioned axially on the wall surface 121, since the inclination angle of the wall surface 121, on which the tooth endpoint is fixed, is 90 degrees, there is a risk that burrs will be formed near the tooth endpoint.In contrast, according to this embodiment, the gear section 129 on the main body section 113 and the tapered section 112 is designed such that the lower web 129a of the gear section 129 is positioned on the radially outer side of the line SL, which extends parallel to the rotational center axis 90 of the worm shaft 2 and passes through the boundary between the wall surface 121 and the tapered section 112, and because the end section of the lower web 129a is positioned in the axial direction on the outer circumferential surface of the tapered section 112, it is possible to suppress the formation of burrs.
[0046] The embodiment described above offers the following operational advantages.
[0047] The worm shaft 2 comprises: the tapered section 112, which is configured such that the outer diameter increases from the wall surface 121 towards the base end of the worm shaft 2; and the main body section 113, which extends from the tapered section 112 towards the base end of the worm shaft 2, wherein the gear section 129 on the main body section 113 and the tapered section 112 is configured such that the lower web 129a of the gear section 129 is positioned on the radially outer side of the line SL, which extends parallel to the rotation center axis 90 of the worm shaft 2 and passes through the boundary between the wall surface 121 and the tapered section 112.Since in this configuration the wall surface 121 and the outer circumferential surface of the tapered section 112 are directly connected, it is possible to reduce the inclination angle θ of the outer circumferential surface of the tapered section 112 to a small value without increasing the wavelength of the worm shaft 2.
[0048] Therefore, it is possible to suppress the formation of burrs on the tapered section 112 when forming the gear section 129 by performing the gear machining on the rod-shaped material 102B with the tapered section 112. Since it is possible to omit or simplify the machining to remove the burrs, it is possible to reduce the manufacturing costs of the worm shaft 2. In other words, according to this embodiment, it is possible to provide a manufacturing method for the worm shaft 2 that is capable of suppressing the formation of burrs on the tapered section 112 when forming the gear section 129 on the tapered section 112. Furthermore, it is possible to provide the worm shaft 2 and the worm reduction gear 100 that are capable of reducing manufacturing costs.
[0049] The following modifications also fall within the scope of the present invention, and it is also possible to combine the configurations shown in the modifications with the configurations described in the above embodiment, or to combine the configurations described in the following various modifications. <Erste Modifikation>
[0050] Although the embodiment described above describes an example in which step S120 of forming the tapered section is performed before step S130 of forming the gear section, the present invention is not limited to this. The rod-shaped material 102B with the tapered section 112 can be prepared in advance, and the gear section 129 can be formed on the tapered section 112 and the main body section 113. According to this modification, similar to the embodiment described above, it is possible to provide a manufacturing method for the worm shaft 2 that is capable of suppressing the formation of burrs on the tapered section 112 when the gear section 129 is formed on the tapered section 112. <Zweite Modifikation>
[0051] Although the embodiment described above describes an example in which the gear machining in step S130 of forming the gear section is carried out at high speed on the material 102B by rotating the disc-shaped tool 190, which is provided with teeth for roughing on the outer circumference, the present invention is not limited to this. Instead of using the disc-shaped tool 190, the gear machining on the material 102B can be carried out at high speed by rotating an annular tool, which is designed with teeth for roughing on an inner circumference. <Dritte Modifikation>
[0052] Although the embodiment described above illustrates the example in which the present invention is applied to the worm gear 100 of the power steering device 10, the present invention can also be applied to the worm gear of other machines, such as a conveyor, a winch, a machine tool, a construction machine, etc.
[0053] The configurations, operation and effects of the embodiment of the present invention, configured as described above, are summarized below.
[0054] The worm shaft 2 is the worm shaft which is freely rotatable by the pair of bearings 4 and 11 at the tip end and the base end of the worm shaft, wherein the worm shaft has the gear section 129 which engages with the worm gear 1, wherein the worm shaft comprises: the insertion section 111 which is formed at the tip end, wherein the insertion section 111 is inserted into the bearing 11; the wall surface 121 which is formed such that it is radially oriented outwards from the end section of the insertion section 111; the tapered section 112 which is formed such that the diameter gradually increases from the wall surface 121 towards the base end;and the main body section 113, which is configured to extend from the tapered section 112 towards the base end face, wherein the gear section 129 is formed on the main body section 113 and the tapered section 112 such that the lower web 129a of the gear section 129 is positioned on the radially outer side of the line SL, which extends parallel to the rotation center axis 90 of the worm shaft 2 and passes through the boundary between the wall surface 121 and the tapered section 112.
[0055] According to this configuration, since the tapered section 112 is shaped such that the diameter increases from the wall surface 121 towards the base end, it is possible to reduce the inclination angle θ of the outer circumferential surface of the tapered section 112 with respect to the rotational center axis 90 of the worm shaft 2 to a small value. Thus, it is possible to suppress the formation of burrs on the tapered section 112 when the gear section 129 is formed on the tapered section 112. Therefore, it is possible to achieve a reduction in the manufacturing costs of the worm shaft 2.
[0056] In the case of the worm shaft 2, the inclination angle θ of the outer circumferential surface of the tapered section 112 with respect to the rotational center axis 90 of the worm shaft 2 is equal to or less than 45 degrees.
[0057] According to this configuration, it is possible to effectively suppress the formation of burrs on the tapered section 112 when the gear section 129 is formed on the tapered section 112.
[0058] According to the worm shaft 2, the inclination angle θ of the outer circumferential surface of the tapered section 112 with respect to the rotational center axis 90 of the worm shaft 2 is equal to or greater than 30 degrees.
[0059] According to this configuration, it is possible to shorten the wavelength of the worm shaft 2.
[0060] The worm gear reduction unit 100 is equipped with a worm wheel 1 which engages with the gear section 129 of the worm shaft 2.
[0061] According to this configuration, it is possible to design the worm gear 100 in such a way that the manufacturing costs can be reduced.
[0062] The previously described manufacturing process of the worm shaft 2 comprises: step S130 of forming the gear section 129 by performing the gear machining for the rod-shaped material 102B with the tapered section 112 (112B) on the tapered section 112 (112B) and on the main body section 113 (the large-diameter cylindrical column section 113B) extending from the tapered section 112 (112B); and finishing step S140 of finishing the gear section 129 formed on the main body section 113 (the large-diameter cylindrical column section 113B).
[0063] The previously described manufacturing process of the worm shaft 2 further includes step S120 of forming the tapered section 112 (112B) on the rod-shaped material 102A before step S130 of forming the gear section is carried out.
[0064] According to these configurations, it is possible to provide a manufacturing process for the worm shaft 2 that is able to suppress the formation of burrs on the tapered section 112 (112B) when the gear section 129 is formed on the tapered section 112 (112B).
[0065] Previously, embodiments of the present invention were described, but the embodiments mentioned above are merely examples of applications of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the embodiments mentioned above.
[0066] With reference to the above description, the contents of application no. 2019-119919, filed in Japan on 27 June 2019, are incorporated herein by reference. QUOTES INCLUDED IN THE DESCRIPTION
[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature
[0000] JP 2017211000 A [0002, 0003] JP 2019119919
[0066]
Claims
[1] A worm shaft freely rotatably supported by a pair of bearings at a tip end side and a base end side of the worm shaft, the worm shaft having a gear portion meshing with a worm wheel, the worm shaft comprising: an insertion portion formed on the tip end side, the insertion portion being inserted into the bearing; a wall surface shaped to be erected radially outward from an end portion of the insertion portion; a tapered portion shaped so that the diameter gradually increases from the wall surface toward the base end side; and a main body portion configured to extend from the tapered portion toward the base end side, wherein the gear portion is formed on the main body portion and the tapered portion such that a lower land of the gear portion is positioned on the radially outer side of a line extending parallel to a rotational center axis of the worm shaft and passing through a boundary between the wall surface and the tapered portion. [2] The worm shaft according to claim 1, wherein an inclination angle of an outer peripheral surface of the tapered portion with respect to a rotational center axis of the worm shaft is equal to or less than 45 degrees. [3] The worm shaft according to claim 1, wherein an inclination angle of an outer peripheral surface of the tapered portion with respect to a rotational center axis of the worm shaft is equal to or greater than 30 degrees. [4] Worm reduction gear comprising: the worm shaft according to claim 1; and wherein the worm wheel is connected to a gear portion of the worm shaft. [5] A method for manufacturing the worm shaft according to claim 1, comprising: a step of forming the gear portion by performing gear machining for a rod-shaped material having the tapered portion on the tapered portion and on the main body portion extending from the tapered portion; and a finishing step of finishing the gear portion formed on the main body portion. [6] A method of manufacturing the worm shaft according to claim 5, further comprising: a tapered portion forming step of forming the tapered portion on the rod-shaped material before performing the gear portion forming step.