Toothed pulley

Abstract

[Problem] To provide a toothed pulley comprising a core metal having a cylindrical portion and a hollow disk portion, and a resin portion including teeth, wherein the resin portion is formed from a thermoplastic resin with high productivity, while ensuring the accuracy of the teeth of the resin portion and suppressing an increase in weight. [Solution] A core metal M comprises: a first core metal 1 which is a hollow disk portion B located on a first end portion side J1 in an axial direction J of a toothed pulley A; and a second core metal 2 which is a cylindrical portion C located radially inward RI of teeth T. A portion for preventing rotation with a resin portion P is formed on an outer peripheral portion E of the first core metal 1. The resin portion P is a thermoplastic resin and is one and the same component including a first core metal-side resin portion P1 covering the outer peripheral portion E of the first core metal 1, and a second core metal-side resin portion P2 located radially outward RO of the second core metal 2 and having the teeth T formed therein. An inner peripheral surface of the resin portion P located radially inward RI of an inner peripheral surface 2A of the second core metal 2 is defined as a positioning guide portion S for a member to which the toothed pulley A is to be attached.

Description

Toothed pulley

[0001] The present invention relates to a toothed pulley that meshes with a toothed belt.

[0002] As a toothed pulley that meshes with a toothed belt, in order to achieve weight reduction while ensuring strength, there is one composed of a core metal having a hollow disk portion and a cylindrical portion, and a resin portion including teeth (see, for example, Patent Documents 1-2). The toothed pulley is manufactured, for example, by insert injection molding in which the core metal is set in an injection molding die as an insert work, molten resin is injected into the die to form the resin portion, and then cooled and solidified.

[0003] The power transmission mechanism of an electric power steering device is, for example, a belt transmission mechanism composed of a driving-side toothed pulley, a driven-side toothed pulley, and a toothed belt. Since the belt transmission mechanism is a speed reducer for increasing torque, the pitch circle diameter of the driven-side toothed pulley is large. The toothed pulley 1 of Patent Document 1 is used for the driven-side toothed pulley.

[0004] The toothed pulley 1 of Patent Document 1 uses a thermosetting resin such as a phenolic resin or an epoxy resin for the tooth portion 3 which is the resin portion, and uses a metal such as steel for the hub base 2 which is the core metal (see

[0031] ,

[0036] -

[0037] of Patent Document 1). The hub base 2 is, for example, a deep drawing part (see

[0036] of Patent Document 1 and FIG.2).

[0005] The toothed pulley of Patent Document 2 uses a synthetic resin such as a polyacetal resin or a phenolic resin for the toothed annular body 2 which is the resin portion, and uses a metal such as steel for the pulley main body 1 which is the core metal (see the 4th line from the bottom right column to the 5th line of the upper left column on the 3rd page, and the 2nd line of the upper right column and the 10th line of the bottom right column on the 2nd page of Patent Document 2). The pulley main body 1 is formed, for example, by press-forming a steel plate into a dish shape (see the 10th line of the bottom right column on the 2nd page and FIG.2 of Patent Document 2).

[0006] German Patent Application Publication No. 102006059946 Japanese Unexamined Patent Publication No. 04-069443

[0007] As shown in Patent Document 1, using a thermosetting resin for the resin part including the teeth improves the precision of the teeth. However, when injection molding the resin part including the teeth with a thermosetting resin, the molding cycle becomes longer, and burrs are produced, requiring secondary processing. Consequently, productivity decreases.

[0008] In contrast, productivity can be improved by using a thermoplastic resin for the resin part containing the teeth, such as polyacetal resin, which is an example of synthetic resin in Patent Document 2. However, if the thickness of the resin part is not set appropriately (thinning while maintaining strength), the difference between the thickness of the resin part and the total thickness of the teeth will become large, and the difference in shrinkage will also become large, which tends to worsen accuracy. On the other hand, the thickness of the core metal can be increased to make the thickness of the resin part thinner, but the weight of the toothed pulley will increase.

[0009] When forming a core metal having a hollow disc portion and a cylindrical portion by repeatedly drawing a metal plate, as in the hub base 2 of Patent Document 1 or the pulley body 1 of Patent Document 2, there is a concern that the flatness of the hollow disc portion of the formed core metal will deteriorate, as will the dimensional accuracy of the inner diameter of the cylindrical portion of the core metal and the cylindricity of the inner surface of the cylindrical portion. Therefore, when performing insert injection molding, it becomes difficult to set the core metal in the mold, and a gap between the core metal and the mold is required to account for variations in the inner diameter of the core metal. Consequently, the accuracy of the concentricity between the tooth tips of the teeth and the inner diameter of the core metal after injection molding of the resin portion including the teeth in the mold decreases.

[0010] The present invention aims to provide a toothed pulley comprising a core metal having a hollow disc portion and a cylindrical portion, and a resin portion including teeth, in which the resin portion is made of a highly productive thermoplastic resin, while ensuring the precision of the teeth of the resin portion and suppressing an increase in weight.

[0011] A toothed pulley according to a first aspect of the present invention is a toothed pulley comprising a core metal having a hollow disc portion and a cylindrical portion, and a resin portion including teeth. The core metal consists of a first core metal which is the hollow disc portion located on the first end side in the axial direction of the toothed pulley, and a second core metal which is the cylindrical portion located radially inward of the teeth. An anti-rotation portion is formed on the outer circumference of the first core metal for contact with the resin portion. The resin portion is a thermoplastic resin and is the same component including a first core metal side resin portion that covers the outer circumference of the first core metal, and a second core metal side resin portion located radially outward of the second core metal on which the teeth are formed. The inner surface of the resin portion radially inward from the inner surface of the second core metal serves as a positioning guide portion for the member to which the toothed pulley is attached.

[0012] A toothed pulley according to a second aspect of the present invention is a toothed pulley according to a first aspect, wherein the anti-rotation portion is formed on the outer peripheral edge of the first mandrel and has a shape in which recesses and protrusions are repeated as the direction is circumferential.

[0013] A toothed pulley according to a third aspect of the present invention is a toothed pulley according to a first aspect, wherein the first core metal has a first bent portion formed by bending the outer peripheral edge of the first core metal toward the second end in the axial direction of the toothed pulley, and the anti-rotation portion is formed on the axial end face of the first bent portion and has a shape in which concave and convex portions are repeated as the direction is circumferential.

[0014] A toothed pulley according to a fourth aspect of the present invention is a toothed pulley according to a second aspect, wherein the second core metal has a fitting recess on the end face on the first end side in the axial direction of the toothed pulley, into which the protrusion on the outer peripheral edge of the first core metal fits.

[0015] A toothed pulley according to a fifth aspect of the present invention is a toothed pulley according to a second aspect, wherein the second core metal has a second bent portion obtained by bending the end of the toothed pulley on the first end side in the axial direction radially inward.

[0016] In the toothed pulley according to the present invention, the hollow disc portion and cylindrical portion of the mandrel are composed of a first mandrel and a second mandrel, which are separate parts. Therefore, the first mandrel, which is the hollow disc portion, does not need to be formed by deep drawing and can be formed by punching alone. Consequently, it becomes easier to ensure the flatness of the hollow disc portion, making it easier to set the mandrel in the injection molding die when performing insert injection molding.

[0017] Furthermore, the inner circumferential surface of the resin portion radially inward from the inner circumferential surface of the second mandrel, which is a cylindrical portion, serves as a positioning guide portion for the member to which the toothed pulley is attached. Therefore, since the inner circumferential surface that serves as the positioning guide portion and the teeth of the toothed pulley are formed by the mold used to shape the resin portion, the concentricity between the member to which the toothed pulley is attached and the teeth of the toothed pulley depends solely on the precision of the mold. Consequently, improving the precision of the mold makes it easy to improve the accuracy of the concentricity.

[0018] Furthermore, since the cylindrical second mandrel does not need to have a function to guide the member to which the toothed pulley is attached, the diameter of the second mandrel can be increased while making it thinner. As a result, the resin part can be made of a highly productive thermoplastic resin, while the wall thickness of the resin part can be made to the required thinness. Therefore, the toothed pulley can be made lighter while ensuring the precision of the teeth of the resin part.

[0019] This is a perspective view of a toothed pulley according to an embodiment of the present invention. This is a partial cross-sectional perspective view of the toothed pulley in Figure 1. This is a longitudinal cross-sectional view of the toothed pulley in Figure 1. This is an enlarged view of the main part of Figure 3A. This is a view from the axial direction showing the core metal removed. This is a perspective view showing the core metal removed. This is a view from the axial direction showing the core metal of the first modified example. This is a perspective view showing the core metal of the first modified example. This is a longitudinal cross-sectional view of a toothed pulley using the core metal of the second modified example. This is an enlarged view of the main part of Figure 6A. This is a view from the axial direction showing the core metal removed from the second modified example. This is a perspective view showing the core metal removed from the second modified example. This is a longitudinal cross-sectional view of a toothed pulley using the core metal of the third modified example. This is an enlarged view of the main part of Figure 8A. This is a view from the axial direction showing the core metal removed from the third modified example. This is a perspective view showing the core metal removed from the third modified example.

[0020] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0021] The toothed pulley according to the embodiment of the present invention is used in the power transmission mechanism of an electric power steering system. Therefore, high precision is required for the toothed pulley according to the embodiment of the present invention.

[0022] In this specification, the direction parallel to the axis of rotation of the toothed pulley (for example, the symbol O in Figure 3A) is referred to as the "axial direction" (for example, the symbol J in Figure 3A), and the "radial direction" and the "circumferential direction" (for example, the symbol D in Figure 4A) are defined with respect to the axis. The radial direction approaching the axis is referred to as the "radial inward direction" (for example, the symbol RI in Figure 3A), and the radial direction moving away from the axis is referred to as the "radial outward direction" (for example, the symbol RO in Figure 3A).

[0023] [Toothed Pulley] As shown in Figures 1-2 and 3A-3B, the toothed pulley A according to an embodiment of the present invention consists of a core metal M having a hollow disc portion B and a cylindrical portion C, and a resin portion P including teeth T. Since the portion of the toothed pulley A including teeth T is made of resin P, the toothed pulley A can be made lighter. The teeth T of the toothed pulley A mesh with the teeth of a toothed belt (not shown). The teeth T of the toothed pulley A according to this embodiment are helical.

[0024] The toothed pulley A is manufactured by insert injection molding, in which a core metal M is set as an insert workpiece in an injection molding die, molten resin is injected into the die to form the resin part P, and then cooled and solidified. The bottom plate K at the first end J1 in the axial direction J of the resin part P has gate marks in the center of the four recessed parts Q shown in Figure 1.

[0025] [Cord] As shown in Figures 2, 3A-3B, the core metal M consists of a first core metal 1, which is a hollow disc portion B located at the first end J1 in the axial direction J of the toothed pulley A, and a second core metal 2, which is a cylindrical portion C located radially inward RI of the teeth T. The first core metal 1 and the second core metal 2 are made from press-formed cold-rolled steel sheet, hot-rolled steel sheet, high-tensile steel sheet, etc. Since the first core metal 1 and the second core metal 2 are separate parts, the flatness of the first core metal 1, which is the hollow disc portion B, can be easily ensured.

[0026] As shown in Figures 4A-4B, a rotation-preventing portion 3 is formed on the outer circumference of the first mandrel 1, preventing it from rotating with the resin portion P. The rotation-preventing portion 3 is formed, for example, on the outer edge of the first mandrel 1, and has a shape in which recesses 3A and protrusions 3B are repeated as the circumferential direction D is reached. As shown in Figures 3B and 4A, there is an axial gap N1 between the recess 3A of the first mandrel 1 and the inner circumferential surface 2A of the second mandrel 2.

[0027] The gap N1 serves as a flow path for the molten resin injected into the mold from the gate during insert injection molding. As shown in Figure 4A, the gaps N1 formed at multiple locations (eight locations in this embodiment) in the circumferential direction D serve as the flow path for the molten resin, thus having the effect of diffusing the weld, which is the confluence of molten resin when the resin part P shown in Figure 1-2 is injection molded. Therefore, dimensional defects and strength reduction of the resin part P due to the weld can be suppressed.

[0028] As shown in Figures 4A-4B, the first core metal 1 has a plurality of mounting holes 1A in the axial direction J (in this embodiment, four round holes equally spaced in the circumferential direction). In the toothed pulley A shown in Figure 1-2, the toothed pulley A can be easily and reliably fixed to the member to which the toothed pulley A is attached by mounting bolts passed through the mounting holes 1A of the first core metal 1.

[0029] As shown in Figures 4A-4B, the first core metal 1 has multiple axial J cutouts (in this embodiment, four circular holes equally spaced in the circumferential direction) 1B. The cutouts 1B make the first core metal 1 lighter, and by inserting the resin part P into the cutouts 1B, they have the function of preventing the resin part P, which includes the teeth T, and the first core metal 1 from rotating in the circumferential direction D.

[0030] [Resin part] As shown in Figures 2, 3A-3B, the resin part P is the same component including a first core metal side resin part P1 that covers the outer circumference E of the first core metal 1, and a second core metal side resin part P2 located radially outward RO of the second core metal 2, on which teeth T are formed. As shown in Figure 3B, the resin part P has a wrap-around part P3 that wraps around from the outer circumference E of the first core metal 1 to radially inward RI of the second core metal 2 and covers the first end side J1 in the axial direction J of the inner circumferential surface 2A of the second core metal 2.

[0031] The inner circumferential surface of the wrap-around portion P3 becomes a positioning guide portion S for the member to which the toothed pulley A is attached. In other words, in this embodiment, the positioning guide portion S is used for radial positioning of the toothed pulley A relative to the nut of the ball screw of the electric power steering device.

[0032] As shown in Figure 1-2, the resin part P has a notch L in the bottom plate K that exposes the mounting hole 1A of the first core metal 1 in the axial direction J. The bottom plate K provided in the resin part P increases the strength and rigidity of the resin part P. Furthermore, because the mounting hole 1A of the first core metal 1 is exposed in the axial direction J by providing the notch L in the bottom plate K, the bottom plate K does not get in the way when attaching the toothed pulley A to the member to which the toothed pulley A is attached.

[0033] As described above, the flatness of the first mandrel 1, which is the hollow disc portion B, can be easily ensured, so when insert injection molding is performed, no gap is created between the first mandrel 1 set in the mold and the mold. Therefore, resin overfilling, where molten resin flows around the mounting hole 1A of the first mandrel 1 and forms on the seating surface of the mounting bolt head, does not occur.

[0034] As shown in Figures 1-2 and 3A-3B, the resin part P has an outward-facing flange F at its first end J1 in the axial direction J, which protrudes radially outward RO beyond the tooth tips of the teeth T. Furthermore, the fitting recess H of the outward-facing flange G, made of synthetic resin, is fitted into the fitting projection I at the second end J2 in the axial direction J of the resin part P. With the outward-facing flange G positioned in the axial direction J and radial direction relative to the resin part P, the outward-facing flange G is attached to the resin part P, for example, by ultrasonic welding. Therefore, the toothed pulley A is a double-flange type, and the movement of the toothed belt that meshes with the toothed pulley A in the axial direction J can be restricted.

[0035] The material of the resin part P is, for example, a thermoplastic resin material such as PBT, PA6, PA66, PA46, PPS, or PEEK. Among these, a preferred embodiment is one in which glass fiber is added in several tens of weight percent as a reinforcing material to PPS, which is superior in terms of heat resistance, mechanical properties, flame retardancy, and dimensional stability.

[0036] [First Modified Example of the Mandrel] In Figures 5A-5B showing the first modified example of the mandrel M, the end face of the first end J1 in the axial direction J of the cylindrical part C of the second mandrel 2 has a fitting recess 5 into which the convex part 3B of the outer peripheral edge of the hollow disc part B of the first mandrel 1 fits. This prevents the first mandrel 1 and the second mandrel 2 from rotating.

[0037] [Second Modification of the Mandrel] In Figures 6A-6B and 7A-7B, which show a second modification of the mandrel M, the outer diameter of the first mandrel 1 is smaller than the outer diameter of the first mandrel 1 in Figures 3A-3B and 4A-4B. As shown in Figures 6B and 7A, there is a gap N2 in the axial direction J between the outer circumferential surface 1C of the first mandrel 1 and the inner circumferential surface 2A of the second mandrel 2, along the entire circumference in the circumferential direction D.

[0038] The first core metal 1 has a first bent portion 4A formed by bending the outer edge of the first core metal 1 toward the second end J2 in the axial direction J. The anti-rotation portion 3 between the first core metal 1 and the resin portion P is formed on the axial end face of the first bent portion 4A and has a shape in which recesses 3C and protrusions 3D are repeated as the circumferential direction D progresses.

[0039] As shown in Figure 6B, the resin portion P has a wrap-around portion P4 that wraps around from the outer circumference E of the first core metal 1 radially inward RI of the second core metal 2, covers the first end J1 in the axial direction J of the inner circumferential surface 2A of the second core metal 2, and then wraps around radially inward RI of the first bent portion 4A to cover the inner circumferential surface of the first bent portion 4A. The inner circumferential surface of the wrap-around portion P4 becomes a positioning guide portion S of the member to which the toothed pulley A is attached.

[0040] In a second modified example of a core metal M in which the outer diameter of the first core metal 1 is relatively small and there is a gap N2 around the entire circumference between it and the inner circumferential surface 2A of the second core metal 2, by providing a first bent portion 4A in the first core metal 1, the wall thickness of the resin portion P radially inward RI of the second core metal 2 can be made thinner, and the variation in the wall thickness can be reduced. Therefore, it becomes easier to ensure the accuracy of the resin portion P, which is a molded product of thermoplastic resin.

[0041] [Third Modification of the Mandrel] In Figures 8A-8B and 9A-9B, which show a third modification of the mandrel M, the outer diameter of the first mandrel 1 is smaller than the outer diameter of the first mandrel 1 in Figures 3A-3B and 4A-4B, and is located radially inward RI from the inner circumferential surface 2A of the second mandrel 2.

[0042] On the outer peripheral portion of the first core metal 1, a rotation prevention portion 3 similar to the first core metal 1 in FIGS. 3A - 3B and 4A - 4B is formed. The second core metal 2 has a second bent portion 4B obtained by bending the first end portion side J1 end portion in the axial direction J of the second core metal 2 radially inward RI. As shown in FIG. 8B, there is a radial gap N3 over the entire circumference in the circumferential direction D (see FIG. 9A) between the surface of the second end portion side J2 of the first core metal 1 and the surface of the first end portion side J1 of the second bent portion 4B of the second core metal 2.

[0043] As shown in FIG. 8B, the resin portion P has a wrapping portion P5 that wraps from the outer peripheral portion of the first core metal 1 to cover the second bent portion 4B and covers the first end portion side J1 in the axial direction J of the inner peripheral surface 2A of the second core metal 2. The inner peripheral surface of the wrapping portion P5 serves as a positioning guide portion S for the member to attach the toothed pulley A.

[0044] In a third modification of the core metal M where the outer diameter of the first core metal 1 is relatively small and the outer diameter of the first core metal 1 is radially inward RI from the inner peripheral surface 2A of the second core metal 2, by providing the second bent portion 4B on the second core metal 2, the thickness of the resin portion P radially inward RI of the second core metal 2 can be made thin, and the variation in the thickness can be reduced. Therefore, it becomes easier to ensure the accuracy of the resin portion P which is a molded product of a thermoplastic resin.

[0045] [Function and Effect] According to the toothed pulley A according to the embodiment of the present invention, the hollow disk portion B and the cylindrical portion C of the core metal M are constituted by the first core metal 1 and the second core metal 2 which are separate parts. Therefore, the first core metal 1 which is the hollow disk portion B does not need to be formed by drawing process and can be formed only by punching process. Therefore, it becomes easy to ensure the flatness of the hollow disk portion B, and it becomes easy to set the core metal M in the injection mold when performing insert injection molding.

[0046] Further, the inner peripheral surface of the resin portion P radially inward RI from the inner peripheral surface 2A of the second core metal 2 which is the cylindrical portion C is used as a positioning guide portion S for the member to which the toothed pulley A is attached. Therefore, since the inner peripheral surface serving as the positioning guide portion S and the teeth T of the toothed pulley A are formed by the mold for molding the resin portion P, the concentricity between the member to which the toothed pulley A is attached and the teeth T of the toothed pulley A depends only on the accuracy of the mold. Thus, by improving the accuracy of the mold, it becomes easy to improve the accuracy of the concentricity.

[0047] Further, since it is not necessary to give the second core metal 2 which is the cylindrical portion C a function of guiding the member to which the toothed pulley A is attached, the diameter of the second core metal 2 can be increased while making it thin. Therefore, while the resin portion P is made of a highly productive thermoplastic resin, the wall thickness of the resin portion P can be made the required thinness. Thus, while ensuring the accuracy of the teeth T of the resin portion P, the weight of the toothed pulley A can be reduced.

[0048] The descriptions of the above embodiments are all illustrative and not restrictive. Various improvements and modifications can be made without departing from the scope of the present invention.

[0049] 1 First mandrel 1A Mounting hole 1B Cutout hole 1C Outer surface 2 Second mandrel 2A Inner surface 3 Anti-rotation part 3A, 3C Recess 3B, 3D Protrusion 4A First bent part 4B Second bent part 5 Fitting recess A Toothed pulley B Hollow disc part C Cylindrical part D Circumferential direction E Outer surface F Outward flange G Outward flange H Fitting recess I Fitting protrusion J Axial direction J1 First end side J2 Second end side K Bottom plate L Notch M Mandrel N1, N2, N3 Gap O Axis of rotation shaft P Resin part P1 Resin part on the first mandrel side P2 Resin part on the second mandrel side P3, P4, P5 Wrap-around part Q Recess RI Radial inward RO Radial outward S Positioning guide part T Teeth

Claims

1. A toothed pulley comprising a core metal having a hollow disc portion and a cylindrical portion, and a resin portion including teeth, wherein the core metal consists of a first core metal which is the hollow disc portion located on the first end side in the axial direction of the toothed pulley, and a second core metal which is the cylindrical portion located radially inward of the teeth, the outer circumference of the first core metal having a rotation-preventing portion with respect to the resin portion, the resin portion being a thermoplastic resin and comprising a first core metal side resin portion covering the outer circumference of the first core metal, and a second core metal side resin portion located radially outward of the second core metal and having the teeth formed thereon, the inner surface of the resin portion radially inward from the inner surface of the second core metal serving as a positioning guide portion for the member to which the toothed pulley is attached.

2. The toothed pulley according to claim 1, wherein the anti-rotation portion is formed on the outer peripheral edge of the first mandrel and has a shape in which recesses and protrusions are repeated as the circumferential direction is reached.

3. The toothed pulley according to claim 1, wherein the first core metal has a first bent portion formed by bending the outer edge of the first core metal toward the second axial end of the toothed pulley, and the anti-rotation portion is formed on the axial end face of the first bent portion and has a shape in which concave and convex portions are repeated as the direction is toward the circumferential direction.

4. The toothed pulley according to claim 2, wherein the second core metal has a fitting recess on the end face of the first axial end of the toothed pulley into which the convex portion of the outer peripheral edge of the first core metal fits.

5. The toothed pulley according to claim 2, wherein the second core metal has a second bent portion obtained by bending the end of the toothed pulley on the axial first end side radially inward.

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