spline shaft

Abstract

This invention provides a lightweight spline shaft that does not require any design changes to the existing driven gear to which it is fitted. [Solution] The spline shaft 1 has a flat portion 11 on the side surface facing the circumferential direction of the teeth. The space (groove) 13 between adjacent teeth in the circumferential direction on the spline shaft is a concave shape obtained by bisecting an ellipse with its major axis in a cross section perpendicular to the axis. The ratio Er of the major axis to the minor axis of the ellipse is 1.5 ≤ Er ≤ 4.

Description

Technical Field

[0001] The present invention relates to a spline shaft provided with concavities and convexities on its outer peripheral surface and used, for example, in a reclining seat backrest angle adjustment device for a vehicle.

Background Art

[0002] Many seats in railway vehicles, airplanes, automobiles, etc. are reclining seats whose backrest inclination angle can be adjusted. The backrest angle adjustment device for such a vehicle reclining seat is formed, for example, by inserting a connecting shaft through spline engagement (connection, fitting) into equally spaced grooves along the circumferential direction of the inner peripheral surface of a center shaft arranged inside each of the left and right seat reclining units provided on the left and right of the seat cushion. The connecting shaft has spline teeth formed at equal intervals in the circumferential direction along the axial direction and is rod-shaped (Patent Document 1).

[0003] In recent years, global warming has become prominent, and as one of the measures to reduce the emissions of greenhouse gases, the weight reduction of vehicles such as railway vehicles and automobiles has been promoted. The weight reduction of a vehicle is equivalent to the weight reduction of its components, and the reclining seat is no exception. For the purpose of weight reduction of the reclining seat and the accompanying cost reduction, hollowing of the connecting rod (spline shaft) has been proposed because it is relatively easy to achieve (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in the automotive industry, for example, it is said that there are tens of thousands of parts used in a car, and there are many suppliers for each of those parts. In the case of a reclining seat backrest angle adjustment device, the spline shaft with a male spline formed on it and the driven gear (with a female spline shape) described in Patent Document 2 may be supplied by different companies. In such a case, if the supplier of the spline shaft changes the shape of the part to reduce costs and weight, ignoring the fit with the driven gear supplied by a different company, it will cause problems in the manufacturing of the reclining seat backrest angle adjustment device.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a lightweight spline shaft without requiring a change in the shape of the driven gear fitted to the spline shaft. [Means for solving the problem]

[0007] The spline shaft according to the present invention has a flat portion on the side surface of the tooth facing the circumferential direction. The space (groove) between adjacent teeth in the circumferential direction of the spline shaft is a concave shape obtained by bisecting an ellipse with its major axis in a cross section perpendicular to the axis. The ratio Er of the major axis to the minor axis of the ellipse is 1.5 ≤ Er ≤ 4.

[0008] In a spline shaft, both sides of the tooth tip in the circumferential direction are arc-shaped in a cross-section perpendicular to the axis, and the radius of curvature R is 0.05 × W ≤ R ≤ 0.17 × W with respect to the tooth's reference width W. Here, "reference width W" refers to the distance between the tooth tip ends in the planar portion of the circumferential side surface of the tooth.

[0009] A spline shaft has 7 teeth.

[0010] The spline shaft is preferably hollow. [Effects of the Invention]

[0011] According to the present invention, a lightweight spline shaft can be provided without requiring any design changes to the existing driven gear to which it is fitted. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a cross-sectional view of a lightweight spline shaft. [Figure 2] Figure 2 is a cross-sectional view of the spline shaft before weight reduction. [Figure 3] Figure 3 is a cross-sectional view showing an example of a selection of weight reduction methods. [Figure 4] Figure 4 is a partial cross-sectional view of a non-rectangular spline shaft. [Figure 5] Figure 5 shows the cross-sectional shape and dimensions of a spline shaft as determined by computer simulation. [Figure 6] Figure 6 shows the stress distribution of the spline shaft obtained through simulation. [Modes for carrying out the invention]

[0013] Figure 1 is a cross-sectional view of the spline shaft 1 after weight reduction, Figure 2 is a cross-sectional view of the spline shaft 6 (comparative example) before weight reduction, and Figure 3 is a partial cross-sectional view showing an example of the selection of weight reduction means.

[0014] Spline shafts 1 and 6 are shafts of spline couplings called "square splines," which have teeth with parallel plane contours in a cross section perpendicular to the axis (JIS B 0006-1993). The radial length of the parallel planes 11,11 on the teeth of spline shafts 1 and 6 with respect to the axis is called the "plane length L," and the distance between the parallel planes is called the "tooth width W1." In addition, the two planes 11,11 that the teeth have in the circumferential direction, which transmit torque to the driven gear 5 that they mesh with, are each called the "(tooth) side surface," even if they are not parallel.

[0015] Spline shafts 1 and 6 both have 7 spline grooves (= teeth) 13 and 61.

[0016] The weight reduction of the spline shaft 6 is carried out within a range that does not reduce the torque transmission capacity with the meshing driven gear 5. One of the means is to reduce the radius of curvature of the arc-shaped curved surface 12 connecting the tooth tip and the side surfaces (parallel planes) 11, 11, and shorten the distance between the tooth tip and the axis while maintaining the planar length L. As a result, the weight of each of the seven teeth is reduced.

[0017] Another means of weight reduction is to change the groove 61 between adjacent teeth, which is convex outward in a cross-section perpendicular to the axis of the spline shaft 6, into a concave shape obtained by bisecting an ellipse along its major axis. As a result, the wall thickness between adjacent teeth is reduced, and the weight of the entire spline shaft 1 is reduced.

[0018] When comparing the spline shaft 1 and the spline shaft 6 in cross-sectional views (FIG. 1, FIG. 2), the cross-sectional area of the spline shaft 1 is clearly smaller than that of the spline shaft 6.

[0019] FIG. 3 is a diagram showing the differences in the shapes of the tooth tips and the grooves 13 of the cross-section of the spline shaft 1 when the radius of curvature R of the arc-shaped curved surface 12 connecting the parallel planes 11, 11 with the tooth tips in the spline shaft 1 and the ratio Er of the major diameter to the minor diameter of the elliptical contour line in the cross-section of the groove 13 are changed. It can be seen from FIG. 3 that the smaller the radius of curvature R of the arc-shaped curved surface 12 and the smaller the ratio Er of the major diameter to the minor diameter of the elliptical contour line in the groove 13, the more the weight is reduced.

[0020] The radius of curvature R of the arc-shaped curved surface 12 at both circumferential ends of the tooth tip is preferably 0.05×W1≦R≦0.17×W1 based on the tooth width W1 of the spline shaft 1. If R is less than 0.05×W1, there is a risk of damaging the side surface of the groove of the driven gear 5, and if R exceeds 0.17×W1, the effect of weight reduction decreases. Also, by setting the radius of curvature R of the arc-shaped curved surface 12 to 0.05×W1≦R≦0.17×W1, it is advantageous in terms of metal flow for the formation of the tooth tip shape during the drawing process.

[0021] The ratio Er of the major axis to the minor axis of the elliptical contour line in the cross-section of the groove 13 is preferably 1.5 ≤ Er ≤ 4, and more preferably 2 ≤ Er ≤ 3. If the ratio Er is less than 1.5, the wall thickness in the radial direction between adjacent teeth (grooves 13) decreases significantly, raising concerns about reduced strength. If the ratio Er exceeds 4, the effect of weight reduction decreases, and the relief of stress concentration also decreases.

[0022] In addition, the spline shaft 1 shown in Figure 1 has a radius of curvature R of 0.1 × W1 at both circumferential ends of the tooth tip, and the ratio Er of the minor axis to the major axis of the cross-sectional contour of the groove 13 is 2.

[0023] Figure 4 is a partial cross-sectional view of a spline shaft 1B where the planes (parts) 11B, 11B on the side surface of the tooth are not parallel.

[0024] Similar to spline shaft 1 in Figure 3, spline shaft 1B also has a continuous arc-shaped curved surface 12 with a specific radius of curvature R between the tooth tip and the planes 11B, 11B. The distance W2 between the radially outer ends of the planes 11B, 11B on the two sides is used as a reference for the spline shaft The radius of curvature R of the arc-shaped surface 12 of ft 1B is 0.1 × W2.

[0025] Furthermore, the tooth width W1 of the spline shaft 1 shown in Figure 1 is the same regardless of the radial distance between its planes 11, 11. Therefore, for the spline shaft 1 as well, we can use the distance W1 between the radially outer ends of the two planes 11, 11, and say that the radius of curvature of its arc-shaped curved surface 12 is 0.1 × W1.

[0026] In the spline shaft 1B, the radius of curvature R of the arc-shaped curved surface 12 is preferably 0.05 × W2 ≤ R ≤ 0.17 × W2.

[0027] The tooth width W1 of spline shaft 1 and the distance W2 between the radially outer ends of the flat surfaces of spline shaft 1B are referred to as the "reference tooth width W".

[0028] In the spline shaft 1B, the space between adjacent teeth (grooves 13) in a cross section perpendicular to the axis is formed in a concave shape when an ellipse is bisected by its major axis. The ratio Er of the major axis to the minor axis of the elliptical contour is preferably 1.5 ≤ Er ≤ 4, and more preferably 2 ≤ Er ≤ 3.

[0029] Next, we will explain the results of computer simulations regarding the stress distribution of the lightweight spline shaft 1C and spline shaft 6.

[0030] Figure 5 shows the cross-sectional shape and dimensions of spline shafts 1C and 6 obtained by computer simulation, and Figure 6 shows the stress distribution diagram of spline shafts 1C and 6 obtained by simulation. Figures 5 and 6(a) show spline shaft 1C, which is an example, and (b) shows spline shaft 6, which is a comparative example.

[0031] The spline shaft 1C and the spline shaft 6 have the same radius of curvature R of the arc-shaped curved surface 12 at the tip of each tooth.

[0032] Computer simulations of stress distribution and other parameters were performed using ANSYS 2023R1 (ANSYS is a registered trademark), sold by ANSYS Japan Co., Ltd. The simulation conditions assumed that the material of each spline shaft was structural steel with a Young's modulus of 200 GPa and a Poisson's ratio of 0.3. The length of spline shaft 1 was 170 mm, with one end 10 mm designated as a fixing portion 21 and the other end 10 mm as a portion 22 to which torsional torque was applied (Figure 5(c)). The assumed torsional torque (torsional moment) applied to the side surface 11 of the teeth was 25 N·m.

[0033] The simulation was performed using the finite element method, with a mesh size of 0.5 mm in each cross-section of the spline shafts 1C and 6, and a smaller mesh size, for example 0.1 mm, near the boundary between the teeth and grooves 13 where the shape changes significantly.

[0034] Referring to Figure 6, in spline shaft 6(b), a large localized stress (684 MPa) is generated due to torsion in the portion where the side surface 11 and the groove 61 are continuous, whereas in spline shaft 1(a), the stress is distributed throughout the entire groove 13.

[0035] From Figure 6, it can be seen that by making the cross-section of the groove 13 a semi-elliptical concave shape divided into two equal parts by its major axis, the stress is distributed throughout the groove, and the possibility of fracture due to stress concentration is reduced.

[0036] In the above-described embodiment, the spline shafts 1, 1B, and 1C can be solid instead of hollow. Even with solid spline shafts, the degree of stress concentration can be reduced and weight reduced by making the cross-sectional shape of the groove semi-elliptical, and further weight reduction can be achieved by making both circumferential ends of the tooth tip curved surfaces with a predetermined radius of curvature.

[0037] Furthermore, the individual components, overall structure, shape, dimensions, number, and material of spline shafts 1, 1B, 1C, and spline shafts 1, 1B, 1C, can be appropriately modified in accordance with the spirit of the present invention. [Industrial applicability]

[0038] The present invention can be used, for example, in a spline shaft used in a backrest angle adjustment device for a reclining seat in a vehicle. [Explanation of Symbols]

[0039] 1,1B,1C Spline Shaft 11,11B Tooth plane (part) 12. Arc-shaped curved surface (arc-shaped curved surfaces on both sides in the circumferential direction of the tooth tip) 13 Groove Er: Ratio of major axis to minor axis R: Radius of curvature of the arc-shaped surface connecting the tooth tip and the parallel plane. W1 Square spline tooth width (reference tooth width W) W2: The distance between the radially outer ends of the flat tooth surfaces (reference tooth width W)

Claims

1. It has a flat surface on the side facing the circumferential direction of the tooth, The space (groove) between adjacent teeth is a concave shape obtained by bisecting an ellipse with its major axis in a cross-section perpendicular to the axis. The ratio Er of the major axis to the minor axis of the ellipse is 1.5 ≤ Er ≤ 4. A spline shaft characterized by the following features.

2. Both sides of the tip of the tooth in the circumferential direction are arc-shaped in a cross-section perpendicular to the axis, The radius of curvature R is 0.05 × W ≤ R ≤ 0.17 × W with respect to the reference width W of the tooth. The spline shaft according to claim 1.

3. The number of teeth is 7. The spline shaft according to claim 1 or claim 2.

4. It is hollow. The spline shaft according to claim 3.

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