JP2015085805A - Intermediate shat, manufacturing method for intermediate shaft and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a sufficient impact energy absorption amount by allowing substantially the whole region of a reduced-diameter part to plastically deform by twisting, when a torque equal to or larger than a reference torque is input, in an intermediate shaft.SOLUTION: An intermediate shaft 12 is formed by cutting a blank which is a casting whose diameter becomes thinner gradually or continuously from one end in an axial direction toward the other end. The intermediate shaft 12 includes: a connection part 34 for forming a press-fit hole 33 in which a press-fit part 34 of a second shaft (input shaft 13) is press-fitted; a spline shaft part 35 which is fitted to a spline hole 30 of a first shaft (upper shaft 11); and a reduced-diameter part 36 which is a cut part arranged between the connection part 34 and the spline shaft part 35. The reduced-diameter part 36 includes a taper part 38 in which the diameter reduces toward the spline shaft part 35, and it absorbs impact energy by plastically deforming by twisting when an excessive torque acts on.

Description

  The present invention relates to an intermediate shaft, an intermediate shaft manufacturing method, and a steering device.

  In Patent Document 1, an intermediate shaft connected to a steering column shaft via a universal joint includes a strength reducing portion that can be broken when excessively input from the steered wheel side. The said strength reduction part is made into the reduced diameter part of a diameter thinner than the part of the both sides of a strength reduction part. Since only the strength reducing portion is damaged at the time of excessive input, failure of other portions is avoided.

JP 2012-62991 A

For example, a shaft for manufacturing a shaft is formed by pressing a material shaft having a first end and a second end into the mold from the first end side, and an intermediate portion of the manufacturing intermediate. It is conceivable to form the reduced diameter portion by cutting the outer periphery of the substrate by cutting.
In the manufacturing intermediate, a first diameter portion is disposed adjacent to the first end portion side which is a pushing side with respect to a reduced diameter portion formation planned region for forming the reduced diameter portion, and the reduced diameter portion is formed. Assume that the second diameter portion is disposed adjacent to the diameter portion on the opposite side to the first diameter portion. In that case, the diameter of the 1st diameter part near the 1st end part which is a pushing side is smaller than the diameter of a 2nd diameter part. That is, at the time of pressing, since the cross-sectional area change rate of the first diameter portion is larger than the cross-sectional area change rate of the second diameter portion, the hardness of the first diameter portion is higher than the hardness of the second diameter portion. As a result, in the final stage shaft, the hardness of the first region of the reduced diameter portion adjacent to the first diameter portion is higher than the hardness of the second region of the reduced diameter portion adjacent to the second diameter portion.

When impact energy is applied to such a shaft due to an excessive torsional load from the steered wheel side (corresponding to a so-called reverse input), only the second region having a low hardness is torsionally deformed in the reduced diameter portion. For this reason, the impact energy absorption amount is insufficient.
An object of the present invention is to provide an intermediate shaft and an intermediate shaft capable of obtaining a sufficient impact energy absorption amount by plastically deforming substantially the entire area of the reduced diameter portion by twisting when a torque larger than a reference torque is input. A shaft manufacturing method and an electric power steering device are provided.

  The invention of claim 1 is formed by cutting a blank, which is a forged product whose diameter gradually decreases from one end (401) to the other end (402) in the axial direction, and has a spline hole. An intermediate shaft (12) for connecting a first shaft (11) having (30) and a second shaft (13) having a press-fit portion (32) at one end in the axial direction, wherein the press-fit portion is press-fit A coupling portion (34) in which a press-fitting hole (33) is formed; a spline shaft portion (35) having a smaller diameter than the coupling portion and fitted in the spline hole; the coupling portion and the spline shaft portion; A reduced-diameter portion (36) that is a cutting portion disposed between the tapered portions, and the reduced-diameter portion includes a tapered portion (38) that decreases in diameter toward the spline shaft portion, and has a reference torque or more. Torsion when large torque is applied Providing an intermediate shaft that functions as a shock energy absorbing portion that is plastically deformed.

In addition, although the alphanumeric character in a parenthesis represents the corresponding component etc. in embodiment mentioned later, this does not mean that this invention should be limited to those embodiment as a matter of course. The same applies hereinafter.
According to a second aspect of the present invention, the reduced diameter portion includes a first end portion (361) adjacent to the coupling portion and a second end portion (362) adjacent to the spline shaft portion. The outer diameter (D1) of the end portion is smaller than the outer diameter (E1) of the coupling portion, and the outer diameter (D2) of the second end portion is smaller than the outer diameter (E2) of the spline shaft portion. May be.

  In the invention of claim 3, the material axis is pushed into the mold along the axial direction and pressed to form a joint portion formation planned region (41P; 41Q), a reduced diameter portion formation planned region (42P; 42Q) and a spline on the outer periphery. Including a step of forming a blank (40P; 40Q) including a shaft portion formation planned region (43P; 43Q), and the reduced diameter portion formation planned region of the blank has a constant outer diameter (42P1; 42Q2) And a tapered portion (42P2; 42Q1, 42Q3) whose outer diameter becomes narrower toward the region where the spline shaft portion is to be formed, and cut the outer periphery of the region where the reduced diameter portion is to be formed of the blank. A method of manufacturing the intermediate shaft (12P; 12Q) including the step of forming 36Q).

  The invention of claim 4 is an electric power steering apparatus comprising the intermediate shaft according to claim 1 or 2, wherein the upper shaft (11) as the first shaft to which the steering wheel (2) is attached, and the upper shaft The intermediate shaft (12) connected to the intermediate shaft, the input shaft (13) as the second shaft connected to the intermediate shaft, and the deceleration rotated by the torque input from the steering assist electric motor (16) Provided is an electric power steering device (1) comprising an output shaft (14) to which a gear (19) is attached, and a torsion bar (15) connecting the input shaft and the output shaft.

  According to the first aspect of the present invention, the hardness of the spline shaft portion having a smaller diameter than that of the joint portion is higher than the hardness of the joint portion. Also in the reduced diameter portion disposed between the coupling portion and the spline shaft portion, the hardness of the region close to the spline shaft portion is higher than the hardness of the region close to the connection portion. On the other hand, in the taper part provided in the reduced diameter part, the outer diameter decreases toward the spline shaft part side. Thereby, in the reduced diameter portion, the torsional strength in the region close to the coupling portion and the torsional strength in the region close to the spline shaft portion can be made substantially uniform. Therefore, when a torque larger than the reference torque is input, the substantially entire region of the reduced diameter portion is plastically deformed by twisting, and a sufficiently large impact energy absorption amount can be obtained.

According to the invention of claim 2, since the diameter-reduced part including the tapered part is smaller in diameter than the coupling part and the spline shaft part on both sides, the diameter is reduced when a torque larger than the reference torque is input. Only the portion can be reliably torsionally deformed.
According to the invention of claim 3, in the blank, since the hardness and the outer diameter are constant in the straight portion of the reduced diameter portion formation scheduled region, the torsional strength becomes uniform. Since the reduced diameter portion formation planned region including the straight portion having a uniform torsional strength is cut to form the reduced diameter portion, it is possible to ensure a wide range where the torsional strength is uniform even in the reduced diameter portion. it can.

  According to the invention of claim 4, in the electric power steering apparatus, when a torque larger than the reference torque is input, a sufficiently large impact energy absorption amount can be obtained.

1 is a schematic cross-sectional view illustrating a schematic configuration of an electric power steering apparatus including an intermediate shaft according to a first embodiment of the present invention. It is sectional drawing of the principal part of the electric power steering apparatus of FIG. It is a partially broken side view of the intermediate shaft concerning a 1st embodiment. It is a side view of the blank which is an intermediate for manufacture of an intermediate shaft concerning a 1st embodiment. It is sectional drawing of the principal part of the electric power steering apparatus containing the intermediate shaft which concerns on 2nd Embodiment of this invention. (A)-(c) is the schematic which shows the manufacturing process of the intermediate shaft which concerns on 2nd Embodiment sequentially. It is a graph which shows the hardness distribution of the blank (forged product) which is an intermediate body for manufacture of the intermediate shaft according to the second embodiment. It is sectional drawing of the principal part of the electric power steering apparatus containing the intermediate shaft which concerns on 3rd Embodiment of this invention. (A)-(c) is the schematic which shows in order the manufacturing process of the intermediate shaft which concerns on 3rd Embodiment. It is a graph which shows the hardness distribution of the blank (forged product) which is an intermediate body for manufacture of the intermediate shaft according to the third embodiment.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering column shaft 3 having a steering wheel 2 connected to one end thereof, and an intermediate shaft 5 connected to the steering column shaft 3 via a universal joint 4. . The electric power steering device 1 further includes a pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6, and a rack shaft 8.

The electric power steering apparatus 1 includes a steering shaft SS for transmitting the rotation of the steering wheel 2 to steered wheels (not shown). The steering shaft SS includes the above-described steering column shaft 3, intermediate shaft 5, pinion shaft 7, and rack shaft 8.
The pinion shaft 7 includes a pinion 7a at a part of the outer periphery thereof. The rack shaft 8 includes a rack 8 a that meshes with the pinion 7 a of the pinion shaft 7 at a part of the outer periphery thereof. The pinion shaft 7 and the rack shaft 8 constitute a steering mechanism A1 including a rack and pinion mechanism.

  The rack shaft 8 is supported in a housing 10 fixed to the vehicle body 9 through a plurality of bearings (not shown) so as to be linearly reciprocable in the axial direction (corresponding to a direction orthogonal to the paper surface). Each end of the rack shaft 8 protrudes to both sides of the housing 10 and is connected to a corresponding steered wheel via a corresponding tie rod (not shown) and a corresponding knuckle arm (not shown).

When the steering wheel 2 is operated and the steering column shaft 3 is rotated, this rotation is converted into an axial linear motion of the rack shaft 8 by the pinion 7a and the rack 8a. Thereby, the turning of a steered wheel is achieved.
The steering column shaft 3 includes an upper shaft 11 serving as a first shaft having a steering wheel 2 coupled to one end thereof, an intermediate shaft 12 coupled to the upper shaft 11, and an input serving as a second shaft coupled to the intermediate shaft 12. Shaft 13. The steering shaft 3 further includes an output shaft 14 to which a worm wheel 19 as a reduction gear, which will be described later, is connected so as to be integrally rotatable, and a torsion bar 15 that connects the input shaft 13 and the output shaft 14.

  The electric power steering apparatus 1 further includes an electric motor 16 that generates a steering assist force, and a speed reducer 17 that transmits the power generated by the electric motor 16 to the output shaft 14. The reduction gear 17 includes a worm 18 as a drive gear that is rotationally driven by an electric motor, and a worm wheel 19 as a driven gear (reduction gear) that meshes with the worm 18.

The electric power steering apparatus 1 further includes a torque sensor 20 that detects a steering torque based on a relative rotational displacement amount between the input shaft 13 and the output shaft 14 via the torsion bar 15, and an ECU (Electronic Control) as a control unit. Unit: Electronic control unit) 21.
The ECU 21 controls the drive of the electric motor 16 (steering assist control) based on a torque detection result given from the torque sensor 20 or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated via the speed reducer 17 and transmitted to the pinion shaft 7 via the output shaft 14, and further converted into a linear motion of the rack shaft 8 to assist steering.

  The electric power steering apparatus 1 includes a hollow steering column 22 fixed to the vehicle body 9. The steering column shaft 3 is disposed inside the steering column 23 and is rotatably supported by the steering column 22. The steering column 22 includes an upper tube 23, a lower tube 24 fitted to the upper tube 23, and a housing 25 fitted to the lower tube 24.

The upper tube 23 is attached to the vehicle body 9 via a bracket 26. The housing 25 is attached to the vehicle body 9 via a bracket 27. In the housing 25, the speed reducer 17 and the torque sensor 20 are accommodated.
The upper shaft 11 as the first shaft is rotatably supported by a bearing 28 held at the upper end in the axial direction of the upper tube 23. The output shaft 14 is rotatably supported by a bearing 29 held by a housing 25.

  As shown in FIG. 2, the upper shaft 11 as the first shaft is constituted by a hollow member. The upper shaft 11 has a first end 111 and a second end 112 that face each other in the axial direction X1. The first end portion 111 is exposed to the outside of the steering column 22 and connects the steering wheel 2 so as to be integrally rotatable. The upper shaft 11 forms a spline hole 30 that opens to the second end portion 112. Specifically, a female spline 31 extending in the axial direction X1 with a predetermined length from the second end 112 is formed on the inner periphery 11a of the upper shaft 11. A plurality of female splines 31 are arranged at equal intervals in the circumferential direction of the inner periphery 11a.

  The input shaft 13 as the second shaft includes a press-fit portion 32 at one end in the axial direction X1. The intermediate shaft 12 includes a coupling part 34 having a press-fitting hole 33 into which the press-fitting part 32 is press-fitted, a spline shaft part 35 fitted in the spline hole 30 of the upper shaft 11 (first shaft), and a coupling part 34. And a reduced diameter portion 36 that is a cutting portion disposed between the spline shaft portion 35 and the spline shaft portion 35. The reduced diameter portion 36 functions as an impact energy absorbing portion that is plastically deformed by torsion when a torque larger than the reference torque is applied.

  The intermediate shaft 12 includes a first end 121 and a second end 122 that face each other in the axial direction. The press-fitting hole 33 of the coupling portion 34 opens at the end surface of the first end portion 121 of the intermediate shaft 12 and extends in the axial direction X1. The spline shaft portion 35 has a smaller diameter than the coupling portion 34. The spline shaft portion 35 includes a plurality of male splines 37 provided on a part of the outer periphery of the intermediate shaft 12 in the axial direction X1. The plurality of male splines 37 extend in the axial direction X1 and are arranged at equal intervals in the circumferential direction.

  As shown in FIG. 3, the reduced diameter portion 36 has a smaller diameter than the coupling portion 34 and the spline shaft portion 35. The reduced diameter portion 36 includes a tapered portion 38 that decreases in diameter toward the spline shaft portion 35 in at least a part of the region in the axial direction X1. A tapered portion 38 may be formed in the entire region of the reduced diameter portion 36 in the axial direction X1. The reduced diameter portion 36 includes a first end portion 361 adjacent to the coupling portion 34 and a second end portion 362 adjacent to the spline shaft portion 35. The outer diameter D2 of the second end 362 is smaller than the outer diameter D1 of the first end 361 (D1> D2).

The outer diameter D1 of the first end 361 is smaller than the outer diameter E1 of the coupling portion 34 (D1> E1). The outer diameter D2 of the second end 362 is smaller than the outer diameter E2 of the spline shaft portion 35 (D2> E2).
The intermediate shaft 12 is a forged product whose outer diameter is gradually or continuously reduced from the first end 401 (one end) to the second end 402 (the other end) in the axial direction X1 as shown in FIG. The blank 40 (corresponding to an intermediate for manufacturing the intermediate shaft 12) is cut and formed.

  The blank 40 forms a joint portion formation scheduled region 41 for forming the joint portion 34 having the press-fit hole 33, a reduced diameter portion formation scheduled region 42 for forming the reduced diameter portion 36, and a spline shaft portion 35. And a spline shaft portion formation scheduled region 43 for this purpose. The reduced diameter portion formation planned region 42 is disposed between the joint portion formation planned region 41 and the spline shaft portion formation planned region 43. In the joint portion formation scheduled region 41, a lower hole 44 for forming the press-fitting hole 33 is provided. The press-fitting hole 33 is formed by finishing the lower hole 44 by cutting.

  The blank 40 is a forged product formed by pressing and pressing a material shaft (round bar) into the mold along the axial direction. In the blank 40, the cross-sectional area reduction rate increases as the outer diameter decreases. For this reason, the thinner the outer diameter, the greater the work hardening and thus the higher the hardness. That is, in the blank 40 that is thinned stepwise or continuously as it goes from the first end portion 401 toward the second end portion 402, it is stepwise or continuous as it goes from the first end portion 401 toward the second end portion 402. The hardness increases. As a result, in the intermediate shaft 12 formed by cutting the blank 40, the relationship among the hardnesses of the coupling portion 11, the reduced diameter portion 12, and the spline shaft portion 13 is as follows. That is, the hardness of the reduced diameter portion 36 is generally lower than the hardness of the coupling portion 34 and is generally higher than the hardness of the spline shaft portion 35.

According to the first embodiment, the hardness of the spline shaft portion 35 having a smaller diameter than the coupling portion 34 is higher than the hardness of the coupling portion 34. Also in the reduced diameter portion 36 disposed between the coupling portion 34 and the spline shaft portion 35, the hardness of the region adjacent to the spline shaft portion 35 is higher than the hardness of the region adjacent to the coupling portion 34.
On the other hand, in the taper part 38 provided in the reduced diameter part 36, an outer diameter becomes small toward the spline shaft part 35 side. Thereby, in the reduced diameter portion 36, the torsional strength in the region close to the coupling portion 34 and the torsional strength in the region close to the spline shaft portion 35 can be made substantially uniform. Accordingly, when a torque larger than the reference torque is input, the substantially entire region of the reduced diameter portion 36 is plastically deformed by twisting to obtain a sufficiently large impact energy absorption amount in the intermediate shaft 12. it can. In addition, it is possible to realize the electric power steering apparatus 1 that can obtain a sufficiently large impact energy absorption amount during reverse input.

As shown in FIG. 3, the entire reduced diameter portion 36 may be constituted by a tapered portion 38. Although not shown, a part of the reduced diameter portion 36 may be configured by the tapered portion 38 and the remaining portion may be configured by the straight portion.
Since the reduced diameter portion 36 including the tapered portion 38 is smaller in diameter than the coupling portion 34 and the spline shaft portion 35 on both sides of the reduced diameter portion 36, when a torque larger than the reference torque is input, the reduced diameter Only the part 36 can be reliably twisted and deformed.
(Second Embodiment)
FIG. 5 is a cross-sectional view of a main part of an electric power steering apparatus 1P including an intermediate shaft 12P according to the second embodiment of the present invention. 6A to 6C sequentially show the manufacturing process of the intermediate shaft 12P.

  As shown in FIGS. 5 and 6C, the intermediate shaft 12P includes a coupling portion 34P having a press-fitting hole 33P, a spline shaft portion 35P having a smaller diameter than the coupling portion 34P, and the coupling portion 34P and the spline shaft portion. And a reduced diameter portion 36P, which is a cutting portion disposed between 35P. The reduced diameter portion 36P is configured by a straight portion 39P having a constant outer diameter. The reduced diameter portion 36P functions as an impact energy absorbing portion that is plastically deformed by torsion when a torque larger than the reference torque is applied.

In the components of the embodiment of FIGS. 5 and 6, the same components as those of the embodiments of FIGS. 2, 3 and 4 are the same as the reference numerals of the components of the embodiments of FIGS. Reference numerals are attached.
First, as shown in FIG. 6A, a round bar 50 as a material shaft is pressed into the mold 51P along the axial direction X1 and pressed. Thereby, as shown in FIG.6 (b), the blank 40P which is a press forged product is obtained. Next, the blank 40P is cut to obtain an intermediate shaft 12P as shown in FIG. The press molding for obtaining the blank 40P shown in FIG. 6 (a) may be a single press molding using a single mold, or the shape is narrowed down step by step using a plurality of molds. There may be several press moldings.

As shown in FIG. 6B, the blank 40P includes a joint portion formation planned region 41P for forming the joint portion 34P, a reduced diameter portion formation planned region 42P for forming the reduced diameter portion 36P, and a spline shaft. And a spline shaft portion formation scheduled region 43P for forming the portion 35P. The outer diameter of the reduced diameter portion formation scheduled region 41P is made equal to the outer diameter of the round bar 50 that is the material axis.
The reduced diameter portion formation planned region 42P is disposed between the joint portion formation planned region 41P and the spline shaft portion formation planned region 43P. The reduced diameter portion formation planned region 42P includes a straight portion 42P1 having an outer diameter equal to the outer diameter D1P of the coupling portion formation planned region 41P, and a tapered portion 42P2 reduced in diameter toward the spline shaft portion formation planned region 43P. .

As shown in FIGS. 6B and 6C, the reduced diameter portion 36P of the intermediate shaft 12P includes a first portion 36P1 formed by cutting the straight portion 42P1 of the reduced diameter portion formation planned region 42P of the blank 40P. The second portion 36P2 is formed by cutting the tapered portion 42P2 of the reduced diameter portion formation scheduled region 42P.
The blank 40P is a forged product formed by pressing the round bar 50 (material axis) into the die 51P along the axial direction and pressing it. In the blank 40P, the cross-sectional area reduction rate increases as the outer diameter decreases. For this reason, the thinner the outer diameter, the greater the work hardening and thus the higher the hardness. That is, in the blank 40P that is thinned stepwise or continuously as it goes from the first end 401P to the second end 402P, it is stepwise or continuous as it goes from the first end 401P to the second end 402P. The hardness increases.

  That is, as shown in FIG. 7, the hardness of the straight portion 42P1 of the reduced diameter portion formation scheduled region 42P is substantially constant. The hardness of the taper portion 42P2 is generally larger than the hardness of the straight portion 42P1. The hardness of the straight portion 42P1 is substantially equal to the minimum hardness of the tapered portion 42P2. Although not shown in FIG. 7, the hardness of the joint portion formation planned region 41P is substantially equal to the hardness of the straight portion 42P1 of the reduced diameter portion formation planned region 42P.

According to the second embodiment, in the blank 40P that is a forged product, in the straight portion 42P1 of the reduced diameter portion formation scheduled region 42P, the outer diameter is constant and the hardness is substantially constant, so the torsional strength is uniform. . The reduced diameter portion formation planned region 42P including the straight portion 42P1 having a uniform torsional strength is cut to form at least a part of the reduced diameter portion 36P of the intermediate shaft 12P, and thus the reduced diameter portion constituted by the straight portion 39P. Even in 36P, a wide range where the torsional strength is uniform can be secured.
(Third embodiment)
FIG. 8 is a cross-sectional view of a main part of an electric power steering apparatus 1Q including an intermediate shaft 12Q according to the third embodiment of the present invention. 9A to 9C sequentially show the manufacturing process of the intermediate shaft 12Q.

  As shown in FIGS. 8 and 9C, the intermediate shaft 12Q includes a coupling portion 34Q having a press-fitting hole 33Q, a spline shaft portion 35Q having a smaller diameter than the coupling portion 34Q, and the coupling portion 34Q and the spline shaft portion. And a reduced diameter portion 36Q, which is a cutting portion disposed between 35Q. The reduced diameter portion 36Q is configured by a straight portion 39Q having a constant outer diameter. The reduced diameter portion 36Q functions as an impact energy absorbing portion that is plastically deformed by torsion when a torque larger than the reference torque is applied.

In the components of the embodiment of FIGS. 8 and 9, the same components as those of the embodiments of FIGS. 2, 3 and 4 are the same as the reference numerals of the components of the embodiments of FIGS. Reference numerals are attached.
First, as shown in FIG. 9A, a round bar 50 as a material axis is pressed into the die 51Q along the axial direction X1 and pressed. Thereby, as shown in FIG.9 (b), the blank 40Q which is a press forged product is obtained. Next, the blank 40Q is cut to obtain an intermediate shaft 12Q as shown in FIG. The press molding for obtaining the blank 40Q shown in FIG. 9A may be a single press molding using a single mold, or the shape is narrowed down step by step using a plurality of molds. Any number of press moldings may be used.

As shown in FIG. 9B, the blank 40Q includes a joint portion formation scheduled area 41Q for forming the joint portion 34Q, a reduced diameter portion formation scheduled area 42Q for forming the reduced diameter portion 36Q, and a spline shaft. And a spline shaft portion formation scheduled region 43Q for forming the portion 35Q.
The reduced diameter portion formation planned region 42Q is disposed between the joint portion formation planned region 41Q and the spline shaft portion formation planned region 43Q. The reduced diameter portion formation planned region 42Q is adjacent to the coupling portion formation planned region 41Q and is adjacent to the first taper portion 42Q1 that is reduced in diameter toward the spline shaft portion formation region 43Q and the first taper portion 42Q1 is adjacent to the small diameter end. And a straight portion 42Q2 having an outer diameter equal to the minimum diameter of the tapered portion 42Q1. The reduced diameter portion formation planned region 42Q further includes a second tapered portion 42Q3 adjacent to the straight portion 42Q2 and having a diameter reduced toward the spline shaft portion formation planned region 43Q. The straight portion 42Q2 is disposed between the first tapered portion 42Q1 and the second tapered portion 42Q3.

  As shown in FIG. 9B, the reduced diameter portion 36Q (corresponding to the straight portion 39Q) of the intermediate shaft 12Q is formed by cutting the first tapered portion 42Q1 of the reduced diameter portion formation planned region 42Q of the blank 40Q. The first portion 36Q1, the second portion 36Q2 formed by cutting the straight portion 42Q2 of the reduced diameter portion formation planned region 42Q, and the second tapered portion 42Q3 of the reduced diameter portion formation planned region 42Q were formed. A third portion 36Q3.

  The blank 40Q is a forged product formed by pressing a round bar 50 as a material shaft into the die 51Q along the axial direction and pressing it. In the blank 40Q, the cross-sectional area reduction rate increases as the outer diameter decreases. For this reason, the thinner the outer diameter, the greater the work hardening and thus the higher the hardness. That is, in the blank 40Q that is thinned stepwise or continuously as it goes from the first end portion 401Q toward the second end portion 402Q, it is stepped or continuous as it goes from the first end portion 401Q toward the second end portion 402Q. The hardness increases.

  Specifically, as shown in FIG. 10, the hardness distribution of the reduced diameter portion formation scheduled region 42 </ b> Q is as follows. That is, the hardness of the straight portion 42Q2 is substantially constant. The hardness of the straight portion 42Q2 is substantially equal to the first taper portion 42Q1 maximum hardness. The hardness of the second tapered portion 42Q3 is generally higher than the hardness of the straight portion 42Q2. The hardness of the straight portion 42Q2 is approximately equal to the minimum hardness of the second tapered portion 42Q3.

Although not shown in FIG. 10, the hardness of the first tapered portion 42Q1 of the reduced diameter portion formation planned region 42Q is generally higher than the hardness of the joint portion formation planned region 41Q. The hardness of the joint portion formation planned region 41Q is substantially equal to the minimum hardness of the first tapered portion 42Q1 of the reduced diameter portion formation planned region 42Q.
According to the third embodiment, in the blank 40Q which is a forged product, the hardness and the outer diameter are constant in the straight portion 42Q2 of the reduced diameter portion formation scheduled region 42Q, so the torsional strength is uniform. The reduced diameter portion formation scheduled region 42Q including the straight portion 42Q2 having a uniform torsional strength is cut to form at least a part of the reduced diameter portion 36Q of the intermediate shaft 12Q, and thus the reduced diameter portion constituted by the straight portion 39Q. Even in 36Q, a wide range where the torsional strength is uniform can be secured.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims of the present invention.

  DESCRIPTION OF SYMBOLS 1; 1P; 1Q ... Electric power steering device, 2 ... Steering wheel, 3 ... Steering column shaft, 5 ... Intermediate shaft, 7 ... Pinion shaft, 8 ... Rack shaft, 11 ... Upper shaft (1st shaft), 12; 12; 12Q ... Intermediate shaft, 13 ... Input shaft (second shaft), 14 ... Output shaft, 15 ... Torsion bar, 16 ... Electric motor, 17 ... Reduction gear, 19 ... Worm wheel (reduction gear), 30 ... Spline hole 31 ... Female spline, 32 ... Press fit part, 33; 33P; 33Q ... Press fit hole, 34; 34P; 34Q ... Coupling part, 35; 35P; 35Q ... Spline shaft part, 36; 36P; 36Q ... Reduced diameter part, 361 ... 1st end part, 362 ... 2nd end part, 36P1 ... 1st part, 36P2 ... 2nd Minute, 36Q1 ... first part, 36Q2 ... second part, 36Q3 ... third part, 37 ... male spline, 38 ... tapered part, 39P; 39Q ... straight part, 40; 40P; 40Q ... blank, 401; 401P; 401Q ... 1st end part (one end), 402; 401Q; 402Q ... 2nd end part (other end), 41; 41P; 41Q ... Coupling part formation plan area, 42; 42P; 42Q ... Shrinkage part formation plan area, 42P1 ... Straight part, 42P2 ... Taper part, 42Q1 ... First taper part, 42Q2 ... Straight part, 42Q3 ... Second taper part, 43; 43P; 43Q ... Spline shaft part formation planned area

Claims (4)

It is formed by cutting a blank, which is a forged product whose diameter gradually decreases from one end in the axial direction toward the other end, and a first shaft having a spline hole and a press-fit portion at one end in the axial direction An intermediate shaft connecting between the second shaft and
A coupling part having a press-fitting hole into which the press-fitting part is press-fitted,
A spline shaft portion smaller in diameter than the coupling portion and fitted in the spline hole;
A reduced diameter portion which is a cutting portion disposed between the coupling portion and the spline shaft portion,
The reduced diameter portion includes a tapered portion that decreases in diameter toward the spline shaft portion, and functions as an impact energy absorbing portion that is plastically deformed by torsion when a torque larger than a reference torque is applied. . In Claim 1, the reduced diameter portion includes a first end adjacent to the coupling portion, and a second end adjacent to the spline shaft portion,
An outer diameter of the first end portion is smaller than an outer diameter of the coupling portion;
An intermediate shaft in which an outer diameter of the second end portion is smaller than an outer diameter of the spline shaft portion. Including a step of forming a blank including a joint portion formation planned region, a reduced diameter portion formation planned region, and a spline shaft portion formation planned region on the outer periphery by pressing the material shaft into the mold along the axial direction and pressing the material shaft; The blank diameter-reduced portion formation planned region includes a straight portion having a constant outer diameter and a tapered portion whose outer diameter becomes narrower toward the spline shaft portion formation planned region side,
The manufacturing method of the intermediate shaft including the process of cutting the outer periphery of the said reduced diameter part formation plan area | region of the said blank, and forming a reduced diameter part.   An electric power steering apparatus comprising the intermediate shaft according to claim 1, wherein the upper shaft as the first shaft to which a steering wheel is attached, the intermediate shaft connected to the upper shaft, and the intermediate shaft An input shaft as the second shaft to be connected, an output shaft to which a reduction gear rotated by torque input from a steering assist electric motor is attached, and a torsion bar connecting the input shaft and the output shaft And an electric power steering device.

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