JP2014122652A - Suspension spring device and suspension coil spring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a suspension coil spring capable of suppressing breakage caused by corrosion generated in an end coil portion.SOLUTION: A compressive residual stress part 50 having a compressive residual stress from a surface of a wire 40 to a first depth is formed between end coil parts 12a and 12b of a coil spring 12. The end coil part 12a includes a first part 12a, a second part 12a, and a third part 12a. The first part 12aalways contacts a spring seat irrespective of load applied to the coil spring 12. The second part 12acontacts the spring seat if the load applied to the coil spring 12 is heavy, and separates from the spring seat if the load is light. The third part 12aalways separates from the spring seat irrespective of a magnitude of the load. A deep residual stress part 51 due to ultrasonic shot-peening is formed in a region of this end coil part 12a including the second part 12a. The deep residual stress part 51 has a compressive residual stress from the surface of the wire 40 to a second depth larger than the first depth.

Description

  The present invention relates to a suspension spring device used in a suspension mechanism of a vehicle such as an automobile, and a suspension coil spring.

  A suspension spring device used in a suspension mechanism of a vehicle such as an automobile includes a suspension coil spring (compression coil spring) and a lower side disposed below the coil spring, as disclosed in, for example, Patent Document 1. And an upper spring seat disposed on the upper side of the coil spring. The coil spring expands and contracts according to the magnitude of the load.

  One of the causes of breakage of the suspension coil spring is that the coating of the coil spring is peeled off by the stepping stone and rust is generated, and this rust grows to form a corrosion pit, and the coil spring breaks starting from the corrosion pit. It has been known. Therefore, as disclosed in Patent Document 2, it has been proposed to form a two-layer coating film on the surface of the suspension coil spring. The two-layer coating film is composed of an epoxy resin-based undercoat layer and an epoxy polyester resin-based topcoat layer formed thereon. Further, as described in Patent Document 3, it has been proposed to perform the first shot peening on the entire coil spring with a large projection energy and then perform the second shot peening with a small projection energy.

  The end winding portion of the suspension coil spring includes a first portion that always contacts the spring seat regardless of the magnitude of the load, a second portion that contacts or separates from the spring seat depending on the magnitude of the load, And a third portion that is always away from the spring seat regardless of the size. For this reason, foreign substances such as sand may be sandwiched between the second portion and the spring seat. The surface of the coil spring has a rust-proof coating, but if the coil spring expands or contracts while a hard foreign object such as sand is sandwiched between the end winding part and the spring seat, the coating film peels off and rust is generated. Or, the surface of the coil spring may be damaged by the foreign matter pinched. When this scratch is rusted and the rust becomes large, the coil spring breaks.

JP 2000-103216 A JP 2005-171297 A JP 2011-000663 A

  When a part of the end winding part comes into contact with or separates from the spring seat as in the coil spring of Patent Document 1, foreign matters such as sand are likely to enter between the lower end winding part and the spring seat. . If this foreign object is sandwiched between the end winding part and the spring seat, the coating film is peeled off and rust is generated, which causes the coil spring to break.

  As in Patent Document 2, a coil spring having a two-layer coating film composed of an undercoat layer and a topcoat layer is effective for stepping stones, but enters between the end winding portion and the spring seat. Less effective against corrosion and scratches caused by sand. Moreover, the coating film having a two-layer structure has a problem that the cost required for coating is high compared to a coil spring having a general coating film. In Patent Document 3, both the first shot peening and the second shot peening are performed on the entire coil spring, and in the first shot peening, the shot is projected on the entire coil spring with a large projection energy, so that energy consumption is reduced. large. In addition, a shot peening apparatus that can withstand a large amount of projection energy is required, and the shot peening apparatus is consumed greatly.

  Accordingly, an object of the present invention is to provide a suspension spring device and a suspension coil spring that can suppress the breakage of the coil spring due to corrosion generated in the end winding portion.

  The suspension spring device according to the present invention includes a lower spring seat, an upper spring seat, and a strand formed in a spiral shape, and between the lower spring seat and the upper spring seat. And a coil spring arranged in a compressed state. The coil spring has a lower end winding portion less than the first turn from the lower end of the strand, and an upper end winding portion less than the first turn from the upper end of the strand, and at least the lower end winding portion. The end winding portion always contacts or separates from the first spring seat in contact with the lower spring seat regardless of the load applied to the coil spring, and the lower spring seat in accordance with the load applied to the coil spring. It has a second part and a third part that is always away from the spring seat regardless of the magnitude of the load. And between the lower end winding part and the upper end winding part, there is a compressive residual stress part to which a compressive residual stress is applied from the surface of the strand to a first depth, and the lower end winding part In the region including the second portion of the end winding portion, a deep layer residual stress portion to which compressive residual stress is applied from the surface of the strand to a second depth deeper than the first depth is provided.

  In one embodiment, the maximum value of the absolute value of the compressive residual stress of the deep residual stress part is larger than the maximum value of the absolute value of the compressive residual stress of the compressive residual stress part. Further, it is preferable that a boundary between the deep residual stress portion and the compressive residual stress portion has a stress transition portion where the compressive residual stress gradually decreases. In addition, a first shot peening dent is formed on the surface of the compressive residual stress portion, a second shot peening dent is formed on the surface of the deep residual stress portion, and the size of the second shot peening dent. Is larger than the size of the first shot peening dent. The deep residual stress portion may be formed on both the lower end winding portion and the upper end winding portion.

  In one embodiment, the lower spring seat has a bottom surface and an outer wall that restrain the lower surface and the outer peripheral surface of the lower end winding portion, respectively, and the lower surface and the outer periphery of the end winding portion. The deep residual stress portion is formed in a range including the surface. In another embodiment, the lower spring seat has a bottom surface and an inner wall that constrain the lower surface and the inner peripheral surface of the lower end winding portion, and the lower surface of the end winding portion and the The deep residual stress portion may be formed in a range including the inner peripheral surface.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a coil spring breaks starting from the corrosion produced by hard foreign materials, such as the sand pinched | interposed between the end winding part of the coil spring for suspension, and a spring seat, and durability of a coil spring Improves. In this coil spring, a deep residual stress portion may be formed, for example, by ultrasonic shot peening in a region including at least the second portion of the end winding portion that is in contact with or away from the spring seat.

The perspective view which shows typically the front part of the vehicle provided with the spring apparatus for suspension. The longitudinal cross-sectional view of the suspension mechanism provided with the spring apparatus for suspension shown by FIG. The perspective view which shows an example of a coil spring. The bottom view which shows typically the end winding part of the coil spring which concerns on 1st Embodiment. The figure which shows distribution of each residual stress of a compression residual stress part and a deep layer residual stress part. Sectional drawing which shows typically the surface vicinity of each of a compression residual stress part and a deep layer residual stress part, and the shot used. Sectional drawing which shows typically a part of ultrasonic shot peening apparatus and coil spring for forming a deep layer residual stress part. The flowchart which shows an example of the manufacturing process of the coil spring shown by FIG. The figure which shows each durability test result of the coil spring which has the compression residual stress part by a general shot peening, and the coil spring which has the deep layer residual stress part by ultrasonic shot peening. Sectional drawing which shows the end winding part of the coil spring which concerns on 2nd Embodiment, and a part of spring seat. The bottom view which shows typically the end winding part of the coil spring shown by FIG. The perspective view which shows typically the rear part of the vehicle provided with the spring apparatus for suspension which concerns on 3rd Embodiment. The side view which looked at the spring apparatus for suspension shown by FIG. 12 from the vehicle side. FIG. 14 is an enlarged cross-sectional view of a part of the suspension spring device shown in FIG. 13. The bottom view which shows typically the end winding part of the coil spring of the spring apparatus for suspension shown by FIG.

A suspension spring device according to a first embodiment will be described below with reference to FIGS.
1 and 2 show a McPherson strut suspension mechanism 11 disposed on the front side of the vehicle 10. The suspension mechanism 11 is disposed on the upper side of the coil spring 12, a coil spring 12 (compression coil spring) which is an example of a coil spring for suspension, a lower spring seat 13 disposed on the lower side of the coil spring 12. An upper spring seat 14, a shock absorber 15, a mount insulator 16, and the like are provided. The coil spring 12 is disposed in a compressed state between the lower spring seat 13 and the upper spring seat 14. The coil spring 12 and the spring seats 13 and 14 constitute a suspension spring device 18.

The shock absorber 15 covers a cylinder 20 in which a fluid such as oil is accommodated, a rod 21 inserted into the cylinder 20, a damping force generation mechanism provided inside the cylinder 20, and a sliding portion of the rod 21. The cover member 22 and the like are included. The rod 21 can be expanded and contracted in the direction of the axis X1 of the shock absorber 15 with respect to the cylinder 20, and resistance is given to the movement of the rod 21 by the damping force generating mechanism. Shock absorber 15 is attached to the vehicle body 30 in an inclined attitude angle θ with respect to the vertical line X _0.

  A bracket 26 for attaching a knuckle member 25 (shown in FIG. 1) is provided at the lower end of the cylinder 20. The lower part of the knuckle member 25 is rotatably supported by the lower arm 27 via a ball joint 28. The lower arm 27 is attached to a cross member 29 extending in the width direction of the vehicle 10 so as to be rotatable in the vertical direction.

  FIG. 3 shows a state where the coil spring 12 is not subjected to a compression load (so-called free state). In this specification, the length of the coil spring 12 under the free state is referred to as a free length. When a load is applied to the coil spring 12, the coil spring 12 bends in a direction in which the length is shorter than the free length. The suspension spring device 18 shown in FIG. 2 is attached to the vehicle body 30 in an assembly state compressed between the lower spring seat 13 and the upper spring seat 14.

  The coil spring 12 shown in FIG. 3 has a strand (wire) 40 formed in a spiral shape. The strand 40 is made of spring steel having a circular cross section. The coil spring 12 has a lower end winding portion 12a less than the first turn from the lower end 40a of the strand 40, and an upper end winding portion 12b less than the first turn from the upper end 40b of the strand 40. . The spiral effective portion 12c between the end winding portions 12a and 12b is wound at a pitch P so that the strands 40 do not contact each other even when compressed to the maximum.

  An example of the wire diameter of the element wire 40 is 12.5 mm, the average coil diameter is 110.0 mm, the free length (length under no load) is 382 mm, the effective number of turns is 5.39, and the spring constant is 33.3 N / mm. is there. The main wire diameter is 8 to 21 mm, but other wire diameters may be used. An example of the coil spring 12 is a cylindrical coil spring, but depending on the specifications of the suspension mechanism, a barrel coil spring, a drum coil spring, a taper coil spring, an unequal pitch coil spring, or a torso in advance in a free state. Various types of compression coil springs such as a coil spring may be used.

  Although the kind of spring steel which is the material of the strand 40 is not specifically limited, For example, SAE9254 based on "Society of Automotive Engineers" of the United States is mentioned. The chemical components (mass%) of SAE 9254 are C: 0.51 to 0.59, Si: 1.20 to 1.60, Mn: 0.60 to 0.80, Cr: 0.60 to 0.80, S: maximum 0.040, P: maximum 0.030, balance Fe. Another example of the steel type may be ultra high strength spring steel. Examples of the chemical component (mass%) of the ultra-high strength spring referred to here are C: 0.40, Si: 1.8, Mn: 0.3, Cr: 1.05, P: 0.010, S: 0.005, Ni: 0.4, Cu: 0.25, V: 0.18, Ti: 0.07, and the balance Fe.

  The coil spring 12 is disposed in a compressed state between the lower spring seat 13 and the upper spring seat 14 and elastically supports a load applied from above the vehicle 10. The lower end winding portion 12 a is in contact with the upper surface of the spring seat 13. The upper end winding portion 12 b is in contact with the lower surface of the spring seat 14. The coil spring 12 expands to the maximum at full rebound and is compressed to the maximum at full bump. “Full rebound” means a state in which the coil spring is stretched to the maximum by the unsprung load when the vehicle body is lifted. The “full bump” is a state in which the coil spring is compressed to the maximum by a load applied from above the vehicle body.

FIG. 4 is a bottom view schematically showing the end winding portion 12 a of the coil spring 12. The end turn portion 12a, with respect to the winding direction of the wire 40, a first portion 12a ₁ of the range indicated by the arrow R1, a second portion 12a ₂ of the range indicated by the arrow R2, and the third portion 12a ₃ have. The first portion 12a ₁ extends from the lower end 40a (0th volume) of the wire 40 to the 0.5th volume, for example, from the 0th to the 0.6th volume, and is applied to the load applied to the coil spring 12. Regardless, it is always in contact with the spring seat 13.

The second portion 12a ₂ continuous to the _first portion 12a ₁ extends from the lower end 40a of the strand 40 to less than the first turn (for example, from the vicinity of the 0.6th turn to the vicinity of the 0.9th turn). The second portion 12 a ₂ contacts or leaves the spring seat 13 according to the load applied to the coil spring 12. That is, the second portion 12a ₂ is separated from the spring seat 13 when the load is small, and contacts the spring seat 13 when the load is large. The third portion 12a ₃ of is spaced from the constantly spring seat 13 regardless of the magnitude of the load.

The upper end turn portion 12b, like the end turn portion 12a of the lower side, and has a first portion 12b _1, a second portion 12b _2, and a third portion 12b _3. The first portion 12b ₁ extends from the upper end 40b (0th winding) of the strand 40 to the 0.5th winding, and is always in contact with the spring seat 14 regardless of the load applied to the coil spring 12. The second portion 12b _{2 that} is continuous with the _first portion 12b ₁ extends from the upper end 40b of the strand 40 to less than the first volume (for example, from about 0.6 to about 0.9). The second portion 12b ₂ contacts or separates from the spring seat 14 according to the load applied to the coil spring 12. The third portion 12b ₃ is always away from the spring seat 14 regardless of the magnitude of the load.

  The coil spring 12 has a compressive residual stress portion 50 formed between the end turns 12a and 12b and deep residual stress portions 51 and 52 formed on the end turns 12a and 12b. A compressive residual stress is applied to the compressive residual stress portion 50 from the surface of the strand 40 to the first depth.

Deep residual stress portion 51 formed in the lower end turn portion 12a is formed in a region including a second portion 12a ₂ of at least the end turn portion 12a. The deep residual stress portion 51 is applied with compressive residual stress up to the second depth. Deep residual stress portion 52 formed in the upper end turn portion 12b is formed in a region including a second portion 12b ₂ of the end turn portion 12b. The deep residual stress portion 52 is also applied with compressive residual stress to the second depth.

In FIG. 3, the deep residual stress portions 51 and 52 are represented by parallel oblique lines (hatching). In FIG. 4, for the convenience of explanation, the deep residual stress portion 51 formed in the lower end winding portion 12a is represented by a satin pattern. The deep residual stress portion 51 is formed in a range covering the second whole portion 12a ₂ of the end turn portion 12a. Thus one end 51a of the deep residual stress unit 51 is located on the first portion 12a ₁ of the end turn portion 12a. The other end 51b of the deep residual stress portion 51 is continuous with the compressive residual stress portion 50 formed in the effective portion 12c.

As described above, the lower deep layer residual stress portion 51 is in a region including the second portion 12a ₂ in the lower end winding portion 12a, that is, a region that may come in contact with or separate from the spring seat 13. Is formed. The deep residual stress portion 51 may be formed over both the second portion 12a ₂ and the third portion 12a ₃ .

Since the first portion 12 a ₁ of the end winding portion 12 a is always in contact with the spring seat 13, one end 51 a of the deep residual stress portion 51 is always in contact with the spring seat 13. The boundary with the other end 51b of the deep residual stress portion 51, that is, the compressive residual stress portion 50 is a stress transition portion where the compressive residual stress gradually decreases as the number of turns from the lower end 40a increases. This stress transition portion prevents the compressive residual stress in the vicinity of the other end 51b from changing abruptly and prevents the tensile residual stress from being generated in the vicinity of the other end 51b.

Deep residual stress portion 52 formed in the upper end turn portion 12b, like the lower side of the deep residual stress portion 51, is formed in a range covering the second whole portion 12b ₂ of the end turn portion 12b Yes. That is, the upper deep layer residual stress portion 52 is formed in a region including the second portion 12b _{2 in} the end winding portion 12b, that is, a region that may come in contact with or separate from the spring seat 14. The deep residual stress portion 52 may be formed over both the second portion 12b ₂ and the third portion 12b ₃ .

  FIG. 5 shows the stress distribution of the compressive residual stress portion 50 (broken line L1) and the stress distribution of the deep residual stress portions 51 and 52 (solid line L2). The horizontal axis in FIG. 5 indicates the depth (distance) from the surface. The vertical axis in FIG. 5 represents the residual stress value, but the compressive residual stress value is represented by minus as a convention in the industry. As indicated by a broken line L1 in FIG. 5, a compressive residual stress is formed in the compressive residual stress portion 50 from the surface to a first depth D1 (depth of about 0.30 mm), and its maximum value (absolute value) H1. Is around 750 MPa.

  On the other hand, as shown by the solid line L2 in FIG. 5, the compressive residual stress is formed in the deep layer residual stress portions 51 and 52 from the surface to the second depth D2 (around 0.8 mm depth). The maximum value (absolute value) H2 of the residual stress has reached 900 MPa. That is, in the deep residual stress portions 51 and 52, compressive residual stress is formed to a position deeper than the compressive residual stress portion 50. Moreover, the maximum value (absolute value) H2 of the compressive residual stress of the deep residual stress portions 51 and 52 is larger than the maximum value (absolute value) H1 of the compressive residual stress of the compressive residual stress portion 50. H2 may be equal to or smaller than H1.

  FIG. 6 is a cross-sectional view schematically showing the vicinity of the surfaces of the compressive residual stress portion 50 and the deep residual stress portions 51 and 52. On the surface of the compressive residual stress portion 50, a first shot peening dent 61 is formed by a shot 60 projected by the first shot peening described below. The compressive residual stress portion 50 is applied with a compressive residual stress from the surface to the first depth D1 (shown in FIG. 5).

  In contrast, second shot peening dents 66 are formed on the surfaces of the deep residual stress portions 51 and 52 by the steel ball shots 65 projected by the second shot peening (ultrasonic shot peening). The deep residual stress portions 51 and 52 are given a compressive residual stress larger than that of the compressive residual stress portion 50 from the surface to the second depth D2 (shown in FIG. 5). The absolute value of the compressive residual stress of the deep residual stress portions 51 and 52 may be equal to or less than the absolute value of the compressive residual stress of the compressive residual stress portion 50.

  In the first shot peening for forming the compressive residual stress portion 50, the impeller (impeller) of the centrifugal accelerator is rotated, and the shot 60 is moved to the entire coil spring 12 by the centrifugal force generated by the high speed rotation of the impeller. Hit it. An example of the shot 60 (shown in FIG. 6) is a cut wire. An example of the shot size is 0.67 mm and a projection speed of 77 m / s. A new cut wire has a cylindrical shape, but a cut wire that has been used to some extent has rounded corners. By this first shot peening, a large number of dents 61 of dent size d1 (shown in FIG. 6) are formed on the surface of the strand 40, and from the surface of the strand 40 to the first depth D1. Compressive residual stress develops.

  FIG. 7 schematically shows an ultrasonic shot peening apparatus 70 that performs the second shot peening. The ultrasonic shot peening apparatus 70 is housed in a housing 71 that functions as a masking means, an ultrasonic vibrator 72 disposed in the housing 71, a drive unit 73, and a housing 71 so as to be movable. A plurality of shots of steel balls 65 are provided. The steel ball shot 65 has a substantially spherical and smooth surface like a ball ball of a ball bearing, for example. The diameter of the steel ball shot 65 is, for example, 3 to 4 mm, which is much larger than the shot size (for example, 0.6 to 1.2 mm) of the shot 60 used in the first shot peening. Moreover, the steel ball shot 65 has a smooth surface and is close to a true sphere as compared with the general shot 60.

  An example of the hardness of the steel ball shot 65 is 670 HV. The casing 71 is placed on the projection area of the strand 40, and the ultrasonic vibrator 72 is vibrated by the drive unit 73, for example, at a frequency of 20 kHz and an amplitude of 150 μm. Thereby, the steel ball shot 65 is projected toward the strand 40 inside the housing 71. For example, the projection time of the steel ball shot 65 is 80 seconds, the projection distance is 90 mm, and the arc height (C class) is 0.289 mm.

  The steel ball shot 65 projected from the ultrasonic transducer 72 toward the strand 40 collides with the surface of the strand 40 and bounces off, and is projected again toward the strand 40 by the ultrasonic transducer 72. By repeating the projection and reflection of the steel ball shot 65 in this way, as shown in FIG. 6, a second shot peening dent 66 having a dent size (a dent diameter) d2 is formed. The impression size d2 of the second shot peening impression 66 is larger than the impression size d1 of the first shot peening impression 61.

  The larger the shot size, the greater the mass. For this reason, the kinetic energy of the steel ball shot 65 struck against the coil spring 12 by the ultrasonic shot peening apparatus 70 is much larger than the kinetic energy of the shot 60 used for the first shot peening. Therefore, in the second shot peening, as indicated by the line segment L2 in FIG. 5, a large compressive residual stress is developed from the surface to the depth D2. Moreover, the maximum value (absolute value) H2 of the compressive residual stress of the deep residual stress portions 51 and 52 is larger than the maximum value (absolute value) H1 of the compressive residual stress of the compressive residual stress portion 50.

  The diameter of the steel ball shot 65 is, for example, 4 mm, which is three times or more larger than the shot size of the shot 60 used in the first shot peening. Moreover, since the surface of the steel ball shot 65 is close to a true sphere, the dent size d2 of the second shot peening dent 66 is larger than the dent size d1 of the first shot peening dent 61. Moreover, the surface of the second shot peening dent 66 is smooth. For this reason, it can suppress that the 2nd shot peening dent 66 formed in the end winding part 12a becomes a starting point of breakage of the coil spring 12.

FIG. 8 shows an example of a manufacturing process when the coil spring 12 is formed hot.
In the heating step S1 in FIG. 8, the material of the coil spring 12 (wire) is heated to an austenitizing temperature _{(A 3} transformation point or higher, 1150 ° C. or less). Next, in the forming step S2, the material is wound in a spiral shape. Thereafter, in the heat treatment step S3, heat treatment of quenching and tempering is performed. In the heat treatment step S3, the strands are tempered to have a hardness of 47 to 59 HRC. Then, hot setting process S4 is performed warm (150-350 degreeC) using the residual heat of heat processing process S3. In the hot setting step S4, a load in the axial direction is applied to the coil spring 12 for a predetermined time.

  Further, in the first shot peening step S5, the first shot peening is performed warmly. In the first shot peening step S5, a shot (iron cut wire) having a shot size (particle diameter) of 0.67 mm is used. This shot is projected at a speed of 77 m / sec onto the strand at a processing temperature of 230 ° C. Thereby, the compressive residual stress part 50 is formed in the whole coil spring 12 to the 1st depth D1. In the first shot peening step S5, a shot having a shot size of 1.1 mm may be projected at a processing temperature of 230 ° C. and a speed of 77 m / sec.

  Further, multi-stage shot peening may be applied to the first shot peening step S5. In multi-stage shot peening, shot peening is performed in two stages or three or more stages. For example, after performing pre-stage shot peening using a large shot having a shot size of 0.87 to 1.2 mm, for example, performing post-stage shot peening using a small shot having a shot size of 0.4 to 0.7 mm. Also good.

  In the second shot peening step S <b> 6, second shot peening (ultrasonic shot peening) is performed using the ultrasonic shot peening apparatus 70. The second shot peening is performed at a lower temperature (for example, room temperature) than the first shot peening. In the second shot peening, a steel ball shot 65 having a diameter of 4 mm that is much larger than the shot 60 of the first shot peening is used. The projection time of the steel ball shot 65 is, for example, 80 seconds.

  As shown in FIG. 7, by projecting a steel ball shot 65 onto the surface of the strand 40 by the ultrasonic shot peening apparatus 70, a deep residual stress portion 51 is formed over the range of the angle α1 on the lower surface of the end winding portion 12 a. The In that case, you may move the ultrasonic shot peening apparatus 70 to the arrow Y direction.

  By moving the ultrasonic shot peening apparatus 70 from one end 51a of the deep layer residual stress portion 51 toward the other end 51b (shown in FIG. 4), the compressive residual stress of the second depth D2 is generated in the deep layer residual stress portion 51. To express. The other end 51 b of the deep residual stress portion 51 is a stress transition portion where the compressive residual stress gradually decreases from the deep residual stress portion 51 toward the compressive residual stress portion 50. Therefore, at the other end 51b of the deep residual stress portion 51, the compressive residual stress is gradually reduced by gradually increasing the moving speed of the ultrasonic shot peening apparatus 70 or by gradually decreasing the projection speed of the steel ball shot 65. To be.

  When forming the deep layer residual stress portion 52 in the upper end winding portion 12b, the upper end winding portion 12b is directed downward by turning upside down from FIG. 7 from the lower side of the end winding portion 12b. A steel ball shot 65 is projected toward the end winding portion 12b by the ultrasonic vibrator 72.

  The outer diameter of the steel ball shot 65 used in the second shot peening step S6 is much larger than the shot size of the shot used in the first shot peening step S5, and the steel ball shot 65 is substantially It is truly a sphere and has a smooth surface. For this reason, the surface of the strand whose roughness has been increased by the first shot peening step S5 can be reduced by the second shot peening step S6, and the surface state is improved. The average surface roughness of the compressive residual stress part 50 obtained by the first shot peening step S5 is, for example, 5.4 μm. In contrast, the average surface roughness of the deep residual stress portions 51 and 52 obtained by the second shot peening process S6 is 5.1 μm.

  When the deep layer residual stress portions 51 and 52 are formed in the end turns 12a and 12b by the second shot peening step S6, the deep layer residual stress portions 51 and 52 are formed by the first shot peening. The compressive residual stress portion 50 that has been canceled is cancelled. For this reason, the region between the deep residual stress portions 51 and 52 remains as the compressive residual stress portion 50.

  After the second shot peening step S6 is completed, the pre-setting step S7 is performed as necessary to adjust the length (free length) of the coil spring when there is no load. The creeping property (sagging resistance) of the coil spring may be improved by this pre-setting step S7. Note that the pre-setting step S7 may be omitted. Next, in the coating step S8, a rust preventive paint is applied to the entire coil spring by electrostatic coating or the like. Finally, quality inspection S9 is performed to complete the coil spring.

  The above explanation is a case where the coil spring 12 is hot molded. On the other hand, when the coil spring 12 is formed cold, heat treatment of quenching and tempering is performed on the wire in the heat treatment process. Thereafter, in the forming step (coiling step), the strand is formed into a spiral shape. Thereafter, a strain relief annealing process is performed. In the strain relief annealing process, the processing strain generated during molding is removed by leaving the coil spring in an atmosphere at a predetermined temperature for a predetermined time. Thereafter, hot setting is performed in the hot setting step. Further, in the first shot peening process, the first shot peening is performed. In the second shot peening process performed thereafter, the second shot peening (ultrasonic shot peening) is performed. Moreover, the length (free length) of the coil spring when there is no load is adjusted by performing a pre-setting process as necessary. Thereafter, the painting process and quality inspection are performed. Note that the pre-setting step may be omitted.

  As described above, in the coil spring 12 of the present embodiment, the compressive residual stress part 50 is formed by the first shot peening process S5, and the deep residual stress part 51 is formed on the end turns 12a and 12b by the second shot peening process S6. , 52 are formed. That is, the coil spring 12 is formed in the compressive residual stress portion 50 between the end winding portions 12a and 12b, the deep residual stress portion 51 formed in the lower end winding portion 12a, and the upper end winding portion 12b. A deep layer residual stress portion 52. A first shot peening dent 61 is formed in the compressive residual stress portion 50, and a second shot peening dent 66 is formed in the deep residual stress portions 51, 52. Moreover, the maximum compressive residual stress H2 of the deep residual stress portions 51 and 52 is larger than the maximum compressive residual stress H1 of the compressive residual stress portion 50. H2 may be the same as H1 or smaller than H1.

  The coil spring 12 is assembled to the shock absorber 15 in a state in which it is compressed between the spring seats 13 and 14 and given a preload (preload), and is further attached to the vehicle body 30. A vertical load is applied to the suspension spring device 18 attached to the vehicle body 30. Depending on the magnitude of this load, the coil spring 12 bends between the lower spring seat 13 and the upper spring seat 14. That is, the coil spring 12 expands and contracts between a full bump (maximum compressed state) and a full rebound (maximum extended state) according to the magnitude of the load.

In a state where the coil spring 12 is extended, a gap between the lower spring seat 13 and the second portion 12a ₂ or between the spring seat 13 and the third portion 12a ₃ is widened. Further, a gap between the upper spring seat 14 and the second portion 12b ₂ or between the spring seat 14 and the third portion 12b ₃ also widens. For this reason, a hard foreign substance such as sand may enter these gaps. In particular, the sand is likely to be caused between the second portion 12a ₂ of the lower spring seat 13 and the end turn portion 12a.

Conversely, when the coil spring 12 is compressed, the gap between the lower spring seat 13 and the second portion 12a ₂ or between the spring seat 13 and the third portion 12a ₃ becomes narrower. Further, the gap between the upper spring seat 14 and the second portion 12b ₂ or between the spring seat 14 and the third portion 12b ₃ is also narrowed. For this reason, if a hard foreign substance such as sand enters the gap between the end turns 12a and 12b, the coating of the coil spring 12 may be peeled off or the strand 40 may be damaged, and the strand 40 may be rusted. Cause.

  In conventional coil springs, if foreign matter such as sand is sandwiched between the end winding and the spring seat, the paint peels off and the strands corrode, and if the corrosion pits become large to a certain extent, the corrosion pits may break. It was. On the other hand, in the above embodiment, since a large compressive residual stress is applied from the surface of the region including the second portion of the end winding portion to a deep position, the coil spring breaks due to corrosion generated in the end winding portion. Was suppressed, and durability could be improved. Depending on the structure of the suspension mechanism, foreign matter such as sand may be prevented from entering between the upper spring seat 14 and the end winding portion 12b. In that case, the deep residual stress portion 51 may be formed only in the lower end winding portion 12a.

  A line segment M1 in FIG. 9 shows the durability test result of the coil spring having only the compressive residual stress portion 50 formed by general shot peening. A line segment M2 in FIG. 9 shows the durability test result of the coil spring having the deep residual stress portions 51 and 52 formed by ultrasonic shot peening. In this durability test, a coil spring having corrosion pits was vibrated a predetermined number of times, and the relationship between the presence or absence of breakage, the depth of the corrosion pits, and the stress amplitude was measured.

  As shown by the line segment M1 in FIG. 9, in the coil spring having only the compressive residual stress portion 50, when the depth of the corrosion pit exceeded 0.2 mm, the coil spring broke near the stress amplitude of 230 MPa. In contrast, the coil spring having the deep residual stress portions 51 and 52 did not break at a stress amplitude of 420 MPa even when the depth of the corrosion pit was as large as 0.4 mm. The coil spring having the deep residual stress portions 51 and 52 was broken from a portion other than the corrosion pits at a stress amplitude of 460 MPa.

  The effects described above have the same tendency regardless of the steel type, and similar results were obtained not only with the aforementioned SAE 9254 and ultra-high strength spring steel, but also with SUP7, for example. Further, according to the present invention, since the corrosion durability of the end winding portion can be increased by using spring steel that is usually used for the suspension coil spring, it is possible to suppress an increase in the material cost of the coil spring. is there.

  FIG. 10 shows a part of the end winding portion 12a of the coil spring 12 and a part of the spring seat 13 according to the second embodiment. FIG. 11 is a bottom view schematically showing the end winding part 12a shown in FIG. The lower surface and the outer peripheral surface of the end turn part 12a of this embodiment are restrained by the bottom surface 13a and the outer wall 13b of the spring seat 13, respectively. For this reason, this end winding part 12a contacts the bottom face 13a of the spring seat 13 and the outer wall 13b in a range indicated by α2. Therefore, the deep residual stress portion 51 is formed over a range α3 wider than α2. About another structure, it is common with the coil spring 12 of 1st Embodiment.

  12 to 15 show an example of the coil spring 12 used in the knee action type suspension mechanism 100 according to the third embodiment. As shown in FIG. 12, a pair of left and right suspension mechanisms 100 are provided on the rear side of the vehicle 10. Since these suspension mechanisms 100 have the same configuration, one suspension mechanism 100 will be described below as a representative.

  FIG. 13 is a side view of the suspension mechanism 100 as viewed from the side of the vehicle 10. The suspension mechanism 100 includes an arm member 101 functioning as a trailing arm, a suspension coil spring 12, a lower spring seat 103 disposed on the lower end side of the coil spring 12, and an upper end side of the coil spring 12. And an upper spring seat 104, a shock absorber 105 (shown in FIG. 12), and the like. The arm member 101 is attached to an arm attachment portion 110 of the vehicle body via a pivot (swing shaft) 111 so as to be swingable in the vertical direction. As shown in FIG. 12, the pair of left and right arm members 101 are coupled to each other by a beam member 112 extending in the width direction of the vehicle 10. The arm member 101 is provided with a hub unit 114 via an axle support portion 113.

  As shown in FIG. 13, the lower spring seat 103 is provided on the arm member 101. The lower spring seat 103 swings relatively in the vertical direction along an arcuate locus X3 (shown in FIG. 13) centered on the pivot 111. The upper spring seat 104 is provided on the spring mounting portion 120 of the vehicle body. The coil spring 12 is compressed between the lower spring seat 103 and the upper spring seat 104 to urge the arm member 101 downward. The coil spring 12 and the spring seats 103 and 104 constitute a suspension spring device 130.

  FIG. 14 shows a part of the end winding part 12 a and a part of the spring seat 103. The lower surface and the inner peripheral surface of the end wound portion 12a are constrained by the bottom surface 103a and the inner wall 103b of the spring seat 103, respectively. For this reason, the lower surface and the inner peripheral surface of the end winding portion 12a are in contact with the bottom surface 103a and the inner wall 103b of the spring seat 103 in the range indicated by α4. As shown in FIG. 14, the deep residual stress portion 51 is formed over a range α5 wider than α4. About another structure, it is common with the coil spring 12 (FIGS. 3-6) of 1st Embodiment.

FIG. 15 is a bottom view schematically showing the end winding part 12a, and the deep residual stress part 51 is represented by a satin pattern. The deep residual stress unit 51, like the coil spring 12 of the first embodiment (FIGS. 3 to 6), is formed in a region including a second portion 12a ₂ of at least the end turn portion 12a.

The coil spring 12 provided in the suspension mechanism 100 expands and contracts between a full bump (maximum compressed state) and a full rebound (maximum extended state) according to the magnitude of the load. For example, when the coil spring 12 extends, the second portion 12 a ₂ of the lower end winding portion 12 a is separated from the lower spring seat 103. For this reason, foreign substances such as sand may enter between the second portion 12 a ₂ and the spring seat 103. On the contrary, when the coil spring 12 is compressed, the second portion 12 a ₂ contacts the spring seat 103. For this reason, if a hard foreign object such as sand is sandwiched between the end winding portion 12a and the spring seat 103, the coating of the coil spring 12 is peeled off or the wire 40 is damaged, causing a corrosion pit. .

However, in the coil spring 12 of this embodiment, the deep residual stress portion 51 is formed in a region including at least the second portion 12a _{2 in} the same manner as the coil spring 12 (FIGS. 3 to 6) described in the first embodiment. Therefore, the coil spring 12 is prevented from being broken due to the corrosion of the end winding portion 12a, and the durability can be improved. Note that a deep layer residual stress portion 52 similar to the lower deep layer residual stress portion 51 may also be formed in the upper end winding portion 12b.

  In carrying out the present invention, the specific shape and dimensions of the coil spring, the number of turns, the material, the spring constant, and the aspect and structure of each element (coil spring, spring seat, etc.) constituting the suspension spring device, Needless to say, the arrangement can be changed in various ways. The present invention can also be applied to a suspension mechanism for vehicles other than automobiles.

10 ... vehicle, 11 ... suspension mechanism, 12 ... suspension coil spring, the end turn portion of 12a ... lower, 12a 1 _... first part, 12a 2 _... second portion, 12a 3 _... third portion, 12b ... upper end winding part, 12b ₁ ... first part, 12b ₂ ... second part, 12b ₃ ... third part, 13 ... lower spring seat, 14 ... upper spring seat, 18 ... for suspension Spring device, 40 ... strand, 40a ... lower end, 40b ... upper end, 50 ... compressive residual stress part, 51 ... deep layer residual stress part, 51a ... one end, 51b ... other end (stress transition part), 52 ... deep layer residual stress part , 70 ... Ultrasonic shot peening device, 100 ... Suspension mechanism, 103 ... Lower spring seat, 104 ... Upper spring seat, 130 ... Suspension spring device.

Claims (8)

A lower spring seat,
An upper spring seat;
A coil spring having a strand formed in a spiral shape and disposed in a compressed state between the lower spring seat and the upper spring seat;
A suspension spring device comprising:
The coil spring is
A lower end winding portion less than the first turn from the lower end of the strand, and an upper end winding portion less than the first turn from the upper end of the strand;
At least the lower end winding portion has a first portion that always contacts the lower spring seat regardless of the load applied to the coil spring, and the lower spring according to the load applied to the coil spring. A second portion that contacts or separates from the seat and a third portion that is always away from the spring seat regardless of the magnitude of the load;
Between the lower end winding part and the upper end winding part, having a compressive residual stress part to which a compressive residual stress is applied from the surface of the strand to the first depth,
A region including the second portion of the lower end winding portion has a deep residual stress portion to which a compressive residual stress is applied from the surface of the strand to a second depth deeper than the first depth. A suspension spring device characterized by that.   2. The suspension spring device according to claim 1, wherein the maximum absolute value of the compressive residual stress of the deep residual stress portion is larger than the maximum absolute value of the compressive residual stress of the compressive residual stress portion.   3. The suspension according to claim 1, further comprising a stress transition portion where a compressive residual stress of the deep residual stress portion gradually decreases at a boundary between the deep residual stress portion and the compressive residual stress portion. Spring device.   A first shot peening dent is formed on the surface of the compressive residual stress portion, a second shot peening dent is formed on the surface of the deep residual stress portion, and the size of the second shot peening dent is 4. The suspension spring device according to claim 1, wherein the suspension spring device is larger than a size of the first shot peening dent. 5.   The suspension spring device according to any one of claims 1 to 4, wherein the deep residual stress portion is formed on both the lower end winding portion and the upper end winding portion.   The lower spring seat has a bottom surface and an outer wall that restrain the lower surface and the outer peripheral surface of the lower end winding portion, respectively, and includes the lower surface and the outer peripheral surface of the end winding portion. The suspension spring device according to any one of claims 1 to 5, wherein the deep residual stress portion is formed.   The lower spring seat has a bottom surface and an inner wall that restrain the lower surface and the inner peripheral surface of the lower end winding portion, respectively, and includes the lower surface and the inner peripheral surface of the end winding portion. The suspension spring device according to any one of claims 1 to 5, wherein the deep residual stress portion is formed in a range. A lower end winding portion less than the first turn from the lower end of the spirally formed strand, and an upper end winding portion less than the first turn from the upper end of the strand;
At least the lower end winding portion always contacts the lower spring seat regardless of the magnitude of the load, and a first portion that contacts or separates from the lower spring seat depending on the magnitude of the load. 2 and a third portion that is always away from the spring seat regardless of the magnitude of the load,
Between the lower end winding part and the upper end winding part, having a compressive residual stress part to which a compressive residual stress is applied from the surface of the strand to the first depth,
A region including the second portion of the lower end winding portion has a deep residual stress portion to which a compressive residual stress is applied from the surface of the strand to a second depth deeper than the first depth. A suspension coil spring characterized by that.

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