JP2006017248A - Rack boot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To securely prevent a rotation following the process of tightening from occurring in adjusting toe-in by improving the shape of a rack boot without using extra material. <P>SOLUTION: Where the wall thickness of one end part is t, the inner diameter thereof is ϕ1, the outer diameter of a mating member is ϕ2, and the inner diameter of a tightening clip is ϕ3, a relation between a compression ratio Y defined by 2t/(ϕ3-ϕ2) and an expansion ratio X defined by (ϕ2/ϕ1) is set to fulfill the requirement of Y ≥ 1.16 and X ≤ (28-Y)/22.9. Since the relation is summarized by two indexes of the compression ratio Y and the expansion ratio X, a dimensional range in which the rack boot is not rotated following the process of tightening can be accurately expressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rack boot used in a rack and pinion type steering gear in which both ends are respectively held by a tie rod end side shaft portion and a gear housing side shaft portion to protect a ball joint portion.

  As a steering gear type that converts the rotational movement of the steering pinion gear into the axial movement of the steering rack, a structure is adopted in which a tie rod is connected to the steering rack via a ball joint and the tire turning angle is changed by the tie rod via a knuckle arm. Are known. In this structure, the coupling portion between the steering rack and the tie rod is covered with a bellows-shaped rack boot, so that problems due to intrusion of foreign matter are prevented. The rack boot is held using a clip or the like on the steering rack end side and a clamp or the like on the gear housing side.

  In such a steering gear type, in order to finely adjust the posture of the left and right tires in the vehicle assembly line, toe-in adjustment is performed in which the length of the tie rod is adjusted by turning the steering rack end side shaft portion. However, since the rack boot is made of rubber or the like, the coefficient of friction is generally large, and it rotates with the tie rod during toe-in adjustment, and there is a case where a twist occurs due to a difference in rotation angle between both ends. If this twist is left as it is, the rack boot may be caught during expansion and contraction, and the rack boot may be damaged.

  Therefore, conventionally, grease is applied to at least the interface between the rack boot and the tie rod to reduce the frictional resistance, thereby preventing the rack boot from rotating together with the tie rod during toe-in adjustment. Japanese Utility Model Laid-Open No. 62-093466 describes that a silicone rubber coating is applied to the fitting surface portion of the rack boot with the shaft member. Since the friction coefficient is reduced by applying the silicone rubber coating, the rack boot can be prevented from rotating together with the tie rod during toe-in adjustment.

However, applying grease increases the man-hours and contributes to the cost increase. Forming a silicone rubber coating also increases the cost of rack boots, which also increases costs. Therefore, as described in JP-A-60-215164, it is conceivable to form a rack boot from a thermoplastic elastomer to which a lubricant is added. However, even in this case, the addition of the lubricant increases the cost of the rack boot, and depending on the shape of the rack boot, the effect of the lubricant cannot be obtained, and it is difficult to completely prevent co-rotation.
Japanese Utility Model Sho 62-093466 JP-A-60-215164

  The present invention has been made in view of the above-described circumstances, and a problem to be solved by reliably preventing co-rotation during toe-in adjustment by devising the shape of the rack boot without using extra material. To do.

A feature of the rack boot of the present invention that solves the above problems is a rack boot that is cylindrical and has a bellows shape, and at least one end thereof is held by a mating member by a fastening clip, wherein the wall thickness of at least one end is t, was a phi _1, when ₂ the outer diameter of the mating member phi, the inner diameter of the fastening clip has a phi _3,
The relationship between the compression ratio (Y) defined by 2t / (φ ₃ −φ ₂ ) and the expansion ratio (X) defined by φ ₂ / φ ₁ is Y ≧ 1.16 and X ≦ (28−Y) / To satisfy 22.9.

  It is preferable to satisfy X ≧ 1.037, and it is preferable to further satisfy X ≦ (9.93−Y) /7.29. Moreover, if it forms from soft resin containing a lubricant, the tolerance | permissible_range of the said relational expression can be extended. The one end is preferably an end held by the tie rod end side shaft.

  According to the rack boot of the present invention, it is possible to reliably prevent co-rotation during toe-in adjustment with only the rack boot main body without applying grease or forming a silicone rubber coating, so that damage during use is avoided while avoiding an increase in cost. Can be prevented.

The inventors of the present invention manufactured various rack boots and repeated the tests, and intensively investigated the relationship between the presence or absence of the co-rotation phenomenon during toe-in adjustment and the dimensions of each part. As a result, it is defined as 2t / (φ ₃ −φ ₂ ) where t is the wall thickness of at least one end, φ ₁ is the inner diameter, φ _{2 is} the outer diameter of the mating member, and φ ₃ is the inner diameter of the fastening clip. The present invention has been completed by finding that a range that does not co-rotate can be expressed with high accuracy by combining the two compression ratios (Y) and the expansion ratio (X) defined by φ ₂ / φ ₁ .

The compression ratio (Y) defined by 2t / (φ ₃ −φ ₂ ) is the ratio of the wall thickness to the allowance at the end of the rack boot, and when Y <1.16, the wall thickness becomes too thin. This makes it difficult to form the rack boot end. Therefore, Y ≧ 1.16.

In the rack boot of the present invention, the wall thickness of at least one end portion is t, the inner diameter of the end portion is φ ₁ , and the outer end portion of at least one of the tie rod end side shaft portion and the steering rack end side shaft portion where the end portion is held. When the diameter is φ ₂ , the relationship between the compression ratio (Y) and the expansion ratio (X) defined by φ ₂ / φ ₁ satisfies Y ≧ 1.16 and X ≦ (28−Y) /22.9.

Since the equation X = (28−Y) /22.9 is indicated by the straight line L ₁ in FIG. 1, the range satisfying the above two relations is the range A indicated by the oblique line rising to the right in FIG. When the expansion ratio (X) exceeds (28−Y) /22.9 (exceeds range A), the rack boots rotate together during toe-in adjustment.

The expansion ratio (X) is the ratio of the outer diameter φ ₂ of the shaft member to the inner diameter φ ₁ of the rack boot end, and corresponds to the strength of the stress acting on the end due to the fitting between the end and the shaft. . If X is too small, the end portion is disengaged from the engaging portion with the shaft member when compressed in use, and therefore it is preferable to satisfy X ≧ 0.977 in order to prevent this push-through. In order to prevent the end portion from being pulled out of the engagement portion with the shaft member when pulled during use, it is desirable to satisfy X ≧ 1.037. If X ≧ 1.037 is satisfied, both push-through and pull-out can be prevented. Therefore, a more preferable range is a range B indicated by a slanted line in FIG.

The rack boot made of TPO has a phenomenon that the coefficient of friction increases over time immediately after assembly. The relationship between the compression ratio (Y) and the expansion ratio (X) described above can be applied to rack boots that are one hour after assembly, but in the case of rack boots that have passed one week after assembly, X ≦ (9.93−Y ) /7.29 is desirable. Since the formula X = (9.93−Y) /7.29 is shown by the straight line L ₂ in FIG. 2, in order not to rotate together even immediately after assembly or after one week, the range shown by the upward slanting line in FIG. It is particularly preferable to satisfy C, that is, both X ≦ (28−Y) /22.9 and X ≦ (9.93−Y) /7.29.

Furthermore, the compression ratio (Y) is particularly preferably in the range of 1.28 to 1.82 in consideration of fluidity during molding and dimensional variation during production. Also, if the expansion ratio (X) is too small, it is difficult to prevent the intrusion of foreign matter, and the larger the expansion ratio (X), the easier it is to rotate together. Therefore, the expansion ratio (X) should be in the range of 1.042 to 1.082. Is particularly desirable. Therefore, as shown by the slanting line in the lower right in FIG. 2, the expansion ratio (X) and the compression ratio (Y) are determined within the range D, and the tie rod end side shaft portion and the gear housing side shaft portion where the ends are held are determined. It is particularly desirable to determine the thickness (t) of the end portion, the inner diameter (φ ₁ ) of the end portion, and the inner diameter (φ ₃ ) of the fastening clip according to at least one outer diameter (φ ₂ ).

  The rack boot of the present invention can be manufactured from a soft resin such as a thermoplastic elastomer, rubber or the like. Although it is generally cylindrical and bellows-shaped, the shape is not particularly limited as long as the shape of at least one end satisfies the above range. The shape in the above range may be either one end held by the tie rod end side shaft portion or the other end held by the gear housing side shaft portion, or both may be in the shape of the above range. . In general, it is desirable that the one end portion held by the tie rod end side shaft portion which is generally small in diameter and easily rotates together has a shape in the above range.

If the rack boot of the present invention is formed from a soft resin containing a lubricant, the allowable range of the above relational expression can be expanded. In a rack boot formed from TPO containing a lubricant, the straight line corresponding to the straight line L ₂ is shown by the straight line L ₃ or the straight line L ₄ in FIG. 2, so that the range C that can prevent co-rotation can be expanded. This increases the degree of freedom of dimensions. The lubricant varies depending on the composition of the resin to be used, but is preferably one that bleeds to the surface of the rack boot, and a silicone lubricant, an aliphatic monoamine lubricant, a paraffin lubricant, or the like can be used. The amount of addition is not particularly limited, and the optimum range may be determined by experiment.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1
FIG. 3 shows the rack boot of the present embodiment in a state assembled to a rack and pinion type steering gear. One end of a rack end shaft 3 is screwed into the tie rod end main body 2, and the other end of the rack end shaft 3 is rotatably coupled to the rack bar 4 via a ball joint 30. The other end of the rack bar 4 is located in the gear housing 5. The connecting portion between the rack end shaft 3 and the rack bar 4 is covered with a rack boot 1 made of TPO to prevent foreign matter from entering.

  At the time of toe-in adjustment, the rack end shaft 3 is rotated to adjust the penetration depth of the rack end shaft 3 into the tie rod end main body 2 and finely adjust the postures of the left and right tires. After the adjustment is completed, the turn rod adjusting shaft 3 and the tie rod end main body 2 are integrally fixed by tightening the nut 31 screwed to the rack end shaft 3.

  The rack boot 1 is formed by injection molding into a bellows-shaped cylinder, one end 10 having a small diameter is held by the rack end shaft 3, and the other end 11 having a large diameter is held by the gear housing 5. As shown in FIG. 4, the one end portion 10 is formed with a ridge 12 projecting from the inner end to the outer periphery. A ring groove 32 is formed on the outer peripheral surface of the rack end shaft 3. Then, the ridge 12 is engaged with the ring groove 32, the clip 33 (fastening clip) is engaged with the clip groove 13 adjacent to the ridge 12, and the one end 10 is attached to the rack end shaft 3 (tie rod) by the spring force of the clip 33. (End side shaft). The other end 11 of the rack boot 1 is held on the outer peripheral surface of the gear housing 5 by a plate band 14.

In the rack boot 1 of this embodiment, the thickness (t) of the clip groove 13 at one end 10 is 1.7 mm, the inner diameter (φ ₁ ) of the clip groove 13 is 15.8 mm, and the outer diameter (φ ₂ ) of the rack end shaft 3. Is 16.8 mm, and the inner diameter (φ ₃ ) of the clip 33 is 19 mm. Therefore, the compression ratio (Y) defined by 2t / (φ ₃ −φ ₂ ) is 1.55, and the expansion ratio (X) defined by φ ₂ / φ ₁ is 1.06. ) And exists within the range C.

  Therefore, the rack boot 1 of the present embodiment has no problem that the one end 10 rotates together with the turn rod adjusting shaft 3 during toe-in adjustment, and is excellent in durability during use. In addition, since the compression ratio (Y) exceeds 1.28, there is no problem in fluidity at the time of molding, and the expansion ratio (X) exceeds 1.037, which prevents both push-through and pull-out during use. Yes.

(Example 2)
The rack boot of this example is the same as that of Example 1 except that it was manufactured using TPO containing a silicone-based lubricant. In this rack boot, since the straight line corresponding to the straight line L ₂ is shown by the straight line L ₃ in FIG. 2, the range C in which co-rotation can be prevented can be expanded, and the degree of freedom in dimensions increases. Therefore, the defect rate can be reduced, and the cost is reduced by improving the yield. Therefore, the increase in cost corresponding to the addition of the lubricant can be absorbed.

It is explanatory drawing which shows the range which can prevent the co-rotation of a rack boot in the relationship between expansion ratio (X) and compression ratio (Y). It is explanatory drawing which shows the range which can prevent the co-rotation of a rack boot in the relationship between expansion ratio (X) and compression ratio (Y). It is principal part sectional drawing shown in the state which assembled | attached the rack boot of one Example of this invention to the rack & pinion type steering gear. It is explanatory drawing which expands and shows the principal part of the rack boot and turnbuckle of one Example of this invention.

Explanation of symbols

1: Rack boot 2: Tie rod end body 3: Rack end shaft (tie rod end side shaft)
4: Rack bar 5: Gear housing
33: Clip (fastening clip)

Claims (5)

A rack boot at least one end forms a bellows in the tubular is maintained in mating member by fastening clip, the thickness of the at least one end portion t, an inner diameter and phi _{1, 2} the outer diameter of the mating member phi, when the inside diameter of the fastening clip was φ _3,
The relationship between the compression ratio (Y) defined by 2t / (φ ₃ −φ ₂ ) and the expansion ratio (X) defined by φ ₂ / φ ₁ is Y ≧ 1.16 and X ≦ (28−Y) / Rack boot characterized by satisfying 22.9.   The rack boot according to claim 1, further satisfying X ≧ 1.037.   The rack boot according to claim 1, further satisfying X ≦ (9.93−Y) /7.29.   The rack boot according to any one of claims 1 to 3, comprising a soft resin containing a lubricant. The rack boot according to claim 1, wherein the one end portion is an end portion held by a tie rod end side shaft portion.

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