JP2013019462A - Rack bush, and rack shaft supporting structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rack bush capable of obtaining a good steering feeling.SOLUTION: The rack bush 1 has a bellows cylindrical shape body 4 having an outer periphery 4a and an inner periphery 4b. The rack bush further has valleys 51, 52, 53 and valleys 61 62 alternately arranged in the outer periphery 4a in an axial direction X1. The rack bush has mountain parts 71, 72, 73 and valleys 81, 82, 83 alternately arranged in the inner periphery 4b in the axial direction X1. Mounting parts 71, 72, 73 are arranged in the back side of the valleys 51, 52, 53. A first inner diameter d1 of the top 72a of the first mountain part 72 is lesser than the outer diameter D of a rack shaft 3 in an unloaded condition. The second inner diameter d2 of the tops 71a. 73a of the second mountain part 71, 73 is larger than the first inner diameter d1 (d2>d1).

Description

  The present invention relates to a rack bush and a rack shaft support structure.

  For example, Patent Literature 1 proposes a rack bush in which grooves extending in the axial direction are alternately formed in the circumferential direction on each of the outer circumference and the inner circumference. As arc-shaped surface portions provided between the grooves on the inner periphery of the rack bush, a small-diameter arc-shaped surface portion having a small central radius and a large-diameter arc-shaped surface portion having a larger central radius than the small-diameter arc-shaped surface portion are provided. The large-diameter arc-shaped surface portion comes into contact with the outer periphery of the rack shaft only when a load perpendicular to the axis is applied to the rack shaft.

  Patent Document 2 proposes a resin rack bush that elastically holds a rack shaft by a support portion provided on the inner periphery of one end.

JP 61-13019 A JP-A-6-115439

By the way, since the rack shaft receives external force from the steered wheel side, the rack shaft may move in the axial direction while being slightly inclined with respect to the central axis of the housing.
In Patent Document 1, since the small-diameter arc-shaped surface portion that is always in contact with the rack shaft is provided in the entire axial length of the rack bush, when the rack shaft moves slightly inclined as described above, the small-diameter arc-shaped surface portion is provided. There is a possibility that the frictional resistance given to the rack shaft by the surface portion is increased. Therefore, the steering feeling may be deteriorated.

  Accordingly, an object of the present invention is to provide a rack bush and a rack shaft support structure capable of obtaining a good steering feeling.

  In order to achieve the above object, the invention of claim 1 surrounds a rack shaft (3) for steering inserted coaxially into a cylindrical housing (2), and the rack shaft is axially (X1). Rack bush (1; 101) that is slidably supported on the outer periphery (4a) and has an outer periphery (4a) and an inner periphery (4b), and is alternately arranged in the axial direction on each of the outer periphery and the inner periphery. Parts (61, 62; 71, 72, 73: 172, 173) and valleys (51, 52, 53; 81, 82), and the crests and troughs of the outer periphery are A bellows and a peak part are opposed to a diameter direction (Y1), and it has a bellows cylindrical main body (4) elastically deformable in the diameter direction, and the peak part of the inner circumference is the first peak part (72), And an inner diameter (d1) of the top (72a) of the first peak is unloaded. And the inner diameter (d2) of the top (71a, 73a; 171a, 173a) of the second peak is larger than the inner diameter of the top of the first peak (D). Providing rack bushings that are

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 inner diameter of the top portion of the second peak portion may be equal to or greater than or equal to the outer diameter of the rack shaft in an unloaded state.

As in claim 3, slits (9, 10) extending in the axial direction may be formed in the main body.
As in claim 4, the main body includes a first end and a second end (41, 42) facing each other in the axial direction, and the slit extends from the first end (9). And a second slit (10) extending from the second end, and the first slit and the second slit may be alternately arranged in the circumferential direction (Z1).

  The invention of claim 5 includes a cylindrical housing, a rack bush that surrounds a rack shaft that is coaxially inserted in the housing and that supports the rack shaft so as to be slidable in the axial direction, The rack bush has an outer periphery and an inner periphery, and has a peak portion and a valley portion alternately arranged in the axial direction on each of the outer periphery and the inner periphery, The outer peripheral crests and troughs are respectively opposed to the inner peripheral troughs and crests in the radial direction, and include a bellows-cylindrical body that is elastically deformable in the radial direction, and the inner peripheral crests are The inner diameter of the top of the first peak is smaller than the outer diameter of the rack shaft in an unloaded state, and the top of the second peak is A rack shaft characterized in that the inner diameter is larger than the inner diameter of the top of the first peak portion. Providing; (A1 A) lifting structure.

  According to a sixth aspect of the present invention, the housing includes an inner periphery (2a), and the inner periphery of the housing is disposed between an inner periphery of the housing and a corresponding valley portion (52) of the outer periphery of the rack bush. And a convex portion (12) for restricting the amount of movement of the rack bush in the axial direction, and in a state where the rack shaft is arranged coaxially with the housing, ridges (61, 62) An axial gap (S1) may be provided between at least one of the inclined surfaces and the convex portion.

According to a seventh aspect of the present invention, in the state where the rack shaft is arranged coaxially with the housing, the curvature radius (R1) of the corresponding valley formed by the corresponding valley portion is the curvature radius of the curved convex portion as the convex portion. It may be made larger than (R2).
In a state where the rack shaft is arranged coaxially with the housing as in claim 8, there is a radial gap (S2) between the convex portion of the housing and the corresponding valley portion of the rack bush. It is provided, and when the rack shaft is eccentric with respect to the housing, the convex portion may be configured to press the corresponding valley portion in the radial direction.

  According to the first aspect of the present invention, in the normal case where the rack shaft moves coaxially with respect to the housing, the first peak portion mainly gives a frictional resistance to the movement of the rack shaft. In addition, since the inner diameter of the top of the second peak is made larger than the inner diameter of the top of the first peak, even when the rack axis moves with a slight inclination with respect to the housing, the second peak becomes the rack axis. Frictional resistance given by contact is negligible. Therefore, the overall frictional resistance can be kept low, and the steering feeling can be improved.

  According to the invention of claim 2, in the normal case where the rack shaft moves coaxially with respect to the housing, substantially only the first peak portion gives a frictional resistance to the movement of the rack shaft. In addition, since the inner diameter of the top of the second peak is equal to or greater than the outer diameter of the rack shaft in an unloaded state, when the rack shaft moves slightly inclined with respect to the housing, the second peak is Has a small frictional resistance to the rack shaft. Therefore, the frictional resistance as a whole can be suppressed lower, and the steering feeling can be further improved.

According to invention of Claim 3, even if a bellows cylinder main body thermally expands, the deformation | transformation by the thermal expansion can be absorbed by a slit. Therefore, regardless of the temperature change, the frictional resistance can be kept low and a good steering feeling can be maintained.
According to invention of Claim 4, the elasticity of radial direction can be equalize | homogenized regarding the circumferential direction by arrange | positioning a slit to a reverse direction alternately. Therefore, a change in frictional resistance accompanying a temperature change can be further suppressed, and a good steering feeling can be maintained.

According to the invention of claim 5, the rack shaft support structure having the same effect as that of claim 1 and having a good steering feeling with reduced frictional resistance can be realized.
According to the sixth aspect of the present invention, as the rack bush moves in the axial direction, the convex portion of the housing engages with any one of the slopes on both sides of the corresponding valley portion on the outer periphery of the rack bush. Thus, the amount of movement of the rack bush in the axial direction is regulated. That is, when starting the rack shaft accompanying steering, the rack bush can move minutely in the axial direction together with the rack shaft. Therefore, the rack shaft can be started smoothly, so that the driver does not feel a catch. As a result, the steering feeling is greatly improved.

According to the invention of claim 7, since the curvature radius of the curvature formed by the corresponding valley is made larger than the curvature radius of the curved projection as the projection, the setting of the magnitude relation between the corresponding valley and the projection is set. Easy.
According to the invention of claim 8, in the state where the rack shaft is arranged coaxially with the housing, the convex portion of the housing does not press the corresponding valley on the outer periphery of the rack bush in the radial direction. The crest of the inner periphery on the back side of the unit does not strongly press the rack shaft. Therefore, the frictional resistance given to the rack shaft can be kept low. In addition, when the rack shaft vibrates in the radial direction and the rack shaft is eccentric with respect to the housing, the convex portion of the housing presses the corresponding valley portion on the outer periphery of the rack bush in the radial direction, and The rack shaft can be received in the radial direction by the inner peripheral ridge on the back side. Therefore, the vibration of the rack shaft can be suppressed and the generation of rattle noise can be suppressed.

It is sectional drawing of the rack bush of one embodiment of this invention. It is a schematic sectional drawing of the rack shaft support structure which supports a rack shaft with the rack bush hold | maintained at the housing. It is a schematic sectional drawing of a rack shaft support structure, and has shown the state by which the rack shaft is coaxially arrange | positioned with respect to the housing. FIG. 2 is a schematic cross-sectional view of a rack shaft support structure, showing a state in which a rack bush is slightly moved together with the rack shaft when the rack shaft is started. It is a schematic sectional drawing of a rack axis | shaft support structure, and has shown the state in which the rack axis | shaft was biased to radial direction with respect to the housing. It is a schematic sectional drawing of the rack shaft support structure containing the rack bush of another embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a rack bush 1 according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a rack shaft support structure A including the rack bush 1.
As shown in FIG. 2, the rack bush 1 surrounds a rack shaft 3 for turning that is coaxially inserted into a cylindrical housing 2, and the rack shaft 3 can be slid in the axial direction X1. To support. Although not shown, both ends of the rack shaft 3 protrude to both sides of the housing 2 and are connected to corresponding tie rods via corresponding ball joints. Each tie rod is connected to a corresponding steered wheel via a corresponding knuckle arm.

  As shown in FIG. 1, the rack bush 1 includes a bellows-cylindrical body 4 having a central axis C1 and elastically deformable in the radial direction Y1. The main body 4 has an outer periphery 4a and an inner periphery 4b. The outer periphery 4a has a plurality of valleys 51, 52, 53 and a plurality of peaks 61, 62 that are alternately arranged in the axial direction X1. The inner periphery 4b has a plurality of peak portions 71, 72, 73 and a plurality of valley portions 81, 82 that are alternately arranged in the axial direction X1.

  In the inner periphery 4b, ridges 71, 72, 73 are arranged on the back side of the valleys 51, 52, 53 of the outer periphery 4a, respectively, and the valleys 51, 52, 53 are respectively ridges 71, 72, 73. And in the radial direction Y1. Further, in the inner circumference 4b, valleys 81 and 82 are arranged on the back side of the peaks 61 and 62 of the outer circumference 4a, respectively, and the peaks 61 and 62 are opposed to the valleys 81 and 82 and the radial direction Y1, respectively. doing.

Among the peak parts 71, 72, 73 on the inner periphery 4b, the peak part 72 constitutes a first peak part, and the other peak parts 72, 73 constitute a second peak part. Hereinafter, the peak portion 72 is also referred to as a first peak portion 72, and the peak portions 71 and 73 are also referred to as second peak portions 71 and 73.
The first inner diameter d1, which is the inner diameter of the top portion 72a of the first peak portion 72, is smaller than the outer diameter D of the rack shaft 3 in an unloaded state (d1 <D). Moreover, the 2nd internal diameter d2 which is an internal diameter of the top parts 71a and 72b of each 2nd peak part 71 and 73 is made larger than the 1st internal diameter d1 of the top part 72a of the 1st peak part 72 (d2 <d1). Specifically, the second inner diameter d2 of the top portions 71a and 73a of the second peak portions 71 and 73 is equal to the outer diameter D of the rack shaft 3 as shown in FIG. 1 (d2 = D) in an unloaded state. Or a predetermined value equal to or greater than (d2 ≧ D).

The main body 4 has a first end 41 and a second end 42 that face each other in the axial direction X1. The main body 4 is formed with a first slit 9 extending from the first end 41 and a second slit 10 extending from the second end 42 as slits extending in the axial direction X1. The first slits 9 and the second slits 10 are alternately arranged in the circumferential direction Z1.
Referring again to FIG. 2, the rack stopper 11 and the rack bush 3 are disposed between the inner periphery 2 a of the housing 2 and the rack shaft 3. The rack stopper 11 is made of, for example, an iron annular plate. The rack stopper 11 is fitted and fixed to the enlarged diameter portion 2 b provided on the inner periphery 2 a of the end portion 21 of the housing 2.

  The rack stopper 11 is in contact with a positioning step 2 c provided at the end of the enlarged diameter portion 2 b of the housing 2. Thereby, the axial movement of the rack stopper 11 with respect to the housing 2 is restricted. The rack stopper 11 regulates the axial movement amount of the rack shaft 3 by contacting the housing (not shown) of the ball joint that connects the rack shaft 3 and the tie rod at the stroke end of the rack shaft 3. Fulfills the function of

  The rack bush 1 is fitted and held in the inner periphery 2 a of the housing 2 on the inner back side of the rack stopper 11. A curved convex portion 12 as a convex portion is provided on the inner periphery 2 a of the housing 2. The curved convex portion 12 may be provided singly or a plurality of curved convex portions 12 may be provided apart from each other in the circumferential direction of the housing 2. Moreover, you may extend in the perimeter of the inner periphery 2a of the housing 2 (in this case, it becomes an annular convex part).

3 shows a state in which the rack shaft 3 is coaxially arranged with the housing 2 (a state in which the center axis C3 of the rack shaft 3 coincides with the center axis C2 of the housing 2, that is, the center axis C1 of the rack bush 1 is the housing 2). The center axis line C2 and the center axis line C3 of the rack shaft 3 coincide with each other.
As shown in FIG. 3, the curved convex portion 12 of the housing 2 is disposed between the inner periphery 2 a of the housing 2 and the corresponding valley portion 52 of the outer periphery 4 a of the main body 4 of the rack bush 1. A gap S <b> 1 in the axial direction X <b> 1 is provided between at least one slope of the peak portions 61 and 62 adjacent to the valley portion 52 and the curved convex portion 12. Specifically, the curvature radius R1 of the curvature formed by the valley 52 is made larger than the curvature radius R2 of the curved projection 12. Thereby, the rack bush 1 is allowed to move by a predetermined movement amount in the axial direction X1 with respect to the housing 2.

Further, as shown in FIG. 4, as the rack bush 1 moves relative to the housing 2 in the axial direction X <b> 1, for example, in the direction of a hollow arrow, the convex portion 12 is adjacent to the valley 52. Alternatively, the amount of movement of the rack bush 1 in the axial direction X1 relative to the housing 2 is regulated by engaging with the slope of 62 (the peak 62 in FIG. 4).
Further, as shown in FIG. 3, the gap S <b> 2 in the radial direction Y <b> 1 between the curved convex portion 12 of the housing 2 and the valley portion 52 of the rack bush 1 in a state where the rack shaft 3 is disposed coaxially with the housing 2. Is provided. As shown in FIG. 5, when vibration is generated in the rack shaft 3 and the rack shaft 3 is eccentric with respect to the housing 2, the gap S <b> 2 in the radial direction Y <b> 1 disappears, and the curved convex portion 12 becomes the valley portion of the rack bush 1. 52 is pressed in the radial direction Y1.

  According to the present embodiment, as shown in FIG. 3, in the normal case where the rack shaft 3 moves coaxially with respect to the housing 2, the first peak portion 72 mainly has a frictional resistance to the movement of the rack shaft 3. give. In addition, since the second inner diameter d2 of the top portions 71a and 73a of the second peak portions 71 and 73 is larger than the first inner diameter d1 of the top portion 72a of the first peak portion 72, the rack shaft 3 Even when the is moved with a slight inclination (not shown), the frictional resistance given by the second peak portions 71 and 73 contacting the rack shaft 3 is slight. Accordingly, it is possible to realize the rack bush 1 and the rack shaft support structure A that can suppress the frictional resistance as a whole and improve the steering feeling.

  In particular, the second inner diameter d2 of the top portions 71a and 73a of the second peak portions 71a and 73 is equal to (d2 = D) or equal to or greater than (d2 ≧ D) the outer diameter D of the rack shaft 3 in a no-load state. Therefore, when the rack shaft 3 moves with a slight inclination with respect to the housing 2, the frictional resistance given to the rack shaft 3 by the second peak portions 71 and 73 is very small. Therefore, the frictional resistance as a whole can be suppressed lower, and the steering feeling can be further improved.

  Further, as shown in FIG. 5, when vibration is generated in the rack shaft 3 and the rack shaft 3 is decentered with respect to the housing 2, the adjacent peak portions 71, 72, Since the arch shape formed between 73 is flattened, the contact area of each peak 71, 72, 73 with respect to the rack shaft 3 can be sufficiently increased. Therefore, it is possible to suppress the vibration of the rack shaft 3 and to suppress the generation of noise such as rattle noise accompanying the vibration.

Moreover, since the slits 9 and 10 extending in the axial direction X1 are formed in the main body 4 of the rack bush 1, even if the bellows cylindrical main body 4 is thermally expanded, the deformation due to the thermal expansion is absorbed by the slits 9 and 10. be able to. Therefore, regardless of the temperature change, the frictional resistance can be kept low and a good steering feeling can be maintained.
In particular, since the first slit 9 and the second slit 10 that extend in opposite directions in the axial direction X1 as the slit are used, and the first slit 9 and the second slit 10 are alternately arranged in the circumferential direction Z1, the rack The elasticity in the radial direction Y1 of the bush 1 can be made uniform in the circumferential direction Z1. Therefore, a change in frictional resistance accompanying a temperature change can be further suppressed, and a good steering feeling can be maintained.

  Further, a curved convex portion 12 disposed between the inner periphery 2 a of the housing 2 and the valley portion 52 of the outer periphery 4 a of the rack bush 1 is provided on the inner periphery 2 a of the housing 2. In a state where the rack shaft 3 is arranged coaxially with the housing 2, a gap S <b> 1 in the axial direction X <b> 1 is provided between at least one of the peak portions 61 and 62 on both sides of the valley portion 52 and the curved convex portion 12. . Therefore, there are the following advantages.

  That is, as the rack bush 1 moves in the axial direction X1, the curved convex portion 12 of the housing 2 engages with one of the slopes of the peaks 61 and 62 on both sides of the valley 52 of the outer periphery 4a of the rack bush 1. By doing so, the movement amount of the rack bush 1 in the axial direction X1 is regulated. At the time of starting the rack shaft 3 accompanying the turning, the rack bush 1 can move minutely in the axial direction X1 together with the rack shaft 3. Therefore, since the rack shaft 3 can be started smoothly, the driver does not feel a catch. As a result, the steering feeling is greatly improved.

In addition, since the curvature radius R1 of the curvature formed by the valley 52 is larger than the curvature radius R2 of the curvature projection 12 as the projection, it is easy to set the magnitude relationship between the valley 52 and the curvature projection 12.
Further, with the rack shaft 3 disposed coaxially with the housing 2, a gap S <b> 2 in the radial direction Y <b> 1 is provided between the curved convex portion 12 of the housing 2 and the valley portion 52 of the outer periphery 4 a of the rack bush 1. Yes. Therefore, in a state where the rack shaft 3 is coaxially arranged with the housing 2, the curved convex portion 12 of the housing 2 does not press the valley portion 52 of the outer periphery 4 a of the rack bush 1 in the radial direction Y 1. The peak portion 72 of the inner periphery 4b does not press the rack shaft 3 strongly. Therefore, the frictional resistance given to the rack shaft 3 can be kept low.

  Further, when the rack shaft 3 vibrates in the radial direction Y1 and the rack shaft 3 is eccentric with respect to the housing 2, the curved convex portion 12 of the housing 2 causes the valley 52 of the outer periphery 4a of the rack bush 1 to extend in the radial direction Y1. In the pressed state, the rack shaft 3 can be received in the radial direction Y1 by the peak portion 72 of the inner periphery 4b on the back side of the valley portion 52. Therefore, the vibration of the rack shaft 3 can be suppressed and the generation of rattle noise can be suppressed.

  Next, FIG. 6 shows a rack shaft support structure A1 including a rack bush 101 according to another embodiment of the present invention. As shown in FIG. 6, in the state where the rack bush 101 is mounted between the housing 2 and the rack shaft 3, the inner diameters of the top portions 171a and 173a of the second peak portions 171 and 173 of the inner periphery 4b of the rack bush 101 ( The second inner diameter d2) may be larger than the outer diameter D of the rack shaft 3 (d2> D). In the constituent elements of the embodiment of FIG. 6, the same reference numerals are given to the same constituent elements as those of the embodiment of FIG.

  In the embodiment of FIG. 6, in a normal case where the rack shaft 3 moves coaxially with respect to the housing 2, only the first peak portion 72 is brought into contact with the rack shaft 3, and the friction resistance applied to the rack shaft 3 is increased. It can be kept smaller. The steering feeling can be further improved. Even when the rack bush 101 is unloaded, the inner diameters (second inner diameter d2) of the top portions 171a and 173a of the second peak portions 171 and 173 are larger than the outer diameter D of the rack shaft 3 (d2>). D) It is possible to achieve substantially the same effect.

The present invention is not limited to the above-described embodiment. For example, a curved concave portion as a concave portion is provided on the inner periphery 2 a of the housing 2, and the curved convex portion as a convex portion is provided on the outer periphery 4 a of the main body 4 of the rack bush 1. You may make it provide in.
In addition, various modifications can be made within the scope of the claims of the present invention.

  DESCRIPTION OF SYMBOLS 1; 101 ... Rack bush, 2 ... Housing, 2a ... Inner circumference, 2b ... Diameter expansion part, 2c ... Positioning step part, 3 ... Rack shaft, 3a ... Outer periphery, 4 ... Main body, 4a ... Outer periphery, 4b ... Inner circumference, 41 ... 1st edge part, 42 ... 2nd edge part, 51, 52, 53 ... (outer periphery) trough part, 61, 62 ... (outer periphery) peak part, 72 ... (inner periphery) 1st peak part, 72a (top of first mountain), 71, 73 ... (inner circumference) second mountain, 71a, 73a, 171a, 173a ... (second mountain), top, 81, 82 ... (inner circumference) ) Trough, 9 ... 1st slit, 10 ... 2nd slit, 12 ... curved convex part (convex part), A; A1 ... rack shaft support structure, C1 ... central axis of rack bush, C2 ... (of housing) ) Center axis, C3 ... Center axis (of rack axis), D ... Outer diameter of (rack shaft), d1 ... First inner diameter (inner diameter of top of first peak), 2 ... The second inner diameter (inner diameter of the top of the second crest), S1 ... (axial) clearance, S2 ... (radial) gap, X1 ... axial direction, Y1 ... radially, Z1 ... circumferential direction

Claims (8)

A rack bushing that surrounds a rack shaft for steering inserted coaxially into a cylindrical housing and supports the rack shaft so as to be slidable in the axial direction;
An outer periphery and an inner periphery, and each of the outer periphery and the inner periphery has peaks and valleys alternately arranged in the axial direction, and the outer periphery peaks and valleys are It has a bellows-shaped main body that is radially opposed to the troughs and peaks and elastically deformable in the radial direction,
The inner peripheral ridge includes a first ridge and a second ridge,
The inner diameter of the top of the first peak is made smaller than the outer diameter of the rack shaft in an unloaded state,
The rack bush characterized by the inside diameter of the top part of the said 2nd peak part being made larger than the internal diameter of the top part of the said 1st peak part.   The rack bush according to claim 1, wherein an inner diameter of a top portion of the second peak portion is equal to or equal to or greater than an outer diameter of the rack shaft in an unloaded state.   The rack bush according to claim 1, wherein a slit extending in the axial direction is formed in the main body. The body includes a first end and a second end that are axially opposed.
The slit includes a first slit extending from the first end, and a second slit extending from the second end,
The rack bush according to claim 3, wherein the first slit and the second slit are alternately arranged in a circumferential direction. A tubular housing;
A rack shaft support structure comprising: a rack bush that surrounds a rack shaft coaxially inserted in the housing and supports the rack shaft slidably in an axial direction;
The rack bush has an outer periphery and an inner periphery, and each of the outer periphery and the inner periphery has a crest and a trough alternately arranged in the axial direction, and the outer crest and trough are respectively , A bellows cylindrical body that is radially opposed to the valleys and peaks of the inner circumference and elastically deformable in the radial direction,
The inner peripheral ridge includes a first ridge and a second ridge,
The inner diameter of the top of the first peak is made smaller than the outer diameter of the rack shaft in an unloaded state,
The rack shaft support structure according to claim 1, wherein an inner diameter of a top portion of the second peak portion is made larger than an inner diameter of a top portion of the first peak portion. The housing includes an inner periphery;
The inner periphery of the housing has a convex portion that is disposed between the inner periphery of the housing and the corresponding valley portion of the outer periphery of the rack bush and restricts the amount of movement of the rack bush in the axial direction.
An axial gap is provided between at least one inclined surface of the peak portion on both sides of the corresponding valley portion and the convex portion in a state where the rack shaft is disposed coaxially with the housing. Item 6. The rack shaft support structure according to Item 5.   The rack shaft according to claim 6, wherein a curvature radius of a curve formed by the corresponding valley portion is larger than a curvature radius of the curved convex portion in a state where the rack shaft is disposed coaxially with the housing. Support structure. In a state where the rack shaft is arranged coaxially with the housing, a radial gap is provided between the convex portion of the housing and the corresponding valley portion of the rack bush,
The rack shaft support structure according to claim 6 or 7, wherein when the rack shaft is eccentric with respect to the housing, the convex portion presses the corresponding valley portion in a radial direction.

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