JP2015127187A - Hollow rack bar, steering device, and method of manufacturing hollow rack bar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow rack bar that becomes lighter than ever while securing sufficient flexural strength, a steering device using the hollow rack bar, and a method of manufacturing the hollow rack bar.SOLUTION: A hollow rack bar 1 is formed of a hollow metallic tube 2 with a denture mold, and a hollow resin tube 3 for forming a shank. A protruding end 22 of the hollow metallic tube is brought into intimate contact with and fitted into an inner wall surface of the hollow resin tube 3. Thus, the hollow metallic tube and the hollow resin tube are connected together. A surface of the protruding end 22 assumes a serration shape, a knurled shape or a telescopic shape.

Description

  The present invention relates to a hollow rack bar, a steering device using the hollow rack bar, and a method for manufacturing the hollow rack bar.

  The rack bar includes a tooth portion and a shaft portion adjacent to the tooth portion. When the rack bar is used in a moving body, for example, an automobile steering (steering) device, the rack bar is engaged with the rotational movement of a steering shaft provided with a pinion portion interlocked with the handle of the automobile and interlocked with the pinion portion. A mechanism for changing the direction of the tire or the like is configured by converting into linear motion via the tooth portion.

  The moving body such as an automobile is required to reduce the weight of parts from the viewpoint of reducing fuel consumption by energy saving and reducing the discharge of carbon dioxide and other high environmental loads. The bar is also being considered for weight reduction. The weight reduction of the rack bar is, for example, a method of replacing a part of the outer periphery of the shaft portion of a solid rack bar by wrapping a prepreg made of carbon fiber reinforced resin (Patent Document 1), a method of hollowing the entire rack bar ( Patent Document 2) and the like have been studied.

JP 2009-292180 A JP 2001-009554 A

However, in the steering mechanism, the rack bar is required to have sufficient bending strength as a whole.
In a solid rack bar, this sufficient bending strength is secured by providing a core made of a metal material from the tooth part to the central axis of the shaft part, so that the prepreg made of carbon fiber reinforced resin can be wound around There is a limit to reducing the weight of the entire rack bar. In the hollow rack bar, since the thickness of the metal material of the shaft portion is thin, there is a limit to reducing the weight by simply replacing a part of the metal material on the outer periphery of the shaft portion with a lightweight resin material.

  The present invention relates to a rack bar that is lighter than before, a method of manufacturing the rack bar for ensuring sufficient bending strength of the rack bar, a steering device using these rack bars, and a movable body including the steering device. The purpose is to provide.

The present invention
[1] A hollow rack bar including a tooth portion and a shaft portion adjacent to the tooth portion, wherein the tooth portion is formed of a hollow metal tube including a tooth mold, and the shaft portion is a hollow resin tube. Formed hollow rack bar,
[2] A steering device using the hollow rack bar according to [1], and
[3] A method for producing a hollow rack bar comprising a tooth portion and a shaft portion adjacent to the tooth portion,
The hollow rack bar is formed of a hollow metal tube having a tooth portion having a tooth shape, the shaft portion is formed of a hollow resin tube, and the hollow metal is disposed in an adjacent portion between the hollow metal tube and the hollow resin tube. The hollow resin tube has a connection portion in close contact with the surface of the tube, the hollow resin tube is made of a fiber reinforced resin, the hollow metal tube and the hollow resin tube are fitted, and the connection portion is induction-heated Then, a method of manufacturing a hollow rack bar, comprising a step of melting a resin constituting the hollow resin tube to form a connection portion in which the hollow resin tube is in close contact with the surface of the hollow metal tube.

  According to the present invention, a rack bar that is lighter than before, a rack bar manufacturing method for ensuring sufficient bending strength of the rack bar, a steering apparatus using these rack bars, and a movement including the steering apparatus The body can be provided.

It is a schematic diagram of an example of embodiment of a hollow rack bar. The suitable example of the surface shape of the outer peripheral surface of the protrusion of a hollow metal pipe is shown. 2A and 2B are sectional views, the right half including the protruding end 22 is an outer side view, and FIG. 2C is a sectional view.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Hollow rack bar)
The rack bar 1 of the present invention (hereinafter also referred to as a hollow rack bar) includes a tooth portion including a tooth mold 21 and a shaft portion 3 adjacent to the tooth portion, and the tooth portion is formed of a hollow metal tube 2. On the other hand, the shaft portion 3 is formed of a hollow resin tube.

As shown in FIG. 1, the hollow rack bar 1 is a hollow tube as a whole, and a tooth portion 2 that is a hollow metal tube made of a metal material having a tooth mold 21 that meshes with a pinion portion of a steering shaft on the surface of the tube; The shaft portion 3 is a hollow resin tube made of a resin material which is adjacent to the tooth portion 2 and does not have the tooth mold 21 on the surface.
In the hollow rack bar 1, the end portion of the shaft portion 3 on the side that is not adjacent to the tooth portion 2 may be adjacent to the cap 4 provided with a metal joint or the like, or may be adjacent to other tooth portions. In addition, a double pinion type hollow rack bar may be used.

  Even when the shaft portion 3 is a hollow resin tube, the tooth portion 2 and the shaft portion 3 are appropriately joined by a method as described later (preferably fitted, more preferably the fitting portion is in close contact). Then, the bending strength of the entire rack bar can be ensured by making the section modulus Za of the tooth portion and the section modulus Zb of the shaft portion substantially the same.

For example, the section coefficient Za of the AA ′ cross section (FIG. 1B, the maximum outer diameter 26 mm, the minimum outer diameter 18.9 mm) of the tooth portion of the root of the tooth mold 21 is
Za = Ia / Sa = 8210.9 / 9.876 = 831.4
(Where, Ia is the moment of inertia of the cross section and Sa is the distance from the neutral axis to the farthest end) of the cross section of the shaft portion (outer diameter 26 mm, inner diameter 22 mm) comparable to this Za The section modulus Zb is
Zb = Ib / Sb = 10932.74 / 13 = 841.0
(Where, Ib is the moment of inertia of the cross section and Sb is the distance from the neutral axis to the farthest end).

  According to the hollow rack bar of the present invention, the rack bar can be greatly reduced in weight compared to the prior art by configuring the shaft portion 3 entirely with a hollow resin tube. For example, for a rack bar formed by a steel pipe having a specific gravity of 8 and occupying 2/3 of the total length, the weight of the rack bar can be halved by replacing the shaft with a hollow resin pipe having a specific gravity of 2 of the same thickness.

  From the viewpoint of giving sufficient bending strength to the hollow rack bar 1, the hollow metal tube 2 and the hollow resin tube 3 are preferably fitted and joined. For this reason, the hollow metal tube 2 is preferably fitted with an inner wall surface of the hollow resin tube 3 on the end thereof, preferably a cylindrical protruding end (hereinafter also referred to as a protruding end 22 using the symbols in FIG. 1). ) Is formed.

  From the viewpoint of making the outer diameter of the fitting portion approximately the same as the outer diameter of the shaft portion 3 other than the fitting portion, the outer diameter of the protrusion 22 is set to a size between the outer diameter and the inner diameter of the shaft portion 3. It is preferable.

  After fitting the hollow resin tube 2 to the projecting end 22 of the hollow metal tube 2, the projecting end 22 is induction-heated to melt at least the inner wall surface of the hollow resin tube 2, and the surface of the projecting end 22 of the hollow metal tube 2 is hollow. It is preferable to form an interface between the inner wall surface of the resin tube 3 and to bond the hollow metal tube 2 and the hollow resin tube 3 in close contact with each other.

From the viewpoint of securing a large area of the interface and securing an anchor effect at the interface and designing a desired joining force, the surface of the projecting end 22 of the hollow metal tube 2 is preferably provided with an uneven shape. The concavo-convex shape is formed by arranging a plurality of streaky convex portions adjacent to each other in the circumferential direction, the height of the plurality of streaky convex portions is 1 mm or less, and the gap between adjacent streaky convex portions is 2 mm or less. It is preferable that Further, it is more preferable that flat portions are provided on both end sides of the streaky convex portions, and the plurality of streaky convex portions are provided to protrude outward from the flat portion at a height of 1 mm or less.
Specifically, as shown in FIG. 2, for example, a serrated shape (FIG. 2A), a knurled shape (FIG. 2B), or a bamboo shoot shape (FIG. 2C) is more preferable.

  As for the connecting portion, more preferably, the protruding end 22 formed at the end of the hollow metal tube 2 is fitted to the inner wall surface of the hollow resin tube 3, and the inner wall surface of the hollow metal tube 3 is brought into close contact with the surface of the protruding end 22. The hollow metal tube 2 and the hollow resin tube 3 are intimately connected, and the surface of the protrusion 22 has a serration shape, a knurled shape or a bamboo shape.

  Since the hollow resin tube 3 is subjected to a strong load while the steering device is operated, the hollow resin tube 3 is preferably made of a resin having a strong strength or a fiber reinforced resin in which fibers are mixed.

  High-strength resins include aromatic polyamides such as aramid, para-type aromatic polyamides such as Kepler (DuPont), meta-type aromatic polyamides such as Nomex (DuPont), copolymer-type aromatic polyamides such as Technora (Teijin), Kapton Examples thereof include aromatic polyimides such as (DuPont) and high-strength polyethylenes such as Dyneema (Toyobo).

  As the fiber reinforced resin, it is preferable to mix at least one fiber selected from the group consisting of the above-described high-strength resin fiber, ceramic fiber such as glass, and carbon fiber in the resin, from the viewpoint of bending strength. Carbon fiber reinforced resin in which carbon fiber is mixed with resin is more preferable.

  Resins used for fiber reinforced resins, preferably carbon fiber reinforced resins, are thermosetting resins such as unsaturated polyester, epoxy resin, polyamide resin and phenol resin, or nylon 66, polyacetal, polycarbonate, PET, methyl methacrylate. A thermoplastic resin such as the above can be used, but an epoxy resin is preferable from the viewpoint of weight reduction and securing of bending strength.

Fiber reinforced resin, preferably carbon fiber reinforced resin, is made of the above-mentioned preferred fiber, preferably carbon fiber and resin, to provide bending strength and dimensional stability against heating in the process of manufacturing a hollow rack bar, steering device From the viewpoint of vibration attenuation during operation, the strength is 900 to 3000 MPa, the rigidity is 55 to 350 GPa, the expansion coefficient is 3 ppm or less, the thermal conductivity is 2 to 300 W · m / ° C., and the specific rigidity is 100 GPa / (Mg / m ³ ) or more. Preferably there is.

  A fiber reinforced resin, preferably a carbon fiber reinforced resin, is produced by impregnating a resin into a fiber sheet. By adjusting the orientation of the fiber of the fiber sheet, the strength, rigidity, elasticity, etc. of the entire fiber reinforced resin can also be adjusted. Mechanical properties can be adjusted.

Further, the fiber orientation of the fiber reinforced resin may be designed so that the fiber orientation is different in each part of the hollow resin tube 3 according to the desired physical properties of each part of the shaft portion of the hollow rack bar. . For example, as described above, when the fitting portion between the tooth portion 2 and the shaft portion is melt-bonded by induction heating, the orientation of the portion corresponding to the fitting portion of the hollow resin tube 3 (for example, the orientation is isotropic) And the orientation of other portions (for example, the orientation may be in the column axis direction) may be different.
For example, when steering operation, the hollow resin tube is adjusted by adjusting the fiber orientation so that the elasticity is different at each part of the hollow resin tube so that abnormal noise and vibration originating from the hollow rack bar can be suppressed. May be designed.

  The shaft portion 3 of the hollow rack bar 1 may be incorporated in a structure that is received by a resin bush. In this case, since grease is disposed between the surface of the hollow resin tube and the bush, the surface of the hollow resin bar Therefore, the surface of the hollow resin tube has an appropriate roughness, preferably Ra is 0.4 or less, or appropriate irregularities are formed.

  The metal material constituting the hollow metal tube may be selected according to the degree of load received during the steering operation, but is preferably made of steel from the viewpoint of formability and durability.

  From the viewpoint that a hollow resin tube can be formed by laminating various different fiber reinforced resin sheets, it is preferable to form the hollow resin tube of the shaft portion by applying a sheet winding method to the fiber reinforced resin sheet.

According to the sheet winding method, for example, first, winding is performed using a thermoplastic resin-based fiber reinforced resin sheet, and then winding is performed using a thermosetting resin-based fiber reinforced resin sheet. A hollow resin tube having a two-layer structure in which the outer layer is a thermosetting resin base can be obtained.
As will be described later, when such a hollow resin tube is induction-heated by fitting the hollow resin tube 3 to the protruding end 22 of the hollow metal tube 2, the vicinity of the protruding end 22 of the inner layer is melted and closely connected to each other. While forming the portion, the outer layer of the thermosetting resin base has an effect that it is hardly affected by the temperature rise due to the heating of the inner layer.

  According to the sheet winding method, for example, a fiber reinforced resin sheet whose fiber orientation is oriented at 90 ° with respect to the tube axis is wound, and then fiber reinforced with the fiber orientation oriented at 45 ° with respect to the tube axis. If the sheet is wound, a hollow resin tube 3 having a two-layer structure in which the fiber orientation is different between the inner layer and the outer layer can be obtained. Such a hollow resin tube 3 can have stable durability against multi-mode vibration applied to the hollow resin tube.

  According to the sheet winding method, a hollow resin tube having various cross-sectional shapes such as a circle, a rectangle, an ellipse, and an oval can be formed by selecting a die, and an inner diameter and / or an outer diameter in the tube axis direction can be formed. Hollow resin that can be made uniform, tapered, or stepped, and the inner diameter and / or outer diameter in the tube axis direction is uniform, tapered, or stepped, respectively. A tube can be obtained. Such a hollow resin tube can be selected according to the connection mode between the hollow rack bar and another instrument.

[Preferred manufacturing method of hollow rack bar]
The hollow metal tube 2 provided in the hollow rack bar includes a step 1 for preparing a hollow metal tube material, a step 2 for quenching and hardening the back surface portion of the outer surface portion for forming a desired tooth shape of the hollow metal tube material, In a state where the cored bar is inserted into the internal cavity of the hollow metal tube material whose back surface is quenched and hardened, the tooth shape is preferably 100 using a forging die having a transfer die surface corresponding to the shape of the tooth shape. It can be manufactured through a step 3 of forming a hollow metal tube 2 constituting a tooth portion by forging at ˜600 ° C. Japanese Patent Laid-Open No. 2007-253190 discloses detailed manufacturing conditions.

  Furthermore, in the said process 2, it is preferable to quench-harden the said back part by high frequency heating. In the step 3, the hollow metal tube material is preferably forged in a cold state.

The steering gear ratio (steering wheel rotation angle / tire cutting angle) of the steering device depends on the specific stroke characteristics determined by the spacing and shape of the teeth of the hollow rack bar. Therefore, for example, by setting the specific stroke lower than the pinion rotation angle near the center of the stroke of the hollow rack bar, the change in the tire turning angle is reduced near the center of the steering wheel to prevent wobbling during straight travel. For this reason, the specific stroke characteristic is generally a VGR region that gradually changes near the center of the stroke.
According to the step 3, since it is only necessary to prepare such a VGR region as a casting mold, the VGR region can be easily formed.

  As the hollow resin tube 3, for example, a commercially available carbon fiber reinforced resin tube having a desired outer diameter and wall thickness can be purchased and used.

  For example, the hollow metal tube 2 obtained through the above steps 1 to 3 and the hollow resin tube 3 is inserted and fitted into the projecting end 22 of the hollow metal tube 2 so that the hollow metal tube and the hollow resin tube After forming the connection portion, the connection portion is induction-heated to melt the resin constituting the hollow resin tube 3, and through a step of forming a connection portion in which the hollow metal tube 2 and the hollow resin tube 3 are in close contact with each other, The hollow rack bar 1 can be manufactured.

  The fitting of the hollow metal tube 2 and the hollow resin tube 3 can be performed, for example, by fitting the inner wall surface of the hollow resin tube 3 so as to cover the protruding end 22 of the hollow metal tube 3. If the resin constituting the hollow resin tube 3 is a thermoplastic resin, when the connecting portion between the hollow metal tube 2 and the hollow resin tube 3 is induction-heated, the surface of the projecting end 22 becomes hot, and the hollow resin tube forms the connecting portion. The resin constituting at least the inner wall surface is melted, and the surface of the protrusion 22 and the inner wall surface of the hollow resin tube are brought into close contact with each other.

  Further, if the resin constituting the hollow resin tube 3 is a thermoplastic resin having a high polarity, the resin itself may be melted at a high temperature by induction heating, and may be brought into close contact with the surface of the protrusion 22.

  If the resin constituting the hollow resin tube 3 is a thermosetting resin, the protruding end 22 of the hollow metal tube is covered and fitted so as to be soft enough to mold the hollow resin tube, and pressure is applied to the protruding end 22. After the inner wall surface of the hollow resin tube 3 is brought into close contact with the surface, the connection portion may be induction-heated to cure the inner wall surface of the hollow resin tube.

  From the viewpoint of increasing the bonding force between the metal constituting the projecting end 22 and the resin constituting the hollow resin tube, the portion where the projecting end 22 and the hollow resin tube are fitted, preferably the outer peripheral surface of the projecting end 22, is preferably subjected to induction heating. It is preferable to arrange, preferably apply, a silane coupling agent.

  When the hollow metal tube and the hollow resin tube are fitted, for example, the hollow resin tube is heated in a heating furnace or the like to expand or have elasticity so as to have an inner diameter corresponding to the outer diameter of the protrusion 22. Thus, the hollow resin tube can be easily inserted into the protruding end 22. The heating is preferably performed between 50 ° C. and the heat resistant temperature of the resin constituting the hollow resin tube (for example, 110 ° C. in the case of an epoxy resin having a heat resistant temperature of about 110 to 250 ° C.).

  The heating temperature of the hollow resin tube 3 can be set according to the inner diameter of the hollow resin tube with respect to the outer diameter of the protrusion 22, the type of thermoplastic resin, the softening point, the expansion coefficient, and the like. For example, in the case of polyamide, the temperature is preferably about 130 to 150 ° C. A suitable lower limit and upper limit of the heating temperature can be designed in consideration of maintaining the accuracy of the hollow resin tube and considering the insertion efficiency of the hollow resin tube into the protruding end 22.

  When the above preferable manufacturing conditions are combined, a more preferable aspect of the manufacturing method of the hollow rack bar including the tooth portion and the shaft portion adjacent to the tooth portion is, for example, a hollow metal tube 2 in which the tooth portion has a tooth shape. The shaft portion is formed of a hollow resin tube 3 and has a connecting portion in which the hollow metal tube and the hollow resin tube are in close contact with each other in the adjacent portion of the hollow metal tube and the hollow resin tube. A connection portion made of reinforced resin, in which the hollow metal tube and the hollow resin tube are fitted together, the connection portion is induction-heated to melt the resin constituting the hollow resin tube, and the hollow metal tube and the hollow resin tube are in close contact with each other Forming a step.

[Steering device and moving body]
The following useful effects are expected from the steering device of the present invention having a configuration in which the hollow rack bar and the steering shaft of the present invention are combined, and the moving body of the present invention including the steering device.
(1) The weight of the hollow rack bar is significantly reduced, so that the steering device is reduced in weight. As a result, the movable body is reduced in weight, and the fuel efficiency of the movable body is improved.
(2) Since the shaft portion of the hollow rack bar has elasticity derived from a resin material that cannot be made of metal, abnormal noise and vibration during operation of the steering device are reduced.
(3) Since the processing such as heat treatment and finishing such as grinding is not required for the shaft portion of the hollow rack bar, the manufacturing efficiency is improved.
(4) Wear of a member that comes into contact with a shaft portion such as a resin bush that receives the shaft portion is reduced.

  The hollow rack bar of the present invention is suitably used for an electric power steering apparatus that has been widely used in recent years, for example, a column type (C-EPS), a pinion type (P-EPS), a dual pinion type (DP-EPS), etc. it can.

  From the viewpoint that the movable body of the present invention is remarkable in the above effects (1) to (4), a ship, an automobile, and an airplane including the steering device of the present invention are preferable, and an automobile including the steering device of the present invention is more preferable. Large vehicles such as trailers and trucks equipped with the steering device of the present invention are more preferable.

1 Hollow rack bar 2 Teeth (hollow metal tube)
21 Tooth type 22 Protrusion 3 Shaft (hollow resin tube)
4 Cap

Claims (6)

A hollow rack bar comprising a tooth portion and a shaft portion adjacent to the tooth portion,
The tooth portion is formed of a hollow metal tube having a tooth shape;
A hollow rack bar in which the shaft portion is formed of a hollow resin tube. In the adjacent part of the hollow metal tube and the hollow resin tube,
The hollow rack bar according to claim 1, further comprising a connection portion in which the hollow metal tube and the hollow resin tube are in close contact with each other. A protruding end is formed at the end of the hollow metal tube,
In the connecting portion, the protruding end of the hollow metal tube and the inner wall surface of the hollow resin tube are fitted, and the inner wall surface of the hollow resin tube is in close contact with the surface of the protruding end, and the hollow metal tube and the Hollow resin pipe is connected,
The hollow rack bar according to claim 2, wherein a surface of the tip has a serration shape, a knurled shape, or a bamboo shoot shape.   The hollow rack bar according to claim 1, wherein the hollow resin tube is made of a fiber reinforced resin.   A steering device using the hollow rack bar according to any one of claims 1 to 4. A method for producing a hollow rack bar comprising a tooth portion and a shaft portion adjacent to the tooth portion,
The hollow rack bar is
The tooth portion is formed of a hollow metal tube having a tooth shape, the shaft portion is formed of a hollow resin tube,
In the adjacent part of the hollow metal tube and the hollow resin tube,
Having a connection part where the hollow resin tube is in close contact with the surface of the hollow metal tube;
The hollow resin tube is made of fiber reinforced resin,
Fitting the hollow metal tube and the hollow resin tube,
A method for manufacturing a hollow rack bar, comprising the step of melting the resin constituting the hollow resin tube by induction heating the connection portion to form a connection portion in which the hollow resin tube is in close contact with the surface of the hollow metal tube. .

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