JP7338252B2 - Rack shaft, steering device, and rack shaft manufacturing method - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a rack shaft, a steering device, and a method of manufacturing a rack shaft.

2. Description of the Related Art A steering device having a rack shaft and a pinion that convert rotation of a steering wheel into linear motion is known. For example, the rack shaft is provided with rack teeth on one side of both sides across the axis when viewed from the axial direction, and a guided portion supported by the rack guide is provided on the other side. The rack teeth are formed, for example, by forging (see Patent Documents 1 and 2, for example).

Japanese Patent Application Laid-Open No. 2018-24901 JP 2018-47473 A

When the rack teeth are formed by forging, the side surface of a columnar intermediate material (work) is pressed by a mold or the like, so that the vicinity of the rack teeth expands radially outward to form an expanded portion. Here, for example, when polishing the guided portion using a tape or the like with abrasive grains, the expanded portion becomes an obstacle and the tape or the like breaks, making it difficult to uniformly polish the entire guided portion. may become.

The present disclosure has been made in view of the above problems. An object of the present invention is to provide a manufacturing method and a steering device having the rack shaft.

In order to achieve the above object, a rack shaft according to one aspect of the present disclosure is a forged rack shaft extending in the axial direction of the shaft center, and having two sides sandwiching the shaft center when viewed from the axial direction. rack teeth arranged along the axial direction provided on one side of the , when viewed from the axial direction, an expanded portion is provided that bulges radially outward from an arc centered on the axial center, and is a first surface that is a surface of the rack teeth and a surface of the guided portion. The second surface is the blasted surface.

When the rack teeth are formed by forging, for example, since the side surface of the columnar intermediate material is pressed radially inward, an expanded portion that bulges radially outward is formed in the vicinity of the rack teeth. Here, for example, when polishing the guided portion using a tape with abrasive grains, it becomes difficult to polish the second surface of the guided portion because the expanded portion becomes an obstacle. Moreover, since scale remains on the first surface of the rack teeth, it is also necessary to remove the scale. As described above, in the case where the expansion portion is formed on the rack shaft, the second surface can be surface-treated by blasting the first surface and the second surface of the rack shaft. can be removed.

A steering device according to one aspect of the present disclosure includes the rack shaft described above and the rack guide that supports the rack shaft. According to this, when the expanded portion is formed in the rack shaft, the second surface can be surface-treated and the first surface can be treated by blasting the first surface and the second surface of the rack shaft. scale can be removed from the

A method for manufacturing a rack shaft according to one aspect of the present disclosure includes rack teeth provided on one side of both sides across an axial center of a rack shaft and arranged along the axial direction of the axial center, and A rack shaft manufacturing method comprising: a guided portion provided on the other side of sandwiched sides and supported by a rack guide, the method comprising: forming the rack teeth by forging; and surface of the rack teeth. and a step of blasting a first surface which is the surface of the guided portion and a second surface which is the surface of the guided portion to form a blasted surface.

According to this, as described above, when the expanded portion is formed on the rack shaft, the second surface can be surface-treated by blasting the first surface and the second surface of the rack shaft, It becomes possible to remove the scale from the first surface. In addition, the blasting process can shorten the processing time of the second surface as compared with the conventional polishing using a tape or the like, resulting in labor saving and manufacturing cost reduction. Furthermore, if the blasting treatment of the first surface and the blasting treatment of the second surface are performed simultaneously, the processing time of the surface treatment process can be further shortened. By changing the particle size of the particles used for the blasting treatment of the first surface and the particle size of the particles used for the blasting treatment of the second surface, the arithmetic mean roughness of the first surface and the second surface can be made different. can be done.

According to the present disclosure, it becomes easy to surface-treat the guided portion supported by the rack guide in the rack shaft formed by forging the rack teeth.

FIG. 1 is a schematic diagram of the steering device of this embodiment. FIG. 2 is a front view of the steering gear unit of this embodiment. FIG. 3 is a cross-sectional view taken along line AA of FIG. 4 is an enlarged cross-sectional view of the rack shaft and the rack guide in FIG. 3. FIG. FIG. 5 is an enlarged schematic diagram of the rack shaft. FIG. 6 is a plan view of the rack shaft of this embodiment. FIG. 7 is a front view of the rack shaft of this embodiment. FIG. 8 is a schematic diagram showing a state in which the rack shaft of the present embodiment is being forged. FIG. 9 is a schematic diagram showing a state in which the rack shaft of the present embodiment is subjected to shot blasting.

Hereinafter, the present disclosure will be described in detail with reference to the drawings. It should be noted that the present disclosure is not limited by the modes for implementing the disclosure below (hereinafter referred to as embodiments). In addition, components in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

FIG. 1 is a schematic diagram of the steering device of this embodiment. FIG. 2 is a front view of the steering gear unit of this embodiment. FIG. 3 is a cross-sectional view taken along line AA of FIG. As shown in FIG. 1, the steering device 80 includes a steering wheel 81, a steering shaft 82, a universal joint 84, a lower shaft 85, a universal joint 86, a pinion shaft 87, and a steering gear unit 1. .

As shown in FIG. 1, steering wheel 81 is connected to steering shaft 82 . One end of the steering shaft 82 is connected to the steering wheel 81 . The other end of steering shaft 82 is connected to universal joint 84 . One end of the lower shaft 85 is connected to the steering shaft 82 via a universal joint 84 . The other end of lower shaft 85 is connected to pinion shaft 87 via universal joint 86 .

As shown in FIGS. 1 and 3, the steering gear unit 1 includes a pinion 3, a rack shaft 4, a rack guide 5, a housing 10, a rack guide screw 15, and a coil spring 16. A pinion shaft 87 is connected to the pinion 3 . The pinion 3 meshes with the rack shaft 4. - 特許庁When the pinion 3 rotates, the rack shaft 4 moves in the width direction of the vehicle. The pinion 3 and rack shaft 4 convert the rotary motion transmitted to the pinion shaft 87 into linear motion. The rack shaft 4 is connected to tie rods 89 . The movement of the rack shaft 4 changes the angle of the wheel. It should be noted that the operation of the steering wheel 81 may be converted into an electric signal, and the angle of the wheel may be changed by the electric signal. That is, a steer-by-wire system may be applied to the steering device 80 .

As shown in FIG. 1 , the steering device 80 includes an electric motor 93 , a torque sensor 94 , a vehicle speed sensor 95 and an ECU (Electronic Control Unit) 90 . The electric motor 93 , torque sensor 94 and vehicle speed sensor 95 are electrically connected to the ECU 90 . The electric motor 93 is, for example, a brushless motor, but may be a motor including brushes (sliders) and commutators (commutators). The torque sensor 94 is attached to the pinion 3, for example. The torque sensor 94 outputs the steering torque transmitted to the pinion 3 to the ECU 90 through CAN (Controller Area Network) communication. The vehicle speed sensor 95 detects the traveling speed (vehicle speed) of the vehicle body on which the steering device 80 is mounted. A vehicle speed sensor 95 is provided on the vehicle body and outputs the vehicle speed to the ECU 90 through CAN communication.

The ECU 90 controls operation of the electric motor 93 . The ECU 90 acquires signals from each of the torque sensor 94 and the vehicle speed sensor 95 . Electric power is supplied to the ECU 90 from a power supply device 99 (for example, a vehicle-mounted battery) while an ignition switch 98 is on. The ECU 90 calculates an assist steering command value based on the steering torque and vehicle speed. The ECU 90 adjusts the power value supplied to the electric motor 93 based on the assist steering command value. The ECU 90 acquires induced voltage information from the electric motor 93 or information output from a resolver or the like provided in the electric motor 93 .

As shown in FIG. 3 , the pinion 3 is supported by the housing 10 via bearings 11 and 12 . The pinion 3 has a plurality of pinion teeth 31 . A rack guide screw 15 is attached to the housing 10 . For example, a thread groove provided on the outer peripheral surface of the rack guide screw 15 meshes with a thread groove provided on the inner peripheral surface of the housing 10 .

A coil spring 16 is arranged between the rack guide screw 15 and the rack guide 5 . A coil spring 16 presses the rack guide 5 against the rack shaft 4 . A rack guide 5 supports the rack shaft 4 . A rack guide 5 presses the rack shaft 4 against the pinion 3 . Thereby, backlash between the rack shaft 4 and the pinion 3 is suppressed.

4 is an enlarged cross-sectional view of the rack shaft and the rack guide in FIG. 3. FIG. FIG. 5 is an enlarged schematic diagram of the rack shaft. FIG. 6 is a plan view of the rack shaft of this embodiment. FIG. 7 is a front view of the rack shaft of this embodiment.

As shown in FIGS. 3 and 4 , the rack guide 5 includes a body portion 51 and guide portions 53 . The body portion 51 has a substantially columnar shape. The body portion 51 is made of, for example, metal. The body portion 51 has one end face 51a and the other end face 51b. The other end surface 51b is arranged on the opposite side of the one end surface 51a.

Specifically, one end face 51a is the right end face in FIG. 3 and the lower end face in FIG. The other end face 51b is the left end face in FIG. 3 and the upper end face in FIG. One end surface 51a is in contact with the coil spring 16 as shown in FIG. The other end face 51b is formed in a semi-cylindrical shape. The guide portion 53 is provided on the other end surface 51b. The guide portion 53 is made of resin or the like, for example. The rack guide 5 does not necessarily have to be of the so-called sliding type. The rack guide 5 may be of a so-called rolling type. That is, the rack guide 5 may have rolling elements.

The rack shaft 4 is a forged product formed by forging. As shown in FIGS. 3 to 7, the rack shaft 4 extends in the axial direction of the axis Ax. Hereinafter, the axial direction of the axis Ax of the rack shaft 4 is simply referred to as "axial direction". The rack shaft 4 includes rack teeth 41 and guided portions 42 . As shown in FIGS. 4, 5 and 7, the rack teeth 41 are positioned on one side of both sides of the axis Ax when viewed from the axial direction, and are positioned on the other side of the two sides. , the guided portion 42 is positioned. Specifically, "one side" is the upper side in FIGS. 4, 5 and 7, and "the other side" is the lower side in FIGS. The rack tooth 41 and the guided portion 42 are located on opposite sides of each other with the axis Ax interposed therebetween.

As shown in FIG. 3 , the rack teeth 41 mesh with the pinion teeth 31 . As shown in FIGS. 6 and 7, the plurality of rack teeth 41 are arranged along the axial direction. As shown in FIGS. 5 and 7, the rack tooth 41 has a tooth tip 411 which is a tooth top and a tooth bottom 412 which is a tooth trough. Moreover, the surface of the rack tooth 41 is also called the first surface 4a. As shown in FIGS. 3 and 4, the surface of the guided portion 42 is a guided surface 421 and is also referred to as a second surface 4b. The guided surface 421 (second surface 4b) has an arc shape centered on the axis Ax when viewed from the axial direction.

The guided surface 421 (second surface 4 b ) is supported by the guide portion 53 while sliding on the surface of the guide portion 53 . The guided surface 421 is provided with a groove 422 extending linearly along the axial direction. The groove 422 is a recess that is recessed radially inward. By filling the grooves 422 with lubricant, the frictional resistance between the guided surface 421 of the rack shaft 4 and the guide portion 53 of the rack guide 5 is suppressed.

The structure of the rack shaft 4 will be described in more detail below with reference to FIG. As shown in FIG. 5 , a first expanding portion 470 and a second expanding portion 480 are provided on both left and right sides of the rack shaft 4 . As described above, the rack teeth 41 are positioned on one of the upper and lower sides sandwiching the axis Ax (upper side in FIG. 5), and the other side sandwiching the axis Ax (lower side in FIG. 5). The portion to be guided 42 is positioned at . A first corner portion 43, a second corner portion 44, a third corner portion 45, and a fourth corner portion 46 are positioned on the one side when viewed from the axial direction. The first corner portion 43 and the second corner portion 44 are located at both ends of the tip 411 of the rack tooth 41 .

The third corner portion 45 and the fourth corner portion 46 are located on the other side (lower side in FIG. 5) than the first corner portion 43 and the second corner portion 44 . A straight line L1 connecting the third corner portion 45 and the fourth corner portion 46 is positioned radially inward of the bottom 412 and closer to the axis Ax. A first portion 47 is positioned on the other side (lower side in FIG. 5) of the third corner portion 45, and a second portion 48 is positioned on the other side (lower side in FIG. 5) of the fourth corner portion 46. is located. A straight line L2 connecting the first portion 47 and the second portion 48 is substantially parallel to the tip 411, the bottom 412 and the straight line L1. A straight line L2 passes through the axis Ax. The guided surface 421 (second surface 4b) has an arc shape centered on the axis Ax when viewed from the axial direction.

Virtual arcs 423 and 424 indicated by two-dot chain lines are also arc-shaped centering on the axis Ax. Arc 423 connects first corner 43 and first portion 47 . Arc 424 connects second portion 48 and second corner 44 . The first corner portion 43 and the third corner portion 45 are connected by a first connecting portion 431 . The second corner portion 44 and the fourth corner portion 46 are connected by a second connecting portion 441 . The first connecting portion 431 and the second connecting portion 441 are arcuate around the axis Ax when viewed from the axial direction. The third corner portion 45 and the first portion 47 are connected by a third connecting portion 451 . The fourth corner portion 46 and the second portion 48 are connected by a fourth connecting portion 461 . The third connecting portion 451 and the fourth connecting portion 461 extend linearly along the vertical direction in FIG.

Here, the portion surrounded by the arc 423, the first connecting portion 431, and the third connecting portion 451 is the first expansion portion 470 (expansion portion). That is, the first expanded portion 470 is a portion that expands radially outward from the arc 423 centered on the axis Ax. A portion surrounded by the arc 424, the second connecting portion 441, and the fourth connecting portion 461 is a second expansion portion 480 (expansion portion). That is, the second expanded portion 480 is a portion that expands radially outward from the arc 424 centered on the axis Ax.

Further, the first surface 4a of the rack tooth 41 and the second surface 4b, which is the surface of the guided portion 42, are blasted surfaces, and the arithmetic mean roughness Ra is, for example, 0.2 or more and 0.6 or less. . The blasting treatment will be described in detail in the rack shaft manufacturing method.

Next, a method for manufacturing the rack shaft will be described. FIG. 8 is a schematic diagram showing a state in which the rack shaft of the present embodiment is being forged. FIG. 9 is a schematic diagram showing a state in which the rack shaft of the present embodiment is subjected to shot blasting.

The method of manufacturing the rack shaft 4 includes a step of forming the rack teeth 41 by cold forging (forging), and forming a first surface 4 a that is the surface of the rack teeth 41 and a guided surface 421 (first surface) that is the surface of the guided portion 42 . and blasting the second surface 4b) to form a blasted surface.

The structure of a forging apparatus 100 for cold forging will be described. As shown in FIG. 8 , the forging device 100 includes a punch 101 , a receiving member 102 , a first support 103 and a second support 104 . The punch 101 is a plate-like member, and has an uneven portion 101a on its lower surface. The uneven portion 101 a has a shape corresponding to the rack teeth 41 . A concave portion 102 a is formed in the upper surface of the receiving member 102 . A cylindrical intermediate material 140 is accommodated in the recess 102a. The first support base 103 supports the receiving member 102 . The second support 104 supports the first support 103 . The procedure for manufacturing the rack shaft will be described below.

First, the intermediate material 140 is accommodated in the concave portion 102a of the receiving member 102. As shown in FIG. Then, the punch 101 is arranged on the intermediate material 140 . The punch 101 is lowered, and the side surface of the intermediate material 140 is pressed downward by the uneven portion 101a of the punch 101 . The rack teeth 41 are formed by this cold forging.

At this time, as described with reference to FIG. 5, the intermediate material 140 is formed with the first expanded portion 470 and the second expanded portion 480 on both left and right sides thereof. That is, by pressing the intermediate material 140 downward with the punch 101, part of the material of the intermediate material 140 moves to the left and right sides and expands, resulting in the first expanded portion 470 and the second expanded portion 480 shown in FIG. It is formed. Note that cold forging is performed multiple times using a plurality of receiving members 102 having different shapes.

Cold forging is followed by blasting. The blast guns 61 and 62 shown in FIG. 9 are held in a left-right separated state. A pipe 61 a is connected to the blast gun 61 . A pipe 62 a is connected to the blast gun 62 . In this embodiment, wet blasting is performed as blasting. Wet blasting is a method in which a slurry (mixed liquid) in which particles 6 (abrasive grains) and a liquid are mixed is sprayed onto an object to be processed using compressed air. Stone, glass, plastic, or the like can be applied as the material of the particles 6 (abrasive grains). The particle size of the particles 6 is, for example, 50 μm or more and 200 μm or less. As the liquid, water or water mixed with a chemical solution can be applied .

As shown in FIG. 9, the blast gun 61 and the rack teeth 41 are arranged to face each other, and the blast gun 62 and the guided surface 421 are arranged to face each other. Particles 6 (abrasive grains) and liquid are ejected by compressed air from the tips of blast guns 61 and 62 through pipes 61a and 62a. The particles 6 ejected from the blast gun 61 hit the surface (first surface 4a) of the rack tooth 41, and the surface (first surface 4a) becomes a blasted surface. Small unevenness is formed on the blasted surface.

The particles 6 ejected from the blast gun 62 collide with the guided surface 421 (second surface 4b), and the guided surface 421 (second surface 4b) becomes a blasting surface. In particular, since scale remains on the surface of the rack teeth 41, the blasting process can simultaneously form the blasted surface and remove the scale. The blasting treatment for the first surface 4a and the blasting treatment for the second surface 4b may be performed at the same time, or may be performed at separate timings. As for the air pressure and the blowing time when the compressed air is blown, for example, 0.2 MPa for 20 seconds or 0.4 MPa for 10 seconds can be applied. The arithmetic average roughness Ra of the surface of the rack teeth 41 and the guided surface 421 after blasting is, for example, 0.2 or more and 0.6 or less. The arithmetic mean roughness Ra is measured using a surface roughness tester according to JIS B 0601-2001.

As explained above, the steering device 80 includes the rack shaft 4 and the rack guide 5 . The rack shaft 4 includes rack teeth 41 provided on one side across the axis Ax and a guided portion 42 provided on the other side and supported by the rack guide 5 when viewed from the axial direction. . A first inflatable portion 470 and a second inflatable portion 480 are provided that bulge outward in the radial direction from the arcs 423 and 424 centering on the axis Ax. The first surface 4a of the rack tooth 41 and the second surface 4b, which is the surface of the guided portion 42, are blasted surfaces.

When the rack teeth 41 are formed by forging, the side surfaces of the columnar intermediate material 140 are pressurized radially inward. is formed. Here, for example, when polishing the guided portion 42 using a tape with abrasive grains, the first expanded portion 470 and the second expanded portion 480 become an obstacle and the tape is damaged, causing the guided portion 42 to be guided. It becomes difficult to uniformly polish the second surface 4b, which is the surface 421 .

Moreover, since scale remains on the first surface 4 a of the rack teeth 41 , it is necessary to remove the scale from the rack teeth 41 . As described above, in the case where the first expanded portion 470 and the second expanded portion 480 are formed on the rack shaft 4, the first surface 4a and the second surface 4b of the rack shaft 4 are blasted surfaces so that the second surface 4b can be uniformly surface treated and scale can be removed from the first surface 4a.

Further, the method for manufacturing the rack shaft 4 includes a step of forming the rack teeth 41 by forging, and performing blasting on the first surface 4a, which is the surface of the rack teeth 41, and the second surface 4b, which is the surface of the guided portion 42. and a blasted surface.

The method for manufacturing the rack shaft 4 of the present embodiment does not require polishing using a tape or the like with abrasive grains. Even if the first expanded portion 470 and the second expanded portion 480 are formed on the rack shaft 4, the second surface 4b can be surface-treated by blasting the first surface 4a and the second surface 4b of the rack shaft 4. , and scale can be removed from the first surface 4a. In addition, the blasting process can shorten the processing time of the second surface 4b more than the conventional polishing using a tape. Therefore, the present embodiment can save labor and further reduce the manufacturing cost as compared with the conventional example. Furthermore, if the blasting treatment of the first surface 4a and the blasting treatment of the second surface 4b are performed simultaneously, the processing time of the surface treatment process can be further shortened. By changing the particle size of the particles 6 used in the blasting treatment of the first surface 4a and the particle size of the particles 6 used in the blasting treatment of the second surface 4b, the arithmetic mean roughness of the first surface 4a and the second surface 4b The height Ra can be made different.

4 rack shaft 4a first surface 4b second surface 41 rack tooth 42 guided portion 5 rack guide 80 steering device 470 first expansion portion (expansion portion)
480 second expansion part (expansion part)
Ax axis

Claims (4)

A forged rack shaft extending in the axial direction of the shaft center,
rack teeth provided on one side of both sides of the axial center when viewed from the axial direction and arranged along the axial direction;
a guided portion provided on the other side of both sides sandwiching the axis and supported by the rack guide;
an expansion portion that expands radially outward from a circular arc centered on the axial center when viewed from the axial direction;
The surface of the guided portion is provided with a groove that is a concave portion that is recessed radially inward, extends linearly along the axial direction, and is filled with a lubricant,
The first surface, which is the surface of the rack teeth, and the second surface, which is the surface of the guided portion, are wet-blasted surfaces, and the arithmetic mean roughness Ra of the wet-blasted surfaces is 0.2 or more and 0.2. is 6 or less;
rack axis. A rack shaft according to claim 1;
and the rack guide that supports the rack shaft,
steering device. A rack tooth provided on one of both sides sandwiching the axis of a rack shaft and arranged along the axial direction of the axis, and a rack tooth provided on the other side of the two sides sandwiching the axis. A rack shaft manufacturing method comprising a guided portion supported by a guide,
a first step of forming the rack teeth in the intermediate material by forging and forming an expanded portion that expands radially outward from an arc centered on the axial center when viewed from the axial direction;
a second step of performing wet blasting on the first surface, which is the surface of the rack teeth, and the second surface, which is the surface of the guided portion, to form a wet blasted surface;
A manufacturing method of a rack axis. Before the first step, the surface of the intermediate material serving as the guided portion is provided with a concave portion that is concave inward in the radial direction, extends linearly along the axial direction, and is filled with a lubricant. A groove is provided in advance for
The arithmetic mean roughness Ra of the wet-blasted surface after the second step is 0.2 or more and 0.6 or less.
The method for manufacturing the rack shaft according to claim 3 .

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