Rack-and-pinion mechanism

Abstract

This rack-and-pinion mechanism comprises: a housing (10); a rack shaft (11) that is reciprocably supported by the housing (10) and has rack teeth on at least a portion of the outer periphery thereof; a pinion shaft (107) that is rotatably supported by the housing (10) and has pinion teeth which mesh with the rack teeth; a hole cover (13) that is externally fitted to the housing (10) and covers a portion of the pinion shaft (107); and an annular lipped seal (20) that is sandwiched between the outer peripheral surface of the housing (10) and the inner peripheral surface of the hole cover (13).

Description

rack and pinion mechanism

[0001] The present invention relates to a rack and pinion mechanism.

[0002] The following Patent Document 1 describes a steering device in which a cover member is press-fitted into a housing that accommodates a portion of a pinion shaft and a rack shaft, covering the portion of the pinion shaft that protrudes from an opening in the housing.

[0003] Patent No. 6705311 specification

[0004] In a rack and pinion mechanism, if a hole cover that covers the periphery of the pinion shaft is press-fitted into a housing that supports the rack shaft, a press-fitting machine is required, which increases manufacturing costs.The present invention aims to reduce the manufacturing cost of fitting a hole cover that covers at least a portion of the pinion shaft into a housing that supports the rack shaft in a rack and pinion mechanism, while ensuring a tight seal between the housing and the hole cover.

[0005] In order to achieve the above object, a rack and pinion mechanism according to one aspect of the present invention includes a housing, a rack shaft supported by the housing so as to be able to move back and forth and having rack teeth on at least a portion of its outer periphery, a pinion shaft supported by the housing so as to be able to rotate and having pinion teeth that mesh with the rack teeth, a hole cover fitted onto the housing and covering a portion of the pinion shaft, and an annular lipped seal sandwiched between the outer peripheral surface of the housing and the inner peripheral surface of the hole cover. The hole cover has one or more claws and a cylindrical female fitting portion, and the housing has a cylindrical male fitting portion into which the pinion shaft is inserted and which fits with the female fitting portion, a flange-shaped seat portion formed below the male fitting portion, and one or more fitted portions formed on the seat portion and which fit with the one or more claws respectively, and the lipped seal is a radial seal in which one or more lips extending circumferentially are formed on the outer peripheral surface of the lipped seal, and is inserted onto the outer periphery of the housing, and above the lipped seal a gap is formed between the outer peripheral surface of the housing and the inner peripheral surface of the hole cover, and the one or more claws fit with each other, thereby creating a clearance fit between the female fitting portion and the male fitting portion and abutting the hole cover and the seat portion.

[0006] According to the present invention, in a rack and pinion mechanism, the manufacturing cost of fitting a hole cover that covers at least a portion of the pinion shaft into a housing that supports the rack shaft can be reduced, and sealing between the housing and the hole cover can be ensured.

[0007] Fig. 2 is an overall perspective view of an example of a rack and pinion type power steering device according to an embodiment; Fig. 3 is a longitudinal sectional view showing an engagement portion between the rack and pinion of the steering gear of Fig. 1; Fig. 4 is an enlarged longitudinal sectional view of part A of Fig. 2; Fig. 5 is a longitudinal sectional view of first to third examples of lipped seals, respectively;

[0008] Embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the configuration, arrangement, etc. of component parts to those described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims.

[0009] (Configuration) Figure 1 is an overall perspective view of an example of a column-type power steering device according to an embodiment. As shown in Figure 1, the column-type power steering device applies steering assist force from a motor 102 attached to the middle of a column 105 to a steering shaft in order to reduce the operating force of a steering wheel 101. The rotation of the steering shaft is transmitted to an intermediate shaft 106, and causes the rack shaft of a rack-and-pinion steering gear 103 to move back and forth via a pinion shaft 107, thereby steering the wheels via tie rods 104.

[0010] Figure 2 is a vertical cross-sectional view showing the meshing portion between the rack and pinion of the steering gear of Figure 1. Figure 3 is an enlarged vertical cross-sectional view of part A of Figure 2. The steering gear 103 of this embodiment is attached to a body frame (not shown), such as a front subframe. A rack shaft 11 is fitted into a housing 10 of the steering gear 103 so as to be slidable in the vehicle width direction perpendicular to the plane of Figure 2. Ball joint sockets (not shown) are screwed into and attached to both ends of the rack shaft 11 in the vehicle width direction, and tie rods 104, 104 connected to the ball joint sockets are connected to wheels via knuckle arms (not shown).

[0011] The pinion shaft 107 includes a pinion 12 having pinion teeth formed thereon that mesh with rack teeth provided on at least a portion of the outer periphery of the rack shaft, and an extension shaft 14 that is bolted to the pinion 12 with bolts 15. In the following description, the extension direction of the pinion shaft 107 (i.e., the axial direction of the pinion shaft 107) will be referred to as the "axial direction," a direction perpendicular to the axial direction will be referred to as the "radial direction," and the rotation direction of the pinion shaft 107 (i.e., the circumferential direction around the pinion shaft 107) will be referred to as the "circumferential direction." In addition, the direction from the lower end of the pinion shaft 107 to the upper end when the pinion shaft 107 is mounted on a vehicle will be defined as the "upward direction," and the direction from the upper end of the pinion shaft 107 to the lower end when the pinion shaft 107 is mounted on a vehicle will be defined as the "downward direction."

[0012] The pinion 12 is inserted into the housing 10 from an opening at the top end of the housing 10 and is journaled on the housing 10 by a ball bearing 16a. In other words, the pinion 12 is rotatably supported on the housing 10. The bolt 15 fastening the pinion 12 to the extension shaft 14 fastens the pinion 12 to the extension shaft 14 at a position above the top end 10a of the housing 10.

[0013] The lower part of the pinion 12 is supported only in the radial direction by a needle bearing 16b on the housing 10. The rotation of the pinion shaft 107 (extension shaft 14 and pinion 12) is transmitted to the rack teeth of the rack shaft 11, and changes the direction of the steering wheel via tie rods 104, 104 shown in FIG. 1 that are connected to the rack shaft 11.

[0014] A guide hole 17a having a circular cross section is formed in the housing 10 in the left-right direction in Fig. 2, and a cylindrical rack guide 17b is fitted into this guide hole 17a so as to be slidable in the left-right direction in Fig. 2. The rack guide 17b has a concave arc-shaped surface with approximately the same curvature as the convex arc-shaped outer peripheral surface of the rack shaft 11. This concave arc-shaped surface comes into contact with the outer peripheral surface of the rack shaft 11, pressing the rack guide 17b against the outer periphery of the rack shaft 11.

[0015] The adjustment cover 17c is rotated to adjust the threaded engagement distance appropriately, and the rack guide 17b is pressed against the rack shaft 11 via the coil spring 17d, pressing the rack guide 17b against the outer periphery of the rack shaft 11. This eliminates backlash at the meshing portion between the pinion shaft 107 and the rack shaft 11, allowing the rack shaft 11 to move smoothly. With the above configuration, the rack shaft 11 is supported by the housing 10 so that it can move back and forth.

[0016] A hole cover 13 is fitted onto the housing 10, covering at least a portion of the pinion shaft 107 protruding from an opening at the top end of the housing 10. A cylindrical male fitting portion 10b that fits with the hole cover 13 is formed on the top of the housing 10, and the pinion shaft 107 is inserted into the male fitting portion 10b. The housing 10 also has a flange-shaped seat portion 10c below the male fitting portion 10b, which has a larger outer diameter than the male fitting portion 10b, and the hole cover 13 abuts against the seat portion 10c, thereby determining the axial position of the hole cover 13 relative to the housing 10.

[0017] The hole cover 13 is made of a material in which a reinforcing filler such as glass or carbon is mixed into an oil-resistant synthetic resin such as nylon or POM. The hole cover 13 extends upward, covering the periphery of the upper part of the pinion shaft 107, and a rubber gasket (not shown) fixed to the upper end of the hole cover 13 abuts against the toe board (vehicle body), restricting the hole cover 13 from moving upward. The hole cover 13 prevents foreign matter from entering the gap between the housing 10 and the pinion shaft 107.

[0018] The hole cover 13 has a cylindrical female mating portion 13a that mates with the male mating portion 10b of the housing 10, a conical tapered portion 13b, at least one claw 13c, a large-diameter portion 13d that is larger in diameter than the female mating portion 13a, and a bottom portion 13e. The seating portion 10c of the housing 10 is formed with at least one mated portion 10d that mates with each of the at least one claw 13c. For example, the hole cover 13 and the housing 10 may have two claws 13c and two mated portions 10d. The mating of the claws 13c with the mated portions 10d creates a clearance fit between the female mating portion 13a and the male mating portion 10b, thereby mating the hole cover 13 and the housing 10. The bottom portion 13e abuts against the housing 10 in the radial direction when subjected to a lateral external force, thereby preventing the hole cover 13 from tipping over. The function of the large diameter portion 13d will be described later.

[0019] Furthermore, the seating portion 10c has an overlapping portion 21 where the upper surface of the upper portion of the housing 10 overlaps and abuts against the lower surface of the lower portion of the hole cover 13 in the radial direction. That is, the hole cover 13 and the seating portion 10c of the housing 10 abut in the axial direction. For example, at the overlapping portion 21, the axial seating surfaces of the housing 10 and the hole cover 13 may abut over substantially the entire circumferential range, over a range where the claws 13c are not provided. By increasing the outer diameter of the seating portion 10c and widening the area of ​​the overlapping portion 21, the load applied per unit area to the portion of the hole cover 13 that abuts against the housing 10 at the overlapping portion 21 is reduced, allowing the hole cover 13 to be made of an inexpensive material with low strength.

[0020] An annular lipped seal 20 is sandwiched between the outer peripheral surface of the housing 10 and the inner peripheral surface of the hole cover 13 to seal between them. FIGS. 4( a) and 4(b) are longitudinal cross-sectional views of a first and second example of the lipped seal 20, respectively. The lipped seal 20 includes an annular seal body 20a and one or more lips 20b formed on the seal body 20a and extending circumferentially on the outer peripheral surface of the lipped seal 20. The lips have a tapered upper portion extending radially. The lipped seal 20 is a radial seal in which the lips 20b are compressed radially to generate a radial tension force (compression reaction force). The tapered shape facilitates insertion of the hole cover into the housing, improving assembly. The lipped seal 20 may be made of a soft, elastic material such as rubber or resin.

[0021] For example, the lipped seal 20 may have multiple lips 20b. For example, the lipped seal 20 may have two lips 20b. For example, grease may be applied to or filled into the outer peripheries of the multiple lips 20b. FIG. 4(c) is a vertical cross-sectional view of a third example of the lipped seal 20. The lipped seal 20 may have a core 20e. By including the core 20e, excessive deformation of the lipped seal 20 during assembly can be suppressed. This prevents the seal shape from being distorted when the lipped seal 20 is inserted, improving assembly ease.

[0022] By using the lipped seal 20 to seal between the outer peripheral surface of the housing 10 and the inner peripheral surface of the hole cover 13, it is possible to ensure a tight seal between the housing 10 and the hole cover 13 without press-fitting the hole cover 13 into the housing 10. Furthermore, by applying a tensioning force to the housing 10 using the lipped seal 20, it is possible to prevent the hole cover 13 from coming off the housing 10 and falling over even if the housing 10 and the hole cover 13 are displaced relative to each other due to an external force from the road surface.

[0023] Furthermore, by using the lipped seal 20, when the hole cover 13 is fitted onto the housing 10, only the lip 20b of the lipped seal 20 is deformed, so the hole cover 13 can be assembled to the housing 10 while suppressing an increase in the tension force of the lipped seal 20.

[0024] See FIG. 3. The lipped seal 20 is inserted onto the outer periphery of the seal arrangement portion 10e between the male mating portion 10b and the seating portion 10c of the housing 10. For example, in the case of the lipped seal 20 shown in FIGS. 4(a) and 4(b), it may be press-fitted onto the outer periphery of the seal arrangement portion 10e. The outer diameter of the housing 10 at the seal arrangement portion 10e may be larger than the outer diameter at the male mating portion 10b and smaller than the outer diameter at the seating portion 10c. By making the outer diameter of the housing 10 at the male mating portion 10b smaller than the outer diameter at the seal arrangement portion 10e, it is possible to prevent the lipped seal 20 from getting caught on the male mating portion 10b when press-fitting the lipped seal 20 into the seal arrangement portion 10e. To prevent the lipped seal 20 from getting caught on the male mating portion 10b, a taper 10f may be formed on the outer periphery of the upper end of the male mating portion 10b.

[0025] Furthermore, for example, the lipped seal 20 may be arranged so as to abut against the end face of the seating portion 10c of the housing 10, thereby determining the axial position of the lipped seal 20 relative to the housing 10. Furthermore, for example, when the lipped seal 20 is arranged in the seal arrangement portion 10e (for example, when the lipped seal 20 abuts against the end face of the seating portion 10c), a gap 22 may be formed above the lipped seal 20 between the outer peripheral surface of the housing 10 and the inner peripheral surface of the hole cover 13.

[0026] By providing the gap 22 above the lipped seal 20, even if an external force from the road surface causes relative displacement between the housing 10 and the hole cover 13 and applies a radial force to the lipped seal 20, a space is secured that allows the lipped seal 20 to expand in the axial direction. This reduces the stress generated in the seal 20 and the hole cover 13, preventing a decrease in the sealing performance of the lipped seal 20. The large diameter portion 13d is formed so that it can bend within the range of the gap 22 when bent by an external force, to the extent that the lipped seal 20, described below, will not break.

[0027] The inner peripheral surface 20c of the lipped seal 20 may be flat as shown in Fig. 4(a), or may have at least one ridge 20d extending circumferentially formed on the inner peripheral surface 20c of the lipped seal 20 as shown in Fig. 4(b). By providing the ridge 20d on the inner peripheral surface 20c of the lipped seal 20, the ridge 20d is compressed in the radial direction when the hole cover 13 is fitted onto the housing 10, improving the sealing performance with the housing 10.

[0028] (Effects of the embodiment) (1) The rack and pinion mechanism includes a housing 10, a rack shaft 11 supported by the housing 10 so as to be reciprocable and having rack teeth on at least a portion of its outer periphery, a pinion shaft 107 supported rotatably by the housing 10 and having pinion teeth that mesh with the rack teeth, a hole cover 13 fitted onto the housing 10 and covering a portion of the pinion shaft 107, and an annular lipped seal 20 sandwiched between the outer periphery of the housing 10 and the inner periphery of the hole cover 13.

[0029] The hole cover 13 has one or more claws 13c, a cylindrical female fitting portion 13a, and a conical tapered portion 13b. The housing 10 has a cylindrical male fitting portion 10b into which the pinion shaft 107 is inserted and which fits with the female fitting portion 13a, a flange-like seating portion 10c formed below the male fitting portion 10b, and one or more fitted portions 10d formed on the seating portion 10c and which fit with the one or more claws 13c, respectively.

[0030] The lipped seal 20 is a radial seal in which one or more lips 20b extending circumferentially are formed on the outer peripheral surface of the lipped seal 20, and is inserted onto the outer periphery of the housing 10. Above the lipped seal 20, a gap 22 is formed between the outer peripheral surface of the housing 10 and the inner peripheral surface of the hole cover 13, and one or more claws 13c are respectively engaged with one or more mating portions 10d, thereby forming a gap fit between the female mating portion 13a and the male mating portion 10b, and the hole cover 13 and the seating portion 10c abut against each other.

[0031] This ensures a tight seal between the housing 10 and the hole cover 13 without press-fitting the hole cover 13 into the housing 10. Furthermore, by applying a tensioning force to the housing 10 with the lipped seal 20, it is possible to prevent the hole cover 13 from coming off the housing 10 and falling over even if the housing 10 and the hole cover 13 are displaced relative to each other due to an external force from the road surface. Furthermore, the claws 13c maintain the axial position of the hole cover 13 and prevent the hole cover 13 from coming off the housing.

[0032] Furthermore, by using the lipped seal 20, only the lip 20b of the lipped seal 20 deforms when the hole cover 13 is fitted onto the housing 10, so the hole cover 13 can be assembled to the housing 10 without increasing the tensioning force of the lipped seal 20. Furthermore, because only the lip 20b of the lipped seal 20 deforms when the hole cover 13 is fitted onto the housing 10, the tensioning force of the lipped seal can be suppressed, and the assembly force can be reduced.

[0033] Furthermore, a gap 22 is formed above the lipped seal 20 between the outer peripheral surface of the housing 10 and the inner peripheral surface of the hole cover 13, ensuring space for the lipped seal 20 to expand in the axial direction even if an external force causes relative displacement between the housing 10 and the hole cover 13 and applies a radial force to the lipped seal 20. This reduces the stress generated in the seal 20 and the hole cover 13, preventing a decrease in the sealing performance of the lipped seal 20.

[0034] (2) A plurality of lips may be formed on the outer periphery of the lipped seal 20. This can improve the sealing performance between the housing 10 and the hole cover 13.

[0035] (3) Grease may be applied to the outer peripheries of the plurality of lips, thereby reducing the force required to assemble the housing 10 and the hole cover 13.

[0036] (4) A ridge extending in the circumferential direction may be formed on the inner peripheral surface of the lipped seal 20. This allows the ridge 20d to be compressed in the radial direction when the hole cover 13 is fitted onto the housing 10, making it easier to assemble the hole cover 13 to the housing 10.

[0037] (5) The lip seal 20 may have a core metal 20e. By including the core metal 20e, excessive deformation of the lip seal 20 during assembly can be suppressed. This prevents the seal shape from being distorted when the lip seal 20 is inserted, improving assembly ease.

[0038] (6) The lip seal 20 may be disposed so as to abut against the seat portion 10c of the housing 10. This allows the lip seal 20 to be positioned relative to the housing 10 in the axial direction.

[0039] (7) The outer diameter of the housing 10 at the male mating portion 10b may be smaller than the outer diameter of the housing 10 at the seal arrangement portion 10e where the lipped seal 20 is arranged in the housing 10. A taper 10f may be formed on the outer peripheral surface of the upper end of the male mating portion 10b. This prevents the lipped seal 20 from getting caught in the male mating portion 10b when the lipped seal 20 is press-fitted into the seal arrangement portion 10e.

[0040] (8) The pinion shaft 107 may include a pinion 12 having pinion teeth formed thereon and an extension shaft 14 bolted to the pinion 12, and the pinion 12 may be rotatably supported by bearings 16a and 16b. In this manner, when the pinion shaft 107 is configured by connecting the extension shaft 14 to the pinion 12 having pinion teeth formed thereon, the hole cover 13 can be made smaller by assembling it to the outer diameter of the housing 10, making it easier to ensure vehicle installation space.

[0041] (9) The bolt 15 that fastens the pinion 12 and the extension shaft 14 may fasten the pinion 12 and the extension shaft 14 at a position above the upper end 10a of the male fitting portion 10b. This ensures a working space when fastening the extension shaft 14 to the pinion 12 with the bolt.

[0042] 10...housing, 10a...upper end, 10b...male mating portion, 10c...seating portion, 10d...receiving portion, 10e...seal arrangement portion, 10f...taper, 11...rack shaft, 12...pinion, 13...hole cover, 13a...female mating portion, 13b...conical narrowing portion, 13c...claw, 13d...large diameter portion, 13e...bottom portion, 14...extension shaft, 15...bolt, 16a...ball bearing, 16b...needle bearing, 17a...guide hole, 17b...rack guide, 17c...adjustment cover, 17d...coil spring, 20...seal, 20a...seal body, 20b...lip, 20c...inner peripheral surface, 20d...ridge, 20e...core metal, 21...overlapping portion, 22...gap, 101...steering wheel, 102...motor, 103...steering gear, 104...tie rod, 105...column, 106...intermediate shaft, 107...pinion shaft

Claims

1. A rack and pinion mechanism comprising: a housing; a rack shaft supported in the housing for reciprocal movement and having rack teeth on at least a portion of its outer circumference; a pinion shaft supported in the housing for rotation and having pinion teeth that mesh with the rack teeth; and a hole cover fitted onto the housing to cover a portion of the pinion shaft, wherein the rack and pinion mechanism comprises an annular lipped seal sandwiched between the outer circumferential surface of the housing and the inner circumferential surface of the hole cover, the hole cover having one or more claws and a cylindrical female fitting portion, the housing having a cylindrical male fitting portion into which the pinion shaft is inserted and which fits with the female fitting portion, a flange-shaped seat portion formed below the male fitting portion, and one or more fitted portions formed on the seat portion and which respectively fit with the one or more claws, the lipped seal being a radial seal in which one or more lips extending circumferentially are formed on the outer circumferential surface of the lipped seal, and the lipped seal is inserted onto the outer periphery of the housing, a gap is formed between the outer peripheral surface of the housing and the inner peripheral surface of the hole cover above the lipped seal, and the one or more claws engage with the one or more mating portions, thereby forming a gap fit between the female mating portion and the male mating portion, and the hole cover abuts against the seating portion.

2. A rack and pinion mechanism as set forth in claim 1, wherein a plurality of said lips are formed on the outer periphery of said lipped seal.

3. The rack and pinion mechanism according to claim 2, wherein grease is applied to the outer periphery of said plurality of lips.

4. A rack and pinion mechanism as set forth in claim 1, characterized in that a circumferentially extending protrusion is formed on the inner peripheral surface of said lipped seal.

5. The rack and pinion mechanism according to claim 1, wherein said lipped seal has a core metal.

6. The rack and pinion mechanism according to claim 1, wherein said hole cover has a conical narrowing portion.

7. A rack and pinion mechanism as claimed in any one of claims 1 to 6, characterized in that the lipped seal is positioned so as to abut against the seating portion of the housing.

8. A rack and pinion mechanism as described in any one of claims 1 to 6, characterized in that the outer diameter of the housing at the male mating portion is smaller than the outer diameter of the housing at a seal arrangement portion where the lipped seal is arranged on the housing, and a taper is formed on the outer circumferential surface of the upper end portion of the male mating portion.

9. A rack and pinion mechanism as claimed in any one of claims 1 to 6, characterized in that the pinion shaft comprises a pinion on which the pinion teeth are formed and an extension shaft bolted to the pinion, the pinion being rotatably supported by a bearing.

10. The rack and pinion mechanism according to claim 9, characterized in that the bolt fastening the pinion and the extension shaft fastens the pinion and the extension shaft at a position above the upper end of the male fitting portion.

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