JP4588487B2 - Rack and pinion type power steering system - Google Patents

Description

  The present invention relates to a rack bush for slidingly supporting a rack shaft, and a rack and pinion type power steering device characterized by a mounting structure of the rack bush.

In a rack and pinion type steering device, sliding support of the rack shaft to the rack housing which is a rack shaft support portion is performed in a gear housing portion near one end of the rack shaft and a housing portion near the other end, etc. Is well known, and the sliding support of the rack shaft in these support portions is made via a rack bush made of synthetic resin, rubber or the like.
Since the rack shaft is supported by the rack bush at the gear housing position near one end, the rack shaft rack teeth and the pinion are engaged with each other. (For example, refer to Patent Document 1 and Patent Document 2). Further, the rack bushes in these sliding support portions are usually structured to be positioned and fixed with respect to the gear housing, the rack housing, etc. (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 3-193556 (2nd page, FIGS. 1 to 2) Japanese Patent Application Laid-Open No. 2002-274396 (page 3 to page 4, FIGS. 1 to 3) Japanese Patent No. 3543352 (pages 5-6, Fig. 1)

  As shown in FIGS. 9A and 9B, the rack shaft 01 is supported by the gear housing portion 04 described in Patent Document 1 described above with a single rack bush 05 made of an elastic member such as synthetic resin or rubber. The rack shaft 01 is supported by the bush 05 by supporting the back side of the meshing portion between the rack tooth 02 and the pinion 03 of the rack shaft 01 and pressing the surface toward the pinion 03. Yes. The rack bush 05 is provided with a plurality of protrusions 06 on the outer periphery of the bush 05 as means for preventing movement in the axial direction in the mounted state, and these protrusions 06 are recessed or stepped on the inner periphery of the gear housing part 04. The structure which engages with a part is provided.

  Further, the rack shaft 01 is supported in the gear housing portion (rack housing) 04 described in Patent Document 2 described above, as shown in FIGS. 10A to 10C, a cylinder made of an elastic member such as a synthetic resin. The bush 05 is provided with a pair of pressing projections 06 in which a part of the cross section of the cylindrical shape is bulged toward the inner surface side of the cylinder. It extends over the entire region in the axial direction, but in the circumferential direction of the bush 05, it is arranged close to the half on one side.

  The rack bush 05 has one end surface of the cylinder abutting against a stepped portion 041 on the inner periphery of the gear housing portion 04 to be axially positioned and press-fitted into the large-diameter portion 042 of the housing portion 04, and a pair of pressing protrusions When 06 is in contact with the back side of the rack tooth 02 of the rack shaft 01, the rack shaft 01 is pressed in the direction of the pinion 03, that is, in the direction of the meshing portion of the rack tooth 02 and the pinion 03. Engagement without rattling is ensured so that the rotational torque of the pinion 03 is smoothly transmitted to the rack shaft 01.

  In the above-mentioned Patent Document 3, as shown in FIG. 11, the first rack bush 05 on the pinion side has a locking flange 051 fitted into the circumferential groove 04a of the steering housing 04, and positioning protrusions are provided. It is positioned so as to be prevented from moving in the axial direction and the rotational direction with respect to the housing 04 by being fitted into a recess provided in the inner peripheral surface of the peripheral groove 04a.

  Further, the second rack bush 06 on the anti-pinion side has a retaining projection 061 fitted in the circumferential groove 07a of the terminal member 07 which is a part of the steering housing, and the positioning projection is formed on the inner circumferential surface of the circumferential groove 07a. A structure is described that is fitted in a positioning recess provided to be positioned so as to be prevented from moving in the axial direction and the rotational direction with respect to the terminal member 07, and two bushes 05 that support the rack shaft 02 are described. , 06 are both positioned and fixed with respect to the housings 04 and 07 so as to be prevented from moving in the axial direction and the rotational direction.

  By the way, the rack bush (elastic member) described in Patent Document 1 has a structure in which protrusions on the outer peripheral portion engage with recesses or step portions formed on the inner periphery (inner surface) of the gear housing to prevent the movement of the bush. The structure of the rack bush is accompanied by a large deformation of the bush when inserted into the inner periphery of the gear housing. For this reason, the bush is inserted unless it is made of a soft material. Can not. In order to facilitate the insertion of the bush, it is conceivable to provide a slit in the bush. In this case, the bush is likely to come off.

  The rack bush (elastic member) described in Patent Document 2 can be easily press-fitted from the axial direction when mounted, but since there is no positioning means that also serves as a detent in the rotational direction, the rotation of the rack bush during press-fitting Accurate positioning in the direction is difficult, and even after installation due to press-fitting, positional deviation in the rotational direction is likely to occur over time, so that proper engagement between the rack teeth of the rack shaft and the pinion cannot be maintained and Sound generation cannot be effectively suppressed.

  On the other hand, like the two rack bushes described in Patent Document 3, those that are both positioned and fixed with respect to the housing are processed with the bushes by processing the engaging portion composed of the concave and convex portions for positioning and fixing the bush. Since it is necessary to perform both of the housings, such processing is time-consuming, and also when fitting the bushes into the housing, it is necessary to align the engaging portions including the uneven portions, which is troublesome. If the engaging portion composed of the concavo-convex portion for positioning and fixing can be omitted, it is also desired to omit it.

  In such a situation, in the sliding support of the rack shaft by the rack bush at the gear housing position where the rack tooth of the rack shaft meshes with the pinion, the structure of the rack bush and the support structure by the bush By making noticeable improvements, it is possible to effectively suppress rattling caused by swinging of the rack shaft and to optimize the meshing between the rack teeth of the rack shaft and the pinion, thereby generating from the meshing portion. It is desired to provide the above-described rack and pinion type power steering device that effectively suppresses the rattling noise, and includes a concavo-convex portion for positioning and fixing in the mounting of the rack bush to the housing. It is desired to provide the rack and pinion type power steering apparatus having a rack shaft support structure with a viewpoint of omitting joint portions.

The present invention relates to an improved structure of a rack and pinion type power steering apparatus for solving the above-described problems, and in particular, the steering apparatus in which the improvement viewpoint is set to prevent rattling at a meshing portion between rack teeth and a pinion. In the rack and pinion type power steering apparatus in which the rack shaft is slidably supported on the gear housing via a bush made of synthetic resin or rubber , the bush is formed on the outer peripheral portion of the inner surface of the gear housing. The bush is fixed in the rack axial direction by a locking member, and the bush has an inner peripheral surface formed by two arcs having different radii on the inner surface. The central angle of the small arc is within 180 °, and the inner peripheral surface of the arc with the small radius is a surface that contacts when the rack shaft is bent. There, the inner peripheral surface by the other arc is characterized by a surface which does not contact even when the deflection of the rack shaft.

The rack shaft is slidably supported on the gear housing via a pressing device that presses the bush, another bush, and the rack shaft against a pinion, and the rack shaft is configured to bend the rack shaft. It is supported at two points (9, 14) when the load is small and low, and is supported at three points (9, 14, 8) when the load of the rack shaft is large .
Further, the rack shaft is supported by the other bush and the pressing device at the time of the low load, and is supported by the other bush, the pressing device and the bush at the time of the high load .
The other bush includes three convex surface portions that support the rack shaft .

The invention according to claim 1 of the present invention is the rack and pinion type power steering device according to the first aspect, wherein the bush includes a convex portion that engages with an engagement concave portion of the inner surface portion of the gear housing on the outer peripheral portion, and is fixed by a locking member. Therefore, the mounting of the bush on the inner surface of the gear housing is performed by engaging the engaging convex portion of the outer peripheral portion of the bush with the engaging concave portion of the inner peripheral portion of the gear housing, so that the positioning of the bush with respect to the housing is easy and reliable. Therefore, it can be easily assembled, and in the mounted state, the relative rotation of the bush with respect to the gear housing is surely prevented.
Further, the bush has an inner peripheral surface formed by two arcs having different radii on the inner surface, and the central angle of the arc having a small radius is set to be within 180 °. Therefore, unnecessary interference with the inner surface of the bush in the movement of the rack shaft. Thus, proper sliding support is achieved while smooth movement of the rack shaft is achieved.
Further, the bush has an inner circumferential surface arc with two different radii on the inner surface, and the inner circumferential surface with the smaller radius arc is a surface that contacts when the rack shaft is bent, and the inner circumferential surface with the other arc. Since the surface does not come into contact even when the rack shaft is bent, the rack shaft can be stably supported to adapt to the load applied to the rack shaft while ensuring the smooth movement of the rack shaft.

The invention according to claim 2 of the present invention is the rack and pinion power steering apparatus according to the invention of claim 1, wherein the rack shaft is configured to press the bush, the other bush, and the rack shaft against the pinion. Is slidably supported by the gear housing via a bearing, and is supported at two points (9, 14) at low loads and at three points (9, 14, 8) at high loads. The rack shaft can be stably supported without difficulty by adapting to such a load, and the rack shaft can be prevented from rattling and the smooth engagement between the rack teeth and the pinion can be achieved. Occurrence is suppressed. Further, the durability of the rack teeth and the pinion is improved.

The invention according to claim 3 of the present invention is the rack and pinion type power steering apparatus according to claim 2 of the present invention, wherein the rack shaft is supported by the other bush and the pressing device when the load is low. Since it is supported by the other bushes, the pressing device and the bushes at the time, the rack shaft can be stably supported without difficulty by adapting to the load applied to the rack shaft, and the rack shaft can be prevented from rattling. Smooth engagement between the teeth and the pinion is achieved, and generation of hitting sound due to the engagement of the gears is suppressed. Further, the durability of the rack teeth and the pinion is improved.

According to a fourth aspect of the present invention, in the rack and pinion type power steering device according to the second or third aspect of the present invention, the bush supports the rack shaft on a circumferential surface which is a single curved surface, Since the other bush supports the rack shaft with three convex surface portions, the sliding support of the rack shaft by the three convex surface portions of the other bush reduces the sliding frictional resistance of the rack shaft, and further the rack shaft outer peripheral portion. The equal support from all directions by the three convex surface portions is not particularly changed by the occurrence of misalignment in the rotation direction of the other bush. Therefore, if positioning for detent is made in the bush, the other It is possible to ensure a stable support state by the bushing of the rack shaft without positioning for preventing the bushing from rotating.

  Therefore, the other bush that supports the rack shaft by the three convex portions does not include means for positively preventing the bush from being rotated, and the bush and the bush in the fitted member to which the bush is fitted. Therefore, it is not necessary to form an engaging portion composed of an uneven portion or the like for preventing rotation, eliminating the need for processing for the engaging portion, and reducing the cost accordingly. Further, when the bush is fitted to the fitting member, the bush and the fitting member of the bush are not formed with uneven portions for positioning the bush. It is very easy because there is no need to pay special attention to

  Hereinafter, an embodiment of the present invention illustrated in FIGS. 1 to 8 will be described.

FIG. 1 shows a schematic overall view of a rack and pinion type power steering apparatus 1 according to the present invention, a part of which is a cross section.
1 and 2, the power steering apparatus 1 includes a steering handle and a steering shaft (not shown), an electric motor M for applying an auxiliary steering force, a rack shaft 2, and a rack shaft 2. The pinion 3 (see FIG. 2) for inputting the steering force of the steering wheel, the teeth 21 of the rack shaft 2 with which the pinion 3 meshes, and the ball joints 4 and 4 at both ends of the rack shaft 2 are connected to each other to operate the rack shaft 2. Tie rods 5 and 5 that transmit to a steering wheel (not shown), a rack housing 6 that encloses and surrounds the periphery of the rack shaft 2, and a gear that is a part of the rack housing 6 that accommodates the meshing portion of the pinion 3 and the rack teeth 21. A housing 61 and the like are provided.

  The electric motor M is integrally attached to the extension housing 62 of the gear housing 61, and the steering force output shaft 31 provided with the pinion 3 via the worm gear mechanism (not shown) in the housing 62 (see FIG. 2). ), The rack shaft 2 can be moved forward and backward with a predetermined stroke in the axial direction in the rack housing 6 through the engagement of the pinion 3 of the steering force output shaft 31 and the rack teeth 21. For this reason, the rack tooth 21 is formed as a tooth portion 21a having a predetermined length. The tooth portion 21a of the rack shaft 2 is a portion in which teeth are formed by cutting out a part of the circular cross-sectional side surface of the rack shaft 2 over the predetermined length (see FIG. 2).

  The forward / backward movement of the rack shaft 2 in the rack housing 6 in the predetermined stroke, that is, the forward / backward movement of the rack shaft 2 in the left-right direction in FIG. The movement of the tie rods 5 and 5 is transmitted to a steering wheel (not shown) for steering to change the direction of the vehicle.

  The rack housing 6 that houses and surrounds the rack shaft 2 includes the gear housing 61 on the right end side shown in FIG. 1 surrounding the vicinity of both ends of the rack shaft 2, the left housing 65 on the left end side, and a gear. A cylindrical housing 63 extending from the left side of the housing 61 and a hollow tube housing 67 connecting between the cylindrical housing 66 extending from the right side of the left housing 65 are provided. A right end outer peripheral portion 67 a is press-fitted and held in an inner peripheral portion 63 a of the left cylindrical housing 63 of the gear housing 61, and a left end outer peripheral portion 67 b is located inside the right side of the cylindrical housing 66 of the left housing 65. The rack shaft 2 is press-fitted and held by the peripheral portion 66a, and thereby the rack shaft 2 is entirely enclosed and enclosed except for both end portions of the rack shaft 2 covered by the bellows 7 and 7.

  As described above, the rack shaft 2 is supported so as to be movable back and forth with a predetermined stroke in the axial direction of the rack housing 6 which is the support portion of the rack shaft 2, that is, in the horizontal direction in the figure. In this embodiment, the rack shaft 2 is supported by the position of the gear housing 61 near the right end of one rack shaft 2, the position of the left housing 65 near the left end of the other rack shaft 2, and The pressing portion 14b (see FIG. 2) of the pressing device 14 on the back of the rack tooth 21 of the meshing portion of the rack tooth 21 and the pinion 3 which will be described later is used.

  One support of the rack shaft 2 by the rack housing 6, that is, the support of the rack shaft 2 at the position of the gear housing 61 near the right end of the rack shaft 2 in the illustration of FIG. 1 is from the right side of the gear housing 61. An extending cylindrical housing 64, that is, a housing 64 extending in a predetermined length in a cylindrical shape so as to coaxially surround the outer peripheral portion 2 a of the rack shaft 2, via a rack bush 8 made of a synthetic resin or the like described later. It is made by being slidably supported.

  Further, the other support of the rack shaft 2 by the rack housing 6, that is, the support of the rack shaft 2 at the position of the left housing 65 near the left end of the rack shaft 2 in FIG. 1 is the left housing 65. The left rack shaft 2 is supported by a sliding bush 90 which is a sliding ring member 9 fitted in an annular recess 65b formed in an inner peripheral portion 65a near the end.

  Both the position of the gear housing 61 and the position of the left housing 65 which are one and the other support portions of the rack shaft 2 are portions constituting both ends of the rack shaft 2, and therefore the support portions of the rack shaft 2 are tie rods. Adjacent to the ball joint portions 4 and 4, which are connecting portions to 5 and 5. For this purpose, bellows 7 and 7 that cover the ball joint portions 4 and 4 for protection thereof are attached to the portion, and the one support portion of the rack shaft 2 extends from the right side of the gear housing 61. An annular recess 64c provided on the outer peripheral portion 64b on the right end side of the cylindrical housing 64 is a structural portion used for mounting the bellows 7, and the other support portion of the rack shaft 2 has a left-hand side. The outer peripheral portion 65c on the left end side of the housing 65 is a structural portion used for mounting the bellows 7.

  The bellows 7 is mounted at the position of the gear housing 61 in the annular recess 64c of the outer peripheral portion 64b of the cylindrical housing 64. One end opening 7a of the bellows 7 is fitted into the annular recess 64c and the opening 7a of the bellows 7 is fitted. The other end opening 7b of the bellows 7 is fitted to the outer peripheral portion 5a of the tie rod 5 and tightened by the tie rod clip 11.

  The bellows 7 is mounted at the position of the left housing 65 at the outer peripheral portion 65c of the housing 65, and one end opening portion 7a of the bellows 7 is fitted into the outer peripheral portion 65c of the housing 65 and tightened with the bellows band 10 At the same time, the other end opening 7 b of the bellows 7 is fitted to the outer peripheral portion 5 a of the tie rod 5 and tightened by the tie rod clip 11.

  The rack shaft 2 is provided with annular stopper rubbers 12 and 12 made of synthetic resin, rubber, or the like having a predetermined width at positions adjacent to the ball joint portions 4 and 4 at both left and right ends. 12 is press-fitted and fixed to slightly narrowed portions 23 on the left and right ends of the rack shaft 2.

  The stopper rubbers 12, 12 are arranged at the inner periphery of the right-extending cylindrical housing 64 of the gear housing 61 at the moving end of the leftward movement of the rack shaft 2 in the left-right movement stroke shown in FIG. The rack shaft 2 moves in the left-right direction by abutting with the end of a stopper piece 13 to be described later fitted into the portion 64a and with the left end 65d of the left housing 65 at the moving end of the rightward movement. Thus, the stroke in the forward and backward movement of the rack shaft 2 in the left-right direction with respect to the rack housing 6 is determined.

  The power steering apparatus 1 generally has the above-described structure, and the outline of the support structure of the rack shaft 2 in the rack housing 6 has been described above. Here, one support portion of the rack shaft 2 is further described. That is, the support structure of the rack shaft 2 at the position of the gear housing 61 will be described in detail with reference to FIG.

  As shown in FIG. 2, the support portion by the cylindrical housing 64 that extends from the left side of the gear housing 61 (the right side of FIG. 1 in the drawing) of the gear housing 61 that is one support portion of the rack shaft 2 is shown in an enlarged manner. ing. The cylindrical housing 64 of the gear housing 61 has a cylindrical shape that extends from the accommodation space of the meshing portion between the rack tooth 21 and the pinion 3 in the gear housing 61 to the left side of the figure in the axial direction of the rack shaft 2. The rack shaft 2 is configured to be movable back and forth in the axial direction of the cylindrical housing 64, that is, in the horizontal direction in the figure.

  The accommodation space of the meshing portion between the rack tooth 21 and the pinion 3 of the gear housing 61 includes a space for the rack tooth 21 of the rack shaft 2 and the pinion 3 meshing with the rack tooth 21, and the rack tooth 21 and the pinion 3 A pressing force for pressing the back side 24 toward the pinion 3 against the pressure due to the engagement of the teeth 21 is applied to the opposite side of the rack teeth 21 of the meshing portion, that is, the back side 24 of the rack teeth 21. An accommodating space for the pressing device 14 that substantially constitutes one support portion of the rack shaft 2 is also provided.

  The pressing device 14 that presses the back side 24 of the rack tooth 2 includes a cylinder 61b formed in a boss portion 61a extending in a direction orthogonal to the axial direction of the rack shaft 2 of the gear housing 61, and a slide in the cylinder 61b. A rack guide 14a having a flat pressing portion 14b that moves movably and abuts against the back side 24 of the rack teeth 21 of the rack shaft 2, and a spring disposed on the back portion (the upper portion in the figure) of the rack guide 14a. 14c and a cap 14d that seals the upper opening 61c of the cylinder 61b by being screwed into the upper opening 61c of the cylinder 61b and presses the spring 14c at the back of the rack guide 14a. By adjusting the amount, the pressing force of the rack guide 14a by the spring 14c is adjusted.

  The cylindrical housing 64 of the gear housing 61 has an enlarged diameter portion 64d having a large outer diameter in the extending end direction, and the end outer peripheral portion 64b is used for mounting the bellows 7 described above. An annular recess 64c is provided. The inner peripheral portion 64a of the cylindrical housing 64 has a hole 64e having a slightly smaller inner diameter on the side of the meshing portion accommodating space between the rack teeth 21 and the pinion 3, and the first stepped portion 64f is formed from the hole 64e having a smaller inner diameter. A first enlarged hole portion 64g that is formed to expand the inner diameter, a second stepped portion 64i that forms a second stepped portion 64h from the enlarged hole portion 64g, and further expands the inner diameter, and this enlarged hole portion. A third enlarged hole portion 64k that forms a third step portion 64j from 64i and is enlarged.

  The hole 64e having a small inner diameter of the inner peripheral portion 64a of the cylindrical housing 64 has a sufficient inner diameter so that the rack tooth 21 of the rack shaft 2 and the shaft part 22 where the rack tooth 21 is not formed can be moved without any trouble. The first enlarged hole portion 64g following the small hole portion 64e is a hole portion into which the rack bush 8 described later is inserted, The inner peripheral portion 64g1 is provided with an engaging recess 64g2 (see FIG. 2B) that serves both as a detent and positioning for the bush 8 to be fitted.

  The engagement concave portion 64g2 of the inner peripheral portion 64g1 of the first enlarged hole portion 64g of the cylindrical housing 64 is substantially the same as the second enlarged hole portion 64i, which is a further enlarged inner diameter portion, and the first enlarged hole portion. The step 64h at the boundary with 64g is a groove formed by cutting directly in the axial direction, so that the rack bush 8 described in detail later has the engagement protrusion 8a of the outer peripheral portion 8b engaged. By being aligned with the concave portion 64g2 and being pushed in the axial direction, it can be inserted into the first enlarged hole portion 64g from the second enlarged hole portion 64i side.

And the 2nd expansion hole part 64i is a hole part by which the stopper piece 13 is inserted, The outer peripheral part 13a (refer FIG. 5) of the stopper piece 13 mentioned later is press-fitted in the inner peripheral part, and the said. The rack bush 8 fitted in the first enlarged hole 64g is prevented from moving in the axial direction.
The third enlarged hole portion 64k following the second enlarged hole portion 64i has a sufficient interval that does not come into contact with the outer peripheral portion 2a of the rack shaft 2 even when the rack shaft 2 is bent under a high load. An annular recess 64c used for mounting the bellows 7 described above is formed in the outer peripheral portion 64b in the vicinity of the opening of the end portion.

  As described above, the rack shaft 2 moves inside the cylindrical housing 64 so as to be movable back and forth in the axial direction, that is, in the left-right direction in the figure. For this purpose, the rack bush 8 is provided in the first enlarged hole portion 64g. The rack shaft 2 is inserted into the cylindrical housing 64 through the bush 8 so as to be able to move forward and backward.

  The rack bush 8 is made of synthetic resin, rubber or the like and has a ring-shaped outer shape with a predetermined width as shown in FIGS. 4A and 4B. The ring has a uniform width, and the ring has an outer peripheral portion 8b. It is a perfect circle, and its outer diameter is substantially the same as the inner peripheral portion 64g1 (see FIG. 2B) of the first enlarged hole 64g of the cylindrical housing 64. The outer peripheral portion 8b of the ring has the bush 8 An engaging projection 8a is provided for positioning with respect to the cylindrical housing 64 at the time of insertion.

  This engagement convex part 8a makes positioning with respect to the cylindrical housing 64 of the bush 8 by fitting with the engagement concave part 64g2 provided in the inner peripheral part 64g1 of the first enlarged hole part 64g of the cylindrical housing 64. In addition, the portion of the ring outer peripheral portion 8b other than the portion where the engaging convex portion 8a is provided has a height higher than that of a plurality of parallel mountain-shaped engaging convex portions 8a extending in the width direction of the ring over the entire periphery. A low uneven portion 8c is provided.

  The inner peripheral portion 8d of the rack bush 8 is similar to a circle in which the peripheral surfaces 8e and 8f of the annular peripheral surface portion formed by arcs of two circles having different radii in front view are continuous with each other on the periphery of the inner peripheral portion 8d. Therefore, the ring forming the bush 8 has a perfect circle, so that the portion corresponding to the peripheral surface 8f by the arc having a large radius is thin and the portion corresponding to the peripheral surface 8e by the arc having the small radius is the wall. It is thick. The rack shaft 2 is supported by the annular peripheral surface of the inner peripheral portion 8d of the bush 8 in a state where the load applied to the rack shaft 2 is no load or a low load and the rack shaft 2 is not bent or is slightly bent. However, when the load applied to the rack shaft 2 is high and the rack shaft 2 bends, the load is applied to the peripheral surface 8e by a circular arc having a small radius, that is, substantially at the thick portion 8g of the ring.

And the said support part corresponding to the surrounding surface 8e by the circular arc with a small radius in the rack shaft 2 is the back side of the rack tooth 21 opposite to the rack tooth 21 formation side.
The peripheral surface 8f formed by the arc having a large radius of the inner peripheral portion 8d of the rack bush 8 corresponds to the side of the rack shaft 2 where the rack teeth 21 are formed, but the peripheral surface 8f does not contact the rack teeth 21 and the rack bush 8 Such positioning of the bush 8 with respect to the rack shaft 2 during mounting of the bushing 8 engages with the inner peripheral portion 64a of the cylindrical housing 64 described above, more specifically, the engaging recess 64g2 of the first enlarged hole portion 64g. This is easily achieved by positioning by the convex portion 8a.

  A peripheral surface 8e formed by an arc having a small radius, which is a substantial rack shaft support portion of the inner peripheral portion 8d of the rack bush 8, has a length corresponding to an angle θ within 180 ° on the peripheral surface of the bush inner peripheral portion 8d. And the rear surface side of the rack tooth 21 of the rack shaft 2 is supported by the peripheral surface within the range of the length, and thereby the contact between the rack shaft 2 and the rack bush 8 more than necessary. By avoiding this, the smoothness of movement for the operation of the rack shaft 2 is not hindered.

The peripheral surface 8e formed by the circular arc having a small radius for supporting the rack shaft 2 is the rack shaft in a state where the rack shaft 2 is not bent or is slightly bent in the no-load or low-load state as described above. 2 so that the rack shaft 2 does not interfere with each other, and the rack shaft 2 is supported by the peripheral surface 8e when the rack shaft 2 is greatly bent in a high load state.
Further, the above-mentioned bush is formed at the substantially central portion in the circumferential direction of the outer peripheral portion 8b of the thick portion 8g of the rack bush 8 which is thick and has a high strength on the peripheral surface 8e formed by an arc having a small radius as a substantial support surface of the rack shaft 2. Eight positioning engaging projections 8a are provided.

  Although the axial movement of the rack bush 8 fitted into the first enlarged hole 64g is blocked by the stopper piece 13 press-fitted into the second enlarged hole 64i, the stopper piece 13 is made of a material such as steel. 5 is a ring member having a predetermined thickness and a predetermined width as shown in FIG. 5, and the outer peripheral portion 13a thereof is press-fitted into the second enlarged hole portion 64i, so that it has substantially the same diameter as the hole portion 64i. The outer diameter of the bush 8 is larger than the outer diameter of the bush 8, and the outer peripheral portion 13a is an annular flat surface 13a1.

  The inner peripheral portion 13b of the stopper piece 13 that is a ring member has a small inner diameter portion 13b1 closer to one end in the axial direction forming the main body of the inner peripheral portion 13b, that is, closer to the rack bush 8 when the piece 13 is press-fitted, and a shaft It has a large inner diameter portion 13b2 that is closer to the other end in the direction, that is, closer to the anti-bush 8 side. The small inner diameter portion 13b1 of the inner peripheral portion 13b of the stopper piece 13 allows the rack shaft 2 to bend within the allowable range and suppresses the deflection exceeding the allowable range.

  On the other hand, the large inner diameter portion 13b2 has a predetermined width for holding the pressure contact friction force required for the stopper piece 13 as a ring member as a stopper, so that the deflection of the rack shaft 2 is relatively within an allowable range. Assuming that a small inner diameter portion 13b1 is provided over the entire width of the ring (see the dotted line portion in FIG. 5), the bent rack shaft 2 comes into contact with the outer end portion 13b11. (See also FIG. 3).

  Therefore, in order to avoid such inconvenience, the inner peripheral portion 13b at the outer end (the left end in the figure) is enlarged in diameter to have a large inner diameter portion 13b2. In this sense, the inner diameter portion 13b2 Is an escape portion in the deflection of the rack shaft 2. The stopper piece 13 having such a structure is press-fitted into the inner peripheral portion 64i1 of the second enlarged hole portion 64i in order to prevent the rack bush 8 from moving as described above. The flat surface 13a1 of the outer peripheral portion 13a is carefully finished, and relatively large chamfering processing 13a2 is applied to both side edges.

  The other support portion of the rack shaft 2, that is, the sliding support of the rack shaft 2 by the above-described sliding ring member 9 by the left housing 65 (see FIG. 1) is shown in FIG. The bush 90 is made of synthetic resin, rubber, etc., like the bush 8, and has a ring-shaped outer shape with a predetermined width, and the width is uniform. As shown in (c), a slit S is provided for cutting the ring at a predetermined angle with respect to the circumferential direction of the ring.

  The outer peripheral portion 90a of the bush 90 is basically a perfect circle and a flat peripheral surface, but at three equally spaced positions in the circumferential direction, that is, at a circumferential length of 120 °, a predetermined length in the circumferential direction. And a deformed portion 90d including a flat portion 90b and a projecting portion 90c having a central arcuate cross section in the circumferential extension of the flat portion 90b. The height of the projecting portion 90c in the deformed portion 90d is such that the top thereof is substantially coincident with the circumference of the outer peripheral portion 90a of the bush 90, but the flat portion 90b sandwiching the projecting portion 90c is flattened. As a result, the thickness of the bush 90 is reduced. However, since a convex surface portion 90h on the inner periphery of the bush 90, which will be described later, substantially corresponds to the deformed portion 90d, the thickness thereof does not change as much as the left.

  The three deformed portions 90d contribute to the support of the rack shaft 2 by the three convex surface portions 90h on the inner periphery of the bush 90 described later with an appropriate elastic effect, and in addition to the presence of the slit S. As a result, the bush 90 contributes to securing the bush 90 having a good position under a relatively light elastic pressure contact force when the bush 90 is fitted into an annular groove 65b of the left housing 65 described later.

  A relatively large chamfer 90e is provided on both sides in the width direction of the outer peripheral portion 90a of the bush 90, and both side portions 90f of the bush following the chamfer 90e are flat surfaces. The inner peripheral portion 90g of the bush 90 is basically a perfect circle, but the inner peripheral portion 90g is formed with three convex surface portions 90h, and these convex surface portions 90h are mutually in the circumferential direction of the inner peripheral portion 90g and the like. The circumferential positions of the convex surface portions 90h are formed within the three deformation portions 90d formed at equal intervals in the circumferential direction of the bush outer peripheral portion 90a. It is formed at the circumferential side corresponding position.

  All of the three convex surface portions 90h have a length extending over the entire width of the bush 90 perpendicular to the circumferential direction of the ring-shaped bush 90, and extend parallel to each other so as to cross the peripheral surface of the bush inner peripheral portion 90g. These convex surface portions 90h have a string-like shape that cuts a part of the arc on the inner periphery of the bush in a cross-sectional view, and the convex surface portion 90h includes an upper surface that is a substantially flat surface. The center 90i in the circumferential direction of a certain upper surface is located on the same circumference centered on the axis of the rack shaft 2 in the fitting to the left housing 65 to be described later for supporting the rack shaft 2, and is flat. The upper surface of each surface is parallel to the extending direction of the rack shaft 2, and the outer peripheral portion of the rack shaft 2 not provided with the rack teeth 21 is abutted and supported by the support portion by the circumferential center 90 i of the upper surface which is a flat surface. The rack shaft 2 is the bush 0 is sliding supported by.

  The bush 90 is also fitted to the left housing 65 as described above with reference to FIG. 1. For this reason, the inner peripheral portion 65a near the left end of the housing 65 is enlarged in FIG. As shown in the drawing, an annular recess 65b for accommodating and fitting the bush 90 is formed. The annular recess 65b extends a predetermined length in the longitudinal direction of the housing inner peripheral portion 65a, and extends in the radial direction of the housing 65. It has a fitting structure for accommodating and fitting the bushing 90 extending to reach a predetermined depth, that is, near the center of the radial thickness of the left housing 65, and the annular inner peripheral surface 65b1 of the annular recess 65b and the Both side portions 65b2 of the recess 65b are simple flat surfaces.

  The bush 90 received and fitted in the annular recess 65b of the inner peripheral portion 65a of the left housing 65 is not pressed strongly into the annular recess 65b, but is given a light elastic pressure contact force by the slit S. The bush 90 in the fitted state is basically a flat outer peripheral portion 90 a of the bush 90, and the flat side surfaces 90 f are the annular surfaces of the left housing 65. Since only the flat annular inner peripheral surface 65b1 of the recess 65b and the recess both side portions 65b2 are held in contact with each other, the anti-rotation means in the fitted state of the bush 90 is not actively provided.

  In the sliding support of the rack shaft 2 by the bush 90 fitted in the left housing 65 in the above-described state, the outer peripheral portion of the rack shaft 2 without the rack teeth 21 in the support portion is 3 of the bush inner peripheral portion 90g. The flat upper surface center 90i of each of the three convex surface portions 90h comes into contact with the outer peripheral portion of the rack shaft 2 with a relatively light elastic pressure contact force. The rack shaft 2 is slidably supported by the bush 90.

  The outer shape of the bush 90 and the shape of the annular recess 65b of the housing 65 that houses and fits the bush 90 are not limited to the above-mentioned shapes, and can be appropriately selected. There is no reason why the shape of the convex surface portion 90h is limited to a shape that exhibits a substantially flat surface in cross section as described above.

  The support of the rack shaft 2 by the above-described bushes, that is, the support by the bushes 8, 90 (9) and the pressing device 14 is an unloaded state where the load is not applied to the rack shaft 2 and the shaft 2 is not bent or low. In a state where the deflection of the shaft 2 is slight due to the load (for example, see FIG. 2), the peripheral surface 8e formed by a small arc of the inner peripheral portion 8d of the rack bush 8 is on the back side of the rack teeth 21 of the rack shaft 2. Do not touch directly. Accordingly, in this state, the rack shaft 2 is supported by the bush 90 which is the above-described sliding ring member 9 and the pressing portion 14b is supported by the supporting device near the left end in FIG. It is substantially supported at two locations on the right side of the figure.

Then, based on the steering operation, a load caused by a reaction force from a wheel (not shown) during traveling is applied to the rack shaft 2, and this load becomes relatively large, that is, when the load becomes high and the deflection of the rack shaft 2 increases. The rack bush 8 contacts the peripheral surface 8e of the inner peripheral portion 8d, and the load on the rack shaft 2 is received by the peripheral surface 8e. Accordingly, in this state, the rack shaft 2 is composed of the peripheral surface 8e of the bush 8, the bush 90 which is the sliding ring member 9 of the other support portion described above, and the pressing portion 14b by the pressing device 14. Supported in place.

  Since the present embodiment has the above-described configuration, the following operational effects can be obtained.

  The rack bush 8 has an inner peripheral portion 8d formed into an annular peripheral surface similar to a circle in which two circular arcs having different radii are continuously formed, and the annular peripheral surface is formed by an arc having a small radius. The surface 8e and a peripheral surface 8f formed by a circular arc having a large radius, and the rack shaft 2 to which a load is applied occupies a length in the range of an angle θ within 180 ° on the annular peripheral surface of the inner peripheral portion 8d. Since only the peripheral surface 8e with a small circular arc is slidably supported, unnecessary interference of the bush 8 with the rack shaft 2 is avoided, and appropriate sliding support is achieved while ensuring smooth movement of the rack shaft 2. The

  Further, the rack shaft 2 is supported on the peripheral surface 8e by the circular arc having a small radius. If the load applied to the rack shaft 2 is no load or a low load, the sliding ring member 9 which is the other support portion described above, that is, The rack shaft 2 is provided at two places, that is, the support by the bush 90 and the pressing portion 14b by the pressing device 14, or at three places where the peripheral surface 8e is further added to the support portion if the load is high. Adapted to the load applied to the shaft 2 and supported in a reasonable and stable state, the smooth engagement between the rack teeth and the pinion is ensured, and the generation of hitting sound due to the meshing of the gear is suppressed, and the gear Improves durability.

  The rack bush 8 is made of an elastic body such as synthetic resin or rubber, and has an engagement protrusion 8a on its outer peripheral portion 8b. When the bush 8 is fitted and attached, the protrusion 8a is inside the cylindrical housing 64 of the gear housing 61. Since the peripheral portion 64a, more specifically, the engaging recess 64g2 of the inner peripheral portion 64g1 of the first enlarged hole portion 64g is fitted, the positioning of the bush 8 in the rotation direction when the rack bush 8 is mounted is easy. In addition, the rack bush 8 can be mounted accurately.

  Further, since the rack bush 8 does not shift in the rotational direction even in long-term use, it is possible to prevent the durability from being deteriorated due to deformation or wear of the bush 8, and the rack teeth 21 and the pinion 3 are not stable. As a result, the durability of the rack shaft 2 and the pinion 3 is improved.

  Further, since the engaging recess 64g2 of the cylindrical housing 64 of the gear housing 61 is a groove portion whose side edge is opened at the second step portion 64h, the rack bush 8 is fitted into the cylindrical housing 64. The engagement convex portion 8a of the outer peripheral portion 8b of the bush 8 is easily aligned with the engagement concave portion 64g2 of the inner peripheral portion 64a (more specifically, 64g1) of the cylindrical housing 64 and pushed in from the axial direction. It can be carried out. Furthermore, since the engaging projection 8a of the outer peripheral portion 8b of the rack bush 8 is provided on the thick portion 8g of the bush 8, its strength is relatively high, and the positioning of the bush 8 by the engaging projection 8a is accurate. Moreover, it is stable.

  A mountain-shaped uneven portion 8c is provided on substantially the entire peripheral surface of the outer peripheral portion 8b of the rack bush 8, and since the uneven portion 8c is relatively easily deformed, the inner peripheral portion of the cylindrical housing 64 of the bush 8 is provided. The fitting to 64g1 is easy, and the support of the rack shaft 2 by the rack bush 8 has the effect of reducing the impact load applied to the rack shaft 2.

  The rack bush 8 in the above-described embodiment of the present invention has a surface on which the outer peripheral portion 8b is provided with the mountain-shaped uneven portion 8c over the entire surface except for the portion provided with the engaging convex portion 8a. 6, it is also possible to adopt a mode in which such a mountain-shaped uneven portion 8 c is not provided on the outer peripheral portion 8 b of the rack bush 8, and in this mode, the stability of the support of the rack shaft 2 by the rack bush 8 is high. high.

  Further, since the rack shaft 2 is supported by the so-called three-point support bush 90 by the bush 90 which is the above-described anti-pinion side sliding ring 9, the rack shaft 2 is supported by the rack shaft 2. The sliding frictional area can be reduced by reducing the sliding contact area due to the contact with the three convex surface portions 90h on the outer peripheral portion, and the bush 90 has no special detent means. Even if the positional deviation in the rotation direction is generated, the uniform support by the bush convex surface portion 90h of the outer periphery of the rack shaft 2 is not changed, so that the balance of the rack shaft 2 is balanced regardless of the load on the rack shaft 2. And stable sliding support can be realized.

  Further, the bush 90 is not press-fitted strongly into the annular recess 65b provided in the inner peripheral portion 65a of the left housing 65, and has an appropriate pressure that can suppress unnecessary movement by light elastic pressure contact force due to the slit. Since the annular recess 65b and the bush 90 are not provided with any special uneven portion for positioning the bush 90, the bush 90 has an annular recess 65b. The fitting is very easy because there is no need to give special consideration to the direction and position of the bush 90, and no means for preventing rotation of the bush 90 is required. Processing is unnecessary, and the cost can be reduced accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view of a rack and pinion type power steering apparatus of the present invention, and a part thereof is shown as a cross section. It is a figure which shows the main structure part of this invention, (a) is the sectional side view, (b) is AA sectional drawing in (a). It is a figure which shows the one operation | movement aspect in (a) of FIG. It is a figure which shows the rack bush of this invention, (a) Side view, (b) is a front view. It is a figure which shows the stopper piece of this invention. It is a figure which shows the rack bush of another aspect of this invention, (a) is a side view, (b) is a front view. It is a figure which shows the rack bush which is a sliding ring member of this invention, (a) is a front view, (b) is BB sectional drawing of (a), (c) is a bottom view of (a). is there. It is a figure which shows the fitting state to the housing of the rack bush in FIG. It is a figure which shows the main structure part in the conventional power steering apparatus, (a) is the sectional side view, (b) is 0A-0A sectional drawing in (a). It is a figure which shows the main structure part in another aspect in the conventional power steering apparatus, (a) is the sectional side view, (b) is 0B-0B sectional drawing in (a), (c) is a perspective view of a bush. It is. It is a figure which shows the fitting state of the bush in the conventional rack shaft support structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Power steering device, 2 ... Rack shaft, 21 ... Rack tooth, 3 ... Pinion, 4 ... Ball joint, 5 ... Tie rod, 6 ... Rack housing, 61 ..Gear housing, 61a... Boss portion, 63... Left cylindrical housing, 64... Right cylindrical housing, 64a. -Annular recess, 64d ... enlarged diameter part, 64e ... small hole, 64f ... first step, 64g ... first enlarged hole, 64g2 ... engagement recess, 64h ... 2nd step, 64i ... 2nd enlarged hole, 64j ... 3rd step, 64k ... 3rd enlarged hole, 65 ... Left housing, 65b ... Annular recess, 66 ... Cylinder housing, 67 ... Hollow tube housing, 67a ... Outer peripheral part, 67b ... Left outer peripheral part, 7 ... Bellows, 8 ... Rack bushing, 8a ... Engaging convex part, 8b ... Bushing outer peripheral part, 8c ... Yamagata 8d... Bushing inner peripheral part, 8e... Peripheral surface with a small radius arc, 8f... Peripheral surface with a large radius arc, 8g.・ Sliding ring member, 90 ... Bush, 90h ... Convex portion, 10 ... Bellows band, 11 ... Tie rod clip, 12 ... Stopper rubber, 13 ... Stopper piece, ... -Pressing device, 14a ... rack guide, 14b ... pressing part, 14c ... spring, 14d ... cap, M ... electric motor.

Claims (4)

In a rack and pinion type power steering device that slidably supports a rack shaft on a gear housing via a bush made of synthetic resin or rubber ,
The bush includes a convex portion that engages with an engagement concave portion of the inner surface portion of the gear housing on an outer peripheral portion,
The bush is fixed in the rack axial direction by a locking member,
The bush has an inner peripheral surface with two arcs of different radii on the inner surface,
The central angle of the arc with a small radius is within 180 °,
The inner peripheral surface by the small arc of the radius is a surface that contacts when the rack shaft is bent,
The rack and pinion type power steering apparatus , wherein the inner circumferential surface of the other arc is a surface that does not contact even when the rack shaft is bent . The rack shaft is slidably supported on the gear housing via a pressing device that presses the bush, another bush, and the rack shaft against a pinion,
The rack shaft is supported at two points (9, 14) when the load on the rack shaft is small and low, and is supported at three points (9, 14, 8) when the rack shaft is heavily loaded at high load. rack pinion on power steering apparatus according to claim 1, characterized in that that. The rack shaft, the low load is supported by the other bushing and the pressing device, the high load is the other bush, claim 2, characterized in that it is supported by the pressing device and the bushing The rack and pinion type power steering device described in 1. The rack and pinion type power steering apparatus according to claim 2 or 3, wherein the other bush includes three convex surface portions that support the rack shaft .

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