JP2012001070A - Rack shaft and method of manufacturing the same and rack pinion type steering gear unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To materialize structure of a rack shaft 7a constituting a rack pinion type steering gear unit and a method of manufacturing the rack shaft 7a, the structure enabling rack teeth 17a to be accurately formed in the process of manufacturing and the bending of the shaft to be accurately measured before bending correction work, and the structure further enabling the turning prevention function of the shaft in use to be increased.SOLUTION: The rack shaft 7a is made by forming the rack teeth 17a on the front face of an intermediate material which is constituted by cutting a drawn material at a prescribed length, wherein the outer circumference of the drawn material has a nearly polygonal cross section in which each apex is a circular arc with an equal radius of curvature around the center axis of the drawn material. The forming work of the rack teeth 17a is performed with an implement which is non-circularly engaged with a part of the outer circumference of the intermediate material, in a state in which the rotation of this intermediate material is inhibited. The bend measurement of the intermediate material is performed on the basis of the measurement of rotation deviation of a part corresponding to the circular arc part in the outer circumference of the intermediate material.

Description

  The present invention relates to an improvement of a rack and pinion type steering gear unit that constitutes a steering device of an automobile, a rack shaft that constitutes the rack and pinion type steering gear unit, and a method of manufacturing the rack shaft.

  2. Description of the Related Art Conventionally, a vehicle equipped with a rack and pinion type steering gear unit has been widely used as a steering device for an automobile. 12 to 16 show an example of a conventional structure of such a steering device. As shown in the overall configuration of FIG. 12, the steering device converts the rotational movement of the steering wheel 1 operated by the driver into a linear movement by a rack and pinion type steering gear unit 5, whereby left and right steering (not shown) It has a configuration that can give a desired steering angle to the wheels. Specifically, in order to realize such a configuration, the steering wheel 1 is fixed to the rear end portion of the steering shaft 2. At the same time, the front end portion of the steering shaft 2 is connected to the base end portion of the pinion shaft 6 constituting the steering gear unit 5 via a pair of universal joints 3 and 3 and the intermediate shaft 4. Further, the base ends of a pair of tie rods 8 and 8 that are connected to the left and right steering wheels, respectively, at both ends of a rack shaft 7 that meshes with the pinion shaft 6 constituting the steering gear unit 5. Are connected.

As shown in detail in FIGS. 13 to 16, the steering gear unit 5 includes a housing 9, a pinion shaft 6, a rack shaft 7, and a pressing means 10.
Of these, the housing 9 is fixed to the vehicle body, and includes a first housing 11 that houses the intermediate portion of the rack shaft 7, a second housing 12 that houses the tip half of the pinion shaft 6, A third housing 13 for housing the pressing means 10 is integrally provided.
The pinion shaft 6 has pinion teeth 14 near the tip of the outer peripheral surface. Such a pinion shaft 6 is supported by the pair of rolling bearings 15 and 16 so as to be rotatable only with respect to the second housing 12 with the first half inserted into the second housing 12. ing.

The rack shaft 7 has rack teeth 17 at a portion near one end of the front surface in the axial direction. The outer peripheral surface of the rack shaft 7 is a cylindrical surface except for a portion where the rack teeth 17 are formed. In other words, the cross-sectional shape of the outer peripheral surface of the rack shaft 7 is circular at a portion deviating from the rack teeth 17 in the axial direction, and corresponds to the rack teeth 17 at a portion where the rack teeth 17 are formed in the axial direction. The part is a straight line and the remaining part is an arc. Such a rack shaft 7 is inserted into the first accommodating body 11 at an axially intermediate portion, and the rack teeth 17 are engaged with the pinion teeth 14 with respect to the first accommodating body 11. An axial displacement is supported through a pair of rack bushings 18 and 18.
In the present specification and claims, “cross-sectional shape” means a cross-sectional shape related to a virtual plane orthogonal to the central axis of a target member unless otherwise specified.

  Both the rack bushes 18 and 18 are formed in a cylindrical shape as a whole by a low friction material such as an oil-resistant synthetic resin, a self-lubricating metal, and an oil-containing metal. In addition, the guide protrusions 20 and 20 are similarly provided at a plurality of circumferential positions on the inner circumferential surfaces of the rack bushes 18 and 18 (in the example shown in FIGS. 14 to 15, three positions at substantially equal intervals in the circumferential direction). At least one circumferential direction of the outer peripheral surface (in the example shown in FIGS. 14 to 15, two positions at equal intervals in the circumferential direction) have engaging convex portions 21 and 21, respectively. Both the rack bushes 18 and 18 are engaged by engaging the engaging protrusions 21 and 21 with engaging recesses 19 and 19 formed at both end portions of the inner peripheral surface of the first container 11. In a state where positioning in the circumferential direction is aimed, it is fitted and fixed to portions near both ends of the inner circumferential surface of the first container 11. Further, in this state, the front end surfaces of the respective guide projections 20 and 20 are brought into contact with the portion of the outer peripheral surface of the rack shaft 7 that is separated from the rack teeth 17 so as to be able to slide in the axial direction. ing.

  The pressing means 10 is housed inside the third housing 13 and includes a pressing member 22 and a spring 23. Of these, the pressing surface, which is the front end surface of the pressing member 22, is placed on the opposite side of the rack shaft 7 to the opposite side of the rack shaft 7 from the rack shaft 7. Axial sliding is possible. In this state, the pressing member 22 is elastically pressed toward the back surface of the rack shaft 7 by the spring 23. Thus, by applying a preload to the meshing portion between the pinion teeth 14 and the rack teeth 17, it is possible to suppress the generation of abnormal noise at the meshing portion and improve the operational feeling of the steering device. The pressing member 22 is entirely made of a low friction material as described above, or has a low friction material layer on a pressing surface that is in sliding contact with the back surface of the rack shaft 7.

  In the steering gear unit 5 configured as described above, the front end portion of the intermediate shaft 4 is connected to the base end portion of the pinion shaft 6 via the universal joint 3. At the same time, the base end portions of the tie rods 8 and 8 are connected to both end portions in the axial direction of the rack shaft 7 via ball joints 24 and 24. These ball joints 24, 24 are fixed to both ends of the rack shaft 7 by screwing or the like.

  In the case of the steering apparatus configured as described above, when the driver operates the steering wheel 1, the rotation of the steering wheel 1 is transmitted through the steering shaft 2, the universal joints 3, 3, and the intermediate shaft 4. And transmitted to the pinion shaft 6. As a result, the rack shaft 7 is displaced in the axial direction, and accordingly, the tie rods 8 and 8 are pushed and pulled, whereby a desired steering angle is given to the left and right steering wheels.

  The conventional rack shaft 7 described above is manufactured in the order of processes as shown in FIG. First, in step 1 (S1), a coil material having a circular cross-sectional shape as a material is prepared. Next, in step 2 (S2), the material is annealed to remove internal strain of the material. Next, in Step 3 (S3), the outer diameter dimension of the material is adjusted to a desired size by subjecting the material subjected to the annealing process to an outer diameter grinding process. Next, in step 4 (S4), the material subjected to the outer diameter grinding process is cut into a predetermined length to obtain a cylindrical intermediate material having a predetermined length. Next, in step 5 (S5), both ends of the intermediate material are processed to form screw holes for screwing and fixing the ball joints 24, 24 on both end surfaces of the intermediate material. . Next, in step 6 (S6), the intermediate material subjected to both end processing is subjected to tooth processing (at least one of plastic processing and cutting processing) on a portion near one end in the axial direction of the front surface, thereby The rack teeth 17 are formed in the portion. Next, in step 7 (S7), the intermediate material subjected to the tooth processing is subjected to a heat treatment to improve mechanical properties such as hardness of the rack teeth 17. Next, in step 8 (S8), the intermediate material subjected to the heat treatment is subjected to a bending process. Next, in step 9 (S9), the rack shaft 7 is completed by performing a surface finishing process on the intermediate material that has been subjected to the rebending process. In the final step 10 (S10), the rack shaft 7 is cleaned, and the manufacturing operation of the rack shaft 7 is completed.

  By the way, in the case of the manufacturing method of the rack shaft 7 as described above, when the intermediate material after the both end processing is subjected to tooth processing, a large rotational force is applied to the intermediate material as one component of the processing force. . However, in the case of the conventional structure described above, it is difficult to sufficiently secure the rotation preventing force of the intermediate material that counters such a rotating force. That is, as a method for obtaining such a rotation preventing force of the intermediate material, a method of pressing a portion of the outer peripheral surface of the intermediate material that is out of the toothed portion with a jig is conceivable. However, since the outer peripheral surface of the intermediate material is a mere cylindrical surface, the rotation prevention force obtained by the method is only a frictional force acting between the outer peripheral surface of the intermediate material and the surface of the jig, Cannot be too big. Therefore, when tooth processing is performed on the intermediate material, the rotational force may overcome the rotation preventing force, and the intermediate material may rotate. At this time, if the intermediate material is slightly rotated, the rack teeth 17 cannot be formed with high accuracy. If the rack teeth 17 cannot be accurately formed, abnormal noise is generated at the meshing portion between the rack teeth 17 and the pinion teeth 14 during use, or the power transmission efficiency at the meshing portion is reduced. As a result, the operation feeling of the steering wheel 1 deteriorates, and further, wear of the meshing portion is promoted, and various problems such as shortening the life of the rack shaft 7 and the pinion shaft 6 occur. To do.

  Further, during the operation of the automobile, a rotational force may act on the rack shaft 7 when the wheels reversely move. However, in the case of the above-described conventional structure, the function of preventing the rotation of the rack shaft 7 with respect to such a rotational force is poor. That is, in the case of the conventional structure described above, the function is achieved by frictional engagement between the cylindrical outer peripheral surface of the rack shaft 7 and the inner peripheral surfaces of the rack bushes 18 and 18 and the pressing surfaces of the pressing members 22. Is hardly exerted and is substantially exerted only by meshing of the rack teeth 17 and the pinion teeth 14. For this reason, when the rotational force acting on the rack shaft 7 is increased, the rack shaft 7 is rotated slightly, but the meshing state of the rack teeth 17 and the pinion teeth 14 becomes inappropriate. there is a possibility. And when this meshing state becomes improper, various problems as described above also occur.

In Patent Documents 1 to 3, a portion having a non-circular cross-sectional shape is provided in a portion of the outer peripheral surface of the rack shaft that is out of the rack teeth, and the inner periphery of the rack bushing is provided in the non-circular cross-sectional portion. There is described a structure in which the function of preventing the rotation of the rack shaft can be enhanced by engaging a pressing surface of a surface or a pressing member.
However, in the case of the structures described in these Patent Documents 1 to 3, the rack shaft is made of a columnar or tubular intermediate material having a predetermined length, and of the outer peripheral surface of the rack shaft, A portion having a non-circular cross-sectional shape that exists in a portion deviated from the rack teeth is formed by forging the intermediate material. That is, the operation of forming the non-circular portion of the cross-sectional shape is performed individually for each rack shaft to be manufactured. Therefore, the manufacturing cost increases accordingly.

JP 2000-238650 A JP 2004-34829 A JP 2008-213756 A

  In view of the circumstances as described above, the present invention has a structure in which a rack shaft having a non-circular cross-sectional shape out of the rack teeth on the outer peripheral surface can be made with high accuracy and low cost, and The invention was invented to provide a manufacturing method thereof and a rack and pinion type steering gear unit provided with the rack shaft.

Of the rack shaft of the present invention, the manufacturing method thereof, and the rack and pinion type steering gear unit, the rack shaft described in claim 1 is made of metal and has a rack tooth on a portion of the front surface (one side surface in the radial direction of the outer peripheral surface) in the axial direction. Have
In particular, the rack shaft according to claim 1 is formed by forming the rack teeth on a part of the front surface of an intermediate material formed by cutting a material to be drawn into a predetermined length. In addition, the cross-sectional shape of the outer peripheral surface of the drawn material is a substantially polygonal shape in which each vertex is an arc having the same radius of curvature with the central axis of the drawn material as the center. In other words, the cross-sectional shape of the outer peripheral surface of the drawn material is a shape in which each vertex portion of the basic polygon is replaced with an arc having the same radius of curvature around the central axis of the drawn material.

  The rack shaft manufacturing method according to claim 2 is the rack shaft manufacturing method according to claim 1 described above, and the cross-sectional shape of the outer peripheral surface of the rack shaft is obtained by drawing a metal material. A drawing material having a substantially polygonal shape in which each vertex is an arc having the same radius of curvature with the central axis as the center (in other words, the cross-sectional shape of the outer peripheral surface of each vertex of the basic polygon is And a step of obtaining an intermediate material formed by cutting the drawn material into a predetermined length, and the intermediate material. Of the outer peripheral surface of the intermediate material, a portion removed from the portion where the rack teeth are to be formed is pressed by a jig that is non-circularly engaged with the portion (for example, the rack teeth on the outer peripheral surface of the intermediate material) The part that is out of the part that should be formed And a portion corresponding to at least two of the straight portions constituting the substantially polygonal shape with respect to the cross-sectional shape is pressed by a jig), and a part of the front surface of the intermediate material in the axial direction Forming the rack teeth.

A rack and pinion type steering gear unit according to a third aspect includes a housing, a rack bush, a rack shaft, a pinion shaft, and a pressing means.
Of these, the housing is fixed to the vehicle body.
The rack bush is formed in a cylindrical shape and is fixed to the inside of the housing.
The rack shaft has rack teeth on a part of the front surface (one side surface in the radial direction of the outer peripheral surface) in the axial direction, and the outer peripheral surface is supported by the inner peripheral surface of the rack bush so as to be slidable in the axial direction. In this state, it is arranged inside the housing.
The pinion shaft has pinion teeth on a part of the outer peripheral surface in the axial direction, and is rotatably supported inside the housing with the pinion teeth meshed with the rack teeth.
The pressing means includes a pressing member, and a portion of the back surface of the rack shaft (the other side surface in the radial direction of the outer peripheral surface) on the side opposite to the pinion shaft is sandwiched by the pressing member. It is arranged inside the housing while being elastically pressed.
In particular, in the rack and pinion type steering gear unit described in claim 3, the rack shaft is the rack shaft described in claim 1 described above.

  When the rack and pinion type steering gear unit according to the present invention is implemented, preferably, as in the invention described in claim 4, an inner peripheral surface of the rack bush and a pressing surface provided at a tip portion of the pressing member are provided. At least one of the surfaces is brought into sliding contact with the outer peripheral surface of the rack shaft in a non-circular engagement state. For example, the at least one surface is brought into sliding contact with a portion of the outer peripheral surface of the rack shaft corresponding to at least two straight portions of the straight portions constituting the substantially polygonal shape with respect to a cross-sectional shape.

  More preferably, as in the invention described in claim 5, one or more protrusions are provided on any one of the inner peripheral surface of the rack bush and the outer peripheral surface of the rack shaft that are in sliding contact with each other. Or a recessed part is formed in the state which follows an axial direction.

  In the case of the rack shaft of the present invention configured as described above, the manufacturing method thereof, and the rack and pinion type steering gear unit, rack teeth can be formed with high accuracy when the rack shaft is manufactured. That is, the rack shaft according to the present invention is formed by forming the rack teeth on a part of the front surface of the intermediate material formed by cutting the material to be drawn into a predetermined length. And the cross-sectional shape of the outer peripheral surface of the intermediate material is non-circular (substantially polygonal shape in which each vertex is an arc having the same radius of curvature with its central axis as the center). For this reason, as in the second aspect of the invention, a portion of the outer peripheral surface of the intermediate material that is out of the portion where the rack teeth are to be formed is pressed by a jig that is non-circularly engaged with the portion. If the rack teeth are formed in a state where the rack teeth are formed, the effect of preventing the rotation of the intermediate material when forming the rack teeth can be sufficiently enhanced. For this reason, the rack teeth can be formed with high accuracy.

  In addition, when the rack shaft of the present invention is manufactured, a necessary cross-sectional shape can be obtained at a portion of the outer peripheral surface of the completed rack shaft that is out of the rack teeth at the stage of obtaining the drawn material. . For this reason, it is not necessary to perform processing for obtaining a necessary cross-sectional shape for the intermediate material of the rack shaft to be manufactured. Therefore, the number of processing steps can be reduced by that amount, and the manufacturing cost can be reduced.

  Further, like a drawn material used as a material for the rack shaft of the present invention, a drawn material having a non-circular cross-sectional shape on the outer peripheral surface is likely to be bent during manufacture. However, in the case of the drawn material used as the material of the rack shaft of the present invention, the cross-sectional shape of the outer peripheral surface is a substantially polygonal shape in which each vertex is an arc having the same radius of curvature centering on the central axis of the drawn material. It has become. In the case of such a drawn material, compared to a drawn material in which the cross-sectional shape of the outer peripheral surface is a simple polygon (a polygon in which each vertex is a non-differentiable corner with respect to a line representing the cross-sectional shape), Bending caused by manufacturing can be suppressed. However, even if such an effect can be obtained, there is a possibility that bending will occur with the manufacture. Therefore, when the rack shaft of the present invention is manufactured, the intermediate material is bent again at any stage of the manufacturing process, as in the case of the conventional rack shaft manufacturing method shown in FIG. It is preferable to carry out.

  Thus, when the process of rebending the intermediate material is performed, it is first necessary to measure the bend generated in the intermediate material. In the case of the rack shaft of the present invention, an R chamfered portion exists in a portion of the outer peripheral surface of the intermediate material corresponding to each arc portion of the cross-sectional shape of the outer peripheral surface. Each of these R chamfered portions has the same center of curvature at the central axis of the intermediate material, and all have the same radius of curvature. For this reason, the bending of the intermediate material is accurately measured by using the respective R chamfered portions in the same manner as the conventional method for measuring the bending of a round bar having a circular cross section. It becomes possible to do. Specifically, the intermediate material is rotated in a state where the intermediate material is supported at two positions in the axial direction of each R chamfer. And it is possible to accurately measure the bending of the intermediate material on the basis of measuring the deflection of each R chamfered portion that occurs with this rotation at a position deviating from the two positions with respect to the axial direction. it can. For this reason, based on the bending of the intermediate material measured in this way, the intermediate material can be bent again with high accuracy.

  Further, in the case of the present invention, the cross-sectional shape of the portion of the outer peripheral surface of the rack shaft that is off the rack teeth is the same non-circular shape over the entire length in the axial direction. Therefore, for example, as in the invention described in claim 4, in the assembled state of the rack and pinion type steering gear unit, at least one of the inner peripheral surface of the rack bush and the pressing surface of the pressing member is attached to the rack. By making sliding contact with the outer peripheral surface of the shaft in a non-circular engagement, the effect of preventing rotation of the rack shaft during use can be enhanced. Therefore, the meshing state of the rack teeth and the pinion teeth can be easily maintained in an appropriate state.

Further, in the case of the rack and pinion type steering gear unit of the present invention, the drawing direction of the drawing material as the material, which is the processing direction of the portion outside the rack teeth, of the outer peripheral surface of the rack shaft, and the portion The sliding directions of the inner peripheral surface of the rack bush and the pressing surface of the pressing member are respectively the axial directions of the rack shaft and coincide with each other. For this reason, the sliding resistance in the axial direction at the sliding contact portion between these surfaces can be reduced.
Furthermore, if the configuration of the invention described in claim 5 is adopted, the sliding contact area between the inner peripheral surface of the rack bush and the outer peripheral surface of the rack shaft is reduced, and a lubricating oil is provided between the two peripheral surfaces. It becomes easy to hold. For this reason, the sliding resistance in the axial direction at the sliding contact portion between these two peripheral surfaces can be further reduced.

The figure equivalent to the expanded aa cross section of FIG. 13 regarding the 1st example of embodiment of this invention. Similarly, the figure equivalent to the expanded bb cross section of FIG. Similarly, the figure equivalent to the c section of FIG. Similarly, the flowchart which shows the manufacturing process of a rack axis | shaft. Sectional drawing (A) of a raw material and an intermediate raw material for manufacturing a rack axis | shaft, and sectional drawing (B) in the position which formed the rack tooth of the 2nd intermediate raw material. The schematic diagram showing the support location of this 2nd intermediate material, and the measurement location of a shake regarding the axial direction at the time of measuring the bending of a 2nd intermediate material. Sectional drawing for demonstrating the support location of this 2nd intermediate material and the measurement location of a radial direction position regarding the circumferential direction at the time of measuring the bending of a 2nd intermediate material. The figure similar to FIG. 6 which shows the other example of the support location of a 2nd intermediate material, and the measurement location of shake regarding an axial direction. The same figure as FIG. 7 regarding the 2nd intermediate | middle raw material from which the formation range of a rack tooth differs. The enlarged view equivalent to the d section of Drawing 1 showing the 2nd example of an embodiment of the invention. Enlargement of the sliding contact portion between the R chamfered portion and the inner peripheral surface of the rack bush, showing an example in which a plurality of concave portions (A) or convex portions (B) extending over the entire axial length is formed on the R chamfered portion of the rack shaft. Sectional drawing. 1 is a partially cutaway side view showing an example of an automotive steering apparatus including a rack and pinion type steering gear unit that is an object of the present invention. The expanded ee sectional drawing of FIG. FIG. 14 is an enlarged aa cross-sectional view of FIG. 13. FIG. 14 is an enlarged bb cross-sectional view of FIG. 13. The expanded ff sectional view of FIG. The flowchart which shows an example of the manufacturing process of the conventional rack shaft.

[First example of embodiment]
A first example of an embodiment of the present invention corresponding to claims 1 to 4 will be described with reference to FIGS. The feature of this example is that the shape of the outer peripheral surface of the rack shaft 7a, the shape of the inner peripheral surface of the pair of rack bushes 18a, 18a, the shape of the tip surface of the pressing member 22a constituting the pressing means 10a, It is in the manufacturing method of the rack shaft 7a. Since the structure and operation of the other parts are the same as those of the conventional structure shown in FIGS. 12 to 16, the same parts are denoted by the same reference numerals, and overlapping illustrations and descriptions are omitted or simplified. Hereinafter, the description will focus on the features of this example.

  In the case of this example, as shown in FIGS. 1 to 3, the outer peripheral surface of the rack shaft 7 a is formed at a portion closer to one end in the axial direction of the front surface of the rack shaft 7 a (upper surface in FIGS. 1 to 3). The cross-sectional shape of the portion deviated from the rack teeth 17a is the same non-circular shape over the entire length in the axial direction. Specifically, each of the apex portions of the regular octagon is replaced with an arc having the same radius of curvature around the central axis of the rack shaft 7a. That is, of the outer peripheral surface of the rack shaft 7a, the flat portions 25 and 25 are arranged in the portions corresponding to the linear portions of the substantially regular octagonal shape, respectively, on the portions that are separated from the rack teeth 17a. In addition, R chamfered portions 26 and 26 are arranged at portions corresponding to the respective arc portions.

In the case of this example, as shown in FIGS. 1 and 2, the inner peripheral surfaces of the rack bushes 18a and 18a are simply cylindrical surfaces. The inner peripheral surfaces of the rack bushes 18a and 18a are brought into contact with only the R chamfered portions 26 and 26 of the outer peripheral surface of the rack shaft 17a so as to be able to slide in the axial direction.
In the case of this example, as shown in FIG. 3, the pressing member 22a constituting the pressing means 10a has a pair of flat pressing surfaces 27, 27 on the tip surface. Then, in a state in which both the pressing surfaces 27, 27 are non-circularly engaged with a pair of flat portions 25, 25 existing on the back surface (the lower surface in FIGS. 1 to 3) of the rack shaft 7a, Axial sliding is possible.

  In the case of this example, the rack shaft 7a is manufactured in the order of steps as shown in FIG. As can be seen by comparing the process sequence of this example shown in FIG. 4 with the conventional process sequence shown in FIG. 17 described above, the rack shaft 7a of this example is the conventional rack shaft 7 (FIGS. 13 to 16). (See reference). However, in the case of this example, the material prepared in the first step (S1) is a drawn material 28 having a cross-sectional shape as shown in FIG. The cross-sectional shape of the outer peripheral surface of the drawn material 28 is substantially the same as the cross-sectional shape of the portion of the outer peripheral surface of the rack shaft 7a that is detached from the rack teeth 17a, including the outer diameter. That is, on the outer peripheral surface of the drawing material 28, the flat portion 25 is respectively provided on the outer peripheral surface of the rack shaft 7 a corresponding to each linear portion of the cross-sectional shape, similar to the portion removed from the rack teeth 17 a. 25, and R chamfered portions 26, 26 are respectively disposed at portions corresponding to the respective arc portions. Such a drawing material 28 is made of a metal material (for example, a coil material having a circular cross-sectional shape) constituting the rack shaft 7a by using a die having a die hole having the same cross-sectional shape as that of the drawing material 28. It can be easily obtained by drawing.

  As described above, in the case of this example, the cross-sectional shape of the outer peripheral surface of the drawing material 28, which is a material, is the same as the cross-sectional shape of the portion of the outer peripheral surface of the rack shaft 7a that is out of the rack teeth 17a. It is substantially the same including the diameter dimension. Therefore, after the subsequent annealing step (S2), the process proceeds to the cutting step (S4) without passing through the outer diameter grinding (see FIG. 17) step (S3). In this cutting step (S4), an intermediate material 29 is obtained, which is formed by cutting the drawing material 28 into a predetermined length. Then, after the subsequent both-end machining step (S5), the process proceeds to the tooth machining step (S6). In the tooth machining step (S6), the rack teeth 17a are formed on a part of the front surface of the intermediate material 29 in the axial direction. As a result, the second intermediate material 30 having a cross-sectional shape as shown in FIG. 5B is obtained at the axial position where the rack teeth 17a are formed. However, in the case of this example, the operation of forming the rack teeth 17a as described above is performed by removing a portion of the outer peripheral surface of the intermediate material 29 that is out of the portion where the rack teeth 17a are to be formed into a non-circular portion. A state of being pressed by an engaged jig (not shown) (for example, a portion of the outer peripheral surface of the intermediate material 29 that is out of the portion where the rack teeth 17a are to be formed, and each of the planar portions 25, 25 in a state where at least two flat portions of 25 are pressed by the jig. In addition, the processing method of the rack teeth 17a in S6 can employ various conventionally known processing methods. For example, a total type in which the rack teeth 17a are processed over the entire length at once. A processing method using a broach can also be employed.

  In the case of this example, after the subsequent heat treatment step (S7), the process proceeds to the rebending step (S8). In this re-bending step (S8), first, the bending of the second intermediate material 30 is measured. Specifically, as shown in FIG. 6, both ends of the second intermediate material 30 in the axial direction (axial direction) are used, as in the case of measuring the bending of a round bar having a circular cross-sectional shape, which is conventionally known. In this state, the second intermediate material 30 is rotated in a state in which the portion separated from the rack teeth 17a is placed on the upper surfaces of the pair of V blocks 31 and 31. Then, the shake of the second intermediate material 30 in the axial direction (the portion that is out of the rack teeth 17a with respect to the axial direction) generated by the rotation is measured by a measuring instrument 32 such as a micrometer or a laser distance measuring instrument. taking measurement. Based on the measurement result, the bending of the second intermediate material 30 is obtained. However, in this case, the axially opposite ends of the second intermediate material 30 are supported by the upper surfaces of the pair of V blocks 31, 31, and the second intermediate material 30 is axially intermediate by the measuring device 32. The measurement of the deflection of each part is performed at each of the R chamfered portions 26 and 26 in the outer peripheral surface of the second intermediate material 30.

上述の様にして第二中間素材３０の曲がりを測定したならば、次いで、この第二中間素材３０の曲り直しの作業を行う。この曲り直しの作業は、この第二中間素材３０に対して、上述の様に測定した曲がりを解消できる方向及び大きさの力を加える事によって行う。 In order to give a more specific explanation on this point, as shown in FIG. 7, the circumferential locations of the R chamfered portions 26, 26 are defined as P _A , P _B , P _C , P, respectively. _These are represented by _D , P _E , P _F , P _G , and P _H. In the case of this example, when measuring the bending of the second intermediate material 30, of the R chamfered portions 26, 26, two R chamfered portions adjacent in the circumferential direction are defined as the pair of V chamfered portions. It is supported by the upper surfaces of the blocks 31 and 31. Then, in this state, the measuring device 32 measures the radial positions of the other two R chamfered portions existing on the opposite side in the radial direction with respect to the two R chamfered portions. Then, such a measurement operation is performed for a combination of a plurality of support locations and measurement locations as shown in Table 1 below while changing the rotation angle position of the second intermediate material 30. And based on this measurement result, the direction and magnitude | size of the deflection | deviation of the axial direction intermediate part of said 2nd intermediate material 30 are calculated | required. Further, based on the direction and magnitude of the deflection, the bending direction (= direction of deflection) and magnitude (= size of deflection / 2) of the second intermediate material 30 are obtained.

If the bending of the second intermediate material 30 is measured as described above, the second intermediate material 30 is then bent again. This re-bending operation is performed by applying a force having a direction and a magnitude capable of eliminating the bending measured as described above to the second intermediate material 30.

  In the case of this example, the rack shaft 7a is completed when the above-described re-bending step (S8) is completed. That is, in the case of this example, after the re-bending step (S8) described above, the final cleaning step (S10) without passing through the surface finishing step (S9, see FIG. 17) The manufacturing operation of the rack shaft 7a is completed. Therefore, in the case of the present example, the portion of the outer peripheral surface of the completed rack shaft 7a that is detached from the rack teeth 17a remains the drawing surface that is the outer peripheral surface of the drawing material 28.

  In the case of the rack shaft, the manufacturing method thereof, and the rack and pinion type steering gear unit of this example as described above, the rack teeth 17a of the rack shaft 7a can be formed with high accuracy. That is, in the case of this example, the cross-sectional shape of the outer peripheral surface of the intermediate material 29 of the rack shaft 7a is non-circular. In addition, the operation of forming the rack teeth 17a on the front surface of the intermediate material 29 is performed by removing a portion of the outer peripheral surface of the intermediate material 29 that is out of the portion where the rack teeth 17a are to be formed. The test is performed with the jig held together. For this reason, the effect of preventing the rotation of the intermediate material 29 when forming the rack teeth 17a can be sufficiently enhanced. Therefore, the rack teeth 17a can be formed with high accuracy.

  Further, in the case of this example, when the rack shaft 7a is manufactured, a portion of the outer peripheral surface of the rack shaft 7a that has been completed is separated from the rack teeth 17a when the drawn material 28 is obtained. The necessary cross-sectional shape can be obtained. For this reason, it is not necessary to perform processing for obtaining a necessary cross-sectional shape for the rack shaft 7a to be manufactured. Therefore, the number of processing steps can be reduced by that amount, and the manufacturing cost can be reduced.

  In the case of this example, the second intermediate material 30 can be accurately bent again in the re-bending step (S8) performed when the rack shaft 7a is manufactured. That is, in the case of this example, there are R chamfered portions 26, 26 at eight circumferentially equidistant positions on the outer peripheral surface of the second intermediate material 30. Each of these R chamfered portions 26, 26 has the same center of curvature at the central axis of the second intermediate material 30, and all have the same radius of curvature. For this reason, as described above, the bending of the second intermediate material 30 is performed on each of the R chamfered portions in the same manner as in the conventional measurement of bending of a round bar having a circular cross-sectional shape. 26, 26 can be used for accurate measurement. For this reason, based on the bending of the second intermediate material 30 measured in this manner, the second intermediate material 30 can be bent again with high accuracy. Therefore, the bend of the rack shaft 7a after completion can be reduced at a high level.

  In the case of this example, the cross-sectional shape of the portion of the outer peripheral surface of the rack shaft 7a that is disengaged from the rack teeth 17a is the same non-circular shape over the entire length in the axial direction. Then, a pair of flat pressing surfaces 27, 27, which are the front end surfaces of the pressing member 22a, are non-circularly engaged with a pair of flat portions 25, 25 existing on the back surface of the rack shaft 7a. In this state, they are in contact with each other so that they can slide in the axial direction. For this reason, based on the non-circular engagement between the flat portions 25, 25 and the pressing surfaces 27, 27, the effect of preventing the rotation of the rack shaft 7a during use can be enhanced. Therefore, the meshing state of the rack teeth 17a and the pinion teeth 14 (see FIGS. 13 and 16) can be easily maintained in an appropriate state.

  In the case of this example, the drawing direction of the drawing material 28 serving as the material, which is the processing direction of the outer peripheral surface of the rack shaft 7a, which is removed from the rack teeth 17a, and the rack bush 18a with respect to the portion. , 18a and the sliding directions of the pressing surfaces 27, 27 of the pressing member 22a are respectively in the axial direction of the rack shaft 7a and coincide with each other. For this reason, out of the surface roughness of the outer peripheral surface of the rack tooth, the surface roughness in the sliding direction with the inner peripheral surface of the rack bush 18a, 18a and the pressing surface 27, 27 is reduced, and each of these surfaces The sliding resistance in the axial direction at the sliding contact portion can be reduced. Further, in the case of this example, as described above, the bending of the rack shaft 7a is small at a high level. For this reason, the sliding resistance in the axial direction at the sliding contact portion between the surfaces can be stabilized. Therefore, the operational feeling of the steering wheel 1 (see FIG. 12) can be improved, and the wear amount of each sliding contact portion can be reduced, and the durability of each sliding contact portion can be enhanced.

When the present invention is carried out, the support position of the second intermediate material 30 and the measurement position of the deflection with respect to the axial direction, which are employed when measuring the bending of the second intermediate material 30, are respectively shown in FIG. For example, the position shown in FIG. 8 may be used instead of the position shown in FIG.
Further, when measuring the bending of the second intermediate material 30, at least one position of the support position of the second intermediate material 30 and the measurement position of the deflection in the axial direction is determined by the rack teeth 17 a. When it coincides with the position in the axial direction, for example, the shake can be measured as follows. That is, with reference to FIG. 9, in such a case, instead of a combination of a plurality of support locations and measurement locations as shown in Table 1 above, as shown in Table 2 below, About the combination of a some support location and a measurement location, the radial direction position of each of these measurement locations is measured. Along with this, as shown in Table 3 below, the combination of a plurality of support locations and measurement locations is measured, and the radial positions of these measurement locations are measured. In this way, it is possible to measure the necessary radial positions of all the measurement points P _B , P _C , P _D , P _E , P _F , P _G , and P _H. For this reason, based on the measurement result, the shake of the second intermediate material 30a at the target axial position can be accurately obtained.

[Second Example of Embodiment]
FIG. 10 shows a second example of an embodiment of the present invention corresponding to claims 1 to 4. In the case of this example, in the outer circumferential surface of the rack bush 18b, the first container of the housing 9 is placed in the same phase as each R chamfer 26 on the outer circumferential surface of the rack shaft 7a in the circumferential direction. 11 is provided with an escape recess 33 that does not come into contact with the inner peripheral surface. As a result, a portion of the rack bush 18b that is in phase with the R chamfered portion 26 in the circumferential direction is a spring plate portion 34 that can be elastically deformed in the radial direction. Then, based on an appropriate radial spring force exerted by each of the spring plate portions 34, the inner peripheral surface of each of the spring plate portions 34 is elastically slidably brought into sliding contact with the respective R chamfered portions 26. Yes.

  In the case of this example having such a configuration, the radial shakiness of the rack shaft 7a can be suppressed based on the elasticity of each of the spring plate portions 34. Further, since the surface pressure of the sliding contact portion between each R chamfered portion 26 and the inner peripheral surface of each spring plate portion 34 can be kept low, the axial sliding resistance at each sliding contact portion is kept low. It is done. Other configurations and operations are the same as those in the first example of the embodiment described above.

Further, when the present invention is carried out, as shown in FIG. 11A, a plurality of concave portions 35, 35 are formed in each of the R chamfered portions 26 existing on the outer peripheral surface of the rack shaft 7a so as to have a total axial length. As shown in FIG. 5B, a plurality of convex portions 36, 36 are provided on each R chamfer 26 on the outer peripheral surface of the rack shaft 7a over the entire length in the axial direction. Can also be formed. By adopting these configurations, the sliding contact area between the outer peripheral surface of the rack shaft 7a and the inner peripheral surface of the rack bush 18a (18b) is reduced, and the lubricating oil can be held between the two peripheral surfaces. A gap is formed. For this reason, the sliding resistance in the axial direction at the sliding contact portion between these two peripheral surfaces can be further reduced.
In addition, the concave portions 35 and 35 and the convex portions 36 and 36 can be formed simultaneously with the manufacture of a drawing material as a material (by drawing).
As described above, the concave portion and the convex portion for reducing the sliding resistance between the outer peripheral surface of the rack shaft and the inner peripheral surface of the rack bush are not provided on the outer peripheral surface of the rack shaft. It can also be provided on the inner circumferential surface.

  Further, in the case of carrying out the present invention, regarding the cross-sectional shape of the outer peripheral surface of the drawn material that is the material of the rack shaft, each apex is a substantially polygonal shape that is an arc having the same radius of curvature around the central axis of the drawn material. Other conditions are not particularly limited. For example, the polygon need not be a regular polygon. The circumferential width of each arc portion (the radius of curvature of each arc portion) can be set to an arbitrary size.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Universal joint 4 Intermediate shaft 5 Steering gear unit 6 Pinion shaft 7, 7a Rack shaft 8 Tie rod 9 Housing 10, 10a Pressing means 11 First container 12 Second container 13 Third container 14 Pinion Teeth 15 Rolling bearing 16 Rolling bearing 17, 17a Rack teeth 18, 18a, 18b Rack bushing 19 Engaging recess 20 Guide projection 21 Engaging projection 22, 22a Press member 23 Spring 24 Ball joint 25 Plane portion 26 R chamfer 27 Pressing surface 28 Drawing material 29 Intermediate material 30 Second intermediate material 31 V block 32 Measuring instrument 33 Escape recessed part 34 Spring plate part 35 Recessed part 36 Convex part

Claims (5)

  In a metal rack shaft having rack teeth on a part of the front surface in the axial direction, the rack teeth are formed on a part of the front surface of the intermediate material formed by cutting the drawn material into a predetermined length. The rack shaft is characterized in that the cross-sectional shape of the outer peripheral surface of the drawn material is a substantially polygonal shape in which each vertex is an arc having the same radius of curvature with the central axis of the drawn material as the center. .   The rack shaft manufacturing method according to claim 1, wherein by performing a drawing process on a metal material, a cross-sectional shape of an outer peripheral surface thereof becomes an arc having an equal curvature radius with each vertex centered on the central axis. A step of obtaining a drawing material having a substantially polygonal shape, a step of obtaining an intermediate material obtained by cutting the drawing material into a predetermined length, and a portion of the outer peripheral surface of the intermediate material on which the rack teeth are to be formed. And a step of forming the rack teeth on a part of the front surface of the intermediate material in the axial direction in a state in which the part removed from the part is pressed by a jig non-circularly engaged with the part. Manufacturing method. A housing, a rack bush, a rack shaft, a pinion shaft, and a pressing means;
Of these, the housing is fixed to the vehicle body,
The rack bush is made in a cylindrical shape, and is fixed to the inside of the housing,
The rack shaft has rack teeth in a part of the front surface in the axial direction, and the outer peripheral surface is arranged inside the housing in a state in which the outer peripheral surface is supported by the inner peripheral surface of the rack bush so as to be slidable in the axial direction. Has been
The pinion shaft has pinion teeth in a part of the outer peripheral surface in the axial direction, and is rotatably supported inside the housing with the pinion teeth meshed with the rack teeth.
The pressing means includes a pressing member, and a portion of the rear surface of the rack shaft that is opposite to the pinion shaft across the rack shaft is elastically pressed by the pressing member. Arranged inside,
In rack and pinion type steering gear unit,
A rack and pinion type steering gear unit, wherein the rack shaft is a rack shaft according to claim 1.   At least one of the inner peripheral surface of the rack bush and the pressing surface provided at the tip of the pressing member is in sliding contact with the outer peripheral surface of the rack shaft in a non-circular engagement state. The rack and pinion type steering gear unit according to claim 3.   One or a plurality of convex portions or concave portions are formed in an axially continuous state on any one of the inner peripheral surface of the rack bush and the outer peripheral surface of the rack shaft that are in sliding contact with each other. The rack and pinion type steering gear unit according to claim 4.

Images