JPS6128860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a press-molding die for a rack for a rack and pinion type steering device, and more particularly to the rack tooth profile and end tooth groove shape formed at both end portions of the rack portion. In general, in the case of racks of rack and pinion type steering devices that have a constant gear ratio, all rack tooth profiles are uniform, so the rack tooth profile can be easily formed by gear cutting using a milling machine or the like. .

However, in the case of the rack of a rack and pinion type steering device with a variable gear ratio, the shape of the rack tooth profile changes for each tooth profile and is not uniform, so it is impossible to form the rack tooth profile by known cutting processes. It was hot.

1-3 illustrate an example of a conventional rack meshing with a helical pinion (not shown) in a rack and pinion steering system having variable gear ratios. The rack 1 includes a cylindrical rack rod 2 and a rack portion 3, and the rack portion 3 has a plurality of rack teeth 4 formed therein.
To manufacture such a rack 1, first, the tooth tip surface 5 of the rack tooth profile 4 is attached to the outer surface of the material of the rack rod 2.
A plane corresponding to the height is formed in the rack portion 3 so as to be parallel to the axis 6 of the rack rod 2. Next, an easy tooth profile that is close to the completed rack tooth profile 4 and that can be machined by gear cutting is formed on the rack part 3 by cutting. Next, the desired rack 1 is obtained by press-molding the tooth surface of the recently cut rack tooth profile using a rack molding die (not shown) having a transfer shape of the completed rack tooth profile 4. It was done. However, in the conventional method of press-molding the rack tooth profile 4, the tooth portions of the rack molding die corresponding to the end tooth grooves 7 formed at both ends in the direction of the axis 6 of the rack rod 2 in the rack portion 3 are It may break or break under the influence of the reaction force of the molding load in the tooth groove 7 and the material flow stress caused by the axial extension of the rack rod 2, and the life of the rack molding mold will be significantly shortened. It had shortcomings such as the fact that the manufacturing cost of the rack could not be reduced because the mold for molding the rack was expensive.

This invention is intended to solve the above-mentioned drawbacks, and is directed to the final end rack tooth profile formed at both ends of the rack part in the rack rod axial direction, or a plurality of final end rack tooth profiles continuous from the final end rack tooth profile. The end rack tooth profile has a root height equal to the other residual rack tooth profile formed in the rack part, and the total tooth height is formed to be smaller than the remaining rack tooth profile toward both ends of the rack part, and Transfer of the rack tooth profile formed in such a way that the end tooth grooves formed at both ends of the rack adjacent to the final end rack tooth profile have an end inclined surface that reaches from the bottom surface of the end tooth groove to the outer peripheral surface of the rack rod. Rack and pinion type steering device that is press-molded with a press-forming mold that has a shape, improves the life of the rack-forming mold, reduces manufacturing costs, and enables mass production with stable, high-precision quality. The aim is to get the luck of the day.

Embodiments of the present invention will be described below with reference to the drawings.

4 to 6 show a first embodiment, in which a rack 11 is connected to a cylindrical rack rod 12 with a rack portion 13.
is provided. The rack portion 13 has final end rack teeth 14 at both ends in the rack rod axial direction.
A plurality of end rack tooth profiles 15 including the final end rack tooth profile 14 continue from the final end rack tooth profile 14, and a plurality of remaining rack tooth profiles 16 are formed between the end rack tooth profiles 15 on both left and right sides. each formed. These rack tooth profiles 14, 15, 16
corresponds to a helical pinion (not shown), and the remaining rack tooth profile 16 effectively meshes with the helical pinion, and the end rack tooth profile 15
The portions are formed to avoid interference with the helical pinion at both ends of the rack portion 13. The tooth tips 17, 18, 19 of the rack teeth 14, 15, 16 are aligned with the axis 2 of the rack rod 12.
It is formed by a plane parallel to 0. Easy tooth profile 1
4, 15, and 16, the tooth root height from the pitch line 21 to the tooth root surface 22 is equal to the end rack tooth profile 15 and the remaining tooth root profile 16, and the total tooth depth from the tooth root surface 22 to the tooth tip surface is the end rack tooth shape. 15 is smaller than the remaining rack tooth profile 16, and furthermore, the total tooth depth of the end rack tooth profile 15 is formed so as to become gradually smaller toward both ends of the rack part 13. End tooth grooves 23 are provided at both ends of the rack part 13 adjacent to the final end rack tooth profile 14, and the end tooth grooves 23 are formed by an end inclined surface 24, an end tooth root surface 25, and a final end rack tooth profile. It is formed by 14 tooth surfaces 26. The end inclined surface 24 of the end tooth groove is a semicircular plane formed by a line that intersects with the end tooth root surface 25 and an arcuate curve that intersects with the outer peripheral surface of the rack bar 12.

The method for manufacturing the rack 11 described above is as in the conventional method, in which the rack teeth 15, 16 and the end tooth grooves 23 are first cut into a shape close to the finished shape, and then the rack teeth 15, 16 and the end The rack 11 is obtained by press-molding the cut tooth surface of the proximal and proximal end tooth grooves and the proximal and distal end tooth groove surfaces using a rack molding mold having teeth in the shape of the transfer of the tooth grooves 23. During press molding, the reaction force of the rack forming load from each tooth surface of the rack teeth 15 and 16 is applied to the tooth part of the press molding die, and the material flow occurs due to the rack rod 12 extending in the axial direction from the center to the outside. Stress is applied from the outer tooth surfaces of the rack tooth profiles 15 and 16, respectively. However, since the total tooth length of the end rack tooth profile 15 is gradually reduced toward both ends of the rack part 13, each tooth of the rack molding die corresponding to the end rack tooth profile 15 is The component of the load in the direction of the axis 20 due to the reaction force and material flow stress from the tooth surface of the end rack tooth profile 15 that is applied to the end rack tooth profile 15 decreases in accordance with the amount of decrease in the total tooth depth of the end rack tooth profile 15, so the tooth of the press molding die. The portion can sufficiently withstand the load in the direction of the axis 20. Furthermore, by bringing the teeth of the press molding die into contact with the end inclined surface 24 formed by a larger flat portion of the end tooth groove than before, the press forming mold The axis 20 of the reaction force in the opposite direction to the material flow stress on the tooth surface of
The directional component now has a larger effect than before.

FIG. 7 shows a second embodiment, in which the end tooth groove 27
The only difference from the first embodiment is the shape of the rack part 13, except that the rack teeth 14, 15, 16 are formed in the rack part 13 in the same manner as in the first embodiment. The end tooth groove 27 has an end inclined surface 28 and an end tooth bottom surface 29.
and the tooth surface 26 of the final end rack tooth profile 14. The tip tooth groove width method A of the end tooth groove 27 is at least equal to the tooth groove width dimension a at the same height as the total tooth depth of the final end rack tooth profile 14 in the remaining rack tooth profile 16 formed in the rack portion 13. Equal to or larger than the tooth groove width dimension a, the end inclined surface 28 of the end tooth groove 27 is aligned with the axis 20 of the rack rod 12.
The angle of inclination θ with respect to the plane orthogonal to the surface is formed to be at least equal to or larger than the pressure angle α of the residual rack tooth profile 16 in which the rack portion 13 is formed. The end inclined surface 28 of the end tooth groove 27 is connected to the line where the end tooth bottom surface 29 intersects with the rack bar 12.
The area of the end inclined surface 28 is a semicircular plane consisting of a circular arc-shaped curve that intersects with the outer circumferential surface of the
It is formed to be larger than the area of one side tooth surface of Nos. 5 and 16. The rack formed as described above is cut into a shape close to the completed shape of the rack tooth profiles 15, 16 and the end tooth grooves 27, and then the teeth of the transfer shape of the rack tooth profiles 15, 16 and the end tooth grooves 27 are cut. This is obtained by press-molding the cut tooth surface of the proximal easy tooth profile and the proximal end tooth groove surface using a rack molding die having a section. The tooth tip width dimension A of the end tooth groove 27 is increased within an allowable range, and furthermore, during press molding, the corresponding tooth part of the press molding die is formed on the end inclined surface 28 of the end tooth groove. By bringing these into contact with each other, the teeth of the press molding die corresponding to the end tooth grooves 27 are made sufficiently strong to withstand the reaction force of the rack tooth forming load from the tooth surface 26 of the final end rack tooth profile 14 and the material flow stress. This will give you the strength to withstand it.

FIG. 8 shows a third embodiment, in which the end tooth groove 30
The only difference from the first or second embodiment is the shape of the rack teeth 14, 15, 16 of the rack portion 13, which are otherwise formed in the same manner as in the first embodiment. The end tooth groove 30 has an end inclined surface 31,
It is formed by the end tooth root surface 32 and the tooth surface 26 of the final end rack tooth profile 14. The tooth tip groove width dimension A of the end tooth groove 30 is the final end rack tooth profile 1 in the remaining rack tooth profile 16 formed in the rack portion 13.
At least equal to or larger than the tooth groove width dimension a at the same height as the total tooth depth of No. 4, and the root width dimension B of the end tooth groove 30 is
3 is at least equal to or larger than the root width dimension b of the remaining rack tooth profile 16 formed in 3, and the tooth tip groove width dimension A is the tooth root width dimension B.
It is designed to be larger than the The end inclined surface 31 of the end tooth groove 30 is a semicircular plane consisting of a line that intersects with the end tooth bottom surface 32 and an arcuate curve that intersects with the outer peripheral surface of the rack rod 12, and the area of the end inclined surface 31 is The area is larger than the area of the tooth surface 26 of the final end rack tooth profile 14 and one side tooth flank of the other rack tooth profiles 15 and 16. The rack formed as described above is cut into a shape close to the completed shape of the rack teeth 15, 16 and the end tooth grooves 30, and then the rack teeth 15, 16 and the end tooth grooves 30
It is obtained by press-molding the tooth surface of the cut proximal easy tooth profile and the proximal end tooth groove surface using a rack molding die having a tooth portion having a transferred shape. The tooth tip width dimension A and the tooth bottom width dimension B of the end tooth groove 30 are increased within an allowable range,
Furthermore, during press molding, by bringing the corresponding teeth of the press molding mold into contact with the end inclined surfaces 31 of the end tooth grooves, the tooth parts of the press molding mold corresponding to the end tooth grooves 30 This provides sufficient strength to withstand the reaction force of the rack tooth forming load from the tooth surface 26 of the final end rack tooth profile and the material flow stress.

The first to third implementation orders of this invention explained above
In the embodiment, if the strength of the teeth of the press molding die is sufficient, the plurality of end rack tooth profiles 15 including the final end rack tooth profile 14 may be replaced by only one final end rack tooth profile 14. is of course allowed.

The press-molding mold for the rack for a rack and pinion type steering device according to the present invention is as described above. In a rack of a rack and pinion type steering device in which a rack tooth profile is formed on a rack rod by plastic working, a rack portion is provided on the rack rod, and the final end of the rack tooth shape is formed at both ends of the rack rod in the axial direction. Or, a plurality of end rack tooth profiles continuing from this final end rack tooth profile have root heights equal to other remaining rack tooth profiles formed in the rack part, and all tooth depths extending toward both ends of the rack part. The end tooth grooves, which are formed successively smaller than the remaining rack tooth profile and are formed at both ends of the rack adjacent to the final end rack tooth profile, reach the outer circumferential surface of the rack rod from the bottom surface of the end tooth groove. If necessary, the tooth tip width dimension A and the end tooth bottom width dimension B of the end tooth groove can be increased within an allowable range, or the end inclined surface of the end tooth groove can be increased. By press-molding with a press molding die having a transfer shape of the rack tooth profile in which the inclination angle θ is greater than the pressure angle of the rack tooth profile, the end tooth groove of the rack molding die used when press-molding the rack is It is said that the breakage or breakage of the corresponding tooth part is improved, the life of the rack molding mold is significantly improved, the rack of the rack and pinion type steering device can be mass-produced with stable and high-precision quality, and manufacturing costs can be reduced. It worked. Also,
By pressing the rack molding die into contact with the inclined surface of the end of the end tooth groove, there was also the effect of reducing the warpage that occurs at both ends of the rack rod compared to the conventional method.

[Brief explanation of the drawing]

Figures 1 to 3 show the rack of a conventional rack and pinion steering system, with Figure 1 being a plan view of the main parts, Figure 2 being a partial sectional view taken along the line 3 is a sectional view taken along the Y--Y line in FIG. 2, and FIGS. 4 to 8 are examples of the press molding die for a rack for a rack and pinion type steering device according to the present invention. Figures 4 to 6 show the first
4 is a plan view of the main part, FIG. 5 is a partial sectional view taken along the Z-Z line in FIG. 4, FIG. 6 is an enlarged sectional view of the main part in FIG. 5, and FIG. FIG. 8 is an enlarged sectional view of the main part of the second embodiment, corresponding to FIG. 6, and FIG. 8 is an enlarged sectional view of the main part, corresponding to FIG. 6 of the third embodiment. 11...Rack, 12...Rack stick, 13...
Rack portion, 14...Final end rack tooth profile, 15...
...End rack tooth profile, 16...Remaining rack tooth profile, 2
3, 27, 30... End tooth groove, 24, 28, 3
1...End inclined surface, A...Tooth tip groove width dimension of end tooth groove, B...Tooth bottom width dimension of end tooth bottom surface, θ
...Inclination angle, α...Pressure angle.

Claims (1)

[Scope of Claims] 1. In a press-molding mold for a rack for a rack and pinion type steering device in which a rack tooth profile is formed on a rack rod by plastic working, the rack rod is provided with a rack portion, and the rack rod in the rack portion is provided with a rack portion. The final end rack tooth profile formed at both ends in the axial direction, or a plurality of end rack tooth profiles continuous from this final end rack tooth profile, have root heights that are different from other remaining rack tooth profiles formed on the rack portion. Equally, all tooth lengths are formed successively smaller than the remaining rack tooth profile toward both ends of the rack part, and end tooth grooves are formed at both ends of the rack part adjacent to the final end rack tooth profile. 1. A press-molding mold for a rack for a rack and pinion type steering device, characterized in that it has a transfer shape of a rack tooth profile having an end inclined surface extending from the bottom surface of the end tooth groove to the outer circumferential surface of the rack rod. 2. The shape of the end tooth groove is such that the width dimension A of the tooth groove at the tooth tip is at least greater than the tooth groove width dimension of the other rack tooth profile at the same height as the total tooth depth of the final end rack tooth profile, and It is characterized by having a transfer shape of a rack tooth profile having a shape in which an inclination angle θ between an end inclined surface of the end tooth groove and a surface perpendicular to the axis of the rack rod is at least equal to or larger than the pressure angle of the rack tooth profile. A press-molding mold for a rack for a rack and pinion type steering device according to claim 1. 3. The shape of the end tooth groove is such that the tooth groove width dimension A at the tip end is at least greater than the tooth groove width dimension of the other rack tooth profile at the same height as the total tooth depth of the final end rack tooth profile, and A rack and pinion type steering device according to claim 1, characterized in that the rack tooth profile is provided with a transferred shape having a bottom width dimension B that is at least larger than the tooth bottom width dimension of another rack tooth profile. Easy press mold.