Abstract
A rack bar includes a shaft portion and a rack toothed portion provided on the shaft portion. The rack toothed portion includes a plurality of rack teeth provided side by side in an axial direction of the shaft portion to mesh with a pinion gear. Each of the rack teeth includes a tooth tip portion, a contact face arranged obliquely relative to the axial direction and configured to contact the pinion gear, and a rounded corner portion between the tooth tip portion and the contact face. A first radius defining a central area of the rounded corner portion with respect to a tooth width direction is larger than a second radius defining another area of the rounded corner portion other than the central area.
Claims
1. A teeth forming die configured to form rack teeth of a rack bar to be meshed with a pinion gear, the teeth forming die comprising a securing portion configured to be secured to an outside clamp case, and a rack teeth transfer portion provided on the securing portion, wherein the rack teeth transfer portion comprises a plurality of rack tooth transfer portions provided side by side in a line, wherein each of the rack tooth transfer portions is configured to transfer a profile of each rack tooth, each of the rack tooth transfer portions comprising a tooth bottom transfer portion configured to transfer a profile of a tooth bottom portion of the rack tooth, a tooth tip transfer portion configured to transfer a profile of a tooth tip portion of the rack tooth, a contact face transfer portion arranged obliquely relative to a direction of the line in which the rack tooth transfer portions are provided side by side and configured to transfer a profile of a contact face of the rack tooth to be brought into contact with the pinion gear, and a rounded corner portion between the tooth tip transfer portion and the contact face transfer portion, wherein a first radius defining a central area of the rounded corner portion with respect to a tooth width direction is larger than a second radius defining another area of the rounded corner portion other than the central area.
2. The teeth forming die according to claim 1, wherein at least one of the first radius and the second radius is different for each of the rack tooth transfer portions.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a perspective view of a steering system in which a rack bar according to an embodiment of the invention is incorporated;
(2) FIG. 2 is an explanatory diagram illustrating a section of the rack bar and a rack teeth forming die of the embodiment of the invention;
(3) FIG. 3 is an enlarged perspective view of a portion of the rack bar in an enlarged fashion;
(4) FIG. 4 is an explanatory diagram illustrating sectional shapes of different portions of a rack tooth of the rack bar in comparison;
(5) FIG. 5 is an enlarged perspective view of a portion of the rack teeth forming die;
(6) FIG. 6 is an explanatory diagram illustrating sectional shapes of different portions of a rack tooth transfer portion of the rack teeth forming die in comparison;
(7) FIG. 7 is a partially cutaway front view of an example of a general rack bar producing system;
(8) FIG. 8 is an enlarged perspective view of a first example of rack teeth of a general rack bar;
(9) FIG. 9 is a perspective view of a second embodiment of rack teeth of a general rack bar; and
(10) FIG. 10 is an explanatory diagram illustrating a profile of rounded corner portions at the top portions of the rack teeth of the general rack bars.
DETAILED DESCRIPTION
(11) FIG. 1 is a perspective view showing a steering system 10 in which a rack bar 200 according to an embodiment of the invention is incorporated, FIG. 2 is an explanatory diagram showing a section of the rack bar 200 and a front view of a teeth forming die 250 which transfers a profile of a rack toothed portion 220 of the rack bar 200, FIG. 3 is a perspective view showing rack teeth 230 of the rack bar 200 in an enlarged fashion, FIG. 4 is an explanatory diagram showing sectional shapes of different portions of the rack tooth 230 in comparison, and FIG. 5 is a partially cutaway perspective view showing rack tooth transfer portions 280 of the teeth forming die 250 in an enlarged fashion. In FIG. 2, C denotes an axis of the rack bar 200, and in FIG. 5, K denotes a tooth width direction of the teeth forming die 250.
(12) As shown in FIG. 1, the steering system 10 includes a steering shaft 12 which connects to a steering wheel (a steering member) 11, a pinion shaft 13 that connects to the steering shaft 12 and which has a pinion gear 13a at a distal end thereof and a rack bar 200 which meshes with the pinion gear 13a. The rack bar 200 connects further to left and right front road wheels WR, WL via tie-rods 30, 30.
(13) FIG. 2 shows the section of the rack bar 200 and a front view of a teeth forming die 250 which transfers a profile of a rack toothed portion 220 of the rack bar 200.
(14) As shown in FIG. 2, the rack bar 200 includes a shaft portion 210 formed from a round hollow rod and the rack toothed portion 220 provided at the center of the shaft portion 210. The rack toothed portion 220 has a plurality of rack teeth 230 configured to mesh with the pinion gear 13 are provided side by side along the axis C of the rack bar 200. Contact faces 233 (contact areas) of the rack teeth are disposed obliquely relative to the axis C.
(15) The teeth forming die 250 has a substantially rectangular parallelepiped shape and includes a securing portion 260 adapted to be secured to an outside clamp case and a rack toothed portion transfer portion 270 that is formed on one of surfaces of the securing portion 260 and which transfers a profile of the rack toothed portion 220. In the rack toothed portion transfer portion 270, a plurality of rack tooth transfer portions 280 are provided parallel along a longitudinal direction of the securing portion 260.
(16) As shown in FIG. 3, the rack tooth 230 includes a tooth tip portion 231 having a flat planar shape at a distal end thereof, tooth tip rounded corner portions 232 defined by a radius R, contact faces 233 which are brought into contact with the pinion gear 13a to thereby transmit steering force, tooth bottom rounded corner portions 234 defined by Rs and a tooth bottom portion 235 which has a flat planar shape. The tooth tip rounded corner portions 232 are each positioned between the tooth tip portion 231 and the contact face 233, and the tooth bottom rounded corner portions 234 are each positioned between the contact face 233 and the tooth bottom portion 235.
(17) FIG. 4 is an explanatory diagram showing sectional shapes of different portions of the rack tooth 230 in comparison. In FIG. 4, a cross section Sa of a portion of the rack tooth 230 near an end of the rack tooth 230 in a tooth width direction H of the rack tooth 230 is illustrated on the left, and a cross section Sb of a central portion of the rack tooth 230 with respect to the tooth width direction H of the rack tooth 230 is illustrated on the right. In addition, in FIG. 4, La denotes a face length of the contact face in Sa, Lb denotes a face length of the contact face in Sb, Ra denotes a radius defining a tooth tip rounded corner portion 232a in Sa, and Rb denotes a radius defining a tooth tip rounded corner portion 232b in Sb. As shown in FIG. 4, the radius Ra is formed smaller than the radius Rb. For example, a ratio of the radius Ra to the radius Rb is 1 to 1.1. By forming the radii in this way, a straight length La is formed larger than a straight length Lb. At least one of the radius Ra and the radius Rb may be different for each of the rack teeth 230.
(18) FIG. 5 is a partially cutaway perspective view showing the rack tooth transfer portions 280 of the teeth forming die 250 in an enlarged fashion. The rack tooth transfer portion 280 includes a tooth tip transfer portion 281 having a flat planar shape and configured to transfer a profile of the tooth tip portion 231, a tooth tip rounded corner portion transfer portion 282 defined by the radius R and configured to transfer a profile of the tooth tip rounded corner portion 232, a contact face transfer portion 283 having a flat planar shape and configured to transfer a profile of the contact face 233, a tooth bottom rounded corner portion transfer portion 284 defined by a radius Rt and configured to transfer a profile of the tooth bottom rounded corner portion 234 and a tooth bottom transfer portion 285 having a flat planar shape and configured to transfer a profile of the tooth bottom portion 235. The tooth tip rounded corner portion transfer portion 282 is positioned between the tooth tip transfer portion 281 and the contact face transfer portion 283, and the tooth bottom rounded corner portion transfer portion 284 is positioned between the contact face transfer portion 283 and the tooth bottom transfer portion 285.
(19) FIG. 6 is an explanatory diagram showing sectional shapes of different portions of the rack tooth transfer portion 280 in comparison. In FIG. 6, a cross section Sc of a portion of the rack tooth transfer portion 280 near an end of the of the rack tooth transfer portion 280 in a tooth width direction K of the teeth forming die 250 is illustrated on the left, and a cross section Sd of a central portion of the rack tooth transfer portion 280 with respect to the tooth width direction K of the rack tooth transfer portion 280 is illustrated on the right. In addition, in FIG. 6, Lc denotes a straight length of the contact face transfer portion 283 in Sc, Ld denotes a straight length of the contact face transfer portion 283 in Sd, Rc denotes a radius defining a tooth tip rounded corner portion transfer portion 282c in Sc, and Rd denotes a radius defining a tooth tip rounded corner portion transfer portion 282d in Sd. As shown in FIG. 6, the radius Rc is formed smaller than the radius Rd. For example, when the ratio of the radius Ra to the radius Rb is 1 to 1.1, a ratio of the radius Rc to the radius Rd is also 1 to 1.1. By forming the radii in this way, the straight length Lc is formed larger than the straight length ld. At least one of the radius Rc and the radius Rd may be different for each of the rack tooth transfer portions 280.
(20) When the rack tooth transfer portion 280 is formed in this way, the radius Rd is formed large which defines the portion lying near the central portion 282d in the direction K of the tooth tip rounded corner portion transfer portion 282, thereby making it possible to extend the life of the teeth forming die 250. Additionally, in the rack bar 200 which is formed by the teeth forming die 250, the straight length L of the rack tooth portion 230 is formed into the short straight length Lb at the central portion in the tooth width direction and into the long straight length La at the end portion in the tooth width direction. By adopting this configuration, the durability and strength and the steering force transmission efficiency of the rack tooth 230 can be maintained to the sufficient level without reducing the area of the contact face 233 with the pinion gear 13a largely.
(21) Thus, as has been described heretofore, according to the invention, the rack bar can have the sufficient steering force transmission efficiency as well as the sufficient durability and strength, and the life of the rack bar forming tooth die can be extended.
(22) While the present invention has been described with reference to a certain exemplary embodiment thereof, the scope of the present invention is not limited to the exemplary embodiments described above, and it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the present invention as defined by the appended claims.
