The present invention relates to a joint structure of a yoke and a shaft with which a joint strength of a metal joint of the yoke and shaft constituting a steering device can be obtained with a very simple structure and a very small size, and to a joining method therefor.
Structures in which a shaft and a yoke are joined by metal joining such as welding have been disclosed. Patent Literature 1 (Japanese Patent Application Publication No. 2003-65351) representing the related art is summarized hereinbelow by using the reference numerals described in Patent Literature 1. An output shaft 13 and an output shaft yoke 14 are joined by friction welding (see Patent Literature 1, FIG. 6). In the output shaft 13, a serration 19 is formed in the inner circumferential surface of a hollow cylindrical main body of a uniform diameter, and an enlarged-diameter portion 30 is provided integrally with one end portion 13a of the main body (see Patent Literature 1, FIG. 5). The enlarged-diameter portion 30 is formed to be thicker than the main body.
The enlarged-diameter portion 30 is formed in a cylindrical shape, and an outer circumferential surface 30a is formed as a substantially flat round surface. The output shaft 13 and the output shaft yoke 14 represent a shaft that transmit rotation and a universal joint in which the shafts are coupled, and in order to transmit a rotation torque reliably, the joining strength is increased by forming the enlarged diameter portion 30, which is thicker than the main body, at the output shaft 13 and increasing the welding surface area with respect to a base end portion 20 of the output shaft yoke 14.
Patent Literature 1: Japanese Patent Application Publication No. 2003-65351
Where the diameter of the output shaft 13 in Patent Literature 1 is increased, the base end portion 20 of the output shaft yoke 14 also needs to be increased in diameter to match the enlarged-diameter portion 30, the size and weight of the output shaft 13 and output shaft yoke 14 are increased and the entire steering device is increased in size. Where the shaft and yoke are increased in size, the freedom of design is decreased. For example, a structure in which interference with other parts is avoided should be considered. A technical problem (objective) to be resolved by the present invention is to strengthen the joining site of friction-joined members with a very simple structure and in a compact configuration and to enable very simple manufacture of the joint.
The inventor has conducted a comprehensive study aimed at the resolution of the abovementioned problems. The results obtained demonstrate that the invention as in claim 1 resolves the abovementioned problems by providing a joint structure of a yoke and a shaft, including: a yoke having a cylindrical portion; a shaft having a joint-side shaft end portion which is metal-joined to the cylindrical portion; and a synthetic resin covering that covers an entire circumference of the joining site of the cylindrical portion of the yoke and the joint-side shaft end portion of the shaft, wherein part of the synthetic resin covering is filled and solidified in a yoke passage hole formed in the cylindrical portion and a shaft passage hole formed in the joint-side shaft end portion of the shaft.
The invention as in claim 2 resolves the abovementioned problems by providing the joint structure of a yoke and a shaft according to claim 1, wherein a joining recess formed as a cylindrical cavity is formed in the cylindrical portion, the joint-side shaft end portion of the shaft is inserted into the joining recess, and the shaft passage hole formed in the joint-side shaft end portion of the shaft and the yoke passage hole coincide with the same diametrical central line.
The invention as in claim 3 resolves the abovementioned problems by providing the joint structure of a yoke and a shaft according to claim 1, wherein an outer diameter of the cylindrical portion is equal to a diameter of the joint-side shaft end portion of the shaft, the two portions are abutted against each other and metal-joined, and part of the synthetic resin covering is filled and solidified in the yoke passage hole formed in the cylindrical portion and the shaft passage hole formed in the joint-side shaft end portion of the shaft.
The invention as in claim 4 resolves the abovementioned problems by providing the joint structure of a yoke and a shaft according to any one of claims 1, 2, and 3, wherein a groove is formed along the circumferential direction in the joint-side shaft end portion of the shaft, and part of the synthetic resin covering is filled and solidified in the groove.
The invention as in claim 5 resolves the abovementioned problems by providing a method for joining a yoke and a shaft, the yoke having a cylindrical portion in which a joining recess is formed at one end side in an axial direction, and the shaft having a joint-side shaft end portion which is to be filled into the joining recess of the cylindrical portion, the method comprising: inserting the joint-side shaft end portion of the shaft into the joining recess and metal-joining the joint-side shaft end portion and the joining recess; drilling a passage hole that passes through the cylindrical portion and the joint-side shaft end portion in a straight line; filling a resin into the passage hole via a mold; and forming a synthetic resin covering over an entire circumference of the joining site of the cylindrical portion and the joint-side shaft end portion.
The invention as in claim 6 resolves the abovementioned problems by providing the method for joining a yoke and a shaft according to claim 5, wherein a through hole that communicates with the joining recess, has an inner diameter less than an inner diameter of the joining recess, and is located on the same diametrical central line is formed at the other end side, in the axial direction, of the cylindrical portion, a core is inserted into the through hole so as to reach the inside of the joining recess, the resin is then filled into the passage hole via the mold, the synthetic resin covering is formed over the entire circumference of the joining site of the cylindrical portion and the joint-side shaft end portion, and the core is removed from the through hole. The invention as in claim 7 resolves the abovementioned problems by providing the method for joining a yoke and a shaft according to claim 5 or 6, wherein a groove is formed along the circumferential direction in the joint-side shaft end portion of the shaft, and part of the synthetic resin covering is filled into the groove.
In the invention as in claim 1, the cylindrical portion of the yoke and the joint-side shaft end portion of the shaft are metal-joined, and the synthetic resin covering that covers the entire circumference of the joining site of the cylindrical portion and the joint-side shaft end portion is configured such that part of the synthetic resin covering is filled and solidified in the yoke passage hole formed in the cylindrical portion and the shaft passage hole formed in the joint-side shaft end portion of the shaft. As a result, it is possible to lock the yoke and shaft in the circumferential direction, increase the strength against a bending load, and raise the rigidity.
Further, the synthetic resin covering increases the strength of the yoke-shaft joint in the rotation direction, facilitates the reduction in size of the yoke and shaft portion of the shaft, enables large torque transmission with a compact configuration, and makes it possible to realize those features with a very simple structure, without performing complex processing.
With the invention as in claim 2, the joining recess is formed in the cylindrical portion, and the joint-side shaft end portion of the shaft is inserted into the joining recess. As a result, the yoke and shaft can be aligned in a simple manner, the joint-side shaft end portion is supported by the joining recess in a metal-joined state, and a stronger joint can be obtained. With the invention as in claim 3, because of the structure in which the cylindrical portion and the joint-side shaft end portion of the shaft have equal diameters and the two portions are abutted against each other and metal-joined, the shape of the joining site of the yoke and shaft can be simplified.
With the invention as in claim 4, because of the configuration in which a groove is formed along the circumferential direction in the joint-side shaft end portion of the shaft, and part of the synthetic resin covering is filled and solidified in the groove, the reinforcement of the yoke and shaft in the axial direction can be further enhanced.
With the invention as in claim 5, the joint-side shaft end portion of the shaft is inserted into the joining recess and the shaft is rotated at a high speed inside the joining recess. As a result, metal joining can be performed in a very reliable and easy manner. Further, the passage hole passing through in a straight line can be drilled very efficiently with a tool, such as a drill, in the cylindrical portion and joint-side shaft end portion, and a subsequent operation of filling a resin into the passage hole via a mold can be easily performed.
With the invention as in claim 6, a through hole that communicates with the joining recess, has an inner diameter less than the inner diameter of the joining recess, and is located on the same diametrical central line is formed at the other end side, in the axial direction, of the cylindrical portion. As a result, the yoke can be reduced in weight. Further, a core is inserted into the shaft recess of the joint-side shaft end portion which has been inserted into the joining recess, and a resin is then filled into the passage hole via the mold.
As a result, the molten synthetic resin does not penetrate into the zone occupied by the core in the shaft recess, and where the core is removed from the through hole, an annular portion is configured by the solidified synthetic resin. Therefore, the resin filled into the passage hole can be reinforced to a greater degree and the amount of the synthetic resin which is to be melted can be decreased, thereby reducing cost.
With the invention as in claim 7, a groove is formed along the circumferential direction in the joint-side shaft end portion of the shaft, and part of the synthetic resin covering is filled into the groove. As a result, the yoke and shaft can be reinforced to a greater degree in the axial direction, this reinforcement can be formed at the same time as the synthetic resin covering is formed with the mold, and the operation efficiency can be increased.
The embodiments of the present invention will be explained hereinbelow with reference to the drawings. The yoke and shaft in the present invention are intermediate shaft members which constitute a steering device for an automobile and are mounted on a steering column to transmit the rotation created by a steering wheel. The configuration in accordance with the present invention is mainly constituted, as depicted in
The present invention includes a plurality of embodiments, and the explanation thereof is started from the first embodiment. The yoke A is made from a metal, and an aluminum material can be used thereof. The yoke is constituted by a bifurcated portion 1 and a cylindrical portion 2. The bifurcated portion 1 is formed integrally with one end side, in the axial direction, of the cylindrical portion 2. More specifically, the bifurcated portion 1 is constituted by two arm pieces 11.
The two arm pieces 11 are arranged and formed parallel to each other with a spacing larger than the outer diameter of the cylindrical portion 2 from two diametrical ends at one end side, in the axial direction, of the cylindrical portion 2. Through holes 11a for connection are formed in the respective arm pieces 11 (see
The cylindrical portion 2 is formed in a cylindrical shape which is comparatively short in the axial direction (see
The joining recess 21 is a depression formed as a cylindrical cavity, and a joint-side shaft end portion 31 of the below-described shaft 3 is to be inserted therein. A bottom surface 21b is formed in the joining recess 21, and the bottom surface 21b is a flat surface perpendicular to the axial direction. The end surface of the joint-side shaft end portion 31 of the shaft 3 which has been inserted into the joining recess 21 abuts upon the bottom surface 21b and friction welding is performed.
Further, a through hole 22 is formed at one end side, in the axial direction, of the cylindrical portion 2 (the side where the bifurcated portion 1 is formed). The through hole 22 is positioned on the same central line as the joining recess 21 and formed such that the inner diameter Db of the through hole 22 is less than the inner diameter Da of the joining recess 21 (see
The shaft 3 is a solid or hollow tube, and the axially end portion thereof which is to be joined to the cylindrical portion 2 is called the joint-side shaft end portion 31. A shaft recess 32 having a shaft opening 32a is formed in a shaft end surface 31a of the joint-side shaft end portion 31 (see
When the joint-side shaft end portion 31 is inserted into the joining recess 21 of the cylindrical portion 2 of the yoke A, the through hole 22 and the shaft recess 32 constitute a cylindrical cavity extending in the axial direction while the diametrically central lines of the through hole and shaft recess coincide (see
A groove 34 is formed in the circumferential direction in the joint-side shaft end portion 31 (see
The process of joining the yoke A and the shaft 3 together is described below. Initially, the joint-side shaft end portion 31 of the shaft 3 is inserted into the joining recess 21 of the yoke A, and the bottom surface 21b of the joining recess 21 and the shaft end surface 31a of the joint-side shaft end portion 31 are brought into contact with each other and rotated relative to each other under applied pressure (
In the process of friction welding of the joining recess 21 of the cylindrical portion 2 and the joint-side shaft end portion 31 of the shaft 3, curled burrs are generated between the joining recess 21 and the joint-side shaft end portion 31. After the joining is completed, the inner circumferential surfaces of the through hole 22 of the cylindrical portion 2 of the yoke A and the through hole 31 of the shaft 3 are subjected to machining, and the burrs generated on the inner circumferential surfaces are removed by the machining.
In this case, the diameter of the joint-side shaft end portion 31 of the shaft 3 is set to be less than the inner diameter of the joining recess 21 and set such that a clearance T appears between the joint-side shaft end portion 31 and the joining recess 21. More specifically, the joint-side shaft end portion 31 has an outer diameter Dc with respect to the inner diameter Da of the joining recess 21, and the size of the clearance T is 2t. The clearance T is a sum of the gaps appearing at both sides, in the diametrical direction, of the joint-side shaft end portion 31.
As a result, the inner diameter Da of the joining recess 21, the outer diameter Dc of the joint-side shaft end portion 31, and the size 2t of the clearance T satisfy the following relationship.
Da−Dc=2t
Therefore, the gap size of either of the joint-side shaft end portion 31 and the joining recess 21 is t. This size t is set to about several millimeters (see (1) in
Where friction welding of the cylindrical portion 2 of the yoke A and the joint-side shaft end portion 31 of the shaft 3 is completed, the yoke passage hole 23 and the shaft passage hole 33 are drilled in the cylindrical portion 2 and the joint-side shaft end portion 31 (see
Then, a mold 5 is disposed such as to cover the entire circumference of the joining site of the cylindrical portion 2 and the joint-side shaft end portion 31. The mold 5 is divided in two and constituted by an upper mold 51 and a lower mold 52 (see
Cavities 51a, 52a the and pouring ports 51b, 52b for forming the synthetic resin covering 4 are formed in the upper mold 51 and lower mold 52, respectively, and the upper mold 51 and the lower mold 52 are disposed such that the cavities 51a, 52a are positioned at the joining site of the yoke A and the shaft 3, more specifically, at the joining site of the cylindrical portion 2 and the joint-side shaft end portion 31 (see
A core 6 is inserted from the through hole 22 of the yoke A. The core 6 is formed in a cylindrical shape and constituted by a small-diameter axial portion 61, a large-diameter axial portion 62, and a step 63 (see
Inside the shaft recess 32 of the shaft 3, the small-diameter shaft portion 61 of the core 6 is set such as to cross the diametrical central line of the shaft passage hole 33 (see
The molten synthetic resin r flows in from the pouring port 51b of the upper mold 51 (or the pouring port 52b of the lower mold 52), and the synthetic resin flows from the cavities 51a, 52a into the yoke passage hole 23 and the shaft passage hole 33 (see
The synthetic resin covering 4 is formed in the joining site of the yoke A and shaft 3 by removing the mold 5 and the core 6 from the joining site after the synthetic resin poured into the mold 5 has solidified. The synthetic resin covering 4 is constituted by a cover portion 41 that covers the joining site on the cylindrical portion 2 of the yoke A and the joint-side shaft end portion 31 of the shaft 3, a joining pin-shaped piece 42 formed by filling and solidifying in the yoke passage hole 23 and the shaft passage hole 33, a fixing protruding piece 43 formed by filling and solidifying in the groove 34, and an annular fixing portion 44 formed along the inner circumferential surface in the shaft recess 32 (see
The joining pin-shaped piece 42 of the synthetic resin covering 4 further increases the reinforcement of the yoke A and shaft 3 in the rotation direction (see
The annular fixing portion 44 can reinforce both ends, in the axial direction, of the joining pin-shaped piece 42 together with the cover portion 41. The hollow annular fixing portion 44 can reduce the amount of the synthetic resin (see
The second embodiment of the present invention will be explained hereinbelow with reference to
In this embodiment, the joint-side shaft end portion 31 of the shaft 3 is inserted into the joining recess 21 of the yoke A, and friction welding is performed in a state in which the shaft end surface 31a and the bottom surface 21b are abutted against each other. After the friction welding has been performed, the yoke passage hole 23 and the shaft passage hole 33 are drilled in the cylindrical portion 2 and the joint-side shaft end portion 31.
In this case, the joint-side shaft end portion 31 is a solid part, and the shaft passage hole 33 becomes a through hole passing through in the diametrical direction. In the same manner as in the first embodiment of the present invention, the upper mold 51 and the lower mold 52 of the mold 5 are disposed at the joining site of the cylindrical portion 2 and the joint-side shaft end portion 31, and the molten synthetic resin is poured thereinto. In the second embodiment, the core 6 is not used (see
The third embodiment of the present invention will be explained hereinbelow with reference to
In this embodiment, the shaft passage hole 33 which is formed in the joint-side shaft end portion 31 of the shaft 3 is configured not to pass through to the hollow portion inside the shaft 3, and a small-diameter hole 33a is formed in the bottom surface thereof (see
The fourth embodiment of the present invention will be explained hereinbelow with reference to
The yoke passage hole 23 and the shaft passage hole 33 are formed (drilled) with a drill 7, or the like, at mutually different positions, instead of being formed at the same straight line orthogonal to the axial direction as in the first to third embodiments (see
A . . . yoke; 2 . . . cylindrical portion; 21 . . . joining recess; 21b . . . bottom surface; 22 . . . through hole; 23 . . . yoke passage hole; 3 . . . shaft; 31 . . . joint-side shaft end portion; 32 . . . shaft recess; 33 . . . shaft passage hole; 34 . . . groove; 4 . . . synthetic resin covering; 5 . . . mold; 6 . . . core.
Number | Date | Country | Kind |
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2012-275590 | Dec 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/083781 | 12/17/2013 | WO | 00 |