JPH09309480A - Bracket for front fork of two wheeler and the like and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow to respond to a compricated form, as well as to improve the strength and the rigidity without increasing the weighT an the cost. SOLUTION: In an under bracket 14 of a two wheeler or the like in which a center boss 19 forming a center hole 18, and a pair of fork bosses 21 forming fork holes 20 are connected at a bridge 22, and inner tubes 13 of front tubes can be inserted into the fork holes 20, the under bracket 14 is made of an aluminum cast, the bridge 22 is formed in a hollow box form, and a hollow 34 of the bridge 22 is not opened to the center hole 28, but opened to the fork holes 22, so as to compose the under bracket 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front fork bracket for a motorcycle or the like, and more particularly to an under bracket and a method for manufacturing the same.

[0002]

2. Description of the Related Art A front fork assembly for a motorcycle holds a front fork at both ends of an under bracket and an upper bracket, which are front fork brackets, and rotatably supports a front wheel with these front forks. Further, a steering shaft arranged in the central portion of the under bracket and the upper bracket is pivotally supported on the head pipe of the vehicle body frame so that the front wheels can be steered.

The under bracket is required to have a high strength and a high rigidity because a bending load and a torsion torque are applied from the front wheel through the front fork. From this point of view, as in the invention described in Japanese Utility Model Publication No. 58-28952, there is one in which the under bracket is formed as a hot forged aluminum product (first prior art).

Further, as in the invention described in Japanese Utility Model Publication No. 7-55194, a fork boss for holding a front fork,
There is a structure in which an under bracket is configured by welding and connecting a center boss that inserts a steering shaft with a pipe material (second conventional technique).

[0005]

However, the first prior art has the following problems (1) to (3). Since the under bracket is formed by hot forging, its shape is restricted and it is difficult to cope with a complicated shape.

Further, since the under bracket is divided into upper and lower parts, and the sectional shape obtained by rotating a U-shape by 90 ° is a basic shape. Therefore, in order to obtain high strength and high rigidity, a thick wall structure or There is no means other than adding ribs,
The weight will increase.

Further, since the extruded material is used in the hot forging, the material cost is high and the processing cost is also high.

The second conventional technique has the following problems. In the case of the under bracket, it is necessary to form a boss for installing a handle stopper and an alarm device that regulates the rotation range of the handle in the pipe material part, but with the pipe material formed by drawing, it is complicated. It cannot correspond to the shape.

Further, in the pipe material, it is necessary to process a welded portion of the fork boss or the center boss into an arc shape, or weld the pipe material to the fork boss or the center boss. Difficult and impractical.

The object of the present invention has been made in consideration of the above circumstances, and it is possible to improve strength and rigidity without increasing weight and cost, and to cope with a complicated shape. To provide a bracket for a front fork and a manufacturing method thereof.

[0011]

According to a first aspect of the present invention, a center boss forming a center hole and a pair of fork bosses forming fork holes on both sides of the center hole are connected by a bridge portion. In a bracket for a front fork of a motorcycle or the like, a steering shaft pivotally supported by a head pipe of a vehicle body can be inserted into the center hole, and an inner tube of a front fork can be inserted into the fork hole. The front fork bracket is made of aluminum alloy casting, the bridge portion is formed in a hollow box shape, and the hollow portion of the bridge portion is not opened in the center hole, but is opened in the fork hole. It was done.

According to a second aspect of the present invention, in the first aspect of the present invention, the fork boss is provided with a clamp portion for tightening the inner tube, and the hollow portion of the bridge portion is a fork hole, and the clamp portion is provided. It is opened at a position facing.

According to a third aspect of the present invention, a front fork bracket for connecting a center boss forming a center hole and a fork boss forming a fork hole at a bridge portion is cast by a gravity die casting method. In this casting step, the bridge portion is formed into a hollow box shape by a shell core integrally formed with the shell core forming the fork hole.

According to the invention described in claim 1, the following (1)
(8). (1) Since the bridge part is configured in the shape of a hollow box, the section modulus and section of the front fork bracket are
The second moment can be increased, and the strength, bending rigidity and torsional rigidity of the front fork bracket can be improved. In particular, because the torsional rigidity can be significantly improved, a situation in which a torsional moment is generated without connecting the two outer tubes of the upright front fork with a stabilizer (braking while cornering a motorcycle etc. The vehicle posture of the two-wheeled vehicle can be stabilized when the vehicle is operated or the brake is released).

(2) Further, since the hollow portion of the bridge portion is not opened to the center hole, the bending rigidity of the center boss of the front fork bracket can be increased, and the bending rigidity of the front fork bracket as a whole is significantly increased. Can be improved.

(3) Further, since the bridge portion is not formed with an opening that affects the rigidity, the strength and rigidity of the front fork bracket is not reduced.

(4) Further, since the front fork bracket is formed by casting, it is possible to easily form a handle stopper, a boss portion for installing an alarm device, and the like, and it is possible to cope with a complicated shape.

(5) Further, since the front fork bracket is formed by aluminum casting and uses the aluminum alloy for casting as a raw material, the material cost is lower than that of the hot forged product using the extruded material of aluminum alloy. In addition, the processing cost for casting is lower than that for hot forging.

(6) Further, since the front fork bracket is manufactured by casting aluminum, the unit weight of the front fork bracket is larger than that of the hot forged front fork bracket. The weight of the front fork assembly equipped with the front fork can be made lighter than that of the front fork assembly using the hot forged front fork bracket.

(7) Since the hollow portion of the bridge portion is not opened in the center hole, when the steering shaft is press-fitted and fixed in the center hole, the contact area between the center boss and the steering shaft can be increased. It is possible to increase the slipping load and slip torque of the steering shaft.

(8) Furthermore, since the hollow portion of the bridge portion is open to the fork hole, the opening area of this hollow portion can be set large. Therefore, after casting the front fork bracket, the sand of the shell core having the hollow portion can be easily discharged from the opening of the hollow portion through the fork hole.

The invention described in claim 2 has the following function (9). (9) The fork boss of the front fork bracket is provided with a clamp part that tightens the outer circumference of the inner tube, and the hollow part of the bridge part opens at a position facing the clamp part. Even if it is opened in the fork hole, there is no problem with the inner tube tightening of the fork boss by the clamp part.

According to the invention of claim 3, the following (10) and
It has the function of (11). (10) Generally, since castings have low strength and elongation, if there are pinholes or the like in the castings, the portions will easily break. In the present invention, since the front fork bracket is manufactured by the gravity die casting method, it is possible to suppress the generation of the pinhole and increase the strength of the front fork bracket.

(11) Further, since the hollow portion of the bridge portion is formed by the shell core integrally formed with the shell core forming the fork hole, the opening of the hollow portion is formed on the bridge portion side of the fork hole. Can be provided.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing a front fork assembly to which an under bracket is applied, which is one embodiment of a front fork bracket for a motorcycle or the like according to the present invention, with a part thereof cut away. FIG. 2 is a plan view showing the under bracket of FIG. 3 (A) and 3 (B) are views taken in the direction of arrows IIIA and IIIB in FIG. 2, respectively. FIG. 4 is a view on arrow IV in FIG. FIG. 5 is a sectional view taken along the line VV in FIG. FIG.
FIG. 3 is a front view of the steering shaft assembled to the under bracket of FIG. 2.

An upright front fork assembly 10 for a motorcycle shown in FIG. 1 holds an inner tube 13 of a front fork 11 at both ends of an under bracket 14 and an upper bracket 15 as front fork brackets, respectively. Front fork 1
A front wheel (not shown) is rotatably supported by a bearing 16 of the outer tube 12 of No. 1, and a steering shaft 17 arranged at the center of each of the under bracket 14 and the upper bracket 15 is used as a head pipe (both not shown) of the vehicle body frame. It is pivotally supported so that the front wheels can be steered.

The front fork 11 is constructed such that the outer tube 12 and the inner tube 13 are slidably fitted and expandable, and incorporates a suspension spring and a damper device (both not shown). This front fork 1
By 1, the shock acting on the front wheels from the road surface is absorbed by the suspension spring, and the stretching vibration of the front fork 11 is suppressed by the damper device.

The under bracket 14 is a member that supports bending load, torsional torque, etc. from the front wheels through the front fork, and is required to have high strength and high rigidity.

As shown in FIGS. 2 and 3, the under bracket 14 has a center boss 19 forming a center hole 18 and fork holes 2 on both sides of the center hole 18.
A pair of left and right fork bosses 21 forming 0 is connected by a bridge portion 22, and is cast by a gravity die casting method using an aluminum alloy for casting as a material. The under bracket 14 is subjected to quenching treatment after casting to enhance its mechanical strength.

As shown in FIGS. 1 and 6, the steering shaft 17 is formed in a cylindrical shape, a stopper portion 23 is bulged at the base end portion, and a male screw portion 24 is engraved at the tip end portion. The front end of the steering shaft 17 is located at the center hole 18 from the rear surface side of the under bracket 14.
6, the base end portion is press-fitted (fitted at room temperature) into the center hole 18, and the stopper portion 23 prevents the stopper portion 23 from coming out downward in FIG. Further, the tip end portion of the steering shaft 17 is inserted into the center hole 25 of the upper bracket 15, the nut 26 is screwed into the male screw 24, and the steering shaft 17 is assembled to the under bracket 14 and the upper bracket 15.

As shown in FIGS. 2 to 4, the pair of left and right fork bosses 21 of the under bracket 14 are provided with a clamp portion 27 at both end positions of the under bracket 14, and a female screw portion 28 is formed on the clamp portion 27. Engraved. Insert the inner tube 13 of the front fork 11 into the fork hole 20, and attach the tightening bolt 29 to the female screw portion 28.
(FIG. 1) is screwed to reduce the diameter of the fork hole 20, and the inner tube 13 is sandwiched and held by the fork boss 21.
The inner tube 13 is also inserted into the fork hole 30 of the upper bracket 15, and is clamped and held by the upper bracket 15 by the tightening bolt 31.

Further, the under bracket 14 has
As shown in FIGS. 2 to 4, a handle stopper 32 that restricts the rotation range of the handle is provided in a protruding manner, and a boss 33 for mounting an alarm device or the like is further formed.

The above-mentioned under bracket 14 is cast by the gravity die casting method as described above. At this time, the bridge portion 22 is formed integrally with the shell core forming the fork hole 20. The child forms a hollow box shape (FIG. 5) in cross section. At this time, the thickness of the bridge portion 22 is, for example, about
8mm is set to be almost uniform.

Further, the hollow portion 34 of the box-shaped bridge portion 22 has a center hole 1 as shown in FIGS.
8 is not opened, but is provided in the fork hole 20 so that the entire surface in the width direction is opened. The opening 35 in the fork hole 20 of the hollow portion 34 is formed at a position facing the clamp portion 27. Generally, since the casting has a high rigidity, the fork boss 21 is appropriately weakened in rigidity by providing the opening 35 at a position facing the clamp portion 27, so that the inner tube 13 can be easily clamped.

Reference numeral 36 in FIGS. 2 and 3 is a sand discharge hole for discharging the sand of the shell core forming the hollow portion 34 of the bridge portion 22 together with the opening 35 after casting.

According to the above embodiment, the following (1) to (11)
effective. (1) Since the bridge portion 22 of the under bracket 14 has a hollow box shape, the under bracket 1
4 and the second moment of area can be increased, and the strength, bending rigidity and torsional rigidity of the under bracket 14 can be improved. In particular, because the torsional rigidity can be significantly improved, a situation in which a torsional moment is generated without connecting the two left and right outer tubes 12 of the upright front fork 11 with a stabilizer (when the motorcycle is cornering) When the brake is operated or released, the vehicle attitude of the motorcycle can be stabilized.

(2) Further, the hollow portion 34 of the bridge portion 22.
Does not open in the center hole 18, the bending rigidity of the center boss 19 of the under bracket 14 can be increased, and the bending rigidity of the entire under bracket 14 can be significantly improved.

(3) Further, the sand discharging hole 3 is provided in the bridge portion 22.
6 is formed, but since the sand discharge hole 36 is not an opening that affects the rigidity of the under bracket,
The strength and rigidity of the under bracket 14 do not decrease.

(4) Further, since the under bracket 14 is formed by casting, the handle stopper 32, the boss 33 for mounting the alarm device, etc. can be easily formed, and a complicated shape can be dealt with.

(5) Further, since the under bracket 14 is formed by aluminum casting and uses an aluminum alloy for casting as a raw material, the material cost is lower than that of a hot forged product using an extruded material of aluminum alloy. it can. Needless to say, the processing cost of casting can be reduced as compared with the case of hot forging.

(6) Further, since the under bracket 14 is manufactured by aluminum casting, the weight of the under bracket 14 alone is larger than that of the hot forged under bracket, but the upright front fork 11 is provided. The weight of the front fork assembly 10 can be reduced as compared with the front fork assembly using the above-mentioned hot forged under bracket.

(7) Further, since the hollow portion 34 of the bridge portion 22 is not opened to the center hole 18, the center hole 18
When the steering shaft 17 is press-fitted and fixed to the steering shaft 17, the contact area between the center boss 19 and the steering shaft 17 can be increased, and the slipping load and slip torque of the steering shaft 17 can be increased.

(8) Further, the hollow portion 34 of the bridge portion 22.
Has its entire width direction opened in the fork hole 20,
The opening area of the opening 35 of the hollow portion 34 can be set large. Therefore, after casting the under bracket 14,
The sand of the shell core in which the hollow portion 34 is formed is removed from the opening 35 of the hollow portion 34 together with the sand discharge hole 36 through the fork hole 2
It can be easily discharged through 0.

(9) The fork boss 21 of the under bracket 14 is provided with a clamp portion 27 for fastening the outer circumference of the inner tube 13 with two fastening bolts 29, and at a position facing the clamp portion 27. Since there is the opening 35 in the hollow portion 34 of the bridge portion 22, even if the hollow portion 34 of the bridge portion 22 is open to the fork hole 20, the fork boss 21 by the clamp portion 27 is formed.
There is no hindrance to the tightening of the inner tube 13.

(10) Generally, since castings have low strength and elongation, if there are pinholes in the castings, the portions will easily break. In this embodiment, since the under bracket 14 is manufactured by the gravity die casting method, it is possible to suppress the occurrence of the pinholes and increase the strength of the under bracket 14.

(11) In addition, the hollow portion 34 of the bridge portion 22
However, since the shell core is integrally formed with the shell core forming the fork hole 20, the opening 35 of the hollow portion 34 can be provided on the bridge portion 22 side of the fork hole 20.

In the above embodiment, the case of the under bracket as the front fork bracket has been described, but the upper bracket may be configured in the same manner as the above under bracket.

[0048]

As described above, according to the front fork bracket for a motorcycle or the like and the method for manufacturing the same of the present invention, it is possible to improve the strength and rigidity without increasing the weight and the cost, and it is complicated. Suitable for various shapes.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing a front fork assembly to which an under bracket, which is one embodiment of a front fork bracket for a motorcycle or the like according to the present invention, is applied.

FIG. 2 is a plan view showing the under bracket of FIG.

3A and 3B are IIIA of FIG. 2, respectively.
It is an arrow view and a IIIB arrow view.

FIG. 4 is a view on arrow IV of FIG.

FIG. 5 is a sectional view taken along the line VV of FIG. 2;

6 is a front view of a steering shaft assembled to the under bracket of FIG. 2. FIG.

[Explanation of symbols]

 10 Front Fork Assembly 11 Front Fork 13 Inner Tube 14 Under Bracket 17 Steering Shaft 18 Center Hole 19 Center Boss 20 Fork Hole 21 Fork Boss 22 Bridge Section 34 Hollow Section 35 Opening

Claims (3)

[Claims] 1. A center boss forming a center hole,
A pair of fork bosses forming fork holes on both sides of the center hole are connected by a bridge portion, and a steering shaft pivotally supported by a head pipe of a vehicle body can be fitted and inserted into the center hole. In a front fork bracket for a motorcycle or the like into which an inner tube of the front fork can be inserted, the front fork bracket is made of aluminum alloy casting, and the bridge portion is formed in a hollow box shape, and A bracket for a front fork of a motorcycle or the like, characterized in that the hollow portion of the bridge portion is configured not to open to the center hole but to open to the fork hole. 2. The front part of the motorcycle according to claim 1, wherein the fork boss is provided with a clamp part for tightening the inner tube, and the hollow part of the bridge part is opened in a fork hole at a position facing the clamp part. Bracket for forks. 3. A front fork bracket for connecting a center boss forming a center hole and a fork boss forming a fork hole by a bridge portion is cast by a gravity die casting method, and the bridge portion is formed in this casting step. Is a method for manufacturing a front fork bracket for a motorcycle or the like in which a shell core integrally formed with the shell core forming the fork hole is formed into a hollow box shape.