JPH01317889A - Rear arm of motorcycle - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of wall thickness of a rear arm around a hollow portion of a light alloy casting by constituting the rear arm of the light alloy hollow casting to form an opening communicating to the hollow portion in a portion of the front side rear arm in a support hole. CONSTITUTION:A rear arm 5 is constituted of an aluminum casting and formed on the front portion with a bearing fitting hole 5c fitting a bearing 14 and on the rear portion with a large diameter support hole 5a. The support hole 5a is formed in the front side portion 5d with an opening 5f affording communication between the support hole 5a and hollow portion 5e. The rear arm 5 combines the intermediate portion of the support hole core forming the support hole 5a with the rear end of the hollow portion core forming the hollow portion 5e to support said both cores in a predetermined position within a die so that molten metal is poured in the die for casting. Thus, the rear arm can be easily manufactured and further, the fluctuation of wall thickness of the rear arm around the hollow portion is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a rear arm of a motorcycle, and more particularly to a rear arm made of a hollow casting of light metal.

BACKGROUND ART In motorcycles and tricycles whose rear wheels are driven by a chain, it is necessary to compensate for the elongation of the chain during use. Therefore, in motorcycles and tricycles in which the rear arm is swingably supported on a pivot at the rear of the body frame, the rear axle is attached to the rear of the rear arm so that it can move in the longitudinal direction of the rear arm, and the position of the rear axle relative to the rear arm is fixed. By adjusting the length, it corresponds to the elongation of the chain.

The rear wheel support device that can adjust the position of the rear axle has a support hole whose diameter can be changed somewhat at the rear end of the rear arm, and a cam member with an axle hole at an eccentric position is fitted into the support hole. A cam member is attached to the rear end of the rear arm in a manner that allows the cam member to be tightened and loosened by compressing the part of the rear arm around the support hole.
(Refer to Publication No. 81689).

In addition, hollow rear arms cast from light metals such as aluminum have been available in the past, but in order to support the core that forms the hollow part during casting, the core is supported on the side of the hollow part of the rear arm. It is necessary to provide an opening for Therefore, the opening is closed with a specially made lid to prevent rainwater from entering the hollow part.

Problems to be Solved by the Invention In conventional rear arms made of hollow castings of light metal, it is necessary to close the opening on the side of the hollow part with a specially made lid, which requires time and effort in machining the opening and lid. This has the disadvantage that the manufacturing cost of the rear arm increases.

The problem to be solved by this invention is to provide a rear arm for a motorcycle made of a hollow cast product that does not have the above-mentioned drawbacks.In other words, it does not require a special lid and is easy to manufacture.
To provide a rear arm for a motorcycle made of a hollow casting with uniform wall thickness.

Means for Solving the Problems The present invention has a structure in which a rear arm is swingably supported at the rear of the vehicle body frame, a support hole whose diameter can be changed to some extent is formed at the rear end of the rear arm, and an axle hole is formed at an eccentric position. In the rear arm of a motorcycle, the cam member is fitted into the support hole, and the cam member is removably attached to the rear end of the rear arm by compressing a portion of the rear arm around the support hole. , the rear arm is made of a hollow casting of light metal, and an opening communicating with the hollow part is formed in the front part of the rear arm inside the support hole, and when the cam member is fitted into the support hole, the opening is opened. It is located on the rear arm of a motorcycle that is blocked.

The rear arm is made of, for example, a cast aluminum product, and the main portion from the front end portion through which the shaft passes through to the front portion of the support hole is hollow. An opening is formed in the portion, and the portion of the hollow portion (hereinafter referred to as hollow portion) on the support hole side communicates with the support hole.

The opening is formed by the rear end of a hollow core that forms a hollow part that is joined to the middle of a support hole core that forms a support hole when the rear arm is cast.

When the hollow core and the support hole core are configured such that the opening is formed between the support hole side portion of the hollow portion and the support hole, the support of the core is ensured. Also.

The opening is formed at a position that is closed by the cam member when the cam member is fitted into the support hole.

Embodiments An embodiment of the present application is shown in FIGS. 1 to 4, and is of a so-called cantilever type in which the rear arm of a motorcycle is composed of one arm and a wheel is supported on one side of the end thereof. This is an application of the invention.

In the figure, 1 is a motorcycle, and 2 is its body frame. A front fork 3 supported at the front of the vehicle body frame 2 is provided with a front wheel 4 so as to be able to freely turn left and right, and a rear wheel 4 is supported at the rear end of a rear arm 5 which is swingably supported at the rear of the vehicle body frame. .

A buffer spring 7 is stretched between the rear part of the rear arm 5 and the vehicle body frame 2. 8 is an automatic two-axle engine with a built-in transmission. 8a is its output shaft,
The rear wheel 6 is driven by a drive chain 11 wound between the output shaft 8a and a sprocket 9 provided on the rear axle.

The rear arm 5 is made of aluminum casting. The front end of the rear arm 5 is swingably supported by a bracket 2a of the vehicle body frame 2 via a bearing 14 by a pivot shaft 12 and a bolt 13.

As shown in Figure 2, the front part of the rear arm has a bearing fitting hole 5c into which the bearing 14 is fitted, and the rear part of the rear arm has a vertically enlarged part in which a large diameter support hole 5a is formed. There is. The main portion between the portion where the bearing fitting hole 5C is located and the front portion 5d of the support hole 5a is a hollow portion 5e. A support hole 5a is provided in the front portion 5d of the support hole 5a.
An opening 5f is formed which communicates the hollow part 5e.

The rear arm 5 connects the midway of the support hole core forming the support hole 5a and the rear end of the hollow portion core forming the hollow portion 5e, and moves the support hole core and the hollow portion core to a predetermined position in the mold. It is supported in position and cast by pouring hot water into the mold. The opening 5
f is formed by the rear end portion of the hollow core. According to this casting method, the rear end of the hollow core is joined to the middle of the support hole core, and the rear end of the hollow core is accurately positioned at a predetermined position in the mold via the support hole core. Because you can
Fluctuations in the wall thickness of the rear arm 5 around the hollow portion 5e can be reduced.

A hollow cylindrical cam member 15 is fitted into the support hole 5a. The cam member 15 has a guide groove 1 extending in the circumferential direction.
6 is formed, and a screw hole 5 is formed in a portion 5d around the support hole 5a.
A bolt-shaped pin 17 is formed with g and passed through the guide groove 16.
is screwed into the screw hole 5g and fixed, and the cam member 1
5 is supported in the support hole 5a so as to be rotatable and not to come off the support hole 5a (that is, immovably in the axial direction).

Both ends of the cam member 15 protrude outward from the rear arm 5,
The central axis C1 of the cam member 15 is located inside the protrusion 15a.
Two ball bearings 18.degree. 18 are fitted so as to form an axle hole on the axis C2 which is eccentric by E relative to the shaft. A cylindrical shaft 6a that supports the rear wheel 6 with a flange and a cylindrical shaft 9a that supports the sprocket 9 with a flange are fitted into the double ball bearings 18.18. A splined portion on the outer circumference of the axle 19 is fitted into the spline groove on the circumference, and a nut 2o is screwed into one end of the axle 19 to integrally connect the cylindrical shafts 6a, 9a and the axle 19, and the rear axle is It is configured.

A slit 5b is formed on the inner surface of the support hole 5a at the rear end of the rear arm 5.
A bolt hole 5h is formed in the portion of the rear arm 5 where the slit 5b is located, and a bolt 21 is inserted into the bolt hole 5h so that the slit 5b can be compressed.
is inserted.

Note that the slit 5b of the support hole 5a is not limited to one that opens toward the rear as shown in FIG. 3, but may be one that is closed at the outer end as shown in FIG. Although the machining of the slit 5b is complicated, it increases the rigidity and elasticity of the rear arm 5, so that when the bolt 21 is loosened, the support hole 5a easily returns to its original shape, making it easier to rotate the cam member 5a. become.

Since the two ball bearings 18 and 18 are arranged in positions that protrude outward from the rear arm 5, when the bolt 21 is tightened, the tightening force is not directly applied, so there is no deformation or deformation. However, the deformation is slight. 22 is a brake disc supported by the flange of the cylindrical shaft 6a, and 23 is a brake caliper that applies braking force to the brake disc.

According to this embodiment, in order to adjust the tension of the drive chain 11 (that is, whether it is too tensioned or too loose), after loosening the bolt 21, as shown in FIG. Hole 9C made in.

A rod B such as a try bar is inserted into the hole 9C provided in the sprocket 9, and the tip of the rod B is engaged with a horizontally long recess 15b provided on the side surface of the cam member 15, thereby making the sprocket 9 and the cam member 15 relative to each other. By rotating the cam member 15 within the support hole 5a, the axle 1 supported by the ball bearing 18.18 located at the eccentric position of the cam member 15 is rotated.
9 etc. in the front-back direction to adjust the tension of the drive chain 11. Further, when rotating the cam member 15 within the support hole 5a, the cam member 15 is guided by the guide groove 16 and the pin 17, and while maintaining a predetermined positional relationship between the cam member 15 and the support hole 5a, The cam member 15 can be rotated smoothly.

If the cam member 15 is fixed by tightening the bolt 21 after the adjustment is completed, the cam member 15 will no longer be able to rotate with respect to the rear arm 5, and the adjustment will not go out of order. In the above adjustment, since the axle 19 is not directly supported by the rear arm 5, there is no need to loosen the axle 19 in any way.

Note that the invention of this application can be applied to things other than cantilever type rear arms.

Effects of the Invention The present invention has a structure in which the rear arm is made of a hollow casting of light metal, and an opening communicating with the hollow part is formed in the front part of the rear arm inside the support hole. During casting, the opening is formed by the rear end of the hollow core, and the middle of the support hole core can be connected to the rear end of the hollow core. The rear end of the child can be accurately positioned at a predetermined position within the mold via the support hole core. Therefore, variations in the wall thickness of the rear arm around the hollow portion can be reduced. Moreover, when the cam member is fitted into the support hole, the opening is closed by its circumferential surface, which eliminates the need for a special lid to close the opening, which simplifies the manufacture of the rear arm and reduces manufacturing costs. can be reduced.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a side view of the motorcycle, FIG. 2 is a plan view of the rear arm, etc. taken along the line ■-■ in FIG. 1, and FIG. 3 is a side view of the motorcycle. III-III
FIG. 4 is a side view of a rear arm, cam member, etc. taken along the same line as FIG. In the figure, 5 is a rear arm, 5a is a support hole, 5b is a slit, 5e is a hollow part, 5f is an opening, 9 is a sprocket, 15
is a cam member.

Claims (1)

[Claims] 1. A rear arm is swingably supported at the rear of the vehicle body frame, a support hole whose diameter can be changed somewhat is formed at the rear end of the rear arm, and a cam member with an axle hole at an eccentric position is fitted into the support hole. In the rear arm of a motorcycle, the cam member is attached to the rear end of the rear arm in a manner that allows it to be tightened and loosened by compressing the part of the rear arm around the support hole.The rear arm is made of a hollow casting of light metal. A motorcycle characterized in that an opening communicating with a hollow part is formed in the front rear arm part in the support hole, and the opening is closed by fitting the cam member into the support hole. rear arm.