Structure of a rear swingarm for a vehicle with saddle seat

Details Structure of a rear swingarm for a vehicle with saddle seat Structure of a rear swingarm for a vehicle with saddle seat

1999-09-09

2001-03-27

Johnson, Brian (Department: 3618)

Land vehicles

Wheeled

Occupant propelled type

C280S288000, C280S288300

Reexamination Certificate

active

06206398

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a structure of a swingarm for a four-wheeled buggy or the like having a saddle seat.
2. Background Art
Japanese Utility Model Publication No. Hei 6-316 discloses a swingarm for a four-wheeled buggy. Front and rear cross members of the swingarm are formed by conventional casting methods and are welded together via a pair of right and left arm members. The front and rear cross members and the right and left arm members, when welded together, define a hexagonal opening in the body of the swingarm.
Generally, in a four-wheeled buggy, a rear swingarm supports right and left rear wheels via an axle which extends across a rear part of the rear swingarm. Such a design provides the rear swingarm with a large torsional rigidity. However, the torsional rigidity is not uniform along the length and width of the rear swingarm. The torsional rigidity should be largest near the front and rear cross members, and gradually become less toward the center of the rear swingarm.
If the right and left arm members are made of pipe material, as demonstrated in the related art, they are unable to cope with the required variations in torsional rigidity; therefore, the conventional rear swingarm must be constructed with a heavy material, and thus the swingarm cannot avoid having higher rigidity than would normally be necessary. Furthermore, when the arm members are assembled by welding, the design of the conventional rear swingarm requires the length of the welded portions of the arm members to be unnecessarily increased which causes an undesirable increase in manufacturing cost.
Additionally, due to the hexagonal opening of the swingarm of the conventional art, the arm members inevitably need to be reinforced using reinforcing patches along points where welding is to occur. In such a case, the foregoing discussed problems are much more pronounced. Moreover, an increase in the weight of the rear swingarm is observed due to the use of the reinforcing patches. The present invention is intended to provide a rear swingarm for a saddle seat vehicle which can overcome the foregoing problems of the related art and can be easily manufactured.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems, the present invention provides a structure of a rear swingarm which is used for a vehicle with a saddle seat, and which is swingably supported at the front end thereof by a body frame, and supports rear wheels at the rear end thereof The rear swingarm is constituted by a cast light alloy as a single member, and has an opening for cut-away excess metal at the center thereof. A front cross member is provided in front of the opening, and a rear cross member is provided behind the opening. A pair of right and left hollow arms connect the front end rear cross members.
The front and rear cross members and the arms of the rear swingarm surround the opening for cut-away excess metal. The opening is wider near the front cross member as compared with the opening width near the rear cross member. Right and left parts of the opening constituting the inner wall of the right and left arms are uniformly rounded, and the width of the arms is gradually increased from the front part to the rear part thereof.
The arms have sectional areas which vary in accordance with the distribution of the required rigidity of the rear swingarm along the length thereof. The rear swingarm of the present invention is designed a varying sectional area which has been found to be difficult to achieve when the rear swingarm arms are made of extruded pipes, or the like, as in the conventional art.
The arms of the rear swingarm of the present invention have sufficient and required rigidity along the entire length thereof. Therefore, a predetermined required torsional rigidity is satisfied for each manufactured rear swingarm produced using the concept of the present invention. Furthermore, the present invention achieves a product which is significantly lighter than that of the conventional swingarm; thus, achieving an increase in performance of a vehicle the swingarm of the present invention is implemented on.
In addition, since the rear swingarm is cast as one integral member, it is not necessary to weld the front and rear cross members and arms, as compared to the situation in the related art where these members are separately formed and welded in order to make them integral. Furthermore, the side wall of the opening for cut-way excess metal is uniformly rounded so as to constitute the arms of the swingarm. This allows the inner walls of the hollowly formed arms to vary smoothly. Such a construction facilitates removal from sand molds when forming the hollow arms. As a result, the rear swingarm can be simply manufactured, while achieving a product of significant superiority over the conventional rear swingarm design.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.


REFERENCES:
patent: 4775025 (1988-10-01), Parker et al.
patent: 5452911 (1995-09-01), Klein et al.
patent: 5476278 (1995-12-01), Levin et al.
patent: 2-286486 (1990-11-01), None
patent: 3-42392 (1991-02-01), None
patent: 4-243679 (1992-08-01), None
patent: Y26316 (1994-01-01), None

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