Front fork

Details Front fork Front fork

1999-07-14

2001-05-22

Mai, Lanna (Department: 3619)

Land vehicles

Wheeled

Occupant propelled type

C188S322170, C267S064260

Reexamination Certificate

active

06234505

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a front fork for a motorcycle which functions as a fork and a shock absorber that absorbs shocks such as vibrations from a road surface.
BACKGROUND OF THE INVENTION
Jikkai-Hei 56-76588 published by the Japanese Patent Office in 1981 describes a front fork of a motorcycle in which an air pressure chamber and a hydraulic chamber are separated by a free piston.
The front fork comprises an inner tube inserted into an outer tube that is open at its upper end. A hollow rod that is open at its upper end is provided at the center of the lower end of the outer tube. A free piston is disposed above the hollow rod and slides on an inner periphery of the inner tube. The free piston is pushed downwardly by a spring and separates a reservoir in the top of the inner tube and a hydraulic chamber in the hollow rod. The reservoir is linked through a check valve provided on the free piston with the hydraulic chamber in the hollow rod.
When the front fork is compressed, an increase of the volume of entry of the inner tube causes the free piston to rise against the spring. When the front fork is extended, the check valve is opened and a volume of oil equal to the retraction of the inner tube is introduced into the hollow rod from the reservoir.
In this conventional front fork, the free piston operates vertically during extension and compression. In particular, during compression, the inner tube slides downward and at the same time the free piston rises while sliding on the inner tube. As a result, the amount of stroke of the free piston is the sum of the stroke of the inner tube and the stroke of the free piston. Thus the degree of stroke of the seal provided on the outer periphery of the free piston is large which has the undesirable consequence that the life span of the seal is reduced as a result.
As reserve oil from the outer periphery of the seal or the gap of the check valve seeps to the lower side of the free piston, the amount of oil on the lower section of the free piston increases and the position of the free piston displaces upwardly. Thus the possibility exists that the initial load on the spring will increase.
SUMMARY OF THE INVENTION
Therefore it is an object of the present invention to increase the life span of the seal provided on the free piston.
It is a further object of the present invention to suppress undesirable increases in the initial load of the spring.
In order to achieve above the objects the present invention provides a front fork for a motorcycle.
The front fork for a motorcycle comprising an outer tube, an inner tube which is inserted to slide freely in the outer tube, a damper cylinder disposed on the bottom of the inner tube, a piston accommodated in the damper cylinder, a piston rod connected to the piston and the outer tube, a spring pushing the outer tube and the piston rod in an extending direction, a tubular guide disposed on an upper end of a damper cylinder and a free piston disposed to displace freely in a vertical direction along the guide, the piston separating an upper reservoir and a lower oil chamber in the inner tube and supporting an end of the spring.


REFERENCES:
patent: 3912054 (1975-10-01), Fabre et al.
patent: 4438909 (1984-03-01), Matsumoto
patent: 4493490 (1985-01-01), Ohma
patent: 4561669 (1985-12-01), Simons
patent: 4795009 (1989-01-01), Tanahashi et al.
patent: 4807860 (1989-02-01), Simons
patent: 4964625 (1990-10-01), Kawamura
patent: 6042091 (2000-03-01), Marzocchi et al.
patent: 2-182592 (1990-07-01), None
patent: 5-126194 (1993-05-01), None
patent: 7-205868 (1995-08-01), None
patent: 8-26169 (1996-01-01), None

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