JPH0368253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a front fork of a motorcycle or the like.

A front fork used for motorcycles, etc. has an inner and an outer cylinder that are slidably fitted together, a seat pipe installed at the bottom of the outer cylinder facing into the inner cylinder, and a piston installed in the seat pipe or the inner cylinder. The inside of the front fork is divided into an upper chamber and a lower chamber, and these chambers are communicated with each other through a hole, and the damping force generated when hydraulic oil passes through the hole during the compression process and extension process acts as a buffer. There are known devices that exhibit this effect.

Incidentally, such a front fork is sometimes provided with a damping force variable mechanism that changes the generated damping force depending on the stroke in order to maintain high handling stability of the motorcycle, etc., but this type of damping force variable mechanism is Conventionally, the damping force variable mechanism has been provided separately from the front fork body, making the overall structure of the front fork complicated and requiring the addition of another mechanism for driving the variable damping force mechanism.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a front fork in which a variable damping force mechanism can be incorporated to simplify the structure.

In order to achieve such an object, the present invention provides a variable damping force mechanism at the upper end of the seat pipe of a front fork, which is constructed by slidably fitting an inner and outer cylinder and installing a seat pipe at the bottom of the outer cylinder. The variable damping force mechanism is configured such that a plunger is vertically slidably held by a case member fixed to the upper end of the seat pipe, and a diaphragm held by the case member is brought into contact with the upper end surface of the plunger. The present invention is characterized in that one end of a valve spring of a check valve is brought into elastic contact with the lower end surface, and a pressure chamber is defined and formed on the lower surface side of the diaphragm to seal a fluid at a predetermined pressure.

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional side view of a front fork according to the present invention, and FIG. 2 is an enlarged detailed sectional view of the upper end of the seat pipe of the front fork.

In the front fork 1 shown in FIG.
is an outer cylinder, and inside this outer cylinder 2, an inner cylinder 3 is inserted from above.
are inserted and fitted so that they can be slid up and down. Further, a seat pipe 4 is installed at the bottom of the outer cylinder 2 with a bolt 5, and the upper end piston portion 4a of the seat pipe 4 is in sliding contact with the inner periphery of the inner cylinder 3 as shown in the figure.
Also, an oil lock piece 6 is fitted around the outer periphery of the base. Incidentally, oil holes 4b..., 4c... are bored in the upper and lower side walls of the seat pipe 4.

A free valve 7 that slides on the outer periphery of the seat pipe 4 and an oil lock collar 8 that should fit on the outer periphery of the oil lock piece 6 during the maximum compression stroke are fitted into the lower inner periphery of the inner cylinder 3. Inner cylinder 3
The upper end of is closed with a fork bolt 9. Further, an oil seal 10 and a rod guide 11 are fitted on the upper inner periphery of the outer cylinder 2 so as to be in sliding contact with the outer periphery of the inner cylinder 3, and furthermore, the upper end of the outer cylinder 2 is covered with a dust seal 12.

Incidentally, a damping force variable mechanism 20, the details of which are shown in FIG. 2, is provided at the upper end of the seat pipe 4. That is, in FIG. 2, reference numeral 21 denotes a check valve case fitted to the inner periphery of the upper end of the seat pipe 4, and the case 21 securely holds a poppet valve case 22 having a substantially cylindrical shape. This poppet valve case 22 has an oil hole 22 as shown in the figure.
a..., 22b... are bored, and a check valve 23 is provided in the check valve case 21 and is biased upward by a spring 24 to close the oil holes 22a... Also, in the poppet valve case 22, a spring 26 is installed in the poppet valve 25 to close the oil hole 22b.
It is biased downward at .

Further, a diaphragm case 27 is further screwed onto the outer periphery of the poppet valve case 22.
A plunger guide 28 is fitted and held on the inner periphery of the diaphragm case 27, and a plunger 29 is inserted through the center of the plunger guide 28 so as to be vertically slidable. The upper end surface of the diaphragm case 27 has its peripheral edge closed by a diaphragm 30 fixed to the case 27, and the diaphragm 30 abuts against the upper end surface of the plunger 29 via a plate 31 as shown in the figure. Ori,
A lower end surface of the plunger 29 receives one end of the spring 26 via a plate 32. A sealed pressure chamber _S5 is formed on the lower surface side of the diaphragm 30, and gas at a predetermined pressure is filled in the pressure chamber _S5 . Note that a small amount of lubricating oil may be placed in the lower part of the pressure chamber _S5 .
Further, an oil chamber _S6 is formed above the poppet valve 25, and a through hole 27a is bored in the side wall of the diaphragm case 27, communicating with the oil chamber _S6 .

The variable damping force mechanism 20 described above is constructed as one integrated unit, which can be integrally attached to the upper end of the seat pipe 4 in a cassette type.

By the way, a coil spring 14 is stretched between the fork bolt 9 in the inner cylinder 3 and the diaphragm case 27 as shown in the figure.

Therefore, inside the front fork 1 are the chambers S ₁ , S ₂ ,
It is divided into S ₃ and S ₄ , and each chamber S ₁ , S ₂ , S ₃ , S ₄
Hydraulic oil is sealed inside, and especially the upper part of chamber _S4 is occupied by gas at a predetermined pressure.

Further, FIG. 3 shows another embodiment, and the only difference is the locations where the oil holes 22a, 22b and the through hole 27a are provided, and the other structures are the same as those of the previous embodiment.

Next, the function of the front fork 1 will be explained.

First, when the inner cylinder 3 moves downward within the outer cylinder 2 during the compression stroke, the volume of the chamber S ₂ decreases, and the oil in the chamber S ₂ flows into the chamber S ₁ through the oil hole 4c... do. The room S ₁
A part of the oil inside flows into the chamber S3 through the oil holes _4b , and the other part of the oil uses its pressure to push open the poppet valve 25 against the elastic force of the spring 26, and the other part of the oil flows into the chamber S3 through the oil holes 4b. Flow into _S4 . A required damping force is generated in the front fork 1 during the compression stroke based on the flow resistance when the oil passes through each flow path.
Note that when the poppet valve 25 is pushed open, the volume of the oil chamber _S6 decreases, and an amount of oil corresponding to this volume reduction flows into the chamber _S4 through the through hole 27a.

Therefore, as the compression stroke increases, the proportion of oil in the chamber S ₄ increases, and therefore the gas occupying the upper part of the chamber S ₄ is gradually compressed, and as a result, the proportion of oil in the chamber S 4 increases.
The internal pressure of S ₄ gradually increases. Then, when the internal pressure of this chamber S ₄ rises to exceed the internal pressure of the pressure chamber S ₅ , the diaphragm 30 bends downward, and the plunger 29 that comes into contact with it moves downward, and as a result, the spring 26
is compressed, its set load becomes higher, and it presses the poppet valve 25 downward with a stronger force.

In this way, when the pressing force of the poppet valve 25 increases as the compression stroke increases, the valve 2
The flow resistance of the oil flowing by pushing open 5 increases, and therefore the damping force also increases continuously, improving the steering stability of the two-wheeled vehicle or the like.

Next, when the inner cylinder 3 moves upward within the outer cylinder 2 during the extension stroke, the oil in the chamber S ₃ passes through the oil hole 4b... to the chamber S ₁
At the same time, the oil in the chamber S4 flows into the chamber _S2 through the free valve 7, and the oil in the chamber _S4 uses its pressure to push the check valve 23 open against the elastic force of the spring 24, and flows into the chamber _S1 . Inflow. Also in this extension stroke, a required damping force is generated within the front fork 1 based on the flow resistance of the hydraulic oil.

In the above, the variable damping force mechanism is compactly incorporated into the front fork, and is driven by internal pressure changes generated within the front fork, so the structure of the front fork 1 can be simplified, and the damping force on the compression side can be reduced. It can be changed continuously depending on the stroke.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal cross-sectional side view of a front fork according to the present invention, FIG. 2 is an enlarged broken detailed view of the upper end of the seat pipe of the front fork, and FIG. 3 is a detailed view of the front fork. FIG. 3 is a sectional view showing another embodiment. In the drawings, 1 is a front fork, 2 is an outer cylinder, 3 is an inner cylinder, 4 is a seat pipe, 20 is a damping force variable mechanism, 22 is a poppet valve case, 25 is a poppet valve, 26 is a spring, and 27 is a diaphragm. The case, 29 is a plunger, 30 is a diaphragm, and S ₁ to S ₆ are chambers.

Claims (1)

[Scope of Claims] 1. A front fork in which an inner and an outer cylinder are slidably fitted together, and an upper end piston of a seat pipe installed at the bottom of the outer cylinder slides into contact with the inner periphery of the inner cylinder,
A damping force variable mechanism is provided at the upper end of the seat pipe, and the damping force variable mechanism allows a case member fixed to the upper end of the seat pipe to hold the plunger in a vertically slidable manner. A diaphragm held by the member is brought into contact with the member, one end of a valve spring of a check valve is brought into elastic contact with the lower end surface, and a pressure chamber is defined on the lower surface side of the diaphragm by sealing a fluid at a predetermined pressure. The front fork is characterized by consisting of: 2. The damping force variable mechanism is composed of a unit,
The front fork according to claim 1, wherein the front fork can be attached to a seat pipe in a cassette manner.