JP2003172395A - Front fork for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a front fork for a motorcycle capable of suppressing increase of the air reaction force at a latter half of a compression stroke, restraining extension of the front fork at an extension stroke, and capable of restraining generation of cavitation in a damper cylinder so as to achieve stability of the damping force. <P>SOLUTION: In this front fork 10 for the motorcycle, oil reservoir chambers B and D communicating with a piston side oil chamber A1, and a main air chamber C on an upper part thereof are provided on an outer periphery of the damper cylinder 18. A sub air chamber E exhibiting a smaller compression ratio than the main air chamber C is provided in the oil reservoir chambers B and D through a movable partition member 43. A suspension spring 66 is divided into an upper part spring 66A and a lower part spring 66B. An annular partition member 67 sliding over an inner periphery of a wheel side tube 12 and the outer periphery of the damper cylinder 18 and partitioning the oil reservoir chamber B into upper and lower oil reservoir chambers B1 and B2 are provided between the two springs 66A and 66B. A communication part 68 for communicating the upper and lower oil reservoir chambers B1 and B2 when the front fork 10 is compressed to a predetermined extent or more is formed between the outer periphery of the damper cylinder 18 and the annular partition member 67. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle body side tube connected to a vehicle body side, and a wheel side tube connected to an axle side slidably inserted thereinto for buffering the vehicle body side tube and the wheel side tube. Relates to a front fork of a motorcycle having an air chamber formed therein, and particularly to a front fork of a motorcycle suitable for use as a front fork of a motorcycle for on-road racing.

[0002]

2. Description of the Related Art Inverting a wheel-side tube slidably inserted into a vehicle-body-side tube and providing an oil reservoir in the lower portion of the vehicle-side tube and the wheel-side tube and an air chamber in the upper portion with an oil level between them. Type front forks are known. The air reaction force characteristic of this air chamber has an air reaction force characteristic that increases in the shape of a square curve in the latter half of the stroke. Therefore, this front fork absorbs road surface vibrations well under normal load conditions in which the front fork expands and contracts at a position slightly compressed from near the fully extended position, but the air reaction force becomes too large in the latter half of the stroke. , The road vibration absorption in the latter half of the stroke becomes poor. For this reason, the oil level in the oil reservoir inside the front fork is lowered, and the volume of the air chamber is increased to reduce the air reaction force in the latter half of the stroke, but the air reaction force in the first half of the stroke is reduced. The front fork will easily bottom out.

Further, for example, a front fork for an on-road race of a motorcycle which runs on a flat road surface at a high speed has the following requirements. (a) In a normal vehicle-side load condition in which the front fork expands and contracts near the slightly depressed position, such as when traveling straight on a flat road surface, a small air reaction force is used to absorb road surface vibrations. I want to raise it. (b) Also, when the front fork largely sinks at high speed, such as when braking to decelerate before entering a corner, we want to suppress the sinking of the front fork with a large air reaction force. (c)
Also, when turning at a constant speed with the front fork sinking like the front stage of cornering after braking, the increase in air reaction force is suppressed and the absorption of road surface vibration during cornering is increased. I want to. (d) Also,
When the front fork expands from a compressed state, such as when accelerating on the rear side of cornering, we want to prevent the front fork from expanding and prevent the front wheels from becoming understeer to improve turning performance.

In Japanese Patent Laid-Open No. 2000-240714, as a front fork of a motorcycle, an air chamber is formed inside a vehicle body side tube and a wheel side tube, and the air chamber has a compression ratio of an oil level because of a cylindrical partition member. It is divided into an inner air chamber C1 that becomes large due to the intrusion and an outer air chamber C2 that has a small compression ratio due to the intrusion of the wheel-side tube, and upper and lower communication holes that allow the air chamber C1 and the air chamber C2 to communicate with each other. It has been proposed to provide the wheel side tube with which the air chamber C1 and the air chamber C2 communicate with each other through the upper and lower communication holes in the latter half of the compression stroke.

According to the front fork of JP-A-2000-240714, at a position where the front fork has a large compression stroke on the front side of the cornering after braking,
The air chamber C1 and the air chamber C2 communicate with each other through the upper and lower communication holes,
The increase in air reaction force can be suppressed. Further, at the position where the front fork starts to extend on the latter stage side of the cornering, the air chamber C1 and the air chamber C2 are communicated by the upper and lower communication holes to the check valve, and the rise of the front fork is suppressed by suppressing the increase of the air reaction force. To prevent understeering of the front wheels.

[0006]

In the front fork of Japanese Patent Laid-Open No. 2000-240714, although the air chamber C1 and the air chamber C2 are connected by both the upper and lower communication holes and the check valve in the first half of the expansion process, they are expanded. In the latter half of the process, only the check valve is used for communication. Therefore, in the latter half of the extension stroke, the air in the air chamber C2 is introduced into the air chamber C1, which tends to be negative pressure due to the large compression ratio, only through the check valve. The pressure tendency cannot be eliminated. The air chamber C1 exerts a back pressure on the oil chamber in the damper cylinder via the oil reservoir, and the negative pressure tendency in the air chamber causes cavitation in the oil chamber of the damper cylinder. Destabilize the damping force of.

The object of the present invention is to suppress the rise of the air reaction force in the latter half of the compression stroke, suppress the expansion of the front fork in the expansion stroke, and suppress the occurrence of cavitation in the damper cylinder to stabilize the damping force. Is to try.

[0008]

According to a first aspect of the present invention, a vehicle body side tube and a wheel side tube are slidably fitted, and a damper cylinder is erected inside the wheel side tube. Inside, is attached a piston rod having a piston that slides on the damper cylinder at the tip,
The piston divides a piston rod-side oil chamber and a piston-side oil chamber in the damper cylinder, and an oil reservoir chamber communicating with the piston-side oil chamber and a main air chamber above it are provided on the outer periphery of the damper cylinder. In a front fork of a motorcycle in which a suspension spring interposed between the vehicle body side tube and the wheel side tube is disposed between the tube and the wheel side tube, a movable partition member is provided in the oil sump chamber to separate the main air chamber from the main air chamber. A sub-air chamber having a small compression ratio is provided, the suspension spring is divided into an upper spring and a lower spring, and the suspension spring is slid between the wheel-side tube inner periphery and the damper cylinder outer periphery between the two springs to form the oil reservoir chamber. Is provided between the upper and lower oil reservoirs, and the front fork is fixed between the outer periphery of the damper cylinder and the annular partition member. When the above compression, is obtained by forming a communicating portion communicating the oil reservoir chamber of the upper and lower.

According to a second aspect of the present invention, in addition to the first aspect of the present invention, the communicating portion is composed of a small diameter portion formed below the large diameter portion of the outer periphery of the damper cylinder via a step portion. Is.

According to a third aspect of the invention, in addition to the first aspect of the invention, a step portion is provided below the large diameter portion of the outer periphery of the damper cylinder, and a small diameter portion is formed below the step portion, and the upper spring is provided. The annular partition member is seated on the step portion by the lower spring biased by a larger preset force, and the annular partition member is separated from the step portion when the front fork makes a compression stroke of a certain amount or more. Thus, the communication portion is formed.

[0011]

According to the invention of claim 1, the following effects are obtained. On the latter half side of the compression stroke of the front fork, the upper and lower oil reservoirs of the annular partition member are communicated with each other by the communicating portion, and as a result,
The high-pressure air in the main air chamber with the large compression ratio acts on the low-pressure air in the sub air chamber with the small compression ratio, and the main air chamber and the sub-air chamber are transferred to the same pressure to suppress an increase in the air reaction force.

On the first half side of the extension stroke of the front fork, the upper and lower oil reservoirs of the annular partition member are in communication with each other by the communication portion, maintaining the same pressure in the main air chamber and the sub air chamber, and reducing the air reaction force. The air reaction force at this time is smaller than the air reaction force of the main air chamber during the compression stroke. Further, in the latter half of the extension stroke in which the front fork is extended, the communication portions of the upper and lower oil reservoirs of the annular partition member are closed, and the main air chamber with a large compression ratio tends to have a relatively negative pressure, resulting in a low air reaction force. It can be suppressed. As a result, the expansion of the front fork is suppressed.

Even if the main air chamber tends to have a negative pressure as described above, the annular partition member shuts off the conduction between the main air chamber above the oil reservoir and the sub air chamber below the oil reservoir. The negative pressure tendency of the main air chamber does not affect the oil chamber. At this time, the oil chamber in the damper cylinder is held at the pressure of the sub-air chamber to suppress the occurrence of cavitation in the damper cylinder and stabilize the damping force.

According to the invention of claim 2, there is the following effect. The annular partition member moves up and down on the outer circumference of the damper cylinder and is located in the small diameter portion of the outer circumference, so that the communication portion can be formed.

According to the invention of claim 3, there is the following action. The annular partition member moves up and down on the outer circumference of the damper cylinder and is separated from the step on the outer circumference to form the communication portion.

[0016]

1 is a schematic diagram showing an extended state of a front fork according to the first embodiment, FIG. 2 is a schematic diagram showing a contracted state of a front fork according to the first embodiment, and FIG. FIG. 4 is a schematic diagram showing a state, FIG. 4 is a schematic diagram showing an opened state of a communication portion, FIG. 5 is a schematic diagram showing an extended state of the front fork of the second embodiment, and FIG. 6 is a contracted state of the front fork of the second embodiment. FIG. 7 is a schematic diagram showing a closed state of the communicating portion, FIG. 8 is a schematic diagram showing an open state of the communicating portion, and FIG. 9 is a schematic diagram showing air reaction forces generated in the main air chamber and the sub air chambers. Is.

(First Embodiment) (FIGS. 1 to 4 and 9) In the front fork 10, as shown in FIGS. 1 and 2, a wheel tube 12 is slidably inserted into a vehicle body tube 11. The vehicle body side tube 11 is connected to the vehicle body side via an upper bracket (not shown), and the wheel side tube 12 is connected to the axle side via an axle bracket 13. A lower bush 14, an oil seal 15, and a dust seal 16 which are in sliding contact with the outer circumference of the wheel side tube 12 are fixed to the inner circumference of the lower open end of the vehicle body side tube 11, and the vehicle body side tube is fitted to the upper outer circumference of the wheel side tube 12. An upper bush 17 that is in sliding contact with the inner circumference of 11 is fixed.

Further, a damper cylinder 18 is erected on the bottom of the axle bracket 13 in the wheel side tube 12, and a rod guide 19 is screwed onto the inner periphery of the upper portion of the damper cylinder 18 and provided on the inner periphery of the rod guide 19. A piston rod 21 can be slidably inserted through the bush 20. On the other hand, a cap 22 is screwed and fixed to the upper end opening of the vehicle body side tube 11, a hollow joint bolt 23 is screwed and fixed to the cap 22, and a hollow rod of the joint bolt 23 has a base end portion of the piston rod 21. It is screwed and fixed by the lock nut 24. A piston 25 is provided at the tip of the piston rod 21, and the piston 25 slides inside the damper cylinder 18. Joint bolt 2
A spring adjuster 26 is inserted into the annular space between the cap 3 and the cap 22, and the spring adjuster 26 is screwed onto the outer periphery of the joint bolt 23 to form a spring load adjusting mechanism 60 described later. A damping force adjusting adjuster 27, which will be described later, is inserted into the hollow upper portion of the joint bolt 23, and the damping force adjusting adjuster 27 is screwed onto the inner circumference of the joint bolt 23 to form a damping force adjusting mechanism 31 described later.

Piston 2 at the tip of piston rod 21
Reference numeral 5 denotes a piston-side oil chamber A1 inside the damper cylinder 18.
And a piston rod side oil chamber A2, and a known extension side damping force generating device 28 is provided in an oil passage connecting the piston side oil chamber A1 and the piston rod side oil chamber A2.

The extension side damping force generator 28 includes a piston 25
An expansion side damping force is generated by the flexural deformation of the expansion side damping valve 30 provided in the expansion side oil passage 29 formed in the above. A pressure side check valve (not shown) is provided in the pressure side oil passage (not shown) formed in the piston 25. At this time, the damping force adjusting adjuster 27 vertically moves the damping force adjusting rod 32 forming the damping force adjusting mechanism 31 to open / close the bypass oil passage 33 of the piston 25.

An oil reservoir chamber B, which is surrounded by a vehicle body side tube 11 and a wheel side tube 12, is connected to the piston side oil chamber A1 via communication passages 41A and 41B provided in the axle bracket 13 on the outer circumference of the damper cylinder 18. And an upper main air chamber C through the oil surface.

A tank 42 is provided on the axle bracket 13, and the tank 42 communicates with the oil chamber A1 on the piston side through the communication passages 41B and 41A, and the oil storage chamber D (which communicates with the oil storage chamber B through the communication passage 41B. A communication passage 41B with a lower oil reservoir B2 described later.
Via the movable partition wall member 43 formed of a free piston, and a sub air chamber E facing the oil reservoir chambers D and B.

When the front fork 10 is compressed, the oil equivalent to the volume of the piston rod 21 that has entered the damper cylinder 18 is transmitted through the communication passages 41A and 41B to the piston side oil chamber A.
1 flows into the oil reservoir chambers D and B, and at the time of extension, the oil corresponding to the volume of the piston rod 21 that exits from the damper cylinder 18 passes from the oil reservoir chambers B and D to the piston side oil chamber A1 via the communication passages 41A and 41B. Return to.

When the front fork 10 is compressed, the main air chamber C is compressed at a higher compression ratio due to the rise of the oil level in the oil reservoir chamber B due to the entry of the wheel side tube 12, and the sub air chamber E is compressed when the front fork 10 is compressed. Two
When the movable partition wall member 43 is moved upward by the movement of 1 into the damper cylinder 18 and the downward movement of the annular partition wall member 67, which will be described later, it is compressed at a smaller compression ratio.

Oil chamber A1 on the piston side of the damper cylinder 18
A known compression-side damping force generating device 44 is provided between the communication passage 41A communicating with the communication passage 41A and the communication passage 41B communicating with the outer circumference of the damper cylinder 18 and the oil reservoir chambers B and D of the tank 42.

The compression-side damping force generator 44 generates a compression-side damping force by the flexural deformation of the compression-side damping valve 47 provided in the compression-side oil passage 46 formed in the valve housing 45. still,
An extension side check valve 45 is provided in the extension side oil passage 48 formed in the valve housing 45. At this time, the damping force adjusting adjuster 50 reciprocates the damping force adjusting rod 52 forming the damping force adjusting mechanism 51 to open / close the bypass oil passage 53 of the valve housing 45.

The upper end surface of the rod guide 19 constitutes a bump stopper 56, which bumps against the bump rubber 57 provided on the outer periphery of the piston rod 21 when the front fork 10 is compressed most. Fulfill. Further, inside the damper cylinder 18, the rod guide 1
A rebound spring 58 is provided in the lower portion of 9, and when the front fork 10 is fully extended, the rebound spring 58 abuts a rebound stopper 59 provided on the outer periphery of the piston rod 21 to perform a cushioning action.

The spring load adjusting mechanism 60 includes an adjuster pin 61 and a slider 6 at the lower end of the spring adjuster 26.
The spring collar 63 is moved up and down through the upper spring receiver 64 provided at the lower end of the spring collar 63,
Lower spring support 65 provided on the outer circumference of the damper cylinder 18
A suspension spring 66 is interposed between the two. That is, the suspension spring 66 includes the body side tube 11 and the wheel side tube 12.
It is interposed between the vehicle body side tube 11 and the wheel side tube 12 inside the oil sump chamber B and the main air chamber C surrounded by and urges the vehicle body side tube 11 and the wheel side tube 12 in the extending direction. The spring collar 63 has a large opening communication hole 63A.
Have.

The suspension spring 66 is the upper spring 6
It is divided into 6A and a lower spring 66B, and an annular partition member 67 is provided between the two springs 66A and 66B. The annular partition wall member 67 slides through a minute gap (throttle passage) between the inner circumference of the wheel-side tube 12 and each of the large diameter portions 69A on the outer circumference of the damper cylinder 18, and the outer circumference of the damper cylinder 18 is surrounded. The oil reservoir chamber B is replaced by the upper and lower oil reservoir chambers B1,
Partition into B2.

Between the outer circumference of the damper cylinder 18 and the annular partition wall member 67, when the front fork 10 is compressed for a certain stroke (ST1) or more, the upper and lower oil reservoir chambers B1, B are provided.
A communication portion 68 that connects the two is formed.

Specifically, as shown in FIGS. 3 and 4, the communicating portion 68 is composed of a small diameter portion 69B formed below the large diameter portion 69A on the outer periphery of the damper cylinder 18 through a step. That is, the front fork 10 has a constant stroke (ST1)
When compressed, the annular partition member 67 moves on the outer periphery of the damper cylinder 18 from the large diameter portion 69A side to the small diameter portion 69B side, and communicates between the annular partition member 67 and the small diameter portion 69B of the damper cylinder 18. The portion 68 is formed.

FIG. 9 (A) shows the air reaction force generated in the main air chamber C2 on the outer periphery of the damper cylinder 18 with respect to each of the compression stroke and the extension stroke of the front fork 10 by one-dot chain lines and two-dot chain lines. Is. still,
It is assumed that the broken line in FIG. 9A occurs in the main air chamber C under the condition that the communication portion 68 is opened and the main air chamber C on the outer periphery of the damper cylinder 18 and the sub air chamber E of the tank 42 have the same pressure. Indicates air reaction force.

That is, in the compression stroke of the front fork 10, the front fork 10 moves to the extension position ST.
During the period from 0 to ST1, the communication part 68 is in the closed state, and the main air chamber C is compressed at a high compression ratio to raise the air reaction force. While the front fork 10 opens the communication portion 68 at ST1 and reaches the maximum compression position ST2, the high-pressure air in the main air chamber C acts on the low-pressure air in the sub-air chamber E with a small compression ratio, which in turn causes the main air chamber C to move. The pressure is changed to the same as that of the sub air chamber E, and the rise of the air reaction force is suppressed.

On the other hand, in the extension stroke of the front fork 10, the front fork 10 moves to the maximum compression position S.
During the period from T2 to ST1, the communication portion 68 is in the open state, and the main air chamber C maintains the same pressure as the sub air chamber E to reduce the air reaction force. While the front fork 10 closes the communication part 68 at ST1 and reaches the extension position ST0, the main air chamber C with a large compression ratio expands rapidly without the oil level of the upper oil reservoir chamber B1 rising. As a result, the pressure tends to be relatively negative, and the air reaction force is suppressed low.

FIG. 9B shows the air reaction force generated in the sub air chamber E of the tank 42 with respect to each of the compression stroke and the extension stroke of the front fork 10 by one-dot chain lines and two-dot chain lines, respectively. . Incidentally, FIG.
The broken line in (B) indicates that the communication portion 68 is open and the damper cylinder 18 is
The air reaction force assumed to be generated in the sub air chamber E under the condition where the main air chamber C on the outer circumference of the sub air chamber E and the sub air chamber E of the tank 42 have the same pressure is shown.

That is, in the compression stroke of the front fork 10, the front fork 10 moves to the extension position ST.
During the period from 0 to ST1, the communication portion 68 is in the closed state, and the sub air chamber E is compressed at a small compression ratio to raise the air reaction force. While the front fork 10 opens the communication portion 68 in ST1 and reaches the maximum compression position ST2, the high-pressure air in the main air chamber C with a large compression ratio acts on the low-pressure air in the sub-air chamber E, and the sub-air chamber E is the main air chamber. The air reaction force is further increased so that the pressure becomes the same as that of the air chamber C.

On the other hand, in the extension stroke of the front fork 10, the front fork 10 moves to the maximum compression position S.
During the period from T2 to ST1, the communication portion 68 is in the open state, and the sub air chamber E maintains the same pressure as the main air chamber C to reduce the air reaction force. While the front fork 10 closes the communication portion 68 at ST1 and reaches the extension position ST0, the sub air chamber E having a small compression ratio is gradually expanded while the movable partition wall member 43 is lowered, and a relatively positive pressure is obtained. The air reaction force is reduced while maintaining the tendency. The reduction rate of the air reaction force of the sub air chamber E in ST1 to ST0 is smaller than the reduction rate of the air reaction force of the broken line where the main air chamber C and the sub air chamber E have the same pressure because the compression ratio of the sub air chamber E is small. .

Therefore, the front fork 10 operates as follows. (During compression) When the front fork 10 is compressed, the wheel-side tube 12 moves upward relative to the vehicle-body-side tube 11 to compress the suspension spring 66, and the main air chamber C and the sub-air chamber E are compressed to suspend the suspension. Spring 66
The reaction force of the spring and the air reaction force of the main air chamber C and the sub air chamber E are generated, and the impact from the road surface is absorbed by the following (1) to (3). Further, the compression side damping force generating device 44 generates a compression side damping force to control the compression speed.

(1) When the motorcycle travels on a relatively flat straight road surface, a normal load is applied to the front fork 10, and the wheel-side tube 12 is slightly depressed from the extension position ST0. With a small stroke, it expands and contracts at a relatively low speed. When the front fork 10 is compressed and the wheel side tube 12 moves upward with respect to the vehicle body side tube 11, the volume of the main air chamber C decreases due to the rise of the oil level of the oil reservoir chamber B, and the sub air chamber E of the movable partition member 43. Volume is reduced by rising. At the time of compression in this state, the annular partition member 67 is located on the large diameter portion 69A side of the damper cylinder 18 to close the communication portion 68, and the upper oil reservoir chamber B1 and the sub air chamber on the main air chamber C side are closed. The oil reservoir chamber D and the lower oil reservoir chamber B2 on the E side are shut off, and the pressure of the main air chamber C with the large compression ratio becomes higher than the pressure of the sub air chamber E with the small compression ratio. However, in this state, since the compression stroke is small and the air reaction force is also small, the road surface vibration absorption is good. Figure 9
The portions of the compression strokes (A) and (B) from ST0 to ST1 on the ST0 side show the spring characteristics of the main air chamber C and the sub air chamber E in this state.

(2) When braking and decelerating before cornering, the vehicle body load moves to the front wheel side, and the wheel side tube 12 moves further upward with respect to the vehicle body side tube 11 and the upper side of the main air chamber C side. The oil level in the oil reservoir chamber B1 rises, and the volume of the main air chamber C decreases. During this braking,
The annular partition wall member 67 still has the large diameter portion 6 of the damper cylinder 18.
The communication portion 68 is closed on the 9A side, only the main air chamber C is compressed with a large stroke, and as a result, the air reaction force is greatly increased and the sinking of the front fork 10 is suppressed. 9A and 9B, the ST1 to ST1 side portions of the compression strokes show the spring characteristics of the main air chamber C and the sub air chamber E in this state.

(3) On the front side of the cornering after braking, centrifugal force acts on the vehicle body, so that the front fork 10 is largely compressed, and the wheel side tube 12 further moves upward with respect to the vehicle body side tube 11 to form an annular shape. The partition member 67 moves to the small diameter portion 69B side of the damper cylinder 18 to open the communication portion 68. In this state, the upper oil reservoir chamber B1 on the main air chamber C side, the oil reservoir chamber D on the sub air chamber E side and the lower oil reservoir chamber B2 are electrically connected, and the high-pressure air in the main air chamber C is transferred to the sub air chamber E. It acts on the low-pressure air, the pressure in the main air chamber C gradually decreases, and the main air chamber C and the sub air chamber E shift to the same pressure to suppress the increase of the air reaction force, and absorb the road surface vibration during cornering. To improve. 9 (A), (B)
In the latter half of the compression stroke of ST1 to ST0, the spring characteristics of the main air chamber C and the sub air chamber E in this state are shown.

(In extension) When the front fork 10 is extended, the wheel side tube 12 moves downward relative to the vehicle body side tube 11 to extend the suspension spring 66, and the main air chamber C and the sub air chamber E are Expand as in (1) and (2). Further, the extension side damping force generating device 28 generates the extension side damping force to suppress the resonance of the suspension spring 66.

(1) At the rear stage side of the cornering, during acceleration while turning to move straight ahead, the vehicle body load moves to the rear wheel side, the front wheel side rises, and the wheel side tube 12 is lower than the vehicle body side tube 11. Start moving. In this state, the annular partition wall member 67 still has the small diameter portion 69B of the damper cylinder 18.
, The communication portion 68 is opened, the main air chamber C and the sub air chamber E maintain the same pressure, and the air reaction force decreases. The air reaction force at this time is the main air chamber during the compression stroke. It is smaller than the air reaction force of C. 9A and 9B, the extension strokes ST2 to ST1 show the spring characteristics of the main air chamber C and the sub air chamber E in this state.

(2) When the front fork 10 further extends on the rear stage side of the cornering, the annular partition wall member 67 moves to the large diameter portion 69A side of the damper cylinder 18 and the communicating portion 68.
Is closed, the upper oil sump chamber B1 on the main air chamber C side, the oil sump chamber D on the sub air chamber E side and the lower oil sump chamber B2 are shut off, and the main air chamber C having the large compression ratio is set on the upper oil sump chamber B1. The oil is rapidly expanded without increasing the oil level, and the air pressure becomes relatively negative, and the air reaction force is suppressed to a low level. Thereby, the extension of the front fork 10 is suppressed. Then, the front fork 10 includes the annular partition member 67 and the damper cylinder 18.
Through a small gap between the large diameter portion 69A and the inner circumference of the wheel side tube 12, the oil is extended from the lower oil reservoir chamber B2 to the upper oil reservoir chamber B1 to extend the main air chamber C and the sub air chamber E. Return to the same pressure as before compression. 9A and 9B, the extension strokes ST1 to ST0 show the spring characteristics of the main air chamber C and the sub air chamber E in this state.

According to this embodiment, there are the following effects. On the latter half side of the compression stroke of the front fork 10, the upper and lower oil reservoir chambers B1 and B2 of the annular partition wall member 67 communicate with each other through the communication portion 68, and as a result, the high pressure air in the main air chamber C having a large compression ratio has a small compression ratio. It acts on the low-pressure air in the sub air chamber E, and consequently the main air chamber C and the sub air chamber E shift to the same pressure, and the rise of the air reaction force is suppressed.

On the first half side of the extension stroke of the front fork, the upper and lower oil reservoir chambers B1 and B2 of the annular partition member 67 are in communication with each other by the communication portion 68, and the same pressure is maintained in the main air chamber C and the sub air chamber E. The air reaction force decreases, and the air reaction force at this time is smaller than the air reaction force of the main air chamber C during the compression stroke. Further, on the latter half side of the extension process in which the front fork 10 extends, the oil reservoir chambers B1 above and below the annular partition member 67,
The communication portion 68 of B2 is closed, and the main air chamber C with a large compression ratio
Is relatively negative, and the air reaction force is suppressed to a low level. Thereby, the extension of the front fork 10 is suppressed.

Even if the main air chamber C tends to have a negative pressure as described above, the annular partition member 67 blocks the conduction between the main air chamber C above the oil reservoir and the sub air chamber E below the oil reservoir. The negative pressure tendency of the main air chamber C does not affect the oil chambers A1 and A2 in the damper cylinder 18. At this time, the oil chambers A1 and A2 in the damper cylinder 18 are held at the pressure of the sub air chamber E, so that the occurrence of cavitation in the damper cylinder 18 is suppressed and the damping force is stabilized.

The annular partition member 67 is the damper cylinder 18.
The communication portion 68 can be formed by moving the outer periphery of the up and down and being located at the small diameter portion 69B of the outer periphery.

(Second Embodiment) (FIGS. 5 to 9) The second embodiment is different from the first embodiment in the structure for forming the communicating portion 68 by the annular partition wall member 67.

That is, the communicating portion 68 is, as shown in FIGS. 5 to 8, a large diameter portion on the outer circumference of the damper cylinder 18, in this embodiment, a step portion 72 below the large diameter portion 71 on the upper circumference of the rod guide 19. And a small diameter portion, that is, a small diameter portion 73 on the outer circumference of the damper cylinder 18 is formed below the stepped portion 72.
Then, the lower partition spring 66B, which is biased with a larger preset force than the upper spring 66A of the suspension spring 66, presses the annular partition wall member 67 so as to be seated on the stepped portion 72, and the front fork 10 has a predetermined stroke (ST1) or more. When compressed, the annular partition member 67
By separating from the stepped portion 70, a communication portion 68 is formed between the annular partition wall member 67 and the small diameter portion 73 of the damper cylinder 18.

In the present embodiment, the annular partition member 67 is also seated on the stepped portion 72, and the wheel-side tube 1 is
The oil reservoir chamber B on the outer periphery of the damper cylinder 18 is connected to the upper and lower oil reservoir chambers B1, B through a minute gap (throttle passage) between the oil reservoir chambers B1 and B2.
Divide into 2.

Therefore, even in the second embodiment, the air reaction force generated in the main air chamber C on the outer periphery of the damper cylinder 18 and the sub air chamber E of the tank 42 is the same as that described in the first embodiment. As shown in FIGS. 9A and 9B,
The operation of the front fork 10 during compression and extension is also the first
The same as described above in the embodiment.

In the second embodiment, the communication portion 68 can be formed by moving the annular partition wall member 67 up and down on the outer circumference of the damper cylinder 18 and separating it from the step portion 72 on the outer circumference thereof.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and the design can be changed without departing from the gist of the present invention. Etc. are included in the present invention.

[0055]

As described above, according to the present invention, the rise of the air reaction force is suppressed in the latter half of the compression stroke, the expansion of the front fork is suppressed in the expansion stroke, and the cavitation in the damper cylinder is prevented. It is possible to suppress and stabilize the damping force.

[Brief description of drawings]

FIG. 1 is a schematic view showing an extended state of a front fork according to a first embodiment.

FIG. 2 is a schematic view showing a contracted state of the front fork of the first embodiment.

FIG. 3 is a schematic diagram showing a closed state of a communication part.

FIG. 4 is a schematic diagram showing an open state of a communication part.

FIG. 5 is a schematic view showing an extended state of a front fork according to the second embodiment.

FIG. 6 is a schematic view showing a contracted state of a front fork according to the second embodiment.

FIG. 7 is a schematic diagram showing a closed state of a communication part.

FIG. 8 is a schematic diagram showing an open state of a communication part.

FIG. 9 is a schematic diagram showing an air reaction force generated in a main air chamber and a sub air chamber.

[Explanation of symbols]

10 front forks 11 Body side tube 12 Wheel side tube 18 damper cylinder 21 piston rod 25 pistons 43 Movable partition member 66 suspension spring 66A upper spring 66B Lower spring 67 annular partition member 68 Communication section 69A Large diameter part 69B Small diameter part 71 Large diameter part 72 steps 73 Small diameter part A1 Piston side oil chamber A2 Piston rod side oil chamber B oil reservoir B1 Upper oil reservoir B2 Lower oil reservoir C main air chamber D oil reservoir E sub air room

Claims (3)

[Claims] 1. A vehicle body side tube and a wheel side tube are slidably fitted, and a damper cylinder is installed upright inside the wheel side tube,
Inside the tube on the vehicle body side, a piston rod provided with a piston that slides on the damper cylinder at its tip is attached, and by the piston, a piston rod side oil chamber and a piston side oil chamber are defined in the damper cylinder, An oil reservoir chamber communicating with the piston-side oil chamber and a main air chamber above the damper-cylinder chamber are provided on the outer periphery of the damper cylinder, and a suspension spring interposed between the vehicle body-side tube and the wheel-side tube is provided between them. In the disposed front fork of the motorcycle, a sub air chamber having a compression ratio smaller than that of the main air chamber is provided in the oil reservoir chamber through a movable partition member, and the suspension spring is divided into an upper spring and a lower spring. Between the two springs, the inner circumference of the wheel-side tube and the outer circumference of the damper cylinder slide to move the oil reservoir chambers above and below the upper and lower oil reservoirs. An annular partition member for partitioning the chamber is provided, between the outer periphery and the annular partition wall member of the damper cylinder,
A front fork for a motorcycle, characterized in that a communication portion is formed which communicates the upper and lower oil reservoirs when the front fork is compressed by a certain amount or more. 2. The front fork of the motorcycle according to claim 1, wherein the communication portion is a small diameter portion formed below a large diameter portion on the outer circumference of the damper cylinder via a step portion. 3. A step portion is provided below the large diameter portion on the outer circumference of the damper cylinder, and a small diameter portion is formed below the step portion, and the lower spring urged by a preset force larger than that of the upper spring. The communication part is formed by allowing the annular partition member to be seated on the step part, and when the front fork makes a compression stroke of a certain amount or more, the annular partition part is separated from the step part. The front fork of the motorcycle according to Item 1.