JPS6348756B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the valve structure of an anti-nose dive mechanism (mechanism for preventing sinking during braking) attached to a front fork of a two-wheeled vehicle.

When the brakes are applied while the two-wheeled vehicle is running, the front fork is compressed based on the axial component force corresponding to the inclination angle of the front fork.

This sinking phenomenon of the front fork is proportional to the braking deceleration, and has the characteristic that the more suddenly the brake is applied, the greater the amount of sinking.

Therefore, the present applicant has developed a system that increases the set pressure of a relief valve installed in the hydraulic oil flow path of the front fork in response to this brake operating force, thereby providing resistance to the operation on the pressure side and suppressing sinking. An anti-nose dive mechanism has been proposed.

By the way, the relief valve used in this mechanism was constructed as shown in FIG.

When the front fork performs compression operation, hydraulic oil flows from port 1 to port 2, and a relief valve 3 is disposed in the middle of this flow.

In this relief valve 3, a cylindrical valve poppet 7 slides on a sleeve 10 containing a valve seat 8, and is pressed against the valve seat 8 by a valve spring 4 that determines the relief setting pressure.

A push rod 9 that compresses the spring 4 in accordance with the brake operating force is slidably housed in the valve housing 5. The piston 14 presses.

Therefore, during braking, the acting force of the spring 4 that presses the poppet 7 against the valve seat 8 increases in accordance with the brake oil pressure, so the relief valve 3 will not open in principle unless this valve opening set pressure is reached. .

For this reason, during braking, the flow of hydraulic oil from the pressure side oil chamber (not shown) to the oil reservoir chamber is regulated, and the front fork is prevented from sinking.

In this case, in order to prevent the compression side damping force from increasing unnecessarily when the brake is not applied, a return spring 15 is provided that pushes the push rod 9 back to a predetermined position when the brake is not applied. Hydraulic oil flows smoothly through the valve gap.

However, when a poppet type relief valve 3 is provided as described above, the structure tends to be complicated, the weight is large, and the response is poor.

In addition, since the pre-leakage characteristic of the relief valve 3 is constant as shown in Figure 2 regardless of the relief set pressure, even if the flow rate increases in a stepwise manner at a certain set pressure, the relief valve 3 3 is delayed due to the relationship with the front leakage characteristic There was a problem with providing pleasure.

An orifice 16 is provided through the poppet 7 and communicates the valve chamber 17 with the port 2 side, thereby creating a damper effect that suppresses excessive response of the poppet 7. It also had the disadvantage that it easily accumulated, making the operation of the poppet 7 unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a relief valve structure for an anti-nose dive mechanism that has a simple valve structure, stable operating characteristics, and less generation of surges.

Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 3, a push rod 22 is slidably supported by a bearing 21 with respect to a valve housing 20. As shown in FIG.

A piston 25 housed in a cylinder chamber 24 to which brake oil pressure is introduced is brought into contact with the end face of the push rod 22.

Therefore, the push rod 22 is the piston 2.
5 and moves to the right in the figure, but a return spring 26 is interposed to oppose this movement of the push rod 22.

The push rod 22 has a head 27 with an enlarged diameter formed at its tip, and the head 27 has a tapered surface 28 on its end surface.

On the other hand, a hollow disk-shaped leaf valve body 30 is secured to the inner surface of the housing 20 by a snap spring 29 .
Interpose 1. The central hole 30 of this leaf valve body 30
The head 27 of the push rod 22 is inserted into A, and together they constitute a relief valve 32.

This relief valve 32 is interposed between ports 33 and 34 for discharging the hydraulic fluid, which contracts when the front fork pressure side is operated, into the oil reservoir chamber.

As shown in FIG. 4, this relief valve 32 is connected to the bearing portion 21 of the push rod 22
The contact diameter A' with respect to the leaf valve body 30 is made smaller (or equal to) than the sliding diameter A with respect to the leaf valve body 30, and when not braking, a thrust force corresponding to this pressure receiving area difference is applied in the return direction of the push rod 22. There is.

For example, if the contact diameter is increased to A″,
The push rod 22 moves in the direction in which the thrust generated by the hydraulic pressure increases the relief setting pressure, that is, to the right in the figure.
This will push out the

The push rod 22 is pushed back by the return spring 26 to the position where the piston 25 hits the stepped portion 24' of the cylinder chamber 24 that supports the piston 25 during this non-braking state (free state).

In addition, in the free state, the tapered surface 28 of the push rod 22 does not come into contact with the leaf valve body 30, and the mutual positions are determined so as to maintain a predetermined gap. The valve 32 does not apply any damping force.

A tapered inner surface 35 is formed on the inner periphery of the valve housing 20 near the outer periphery of the leaf valve body 30 so that as the leaf valve body 30 is pushed by the push rod 22, the gap between the leaf valve body 30 and the leaf valve body 30 decreases. This allows a variable front leakage passage 3
6 is configured to control the amount of pre-leakage when the relief valve 32 is activated, that is, to reduce the pre-leakage as the relief setting pressure increases, thereby preventing a delay in opening of the relief valve 32.

The present invention is constructed as described above, and its operation will be explained next.

During normal running, since no brake oil pressure is generated, the push rod 22 is pushed back by the return spring 26 and is in the state shown in FIG. 3.

In this state, the relief valve 32 is fully open, creating almost no resistance to the flow of hydraulic oil.

Next, during braking, the push rod 22 is pushed into close contact with the leaf valve body 30 by the brake oil pressure generated in response to the braking force.

As a result, when the front fork tries to sink due to braking, the flow of pressure side hydraulic oil is
As long as the set pressure of the relief valve 32 is not exceeded, the compression action is not performed and sinking during braking is prevented.

On the other hand, this relief setting pressure increases as the relief spring 31 of the leaf valve body 30 is compressed in proportion to the amount by which the push rod 22 is pushed. The initial opening degree (pre-leakage opening degree) of the relief valve 32, which is the gap between the inner circumference of the relief valve 32 and the inner circumference of the leaf valve 32, that is, the amount of pre-leakage, decreases as the leaf valve body 30 is pushed by the push rod 22 and moves.
As shown in the figure, the operating characteristics of the relief valve 32 are such that as the relief setting pressure increases, the amount of leakage decreases, and therefore the response becomes excellent.

When the leaf valve body 30 exceeds a predetermined relief setting pressure, it separates from the tapered surface 28 of the push rod 22 and begins to open, but before it opens, hydraulic oil flows out from the outer peripheral gap of the leaf valve body 30 as a pre-leak. The amount of front leakage decreases as the relief setting pressure (in other words, brake oil pressure) increases, so if an external force on the compression side acts on the front fork during braking, the relief setting pressure is immediately reached and the relief valve 32 is closed. Therefore, the relief valve 32 can be operated with good responsiveness. This makes it possible to flow hydraulic oil without delay in response even when the flow rate increases stepwise during braking, and also prevents the generation of surge pressure, which has been a problem in the past.

On the other hand, the push rod 22 receives hydraulic pressure in the return direction from the leaf valve body 30 in accordance with the pressure receiving area difference {π/4(A ² −A' ² )}, so the push rod 22 absorbs the pressure of the hydraulic oil. This prevents the leaf valve body 30 from moving to the right and pushing out the leaf valve body 30 to the right, so the relief set pressure automatically increases as hydraulic pressure is generated, or the damping during normal pressure side operation. Unnecessary increase in force can be prevented.

Next, FIG. 6 shows an embodiment in which a front leak passage 36 is formed between the push rod 22 and the leaf valve body 30. It is inserted into the hole 30A, and the gap between the two is made variable according to the amount of displacement of the push rod 22.

In this case as well, the amount of pre-leakage can be reduced in accordance with the increase in the relief setting pressure in the same manner as described above.

As described above, according to the present invention, it is possible to reduce the amount of front leakage in accordance with the increase in the relief setting pressure, and the weight is reduced by making the leaf valve body plate-shaped, so that the valve responsiveness is improved. This has the effect of preventing the generation of surge pressure.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the conventional device, Fig. 2 is its valve characteristic diagram, Fig. 3 is a sectional view of the first embodiment of the present invention, Fig. 4 is an enlarged sectional view of its main parts, and Fig. 5 is its valve characteristic diagram. The valve characteristic diagram and FIG. 6 are enlarged cross-sectional views of main parts of the second embodiment. 20...Valve housing, 21...Bearing part,
22...Push rod, 25...Piston, 2
6...Return spring, 28...Tapered surface,
30...leaf valve body, 31...relief spring, 32...relief valve, 35...tapered inner surface, 36...front leak passage.

Claims (1)

[Scope of Claims] 1. In an anti-nose dive mechanism for a front fork, in which a relief valve is interposed between ports through which hydraulic oil flows during pressure side operation, and the set pressure of the relief valve is increased in accordance with the brake operating force. , the relief valve is composed of a push rod that responds to the brake operating force, and a leaf valve body located at the tip of the push rod and biased by a relief spring, and on the inner or outer periphery of the leaf valve body, An anti-nose dive mechanism characterized in that a front leak passage is formed in which the gap between the push rod and the leaf valve element increases and decreases as the push rod moves in response to brake operating force. 2. The anti-nose dive mechanism according to claim 1, wherein the push rod has a bearing portion whose cross-sectional area is equal to or larger than the pressure-receiving area inside the contact portion with the leaf valve body.