JPH0124677B2 - - 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 driving a two-wheeled vehicle, 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.

Specifically, a push rod 5 is supported by a bearing 6 so as to be freely slidable relative to the valve housing 4.

A piston 8 housed in a cylinder chamber 7 to which brake oil pressure is introduced is brought into contact with the end face of the push rod 5.

Therefore, the push rod 5 is pressed by the piston 8 and moves downward in the figure, but a return spring 9 is interposed to oppose this movement of the push rod 5.

The push rod 5 has a head 10 with an enlarged diameter formed at its tip, and the head 10 has a tapered surface 11 on its end surface.

On the other hand, a hollow disk-shaped leaf valve body 13 is secured to the inner surface of the housing 4 by a snap spring 12 .
A relief spring 14 is interposed so as to be in pressure contact with 2. The head 10 of the push rod 5 is inserted into the central hole of the leaf valve body 13, and the relief valve 3 is constituted by the head 10 of the push rod 5.

This relief valve 3 has a contact diameter with respect to the leaf valve body 13, that is, a valve seat diameter D, larger than the bearing diameter d of the sliding portion of the push rod 5 with respect to the bearing part 6, and when not braking, this pressure receiving area difference is The push rod 5 is moved by the resultant force of the corresponding thrust and the tension of the return spring 9.
is biased in the return direction.

Therefore, since no brake oil pressure is generated during normal driving, the push rod 5 is pushed back by the thrust in the return direction and the biasing force of the return spring 9, and the relief valve 3 is fully open, causing the hydraulic oil to flow out. Creates almost no resistance to flow.

Next, during braking, the push rod 5 is pushed into close contact with the leaf valve body 13 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 pressure does not exceed the set pressure of the relief valve 3, the compression action is not performed and sinking during braking is prevented.

This relief setting pressure is increased by compressing the relief spring 14 of the leaf valve body 13 in proportion to the amount by which the push rod 5 is pushed.

By the way, even if the relief valve 3 is closed during braking, if the braking operation continues for a long time or if the brake is pushed up from the road surface while braking,
Hydraulic oil leaks and escapes to the oil sump chamber, causing the front fork to gradually contract. As a result, the load shared by the front fork's suspension spring increases, making it relatively stiff, but even with this increase in spring load, the set pressure of the relief valve 3 tends to increase, so when it contracts like this, it becomes even more stiff. There was a problem that the absorbency was poor when a shock was applied.

In other words, if the front fork gradually sinks while the anti-nose dive mechanism is operating, the pressure in the high-pressure side oil chamber will increase due to the difference between the push rod bearing diameter d and the valve seat diameter D of the leaf valve body 13. Push rod 5 is determined by the pressure receiving area difference based on
A force in the direction of pressing the leaf valve body 13 acts,
The acting force at this time reduces the acting force that pushes the push rod 5 in the return direction in response to the pressure on the oil reservoir side that increases as the front fork sinks, so the setting force of the relief valve 3 is reduced. It becomes impossible to effectively reduce the amount depending on the amount of sinking of the front fork. As a result, even if the vehicle is pushed up from the road surface, the impact cannot be easily absorbed, resulting in a decrease in steering stability.

If the setting is opposite to the above, that is, if the valve seat diameter D is smaller than the bearing diameter d, then an acting force will be generated that pushes the push rod 5 in the return direction by the pressure receiving area difference, and this will push the push rod 5 in the return direction. pressure of
Since this is added to the force exerted by P _L in the push rod return direction, the setting force of the relief valve 3 decreases too much, making it impossible to obtain appropriate shock absorption characteristics.

The present invention is aimed at solving these problems, and provides an anti-nose shock absorber for two-wheeled vehicles that corrects the set value of the relief valve according to the internal pressure of the front fork to improve shock absorption during braking. Provides a dive mechanism.

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

In the present invention, as shown in FIG. 2, the bearing diameter d of the push rod 5 driven by brake pressure and the contact diameter of the leaf valve body 13 that contacts the tapered surface 11 of the head 10, that is, the valve seat diameter. D are set approximately equal.

When the bearing diameter d of the push rod and the valve seat diameter D are made approximately equal in this way, the pressure P _H in the pressure side oil chamber of the front fork does not produce a thrust force on the push rod 5 in any axial direction.

On the other hand, when the push rod 5 is pressed during braking to exert the anti-nose dive function, the setting force of the relief valve 3 is determined by the stroke of the push rod 5, and as mentioned above, the pressure side oil Since the pressure P _H in the chamber is not involved in the movement of the push rod 5, the brake pressure P _B acting on the cylinder chamber 7, the spring force of the return spring 9 opposing this, and the front fork force acting on the shaft end of the push rod 5 are It changes depending on the balance with the pressure P _L in the oil reservoir chamber.

Here, the pressure P _L in the front fork oil sump chamber is
Since it increases in proportion to the amount of contraction of the front fork, the setting force of the relief valve 3 is eventually suppressed (weakened) as the front fork sinks.

Therefore, when braking is performed continuously for a long time, when hydraulic oil leaks from the relief valve 3 and the front fork gradually sinks (contracts), the internal pressure (pressure P _L ) increases accordingly. As a result, the acting force that presses the push rod 5 in the return direction increases.

Therefore, the setting force of the relief valve 3 is reduced according to the amount of depression of the front fork, and when the vehicle is pushed up from the road surface in this condition, the relief valve 3 opens relatively easily and absorbs the impact. This is possible.

In the above description, the same reference numerals are used for the same parts as in the conventional art.

As explained above, the present invention makes the bearing diameter of the push rod and the valve seat diameter almost equal,
Since the relief valve setting is determined by the differential pressure between the brake pressure and the front fork oil reservoir chamber pressure without being affected by the pressure side hydraulic oil pressure, the front fork When the vehicle sinks, the setting force of the relief valve can be weakened depending on the amount of sinking, effectively absorbing the impact and improving maneuverability.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional device, and FIG. 2 is a sectional view of the present invention. 1, 2...Port, 3...Relief valve, 5
... Push rod, 6 ... Bearing section, 7 ... Cylinder chamber, 9 ... Return spring, 10 ... Head, 13 ... Leaf valve body, 14 ... Relief spring.

Claims (1)

[Claims] 1. In a front fork anti-nose dive mechanism in which a relief valve is interposed in a passage through which hydraulic oil discharged during pressure side operation flows, and the setting force of this relief valve is increased in accordance with brake operation, the relief valve is Consisting of a push rod that responds to brake oil pressure and a leaf valve element located at the tip of the push rod and biased by a relief spring, the bearing diameter of the push rod and the valve seat diameter of the leaf valve element in contact with the push rod are An anti-nose dive mechanism characterized by being set so that the and are almost equal.