JPH0614002Y2 - Seal for valve stem - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a seal attached to a valve guide portion of an intake / exhaust valve of a four-cycle engine, and more particularly to a structure of a lip portion thereof.

<Prior Art> It is necessary to constantly supply a certain amount of lubricating oil to a valve guide portion of an intake / exhaust valve of an engine in order to smoothly slide the stem. Now, if the supply of this lubricating oil is cut off, seizure will occur in the valve guide portion. Conversely, if the amount of lubricating oil supplied is too large, not only will the oil consumption increase, but carbon will adhere to the stem, etc., It interferes with intake and exhaust operation.

Therefore, in general, a seal is attached to the valve guide part of the intake / exhaust valve, and this seal causes a small amount of oil leakage (oil leakage) from the outside of the valve to the valve guide part to lubricate the valve guide part. I try to supply oil.

FIG. 3 is a sectional view of a valve guide portion provided with a seal. In the figure, reference numeral 1 is a valve body, 2 is a spring, 3
Is a spring retainer, and 4 is a stem. The stem 4 is made up of a cylindrical valve guide 5 and a cylinder housing 6
The valve guide 5 has a seal 7 attached thereto.

The seal 7 includes a cored bar 8, a tightening ring 9 composed of a coil spring, and a seal body 10 made of an elastic material.
As shown in FIG. 4 (A) or (B) in an enlarged manner, the seal body 10 includes a fitting portion 10a fitted to the outer periphery of the stem guide 5 by a core metal 8 and an axial direction of the core metal 8. Lip that makes elastic contact with stem 4 by tightening tightening ring 9 on the outside
It consists of 10b.

<Problems to be solved by the invention> By the way, in the conventional seal of this type, as shown in FIG.
The tip 10c of the lip 10b is rounded so that the inner contact angle α is set larger than the outer contact angle β.

According to the fluid lubrication inverse theory, the oil leak amount Q per unit time with respect to the uniform velocity v is expressed by the following equation (1).

Q = πDHa ・ v / 2-πDHb ・ v / 2 (1) where D is the outer diameter of the stem, v is the stem speed, and Ha is the oil film thickness when the stem moves from the oil side to the stem guide side. , Hb is the oil film thickness when the stem moves from the stem guide side to the oil side, and each oil film thickness Ha, Hb is expressed by the following equations (2), (3).

In equations (2) and (3), μ is the viscosity coefficient of oil, p is the contact pressure of the lip, | dp / dx | maxA is the maximum contact pressure gradient on the oil side, and |
dp / dx | maxB is the maximum contact pressure gradient on the stem guide side.

From the above equations, if the lip shape is designed so that | dp / dx | maxA <| dp / dx | maxB, the oil leak amount Q becomes Q> 0.
It can be seen that an oil leak occurs. In the conventional seal, as mentioned above, by rounding the tip of the lip and making the inner contact angle α larger than the outer contact angle β, the contact pressure that gives | dp / dx | maxA <| dp / dx | maxB. The distribution is realized.

However, the speed characteristic of the oil leak amount Q in this case is The oil leak amount Q increases exponentially as the stem speed v increases, and has a drawback that it becomes excessive in the high speed range.

In this way, with the conventional seal that controls the oil leak amount by the oil film thickness that depends on the speed, a required amount of oil leak occurs when the engine rotates at a low speed, but at the time when the engine rotates at a high speed, the number of times the valve is opened and closed increases. As a result, the amount of oil leak increases more than necessary, which causes inconvenience that carbon adheres to the stem 4 and the like.

For such an increase in oil leak, see Fig. 4 (B).
This can be dealt with by sharply forming the tip of the lip 10b and setting the outer contact angle β thereof to be larger than the inner contact angle α as shown in FIG. According to this configuration, in the above-mentioned lubrication theory, | dp / dx | maxA> | dp / d
Since x | maxB, that is, Q ≦ 0 is likely to occur and the oil may be completely sealed, it is not suitable for use as a seal for a valve stem.

The present invention has been made in view of the above problems, and provides a seal that can always supply a constant amount of lubricating oil to a valve guide portion in one reciprocation regardless of the slow speed of the engine. With the goal.

<Means for Solving the Problems> In order to achieve the above object, the present invention has a fitting portion fitted to a stem guide by a core metal and a lip elastically contacting the stem by tightening a tightening ring. In the valve stem seal, the lip has a shape in which the outer contact angle is larger than the inner contact angle, and a large number of hard particles are embedded in at least the tip portion of the lip.

<Operation> According to the above configuration, the initial wear of the lip causes the hard particles embedded in the tip of the lip to appear on the surface. The hard granules prevent wear of the lip and keep the contact width of the tip of the lip almost constant even when the engine rotates at high speed.
The contact portion at the tip of the lip becomes a discontinuous contact due to the presence of the hard particles, and a physical minute passage is formed in the contact portion. Since the lip shape is a sealed type, the oil leak amount is given not by the hydrodynamic oil film thickness, but by the flow rate passing through the minute passage.

In this case, the oil leak amount Q is expressed by the following equation, where A is the cross-sectional area of the oil passage and v is the stem speed.

Q = Av (5) By the way, the cross-sectional area A of the oil passage has a characteristic of decreasing as the stem speed v increases. That is, the sliding frictional heat per unit time increases as the stem speed v increases, and as a result, the temperature of the sliding portion rises. Due to the temperature rise of the sliding portion, the elastic material (rubber) of the contact portion is easily deformed, the balance between the coil spring forming the tightening ring, the rubber and the minute passage is lost, and the cross-sectional area of the oil passage is reduced. Therefore, the cross-sectional area of the oil passage is a decreasing function of the stem speed.

Therefore, the rate characteristics of the oil leakage amount of the present invention seals, Qarufav ^alpha (However, 0 <alpha <1) is represented by ... (6). The speed characteristic is shown in the characteristic diagram of FIG. 5 together with the speed characteristic of the oil leak amount of the conventional seal.

As is clear from the above characteristic diagram, the seal of the present invention does not increase the oil leak amount even when the engine rotates at high speed, and suppresses the oil leak amount as small as when rotating at low speed.

<Embodiment> Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a sectional view of a valve stem seal according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part thereof.

The seal of this embodiment has the same basic structure as a conventional seal of this kind, and includes a core metal 11, a tightening ring 12 formed of a coil spring, and a seal body 13 made of an elastic material. The seal body 13 includes a fitting portion 13a fitted to the outer periphery of the stem guide by the core metal 11, and the core metal 1.
1 outwardly in the axial direction, and a lip 13b elastically contacting the stem by tightening the tightening ring 12.

The seal of this embodiment is different from the conventional example in that the lip 13
It is in the constituent material. That is, the lip 13 is made of a heat resistant rubber such as fluororubber, and in the composition thereof,
Hard granules 1 made of glass or other inorganic materials
Many are mixed. When the granules 14 are glass spheres, the diameter is 1 to 200 μm, and the compounding amount is 3 to 3
It is suitable to be 0% by weight.

Although the tip of the lip 13b is formed to be sharp, when the stem is inserted, the sharp tip of the lip is elastically deformed and comes into contact with the peripheral surface of the stem so as to have a required contact width W, and in the width direction thereof. The outer contact angle β is set to be larger than the inner contact angle α (β> α).

The lip 15 having the above structure is attached to the valve guide portion. The mounting state is the same as in the case of the conventional example shown in FIG.

Now, when the valve stem begins to open and close, the lip
Due to the initial wear of the tip portion of 13b, the hard granules 14, ... Inside the lip 13b appear on the surface.
Since these granules 14 ... come into sliding contact with the stem,
A passage with a minute interval is formed between the stem surface and a small amount of oil leak. Further, since the granules 14 have the effect of preventing wear, the contact width W of the tip portion of the lip 13b is kept substantially constant even when the engine is rotating at high speed, so that the amount of oil leak does not increase.

On the other hand, since the outer contact angle β of the tip of the lip 13b is larger than the inner contact angle α, the oil movement has a directional property, and the sealing effect accompanying the directional property of the oil causes an oil leak. An excessive amount is suppressed.

It should be noted that the hard particles 14 need only be embedded in at least the tip of the lip 13b.

<Effect of the Invention> As described above, according to the present invention, the hard particles embedded in the tip of the lip appear on the lip surface and come into sliding contact with the stem. The passage of minute intervals is secured, and as a result, a small amount of oil leak occurs.

In the case of the present invention, the amount of oil leakage does not depend on the hydrodynamic oil film thickness that increases with the speed of the stem, but conversely is determined by the cross-sectional area of the minute passage of hard particles that decreases with the speed. Even in the high-speed rotation range,
The amount of oil leak does not increase, and the amount of oil leak is kept substantially constant regardless of the slow speed of engine rotation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a valve stem seal according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of an essential part thereof, FIG. 3 is a cross-sectional view of a valve stem having a seal, and FIG. 3A and 3B are enlarged cross-sectional views of the main part of the conventional seal, and FIG. 5 is a characteristic diagram showing the speed characteristics of the oil leak amount of the seal of the present invention and the conventional example, respectively. 11 ... core metal, 12 ... tightening ring, 13 ... seal body, 13a ... fitting part, 13b ... lip, 14 ... hard particles.

Claims (1)

[Scope of utility model registration request] 1. A valve stem seal having a fitting portion fitted to a stem guide by a core metal and a lip elastically contacting the stem by tightening a tightening ring, wherein the outer contact angle is the inner contact of the lip shape. A seal for a valve stem, characterized in that it is a sealed type larger than a corner, and a large number of hard particles are embedded in at least the tip of this lip.