JPH09242515A - Tappet structure - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To optimize the thickness of a flange portion and a ceramic chip, and to have a sufficient strength against an impact applied when a valve is opened. SOLUTION: A slider portion 22c to be fitted into a lower portion of a push rod 17 and a flange portion 22d provided at the lower portion of the slider portion 22c are formed so as to be widened toward the end, and a ceramic chip 23 in contact with a cam 16 of a camshaft 13 has a flange portion 22d. Is brazed to the bottom surface 22a so as to cover the bottom surface 22a. When the thickness of the ceramic chip 23 is T ₁ and the thickness of the peripheral edge of the flange portion 22d is T ₂ , 0.12
<T ₁ / T ₂ <0.40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tappet provided under a push rod. More specifically, the present invention relates to a structure of a tappet in which a ceramic tip contacting a cam of a camshaft is brazed so as to cover a bottom surface of a tappet body.

[0002]

2. Description of the Related Art A four-cycle engine is usually equipped with a valve system. The valve is generally shaped like a mushroom and is closed by the force of a coil spring. By opening this valve, it is possible to perform intake and exhaust in the operation process of 4 cycles,
Gas can be exchanged between the combustion chamber and the cylinder from the opened valve. The device that opens the valve by pressing it connects the rotation of the crankshaft to the camshaft with a timing belt, chain, or gear, and opens and closes the valve via a rocker arm by rotating the substantially oval cam provided on the camshaft with the shaft. Let The valve system can be classified according to the position where the camshaft is provided. The so-called overhead camshaft system and the overhead valve system (hereinafter referred to as OH
V).

As shown in FIG. 4, in the OHV, one end of a rocker arm 18 is pushed up through a pair of push rods 17 which are erected by the rotation of a cam shaft 12 positioned horizontally on the cylinder side, and the arm 18 is a seesaw type. The valve 19 is pushed down and opened.
The cam 1 of the camshaft 12 is located below the push rod 17.
A tappet 21 that abuts 6 is mounted, and the push rod 17 is configured to move up and down by rotation of the cam 16 via the tappet 21. According to this OHV, valve 1
Since 9 can be located above the head of the cylinder, the combustion chamber can be formed in a hemispherical shape or a wedge shape, so that the degree of freedom in design can be increased.

On the other hand, the tappet 21 provided at the lower portion of the push rod 17 has a slider portion which is fitted into the lower portion of the push rod 17 and a flange portion which is provided at the lower portion of the slider portion so as to spread toward the bottom. Wear resistance is required because they always contact and rub against the cam 16. Particularly in recent years, the tappet 21 is required to have very high wear resistance in order to cope with higher engine output and the like. In order to satisfy this requirement of wear resistance, a technique of brazing a ceramic chip so as to cover the bottom surface of the tappet body has been developed. The brazing of this ceramic tip is done by applying heat to the bottom of the tappet body by applying an appropriate load between the bottom and the ceramic tip according to the type of brazing material or the material of the ceramic tip or tappet body. Ceramic chips are brazed. By brazing the ceramic chip on the bottom surface of the tappet body in this manner, the durability of the tappet 21 that abuts on the cam 16 can be improved by utilizing the excellent wear resistance of the ceramic.

[0005]

However, when the ceramic chip is brazed to the bottom surface of the tappet body, a brazing material is interposed between them and the brazing is performed at a predetermined temperature. If not configured in an appropriate ratio, excessive internal stress may be accumulated in the ceramic chip during cooling after brazing due to the difference in thermal expansion coefficient. The accumulation of the internal stress causes a decrease in the bonding strength of the ceramic chip, which causes a problem that the strength of the tappet against external force is decreased. In particular, when the valve is opened, the tappet may be damaged during use because the external force is concentrated and applied to the vicinity of the peripheral edge of the ceramic tip with which the cam abuts. In order to solve this problem, it is conceivable to interpose a stress absorbing material between the ceramic chip and the bottom surface, but this results in an increase in the number of working steps and a complicated structure, which raises the unit price of the tappet.

It is an object of the present invention to provide a tappet structure having an adequate thickness for the flange portion and the ceramic chip and having sufficient strength against the impact applied when the valve is opened.

[0007]

The invention according to claim 1 is
As shown in FIGS. 1 and 4, there is a slider portion 22c that fits into the lower portion of the push rod 17 and a flange portion 22d that widens toward the bottom of the slider portion 22c, and is in contact with the cam 16 of the cam shaft 13. Chip 2
Bottom surface 2 so that 3 covers the bottom surface 22a of the flange portion 22d.
It is an improvement of the tappet brazed to 2a. The characteristic configuration is that the thickness of the ceramic chip 23 is T ₁ ,
When the thickness of the peripheral edge of the flange portion 22d is T ₂ , it is 0.
12 <T ₁ / T ₂ <0.40. T ₁ /
If T ₂ is less than 0.12, the stress absorbed by the ceramic chip 23 at the time of brazing will be larger than the stress absorbed by the flange portion 22d, and the internal stress of the ceramic chip 23 will be excessive. Further, when T ₁ / T ₂ exceeds 0.40, the ceramic chip 23 does not absorb the stress at the time of brazing and the bonding strength of the ceramic chip 23 decreases.

Examples of the material of the tappet body 21a include structural carbon steel and structural alloy steel.
M630, SNCM616, and S48C are illustrated. The tappet body 21a is manufactured by forging or cutting such a steel material, and the bottom surface 22a is ground or polished in a post process. The ceramic chip 23 includes Si ₃ N ₄ , SiC,
Examples include Al ₂ O ₃ and zirconia. The plate thickness is set so that at least strength that can withstand the impact received from the cam can be secured, and 1.0 mm to 2.0 mm is preferable,
1.2 mm to 1.8 mm is more preferable. It is preferable that the brazing means is heat-bonded by a silver braze containing Ti. Ag-Cu-Ti system, Ag-T system for brazing material
Examples include i-based, Cu-Ti-based, and Ag-Cu-Ni-Ti-based. Further, the brazing surface of the ceramic chip 23 may be previously metallized by a vapor deposition method or the like. In that case, Ag—Cu based and Ag—Cu—In based brazing materials are preferable. The atmosphere when brazing is vacuum, argon gas,
Non-oxidizing atmosphere such as hydrogen gas or nitrogen gas is preferable, and Ti
In the case of the contained brazing material, brazing is particularly preferable in a vacuum or an atmosphere of argon gas.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIG. 4, in the OHV of this embodiment, the cam shaft 12 is horizontally arranged on the cylinder side where the piston moves up and down. The camshaft 12 and the crankshaft 13 are connected by a gear 14, and when the crankshaft 13 rotates, the camshaft 12 rotates and a pair of substantially oval cams 16 provided on the camshaft 12 stand upright. It is configured to move the push rod 17 up and down. When the pair of push rods 17 move upward, one end of the rocker arm 18 is pushed up, the arm 18 rotates in a seesaw manner, and the other end pushes down the valve 19 to open it, and by pushing it down, the valve 19 is closed by the force of the coil spring 20. It has become. The camshaft 1 is located below the push rod 17.
A tappet 21 that comes into contact with the second cam 16 is mounted, and the push rod 17 is configured to move up and down by rotation of the cam 16 via the tappet 21. A pair of tappets 2
Since 1 has the same structure, one tappet 21 will be described below.

As shown in FIGS. 1 and 2, the tappet 21
The ceramic chip 23 is the bottom surface 22 of the tappet body 22.
It is brazed to cover a. The tappet body 22 is
The slider 22c has a hole 22b into which the lower end of the push rod 17 is inserted. A recess 22e with which the lower portion of the push rod 17 is engaged is formed in the lower portion of the hole 22b. The tappet body 22 is made by cutting a metal member of S48C, and the slider portion 22c has a 22.5 mm flange portion 22d having an outer diameter of 38.5 mm. The lower surface of the flange portion 22d, that is, the bottom surface 22a, is polished to have a surface roughness Ra of 0.2 to 0.3 μm. Ceramic chip 2
3 is Si ₃ N ₄ . The ceramic chip 23 is a silicon nitride sintered body and has a diameter of 38 mm with both surfaces polished and finished.
The surface roughness Ra of the joint surface is 0.2 to 0.3 μ
It is polished so that it becomes m.

A characteristic feature of the present invention is that 0.12 <T ₁ / T ₂ <0.40, where T ₁ is the thickness of the ceramic chip 23 and T ₂ is the thickness of the peripheral edge of the flange portion 22 d. It has been configured to be. The ceramic chip 23 is brazed to the bottom surface 22a by arranging the ceramic chip 23 on a base plate that is peelable from the brazing material 24,
The tappet body 22 is formed so that the bottom surface 22a of the tappet body 22 is superposed on the ceramic chip 23 via the brazing material 24.
And put it on. A load is applied to the upper portion of the tappet body 22, and the ceramic chip 23 is brazed to the bottom surface 22a of the tappet body 22 by heat treatment in this state.

[0012]

Next, examples of the present invention will be described together with comparative examples. <Examples 1 to 3> Three tappets 21 shown in FIGS.
Type manufactured. These tappets 21 have the thickness T1 of the ceramic chip 23 and the flange portion 2 as shown in Table 1.
The thickness T2 of the peripheral edge of 2d is 0.12 <T ₁ / T ₂ <0.40.
Were set to satisfy the above conditions. All of these tappets 21 have a tappet body 22 made of S48C and a bottom surface diameter of 38.5 mm, while the ceramic tip 23 has three types of ceramic chips 23 made of Si ₃ N ₄ having a diameter of 38 mm. 22
Brazing was carried out on a with a brazing material 24 of Ag-Cu-Ti system. The brazing is Ag with the same diameter as the ceramic chip 23.
-A foil of the Cu-Ti brazing material 24 is laid on the ceramic chip 23, the tappet body 22 is further placed on this, and a load of 20 kgf / cm ² is applied to these in this state, and heated to 850 ° C in a vacuum. Then, three types (Example 1, Example 2 and Example 3) of tappets were manufactured by laminating and adhering.

<Comparative Examples 1 to 4> As shown in Table 1, the thickness T1 of the ceramic chip and the thickness T2 of the peripheral edge of the flange portion are set.
Were set so as not to satisfy 0.12 <T ₁ / T ₂ <0.40, and four types of tappets (Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4) were manufactured. Other than the above, the shape, size and material of the tappet body and the ceramic chip were the same as those in Examples 1 to 3 above.

<Comparative Test and Evaluation> The tappets of Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to a comparative test on the impact strength of each ceramic chip by means of a device 31 shown in FIG. Table 1 shows the results. Device 3 shown in FIG.
1 is a slider part 2 which allows a tappet 21 to move vertically.
A support member 31a for holding 2c, a pressurizing member 31b provided above the tappet 21 and indirectly applying a load P,
It is composed of a hemispherical receiving member 31c that is in contact with the periphery of the ceramic chip 23. The receiving member 31c was positioned 3 mm inside from the peripheral edge of the ceramic chip 23, and an impact load was applied to the tappet 21 from above via the pressing member 31b, and the load P when the ceramic chip 23 was damaged was measured as the impact strength.

[0015]

[Table 1]

As is clear from Table 1, the tappets of Examples 1 to 3 exhibited a value of 3.4 tons or more, which is generally said to have sufficient strength against impact. On the other hand, the tappets of Comparative Examples 1 to 4 were below this value. This is considered to be due to excessive stress absorption of the ceramic chip due to the fact that the thickness of the flange portion and the thickness of the ceramic chip are not configured in an appropriate ratio.

[0017]

As described above, according to the present invention, when the thickness of the ceramic chip is T ₁ and the thickness of the peripheral edge of the flange portion is T ₂ , 0.12 <T ₁ / T ₂ <0.40
Since it is configured as described above, the stress due to the difference in the thermal expansion coefficient at the time of brazing can be evenly distributed to optimize the thickness of the flange portion and the ceramic chip. As a result, it is possible to obtain sufficient strength against the impact applied when the valve is opened, without lowering the bonding strength to the bottom surface of the ceramic chip.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of a tappet of the present invention.

FIG. 2 is an exploded perspective view of the tappet.

FIG. 3 is a block diagram of an impact test of the tappet.

FIG. 4 is a structural diagram showing an OHV using the tappet of the present invention.

[Explanation of symbols]

 13 cam shaft 16 cam 17 push rod 21 tappet 22 tappet body 22a bottom surface 22c slider portion 22d flange portion 23 ceramic chip

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayoshi Ohno, Mayor of Sodegaura, Chiba Prefecture, No. 2 580-99, Kasaya Seiko Co., Ltd. Within Automotive Industry Co., Ltd.

Claims (1)

[Claims] 1. A camshaft (1) having a slider portion (22c) fitted into the lower portion of a push rod (17) and a flange portion (22d) provided at the lower portion of the slider portion (22c) so as to widen toward the end.
The bottom surface (22a) so that the ceramic chip (23) contacting the cam (16) of 3) covers the bottom surface (22a) of the flange portion (22d).
When the thickness of the ceramic chip (23) is T ₁ and the thickness of the peripheral edge of the flange portion (22d) is T ₂ , in the tappet adhered to
Structure of tappet, characterized in that T ₁ / T ₂ <0.40.