JPH09242513A - Tappet - Google Patents

Abstract

(57) An object of the present invention is to have an appropriate amount of crowning, improve the bonding strength of a ceramic chip, and have sufficient strength against external force. SOLUTION: A tappet 21 is provided below a push rod 17.
The tappet 21 is brazed to the bottom surface 21b so that the ceramic tip 22 contacting the cam of the camshaft covers the bottom surface of the tappet body 21a. The ceramic chip 22 is brazed to the bottom surface 21b via a copper plate 23 having a thickness of 0.1 mm or more and 0.2 mm or less.

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 tappet in which a ceramic tip contacting the cam of a camshaft is brazed so as to cover the bottom surface of the 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. 3, in the OHV, one end of a rocker arm 18 is pushed up through a pair of push rods 17 standing upright by 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, since the tappet 21 provided under the push rod 17 is always in contact with the cam 16 and the cam 16 rotates, the tappet 21 always rubs against the cam 16, so that wear resistance is required. 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. Thus, the excellent wear resistance of ceramics can be used to improve the durability of the tappet 21 that abuts on the cam 16, and as a result, the reliability of the engine can be improved.

[0005]

However, since the brazing material is interposed between the ceramic chips and the brazing at a predetermined temperature, the ceramic chips and the tappet main body are brazed by the difference in the coefficient of thermal expansion between the ceramic chips and the tappet body. There is a problem that internal stress is accumulated in the ceramic chip during cooling after brazing, resulting in damage to the ceramic chip or reduction in bonding strength of the ceramic chip. In order to eliminate this problem,
It is possible to interpose a stress absorbing material between the ceramic chip and the bottom surface, but depending on the amount of stress absorption, external force is locally applied to the ceramic chip and the strength of the tappet against external force is reduced, causing damage to the tappet during use. It may occur. On the other hand, it is necessary to provide a so-called crowning shape having a bulge in the central portion called a crowning amount for preventing uneven contact with the cam on the sliding surface of the tappet with the cam. It is also possible to form by utilizing. An object of the present invention is to provide a tappet having an appropriate amount of crowning, improving the bonding strength of a ceramic chip, and having sufficient strength against external force.

[0006]

The invention according to claim 1 is
As shown in FIGS. 1 and 3, improvement of the tappet in which a ceramic chip 22 provided on the lower portion of the push rod 17 and contacting the cam of the camshaft 13 is brazed to the bottom surface 21b so as to cover the bottom surface of the tappet body 21a. Is.
The characteristic structure is that the ceramic chip 22 is 0.1 m long.
It is where it is brazed to the bottom surface 21b through a copper plate 23 having a thickness of not less than m and not more than 0.2 mm. The copper plate 23 absorbs stress due to the difference in thermal expansion coefficient during brazing, and prevents concentration of external force applied to the ceramic chip 22 during use.

Examples of the material of the tappet body 21a include structural carbon steel and structural alloy steel.
M630 and SNCM616 are illustrated. The tappet body 21a is manufactured by forging or cutting such a steel material, and the bottom surface 21b is ground or polished. Examples of the ceramic chip 22 include Si ₃ N ₄ , SiC, Al ₂ O ₃ , and zirconia. The plate thickness is set so that at least the strength to withstand the impact received from the cam can be secured,
1.0 mm to 2.0 mm is preferable, and 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. As the brazing material system, Ag-Cu-Ti system, Ag-Cu-Ti-Zn system,
Ag-Ti system, Cu-Ti system, or Ag-Cu-Ni-
Ti-based materials can be used. Further, the brazing surface of the ceramic chip 22 may be preliminarily subjected to a metallizing process 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 of the brazing material is preferably non-oxidizing atmosphere such as vacuum, argon gas, hydrogen gas, nitrogen gas,
In the case of a brazing material containing Ti, brazing is particularly preferable in a vacuum or an atmosphere of argon gas. The copper plate 23 has a thickness of 0.1 mm or more and 0.2 mm or less, and the diameter thereof is the same as the ceramic chip 22 or the ceramic chip 22.
It is preferable that the diameter is slightly smaller. Copper plate 23
If the thickness is 0.1 mm or less, the stress due to the difference in thermal expansion coefficient during brazing cannot be sufficiently absorbed,
If it is 0.2 mm or more, the strength against external force during use may be reduced.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIG. 3, in the OHV of this embodiment, the cam shaft 12 is horizontally arranged on the cylinder side where the piston 11 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 moves 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 moving it downward, the valve 19 moves the coil spring 20. It is designed to close by force. A tappet 21 that comes into contact with the cam 16 of the camshaft 12 is attached to the lower portion of the push rod 17, and the push rod 17 is configured to move up and down by rotation of the cam 16 via the tappet 21. Since the pair of tappets 21 have the same structure, one tappet 21 will be described below.

As shown in FIGS. 1 and 2, the tappet 21
The ceramic chip 22 is the bottom surface 2 of the tappet body 21a.
It is brazed to cover 1b. Tappet body 21a
Is manufactured by cutting a metal member of JIS; SNCM630, and the ceramic chip 22 is Si ₃ N ₄ . The ceramic chip 22 is a silicon nitride sintered body,
A disk having a diameter of 38 mm and a thickness of 1.5 mm, both surfaces of which are polished, and the surface roughness Ra of the joint surface is 0.2 to 0.3 μm.
To be polished. The tappet body 21a has a large diameter portion of 38.5 mm, a small diameter portion of 22.8 mm, and a height of 5.5.
The bottom surface of the large diameter part, that is, the bottom surface 2
1b is ground to have a surface roughness Ra of 0.2 to 0.3 μm. The small diameter portion has a hole 21c into which the lower end of the push rod 17 is inserted, and the push rod 1 is provided below the hole 21c.
A recess 21d with which the lower part of 7 is engaged is formed.

A characteristic structure of the present invention is that the ceramic chip 22 is brazed to the bottom surface 21b through a copper plate 23 having a thickness of 0.1 mm or more and 0.2 mm or less. The copper plate 23 is formed in a disk shape having the same diameter as the ceramic chip 22. The brazing of the ceramic chip 22 and the copper plate 23 is performed through a Ti-Cu-Ag-based active brazing material (foil) 25 having a diameter of 38 mm and a thickness of 50 μm, and the bottom surface 21 b of the tappet body and the copper plate 23 are bonded together. The brazing is made of Ag-C with a diameter of 38 mm and a thickness of 50 μm.
It is performed through a u-based brazing material (foil) 24. When brazing, the ceramic chip 22, the copper plate 23 and the respective brazing materials (foil) 24, 25 are concentrically overlapped with each other, the ceramic chip 22 is placed on the bottom surface 21b so as to sandwich the copper plate 23, and the bonding surfaces are mutually predetermined. It is brazed by holding it in a vacuum at 850 ° C. for 15 minutes while applying a pressure of, and cooling with N ₂ gas displacement.

[0011]

Next, embodiments of the present invention will be described. Example 1 The tappet 21 shown in FIGS. 1 and 2 was manufactured by the following method. First, the tappet body 21a having a bottom surface diameter of 38.5 mm, the thickness of 1.5 mm, and the diameter of 38 m
m ceramic chips 22 were prepared. The bottom surface 21b of the ceramic chip 22 has a thickness of 0.1 mm and a diameter of 3 mm.
Brazing was performed through the copper plate 23 formed to 8 mm. For brazing, Ag-Cu with the same diameter as the ceramic chip 22
A foil of a Ti-based brazing material 25 and a Ag-Cu-based brazing material 24 was used. That is, the ceramic chip 22 is placed on the bottom surface 2 via the copper plate 23 on which the brazing materials 25 and 24 are superposed on both sides.
1b, and load 20gf / cm ² on them in this state.
Was added, and the tappet laminated and adhered by heating to 850 ° C. in a vacuum was used as Example 1.

<Comparative Examples 1 and 2> Although not shown, in Comparative Examples 1 and 2, the thickness of the copper plate was 0.3 mm and 0.5 mm, respectively, and the ceramic chip was placed on the bottom surface of the tappet body through these copper plates. The configuration is the same as that of the first embodiment except that brazing is performed. <Comparative Example 3> A tappet obtained by brazing the tappet body of Example 1 and a ceramic chip without a copper plate was used as Comparative Example 3. <Comparative Test and Evaluation> For the tappets of Example 1 and Comparative Examples 1 to 3, the crowning amount and the strength of the ceramic chips against impact were compared and tested. Table 1 shows the results. The amount of crowning is measured with a shape measuring instrument,
The impact strength was measured by visually observing the presence or absence of a change in appearance after impacting the ceramic chip with a drop impact tester and measuring the load at which the appearance change occurred.

[0013]

[Table 1]

As is clear from Table 1, it has been found that the impact strength varies depending on the thickness of the copper plate. Generally, the thickness of the copper plate is required to be 0.2 mm or less in order to obtain the optimum impact strength of 3 tons or more. When the thickness of the copper plate is 0.1 mm, the impact strength is higher than that in the case of Comparative Example 3 in which the copper plate is not present. It is considered that the copper plate has improved impact resistance. Optimal crowning amount 20μm-30μm
In order to obtain the above, the thickness of the copper plate needs to be in the range of 0.1 to 0.2 mm.

[0015]

As described above, according to the present invention, the ceramic chip is brazed to the bottom surface through the copper plate having the thickness of 0.1 mm or more and 0.2 mm or less,
The copper plate absorbs the stress caused by the difference in the thermal expansion coefficient during brazing, and prevents the concentration of external force applied to the ceramic chip during use. As a result, the bonding strength to the bottom surface of the ceramic chip can be improved and sufficient strength against external force can be obtained. In addition, the thickness of the copper plate is 0.1 mm or more and 0.2 m
By setting m or less, an appropriate amount of crowning can be obtained at the time of brazing, the reliability of the tappet can be further enhanced, and the reliability of the engine can be improved.

[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 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 21a tappet body 21b bottom surface 22 ceramic tip 23 copper plate

 ─────────────────────────────────────────────────── ─── 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 push rod (17) is provided below the
In the tappet (21) adhered to the bottom surface (21b) so that the ceramic tip (22) contacting the cam (16) of the camshaft (13) covers the bottom surface (21b) of the tappet body (21a), the ceramic Tip (22) is 0.1 mm or more and 0.2 mm
A tappet characterized by being brazed to the bottom surface (21b) through a copper plate (23) having the following thickness.