JPH04350308A - Valve lifter for engine - Google Patents

Abstract

PURPOSE:To relieve stresses during casting to prevent the generation of cracks and obtain a high joining strength by insert-casting a ceramic top board integral ly with light-alloy skirt parts. CONSTITUTION:A connecting groove 15 is formed in the necked part of a ceramic top board 11 in the circumferential direction. The groove 15 is cut apart at plural places, and recessed parts 16 formed in the diametrical direction are provided. The groove 15 and the recessed parts 16 are filled with light alloy by casting to form skirt parts 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine valve lifter formed of a ceramic top plate and a light alloy skirt.

0002

[Prior Art] Conventionally, a valve lifter, which is interposed between a cam of a camshaft and a valve stem in an engine's valve operating mechanism, is supported so that it can slide freely by forming the top plate that the cam contacts with ceramic. A technique is known in which the skirt portion is made of a light alloy such as an aluminum alloy to reduce the weight, as can be seen, for example, in Japanese Utility Model Application Publication No. 16703/1983.

[0003] The weight reduction of the valve lifter described above reduces the inertial mass of the valve train system and reduces mechanical resistance loss, resulting in fuel efficiency and high output of the engine. The end parts of the cam and valve stem need wear resistance, and ceramic is a suitable material because it has high hardness, but it is difficult to make the entire valve lifter from ceramic. However, from these points, a combination of a ceramic top plate and a light alloy skirt has been proposed.

0004

[Problem to be Solved by the Invention] However, when constructing a valve lifter with a ceramic top plate and a light alloy skirt as described above, it is difficult to ensure high bonding strength between the two, and improvement is required. As a joining method, it is possible to combine the top plate and the skirt part, which are formed separately, by a plastic bond such as caulking, but this plastic bond lacks the bonding strength and the top plate and the skirt part There is a risk of separation and there is a problem of low productivity.

[0005] Regarding the above point, it is promising in terms of productivity to cast a ceramic top plate and join and integrate the two parts when casting the skirt part with a light alloy. Generally speaking, both have poor wettability and poor adhesion, and if the flowability of the joint is low, the joint strength will be low, and the difference in thermal expansion will cause insufficient adhesion, causing the top plate and skirt to become relative to each other. In addition, there is a risk that cracks may occur in the joints during use due to residual shrinkage stress after casting, so it is necessary to improve mechanical reliability.

Specifically, in a valve lifter in which the top plate is made of ceramic and the skirt part is made of a light alloy, an annular groove is formed on the outer periphery of the back of the top plate and molten light alloy is poured into the valve lifter to increase the mechanical joint strength. With a structure in which only an annular groove is formed, after the light alloy is subjected to heat treatment such as T6 treatment to increase its mechanical properties such as strength and hardness after casting, the joint between the two becomes loose and moves in the direction of rotation. There are cases. This is the thermal expansion coefficient (approximately 6 x 10-6/℃) of the ceramic (for example, Si3 N4) of the top plate.
There is a large difference between the coefficient of thermal expansion (approximately 20 x 10-6/°C) of the light alloy (for example, aluminum alloy) of the skirt part, and the connection of the groove is only mechanical, so heat treatment ( T6 treatment), particularly when performing rapid cooling (water cooling) after solution treatment, loosening occurs due to cooling while the dimensions are slightly changed due to thermal expansion. Furthermore, if the depth of the annular groove is small, the top plate may come off during water cooling or solution heating.

[0007] Furthermore, if the width of the entrance part of the annular groove is narrow or the depth is large, the flowability of the molten metal is low and the molten metal is not filled deep inside, forming a cavity inside, resulting in poor adhesion. Therefore, the bonding strength decreases. Furthermore, the stress that acts on the joint between the two after casting is such that compressive stress due to contraction of the light alloy acts to press the annular groove toward the center, and also causes the flange of the annular groove to move toward the skirt. This stress acts to widen the groove, and this stress tends to cause cracks to occur from the deep part of the annular groove toward the center. In particular, if the radius of curvature of the inner part (bottom) of the annular groove is small, the flowability of the molten metal will be low, and stress concentration will be high in response to the action of the compressive stress, making cracks more likely to occur. It is.

In view of the above circumstances, the present invention aims to reduce the stress during casting and prevent the occurrence of cracks from the grooves when the ceramic top plate and the light alloy skirt are integrated by casting. It is an object of the present invention to provide an engine valve lifter which can obtain high joint strength.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the engine valve lifter of the present invention has a connecting groove formed in the neck of a ceramic top plate in the circumferential direction, and the groove is divided at a plurality of points. A recess is provided in the radial direction, and a skirt is formed by filling the groove and recess with a light alloy by casting.

[0010] It is also preferable that the flange between the recesses is formed by casting the skirt, and that the groove is formed of a flat surface and an arcuate portion.

[0011]

[Operations and Effects] In the engine valve lifter as described above, a plurality of recesses are formed in the annular coupling groove formed in the neck of the top plate, so that the molten metal flows deep into the groove through the recesses. Good flowability can be obtained, and by filling the recess with the light alloy, the direction of shrinkage stress caused by casting is not only the compressive stress in the center direction, but also from the recess in the circumferential direction. This also acts to relieve the stress on the inner part of the groove and prevent the occurrence of cracks. In addition, the light alloy filled in the recess has the function of preventing the top plate from rotating, and the above-mentioned improved flowability provides high adhesion, greatly increasing the bonding strength between the two.
Even after heat treatment, the top plate does not loosen and can be made lighter.

Furthermore, if the flange between the recesses is cast into the skirt, the joint strength will be further increased, and if the groove is formed with a flat surface and a circular arc, the flowability of the molten metal will be further improved and the stress will be reduced. This will help ease concentration.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a valve lifter according to an embodiment, FIG. 2 is a bottom view of its top plate, and FIG. 3 is an enlarged cross-sectional view of its main parts.

The valve lifter 10 is composed of a disk-shaped top plate 11 and a cylindrical skirt portion 12, and the top plate 11 has a top surface that comes into sliding contact with a cam of a valve mechanism (not shown).
The skirt portion 12 is slidably supported by the cylinder head, and the end portion of the valve stem contacts the bottom surface of the top plate 11 and reciprocates in accordance with the cam shape to open and close the intake or exhaust valve. be.

The top plate 11 is made of ceramic (for example, Si3
N4), a disk-shaped base 11a;
A protrusion 11b having a smaller diameter than the base 11a is formed at the center of the back surface of the base 11a, and the protrusion 11b has a diameter smaller than that of the base 11a.
Base part 11a Annular coupling groove part 1 in the circumferential direction of the neck part
5 is formed. Due to the formation of the coupling groove 15, the outer peripheral portion of the protrusion 11b is formed into a flange 11c. In addition, semicircular recesses 16 formed in the radial direction by cutting out the flange 11c are provided at a plurality of locations (four locations in the figure) of the coupling groove 15, and the recesses 16 allow the coupling groove 15 to is divided.

On the other hand, the skirt portion 12 is made of aluminum alloy (
For example, JIS. It is cast from a light alloy such as AC2A, AC9A, AC9B), and is integrated with the top plate 11 by casting. When the skirt portion 12 is cast from this light alloy, the light alloy is filled into the coupling groove 15 and the recess 16 of the top plate 11, and the two are joined.

The shape of the coupling groove 15 is such that the upper surface 15a and the lower surface 1 of the groove 15 are
5b is a flat surface parallel to the top surface, and the deep part is an arcuate surface 15c
The radius of curvature of this arcuate surface 15c is 1 of the groove width.
It is set slightly larger than /2. In the joined state, the flange portion 11c between the recesses 16 is cast by the light alloy of the skirt portion 12.

Note that when casting the skirt portion 12,
In order to improve the flowability of the hot water, the top plate 11 should be sufficiently preheated (4
For example, aluminum alloy (AC2
A) The molten metal temperature is set to 720°C (preferably 650°C or higher). Further, after the casting, the aluminum alloy of the skirt portion 12 is subjected to a heat treatment such as a known T6 treatment in order to improve the strength thereof.

Next, FIG. 4 shows a modified example of the shape of the skirt portion. In the example of FIG. 1, the flange portion 11c of the top plate 11 is
In contrast, in this example, the wall of the skirt part 18 is made thinner, and the bottom side of the flange part 11c is not cast in light alloy. It shows.

FIG. 5 shows a modified top plate 11',
Rectangular notched recesses 19 are formed at two locations on the circumference, and the rest is formed in the same manner as in FIG. 2.

Furthermore, FIG. 6 shows another modification of the top plate 11'', in which a large number of recesses 20 are formed and the outer periphery of the protrusion 11b is formed into a tooth-shaped protrusion 21.

In the structure of the above-described embodiment, since the recess 16 is formed together with the joining groove 15, molten metal flows into the joining groove 15 from the outer peripheral portion during casting of the skirt portion 12, and the recess 16 Since the molten metal flows into the groove from both sides, the molten metal is filled to the depths of the coupling groove 15, resulting in good flowability and improved adhesion between the two. Furthermore, by filling the light alloy into the recess 16,
This mechanically prevents the top plate 11 from rotating relative to the skirt portion 12, which prevents the top plate 11 from loosening, and prevents shrinkage stress after casting from acting on the top plate 11 as compressive stress in the center direction. In addition, from the concave portion 16 to the flange portion 11c
Stress also acts in the circumferential direction, and the stress is relaxed compared to the case where stress acts only in the central direction, preventing cracks from forming from the grooves 15, and improving the yield strength of the top plate 11 itself. The bonding strength also increases.

Note that it is preferable to provide the recesses 16 in a plurality of locations while taking into consideration the strength of the grooves in the ceramic.Although the shape of the recesses 16 is arbitrary, it is preferable to form them in the shape of a protrusion as shown in FIG. Stress relaxation becomes even greater.

Regarding the shape of the coupling groove 15, the groove width (height in the vertical direction) is, for example, 30 mm in diameter.
, in the top plate 11 with a thickness of 5.6 mm, the groove width is 0.5 mm.
If the groove is narrow, such as less than mm, the molten metal will not flow well, and the molten metal will not be filled deep into the groove, resulting in voids being formed inside the groove, resulting in poor adhesion and bonding properties, and the filling thickness, which contributes to bonding force, will be thin and light. On the other hand, if the groove width is made wider than 2.0 mm, the flowability of the hot metal will be good.
As the thickness of the base portion 11a or the flange portion 11c decreases, the strength of the top plate 11 decreases. Regarding the radius of curvature of the arcuate surface 15c of the coupling groove 15, even if the groove width is to a certain extent, if the radius of curvature at the inner part is small, the tip will not be filled and a void will be formed. As the joint strength decreases, the stress concentration at the tip of the groove 15 increases, and due to the action of shrinkage stress, a slight impact causes cracks to occur from this part and breakage.From this point, the radius of curvature of the arcuate surface 15c increases. For example, when the groove width is 1.0 mm, it is preferable to form the groove as large as 0.75 mm from the viewpoint of alleviating stress concentration and filling property of the molten metal. The depth of the groove 15 should be approximately 1.5 times the width of the groove, since the larger the depth, the lower the filling performance and the lower the strength of the top plate 11, while the smaller the depth, the smaller the amount of filling and the lower the bonding strength. is suitable.

Furthermore, by making the upper and lower surfaces of the groove 15 flat, ceramic molding is possible, and the light alloy is less likely to flow out from the bonding groove 15 when the filled light alloy shrinks on cooling. Adhesion is obtained, and the light alloy after cooling is able to hold the flange 11c etc. well. Furthermore, if the groove 15 is shaped so that the groove width is larger inside than at the entrance, the bonding strength will be increased, but it is difficult to form the bonding groove 15 in this shape by shaping ceramics. Accompany.

[0026]Here, the results of an experiment in which the bonding strength with respect to the shape of the coupling groove 15 was measured will be shown. The top plate 11 used in the experiment was made of Si3N4, and the diameter of the base 11a was 3.
0 mm, and the outer diameter of the protrusion 11b (flange 11c) is 22.
6 mm, the thickness of the base 11a is 3.1 mm, the depth of the groove 15 is 1.5 mm, the number of recesses (width 3.5 mm) is two (see Fig. 5), and the following groove shape (groove width , radius of curvature), as shown in Fig. 1, the valve lifter 10 is obtained by casting aluminum alloy, and then the skirt portion 12 is fixed and pressure is applied to the top plate 11 from the bottom side with a plunger to break the joint. This is a measurement of the strength at a certain time.

A (product of the present invention)...Groove width 1.0mm, radius of curvature 0.75mm...Strength 1080 Kgf B
(Comparison product 1)…Groove width 1.0mm, radius of curvature 0.20
mm...Strength 540 Kgf
C (comparative product 2)...Groove width 0.5mm, radius of curvature 0
．． 75mm...strength 260 Kgf In the above results, the strength required for the valve lifter 10 is 1000K
gf or more, the product of the present invention satisfies the required strength, comparative product 1 has a small radius of curvature, and comparative product 2 has a narrow groove width, so the flow of the metal is insufficient and the bonding strength is low. ing. The strength of plastic bonding by caulking is about 600 to 700 kgf, which is insufficient compared to the required strength.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of an engine valve lifter according to an embodiment of the present invention.

[Figure 2] Bottom view of the top plate in Figure 1

[Figure 3] Enlarged cross-sectional view of main parts of the top plate

[Fig. 4] Cross-sectional view of main parts showing another example of a valve lifter

[Figure 5
] Bottom view showing another example of the top plate

[Figure 6] Bottom view showing still another example of the top plate

[Explanation of symbols]

10 Valve lifter 11 Top plate 11c Tsuba 12, 18 Skirt part 15　　　Connection groove part 16, 19, 20 Recessed part 15a, 15b Flat surface 15c Arc surface

Claims (3)

[Claims] 1. A coupling groove is formed in the neck of a ceramic top plate in the circumferential direction, and the groove is divided at a plurality of places to form concave portions in the radial direction. A valve lifter for an engine, characterized in that the valve lifter is formed by filling it with a skirt and integrally forming a skirt part. 2. The engine valve lifter according to claim 1, wherein a flange portion between the recesses in the top plate is cast into a skirt portion. 3. The coupling groove portion is formed by upper and lower flat surfaces and a deep circular arc surface.
Valve lifter for the engine listed.