JP2780243B2 - Strength test method for ceramic valves - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for testing the strength of an engine valve made of ceramics.

[Conventional technology]

Valves used in engines of automobiles and the like are exposed to high-temperature gas, and are repeatedly impacted by valve seats of the engine due to continuous opening / closing operations by cams. For this reason, the valve must be made of heat-resistant material, have excellent high-temperature strength and high-temperature corrosion resistance, and also have excellent impact resistance.

For this reason, heat-resistant alloys have been used for valves in the past, but recently, silicon nitride, silicon carbide, and sialon, which are lighter than metals and have excellent heat resistance, oxidation resistance, and corrosion resistance, have been used. Ceramics such as these have been developed, and attempts have been made to form valves using these ceramics.

[Problems to be solved by the invention]

However, ceramics, unlike metallic materials, have low toughness, and even minute defects on the surface are likely to cause destruction. Therefore, the strength of a ceramic valve tends to greatly change depending on the shape and the processing state (grinding state) of the surface. Therefore, ceramic valves are
Prior to use, each must be tested for its predetermined strength. The strength test includes a bending test for the root of the stem and the head of the valve (which can mainly be used to detect defects such as surface scratches and surface fineness), and a tensile test for the stem (conditions in the stem). You can know).

Accordingly, an object of the present invention is to provide a method for testing bending strength and tensile strength depending on the surface and internal state of a ceramic valve.

[Means for solving the problem]

The present inventor has conducted various studies to achieve the above object, and as a result, performing a bending test in which bending stress is applied to the entire head portion of the valve and the entire stem portion of the valve, the surface grinding state of the valve is reduced. It has been found that it is possible to know whether or not the strength has reached a level that provides sufficient strength, and it is also possible to know the original strength of the valve by performing a tensile test in the axial direction of the valve, thereby completing the present invention.

That is, a stem having a cotter groove at the tip,
According to the method of the present invention for testing the strength of a ceramic valve for an engine comprising an umbrella-shaped head portion continuous to a root portion of the stem portion, the head portion is held by a chuck rotating coaxially with the stem portion. Along with attaching a rotatable jig to the tip of the stem, applying a load substantially perpendicular to the tip of the stem by the jig while rotating the valve about the axis of the stem. The bending moment that maximizes the vicinity of the base of the head is given to the valve, and the strength at the base of the head is tested.

Another method of the present invention for testing the strength of a ceramic valve having the above-mentioned shape is a jig having a holding portion capable of rotating a head portion and a tip portion of a stem portion of the valve coaxially with the stem portion. The jig is supported by a fulcrum, and the same load is applied to the jigs inside the fulcrums while rotating the valve around the axis of the stem portion. A four-point bending test of the valve is performed by applying a uniform bending moment, and the strength of the stem is tested.

Another method of the present invention for testing the strength of the ceramic valve having the above-mentioned shape is to attach a cotter and a retainer to the tip of the stem portion, and to attach the head portion and the retainer to a universal joint by a chuck. It is characterized in that a tensile strength test is performed while keeping the direction of the tensile force consistent with the central axis direction of the valve.

(Examples and actions)

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing a bending test of a ceramic valve according to one embodiment of the present invention.

First, the valve 1 includes an umbrella-shaped head portion 2 and a stem portion 3, and a groove 3 a for attaching a cotter is formed at the tip of the stem portion 3. Here, the bulb 1 is held by jigs 4 and 5 at the tip of the head 2 and the stem 3 respectively.

The jig 4 has a rotating member 41 and a tubular member 42 that holds the rotating member 41. The rotating member 41 has a cylindrical portion 41a and a disk-shaped portion 41b integrally joined to the cylindrical portion 41a and having a threaded portion on the outer periphery.
And a ring member 41c having a female thread portion on the inner periphery, and the ring member 41c has an inner flange portion 41d at one end. The disk-shaped portion 41b and the ring member 41c are screwed together to form a chuck portion. The cylindrical portion 41a is rotatably held by the tubular member 42 via a plurality of ball bearings 43. The valve 1 is coaxially fixed to the cylindrical portion 41a by abutting the end surface of the head portion 2 on the end surface of the disk-shaped portion 41b of the chuck portion and fastening the ring member 41c.

On the other hand, the jig 5 includes a cylindrical member 51 and a plurality of ball bearings 52.
And the tip of the stem 3 is rotatably held.

As described above, the valve 1 is rotatably held around the axis thereof by the two jigs 4 and 5, and the jig 5 is rotated with the rotating member 41 of the jig 4 by the jig 5 with respect to the axis of the valve 1. And apply a load almost vertically. At this time, valve 1
As shown in FIG. 1, the bending moment increases as the distance from the head 2 increases. Since the diameter of the head portion 2 is increased, the head portion 2 has a sufficient strength against the lifting stress. Therefore, according to the method shown in FIG. 1, the strength near the base of the head portion 2 is mainly tested. Become.

In addition, the result of such a bending test generally indicates whether or not the state of the surface of the specimen has reached a level at which the specimen has sufficient strength. The reason for this is that the greatest stress is generated when a bending force is applied to the specimen at its surface, and the strength varies significantly depending on the processing (grinding) state of the surface. Therefore, in the above-described bending test, it is known whether or not the surface grinding state near the base of the head portion has reached a level that gives sufficient strength.

In this method, the valve 1 is moved together with the rotating part 41 of the jig 4 by at least one while applying a load to the cylindrical member 5.
If rotated, the surface condition near the base can be tested over the entire circumference.

Next, a method for testing the strength of the stem portion 3 using a four-point bending test will be described.

FIG. 2 is a schematic sectional view showing a four-point bending test of the ceramic valve according to one embodiment of the present invention. FIG. 3 is a sectional view showing the stem end of the valve and the jig 7 in the test method shown in FIG. FIG. 3 is a partial schematic cross-sectional view showing the engagement state of FIG.
Here, the bulb 1 is held by jigs 6 and 7 at the tip of the head 2 and the stem 3 respectively.

The jig 6 has a rotating member 61 and a tubular member 62 for holding the rotating member. The rotating member 61 is integrally formed with the cylindrical portion 61a and the cylindrical portion 61a and has a disk-shaped portion 61b having a threaded portion on the outer periphery.
And a ring member 61c having a female screw portion on the inner periphery, and the ring member 61c has an inner flange portion 61d at one end. The disk-shaped part 61b and the ring part 61c form a chuck part by being screwed together. The cylindrical portion 61a is rotatably held by the cylindrical member 62 via a plurality of ball bearings 63. The valve 1 is coaxially fixed to the cylindrical portion 61a by abutting the end surface of the head portion 2 on the end surface of the disk-shaped portion 61b of the chuck portion and fastening the ring portion 61c.

On the other hand, the jig 7 has a rotating member 71 and a tubular member 72 for holding the rotating member 71.
And is rotatably held by the tubular member 72 via the.

At the end of the rotating member 71, a hole for inserting the tip of the stem of the valve 1 is provided as shown in detail in FIG. This hole has such a depth that the cotter groove of the stem portion is sufficiently inserted therein. The diameter of the hole is slightly larger than the outer diameter of the tip of the stem.

Thus, the jigs 6 and 7 are attached to the valve 1 from both sides thereof.
And a four-point bending test is performed. At this time, the fulcrum 8,
8 and the two internal load points are set so that they are both located on the jigs 6 and 7, and the valve 1 is positioned between the two internal load points. When the same load is applied in the direction of the arrow to the point of the two arrows pointing vertically downward shown in FIG. 2 as the internal load point, as shown in the figure, the bending moment applied between the internal load points becomes a valve. Are uniform along the central axis of Therefore, according to this method, the strength test of the entire stem member can be performed at once.

In this method, while applying a load in the same manner as in the above-described bending test, the valve 1 is rotated at least one turn together with the rotating members 61 and 71 holding both sides thereof,
The entire surface of the stem is tested for defects that reduce valve strength.

By the way, the cotter groove formed at the tip of the stem portion 3 is a portion where defects due to machining are likely to remain, and is a portion where a large stress is applied during actual use. Therefore, it is necessary to also conduct a strength test in this portion. .

Therefore, in the method of the present invention, the tip of the stem portion and the jig 7
As shown in FIG. 3, the rotary member 71 is engaged with the rotary member 71 to perform a strength test of the cotter groove. As described above, there is a slight clearance between the stem portion 3 and the rotating member 71, but when a load is applied to the jig 7, the two come into contact with each other. For example, assuming that a load is applied vertically downward from FIG. 3, portions 71 a and 71 b of the inner wall surface of the hole come into contact with the stem 3. At this time, the magnitude of the stress generated on the surface of the tip portion of the stem portion of the valve 1 is as shown in the graph shown in the lower part of FIG. Therefore, if the method of holding the tip portion of the stem portion as shown in FIG. 3 is employed, a sufficiently large stress can be applied to the cotter groove portion, and the strength test of this portion is performed simultaneously with the strength test of the entire stem portion. It can be carried out.

The magnitude S of the stress generated in the cotter groove is arbitrarily changed by changing the ratio (l / L) of the depth L of the hole formed in the rotating member 71 to the distance l from the stem end face to the cotter groove. Can be adjusted.

By performing the two bending tests described above, it is possible to know whether or not the grinding state has reached a level that provides sufficient strength over the entire surface of the valve. It is not possible to know exactly whether there is a defect present in the data. Therefore, it is preferable to conduct a tensile test in the axial direction of the stem to check for the presence or absence of a defect inside the valve.

FIG. 4 is a schematic sectional view showing a tensile test of a ceramic valve according to one embodiment of the present invention.

First, the valve 1 is equipped with a cotter 10 and a retainer 11 at the tip of the stem 3. This mounting is performed in the same manner as when the valve 1 is actually mounted on the engine. However, a wedge-shaped cotter 10 having a convex portion that fits into a cotter groove provided in the stem portion 3 has an inner wall surface. It is mounted so as to be fitted between the tapered cylindrical retainer 11 and the stem portion 3.

As shown in FIG. 4, the valve 1 with the cotter and the retainer is mounted on the head 2 and the retainer 11 respectively.
It is held by two chucks 12 and 13. The method of holding the valve 1 by the chucks 12 and 13 at this time can be performed in the same manner as the method shown in FIGS. 1 and 2. Universal joints 14 and 14 are connected to the chucks 12 and 13, respectively, so that the direction of the pulling force always coincides with the direction of the central axis of the valve 1.

Thus, when the valve 1 is held by the chucks 12 and 13 and a pulling force is applied to the valve 1 in the direction of the arrow in the figure, the same stress is applied to any part in the cross section perpendicular to the central axis of the valve 1. become. Therefore, according to this method, it is possible to know whether or not there is a defect that reduces the strength not only in the surface portion but also inside the bulb.

In this method, the cotter and the retainer are actually attached to the stem, and the tensile test is performed while holding the head and the retainer.Therefore, the test can be performed under conditions close to those in which the valve is actually used. And a more reliable strength test.

All three tests described above can be performed at room temperature. In this case, the strength of the ceramic material used as the valve material at high and normal temperatures may be experimentally obtained in advance, and calibration may be performed based on the results. Generally, strength at high temperature is smaller than strength at room temperature,
The load applied in the strength test performed at room temperature may be set slightly larger.

Although the present invention has been described with reference to the accompanying drawings, the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention. For example, valve 1
The method of holding the head portion 2 by the jig can be variously changed in addition to the method using the chuck shown in the drawings, and the method of mounting the cotter and the retainer to the stem portion can be appropriately changed by bonding, shrink fitting, mechanical mounting, or the like. Can be changed.

Further, the method of the present invention can be applied not only to ceramic valves but also to ceramic rod-shaped parts.

If a strength test of a ceramic valve is performed using these three test methods, a reliable strength can be guaranteed. Depending on the shape of the valve head, the strength can be guaranteed only by the combination of the four-point bending test and the tensile test described above. When more reliable strength is required, the acoustic emission signal measurement method can be further improved. Should be added.

〔The invention's effect〕

By using the bending test method of the present invention, it is possible to know whether the grinding state is good or bad at the base of the valve head and the entire surface of the stem of the valve. Further, the presence or absence of a defect inside the valve can be known by a tensile test in the direction of the central axis of the stem portion.

Therefore, by combining the two bending test methods and the tensile test of the present invention, it is possible to guarantee a reliable strength for a ceramic valve.

In particular, in the method of the present invention, since the test includes a portion subjected to a large stress, such as a cotter groove or a base of a head portion, the reliability of strength assurance by the method of the present invention is higher. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a bending test method of a valve according to an embodiment of the present invention, and a graph showing the magnitude of a bending moment generated by this test is also shown. FIG. 3 is a schematic cross-sectional view showing a four-point bending test according to another embodiment, and also includes a graph showing the magnitude of a bending moment generated by this test. FIG. 3 shows a test method shown in FIG. It is a partial schematic cross-sectional view showing a state of holding the stem end by a jig,
A graph showing the magnitude of the stress generated on the surface of the tip portion of the stem portion is also shown. FIG. 4 is a schematic sectional view showing a valve tensile test method according to still another embodiment of the present invention. 1 Ceramic valve 2 Head 3 Stem 3a Cotter groove 4,5,6,7 Jig 8 Supporting top 10 Cotta 11 Retainer 12,13 …… Chuck 14 …… Universal joint 41,61,71 …… Rotating member 42,62,72 …… Cylinder member 43,63,73 …… Ball bearing

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Sho 62-20352 (JP, U) Japanese Utility Model Sho 62-79142 (JP, U) Japanese Utility Model Hei 2-35055 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) G01N 3/00-3/62 G01M 13/00

Claims (5)

(57) [Claims] A stem having a cotter groove at a tip thereof;
In a strength test method for a ceramic valve for an engine comprising an umbrella-shaped head portion continuous to a root portion of the stem portion, the head portion is held by a chuck coaxially rotating with the stem portion, and the stem portion is held. A rotatable jig is attached to the tip of the stem, and a load is applied almost perpendicularly to the tip of the stem by the jig while rotating the valve around the axis of the stem. Providing a bending moment that maximizes the vicinity of the root to the valve and testing the strength of the head at the root. 2. A stem having a cotter groove at a tip thereof,
In a strength test method for a ceramic valve for an engine comprising an umbrella-shaped head portion continuous to a root portion of the stem portion, a head portion of the valve and a tip portion of the stem portion can be coaxially rotated with the stem portion, respectively. While holding with a jig having a suitable holding portion, supporting both jigs by a fulcrum, while rotating the valve about the axis of the stem portion,
The same load is applied to the two jigs inside the two fulcrums to give a uniform bending moment to the valve, and a four-point bending test of the valve is performed to test the strength of the stem portion. how to. 3. The method according to claim 2, wherein the first jig holding the head portion includes a first rotating member including a columnar portion and a chuck portion holding a head portion of the valve; A second jig for holding the tip of the stem portion, the second jig holding the tip portion of the stem portion rotatably, and a second jig having a hole for inserting the tip portion of the stem portion at the tip. A method comprising: a rotating member; and a second cylindrical member rotatably holding the second rotating member, wherein the valve is held rotatably about an axis, and a four-point bending test is performed. 4. The method according to claim 3, wherein the hole formed in the second rotating member has a depth such that the cotter groove of the stem portion is sufficiently inserted therein. The diameter of the stem is slightly larger than the outer diameter of the tip of the stem. 5. A stem having a cotter groove at a tip thereof,
In a strength test method of a ceramic valve for an engine comprising an umbrella-shaped head portion continuous to a root portion of the stem portion, a cotter and a retainer are attached to a tip portion of the stem portion, and the head portion and the retainer are respectively mounted. A method of holding by a chuck connected to a universal joint, and performing a tensile strength test while always making a direction of a tensile force coincide with a central axis direction of the valve.