JPH01190951A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the abrasion resistance and aluminum coagulation resistance of the groove part of a piston ring by forming each alumite treatment layer onto the upper and lower surfaces of the groove part of a top ring and depositing the primary crystal Si in dispersion onto the surface of the alumite treatment layer. CONSTITUTION:A piston basic member 1 is made of hyper-eutectic Al-Si group alloy. The alumite treatment layers 12 and 13 through the anode oxidation are formed on the upper and lower surfaces 10 and 11 of the groove part 6 of a top ring. The primary crystal Si particles 14 are exposed in dispersion in the alumite treatment layers 12 and 13. Therefore, the abrasion resistance and aluminium coagulation resistance of the groove part of a piston ring can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a piston for an internal combustion engine made of an Al-8i alloy, and more particularly to a piston having a reinforced top ring groove.

Conventional technology In recent years, with the increase in engine output due to bits such as turbochargers, the heat load on pistons for internal combustion engines has become particularly severe at the top ring groove. In the groove portion, there is a problem in that wear and scuffing easily occur between the groove portion and the top ring, which is the mating material. Therefore, in order to improve the heat resistance and wear resistance of the top ring groove, pistons whose top ring grooves were compositely reinforced with ceramic M fibers (for example, Japanese Patent Application No. 58-7
No. 5184, etc.) have been proposed. Although not related to the top ring groove, we have also proposed a piston in which a hard alumite layer is formed on the top surface of the piston by anodizing to prevent cracks from occurring due to thermal and mechanical stress on the top surface (
For example, Japanese Patent Laid-Open No. 61-229963).

Problems to be Solved by the Invention As mentioned above, the hebta alloy piston whose top ring groove is compositely reinforced with ceramic fibers is still prone to wear and scuffing, especially when subjected to severe heat loads, and the durability and reliability of the piston are affected. It was difficult to fully satisfy the requirements. Further, in the method of forming a hard alumite layer on the top surface of the piston, the top ring groove is not strengthened even though the top surface of the piston is strengthened, so the problems of wear and scuffing of the top ring groove are not solved. Furthermore, it is conceivable to form hard alumite 1 by anodizing not only on the top surface of the piston but also on the entire surface of the piston, but in this case, scuffing may occur due to lack of oil film on the skirt of the piston, etc. .

This invention was made against the background of the above-mentioned circumstances, and improves the wear resistance and heat resistance of the top ring groove, which is subjected to severe thermal loads, thereby preventing wear and scuffing in the top ring groove. The purpose is to provide a piston with improved durability and reliability.

Means for Solving the Problems The piston for an internal combustion engine of the present invention has a Si content of 14 to 14.
The piston base material is made of a hypereutectic Af-8i alloy within the range of 30 wt%, and an anodized layer with a thickness of 10 to 50 mm is formed on at least the upper and lower surfaces of the inner surface of the top ring groove, and It is characterized in that primary crystals 8i with a size of 10 to 40 μm are exposed on the surface of the alumite treated layer.

Function: In the piston of this invention, hypereutectic A&
-Since the 8i alloy is used, its structure is α-A2
The primary crystal S1 is dispersed and crystallized in the matrix. And especially the alumite treatment yJ! Even on at least the upper and lower surfaces of the top ring groove where the layer is formed, primary crystal Si is dispersed and exposed on the surface of the alumite treated layer.

The alumite treatment layer itself is hard and is a non-metallic layer, so it is difficult to cause corrosion to the piston ring, which is the mating material. Although abrasion resistance and scuff resistance are improved, this alone is not necessarily sufficient.

That is, if the alumite treatment layer itself is worn away and the base material is exposed, scuffing and wear will rapidly progress. Therefore, in the piston of this invention, a hypereutectic Af-Si alloy is used as the base material, extremely hard primary crystal Si with an H shift of about 50 is distributed and exposed on the surface of the alumite treated flI layer, and the hard primary crystal S1 It supports the load from the mating material and prevents the progress of wear on the alumite treated layer.

In other words, alumite 5I! ! The synergistic effect of the physical layer and the primary Si makes it possible to significantly improve the wear resistance and adhesion resistance of the top ring groove.

Here, the portions on which the alumite treatment layer is formed are at least the upper and lower surfaces of the inner surface of the top ring groove. That is, this is because these upper and lower surfaces are most likely to wear, but of course the alumite treatment layer may be formed on the entire inner surface of the top ring groove. However, parts other than the top ring groove,
In particular, it is desirable not to form an alumite treatment layer on the outer peripheral surface (skirt portion) of the piston. This is because if an alumite treatment layer is formed on the skirt portion, the oil film breaks at that portion and scuffing is likely to occur.

If the thickness of the alumite treatment layer is less than 101JIR, sufficient wear resistance will not be obtained, while if it exceeds 50IJa, surface roughness will become large and the processing cost will increase. limited within range.

In addition, when the size of primary Si is less than 10IIIn,
Because it is difficult to sufficiently support the load of the mating material,
It is difficult to show sufficient abrasion resistance, and on the other hand, if it exceeds 40 strands, the abrasiveness to the other material increases and the top ring, which is the mating material, becomes more likely to wear out, and the alumite treatment layer becomes more prone to cracking. Because it becomes easy to peel off, primary crystal S
The size of 1 was set within the range of 10 to 40 μm. Note that the size of primary Si can be adjusted by controlling the cooling rate during piston casting.

The base material A&-8i alloy has a Si content of 12wt.
% or more, it becomes a hypereutectic alloy in which the initial SI crystallizes, but if the Si content is less than 14 wt%, the amount of primary Si crystallized is insufficient and it becomes difficult to sufficiently support the load of the mating material. There is a risk that On the other hand, if the Si-containing Φ is excessive, there will be too much ink in the primary crystal S1, which will increase the wear of the mating material, and the Si
If l exceeds 30w%, the manufacturability, especially the VI buildability (occurrence of cracks) and processability will deteriorate, so the Sil should be 14 to 3.
It was set within the range of 0 wt%. In addition, within this range, especially 14
It is preferably within the range of ~2511%.

Example [Example 11 Figures 1 to 3 show a screw thread according to an example of the present invention.

In FIGS. 1 to 3, the piston base material 1 is A l −
17wt%S i -4,5wt%Cu -0,55w
It is formed from a hypereutectic, l'-8i alloy having a component composition of t%MQ. The upper part of the side outer peripheral surface 2 of the piston base material 1 receives compression rings 4 and 5 for preventing combustion gas from leaking from the combustion chamber through the gap between the piston and the cylinder wall surface of the cylinder block 3. Two ring grooves 6.7 (top ring bay 6
A second ring groove 7) and a ring groove 9 for receiving an oil ring 8 from which excess oil has been scraped off are formed. In particular, an alumite treatment layer 12.13 is formed by anodic oxidation on the upper surface 10 and lower surface 11 of the top ring groove 6, which receives the top ring 4 and slides on the top ring 4, of the ring groove 6.7.9. has been done. This alumite treatment! In layer 12.13,
As schematically shown in FIG. 3, primary crystal Si particles 14 are dispersed and exposed.

Such a piston was manufactured as follows. That is, first, a molten alloy having the above-mentioned composition is poured into a mold for high-pressure piston casting, and the molten alloy is solidified while being pressurized with a pressure of 1000 Kf1/cm using a plunger that fits liquid-tightly into the crown shape. , a piston preform was obtained. Then, after heat-treating the preformed body by T6 treatment,
It was processed to predetermined dimensions to form a ring vortex portion 6.7.9. After that, the top surface 10 and bottom surface 1 of the top ring groove 6 are
1 is anodized using an electrolytic bath, such as a sulfuric acid bath, a sulfuric acid bath, or a mixed acid bath thereof, to form an alumite treatment 1 with a thickness of approximately 201 JII and a hardness of Hv 400.
112°13 was formed. Note that the size of primary Si at this time is about 20 mm.

[Example 21] The influence of the Si content in the A1-5i base alloy was investigated as follows.

Using the A1-5r alloy of each Sil shown in Table 1, a piston base material was cast in the same manner as in Example 1, and a block test piece with a size of 16 x 6 x 10M was cut out from each piston base material. An alumite treatment layer having a thickness of 20 μm was formed on the 16×6 test surface of the block test piece in the same manner as described above.

Table 1 These block test pieces were sequentially set in a friction and wear tester, and the outer diameter was 35 mg, the inner diameter was 30 M, and @io
A cylindrical test piece made of JIS 5UJ2 steel of
A cylindrical test piece was heated to 0.000 mA at a load of 15-1 and a rotational speed of 1 sorpn while supplying gas motor oil (product name: 5W-30).
A wear test was conducted by rotating for 5 hours. The test results are shown in FIG. 4 in correspondence with the Sil of each test piece.

As shown in Fig. 4, the amount of Si in the piston material (block test piece with an alumite treatment layer formed) was 9 wt.
%, the alumite treatment layer (thickness of about 20 mm) was worn away and disappeared, and further wear progressed rapidly. This is considered to be because primary Si did not crystallize at all. Further, when the Sil content was 12 wt%, the wear resistance was slightly improved, but the wear progressed until the alumite treatment layer almost disappeared. This is considered to be because the amount of primary Si crystallized, which should support the load, is extremely small. On the other hand, Sil is 14wt%
With the above, the wear of the test piece was significantly reduced, and the alumite treatment J! ! It exhibits excellent wear resistance due to the synergistic effect of the layer and primary Si.

Furthermore, the wear of the cylindrical test piece, which is the mating material, tends to increase as the length of 81 m increases. This has high hardness (
lv 750) This is thought to be due to an increase in the amount of primary Si crystallization.

Based on the above test results and the fact that if 5rii exceeds 30 wt%, castability and workability deteriorate, as mentioned above, the Si content should be in the range of 14 to 30 vt%, preferably 14 to 25 wt%. It was within the range.

[Example 3] The influence of the size of primary Si was investigated as follows.

A i' -17w1%5 i -4, Ovt%CU-
Using a hypereutectic Al-8i alloy consisting of 0.5 wt% M9, pistons were cast in the same manner as in Example 1, and by changing the cooling rate at that time, various sizes as shown in Table 2 were obtained. A piston containing primary Si crystals was prepared. A block test piece similar to that in Example 2 was cut from each piston, and the test surface of this block test piece was coated with a thickness of 20. An alumite treated layer B was formed.

Table 2 These block test pieces were sequentially set in a friction and wear tester, and a wear test was conducted under the same conditions as Example 2 using a cylindrical test piece similar to that used in Example 2 as a mating member. . The results are shown in FIG. 5 in correspondence with the size of primary Si.

As shown in Figure 5, in the piston material (block-shaped specimen), when the size of the primary Si crystal is as small as 5, the alumite treatment layer is worn away and disappears, and even more rapid wear occurs. It progressed. On the other hand, the size of primary crystal 5i is 1
When it was 0 or more, the effect of supporting the load Φ was expressed, and the wear was significantly reduced, and when it was 25 or more, the wear resistance was almost constant.

On the other hand, the wear of the cylindrical test piece, which is the counterpart material, is as follows:
If it becomes more than a trend, it will gradually become larger and the opponent's aggressiveness will appear. In particular, when the size of primary Si is 30 or more, the aggressiveness toward the opponent tends to increase considerably.

The above test results and the size of primary Si are 40
If IJII is exceeded, cracks are likely to occur in the alumite treated layer, so as mentioned above, the size of the primary Si crystal is set within the range of 10 to 40 fi, preferably 10 to 30 fi.

[Example 4] The 14 types of piston base materials shown in Table 3 were made in the same manner as in Example 1, and as in Example 1, a 20 to 25 μm thick layer was formed on the top and bottom surfaces of the top ring groove. An alumite treatment layer was formed. For these pistons, the hardness Hv 4
In combination with a steel top ring made of 00 SUS 420J2, it was installed in a 4-cylinder, 4-cycle diesel engine with a turbo P-jar, and the durability test WA (
5400 rpm x full load x 300 hours).

After completing the actual machine durability test shown in Table 3, the maximum wear depth of the bottom surface of the top ring groove of the piston and the maximum wear depth of the bottom surface of the mating ring, which is the mating material, were investigated, and FIG. 6 shows the results.

As shown in FIG. 6, for the pistons labeled A and B,
Anodized layer on the bottom of the top ring groove (thickness 20~
25) has worn out and disappeared, and the wear is progressing further. This is because the amount of primary Si crystallized is too small or the size of the primary Si is small, so the alumite treatment layer is worn away, and at that point, the base material Al-5r alloy and top ring contact each other. It is thought that this caused aluminum adhesion between the top ring and the top ring, which caused significant wear. On the other hand, in the pistons labeled C and D, the lower surface of the top ring groove has less wear, and the alumite treatment layer remains. However, for the piston with mark @D, primary crystal S
Since the magnitude of i is a little large, some aggressiveness appears, and the wear on the lower surface of the piston ring is slightly greater than when a piston with code C is used.

[Example 51] Using the piston with code C in Example 4 (with an alumite treatment layer formed on the top and bottom surfaces of the top ring groove), four types of materials shown in Table 4 were used as the mating top ring material. Use 1. An actual machine durability test similar to that in Example 4 was conducted for each combination.

Table 4 Figure 7 shows the results of investigating the maximum wear depth on the bottom surface of the top ring groove and the maximum wear depth on the bottom surface of the top ring in each piston after the above actual machine durability test.

As shown in Figure 7, when a piston ring of FCC70, which has a lower hardness than the alumite treatment layer, is used, the ring side will wear significantly, but the hardness is equal to or higher than the hardness of the alumite treatment layer (Hv It has been found that if a ring having a hardness of 350 or higher is used, the wear on the ring side is significantly reduced. Therefore, in the case of the piston of the present invention, it is desirable to use a P ring having a hardness of Hv 350 or more in order to reduce wear of the top ring.

Effects of the Invention As is clear from the above embodiments, the piston for an internal combustion engine of the present invention has an alumite treatment layer formed on at least the upper and lower surfaces of the inner surface of the top ring groove, and an appropriate size on the surface of the alumite treatment layer. By dispersing and crystallizing the primary Si crystals, the wear resistance of the top ring groove can be improved.
The aluminum corrosion resistance has been significantly improved compared to conventional products, and therefore, it can be used in internal combustion engines that are subjected to particularly large heat loads, and their durability and reliability can be greatly improved compared to conventional products. be able to.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing the overall structure of an example of Komei's piston for internal combustion engine, and Fig. 2 shows the main parts of the piston shown in Fig. 1 (
3rd longitudinal cross-sectional view showing an enlarged view of the area (near the top ring groove)
The figure is a sectional view schematically showing the structure of the lower surface of the top ring groove. Fig. 4 is a graph showing the results of the friction and wear test in Example 2, Fig. 5 is a graph showing the results of the friction and wear test in Example 3, and Fig. 6 is the maximum after the actual machine durability test in Example 4. Diagram showing wear depth, Figure 7 is Example 5
FIG. 2 is a diagram showing the maximum wear depth after an actual machine durability test. 1... Piston base material, 6... Top ring groove,
10...Top ring groove top surface, 11...Top ring groove bottom surface, 12.13...Alumite treatment 3! ! ! Layer 14...Primary Si particles. Patent attorney representing applicant Toyota Motor Corporation! 1) Oxygen deficiency (1 other person) Figure 1 Figure 2 Figure 3 Figure 4 Cause S! t(, W L ”A ) Figure 5 Primary crystal Sia person □im)

Claims (1)

[Claims] Hypereutectic Al- with a Si content in the range of 14 to 30 wt%
The piston base material is made of a Si-based alloy, and at least the top and bottom surfaces of the inner surface of the top ring groove have a thickness of 10 to 10 mm.
A 50 μm alumite treated layer is formed, and primary crystals S with a size of 10 to 40 μm are formed on the surface of the alumite treated layer.
A piston for an internal combustion engine, characterized in that i is exposed.