JPH0343340B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston ring used in a cylinder bore whose mating material is made of ceramic such as silicon nitride sintered body.

In internal combustion engines, combustion chambers are made insulated to improve fuel efficiency. Due to this heat insulation of the combustion chamber, the sliding surface between the piston ring and the cylinder liner becomes high temperature, making it easy to break the oil film, and as a result, the piston ring and the cylinder liner pipe are likely to seize or suffer excessive wear. For this reason, in recent years, consideration has been given to using cylinder bores made of ceramics, such as silicon nitride sintered bodies, as cylinder liner materials.

On the other hand, the sliding parts of piston rings are thermally sprayed with molybdenum or iron-chromium alloy powder to improve their wear resistance and oil film retention.

However, even with such improved piston rings, when used in ceramic bores such as silicon nitride sintered bodies, the piston rings cannot be said to have sufficient wear resistance, and the walls of the ceramic bore, which is the mating material, There was also a lot of wear.

The present invention was developed in view of the above circumstances, and an object of the present invention is to provide a piston ring for a ceramic bore that has wear resistance and is less aggressive to the ceramic bore that is the mating material.

In order to achieve this objective, the present inventor investigated and researched various thermal spray materials.

As a result, the inventor of the present invention discovered that in a piston ring used for a ceramic bore such as a silicon nitride sintered body, the sprayed layer serving as a sliding layer is composed of alumina, titania, and chromium oxide, and further, 60% by weight of alumina and titania, and 60% by weight of alumina and titanium, and the balance (40% by weight) It was discovered and confirmed that the critical significance of attack on the other material is obtained near chromium oxide, and alumina and titania 40 to 80
The present invention was developed based on the fact that if the remaining 20 to 60% by weight is chromium oxide, a thermal sprayed layer with excellent wear resistance and less aggressiveness against the ceramic bore, which is the mating material, can be obtained. It is completed.

That is, the piston ring for a ceramic bore of the present invention includes a piston ring body made of metal and a sliding layer formed on the sliding surface of the piston ring body, and the sliding layer is made of alumina, titania, and chromium oxide. It is formed with a thermal sprayed metal of 40-80% by weight of alumina and titanium, with the balance being 20% by weight.
~60% by weight is chromium oxide, and is characterized by low aggressiveness to cylinder bores made of ceramic sintered bodies.

The main body of the metal piston ring of the present invention is:
Refers to the piston ring material before a sliding layer is formed on its sliding surface. As such a piston ring body, a conventional piston ring material can be used as is. As for the types of piston rings, compression rings, oil rings, and various conventional piston rings can be used.

The sliding layer formed on the sliding surface of the piston body is
It is unique in that it is made of alumina, titania, and chromium oxide thermally sprayed metallization. The composition ratio of the sliding layer is 40 to 80% by weight of alumina and titania.
% by weight, the balance 20-60% is chromium oxide. Here, alumina and titania may be a mixture of single oxides, but it is preferable to use alumina and titania mixed oxides mixed in molecular order. This makes the uniformity of alumina and titania more reliable, and the structure of the sliding layer more stable.

The optimum mixing ratio of alumina and titania is 40 parts by weight of alumina and 60 parts by weight of titania, and in practice, 35 to 45 parts by weight of alumina and 55 to 65 parts by weight of titania are preferable. Incidentally, titania has the effect of improving alumina's wear resistance and heat cycle resistance.

The particle size of alumina, titania and chromium oxide is preferably between 10 microns and 44 microns.

The porosity of the pores present in the sliding layer is preferably 3 to 10%. Note that the pores have the role of retaining oil. The thickness of the sliding layer is 50 microns or more, preferably 100 microns
~300 microns is preferred.

For reference, we will explain the results of a model test in which the composition of the sliding layer was changed and the wear resistance of the piston ring and the aggressiveness of the mating material were tested. As a model material for the piston ring body, the outer diameter is 35 mm, the inner diameter is 31 mm, and the thickness is
8.75 mm ring-shaped bearing steel (SUJ2) rotating wear test pieces A to G were prepared. And this test piece A
~Alumina and titania composite powder on the outer circumferential surface of G.
(Al ₂ O ₃ : 40%, remainder TiO ₂ ) and chromium oxide powder were plasma sprayed with different blending ratios.

The blending ratio is 100% alumina and titania alloy powder for test piece A, 90% for test piece B, and 80% for test piece C.
%, test piece D: 60%, test piece E: 40%, test piece F: 30%, test piece G: 0%, and the remainder was chromium oxide powder. Here, test piece C, test piece D, test piece E
is the product of the present invention. In addition, test piece A, test piece B, test piece F, and test piece G serve as comparative examples.

Furthermore, as a comparative example, using the same type of test piece,
Iron chromium alloy powder (Cr: 65%,
A test piece H was used, which was thermally sprayed with C: 8.2%, Si: 1.5%, and the balance was Fe (balance: Fe), and a test piece was also plated with hard chrome.

In addition, in this test, the mating member corresponding to the ceramic cylinder bore was 15.75 mm in length and 6.35 mm in width.
A block test piece K made of a silicon nitride sintered body obtained by hot pressing with a height of 10.2 mm was used, and a block test piece J of alloy cast iron having the same shape was also used as a comparative example.

Then, the end faces (15.75 mm x 6.35 mm) of the block test pieces K and J and the ring-shaped test pieces A~
Place it so that it is in contact with the outer peripheral surface of I, supply motor oil (10W-30) as a lubricant to the contact surface,
A wear test was conducted for 3 hours at a rotation speed of 160 rpm and a load of 300 kg.

The test results are shown in Figure 1. In FIG. 1, the upper part shows the amount of wear on the block test pieces K and J. Specifically, the depth (in microns) of the wear marks on the block test pieces K and J is used as an index.
In Figure 1, the lower part is a ring-shaped rotating test piece A.
〜I shows the wear amount, specifically rotating test piece A〜
The weight loss (unit: milligrams) is expressed using the wear loss of I as an index.

From the test results shown in Figure 1, when the mating material is block test piece K made of silicon nitride sintered body, the alumina titania powder is 40 to 80%, and the chromium oxide is 20%.
Assuming specimens C, D, and E have a composition of ~60%,
In other words, if the sprayed metal contains the three components of alumina, titania, and chromium oxide, the amount of wear on the block test piece K made of silicon nitride sintered body, which is the mating material, will be 5~
It can be seen that it is extremely small at around 6.5 microns.

Furthermore, it can be seen that the wear amount of the block test piece K made of silicon nitride sintered body is the lowest in the test piece D, which has a composition of 60% alumina titania powder and 40% chromium oxide.

On the other hand, block test piece J whose counterpart material was made of alloy cast iron
If the alumina titania powder is 40~80
%, even if the specimens D and E have a composition of chromium oxide of 20 to 60%, that is, the sprayed metal is alumina,
Even though it contains three components: titania and chromium oxide,
It can be seen that the amount of wear of block test piece J, which is the mating material, is extremely large, around 14.9 microns and 14.8 microns.

Examples will be explained below.

A piston ring of the present invention was manufactured, which comprises a piston ring main body 1 made of spheroidal graphite cast iron and a sliding layer 2 formed on its outer peripheral surface by plasma spraying, as shown in FIG.

Alumina and titania composite powder as sliding layer 2
Two types of piston rings were manufactured: one with 60% chromium oxide, one with 40% chromium oxide, and one with 40% alumina/titania composite powder and 60% chromium oxide.

The thickness of the sliding layer of this piston ring is 0.10~
It is 0.15mm. Further, the porosity of the sliding layer is 5%. These sliding layers are made by thermally spraying the above-mentioned mixed powder onto the outer peripheral surface of the piston ring body, and then applying the usual grinding process.
It is wrapped to give a surface roughness of 0.5 to 2.0 microns. These two types of piston rings were installed in different diesel engines, and durability tests were conducted using actual engines.
The diesel engine used was a 4-cycle, 4-cylinder engine with a displacement of 2188 c.c., a cylinder hole diameter of 90 mm, and a stroke of 86 mm, and the cylinder bore was made of a silicon nitride sintered body manufactured by a hot pressing method. In addition, the test conditions are engine rotation speed
5200 rpm full load, using light oil as fuel,
A 500 hour durability test was conducted.

In this durability test, both types of piston rings operated well, and the amount of wear on the piston rings was extremely small. Further, almost no wear was observed in the cylinder bore made of the silicon nitride sintered body, which was the mating material, and no vertical scratches called scuffing were observed at all.

This durability test proved that the piston ring of the present invention has sufficient durability as a piston ring for an engine whose cylinder bore is made of ceramics, and is less aggressive to mating materials, making it an excellent piston ring. .

[Brief explanation of drawings]

Figure 1 is a bar graph showing the results of the friction test, Figure 2 is a bar graph showing the results of the friction test.
The figure shows a cross-sectional view of a piston ring obtained in an example of the present invention. In the figure, reference numeral 1 indicates a piston ring body, and 2 indicates a sliding layer.

Claims (1)

[Scope of Claims] 1. A piston ring consisting of a metal piston ring body and a sliding layer formed on the sliding surface of the piston ring body, wherein the sliding layer is a thermally sprayed coating of alumina, titania, and chromium oxide. Made of gold, 40-80% by weight of alumina and titanium, balance 20%
A piston ring for ceramic bores that contains up to 60% by weight of chromium oxide and is characterized by low aggressiveness to cylinder bores made of ceramic sintered bodies.