JPH04228548A - Sliding means for valve gear mechanism - Google Patents

Abstract

PURPOSE:To provide a sliding means for valve gear mechanism having superior wear resistance and excellent in durability. CONSTITUTION:In the sliding member for valve gear mechanism where hard phases are dispersed in a matrix phase of a sliding surface layer, the size of the grains of the above hard phases, average grain spacing, and visual field space factor are set at 4-15mum, 5-15mum, and 10-50%, respectively.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a cam or a rocker arm (its sliding contact surface with the cam) that is in sliding contact with a cam, a valve mechanism, and a valve mechanism for an internal combustion engine.
This invention relates to a sliding means for a cam sliding member such as a lifter.

0002

[Prior Art] In the valve mechanism of an internal combustion engine designed to achieve high output and high speed, large surface pressure is applied to the cam and the cam sliding member, causing the cam to come into sliding contact at high speed. Even if lubricating oil is supplied between the cam sliding member and the cam sliding member to lubricate the space between the two, high wear resistance is required. For this reason, conventionally,
The sliding means is made of forged steel, cast steel, alloyed cast iron, etc., and the sliding surface is subjected to surface treatments such as surface hardening by heat treatment, carburizing and quenching, chill hardening, and hard Cr plating. However, carburized and quenched materials have scuff resistance (note: scuff is
Chill hardened materials have poor durability, and hard Cr plating materials may peel off due to local contact or wear and tear. Each has its own problems.

[0003] In an attempt to solve this problem,
Japanese Patent Publication No. 59-7003, Japanese Patent Publication No. 60-63350
There was something described in the issue. Said Special Public Service 1987-7
003 discloses a cast iron cam whose sliding surface is made of pearlite and contains 30 to 45% carbide, and whose sliding surface is made of iron and has a base hardness of HV 250 to 6.
50, the volume ratio of the hard phase is 5-35%, HV 8
The hard phase of 80 to 1800 μm accounts for 65% or more of the total hard phase, the hard phase of 5 to 150 μm in size accounts for 80% or more of the total hard phase, and the porosity is 10% or less and 1250 μm or more.
P. which produces liquid phase sintering at a sintering temperature of °C. It is combined with a cam sliding member made of a sintered alloy containing 0.2 to 5% by weight of one or more elements such as B. In addition, in the cam sliding member that is in sliding contact with the cam described in JP-A No. 60-63350, the cam sliding member is made of a specific carbide.
A carbide-based sintered alloy is formed from a 60% (by weight) hard layer and the remaining bonding layer made of an iron group metal containing a specific element, and the hard layer has an average particle size of 0.5 to 10 μm. and the sintered alloy is dispersed with HV
It is formed to have a hardness of HV 500 to 1200, preferably HV 600 to 1000.

0004

[Problem to be solved] However, the publications described in the above-mentioned gazettes and published publications focus only on the hardness, volume ratio, size, and average particle diameter of the hard phase, which have a large effect on wear resistance. However, there was no consideration given to how to manage the lubricating oil existing between the cam and the cam sliding member, and how to achieve lubrication between the two. Abrasion resistance could not be obtained.

[0005]

[Means and operations for solving the problems] The present invention describes how the sliding surfaces of the cam and the cam sliding member wear out, and in relation to this, how the lubricating oil between the sliding surfaces is distributed. The invention was made with an eye to whether the hard phase contributes to lubrication, and in a sliding means of a valve mechanism in which a hard phase is dispersed in the base phase of the sliding surface layer, 80% or more of the hard phase The hard phase has a size of 4 to 15 μm, the hard phase is dispersed at an average particle spacing of 5 to 15 μm, and the hard phase has a viewing area ratio of 10 to 50%.

When the sliding contact portion of the cam or cam sliding member wears, the base phase is more easily worn than the hard phase, the surface of the base phase is depressed from the surface of the hard phase, and the lubricating oil layer on the surface of the base phase is Although it is thicker than the lubricating oil layer on the surface, in the present invention, since the size of the hard phase, the average particle spacing, and the viewing area ratio are set as described above, it does not matter what shape the particles of the hard phase have. However, the lubricating oil in the thick lubricating oil layer on the surface of the base phase flows in the same direction due to the sliding of the cam surface, flows into the thin lubricating oil layer on the hard phase surface, and the lubricating oil in the thick lubricating oil layer on the surface of the base phase flows in the same direction as the cam surface slides. Sufficient lubrication is provided to the sliding contact surface of the mating member, and wear is suppressed as much as possible not only on the hard phase surface of the cam sliding member but also on the hard phase surface of the cam. By sufficiently bearing the pushing load of the cam, the pushing load of the cam applied to the base phase is reduced, the amount of wear of the base phase is also suppressed, and the durability of the cam sliding member and the cam is significantly improved.

[0007] It should be noted here that simply specifying these factors does not mean that they have been specified in the original sense; the method for measuring the form of existence of carbides must be clearly defined. be.

[0008] Therefore, the measurement method adopted by the present inventors is as follows. ■ Size of carbide (particle diameter): JI
S-G-0552 “Steel ferrite grain size test method”
This is an application of the cutting method used in 2007, in which the cut cross section of the sample is polished and corroded, and the corroded surface is observed with a microscope or photographed using a microscope, and two orthogonal lines of a certain length are drawn. From the total number and length of carbide particles cut in minutes, the average particle diameter is determined by the following formula.

[0009]

[Equation 1] Sum of cutting lengths of each particle by line segment/Number of particles = Average particle diameter

[0010] In the case of carbide particles that are only partially cut at both ends of a line segment, only one of them is counted, and if the carbide particles that are not cut are only at one end of the line segment, they are not counted. Further, the magnification of the microscope is selected so that the number of carbide particles cut by one line segment is at least 10 in one field of view, and the measurement is performed in multiple fields so that the total number of carbide particles is 50 or more. Measurement example: According to Figure 1,

[
0011

[Equation 2] Average particle diameter = d1 + d2... + d7 / 7

[
[0012] ■ Average particle spacing of carbide: according to the above section (■),
The average value of the distance between adjacent carbide particles cut by two orthogonal line segments of a certain length is determined by the following equation.

[0013]

[Equation 3] Sum of interparticle spacing length/number of interparticles = average particle spacing

[0014] When both ends of the line segment each cut a part of the carbide particle, the length between only one carbide particle and its adjacent particle is counted, and only one end of the line segment cuts a part of the carbide particle. When cutting a part of the particle, the length between the particle and the adjacent particle is not taken into account. In addition, the magnification of the microscope is selected so that the number of intervals between carbide particles cut by one line segment is at least 10 in one field of view, and multiple fields of view are measured so that the total number of intervals is 50 or more. . Measurement: According to Figure 1, it is as follows.

[0015]

[Equation 4] Average particle spacing = l1 + l2 +... l5 /5

[0016] Amount of carbide (viewing area ratio): The cut cross section of the sample was polished and corroded, the corroded surface was photographed using a microscope, and the viewing area ratio was calculated using the line segment method shown in Figure 2. demand. A rectangular field of constant area is determined, parallel scanning lines 1 are drawn at a predetermined interval length (d0) corresponding to the size of the carbide particles, and the lengths of the lines of intersection with each carbide particle 2 are determined as l1 and l.
2,...ln, and the length of the scanning line 1 is L, the visual field occupation area ratio is determined by the following equation.

[0017]

[Formula 5] (l1 l2...ln) x d (total area of carbide particles)/L x d0 x (m+1) (visual field area) = visual field occupation area ratio (however, m is the number of scanning lines 1)

0
Note that this method can also be executed by an image analysis device.

Test Example A piece (sliding member) to be attached to the cam sliding surface of the rocker arm and a cam were prepared by the following methods (1) and (2).

■The target composition of the sliding member is C-2.
．． 5%, Cr-17.0%Mo
−3.0%, W −0.
13%V - 0.15%, Mn
- 0.3%Sn - 0.8%,
P - 0.25% Ni - 3.0%
, Fe - balance (all above, weight%), 250 to 350 mesh powder is 15 to 25
Volume % Fe-C-Cr-Mo-W-V-Mn-
C, Fe-Ni alloy, and Fe-P alloy powders were added to the Sn alloy powder, mixed and compressed, and then compressed in vacuum or in an ammonia gas atmosphere at a temperature of 1190°C for 6 hours.
Sintering was performed under conditions of 0 minutes.

Next, the sintered product was brazed to the sliding surface of the rocker arm against the cam, and then carburized, quenched, tempered, and polished to obtain a sliding member A. After the sintered product is brazed to the rocker arm's sliding surface against the cam, it is carburized and quenched, tempered, polished, and then salt bath nitrocarburized (temperature
580° C. for 70 minutes) to obtain a sliding member B. The hardness of the base phase of sliding member A is HV 600 to 900,
The carbide hardness was HV 1,000 to 1,300, and the density was 7.65 to 7.70 g/cm3. Further, when the existence form of carbide in the sliding member was investigated by the above-mentioned measuring method, the average particle diameter was 4.5 μm, the average particle spacing was 11 μm, and the visual field occupation area ratio was 30%. The sliding member obtained by sintering has hard metal carbide dispersed in the base phase of martensite, and in addition to improving its own wear resistance, the type, amount, size, and
Appropriate selection of the dispersion state can reduce wear on the mating cam.

The reasons for adding each element are as follows. C
r strengthens the base phase and reacts with C to form a hard carbide, improving wear resistance. However, if the amount added is less than 5% by weight, the required hardening cannot be expected;
If it is added in excess of this amount by weight, the mating cam is likely to be worn out, resulting in a large total amount of wear, as well as disadvantages such as a marked decrease in sinterability. Like Cr, Mo strengthens the base phase and reacts with C to form hard carbides, thereby improving wear resistance. However, if the amount added is less than 1% by weight, the desired effect cannot be obtained, and if it is added in excess of 5% by weight, the material becomes brittle. Both W and V react with C to form an MC type (where M represents the symbol of a metal element) hard carbide, contributing to improvement in wear resistance. If the amount of at least one of the two components added is 0.1% by weight or more, the desired effect will not be obtained, and if the amount added exceeds 4% by weight, machinability will decrease and the mating material will be likely to wear. Become. Sn is
It diffuses into a solid solution in the base phase and has the effect of suppressing austenitization caused by Ni. If the amount added is less than 0.2% by weight, no effect will be observed, and if it is added more than 5% by weight, the carbide particles will become coarser, reducing mechanical strength and deteriorating wear resistance. Ni strengthens the base phase and prevents carbides from falling off. It also has the effect of improving sinterability and improving compatibility with the mating cam. Additionally, 5 without Sn
If added in excess of 5.5% to 10% by weight, an austenite phase will be formed in the base phase and the wear resistance will decrease, but if the Sn content is within the above range, good wear resistance can be achieved with an addition amount of 5.5 to 10% by weight. Show your gender. C strengthens the base phase and C
r, reacts with other additive components to precipitate a hard phase and improve wear resistance. However, if it is less than 1% by weight, the desired effect cannot be obtained, and if it exceeds 4% by weight, the toughness will decrease. P and B are elements that have the effect of promoting sintering and increase the density of the sintered member, and at least one of them may be added. If the amount added is less than 0.05% by weight, the desired effect cannot be obtained, and if it is added in excess of 5% by weight, an excessive liquid phase is generated during sintering, resulting in a large dimensional change rate, which is not preferable.

■ A cam made of JIS G5501-FC30 (gray cast iron) was prepared. This cam is chilled over an angular range of ±90 degrees around the cam nose, and the surface layer of the cam over an angular range of ±30 degrees around the cam nose is chilled using a plasma torch. Then, 1.5% by weight of Cr powder and 1% by weight of Mo powder were added to the molten pool, followed by rapid cooling by self-cooling. The obtained cam 3 is shown in FIGS. 3 and 4 (in the figures, 4 indicates the cam nose, 5 indicates the chill layer, and 6 indicates the remelted hardened layer). The hardness of chill layer 5 is H
R 45, and the hardness of the remelt hardened layer 6 was HR 60. In addition, C added to the molten pool during remelting hardening treatment
R powder and Mo powder are carbide stabilizing elements, and V and Hb also have similar functions. These elements are
It can be added in the form of a single powder, an alloy powder of them, or a compound powder of carbon or the like. However, if the amount of carbide stabilizing elements added is less than 0.5% by weight, the amount of carbide in the re-melt hardened layer will be small and a significant improvement in wear resistance cannot be expected; Even if
It has little effect on improving wear resistance and is economically disadvantageous.

■ Using a plurality of cams 3 obtained in the above section (■), and preparing a plurality of sliding members A with different carbide presence states obtained by the same method as in the above section (■), each sliding member A and the cam is incorporated into an internal combustion engine, 2000 rpm, 30
After 0 hours of operation, the amount of wear on the sliding member and cam was examined for each combination, and the results are shown in FIGS. 5 to 7. In addition, sliding member B was similarly installed in an internal combustion engine and operated at 6000 rpm for 400 hours.
The amount of wear was investigated and compared with the amount of wear of sliding member A.
Shown in the figure.

■Figure 5 shows sliding member (rocker arm) A
This figure shows the influence of the particle size of carbides contained in the structure of the steel on the amount of wear. According to Fig. 5, when the average particle size of carbide exceeds 15 μm, the amount of cam wear increases rapidly, and when the average particle size is 4 μm or less, it is difficult to measure the particle nature, and within this range, the amount of cam wear increases. There is a tendency to increase. In addition, the amount of wear of sliding member A is determined by the average particle diameter of carbide being 6 μm.
Although it tends to increase slightly when exceeding m, it remains almost constant. Therefore, the average particle diameter is 4 when the amount of wear on the cam is 7 to 27 μm and the amount of wear on the sliding member A is 6 to 17 μm.
It is desirable to select a particle size in the range of 15 μm to 15 μm, and if 80% or more of the carbides have a particle size of 4 to 15 μm, the particle size falls within this range.

■Figure 6 shows sliding member (rocker arm) A
This figure shows the influence of the average particle spacing of carbides contained in the structure of the steel on the amount of wear. According to FIG. 6, when the average particle spacing of carbide exceeds 15 μm, the amount of wear on the sliding member A increases, and when the average particle spacing exceeds 20 μm, the amount of wear on the cam increases, causing the scuffing phenomenon. Furthermore, if the average particle spacing is less than 5 μm, the strength of the base phase in the sliding member A decreases, cracks occur, and cam wear tends to increase. Therefore, the average particle spacing is 5 when the amount of wear on the cam is 9 to 19 μm and the amount of wear on the sliding member A is 5 to 16 μm.
It is desirable to select a range of ~15 μm.

■Figure 7 shows sliding member (rocker arm) A
Fig. 8 shows the influence of the visual area occupied area ratio of carbides contained in the structure on the amount of wear, and Fig. 8 shows the relationship between the area ratio of the carbide viewed area occupied and the amount of wear of sliding members A and B. There is. According to FIGS. 7 and 8, it can be seen that as the visual field occupation area ratio increases, the amount of wear on the cam increases almost linearly, and the amount of wear on the sliding member decreases almost linearly. Also,
If the viewing area ratio exceeds 50%, cracks are likely to occur during heat treatment, so it is desirable to keep the viewing area ratio below. If the visual field occupying area ratio is less than 10%, the effect of carbide cannot be expected, so the visual field occupying area ratio is 1
It should be 0% or more. Therefore, the amount of cam wear is 12
~14.4μm, the amount of wear on the sliding member is 3.7~11
．． It is desirable to select a field area ratio of 10 to 50%, which is 0 μm. Further, by performing salt bath soft nitriding treatment, the amount of wear can be further reduced.

Further, Examples 1 to 4 in which the particle diameter of the carbide, the average particle interval of the carbide, and the ratio of the viewing area occupied by the carbide of the cam sliding contact piece which is the first sliding member were variously changed, and the present example The amount of wear compared to the comparative example that does not correspond to the above is as follows.

[0029]

[Table 1]

[Brief explanation of the drawing]

[Figure 1] Diagram showing a method for measuring the average particle size of carbides contained in the alloy base phase

[Figure 2] Diagram showing the method of measuring the average interparticle distance as well

[Figure 3] Cross-sectional view of a cast iron cam whose surface has been remelted and hardened

[Figure 4] Cross-sectional view along the IV-IV line

[Fig. 5] Graph showing the relationship between the average particle diameter of carbide and the amount of wear of the cam and sliding member (rocker arm) A

[Figure 6] Carbide average particle spacing, cam and sliding member (rocker arm) A
Graph showing the relationship between the amount of wear and

[Fig. 7] Graph showing the relationship between the visual field occupation area ratio of carbide and the amount of wear of the cam and sliding member (rocker arm) A

[Fig. 8] A graph showing the relationship between the visual field occupation area ratio of carbide and the cam and sliding members (rocker arms) A and B in contrast.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Scanning line, 2...Carbide particles, 3...Cam, 4...Cam nose, 5...Chill layer, 6...Remelting hardening treatment layer.

Claims (1)

[Claims] Claim 1: In a sliding means of a valve mechanism in which a hard phase is dispersed in a base phase of a sliding surface layer, 80% of the hard phase
The above particles have a size of 4 to 15 μm, the hard phase is dispersed with an average particle spacing of 5 to 15 μm, and the hard phase has a visual field occupation area ratio of 10 to 50%. sliding means.