JPS6316463B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a cam for a camshaft of an internal combustion engine and a method for surface treatment thereof. (Prior art) As a surface hardening treatment for the cam surface of a cast iron camshaft for an internal combustion engine, an alloy is added and a remelting hardening treatment, so-called alloy addition remelting treatment, is performed to form an alloy chill layer on the cam surface. . (Problems to be Solved by the Invention) Since the cam surface provided with such an alloy chill layer has high hardness, if the polished surface is used as it is, unless the surface roughness is extremely good, During the initial operation of the engine, damage may be caused to the sliding surfaces of the other rocker arm, tappet, etc. Therefore, salt bath nitriding treatment is performed on cast chill cams to form a nitrided layer on the cam surface, but in the case of alloy-added remelt cams as described above, the salt bath nitriding treatment results in even higher hardness. It does not necessarily improve initial conformability. The object of the present invention is to provide a cam for an internal combustion engine camshaft, which improves the initial conformability of an alloy-added remelt cam compared to an untreated surface, and prevents damage to the mating sliding surface during initial operation. The present invention also provides a surface treatment method for the same. (Means for Solving the Problems) In order to solve the above-mentioned problems and achieve the objects, the present invention provides an alloy chill layer 8 by adding an alloy to the cam 2 surface of the cast iron camshaft 1 and subjecting it to remelting hardening treatment. After polishing the 8 surfaces of the chilled alloy layer, the polished surface 9 is homo-treated to form an iron tetroxide film layer 10 on the chilled alloy layer 8 to impart initial conformability. The method is characterized in that a cam 2 of a camshaft 1 of an internal combustion engine is obtained. (Function) On the alloy chill layer 8 formed on the cam 2 surface of the cast iron camshaft 1 of the internal combustion engine, an iron tetroxide coating layer 10 having a slightly lower hardness than the chilled alloy layer 8 is further formed by homogenization. Since the iron tetroxide film layer 10 sometimes comes into sliding contact with the sliding surface of the rocker arm, tappet, etc. on the other side, the initial conformability is better than when the alloy chill layer 8 comes into direct sliding contact, and the sliding surface of the other side Protection can be achieved. (Example) An example will be described below based on the attached drawings. As shown in FIG. 1, a cam 2 installed on a cast iron camshaft 1 of an internal combustion engine has a cam portion 4 that bulges out from a base circle 3. A cam top portion 6 with a small radius of curvature is provided between the tip portions of the portions 5, 5. In the cam 2 forming such a cam profile,
In the embodiment, the surface of the cam part 4, which has a high surface pressure during use, is rough-cut by cam turning, cam milling, cam grinding, etc., and the rough-cut surface 7 of the cam part 4 is subjected to alloy addition remelt treatment. Specifically, as shown in FIG. 2, the shaft end of the camshaft 1 is supported by a chuck 21 and a center 22, the camshaft 1 is rotated by a motor 23, and a plasma torch 24 is placed above one cam 2 on the camshaft 1. The nozzle 25 is faced while maintaining a clearance. As shown in FIG. 3, the nozzle 25 has a chip 27 disposed inside a hollow shield cap 26, a shield gas passage 28 such as an inert gas is provided between the shield cap 26 and the chip 27, and argon (Ar) gas is provided at the center of the chip 27. A working gas passage 29 such as gas is provided, an electrode 31 made of tungsten or the like is provided in the working gas passage 29, and metal powder introduction pipes 32, 32 are connected to the passage 2.
Intersect with the extension line of the 9th axis. plasma torch 2
4 is supported by a holder 36 provided on a base frame 35 so as to be movable up and down, and the base frame 35 is movable by a motor 38 via a feed screw 37. By reciprocating the cam part 4 and in conjunction with the rotation of the camshaft 1, a meandering processing locus a as shown in FIG. 4 is formed on the rough-cut surface 7 of the cam part 4. In addition, in FIG. 2, 41 is a control device, 42 is a power supply,
43 is a metal powder supply device, 44 is an ultrasonic vibration device, and 45 is a valve. In this way, the rough-cut surface 7 of the cam portion 4 is subjected to an alloy addition remelt treatment by supplying alloy powder into a plasma arc, thereby forming an alloy chill layer 8 on the rough-cut surface 2 . Then, the surface of the cam 2 including the 8 surfaces of the chilled alloy layer is polished with a rotating grindstone, and the camshaft 1 is placed in a homo furnace.
, turn on electricity, introduce steam, and perform homogenization. As a result of this homo treatment, the polished surface 9 becomes as shown in Figure 1.
An iron tetroxide (Fe ₃ O ₄ ) film layer with a thickness of about 1 to 5 μm, a so-called homo layer 10, is formed on top and cooled. This homo layer 1
0, that is, the Fe ₃ O ₄ film layer is an alloy chill layer 8 as is known.
It has a slightly softer hardness (approximately HmV500) than that of the alloy, and the adhesion between the chilled alloy layer 8 and the homogeneous layer 10 is extremely good and dense. This is because Cr and Mo contained in the chilled alloy layer 8 are also contained in the Fe ₃ O ₄ coating layer 10, and Cr and Mo are contained in the boundary between both layers 8 and 10. Incidentally, the alloy chill layer 8 may be formed on the entire surface of the cam 2, or may be formed only on the cam top portion 6 where the surface pressure is highest. In the above, the homo processing conditions include cam 2
After polishing the surface, the camshaft 1 was heated to a temperature of 550 in the furnace.
Place in a homogenizer at ℃ and perform homogenization for 45 minutes.
As a result, the iron tetroxide film layer 10 having a hardness of about HmV500 is formed as described above. The present invention and the conventional method will be compared below. First of all, the material of the camshaft is as shown in the following table.
On the FC30, the surface of the Rocker arm is HCr (hard chrome) plated. The test piece was the cam of the present invention, which was made by applying alloy addition remelt treatment to FC30 and then homo treatment.
The test piece is a conventional cam made by remelting FC30 with alloy addition and salt bath nitriding, and the test piece is a conventional cam made by simply remelting and salt bath nitriding.

【table】

[Table] The following table shows the conditions for carrying out the alloy addition remelt treatment, homo treatment, salt bath nitriding treatment, and HCr plating treatment, as well as the layer thickness and hardness formed by each treatment.

[Table] In the above, the powder particle size used in the remelting process, powder supply amount, gas introduction rate, plasma generation conditions, water vapor introduction amount in the homoprocessing, nitriding bath composition, electrolytic plating composition, and electrolytic conditions are as listed below. . 1 Powder particle size used in remelt treatment 5~
200μ (average particle size 50μ) 2 Gas introduction speed (The supply speed of the powder itself is not measured, but it is introduced into the Ar gas as a carrier gas, so the gas introduction speed is shown) 3
~20m/sec ・8m/sec in the example 3 Powder supply rate 0.5~3.0g/min ・1.0g/min in the example 4 Same plasma generation conditions Plasma current 30~200A ・120A in the example Plasma voltage 20~40V・ 30V in the example Plasma gas amount (Example) 1/min Plasma torch speed (Example) 0.5 m/min 5 Homo processing conditions Furnace pressure 10 mm H ₂ O or more Steam introduction amount (water dripping) 10 to 30/hour ・ Implementation In the example, the camshaft after polishing the cam surface is placed in a homogenization furnace with a furnace temperature of 550°C, subjected to homogenization treatment for 45 minutes, and then cooled with forced air. Forced air cooling 70 to 200°C/min - 80°C/min in the example During forced air cooling, the temperature in the furnace is set to 150°C or higher to prevent condensation. 6 Salt bath composition of salt bath nitriding (LCN)

[Table] * Treatment by continuously injecting air into a salt bath 7 Electrolytic plating composition ・ Composition (aqueous solution) Chromic anhydride (CrO ₃ ) 250g/ Sulfuric acid (H ₂ SO ₄ ) 2.5g/ ・ Conditions Liquid temperature 45~ 50℃ (Example 50℃) Current density 50-70A/dm ² (Example 60A/d
^m2 ) Next, using the three types of test pieces mentioned above, determine the displacement
Figures 5 and 6 show the results of a motoring test using an 1800 c.c. internal combustion engine using an oil mixture containing 3% water. In other words, for 50 hours of durability, the conventional test piece had cam wear of 0.37mm and Rocker arm wear of 20μ, while the same test piece had cam wear of 0.25mm and Rocker arm wear of 20μ.
80μ and galling occurs,
It is understood that according to the test piece according to the present invention, the amount of cam wear was kept to a significantly low level of 0.09 mm and the amount of rocker arm wear was kept to a significantly low level of 0.09 mm. In this way, when comparing the hardness of cams obtained by alloy addition remelt treatment + salt bath nitriding treatment and cams obtained by alloy addition remelt treatment + homo treatment, the hardness of the cam obtained by homo treatment (approximately
The hardness of the cam produced by salt bath nitriding treatment (approximately HmV 700 to 800) is clearly higher than that of cams treated with salt bath nitriding (HmV 500).
This also causes wear and galling on the cam. However, according to the homo-processed cam according to the present invention, the initial conformability can be improved because the cam does not have enough hardness to significantly wear out the mating rocker arm. By the way, the reason why the homo layer 10 is set to 1 to 5μ is that
If it is less than 1μ, wear will progress and the homolayer will disappear before initial break-in is achieved, and the intended initial break-in may be insufficient, and if it exceeds 5μ, the homolayer will tend to peel off, which is undesirable. It's for a reason. Next, the cam surface of the camshaft was homo-treated after alloy addition remelt treatment, and the Rotsuker arm was
A supplementary note regarding the case of HCr plating treatment. When a cam surface that has been subjected to alloy addition remelt processing is processed with a finishing whetstone, microscopically high hardness metal remains on the cam surface, creating an uneven surface with a surface roughness of approximately 3S. When the homogeneous treatment is applied, an iron tetroxide film is formed to fill the uneven surface, and although the coefficient of friction (μ) decreases, the surface roughness becomes approximately 15S. However, after the initial break-in with the other Rotsuker arm, the surface roughness improves dramatically, reaching approximately 0.3S. In other words, the dense laminate (HOMO layer) of iron tetroxide (Fe ₃ O ₄ ) film comes into contact with the rocker arm and acts as a granular abrasive, and its abrasive action creates a surface lap, which improves the surface of the alloy cam surface. Improves roughness and reduces wear. Thereafter, sufficient surface roughness will be permanently maintained. On the other hand, if there is any galling during the initial break-in, the Rotsuker arm side will be damaged, which will damage the cam surface. In addition, since the iron tetroxide (Fe ₃ O ₄ ) film is densely porous, it is also excellent in terms of oil retention. (Effects of the Invention) As described above, according to the present invention, an iron tetroxide coating is further applied to the chilled alloy layer formed on the cam surface of a cast iron camshaft for an internal combustion engine to impart initial conformability through homogenization. Since the layer is formed, the initial conformability of the alloy-added remelt cam can be improved compared to an untreated surface with only a mere alloy chill layer, and therefore damage to the mating sliding surface can be prevented.

[Brief explanation of the drawing]

Fig. 1 is an explanatory front view of the cam, Fig. 2 is a schematic configuration diagram of the remelting and hardening processing device, Fig. 3 is a vertical cross-sectional view of the plasma torch nozzle, and Fig. 4 is a perspective view of the cam showing its processing trajectory. , FIG. 5, and FIG. 6 are data diagrams showing the relationship between the amount of cam wear and the amount of rocker arm wear based on the test results comparing the initial run-in properties between the embodiment and the conventional method. In the drawings, 1 is a cast iron camshaft, 2 is a cam, 8 is an alloy chill layer, 9 is a polished surface, and 10 is an iron tetroxide film layer.

Claims (1)

[Scope of Claims] 1. A chilled alloy layer formed by adding a remelted alloy and an iron tetroxide film layer for imparting initial conformability to the chilled alloy layer are formed on the cam surface of a cast iron camshaft. Cam of the camshaft of an internal combustion engine. 2. Adding an alloy to the cam surface of a cast iron camshaft and performing a remelting hardening process to form a chilled alloy layer; Polishing the surface of the chilled alloy layer; Homo-processing the polished surface to form the chilled alloy layer. A method for surface treatment of a cam of a camshaft of an internal combustion engine, comprising: forming an iron tetroxide film layer to impart initial conformability to the layer;