JPH049623B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method of manufacturing a rocker arm suitable for manufacturing a rocker arm which is a valve train component of an automobile engine. (Prior Art) Conventionally, a rocker arm, which is a valve train component of an automobile engine, has a structure as shown in FIG. 1, for example. The rocker arm 1 shown in the figure is provided with a pad 3 on the surface of the rocker arm body 2 that contacts the cam.Since superior wear resistance is required on the surface that contacts the cam, the pad is formed from a separate material. 3 was used. When manufacturing such a rocker arm 1, a rocker arm pad 3 as shown in FIG. 2 is manufactured by sintering, casting, etc. using a hard metal, and then the rocker arm pad 3 is manufactured as shown in FIG. As shown, the rocker arm 1 is formed by disposing it at a predetermined position in the mold 4 and supplying molten aluminum alloy under pressure from the runner 5 of the mold 4 to enclose the pad 3 using a die-casting method. I was doing it. However, in such conventional cases, peeling tends to occur at the cast-in interface with the pad 3 while the rocker arm 1 is in use, so as a countermeasure, the pad 3 is separated as shown in Fig. 2. A reverse taper part 3a was provided in the cast-in part, but even if such a reverse taper part 3a is provided, loosening is likely to occur, vibration and wear increase, and the expensive pad 3 is not provided with the reverse taper part 3a. There was a problem in that the amount of material used increased due to the provision of a 2-way line, which also led to an increase in costs. On the other hand, in recent years, the development of fiber-reinforced metals has progressed, and their application to wear-resistant parts is progressing (for example,
(Japanese Patent Publication No. 55-24763, Japanese Patent Publication No. 58-93948). As a method for manufacturing this fiber-reinforced metal, there is a manufacturing method shown in FIG. 4, for example. In this method, a water-permeable filter 7 is installed at the bottom of a suction container 6. First, a short fiber dispersion slurry 8 containing an organic/inorganic binder is prepared, and then this slurry 8 is put into the suction container 6. The slurry 8 is sucked by a vacuum suction method and only the liquid is passed through a filter 7, and a fiber molded body 9 is produced on this filter 7. Further, the fiber molded body 9
After drying, it is processed into a predetermined size and heat-treated to remove the organic binder.Then, as shown in FIG. There is a method of manufacturing composite materials by supplying molten aluminum alloy using a high-pressure solidification method. However, in such conventional methods, since a vacuum forming method is used to produce the fiber molded body 9, it is difficult to obtain a fiber molded body with a volume percentage of 10% or more from the viewpoint of suction force during vacuum forming. This was a problem. In addition, press molding is sometimes used to increase the volume fraction, but in this case there are problems such as fiber cutting and spring back.
It was difficult to mold. Even when such fiber-reinforced metals with a low fiber volume fraction are used, the wear resistance is improved to some extent, but it is not suitable for parts that are subject to severe wear conditions. For example, when it comes to wear on the Rocker arm pads and camshafts, the surface pressure is calculated from the Hertz's surface pressure formula using the current materials, and the maximum
60Kgf/cm ² , and the circumferential speed also varies depending on the engine speed, but 0 to 75m/sec (at 5000RPM)
At circumferential speeds in the range of , complex and severe wear conditions occur where both surface pressure and circumferential speed change continuously. Therefore, conventional composite materials such as short fiber-reinforced metals are not suitable as wear-resistant parts used under the severe wear conditions mentioned above, and composite members with new wear-resistant properties are required. .
In addition, in the conventional high-pressure casting method using a fiber molded body, the compressive strength of the fiber molded body is insufficient, and the fiber molded body deforms and cracks due to the penetration resistance of the molten alloy during high-pressure casting. There was a problem that a fiber volume fraction and uniform dispersion of fibers could not be obtained. (Purpose of the Invention) This invention was made by focusing on the various problems of the prior art as described above, and has excellent wear resistance at the contact surface with the cam, and is particularly suitable for use under severe wear conditions. It is an object of the present invention to provide a rocker arm that can withstand use sufficiently and has extremely low risk of deformation or cracking at the contact surface with a cam. (Structure of the Invention) The present invention uses a molten metal forging device equipped with a mold having a cavity in the shape of a Rocker arm, and injects particles with an average particle size of 20 μm or less into the cavity at a position corresponding to the contact surface with the cam of the Rocker arm. After arranging a rocker arm pad made of a porous ceramic sintered body having a volume fraction of 30 to 60%, a molten light alloy is cast at high pressure into the cavity of the mold by molten metal forging. Then, the molten light alloy is infiltrated and solidified into the gap of the rocker arm pad made of the porous ceramic sintered body, and the light alloy is applied to the contact surface with the cam of the rocker arm body formed by forging the molten light alloy. The present invention is characterized by a structure in which a rocker arm is integrated with a rocker arm pad made of a porous ceramic sintered body that is continuously infiltrated with the rocker arm body. Next, this invention will be explained in detail. First, regarding this invention, the porous ceramic sintered body used as the rocker arm pad is made of non-oxide ceramic materials such as silicon nitride and silicon carbide, and oxide-based ceramic materials such as zirconia and alumina. Depending on the specifications, for example, alumina is an excellent material as it is hard and inexpensive. Moreover, among aluminas, α-alumina, which is particularly hard, is good. In addition, as for the characteristics of the raw material powder, the particle shape should be close to spherical in order to reduce the surface area, improve wetting characteristics with molten light alloys such as aluminum alloys, and provide uniform contact bonding points within the sintered body. . The finer the grain size of ceramics such as alumina, the better from the viewpoint of wear resistance. However, as the average particle size of ceramics decreases, the surface area of ceramics increases accordingly.
During casting, the penetration resistance of the molten light alloy into the sintered body increases, making it difficult for the molten light alloy to penetrate into the sintered body, and the bonding strength at the interface between the ceramic and the light alloy tends to weaken. However, this can be countered by increasing the pressure applied to the molten alloy during casting, or by increasing the preheating temperature of the sintered body and the preheating temperature of the molten light alloy. On the other hand, the upper limit of ceramic particle size is determined by wear resistance properties, machining, etc., but as the particle size increases, sinterability deteriorates, the bond between particles deteriorates, and particles tend to fall off during wear. Galling wear is likely to occur. In addition, when the particle size becomes large, cracks are likely to occur during machining due to the tips of the tool teeth or the machining shock of the grinder, and furthermore, a level difference occurs between the ceramic particles and the light alloy base, which is necessary for the sliding surface of the pad etc. The surface roughness cannot be made sufficiently good. Therefore, various experiments have shown that it is generally desirable for the average particle diameter of ceramics to be 20 μm or less in diameter, and more preferably 5 μm or less. When manufacturing rocker arm pads made of porous ceramic sintered bodies,
In order to adjust the particle content of the ceramic, it has been found that it is preferable to add an appropriate amount of fibrous ceramics such as short ceramic fibers or whiskers, if necessary. Next, an embodiment of a method for manufacturing a rocker arm pad made of a porous ceramic sintered body will be described. There are several methods for manufacturing a rocker arm pad made of a porous ceramic sintered body mainly composed of particles of alumina, etc., such as a doctor blade method, an injection molding method, and a press molding method. One example is 1% by weight of starch and 0.5% colloidal silica as organic binders.
% by weight, and the rest is alumina ceramics, which is stirred as a slurry aqueous solution.
The molded body is produced by suction molding through a filter. At this time, the adjustment of the particle volume fraction is as follows:
This can be carried out by pressurizing and compressing the molded body to obtain an arbitrary volume ratio. Thereafter, it is sufficiently dried at, for example, about 120°C, and then fired and sintered at, for example, 1500°C in the atmosphere to obtain a sintered body. Here, the particle volume ratio is determined to ensure high wear resistance in parts where wear resistance is required, such as rocker arm pads.
For example, in the case of α-alumina sintered bodies, the average particle size is 20 μm or less, and the particle volume fraction is 30 μm or less.
It has been found from various experiments that a range of % to 60% is preferable. In this case, the particle volume fraction is 30
If it is smaller than 60%, the cam part of the camshaft (currently chilled cast iron) that is the mating material in the case of the above-mentioned Rocker arm pad will cause severe wear, and if it is larger than 60%, it will cause aggressiveness to the mating material. This is undesirable because it increases the amount of water and causes significant wear on the cam portion of the camshaft. Furthermore, the particle volume fraction
If it exceeds 60%, the penetration resistance of the light alloy molten metal during casting will increase, and the subsequent T
The solution treatment (500° C. → water cooling) during the -6 treatment causes many cracks to occur in the α-alumina bond, which is not preferable. On the other hand, as another example of manufacturing a rocker arm pad made of a porous ceramic sintered body, there is the doctor blade method as described above. In this case,
Using a stirred slurry-like aqueous solution of ceramic powder to which an organic binder etc. have been added, the ceramic slurry is supplied to a green sheet manufacturing apparatus using a doctor blade method, and the slurry is continuously flowed out through the gap between the doctor blades. It is solidified by evaporating the solvent to obtain a ceramic green sheet. Next, the green sheet is processed to a size that allows it to be set in a mold and takes into account shrinkage during sintering, and then gradually heated in a furnace and sintered at, for example, 1500°C. The volume fraction of the porous ceramic sintered body obtained in this way varies depending on the required wear resistance conditions, etc., but for example, when it is an α-alumina sintered body and is applied to a rocker arm pad, It has become clear from various experiments that in order to ensure high wear resistance, it is better to set the amount in the range of 20 to 60% by volume to meet the wear resistance conditions. In other words, if the volume ratio is smaller than 20%, the pad part will be severely worn by the cam part of the camshaft (currently made of chilled cast iron), which is the mating material, and if it is larger than 60%, the cam part of the camshaft will be worn out. This is not preferable because it becomes noticeable. Also, if it exceeds 60%, the subsequent T-6
This is not preferable since there is a risk that many cracks will occur in the joints of the α-alumina sintered bodies during treatment. Next, the rocker arm pad made of the porous ceramic sintered body sintered as described above is placed in the mold 11 of the molten metal forging apparatus shown in FIG. Here, in the molten metal forging apparatus shown in FIG. 5, the mold 11 is composed of an upper mold 12 and a lower mold 13,
A cavity 14 and a runner 15 are formed by both molds 12 and 13, and the lower mold 13 is equipped with a plunger 16. Therefore, the rocker arm pad 17 made of the ceramic sintered body is placed in the cavity 14 corresponding to the contact surface with the cam that requires wear resistance of the rocker arm 1 to be manufactured, and then the rocker arm pad 17 made of the ceramic sintered body is placed inside the sleeve. After supplying molten light alloy such as aluminum to the plunger 16 using a pressurizing device (not shown),
The molten light alloy is filled into the mold cavity 14 through the runner 15, and the pressure of the molten metal is maintained until the end of solidification, and the molten light alloy is filled into the gap between the rocker arm pads 17 made of sintered ceramics. By infiltrating and solidifying and then separating the upper mold 12 and lower mold 13, a rocker arm whose abrasion resistance of the contact surface with the cam has been significantly improved is taken out. The casting conditions for molten metal forging include a molten metal temperature of 750 to 800℃ and a plunger pressure of 500 to 800℃.
1200Kgf/cm ² , preheating temperature of rocker arm pad 17 made of porous ceramic sintered body from 200Kgf/cm 2
It is preferable to set the temperature to 300°C in order to allow the light alloy molten metal to completely penetrate into the gap in the rocker arm pad made of the porous ceramic sintered body. By doing so, a rocker arm having the following excellent features can be obtained. By using rocker arm pads made of porous ceramic sintered bodies, the compressive strength is higher than when conventional short fiber molded bodies are used because the particles are already sintered at the time of casting.
No compression fracture or cracking of the sintered body due to penetration resistance of the molten alloy. Compared to the ceramic pad material shown in Figure 2, it uses a porous sintered body with a high porosity, so it is resistant to thermal shock, and the pad does not crack when casting molten light alloy. A porous sintered body with a high porosity can also be used, so in that case, the light alloy base that has penetrated into the ceramic sintered body exists continuously, and there is no interface. There should be no peeling or peeling of the composite sintered body part. Compared to the case of using a short fiber molded article by the vacuum forming method shown in FIG. 4, it is possible to increase the ceramic volume fraction, and it is possible to apply it to a rocker arm that requires severe wear resistance. Since the ceramic particles are bonded by sintering, there is no loss of ceramic particles during use, and wear resistance is significantly improved. Compared to the case of using the pad 3 shown in FIG. 2, there is no need for a reverse tapered part 3a for cast-in,
In addition, by using a semi-finished ceramic sintered body, it can be manufactured at low cost without requiring complicated processes. Regarding the Rocker arm pad part, by simultaneously high-pressure casting the part of the particle-dispersed composite material and other parts, we were able to eliminate the nests in other parts.
Casting defects such as pinholes are reduced, heat treatment is possible compared to die casting methods, which improves strength and further reduces weight. As for the main body of the Rocker arm, since it is formed by molten metal forging, the structure is dense, there are no casting defects, and it has excellent mechanical properties. Regarding the entire Rotsuker arm, when high-pressure casting is performed using conventional shapes and materials, burrs are generated around the pads, and it takes a considerable amount of man-hours to remove the burrs.However, according to this invention, the burrs are also removed from the Rotsuker arm body. Since it is connected continuously with the pad, there is no need to deburr the area around the pad. etc. (Example 1) Here, α-alumina (Al ₂ O ₃ ) powder was used, and the average particle diameter was 0.08, 1, 5, 10, 20, 50,
Prepare 100 μm particles each with a particle volume ratio of 15,
Alumina green sheets each having a thickness of 3 mm were prepared by mixing 20, 40, 60, and 70% using the doctor blade method described above. Next, each green sheet was cut into a size that could be placed in a mold, and then fired in the atmosphere in a furnace at 1500°C to produce rocker arm pads made of α-alumina sintered bodies. Next, the rocker arm pads made of each sintered body were preheated to 300°C and individually placed in the molten metal forging mold 11 shown in FIG. By injecting and pushing out the plunger 16
The pressure was maintained at 700 Kgf/cm ² until solidification was completed. Next, the rocker arm obtained in this way was subjected to T6 treatment, and then processed into a pin shape of 5 x 5 x 10 mm. At this time, the sintered body was processed so that the end face was located, and the test was carried out. After cutting into pieces, an abrasion test was conducted using each test piece. The wear test method will be described below. First, the configuration of the device used in the test will be explained. In FIG. 6, 21 is a rotatable holder for holding the test piece 22, 23 is a holder for holding a mating disk 24, 25 is a lubricating oil supply path, and 26 is a load cell. In addition, as shown in FIG. 7, the test piece 22 has W=5×5 mm and L=
Although it was machined to a diameter of 10 mm, the end face of the composite sintered body was set to R=7 mm as a material equivalent to a rocker arm pad material. Therefore, during the test, a pin-shaped test piece 22 is fixed to one holder 21, and a disk 24 as a mating member is fixed to the other holder 23. In this evaluation, chilled cast iron, which is one of the materials commonly used in the cam portion of a camshaft, was used as the material for the disk 24. Next, the holder 21 is rotated by a motor (not shown) and at the same time the holder 23 is pushed in the right direction as indicated by the arrow. At that time, apply approximately 300 to 400 c.c. of motor oil (oil temperature 150°C) from the lubricating oil supply path 25.
The sample is supplied to the center portions of the holder 23 and the disk 24 at a rate of 10 minutes, and is sprayed outward from the center portion toward the test piece 22. In this kind of wear resistance evaluation, since the wear between the camshaft and the Rocker arm under normal conditions is particularly severe when the engine is running at low speed, a sliding speed of 1.0 m/sec, which corresponds to an engine speed of 1000 revolutions, was used. The surface pressure was set to 150Kgf. The wear amount was measured using the wear width for the pin-shaped test piece 22 and the wear amount for the disk 24. At this time, each test piece 22 was tested for 10 minutes. Also, as a reference example, the current pad material (iron-based sintered body: Fe-16%Cr-4%Mo-2.2%C;
Product name MX-300) and aluminum alloy, α
-Using alumina sintered bodies, silicon nitride sintered bodies, and partially stabilized zirconia sintered bodies (ceramics test pieces all have a theoretical density of 98% or higher), these materials can also be processed into pin-shaped test pieces. and subjected to the test. The results of these tests are shown in Tables 1 and 2.

【table】

【table】

[Table] From the results shown in Tables 1 and 2, the volume fraction and particle size of α-alumina when a porous ceramic sintered body using α-alumina is composited into the rocker arm pad part. The preferable range of is now clear. First, the volume fraction of α-alumina is preferably in the range of 30 to 60%; if it is lower than 30%, the strength of the sintered bond between the particles will be weakened and the particles will fall off during the test. wear increases. In addition, if it exceeds 60%, 99% shown in Table 2
As is clear from the above comparative example of the α-alumina sintered body, the wear on the disk side becomes significant. On the other hand, from the perspective of particle size, even if the particle size becomes smaller, if the volume fraction increases, the surface area increases during high-pressure casting, so the resistance to molten metal penetration increases, and the molten metal does not penetrate into the alumina particles, causing the particles to fall off. The particles then become an abrasive, and the amount of wear on the disk side increases. In addition, if the particle size is 40 μm or more, as mentioned above, a step will occur between it and the alloy base during processing, and cracks will easily occur within the particle, which will cause it to fall off, and the amount of wear will also increase. increase. From the results shown in Table 1, a more preferable range of particle diameter is 10 μm or less. (Example 2) In order to further confirm the results of Example 1, an actual engine durability evaluation was conducted. That is, Example 1
After processing the α-alumina sintered body (particle size: 10 μm, volume fraction: 40%) prepared in 1 to predetermined dimensions, it was preheated to 300°C and molded into mold 11 of the molten metal forging apparatus shown in Fig. 5.
Aluminum alloy (AC4B) maintained at 750°C is supplied into the sleeve, and the plunger 16 is raised with a pressure of 800 kgf/cm ² to deposit aluminum into the mold 11. The molten aluminum alloy was filled and the same pressure as above was applied to the molten aluminum alloy until it solidified, and then the aluminum alloy composite rocker arm was taken out from the mold 11. Next, as a comparative example, iron-based sintered body (Fe-16% Cr-4
%Mo-2.2%C; trade name MX-300) and 98.0%
After processing an α-alumina sintered body having a volume fraction into the shape shown in FIG. 2, a rocker arm was manufactured by the above-mentioned casting method. Subsequently, when the weights of these rocker arms were measured, it was found that the rocker arm of the present invention was 5 g lighter than the rocker arm of the comparative example. Next, use engine oil (10W-30) to achieve actual vehicle idle durability (engine speed: 600 rpm,
1000Hr) test was conducted. Wear resistance was evaluated using the wear weight for the rocker arm pad section and the cam nose wear amount (μm) for the camshaft cam section. The results are shown in Table 3. In addition,
The material of the cam nose component used as a mating material was the currently used chilled cast iron.

[Table] As is clear from the results shown in Table 3, the product using the sintered body of the present invention showed good wear resistance equal to or better than that of the current material in actual machine tests, and We were able to prevent peeling at the interface, reduce weight, and reduce cost. (Effect of the invention) As explained above, according to this invention,
Using a molten metal forging device equipped with a mold having a cavity in the shape of a Rocker arm, a portion of the cavity containing mainly particles with an average particle diameter of 20 μm or less and a volume of 30 to 60% is placed at a position corresponding to the contact surface with the cam of the Rocker arm. After arranging a rocker arm pad made of a porous ceramic sintered body having a high density, a light alloy molten metal is high-pressure cast by molten metal forging into the cavity of the mold, thereby forming the porous ceramic sintered body. The molten light alloy is infiltrated and solidified into the gap of the molten rocker arm pad, and the light alloy is continuous with the cam on the contact surface of the cam of the rocker arm body formed by forging the molten light alloy. Since the structure is such that the rocker arm is integrated with a rocker arm pad made of a porous ceramic sintered body infiltrated with the rocker arm, the light alloy molten metal is sufficiently filled into the gap between the rocker arm pad made of the porous ceramic sintered body. It is possible to obtain a Rocker arm that has been infiltrated and solidified, and the interface between the composite Rocker arm pad and the Rocker arm body is not clearly visible and is almost continuous, making it possible to obtain a Rocker arm that has been solidified by penetration. There is no cracking or peeling at the interface of the Rotsuker arm pad, and it can withstand use under particularly severe wear conditions, and the Rotsuker arm body is formed by molten metal forging. This makes it possible to have a dense structure with no casting defects and excellent mechanical properties.Furthermore, since the space between the rocker arm body and the rocker arm pad is continuous, the structure around the pad part is It is possible to manufacture a rocker arm that does not require deburring work, and it brings about the great effect that it is possible to obtain a rocker arm that requires locally high wear resistance.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the conventional Rocker arm, Figure 2
The figure is a perspective view of the pad portion of the rocker arm shown in Figure 1, Figure 3 is a partial explanatory view of a mold for casting the rocker arm shown in Figure 1, Figure 4 is a cross-sectional view of a conventional fiber molded body manufacturing apparatus, and Figure 5 The figure is a longitudinal cross-sectional view of a molten metal forging device that can be used in the present invention, Figures 6a and b are cross-sectional and side views of a wear tester, and Figure 7 is a pin-shaped test piece used in the wear test. FIG. DESCRIPTION OF SYMBOLS 1... Rocker arm, 11... Molten metal forging device mold, 14... Cavity, 17... Rocker arm pad made of porous ceramic sintered body.

Claims (1)

[Claims] 1. Using a molten metal forging device equipped with a mold having a cavity in the shape of a Rocker arm, in the cavity, at a position corresponding to the contact surface with the cam of the Rocker arm, a powder mainly composed of particles with an average particle size of 20 μm or less and 30 to 60% After disposing a rocker arm pad made of a porous ceramic sintered body having a volume fraction, the porous ceramic sintered body is formed by high-pressure casting a light alloy molten metal into the cavity of the mold by molten metal forging. The molten light alloy is infiltrated and solidified into the gap between the Rocker arm pads, and the light alloy is continuously formed between the Rocker arm body and the cam contact surface of the Rocker arm body formed by forging the light alloy molten metal. 1. A method for manufacturing a rocker arm, the method comprising: obtaining a rocker arm integrated with a rocker arm pad made of a porous ceramic sintered body infiltrated with a rocker arm.