JP7625879B2 - Cylinder head for internal combustion engine and manufacturing method thereof - Google Patents

Description

The present invention relates to a cylinder head for an internal combustion engine and a manufacturing method thereof, and in particular to a cylinder head in which a valve seat is formed by the cold spray method.

A method for manufacturing a sliding member is known in which a valve seat with excellent high-temperature abrasion resistance is formed by spraying raw material powder such as metal onto the valve seat of an internal combustion engine using a cold spray method (Patent Document 1).

International Publication No. 2017/022505

This type of valve seat requires wear resistance against repeated impacts from the intake and exhaust valves, as well as adhesion to the base material. To improve the wear resistance of the valve seat, a hard material can be used for the raw powder of the cold spray, but a hard material will be difficult to plastically deform, and adhesion to the base material will decrease. Conversely, to improve the adhesion of the valve seat, a soft material can be used for the raw powder of the cold spray, but this will decrease wear resistance. Thus, there is a trade-off between wear resistance and adhesion in the cold spray method, and it has been difficult to achieve both.

The problem that this invention aims to solve is to provide an internal combustion engine cylinder head that has excellent wear resistance and adhesion in appropriate locations, and a manufacturing method thereof.

The present invention solves the above problem by using a raw material powder containing a soft material and a hard material as the main components to form a valve seat by cold spraying, so that the content ratio (area ratio) of the hard material in the cross section of the valve seat of the intake port is smaller than the content ratio (area ratio) of the hard material in the cross section of the valve seat of the exhaust port.

According to the present invention, the valve seats of the intake ports are made of a soft material, while the valve seats of the exhaust ports are made of a hard material, resulting in a cylinder head with excellent wear resistance and adhesion in appropriate locations.

1 is a cross-sectional view showing a cylinder head including a valve seat according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the periphery of the valve in FIG. 1 . 1 is a configuration diagram showing one embodiment of a cold spray device used in a manufacturing method according to the present invention. FIG. 3A to 3C are process diagrams showing a procedure for manufacturing a cylinder head using the manufacturing method according to the present invention. 1 is a perspective view of a cylinder head blank including a valve seat according to one embodiment of the present invention; FIG. 6A is a cross-sectional view showing an intake port taken along line VI-VI in FIG. 5 , (B) is a cross-sectional view showing the intake port after an annular valve seat portion has been formed in a cutting process, (C) is a cross-sectional view showing the intake port after a valve seat has been formed, and (D) is a cross-sectional view showing the intake port with a valve seat formed. 1A is a cross-sectional view showing a first valve seat formed in a valve seat portion of an intake port, and FIG. 1B is a cross-sectional view showing a second valve seat formed in a valve seat portion of an exhaust port. 4 is a graph showing the relationship between the amount of wear and the content (area %) of a hard material contained in a valve seat of an intake port. 1A is a SEM photograph showing raw material powder of a hard material produced by water atomization, and FIG. 1B is a SEM photograph showing raw material powder of a hard material produced by gas atomization. 1A is a schematic diagram showing a film formation state when the nozzle moving speed is low, and FIG. 1B is a schematic diagram showing a film formation state when the nozzle moving speed is high.

Below, one embodiment of the present invention will be described with reference to the drawings. First, an internal combustion engine 1 equipped with valve seats 16b, 17b to which the present invention is preferably applied will be described. Figure 1 is a cross-sectional view of the internal combustion engine 1, and mainly shows the configuration around the cylinder head.

The internal combustion engine 1 comprises a cylinder block 11 and a cylinder head 12 attached to the top of the cylinder block 11. The internal combustion engine 1 is, for example, an in-line four-cylinder gasoline engine, and the cylinder block 11 has four cylinders 11a arranged in the depth direction of the drawing, one of which is shown in FIG. 1. Each cylinder 11a houses a piston 13 that reciprocates up and down in the drawing, and each piston 13 is connected to a crankshaft 14 extending in the depth direction of the drawing via a connecting rod 13a.

The mounting surface 12a of the cylinder head 12 to the cylinder block 11 has four recesses 12b that form the combustion chamber 15 of each cylinder 11a at positions corresponding to each cylinder 11a. The combustion chamber 15 is a space for burning a mixture of fuel and intake air, and is composed of the recesses 12b of the cylinder head 12, the top surface 13b of the piston 13, and the inner surface of the cylinder 11a.

The cylinder head 12 has an intake port 16, which connects the combustion chamber 15 to one side 12c of the cylinder head 12. The intake port 16 has a curved, approximately cylindrical shape, and guides intake air from an intake manifold (not shown) connected to the side 12c into the combustion chamber 15. The cylinder head 12 also has an exhaust port 17, which connects the combustion chamber 15 to the other side 12d of the cylinder head 12. The exhaust port 17 has a curved, approximately cylindrical shape like the intake port 16, and discharges exhaust gas generated in the combustion chamber 15 to an exhaust manifold (not shown) connected to the side 12d. The internal combustion engine 1 of this embodiment has two intake ports 16 and two exhaust ports 17 for each cylinder 11a.

The cylinder head 12 is equipped with an intake valve 18 that opens and closes an intake port 16 relative to the combustion chamber 15, and an exhaust valve 19 that opens and closes an exhaust port 17 relative to the combustion chamber 15. The intake valve 18 and the exhaust valve 19 each have a round rod-shaped valve stem 18a, 19a and a disk-shaped valve head 18b, 19b provided at the tip of the valve stem 18a, 19a. The valve stems 18a, 19a are slidably inserted into approximately cylindrical valve guides 18c, 19c assembled to the cylinder head 12. This allows the intake valve 18 and the exhaust valve 19 to move freely along the axial direction of the valve stems 18a, 19a relative to the combustion chamber 15.

Figure 2 shows an enlarged view of the communication between the combustion chamber 15 and the intake port 16 and exhaust port 17. The intake port 16 has a substantially circular opening 16a at the communication with the combustion chamber 15. An annular valve seat 16b that abuts against the valve head 18b of the intake valve 18 is formed on the annular edge (valve seat) of this opening 16a. When the intake valve 18 moves upward along the axial direction of the valve stem 18a, the upper surface of the valve head 18b abuts against the valve seat 16b, closing the intake port 16. Conversely, when the intake valve 18 moves downward along the axial direction of the valve stem 18a, a gap is formed between the upper surface of the valve head 18b and the valve seat 16b, opening the intake port 16.

The exhaust port 17, like the intake port 16, has a substantially circular opening 17a at the communicating portion with the combustion chamber 15, and an annular valve seat 17b that abuts against the valve head 19b of the exhaust valve 19 is formed on the annular edge (valve seat) of this opening 17a. When the exhaust valve 19 moves upward along the axial direction of the valve stem 19a, the upper surface of the valve head 19b abuts against the valve seat 17b to close the exhaust port 17. Conversely, when the exhaust valve 19 moves downward along the axial direction of the valve stem 19a, a gap is formed between the upper surface of the valve head 19b and the valve seat 17b, opening the exhaust port 17. The diameter of the opening 16a of the intake port 16 is set to be larger than the diameter of the opening 17a of the exhaust port 17.

In a four-stroke internal combustion engine 1, only the intake valve 18 is opened when the piston 13 descends, thereby introducing the air-fuel mixture from the intake port 16 into the cylinder 11a (intake stroke). Next, the intake valve 18 and exhaust valve 19 are closed, and the piston 13 is raised to approximately top dead center to compress the air-fuel mixture in the cylinder 11a (compression stroke). Then, when the piston 13 reaches approximately top dead center, the compressed air-fuel mixture is ignited by an ignition plug, causing the mixture to explode. This explosion causes the piston 13 to descend to bottom dead center, and the explosion is converted into rotational force via the connected crankshaft 14 (combustion and expansion stroke). Finally, when the piston 13 reaches bottom dead center and begins to rise again, only the exhaust valve 19 is opened, and the exhaust gas in the cylinder 11a is discharged to the exhaust port 17 (exhaust stroke). The internal combustion engine 1 generates power by repeating the above cycle.

The valve seats 16b, 17b are formed by directly forming a metal film on the annular edge of the openings 16a, 17a of the cylinder head 12, i.e., the valve seating portion, by the cold spray method. In the cold spray method, a working gas at a temperature lower than the melting point or softening point of the raw material powder is made into a supersonic flow, and the raw material powder carried by a carrier gas is injected into the working gas and sprayed from the nozzle tip, and the raw material powder is made to collide with the substrate in a solid state, forming a coating by plastic deformation of the raw material powder. Compared to the thermal spray method in which the material is melted and attached to the substrate, the cold spray method has the following characteristics: a dense coating that does not oxidize in the atmosphere is obtained, thermal deterioration is suppressed because the thermal effect on the material particles is small, the film formation speed is fast, thick films can be formed, and the adhesion efficiency is high. In particular, the fast film formation speed and thick films can be formed, making it suitable for use as a structural material such as the valve seats 16b, 17b of the internal combustion engine 1.

Figure 3 is a schematic diagram of the cold spray device 2 used to form the valve seats 16b and 17b. The cold spray device 2 in this example includes a gas supply unit 21 that supplies a working gas and a carrier gas, a raw material powder supply unit 22 that supplies raw material powder for the valve seats 16b and 17b, a spray gun 23 that sprays the raw material powder as a supersonic flow using a working gas below its melting point, and a refrigerant circulation circuit 27 that cools the nozzle 23d.

The gas supply unit 21 includes a compressed gas cylinder 21a, a working gas line 21b, and a carrier gas line 21c. The working gas line 21b and the carrier gas line 21c each include a pressure regulator 21d, a flow control valve 21e, a flow meter 21f, and a pressure gauge 21g. The pressure regulator 21d, the flow control valve 21e, the flow meter 21f, and the pressure gauge 21g are used to adjust the pressure and flow rate of the working gas and the carrier gas from the compressed gas cylinder 21a.

A heater 21i such as a tape heater is installed in the working gas line 21b, and the heater 21i heats the working gas line 21b by receiving power from a power source 21h via power supply lines 21j, 21j. The working gas is heated by the heater 21i to a temperature lower than the melting point or softening point of the raw material powder, and then introduced into the chamber 23a of the spray gun 23. A pressure gauge 23b and a thermometer 23c are installed in the chamber 23a, and the detected pressure and temperature values are output to a controller (not shown) via respective signal lines 23g, 23h, and are used for feedback control of the pressure and temperature.

The raw powder supplying section 22 includes a raw powder supplying device 22a, a measuring device 22b, and a raw powder supplying line 22c. The carrier gas from the compressed gas cylinder 21a passes through the carrier gas line 21c and is introduced into the raw powder supplying device 22a. A predetermined amount of raw powder measured by the measuring device 22b is transported into the chamber 23a via the raw powder supplying line 22c.

The spray gun 23 sprays the raw material powder P, which has been transported into the chamber 23a by the carrier gas, from the tip of the nozzle 23d as a supersonic flow by the working gas, and causes it to collide with the substrate 4 in a solid phase or in a solid-liquid coexistence state to form a metal film 5. In this embodiment, a cylinder head 12 is used as the substrate 4, and the raw material powder P is sprayed by the cold spray method onto the annular edges (valve seats) of the openings 16a and 17a of the cylinder head 12 to form valve seats 16b and 17b as the metal film 5.

Nozzle 23d has a flow path (not shown) through which a refrigerant such as water flows. At its tip, nozzle 23d has a refrigerant inlet 23e that introduces the refrigerant into the flow path, and at its base end, a refrigerant outlet 23f that discharges the refrigerant in the flow path. Nozzle 23d cools itself by introducing the refrigerant from refrigerant inlet 23e into the flow path, flowing the refrigerant in the flow path, and discharging the refrigerant from refrigerant outlet 23f.

The refrigerant circulation circuit 27 that circulates the refrigerant through the flow path of the nozzle 23d includes a tank 271 that stores the refrigerant, an inlet pipe 274 connected to the above-mentioned refrigerant inlet portion 23e, a pump 272 that is connected to the inlet pipe 274 and flows the refrigerant between the tank 271 and the nozzle 23d, a cooler 273 that cools the refrigerant, and a discharge pipe 275 connected to the refrigerant discharge portion 23f. The cooler 273 is, for example, a heat exchanger, and cools the refrigerant whose temperature has increased by cooling the nozzle 23d by exchanging heat with a refrigerant such as air, water, or gas.

The refrigerant circulation circuit 27 draws the refrigerant stored in the tank 271 by the pump 272, and supplies the refrigerant to the refrigerant introduction section 23e via the cooler 273. The refrigerant supplied to the refrigerant introduction section 23e flows through the flow path in the nozzle 23d from the front end side to the rear end side, and cools the nozzle 23d by exchanging heat with the nozzle 23d during that time. The refrigerant that has flowed to the rear end side of the flow path is discharged from the refrigerant discharge section 23f to the discharge pipe 275 and returns to the tank 271. In this way, the refrigerant circulation circuit 27 circulates the refrigerant while cooling it to cool the nozzle 23d, so that the adhesion of the raw material powder P to the spray passage of the nozzle 23d can be suppressed. The raw material powder P will be described later.

In the cold spray device 2 of this embodiment, the cylinder head 12 on which the valve seats 16b, 17b are formed is fixed to a base, while the tip of the nozzle 23d of the spray gun 23 is rotated along the annular edge (valve seat) of the openings 16a, 17a of the cylinder head 12 to spray the raw material powder. Since the cylinder head 12 is not rotated, a large occupied space is not required, and the spray gun 23 has a smaller moment of inertia than the cylinder head 12, so it has excellent rotation transient characteristics and responsiveness. However, since the cylinder head and its manufacturing method of the present invention only require the cylinder head 12, which is the base material, and the nozzle 23d to move relative to each other, the nozzle 23d of the spray gun 23 may be fixed while the cylinder head 12 is rotated and oscillated, or the cylinder head 12 may be rotated and oscillated together with the nozzle 23d of the spray gun 23.

Next, a method for manufacturing the cylinder head 12 having the valve seats 16b, 17b will be described. FIG. 4 is a process diagram showing the machining process of the valve portion in the manufacturing method of the cylinder head 12 of this embodiment. As shown in the figure, the manufacturing method of the cylinder head 12 of this embodiment includes a casting process S1, a cutting process S2, a coating process S3, and a finishing process S4. Note that the machining processes other than those for the valve portion are omitted to simplify the description.

In the casting process S1, aluminum alloy for casting is poured into a mold in which a sand core is set, and a cylinder head rough material 3 with an intake port 16, an exhaust port 17, etc. formed in the main body is cast. Here, the cylinder head rough material 3 refers to a semi-finished product in the middle of manufacturing before being processed into the final product, the cylinder head 12. The intake port 16 and the exhaust port 17 are formed by the sand core, and the recess 12b is formed by the mold. Figure 5 is a perspective view of the cylinder head rough material 3 cast in the casting process S1, seen from the mounting surface 12a side to the cylinder block 11. The cylinder head rough material 3 has four recesses 12b, and two intake ports 16 and two exhaust ports 17 provided in each recess 12b. The two intake ports 16 and two exhaust ports 17 of each recess 12b are gathered into one in the cylinder head rough material 3, and are connected to openings provided on both sides of the cylinder head rough material 3, respectively.

Figure 6 (A) is a cross-sectional view of the cylinder head blank 3 taken along line VI-VI in Figure 5, showing the intake port 16 after the casting process S1 is completed. The intake port 16 has a circular opening 16a exposed in the recess 12b of the cylinder head blank 3.

Figure 6 (B) is a cross-sectional view showing the state in which the annular valve seat portion 16c is formed in the cutting process on the intake port of Figure 6 (A). In the cutting process S2, the cylinder head raw material 3 is milled using an end mill, a ball end mill, or the like, to form the annular valve seat portion 16c at the opening 16a of the intake port 16, as shown in Figure 6 (B). The annular valve seat portion 16c is an annular groove that forms the base shape of the valve seat 16b, and is formed on the outer periphery of the opening 16a. In the manufacturing method of the cylinder head 12 of this embodiment, the raw material powder P is sprayed on the annular valve seat portion 16c by the cold spray method to form a film, and the film is used as the basis for processing into the valve seat 16b. Therefore, the annular valve seat portion 16c is formed to be one size larger than the valve seat 16b.

Figure 6 (C) is a cross-sectional view showing the state in which the valve seat 16b is formed in the coating process S3 on the intake port 16 of Figure 6 (B). In the coating process S3, the raw material powder P is sprayed onto the annular valve seat portion 16c of the cylinder head rough material 3 using the cold spray device 2 of this embodiment to form the valve seat 16b. More specifically, in this coating process S3, as shown in Figure 6 (C), while the annular valve seat portion 16c and the nozzle 23d of the spray gun 23 are kept at a constant distance from each other in the same posture, the cylinder head rough material 3 is fixed, while the nozzle 23d of the spray gun 23 is rotated so that the raw material powder P is sprayed onto the entire circumference of the annular valve seat portion 16c.

The tip of the nozzle 23d of the spray gun 23 is held by the hand of an industrial robot above the cylinder head 12 fixed to a base. The base or industrial robot sets the position of the cylinder head 12 or the spray gun 23 so that the central axis Z of the intake port 16 in which the valve seat 16b is formed is vertical and overlaps with the rotation axis of the spray gun 23. In this state, the raw material powder P is sprayed from the nozzle 23d onto the annular valve seat portion 16c while the spray gun 23 is rotated around the rotation axis, forming a coating around the entire circumference of the annular valve seat portion 16c.

While this covering step S3 is being performed, the nozzle 23d introduces the refrigerant supplied from the refrigerant circulation circuit 27 into the flow path from the refrigerant inlet 23e. The refrigerant cools the nozzle 23d as it flows from the tip to the rear end of the flow path formed inside the nozzle 23d. The refrigerant that has flowed to the rear end of the flow path is discharged from the flow path by the refrigerant outlet 23f and collected.

When the spray gun 23 completes one rotation around the rotation axis and the formation of the valve seat 16b is complete, the rotation of the spray gun 23 is temporarily stopped. While the rotation is stopped, the industrial robot to which the spray gun 23 is attached moves the spray gun 23 so that the central axis Z of another intake port 16 in which the valve seat 16b is to be formed next coincides with the reference axis of the industrial robot. Then, after the industrial robot has finished moving the spray gun 23, the rotation of the spray gun 23 is resumed, and the valve seat 16b is formed in the next intake port 16. By repeating this operation thereafter, the valve seats 16b, 17b are formed in all the intake ports 16 and exhaust ports 17 of the cylinder head rough material 3.

Returning to FIG. 4, in the finishing process S4, the valve seats 16b and 17b, the intake port 16, and the exhaust port 17 are finished. FIG. 6(D) is a cross-sectional view showing an intake port on which the valve seat 16b is formed. In the finishing process of the valve seats 16b and 17b, the surfaces of the valve seats 16b and 17b are cut by milling using a ball end mill, and the valve seat 16b is shaped into a predetermined shape. In the finishing process of the intake port 16, a ball end mill is inserted into the intake port 16 from the opening 16a, and the inner surface of the intake port 16 on the opening 16a side is cut along the processing line PL shown in FIG. 6(D). The processing line PL is a range in which the excess coating SF formed by scattering and adhering the raw material powder P in the intake port 16 is formed relatively thick, more specifically, a range in which the excess coating SF is formed thick enough to affect the intake performance of the intake port 16.

In this way, the finishing process S4 can eliminate the surface roughness of the intake port 16 caused by casting, and can also remove the excess coating SF formed in the coating process S3. As with the intake port 16, the exhaust port 17 has a valve seat 17b formed through the formation of a small diameter portion in the exhaust port 17 by casting, the formation of an annular valve seat portion by cutting, cold spraying of the annular valve seat portion, and finishing. Therefore, a detailed explanation of the procedure for forming the valve seat 17b for the exhaust port 17 will be omitted.

Now, the valve seats of the cylinder head 12 are required to have high heat resistance, wear resistance, and adhesion to withstand the impact force from the valves in the combustion chamber 15, and high thermal conductivity for cooling the combustion chamber 15. The raw material powder P used to form the valve seats 16b and 17b of this embodiment is preferably a metal that is harder than the aluminum alloy for casting that constitutes the cylinder head 12 and that can obtain the heat resistance, wear resistance, adhesion, and thermal conductivity required for the valve seats. Here, in order to increase the wear resistance of the performance required for the valve seats, a hard material can be used for the raw material powder, but if the material is hard, it becomes difficult to plastically deform and the adhesion to the base material decreases. Conversely, to improve the adhesion of the valve seats, a soft material can be used for the raw material powder, but if the material is soft, the wear resistance decreases. Thus, there is a trade-off between wear resistance and adhesion in the cold spray method, and it is difficult to achieve both of these properties.

Therefore, in the cylinder head 12 and its manufacturing method of this embodiment, a material containing a soft material and a hard material as main components is used for the raw material powder P by the cold spray method, and the content ratio of the hard material in the cross section of the metal film constituting the valve seats 16b, 17b (defined as an area percentage, so also called the area ratio) is formed so that the area ratio of the valve seat 16b of the intake port 16 is smaller than the area ratio of the valve seat 17b of the exhaust port 17. In other words, the film is formed so that the area where adhesion is required more than heat resistance and wear resistance is rich in soft material, while the area where heat resistance and wear resistance are required more than adhesion is rich in hard material. This makes it possible to obtain a cylinder head 12 having valve seats 16b, 17b with excellent wear resistance and adhesion in appropriate locations.

Although the intake port 16 of an internal combustion engine faces the combustion chamber 15, it is cooled by the intake air, and therefore is in a temperature environment of approximately 80 to 200°C. Therefore, it is preferable to prioritize ensuring adhesion as long as it can meet the heat resistance and wear resistance of 200°C or less. In contrast, the exhaust port 17 of an internal combustion engine is constantly exposed to a combustion gas atmosphere, and is therefore in a temperature environment of 300°C or more. Therefore, it is preferable to prioritize ensuring heat resistance and wear resistance of at least 300°C or more.

Figure 7 (A) is a cross-sectional view showing the valve seat 16b of the intake port 16, and Figure 7 (B) is a cross-sectional view showing the valve seat 17b of the exhaust port 17. In Figure 7, black circles indicate the hard material HM, and the other film parts are the soft material SM. The content ratio (area %) of the hard material HM in the valve seat 16b shown in Figure 7 (A) is smaller than the content ratio (area %) of the hard material HM in the valve seat 17b shown in Figure 7 (B). More preferably, the content ratio of the hard material HM in the valve seat 16b shown in Figure 7 (A) is 5 to 20 area %, while the content ratio of the hard material HM in the valve seat 17b shown in Figure 7 (B) is 50 to 90 area %.

Figure 8 is a graph showing the relationship between the amount of wear and the content (area %) of the hard material HM contained in the valve seat 16b of the intake port 16. If the mixing ratio of the hard material in the cross section of the metal film that makes up the valve seat 16b is less than 5 area %, the amount of wear of the valve seat 16b in response to the hammering input from the valve becomes significantly large, but if the mixing ratio of the hard material exceeds 5 area %, the amount of wear converges to an almost constant value. Therefore, taking into account the adhesion of the metal film, it is preferable that the mixing ratio of the hard material HM in the valve seat 16b be 5 to 20 area %.

The mixing ratio of the hard material to the soft material is defined as the area ratio in the cross section of the metal film because the rate at which the raw powder of the hard material is sprayed from the nozzle and adheres (the so-called adhesion efficiency) is different from the rate at which the raw powder of the soft material is sprayed from the nozzle and adheres, and even if the mixing ratio of the hard material to the soft material before deposition is defined as a weight ratio or the like, it will differ from the mixing ratio in the metal film. In other words, since the adhesion efficiency of the raw powder of the hard material is lower than that of the raw powder of the soft material, if you want to set the mixing ratio of the hard material in the metal film to 10 area%, for example, set the mixing weight percentage of the raw powder of the hard material sprayed from the nozzle to a value greater than 10%.

As the soft material of this embodiment, it is preferable to use copper, a copper alloy, iron or an iron alloy. As the copper alloy, a precipitation hardened copper alloy can be exemplified. As the precipitation hardened copper alloy, a Corson alloy containing nickel and silicon, a chromium copper containing chromium, a zirconium copper containing zirconium, etc. can be used. Furthermore, for example, a precipitation hardened copper alloy containing nickel, silicon and chromium, a precipitation hardened copper alloy containing nickel, silicon and zirconium, a precipitation hardened alloy containing nickel, silicon, chromium and zirconium, a precipitation hardened copper alloy containing chromium and zirconium, etc. can also be applied. In addition, as the iron-based material, pure iron or low carbon steel of about 0.1% (for example, Fe-0.1C-0.1Si, etc.) can be exemplified. In addition, as the iron alloy, stainless steel such as SUS316L can be exemplified. In this embodiment, the soft material means a material as a main component whose average hardness is substantially softer than that of a hard material. The soft material of this embodiment has a Vickers hardness of less than 500 HV, preferably 100 to 400 HV, when formed into a film by itself.

The hard material of this embodiment refers to a material as a main component that has a substantially harder average hardness than the soft material described above. Examples of hard materials of this embodiment include iron or iron-based alloys, cobalt or cobalt-based alloys, chromium or chromium-based alloys, nickel or nickel-based alloys, and molybdenum or molybdenum-based alloys. Examples of hard materials of this embodiment include SKD (die steel), SKH (high-speed steel), and Fe-Mo-Si alloy powder. SKD material, also known as die steel, is a material in which Cr, Mo, and V are added to SK material. The composition of SKD61 material is described in JIS4404, and a representative composition is Fe-0.4C-1.0Si-0.4Mn-5.2Cr-1.3Mo-0.9V (numbers are weight %). Also, there are two types of SKH material, known as high speed steel, a mono-glutinous type and a molybdenum type. The composition of SKH51 material is described in JIS 4403, and a representative composition is Fe-0.9C-0.3Si-0.4Mn-4.2Cr-5.0Mo-2.0V-6.5W (numbers are by weight). These hard materials may be used alone or in appropriate combination of two or more types. The hard material of this embodiment is a material with a Vickers hardness of 500HV or more, preferably 600 to 1000HV, when formed alone.

In the case of producing the powders of the soft material and hard material of this embodiment, although there is no particular limitation, the hard material is preferably produced by the water atomization method, and the soft material is preferably produced by the gas atomization method. FIG. 9(A) is an SEM photograph showing the raw powder of the hard material produced by the water atomization method, and FIG. 9(B) is an SEM photograph showing the raw powder of the hard material produced by the gas atomization method. The water atomization method is a manufacturing method in which high-pressure water is sprayed onto a metal melted at high temperature to cause it to scatter, and then it is rapidly cooled and solidified in the process of falling, thereby obtaining a powder. Because the cooling rate is fast, it solidifies before the surface tension acts. Therefore, the obtained powder has an irregular shape with multiple protrusions on the surface. Even if it is a hard material, according to the powder produced by the water atomization method, in addition to the anchor effect of the multiple protrusions, the protruding parts are easily deformed, and therefore the adhesion is high. In addition, the production by the water atomization method is easier than the production by the gas atomization method.

In contrast, gas atomization is a manufacturing method in which high-pressure gas is sprayed onto metal molten at high temperature, scattering it, and as it falls it cools and solidifies, yielding powder. Because the cooling rate is slow, surface tension acts as it solidifies. As a result, the resulting powder is spherical. Because soft material powder produced by gas atomization is spherical, the packing density is high and adhesion is further improved. In contrast, soft material powder produced by water atomization does not have sufficient material strength, making it disadvantageous in terms of wear resistance.

Next, to form a film having different content ratios of hard material and soft material contained in the film, as in the valve seats 16b and 17b of the embodiment shown in Figures 7(A) and (B), the content ratio of the raw material powder of the hard material HM and the raw material powder of the soft material SM in the raw material powder supply section 22 of the cold spray device 2 in Figure 3 is adjusted to a content ratio corresponding to the soft material rich shown in Figure 7(A) to form a film of the valve seat 16b, and separately, the content ratio of the raw material powder of the hard material HM and the raw material powder of the soft material SM in the raw material powder supply section 22 is adjusted to a content ratio corresponding to the hard material rich shown in Figure 7(B) to form a film of the valve seat 17b. Alternatively, two cold spray devices 2 having different content ratios of the raw material powder of the hard material HM and the raw material powder of the soft material SM in the raw material powder supply section 22 may be used to form two specifications of the valve seats 16b and 17b.

Alternatively, a single cold spray device 2 having the same content ratio of raw material powder of hard material HM and raw material powder of soft material SM in the raw material powder supply section 22 may be used to form two types of valve seats 16b, 17b by controlling the moving speed of the nozzle 23d. In other words, when forming a metal film 5 on the valve seats 16b, 17b, etc., the content ratio of the hard material and the soft material can be controlled by changing the density of the raw material powder P during spraying.

Figure 10(A) is a schematic diagram showing the film formation state when the movement speed of the nozzle 23d of the cold spray device 2 is low, and Figure 10(B) is a schematic diagram showing the film formation state when the movement speed of the nozzle 23d is high, showing raw material powder P consisting of a soft material SM and a hard material HM. The density of the raw material powder P during spraying is determined by the amount of raw material powder P discharged from the nozzle 23d and the movement speed of the nozzle 23d. Therefore, when the content ratio of hard material HM and soft material SM in raw material powder P is constant and the amount of raw material powder P discharged from nozzle 23d is constant, when the moving speed of nozzle 23d is relatively slow, the density (weight per unit volume) of raw material powder P containing hard material HM and soft material SM during spraying becomes large as shown in FIG. 10(A), and conversely, when the moving speed of nozzle 23d is relatively fast, the density of raw material powder P containing hard material HM and soft material SM during spraying becomes small as shown in FIG. 10(B).

Here, the mechanism by which the raw material powder P sprayed from the nozzle 23d adheres to the surface of the substrate 4 is as follows. That is, since the powder of the hard material HM is harder than the powder of the soft material SM, there is a high probability that the powder of the hard material HM will bounce back when it collides with the substrate 4. However, as shown in FIG. 10(A), if the density of the raw material powder P is high and there is a lot of powder of the soft material SM around the powder of the hard material HM, the powder of the hard material HM will be suppressed by the surrounding powder of the soft material SM even if it tries to bounce back. As a result, the amount of hard material HM that does not bounce back and adhere to the substrate 4 is reduced, and the substrate 4 becomes relatively rich in hard material. On the other hand, as shown in FIG. 10(B), if the density of the raw material powder P is low and there is not a lot of powder of the soft material SM around the powder of the hard material HM, the powder of the hard material HM will not be suppressed by the surrounding powder of the soft material SM when it tries to bounce back. As a result, the hard material HM that bounces back and does not adhere to the substrate 4 increases, resulting in a relatively rich soft material.

In this way, when the content ratio of the hard material HM and the soft material SM in the raw material powder P is constant and the amount of raw material powder P discharged from the nozzle 23d is constant, when the moving speed of the nozzle 23d is relatively slow, the hard material becomes rich as shown in Figure 10 (A), and conversely, when the moving speed of the nozzle 23d is relatively fast, the soft material becomes rich as shown in Figure 10 (B). Therefore, when the content ratio of the hard material HM and the soft material SM in the raw material powder P is constant and the amount of raw material powder P discharged from the nozzle 23d is constant, when the valve seat 16b shown in Figure 7 (A) is formed, the moving speed of the nozzle 23d is set to a relatively high speed, and when the valve seat 17b shown in Figure 7 (B) is formed, the moving speed of the nozzle 23d is set to a relatively low speed. This allows two types of valve seats 16b and 17b to be formed using a single cold spray device 2 that has the same content ratio of raw material powder of hard material HM and raw material powder of soft material SM in the raw material powder supply section 22.

As described above, the density of the raw material powder P during spraying is determined by the amount of raw material powder P discharged from the nozzle 23d and the moving speed of the nozzle 23d. Therefore, when the moving speed of the nozzle 23d is constant, when the amount of raw material powder P discharged from the nozzle 23d is relatively large, the raw material powder P becomes rich in hard material as shown in FIG. 10(A). Conversely, when the amount of raw material powder P discharged from the nozzle 23d is relatively small, the raw material powder P becomes rich in soft material as shown in FIG. 10(B). Therefore, when the content ratio of the hard material HM and the soft material SM in the raw material powder P is constant and the moving speed of the nozzle 23d is constant, the amount of raw material powder P discharged from the nozzle 23d may be set to a relatively small value when forming the valve seat 16b shown in FIG. 7(A), and when the valve seat 17b shown in FIG. 7(B) is formed, the amount of raw material powder P discharged from the nozzle 23d may be set to a relatively large value. This also makes it possible to deposit two types of valve seats 16b and 17b using a single cold spray device 2 in which the raw material powder of the hard material HM and the raw material powder of the soft material SM in the raw material powder supply section 22 are in the same content ratio.

As described above, according to the cylinder head and manufacturing method of this embodiment, the content ratio of the hard material HM in the cross section of the valve seat 16b is smaller than the content ratio of the hard material HM in the cross section of the valve seat 17b, so that a cylinder head having a valve seat with excellent wear resistance and adhesion in appropriate locations can be obtained.

In addition, with the cylinder head and manufacturing method of this embodiment, the content of the hard material HM in the cross section of the valve seat 16b is 5 to 20 area percent, so that adhesion can be improved while ensuring wear resistance.

In addition, according to the cylinder head and manufacturing method thereof of this embodiment, the particles of the hard material HM have multiple protrusions on the surface in the cross section of the metal film, so that even though it is a hard material, in addition to the anchor effect of the multiple protrusions, the protruding parts are easily deformed, and therefore adhesion is high.

In addition, according to the cylinder head and manufacturing method thereof of this embodiment, the hard material HM is a powder produced by the water atomization method, so in addition to the anchor effect of the multiple protrusions, the protruding parts are easily deformed, which increases adhesion. Also, manufacturing by the water atomization method is easier than manufacturing by the gas atomization method.

In addition, according to the cylinder head and manufacturing method thereof of this embodiment, the soft material SM is a powder produced by gas atomization, and because it has a spherical shape, the packing density is high and adhesion is further improved. In contrast, powder of the soft material SM produced by water atomization does not have sufficient material strength and is disadvantageous in terms of wear resistance.

In addition, according to the cylinder head and the manufacturing method thereof of this embodiment, the moving speed of the nozzle when forming the valve seat 16b is made faster than the moving speed of the nozzle when forming the valve seat 17b, or the amount of raw material powder P discharged from the nozzle when forming the valve seat 16b is made less than the amount of raw material powder P discharged from the nozzle when forming the valve seat 17b. Therefore, it is possible to form the valve seats 16b and 17b of two specifications using one cold spray device 2 in which the raw material powder of the hard material HM and the raw material powder of the soft material SM in the raw material powder supply section 22 have the same content ratio.

The valve seat 16b corresponds to the first valve seat according to the present invention, and the valve seat 17b corresponds to the second valve seat according to the present invention.

LIST OF SYMBOLS 1...INTERNAL COMBUSTION ENGINE 11...CYLINDER BLOCK 11a...CYLINDER 12...CYLINDER HEAD 12a...MOUNTING SURFACE 12b...RECEPTION 12c, 12d...SIDE 13...PISTON 13a...CONNECTING ROD 13b...TOP SURFACE 14...CRANKSHAFT 15...COMBUSTION CHAMBER 16...INHALT PORT 16a...OPENING 16b...VALVE SEAT 16c...ANNULAR VALVE SEAT PORTION 17...EXHAUST PORTION 17a...OPENING 17b...VALVE SEAT 18...INHALT VALVE 18a...VALVE STEM 18b...VALVE HEAD 18c...VALVE GUIDE 19...EXHAUST VALVE 19a...VALVE STEM 19b...VALVE HEAD 19c...VALVE GUIDE 2...Cold SPRAY APPARATUS 21...GAS SUPPLY 21a...COMPRESSED GAS BOTTOM 21b...WORKING GAS LINE 21c...CARRIER GAS LINE 22...RAW MATERIAL POWDER SUPPLY SECTION 22a, 221a, 222a...raw material powder supply device 22b...measuring device 22c, 221c, 222c...raw material powder supply line 23...spray gun 23a...chamber 23d...nozzle 3...cylinder head raw material 4...substrate 5...metal film

Claims (6)

A method for forming a valve seat made of a metal film by spraying a raw material powder containing a soft material and a hard material as main components through a nozzle by a cold spray method onto a valve seat portion of a cylinder head of an internal combustion engine, comprising:
forming a film such that a content ratio of a hard material in a cross section of a first valve seat formed in a valve seat portion of an intake port is smaller than a content ratio of a hard material in a cross section of a second valve seat formed in a valve seat portion of an exhaust port;
The content ratio of the hard material and the soft material in the raw material powder is kept constant;
The amount of the raw material powder discharged from the nozzle is kept constant;
A method for manufacturing a cylinder head, comprising the steps of: making a moving speed of the nozzle when forming a film on the first valve seat faster than a moving speed of the nozzle when forming a film on the second valve seat. A method for forming a valve seat made of a metal film by spraying a raw material powder containing a soft material and a hard material as main components through a nozzle by a cold spray method onto a valve seat portion of a cylinder head of an internal combustion engine, comprising:
forming a film such that a content ratio of a hard material in a cross section of a first valve seat formed in a valve seat portion of an intake port is smaller than a content ratio of a hard material in a cross section of a second valve seat formed in a valve seat portion of an exhaust port;
The content ratio of the hard material and the soft material in the raw material powder is kept constant;
The nozzle moving speed is kept constant;
A method for manufacturing a cylinder head, comprising the steps of: forming a first valve seat by using a nozzle that ejects a smaller amount of raw material powder than by using a nozzle that ejects a second valve seat by using a nozzle that ejects a smaller amount of raw material powder. 3. The method according to claim 1 , wherein the hard material is a powder produced by a water atomization method. The method according to claim 3 , wherein the soft material is a powder produced by a gas atomization method. 5. The method for manufacturing a cylinder head according to claim 1, wherein the soft material is copper, a copper alloy, iron or an iron alloy, and the hard material is cobalt, a cobalt alloy, SKD (die steel), SKH (high speed steel) or an Fe- Mo -Si alloy powder. The method for manufacturing a cylinder head according to any one of claims 1 to 5 , wherein the soft material has a Vickers hardness of less than 500 HV, and the hard material has a Vickers hardness of 500 HV or more.

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