Cylinder head for internal combustion engine and manufacturing method thereof

Abstract

To provide a cylinder head with its wear resistance and adhesiveness being excellent at appropriate sites and a method for producing the same.SOLUTION: A cylinder head 12 of an internal combustion engine has a valve seat 16b composed of a metal film at a valve seat part of an intake port 16 and a valve seat 17b composed of a metal film at a valve seat part of an exhaust port 17. The metal film contains a soft material SM and a hard material HM as the main components. The content of the hard material in the cross section of the valve seat 16b is lower than the content of the hard material in the cross section of the valve seat 17b.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a cylinder head for an internal combustion engine and a manufacturing method thereof, and more particularly to a cylinder head in which a valve seat is formed by a cold spray method. [Background technology]

[0002] 2. Description of the Related Art A method for manufacturing a sliding member is known in which a valve seat having excellent high-temperature abrasion resistance is formed by spraying raw material powder of metal or the like onto a valve seating portion of an internal combustion engine by a cold spray method (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 022505 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] This type of valve seat requires wear resistance against repeated impacts from the intake and exhaust valves, and adhesion to the substrate. 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 is difficult to plastically deform, and adhesion to the substrate decreases. Conversely, to improve the adhesion of the valve seat, a soft material can be used for the raw powder of the cold spray, but wear resistance decreases. Thus, there is a trade-off between wear resistance and adhesion in the cold spray method, and it has been difficult to achieve both.

[0005] An object of the present invention is to provide a cylinder head for an internal combustion engine which is excellent in wear resistance and adhesion at appropriate locations, and a method for manufacturing the same. [Means for solving the problem]

[0006] The present invention solves the above problem by using raw material powder containing a soft material and a hard material as 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. Effect of the Invention

[0007] According to the present invention, the valve seats of the intake ports are made of a soft material-rich material, while the valve seats of the exhaust ports are made of a hard material-rich material, so that a cylinder head having excellent wear resistance and adhesion in appropriate locations can be obtained. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a cylinder head including a valve seat according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the periphery of the valve in FIG. 1. [Diagram 3] 1 is a configuration diagram showing one embodiment of a cold spray device used in a manufacturing method according to the present invention. FIG. [Figure 4] 3A to 3C are process diagrams showing a procedure for manufacturing a cylinder head using the manufacturing method according to the present invention. [Diagram 5] 1 is a perspective view of a cylinder head blank including a valve seat according to one embodiment of the present invention; FIG. [Figure 6] 6(A) is a cross-sectional view showing the 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. [Figure 7] FIG. 2A is a cross-sectional view showing a first valve seat formed in a valve seat portion of an intake port, and FIG. 2B is a cross-sectional view showing a second valve seat formed in a valve seat portion of an exhaust port. [Figure 8]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. [Figure 9] (A) is an SEM photograph showing raw powder of a hard material produced by water atomization, and (B) is an SEM photograph showing raw powder of a hard material produced by gas atomization. [Figure 10] FIG. 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, an internal combustion engine 1 having valve seats 16b, 17b to which the present invention is preferably applied will be described. Fig. 1 is a cross-sectional view of the internal combustion engine 1, and mainly shows the configuration around the cylinder head.

[0010] The internal combustion engine 1 includes a cylinder block 11 and a cylinder head 12 attached to the upper part 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.

[0011] Four recesses 12b constituting the combustion chamber 15 of each cylinder 11a are formed in the mounting surface 12a of the cylinder head 12 to the cylinder block 11 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 constituted by the recesses 12b of the cylinder head 12, the top surface 13b of the piston 13, and the inner circumferential surface of the cylinder 11a.

[0012] The cylinder head 12 includes an intake port 16, which communicates the combustion chamber 15 with one side surface 12c of the cylinder head 12. The intake port 16 has a curved, generally cylindrical shape, and guides intake air from an intake manifold (not shown) connected to the side surface 12c into the combustion chamber 15. The cylinder head 12 also includes an exhaust port 17, which communicates the combustion chamber 15 with the other side surface 12d of the cylinder head 12. The exhaust port 17 has a curved, generally 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 surface 12d. The internal combustion engine 1 of this embodiment includes two intake ports 16 and two exhaust ports 17 for each cylinder 11a.

[0013] The cylinder head 12 includes 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 include round rod-shaped valve stems 18a and 19a, respectively, and disk-shaped valve heads 18b and 19b provided at the tips of the valve stems 18a and 19a. The valve stems 18a and 19a are slidably inserted into approximately cylindrical valve guides 18c and 19c assembled to the cylinder head 12. This allows the intake valve 18 and the exhaust valve 19 to move relative to the combustion chamber 15 along the axial direction of the valve stems 18a and 19a, respectively.

[0014] 2 shows an enlarged view of the communication portion 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 portion with the combustion chamber 15. An annular valve seat 16b that abuts against a valve head 18b of an intake valve 18 is formed on the annular edge (valve seat) of the 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 to close 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 to open the intake port 16.

[0015] Like the intake port 16, the exhaust port 17 has a substantially circular opening 17a at a portion communicating with the combustion chamber 15, and an annular valve seat 17b that abuts against a valve head 19b of an exhaust valve 19 is formed on an annular edge (valve seat) of the 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 to open 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.

[0016] In the four-stroke internal combustion engine 1, when the piston 13 descends, only the intake valve 18 is opened, 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 the top dead center to compress the air-fuel mixture in the cylinder 11a (compression stroke). Then, when the piston 13 reaches approximately the 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 the 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 the bottom dead center and starts 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.

[0017] 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 a substrate in a solid phase state, forming a coating by plastic deformation of the raw material powder. Compared with 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, a high coating speed is possible, a thick coating can be formed, and adhesion efficiency is high. In particular, since the coating speed is high and a thick coating can be formed, it is suitable for use as a structural material such as the valve seats 16b, 17b of the internal combustion engine 1.

[0018] 3 is a schematic diagram of the cold spray device 2 used to form the above-mentioned valve seats 16b, 17b. The cold spray device 2 of 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, 17b, a spray gun 23 that sprays the raw material powder as a supersonic flow using a working gas at or below its melting point, and a refrigerant circulation circuit 27 that cools the nozzle 23d.

[0019] 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 include a pressure regulator 21d, a flow control valve 21e, a flow meter 21f, and a pressure gauge 21g, respectively. 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.

[0020] 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 signal lines 23g, 23h, respectively, for feedback control of the pressure and temperature.

[0021] Meanwhile, the raw material powder supplying section 22 includes a raw material powder supplying device 22a, a measuring device 22b and a raw material powder supplying line 22c attached thereto. Carrier gas from a compressed gas cylinder 21a passes through the carrier gas line 21c and is introduced into the raw material powder supplying device 22a. A predetermined amount of raw material powder measured by the measuring device 22b is conveyed into the chamber 23a through the raw material powder supplying line 22c.

[0022] The spray gun 23 sprays the raw material powder P, which has been carried 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 state or 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 onto the annular edges (valve seating portions) of the openings 16a, 17a of the cylinder head 12 by a cold spray method, thereby forming valve seats 16b, 17b as the metal film 5.

[0023] Nozzle 23d has a flow path (not shown) through which a coolant such as water flows. Nozzle 23d has coolant inlet 23e at its tip for introducing the coolant into the flow path, and coolant outlet 23f at its base end for discharging the coolant in the flow path. Nozzle 23d cools nozzle 23d by introducing the coolant from coolant inlet 23e into the flow path, flowing the coolant in the flow path, and discharging the coolant from coolant outlet 23f.

[0024] 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 that is 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.

[0025] The refrigerant circulation circuit 27 sucks the refrigerant stored in the tank 271 by the pump 272, and supplies the refrigerant to the refrigerant introduction part 23e via the cooler 273. The refrigerant supplied to the refrigerant introduction part 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 part 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 adhesion of the raw material powder P to the injection passage of the nozzle 23d can be suppressed. The raw material powder P will be described later.

[0026] 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 portion (valve seat portion) 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 since the spray gun 23 has a smaller moment of inertia than the cylinder head 12, 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 relatively, 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.

[0027] Next, a manufacturing method of the cylinder head 12 having the valve seats 16b, 17b will be described. Fig. 4 is a process diagram showing the machining steps of the valve parts 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 step S1, a cutting step S2, a covering step S3, and a finishing step S4. Note that the machining steps other than those of the valve parts are omitted for the sake of simplicity of explanation.

[0028] In the casting process S1, aluminum alloy for casting is poured into a metal mold in which a sand core is set, and a cylinder head blank 3 having an intake port 16, an exhaust port 17, etc. formed in the main body is cast. Here, the cylinder head blank 3 refers to a semi-finished product in the middle of manufacturing before being processed into a cylinder head 12 as a final product. The intake port 16 and the exhaust port 17 are formed by the sand core, and the recesses 12b are formed by the metal mold. FIG. 5 is a perspective view of the cylinder head blank 3 cast in the casting process S1, seen from the mounting surface 12a side to the cylinder block 11. The cylinder head blank 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 blank 3, and are connected to openings provided on both sides of the cylinder head blank 3, respectively.

[0029] 6(A) is a cross-sectional view of the cylinder head blank 3 taken along line VI-VI in FIG. 5, showing the intake port 16 after the casting process S1 is completed. The intake port 16 is provided with a circular opening 16a exposed in the recess 12b of the cylinder head blank 3.

[0030] FIG. 6(B) is a cross-sectional view showing the state in which the annular valve seat portion 16c is formed in the intake port of FIG. 6(A) in the cutting process. In the cutting process S2, the cylinder head blank 3 is milled using an end mill, a ball end mill, or the like, to form the annular valve seat portion 16c in the opening 16a of the intake port 16, as shown in FIG. 6(B). The annular valve seat portion 16c is an annular groove that is 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 coating, and the coating is used to process the valve seat 16b. Therefore, the annular valve seat portion 16c is formed to be one size larger than the valve seat 16b.

[0031] Fig. 6(C) is a cross-sectional view showing a state in which a valve seat 16b is formed in the intake port 16 of Fig. 6(B) in the coating process S3. In the coating process S3, the raw material powder P is sprayed onto the annular valve seat portion 16c of the cylinder head blank 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 Fig. 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 attitude, the cylinder head blank 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.

[0032] 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 the 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 spray gun 23 is rotated about the rotation axis while spraying the raw material powder P from the nozzle 23d onto the annular valve seat portion 16c, thereby forming a coating around the entire circumference of the annular valve seat portion 16c.

[0033] During the covering step S3, the nozzle 23d introduces the coolant supplied from the coolant circulation circuit 27 into the flow path from the coolant inlet 23e. The coolant cools the nozzle 23d while flowing from the front end side to the rear end side of the flow path formed inside the nozzle 23d. The coolant that has flowed to the rear end side of the flow path is discharged from the flow path by the coolant outlet 23f and collected.

[0034] When the spray gun 23 completes one rotation around the rotation axis to complete the formation of the valve seat 16b, 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 next formed coincides with the reference axis of the industrial robot. Then, after the industrial robot has completed 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 of the intake ports 16 and exhaust ports 17 of the cylinder head blank 3.

[0035] 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 circumferential 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, which is 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.

[0036] In this way, the finishing step S4 can eliminate surface roughness of the intake port 16 caused by casting, and can also remove excess coating SF formed in the coating step 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 description of the procedure for forming the valve seat 17b for the exhaust port 17 will be omitted.

[0037] Now, the valve seats of the cylinder head 12 are required to have high heat resistance, wear resistance, and adhesion to withstand the impact of 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, 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 among the performances required for the valve seats, a hard material may 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, in order to improve the adhesion of the valve seats, a soft material may 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.

[0038] Therefore, in the cylinder head 12 and its manufacturing method of the present 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 in area percentage, also called 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. That is, the film is formed so that the soft material is rich in the area where adhesion is required more than heat resistance and wear resistance, while the hard material is rich in the area where heat resistance and wear resistance are required more than adhesion. This makes it possible to obtain the cylinder head 12 having the valve seats 16b, 17b with excellent wear resistance and adhesion in appropriate places.

[0039] Although the intake port 16 of the internal combustion engine faces the combustion chamber 15, it is cooled by the intake air and is therefore in a temperature environment of about 80 to 200°C. Therefore, it is preferable to give priority to ensuring adhesion as long as heat resistance and wear resistance at 200°C or less can be met. In contrast, the exhaust port 17 of the 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 give priority to ensuring heat resistance and wear resistance at least of 300°C or more.

[0040] FIG. 7(A) is a cross-sectional view showing the valve seat 16b of the intake port 16, and FIG. 7(B) is a cross-sectional view showing the valve seat 17b of the exhaust port 17. In FIG. 7, black circles indicate the hard material HM, and the other film portions are the soft material SM. The content ratio (area %) of the hard material HM in the valve seat 16b shown in FIG. 7(A) is smaller than the content ratio (area %) of the hard material HM in the valve seat 17b shown in FIG. 7(B). More preferably, the content ratio of the hard material HM in the valve seat 16b shown in FIG. 7(A) is 5-20% by area, whereas the content ratio of the hard material HM in the valve seat 17b shown in FIG. 7(B) is 50-90% by area.

[0041] 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 constituting the valve seat 16b is less than 5 area %, the amount of wear of the valve seat 16b due 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 a substantially constant value. Therefore, in consideration of the adhesiveness as a metal film, it can be said that the mixing ratio of the hard material HM in the valve seat 16b is preferably 5 to 20 area %.

[0042] The mixing ratio of the hard material and the soft material is defined by the area ratio in the cross section of the metal film because the ratio of the raw powder of the hard material sprayed from the nozzle and adhering (so-called adhesion efficiency) is different from the ratio of the raw powder of the soft material sprayed from the nozzle and adhering, and even if the mixing ratio of the hard material and the soft material before deposition is defined by weight ratio, etc., it differs 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 the adhesion efficiency of the raw powder of the soft material, for example, if you want to set the mixing ratio of the hard material in the metal film to 10 area%, you set the mixing weight % of the raw powder of the hard material sprayed from the nozzle to a value greater than 10%.

[0043] 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 hardening copper alloy can be exemplified. As the precipitation hardening 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 hardening copper alloy containing nickel, silicon and chromium, a precipitation hardening copper alloy containing nickel, silicon and zirconium, a precipitation hardening alloy containing nickel, silicon, chromium and zirconium, a precipitation hardening copper alloy containing chromium and zirconium, etc. can also be applied. In addition, as the iron-based material, pure iron or low carbon steel with 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 is a material that has a Vickers hardness of less than 500 HV, preferably 100 to 400 HV, when formed into a film by itself.

[0044] The hard material of this embodiment means a material as a main component whose average hardness is substantially harder than the soft material described above. Examples of the hard material 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 the hard material 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 materials, called high speed steel, a monoglutinous type and a molybdenum type. The composition of SKH51 materials is described in JIS4403, and a representative composition is Fe-0.9C-0.3Si-0.4Mn-4.2Cr-5.0Mo-2.0V-6.5W (numbers are 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.

[0045] When producing the powders of the soft material and hard material of this embodiment, although not particularly limited, the hard material is preferably produced by the water atomization method, whereas 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 quenched and solidified in the process of falling to obtain a powder. Because the cooling rate is fast, it solidifies before the surface tension acts. For this reason, 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, so that the adhesion is high. In addition, the production by the water atomization method is easier than the production by the gas atomization method.

[0046] In contrast, gas atomization is a manufacturing method in which high-pressure gas is sprayed onto metal molten at high temperature to scatter it, and as it falls, it cools and solidifies, obtaining 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, which is disadvantageous in terms of wear resistance.

[0047] Next, to form a film having different content ratios of the hard material and the soft material contained in the film like 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 supplying 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 supplying 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 supplying section 22 may be used to form two specifications of the valve seats 16b and 17b.

[0048] Alternatively, two types of valve seats 16b, 17b may be formed by controlling the moving speed of the nozzle 23d using one cold spray device 2 having the same content ratio of raw material powder of the hard material HM and raw material powder of the soft material SM in the raw material powder supplying part 22. That is, when forming a metal film 5 for 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.

[0049] 10(A) is a schematic diagram showing a film formation state when the moving speed of the nozzle 23d of the cold spray device 2 is low, and Fig. 10(B) is a schematic diagram showing a film formation state when the moving 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 discharge amount of the raw material powder P from the nozzle 23d and the moving speed of the nozzle 23d. Therefore, when the content ratio of hard material HM and soft material SM in the raw material powder P is kept constant and the amount of raw material powder P discharged from the nozzle 23d is kept constant, when the moving speed of the nozzle 23d is relatively slow, the density (weight per unit volume) of the raw material powder P containing the hard material HM and the soft material SM during spraying becomes large, as shown in Figure 10(A), and conversely, when the moving speed of the nozzle 23d is relatively fast, the density of the raw material powder P containing the hard material HM and the soft material SM during spraying becomes small, as shown in Figure 10(B).

[0050] Here, the mechanism by which the raw material powder P injected 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 the hard material HM that does not bounce back and adhere to the substrate 4 is reduced, and the substrate 4 is 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 amount of the hard material HM that does not bounce back and adhere to the substrate 4 is increased, and the substrate 4 is relatively rich in soft material.

[0051] 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 discharge amount of the raw material powder P from the nozzle 23d is constant, when the moving speed of the nozzle 23d is relatively slow, the raw material powder becomes rich in hard material as shown in Fig. 10(A), and conversely, when the moving speed of the nozzle 23d is relatively fast, the raw material powder 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 discharge amount of the raw material powder P from the nozzle 23d is constant, the moving speed of the nozzle 23d is set to a relatively high speed when forming the valve sheet 16b shown in Fig. 7(A), and the moving speed of the nozzle 23d is set to a relatively low speed when forming the valve sheet 17b shown in Fig. 7(B). As a result, two types of valve seats 16b, 17b can be formed 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 supplying section 22 have the same content ratio.

[0052] As described above, the density of the raw material powder P during spraying is determined by the discharge amount of the raw material powder P from the nozzle 23d and the moving speed of the nozzle 23d, so when the moving speed of the nozzle 23d is constant, when the discharge amount of the raw material powder P from the nozzle 23d is relatively large, the raw material powder P becomes rich in hard material as shown in Fig. 10(A), and conversely, when the discharge amount of the raw material powder P 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 discharge amount of the raw material powder P 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 discharge amount of the raw material powder P 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, 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 supplying section 22 have the same content ratio.

[0053] As described above, according to the cylinder head and manufacturing method thereof 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 at appropriate locations can be obtained.

[0054] Furthermore, according to the cylinder head and manufacturing method thereof of this embodiment, the content of the hard material HM in the cross section of the valve seat 16b is 5 to 20 area %, so that the adhesion can be improved while ensuring the wear resistance.

[0055] Furthermore, 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 the material is hard, in addition to the anchor effect provided by the multiple protrusions, the protruding portions are easily deformed, thereby increasing adhesion.

[0056] In addition, according to the cylinder head and the manufacturing method thereof of this embodiment, the hard material HM is a powder manufactured by the water atomization method, so in addition to the anchor effect of the multiple protrusions, the protrusions are easily deformed, so that the adhesion is high. Furthermore, manufacturing by the water atomization method is easier than manufacturing by the gas atomization method.

[0057] In addition, according to the cylinder head and the manufacturing method thereof of this embodiment, the soft material SM is a powder produced by gas atomization, and therefore has a spherical shape, which increases the packing density and further improves adhesion. In contrast, the powder of the soft material SM produced by water atomization does not have sufficient material strength and is disadvantageous in terms of wear resistance.

[0058] Furthermore, 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, 17b of two specifications using one cold spray device 2 in which the raw material powder supply section 22 has the same content ratio of the raw material powder of the hard material HM and the raw material powder of the soft material SM.

[0059] The valve seat 16b corresponds to a first valve seat according to the present invention, and the valve seat 17b corresponds to a second valve seat according to the present invention. [Explanation of symbols]

[0060] 1. Internal combustion engine 11...Cylinder block 11a...Cylinder 12...Cylinder head 12a…Mounting surface 12b…Recess 12c,12d…side 13…Piston 13a…Connecting rod 13b…Top surface 14…Crankshaft 15…Combustion chamber 16…Intake port 16a...Opening 16b...Valve seat 16c...Annular valve seat section 17…Exhaust port 17a...Opening 17b…Valve seat 18…Intake 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 device 21...Gas supply section 21a…Compressed gas cylinders 21b…Working gas line 21c…Carrier gas line 22...Raw material powder supply section 22a,221a,222a...Raw material powder supply device 22b…Measuring instrument 22c, 221c, 222c…Raw powder supply line 23…Spray gun 23a…Chamber 23d…Nozzle 3…Cylinder head raw material 4...Base material 5...Metal film

Claims

1. 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.

2. 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, wherein an amount of the raw material powder discharged from the nozzle when forming the first valve seat is less than an amount of the raw material powder discharged from the nozzle when forming the second valve seat.

3. 3. The method according to claim 1, wherein the hard material is a powder produced by a water atomization method.

4. The method according to claim 3, wherein the soft material is a powder produced by a gas atomization method.

5. 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.

6. 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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