Patent Application
20230399961
The present invention relates to a semimanufactured cylinder head (cylinder head blank) used in an internal-combustion engine and a method of manufacturing a cylinder hear.
A method of manufacturing sliding members is known, which includes spraying a raw material powder such as metal powder onto the seating portions for engine valves using a cold spray method thereby to form valve seats having excellent high-temperature wear resistance (Patent Document 1).
Unfortunately, however, the valve seats of an engine have a problem in that the valve seat films formed by the cold spray method may crack or delaminate due to impact caused by striking input of intake and exhaust valves or wear due to repeated collisions.
A problem to be solved by the present invention is to provide a semimanufactured cylinder head equipped with valve seat films having excellent interfacial adhesion and high strength and a method of manufacturing a cylinder head.
The present invention solves the above problem by forming the cross section of a film formation portion along the radial direction into a groove shape including a flat bottom surface and a pair of side surfaces adjacent to the bottom surface. The film formation portion is to be sprayed with a raw material powder by using a cold spray method to form a film.
According to the present invention, the compressive residual stress of a metal film formed on the film formation portion by using a cold spray method acts on the pair of side surfaces of the groove shape of the film formation portion, and it is therefore possible to manufacture a cylinder head equipped with the metal film having excellent interfacial adhesion and high strength.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the description will be directed to an internal-combustion engine 1 equipped with a cylinder head that is manufactured by using a semimanufactured cylinder head according to the present invention with a manufacturing method according to the present invention.
The internal-combustion engine 1 includes a cylinder block 11 and a cylinder head 12 that is mounted on the upper portion 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 sheet. The cylinders 11a house respective pistons 13 that reciprocate in the vertical direction in the figure. Each piston 13 is connected to a crankshaft 14, which extends in the depth direction of the drawing sheet, via a connecting rod 13a.
The cylinder head 12 has a mounting surface 12a for being mounted on the cylinder block 11. The mounting surface 12a is formed with four recessed portions 12b at positions corresponding to respective cylinders 11a. The recessed portions 12b define combustion chambers 15 of the cylinders. Each combustion chamber 15 is a space for combusting a mixture gas of fuel and intake air and is defined by a recessed portion 12b of the cylinder head 12, a top surface 13b of the piston 13, and an inner surface of the cylinder 11a.
The cylinder head 12 includes intake ports 16 that connect between the combustion chambers 15 and one side surface 12c of the cylinder head 12. The intake ports 16 have a curved, approximately cylindrical shape and guide intake air from an intake manifold (not illustrated) connected to the side surface 12c into respective combustion chambers 15. The cylinder head 12 further includes exhaust ports 17 that connect between the combustion chambers 15 and the other side surface 12d of the cylinder head 12. The exhaust ports 17 have a curved, approximately cylindrical shape like the intake ports 16 and exhaust the exhaust gas generated in respective combustion chambers 15 to an exhaust manifold (not illustrated) connected to the side surface 12d. In the internal-combustion engine 1 according to the present embodiment, one cylinder 11a is provided with two intake ports 16 and two exhaust ports 17.
The cylinder head 12 is provided with intake valves 18 that open and close the intake ports 16 with respect to the combustion chambers 15 and exhaust valves 19 that open and close the exhaust ports 17 with respect to the combustion chambers 15. Each intake valve 18 includes a round rod-shaped valve stem 18a and a disk-shaped valve head 18b that is provided at the tip of the valve stem 18a. Likewise, each exhaust valve 19 includes a round rod-shaped valve stem 19a and a disk-shaped valve head 19b that is provided at the tip of the valve stem 19a. The valve stems 18a and 19a are slidably inserted into approximately cylindrical valve guides 18c and 19c, respectively. This allows the intake valves 18 and the exhaust valves 19 to be movable along the axial directions of the valve stems 18a and 19a, respectively, with respect to the combustion chambers 15.
Like the intake port 16, the exhaust port 17 includes an approximately circular opening portion 17a at the portion communicating with the combustion chamber 15, and the opening portion 17a has an annular edge portion (seat portion for valve) formed with an annular valve seat film 17b that can abut against the valve head 19b of an exhaust valve 19. 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 film 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 film 17b to open the exhaust port 17. The diameter of the opening portion 16a of the intake port 16 is set larger than the diameter of the opening portion 17a of the exhaust port 17.
The internal-combustion engine 1 is a four-cycle engine, in which only the intake valve 18 opens when the corresponding piston 13 moves down, and the mixture gas is thereby introduced from the intake port 16 into the cylinder 11a (intake stroke). Subsequently, the intake valve 18 and the exhaust valve 19 are brought into the closed state, and the piston 13 is moved up to almost the top dead center to compress the mixture gas in the cylinder 11a (compression stroke). Then, when the piston 13 reaches almost the top dead center, the compressed mixture gas is ignited by a spark plug to explode. This explosion makes the piston 13 move down to the bottom dead center and is converted into the rotational force via the connected crankshaft 14 (combustion/expansion stroke). Finally, when the piston 13 reaches the bottom dead center and starts moving up again, only the exhaust valve 19 is opened to exhaust the exhaust gas in the cylinder 11a to the exhaust port 17 (exhaust stroke). The internal-combustion engine 1 repeats the above cycle to generate the output.
The opening portions 16a and 17a of the cylinder head 12 have respective annular edge portions, or seat portions for valves, and the valve seat films 16b and 17b are formed directly on the annular edge portions by using a cold spray method. The cold spray method refers to a method that includes making a supersonic flow of an operation gas having a temperature lower than the melting point or softening point of a raw material powder, injecting the raw material powder carried by a carrier gas into the operation gas to spray the raw material powder from a nozzle tip, and causing the raw material powder in the solid phase state to collide with a base material to form a film by plastic deformation of the raw material powder. Compared with a thermal spray method in which the material is melted and deposited on a base material, the cold spray method has features that a dense film can be obtained without oxidation in the air, thermal alteration is suppressed because of less thermal effect on the material particles, the film formation speed is high, the film can be made thick, and the deposition efficiency is high. In particular, the cold spray method is suitable for the use for structural materials such as the valve seat films 16b and 17b of the internal-combustion engine 1 because the film formation speed is high and the films can be made thick.
The gas supply unit 21 includes a compressed gas cylinder 21a, an operation gas line 21b, and a carrier gas line 21c. Each of the operation gas line 21b and the carrier gas line 21c includes a pressure regulator 21d, a flow rate control valve 21e, a flow meter 21f, and a pressure gauge 21g. The pressure regulators 21d, the flow rate control valves 21e, the flow meters 21f, and the pressure gauges 21g are used for adjusting the pressure and flow rate of each of the operation gas and carrier gas from the compressed gas cylinder 21a.
The operation gas line 21b is installed with a heater 21i such as a tape heater, and the heater 21i heats the operation gas line 21b by being supplied with power from a power source 21h through power supply lines 21j and 21j. The operation 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 a chamber 23a of the spray gun 23. The chamber 23a is installed with a pressure gauge 23b and a thermometer 23c that have a signal lines 23g and 23h, respectively, and the detected pressure value and temperature value are output to a controller (not illustrated) via the signal lines 23g and 23h and are used for feedback control of the pressure and temperature.
On the other hand, the raw material powder supply unit 22 includes a raw material powder supply device 22a, which is provided with a weighing machine 22b and a raw material powder supply line 22c. The carrier gas from the compressed gas cylinder 21a is introduced into the raw material powder supply device 22a through the carrier gas line 21c. A predetermined amount of the raw material powder weighed by the weighing machine 22b is carried into the chamber 23a via the raw material powder supply line 22c.
The spray gun 23 sprays the raw material powder P, which is carried into the chamber 23a by the carrier gas, together with the operation gas as the supersonic flow from the tip of the nozzle 23d and causes the raw material powder P in the solid phase state or solid-liquid coexisting state to collide with a base material 4 to form a metal film 5. In the present embodiment, the cylinder head 12 is applied as the base material 4, and the raw material powder P is sprayed onto the annular edge portions of the opening portions 16a and 17a of the cylinder head 12 by using the cold spray method to form the valve seat films 16b and 17b as metal films 5.
The nozzle 23d has a flow channel (not illustrated) through which a coolant such as water flows. The tip of the nozzle 23d is provided with a coolant introduction port 23e through which the coolant is introduced into the flow channel, and the base end of the nozzle 23d is provided with a coolant discharge port 23f through which the coolant in the flow channel is discharged. The nozzle 23d is cooled through introducing the coolant into the flow channel from the coolant introduction port 23e, flowing the coolant in the flow channel, and discharging the coolant from the coolant discharge port 23f.
The coolant circulation circuit 27 which circulates the coolant through the flow channel of the nozzle 23d includes a tank 271 that stores the coolant, an introduction pipe 274 that is connected to the above-described coolant introduction port 23e, a pump 272 that is connected to the introduction pipe 274 and flows the coolant between the tank 271 and the nozzle 23d, a cooler 273 that cools the coolant, and a discharge pipe 275 that is connected to the coolant discharge port 23f. The cooler 273 is composed, for example, of a heat exchanger or the like and cools the coolant by exchanging heat between the coolant whose temperature is increased by cooling the nozzle 23d and a refrigerant such as air, water, or gas.
The coolant circulation circuit 27 vacuums up the coolant stored in the tank 271 using the pump 272 and supplies the coolant to the coolant introduction port 23e via the cooler 273. The coolant supplied to the coolant introduction port 23e flows through the flow channel in the nozzle 23d from the tip side toward the rear end side while exchanging heat with the nozzle 23d to cool it. The coolant flowed to the rear end side of the flow channel is discharged from the coolant discharge port 23f to the discharge pipe 275 and returns to the tank 271. Thus, the coolant circulation circuit 27 cools the nozzle 23d by circulating the coolant while cooling it, and it is therefore possible to suppress the adhesion of the raw material powder P to the injection passage of the nozzle 23d.
The valve seats of the cylinder head 12 are required to have high heat resistance and wear resistance that can withstand the striking input from the valves in the combustion chambers 15, and also required to have high heat conductivity for cooling the combustion chambers 15. In response to these requirements, according to the valve seat films 16b and 17b formed of the powder of precipitation-hardened copper alloy, for example, the valve seats can be obtained which are excellent in the heat resistance and wear resistance and harder than the cylinder head 12 formed of an aluminum alloy for casting.
Moreover, the valve seat films 16b and 17b are formed directly on the cylinder head 12, and higher heat conductivity can therefore be obtained as compared with conventional valve seats formed by press-fitting seat rings as separate components into the port opening portions. Furthermore, as compared with the case in which the seat rings as separate components are used, subsidiary effects can be obtained such as that the valve seats can be made close to a water jacket for cooling and the tumble flow can be promoted due to expansion of the throat diameter of the intake ports 16 and exhaust ports 17 and optimization of the port shape.
The raw material powder P used for forming the valve seat films 16b and 17b is preferably a powder of metal that is harder than an aluminum alloy for casting and with which the heat resistance, wear resistance, and heat conductivity required for the valve seats can be obtained. For example, it is preferred to use the above-described precipitation-hardened copper alloy. The precipitation-hardened copper alloy for use may be a Corson alloy that contains nickel and silicon, chromium copper that contains chromium, zirconium copper that contains zirconium, or the like. It is also possible to apply, for example, a precipitation-hardened copper alloy that contains nickel, silicon, and chromium, a precipitation-hardened copper alloy that contains nickel, silicon, and zirconium, a precipitation-hardened copper alloy that contains nickel, silicon, chromium, and zirconium, a precipitation-hardened copper alloy that contains chromium and zirconium, or the like.
The valve seat films 16b and 17b may also be formed by mixing a plurality of types of raw material powders; for example, a first raw material powder and a second raw material powder. In this case, it is preferred to use, as the first raw material powder, a powder of metal that is harder than an aluminum alloy for casting and with which the heat resistance, wear resistance, and heat conductivity required for the valve seats can be obtained. For example, it is preferred to use the above-described precipitation-hardened copper alloy. On the other hand, it is preferred to use, as the second raw material powder, a powder of metal that is harder than the first raw material powder. The second raw material powder for application may be an alloy such as an iron-based alloy, a cobalt-based alloy, a chromium-based alloy, a nickel-based alloy, or a molybdenum-based alloy, ceramics, or the like. One type of these metals may be used alone, or two or more types may also be used in combination.
With the valve seat films formed of a mixture of the first raw material powder and the second raw material powder which is harder than the first raw material powder, more excellent heat resistance and wear resistance can be obtained than those of valve seat films formed only of a precipitation-hardened copper alloy. The reason that such an effect is obtained appears to be because the second raw material powder allows the oxide film existing on the surface of the cylinder head 12 to be removed so that a new interface is exposed and formed to improve the interfacial adhesion between the cylinder head 12 and the metal films. Additionally or alternatively, it appears that the anchor effect due to the second raw material powder sinking into the cylinder head 12 improves the interfacial adhesion between the cylinder head 12 and the metal films. Additionally or alternatively, it appears that when the first raw material powder collides with the second raw material powder, a part of the kinetic energy is converted into heat energy, or heat is generated in the process in which a part of the first raw material powder is plastically deformed, and such heat promotes the precipitation hardening in a part of the precipitation-hardened copper alloy used as the first raw material powder.
The cold spray apparatus 2 of the present embodiment may be used as follows. The cylinder head 12 to be formed with the valve seat films 16b and 17b is fixed to a base table 45, while the tip of the nozzle 23d of the spray gun 23 is rotated along the annular edge portions of the opening portions 16a and 17a of the cylinder head 12 to spray the raw material powder. The cylinder head 12 is not rotated, so it does not require a large occupied space, and the inertia moment of the spray gun 23 is smaller than that of the cylinder head 12, so it is excellent in the rotational transient characteristics and responsiveness. However, for the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present invention, the cylinder head 12 as the base material and the spray gun 23 need only move relative to each other; therefore, the nozzle 23d of the spray gun 23 may be fixed while the cylinder head 12 may be rotated and swung, or the cylinder head 12 may be rotated and swung together with the nozzle 23d of the spray gun 23.
The description will then be directed to a method of manufacturing the cylinder head 12 including the valve seat films 16b and 17b.
In the casting step S1, an aluminum alloy for casting is poured into a mold in which sand cores are set, and casting is performed to mold a semimanufactured cylinder head 3 having intake ports 16, exhaust ports 17, etc. formed in the main body portion. Here, the semimanufactured cylinder head 3 refers to a semi-finished product in middle of production before being processed into the cylinder head 12 as the final product. The intake ports 16 and the exhaust ports 17 are formed by the sand cores, and the recessed portions 12b are formed by the mold.
In the subsequent cutting step S2, milling work is performed on the semimanufactured cylinder head 3 as illustrated in
In the method of manufacturing the cylinder head 12 according to the present embodiment, as illustrated in
The valve seats formed by the cold spray method have an advantage that the heat resistance and wear resistance are excellent and the high heat conductivity can be obtained, while being required to have interfacial adhesion and high strength that can withstand the striking input from the intake and exhaust valves in the combustion chambers 15. To this end, in the method of manufacturing the cylinder head 12 according to the present embodiment, the annular valve seat portion 16c is formed such that, as illustrated in
As illustrated in
As illustrated in a comparative example of
In contrast, as illustrated in
Moreover, when the boundary surfaces GC between the flat bottom surface G1 and the side surfaces G2 and G2 are formed in a gentle arc shape, the raw material powder P sprayed by the cold spray method adheres evenly to the boundary surfaces GC. This can enhance the interfacial adhesion of the valve seat film 16b formed on the annular valve seat portion 16c.
As illustrated in
On the other hand, the smaller the groove angle Gθ in the groove shape of the annular valve seat portion 16c, the smaller the compressive residual stresses (black arrows in
Thus, by setting the groove angle Gθ in the groove shape of the annular valve seat portion 16c to 30°≤Gθ≤45°, it is possible to form the valve seat film 16b having higher strength, which is not subject to restrictions in the manufacturing steps after film formation and can suppress the occurrence of cracks due to the concentration of the impact loads on the edge portions of the valve seat film 16b.
The groove angle Gθ in the groove shape may have to be 30°≤Gθ≤45° only on one side in the radial direction of a tool and is not restricted on the other side during the machining, so the groove angle may be outside the above range on the other side.
Referring again to
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 table. The base table 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 to be formed with the valve seat film 16b is vertical and overlaps the rotation axis of the spray gun 23. In this state, the spray gun 23 is rotated around the rotation axis while spraying the raw material powder P from the nozzle 23d onto the annular valve seat portion 16c, thereby forming a film on the entire circumference of the annular valve seat portion 16c.
While the coating step S3 is being carried out, the nozzle 23d introduces the coolant supplied from the coolant circulation circuit 27 into the flow channel through the coolant introduction port 23e. The coolant cools the nozzle 23d while flowing from the tip side to the rear end side of the flow channel formed inside the nozzle 23d. The coolant that has flowed to the rear end side of the flow channel is discharged from the channel through the coolant discharge port 23f and recovered.
When the spray gun 23 makes one rotation around the rotation axis to complete the formation of the valve seat film 16b, the rotation of the spray gun 23 is temporarily stopped. During this stop of rotation, 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 to be subsequently formed with the valve seat film 16b coincides with the reference axis of the industrial robot. Then, after the industrial robot completes the movement of the spray gun 23, the rotation of the spray gun 23 is resumed to form the valve seat film 16b in the next intake port 16. This operation is then repeated thereby to form the valve seat films 16b and 17b for all the intake ports 16 and exhaust ports 17 of the semimanufactured cylinder head 3.
According to the valve seat film 16b formed based on the groove shape of the annular valve seat portion 16c of the present embodiment, even when the shear force acts on the valve seat film 16b due to the combustion pressure of the engine, this force can be received by the side surfaces G2 and G2 of the groove shape. Although the film thickness W of the valve seat film 16b is not particularly limited, the film thickness W suitable for the groove shape of the annular valve seat portion 16c according to the present embodiment is preferably 300 μm to 1500 μm. This allows the side surfaces G2 and G2 of the groove shape to receive the shear force due to the combustion pressure which tends to concentrate on the edge portions of the valve seat film 16b, and it is therefore possible to manufacture a cylinder head including the valve seat film 16b having higher strength.
Referring again to
Thus, according to the finishing step S4, the surface roughness of the intake port 16 due to the cast molding is eliminated, and the excessive film SF formed in the coating step S3 can be removed.
As described above, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the cross-sectional shape along the radial direction of the annular valve seat portion 16c is formed in a groove shape including the flat bottom surface G1 and the pair of adjacent side surfaces G2, and the compressive residual stresses of the metal film 5 act on the pair of side surfaces G2 of the groove shape; therefore, it is possible to manufacture the cylinder head 12 including the valve seat film 16b having excellent interfacial adhesion and high strength.
Moreover, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the compressive residual stresses of the metal film 5 acting on the side surfaces G2 and G2 of the groove shape of the annular valve seat portion 16c counteract the impact loads due to the striking input from the valve, and the impact loads concentrating on the edge portions of the valve seat film 16b can therefore be reduced to suppress the cracking and delamination of the valve seat film 16b.
Furthermore, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the boundary surfaces GC between the flat bottom surface G1 and the side surfaces G2 and G2 in the groove shape of the annular valve seat portion 16c are formed in a gentle arc shape, and the impact loads due to the striking input from the valve are thereby distributed on the curved surfaces to alleviate the stress concentration; therefore, the valve seat film 16b having higher strength can be formed.
In addition, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the boundary surfaces GC between the flat bottom surface G1 and the side surfaces G2 and G2 in the groove shape of the annular valve seat portion 16c are formed in a gentle arc shape, and the raw material powder P sprayed using the cold spray method thereby adheres evenly to the boundary surfaces GC; therefore, it is possible to enhance the interfacial adhesion of the valve seat film 16b formed on the annular valve seat portion 16c.
Moreover, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the groove angle Gθ, which is an acute-side dihedral angle formed between the flat bottom surface G1 and one side surface G2 in the groove shape of the annular valve seat portion 16c, is set to 30°≤Gθ≤45°, and it is therefore possible to form the valve seat film 16b having higher strength, which is not subject to restrictions in the manufacturing steps after film formation and can suppress the occurrence of cracks due to the concentration of the impact loads on the edge portions of the valve seat film 16b.
The groove angle Gθ in the groove shape may have to be 30°≤Gθ≤45° only on one side in the radial direction of a tool and is not restricted on the other side during the machining, so the groove angle may be outside the above range on the other side.
Furthermore, according to the semimanufactured cylinder head and the method of manufacturing a cylinder head of the present embodiment, the film thickness W of the valve seat film 16b is 300 μm to 1500 μm, and the side surfaces G2 and G2 of the groove shape can receive the shear force due to the combustion pressure which tends to concentrate on the edge portions of the valve seat film 16b; therefore, it is possible to manufacture a cylinder head including the valve seat film 16b having higher strength.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/039607 | 10/21/2020 | WO |
