Patent Application
20210268576
The present invention relates to a method for manufacturing a cylinder head of an internal-combustion engine and relates also to a semimanufactured cylinder head used for manufacturing a cylinder head.
A sliding member and a method for manufacturing the sliding member are known (Patent Document 1). The sliding member includes a film layer formed on a base material. The film layer is composed of a particle aggregate of a precipitation-hardened copper alloy. The method for manufacturing the sliding member includes spraying metal powder of the precipitation-hardened copper alloy onto the base material using a cold spray method to form the previously described film layer.
The invention of Patent Document 1 also proposes an approach to using the sliding member in an internal-combustion engine. In this approach, the valve seat for an engine valve is formed by spraying metal powder of the precipitation-hardened copper alloy onto an engine valve seating portion of a cylinder head using a cold spray method to provide the previously described film layer.
Unfortunately, however, when the metal powder is sprayed onto the seating portion of the cylinder head using a cold spray method, the metal powder may be scattered also around the seating portion to form an unnecessary excess film. If such an excess film is formed in an intake or exhaust port of the cylinder head, a problem may arise in that the size of the port varies and the fuel efficiency and output performance of the engine deteriorate.
A problem to be solved by the present invention is to provide a method for manufacturing a cylinder head and a semimanufactured cylinder head with which a valve seat film can be formed using a cold spray method while suppressing the formation of an excess film in a port.
The present invention solves the above problem through manufacturing a semimanufactured cylinder head having a shielding curtain portion and spraying metal powder onto an annular valve seat portion using a cold spray method to form a valve seat film. The shielding curtain portion projects in an annular shape from an annular edge portion of an opening portion of a port for intake or exhaust toward the center of the port. The annular valve seat portion is located on an outer side of the port than the shielding curtain portion.
According to the present invention, the shielding curtain portion partially shields the inside of the port, and the valve seat film can therefore be formed using a cold spray method while suppressing the formation of an excess film in the port.
Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. First, an internal-combustion engine 1 including a cylinder head manufactured by the manufacturing method according to one or more embodiments of the present invention will be described. The cylinder head is manufactured using a semimanufactured cylinder head according to one or more embodiments of 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, a 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 to the cylinder block 11. The mounting surface 12a is provided with four recesses 12b at positions corresponding to respective cylinders 11a. The recesses 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 recess 12b of the cylinder head 12, a top surface 13b of the piston 13, and an inner circumferential surface of the cylinder 11a.
The cylinder head 12 includes ports for intake (referred to as intake ports, hereinafter) 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 supply 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 ports for exhaust (referred to as exhaust ports, hereinafter) 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 by the combustion of the mixture gas 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 one or more embodiments of the present invention, 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 an approximately 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 an approximately 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 with respect to the combustion chambers 15 along the axial directions of the valve stems 18a and 19a.
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 provided with an annular valve seat film 17b that abuts 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 comes into contact with the valve seat film 17b to close the exhaust port 17. 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.
In the four-cycle internal-combustion engine 1, for example, only the intake valve 18 opens when the corresponding piston 13 moves down, and the mixture gas is introduced from the intake port 16 into the cylinder 11a. Subsequently, in a state in which the intake valve 18 and the exhaust valve 19 are closed, the piston 13 moves up to compress the mixture gas in the cylinder 11a, and when the piston 13 approximately reaches the top dead center, the mixture gas is ignited to explode by a spark plug, which is not illustrated. 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. 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. 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, and the valve seat films 16b and 17b are formed directly on the annular edge portions 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 metal powder, injecting the metal powder carried by a carrier gas into the operation gas to spray the metal powder from a nozzle tip, and causing the metal powder in the solid phase state to collide with a base material to form a metal film by plastic deformation of the metal 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 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 the operation gas and carrier gas from the compressed gas cylinder 21a.
The operation gas line 21b is installed with a heater 21i heated by a power source 21h. The operation gas is heated by the heater 21i to a temperature lower than the melting point or softening point of the metal powder and then introduced into a chamber 23a in the cold spray gun 23. The chamber 23a is installed with a pressure gauge 23b and a thermometer 23c, which are used for feedback control of the pressure and temperature.
On the other hand, the metal powder supply unit 22 includes a metal powder supply device 22a, which is provided with a weighing machine 22b and a metal powder supply line 22c. The carrier gas from the compressed gas cylinder 21a is introduced into the metal powder supply device 22a through the carrier gas line 21c. A predetermined amount of the metal powder weighed by the weighing machine 22b is carried into the chamber 23a via the metal powder supply line 22c.
The cold spray gun 23 sprays the metal 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 a nozzle 23d and causes the metal powder P in the solid phase state or solid-liquid coexisting state to collide with a base material 24 to form a film 24a. In one or more embodiments of the present invention, the cylinder head 12 is applied as the base material 24, and the metal powder P is sprayed onto the annular edge portions of the opening portions 16a and 17a of the cylinder head 12 using the cold spray method to form the valve seat films 16b and 17b.
The valve seats of the cylinder head 12 are required to have high heat resistance and wear resistance to withstand the impact input from the valves in the combustion chambers 15 and high thermal 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 thermal 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 metal powder 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 thermal 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 metal powders, for example, a first metal powder and a second metal powder. In this case, it is preferred to use, as the first metal 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 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 metal powder, a powder of metal that is harder than the first metal powder. The second metal 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 metal powder and the second metal powder which is harder than the first metal 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 metal 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 metal 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 metal powder collides with the second metal 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 metal powder is plastically deformed, and such heat promotes the precipitation hardening in a part of the precipitation-hardened copper alloy used as the first metal powder.
A method for manufacturing the cylinder head 12 including the valve seat films 16b and 17b will then be described.
In the casting step S1, an aluminum alloy for casting is poured into a mold in which sand cores are set, and a semimanufactured cylinder head having intake ports 16 and exhaust ports 17 formed in the main body is cast-molded. The intake ports 16 and the exhaust ports 17 are formed by the sand cores, and the recesses 12b are formed by the mold.
In the cutting step S2, milling work is performed on the semimanufactured cylinder head 3, such as using an end mill or a ball end mill, to form an annular valve seat portion 16f and the above-described shielding curtain portion 16g.
The annular valve seat portion 16f is an annular groove that serves as the base shape of a valve seat film 16b, and is formed on the outer circumference of the opening portion 16a. That is, in the method for manufacturing the cylinder head 12 of the present embodiment, metal powder is sprayed onto the annular valve seat portion 16f using the cold spray method to form a metal film, and the valve seat film 16b is formed based on the metal film. The annular valve seat portion 16f is therefore formed with a size slightly larger than the valve seat film 16b.
The shielding curtain portion 16g is an eave-shaped member that projects in an annular shape from the annular edge portion of the opening portion 16a toward the central axis C of the intake port 16, and is located on the inner side of the intake port 16 than the annular valve seat portion 16f. The surface of the shielding curtain portion 16g on the opening portion 16a side is a flat surface orthogonal to the central axis C of the intake port 16. The shielding curtain portion 16g is formed by performing the cutting work on the above-described small-diameter portion 16c when forming the annular valve seat portion 16f. The shielding curtain portion 16g is provided to suppress the formation of an excess film on the inner circumferential surface of the intake port 16 when the valve seat film 16b is formed in the subsequent coating step S3.
In the coating step S3, metal powder is sprayed onto the annular valve seat portion 16f of the semimanufactured cylinder head 3 using the cold spray apparatus 2 to form the valve seat film 16b. More specifically, in the coating step S3, the semimanufactured cylinder head 3 and the nozzle 23d are relatively moved at a constant speed so that the metal powder is sprayed onto the entire circumference of the annular valve seat portion 16f while keeping constant the posture of the annular valve seat portion 16f and the nozzle 23d of the cold spray gun 23 and the distance between the annular valve seat portion 16f and the nozzle 23d.
In this embodiment, for example, the semimanufactured cylinder head 3 is moved with respect to the nozzle 23d of the cold spray gun 23, which is fixedly arranged, using a work rotating apparatus 4 illustrated in
The tilt stage unit 42 is a stage that supports the work table 41 and rotates the work table 41 around an A-axis arranged in the horizontal direction to tilt the semimanufactured cylinder head 3. The XY stage unit 43 includes a Y-axis stage 43a that supports the tilt stage unit 42 and an X-axis stage 43b that supports the Y-axis stage 43a. The Y-axis stage 43a moves the tilt stage unit 42 along the Y-axis arranged in the horizontal direction. The X-axis stage 43b moves the Y-axis stage 43a along the X-axis orthogonal to the Y-axis on the horizontal plane. This allows the XY stage unit 43 to move the semimanufactured cylinder head 3 to an arbitrary position along the X-axis and the Y-axis. The rotation stage unit 44 has a rotation table 44a that supports the XY stage unit 43 on the upper surface, and rotates the rotation table 44a thereby to rotate the semimanufactured cylinder head 3 around the Z-axis in an approximately vertical direction.
The tip of the nozzle 23d of the cold spray gun 23 is fixedly arranged above the tilt stage unit 42 and in the vicinity of the Z-axis of the rotation stage unit 44. The work rotating apparatus 4 uses the tilt stage unit 42 to tilt the work table 41 so that, as illustrated in
Moreover, the shielding curtain portion 16g has a hole communicating with the intake port 16 at the central part, rather than shielding the entire surface of the intake port 16, and therefore allows the sprayed metal powder P to escape into the intake port 16. According to this structure, the flow velocity of the metal powder P sprayed onto the annular valve seat portion 16f does not decrease, and the valve seat film 16b can therefore be formed reliably.
As illustrated in a comparative example of
The work rotating apparatus 4 temporarily stops the rotation of the rotation stage unit 44 when the semimanufactured cylinder head 3 makes one rotation around the Z-axis to complete the formation of the valve seat film 16b. While the rotation is stopped, the XY stage unit 43 moves the semimanufactured cylinder head 3 so that the central axis C of the intake port 16 to be subsequently formed with the valve seat film 16b coincides with the Z-axis of the rotation stage unit 44. After the XY stage unit 43 completes the movement of the semimanufactured cylinder head 3, the work rotating apparatus 4 restarts the rotation of the rotation stage unit 44 to form the valve seat film 16b for 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 the exhaust ports 17 of the semimanufactured cylinder head 3. When the valve seat film formation target is switched between an intake port 16 and an exhaust port 17, the tilt stage unit 42 changes the tilt of the semimanufactured cylinder head 3.
In the finishing step S4, finishing work is performed on the valve seat films 16b and 17b, the intake ports 16, and the exhaust ports 17. In the finishing work performed on the valve seat films 16b and 17b, the surfaces of the valve seat films 16b and 17b are cut by milling work using a ball end mill to adjust the valve seat films 16b into a predetermined shape.
In the finishing work performed on the intake ports 16, a ball end mill is inserted from the opening portion 16a into each intake port 16 to cut the inner circumferential surface of the intake port 16 on the opening port 16a side along a working line PL illustrated in
Thus, according to the finishing step S4, the surface roughness of the intake port 16 due to the cast molding is eliminated, and the shielding curtain portion 16g can be removed.
Like the intake ports 16, each exhaust port 17 is formed with the valve seat film 17b through the formation of a small-diameter portion in the exhaust port 17 by the cast molding, the formation of an annular valve seat portion and a shielding curtain portion by the cutting work, the cold spraying onto the annular valve seat portion, and the finishing work. Detailed description will therefore be omitted for the procedure of forming the valve seat films 17b on the exhaust ports 17.
As described above, according to the semimanufactured cylinder head 3 and the method for manufacturing the cylinder head 12 of the present embodiment, the valve seat film 16b is formed through forming the shielding curtain portion 16g, which projects in an annular shape from the annular edge portion of the opening portion 16a of the intake port 16 toward the center C of the port, and spraying the metal powder P onto the annular valve seat portion 16f, which is located on the outer side of the intake port 16 than the shielding curtain portion 16g, using a cold spray method. This allows the shielding curtain portion 16g to partially shield the intake port 16 from the metal powder P sprayed onto the annular valve seat portion 16f, and the scattered metal powder P can be attached to the shielding curtain portion 16g, thus suppressing the formation of an excess film in the intake port 16. Moreover, the shielding curtain portion 16g reduces the flow velocity of the metal powder P flowing into the intake port 16, and it is therefore possible to suppress the formation of an excess film on the inner side of the intake port 16. Furthermore, the shielding curtain portion 16g allows the metal powder P to escape from the central hole to the intake port 16 and thereby prevents the flow velocity reduction of the metal powder P sprayed onto the annular valve seat portion 16f, and the valve seat film 16b having high strength can thus be formed.
The shielding curtain portion 16g is formed through forming the small-diameter portion 16c integrally with the semimanufactured cylinder head 3 in the casting step S1 and performing the cutting work on the small-diameter portion 16c in the cutting step S2, but these casting step S1 and cutting step S2 are steps that are also performed in the conventional manufacturing process for the cylinder head 12. In addition, while the shielding curtain portion 16g is removed in the finishing step S4 after the formation of the valve seat film 16b, this finishing step S4 is also a step that is performed in the conventional manufacturing process for the cylinder head 12. Thus, the number of manufacturing steps for the cylinder head 12 does not increase due to the formation of the shielding curtain portion 16g, and the manufacturing cost for the cylinder head 12 does not increase significantly. Furthermore, the shielding curtain portion 16g is removed after the formation of the valve seat film 16b and therefore does not affect the intake performance of the intake port 16. These effects can be similarly obtained in the formation of the valve seat film 17b for the exhaust port 17.
A method for manufacturing the cylinder head 12 according to the second embodiment will then be described. This embodiment differs from the first embodiment in the shape of the shielding curtain portion formed from the small-diameter portion 16c in the cutting step S2 and the function of the shielding curtain portion in the coating step S3, but the other steps are the same as those in the first embodiment, so the description for those other than the cutting step S2 and the coating step S3 will be omitted by borrowing the description of the first embodiment.
According to the semimanufactured cylinder head 3 and the method for manufacturing the cylinder head 12 of this embodiment, the flow direction of the metal powder P is controlled by the control surface 16j of the shielding curtain portion 16i so that the metal powder P hits the inner surface on the opposite side within the working line, and the scattered metal powder P can therefore be attached as the excessive film SF within the range of the working line PL. It is thus possible to suppress the formation of an excessive film on the inner side of the intake port 16. Moreover, the shielding curtain portion 16i and the excessive film SF in the working line PL do not adversely affect the intake performance of the intake port 16 and the exhaust performance of the exhaust port 17 because the inside of the working line PL is subjected to the finishing work in the finishing step S4.
A method for manufacturing the cylinder head 12 according to the third embodiment will then be described. This embodiment includes a casting step, a cutting step, a coating step, and a finishing step as in the first embodiment, but is different from the first embodiment in that a shield plate that is a separate component from the semimanufactured cylinder head is used as the shielding curtain portion. In the third embodiment, the same configurations as those of the first embodiment are denoted by the same reference numerals, and the detailed description will be omitted.
In the coating step of this embodiment, the semimanufactured cylinder head 3A is set on the work rotating apparatus 4 as in the first embodiment. Then, the semimanufactured cylinder head 3A is moved by the tilt stage unit 42 and the XY stage unit 43 so that the central axis C of the intake port 16 to be formed with the valve seat film 16b is vertical and coincides with the Z-axis of the rotation stage unit 44. Subsequently, as illustrated in
As illustrated in
As illustrated in
The shield plate 5 is formed of a material harder than the metal powder P, but an excessive film SF1 is still formed on the upper surface. It is therefore preferred to replace the shield plate 5 periodically or when the excess film SF1 becomes so thick as to impair the function of the shield plate 5. The insertion and removal of the shield plate 5 with respect to the shield plate insertion portion 16k may be performed manually or by an automated machine such as a robot.
According to the method for manufacturing the cylinder head 12 of this embodiment, the use of the shield plate 5 can suppress the formation of an excess film in the intake port 16 and the exhaust port 17 as in the first embodiment without significantly changing the conventional casting step and cutting step for the cylinder head 12. Moreover, the shield plate 5 is provided with the opening 51 to allow the metal powder P to escape to the intake port 16 and it is therefore possible to suppress the flow velocity reduction of the metal powder P sprayed onto the annular valve seat portion 16f and form the valve seat film 16b having sufficient strength.
In each of the above-described embodiments, the semimanufactured cylinder head 3 is formed with the small-diameter portion 16c in the casting step S1, but when the cylinder head 12 is manufactured after a semimanufactured cylinder head 3 provided with the small-diameter portion 16c is supplied from another manufacturer, the casting step S1 can be omitted as a matter of course. In the above-described embodiments, the nozzle 23d of the cold spray gun 23 is fixedly arranged and the semimanufactured cylinder head 3 is rotated and moved, but on the contrary, the semimanufactured cylinder head 3 may be fixedly arranged and the nozzle 23d may be moved.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/024687 | 6/28/2018 | WO | 00 |
