Cylinder head for internal combustion engine and internal combustion engine

Abstract

Provided are: a cylinder head that can prevent knocking caused by premature ignition in a combustion chamber of an internal combustion engine that uses decarbonized fuel containing hydrogen; and an internal combustion engine. A cylinder head (2) of an internal combustion engine, the internal combustion engine using decarbonized fuel containing hydrogen, is provided with a poppet-type intake valve (5) and an exhaust valve (6) that open and close an intake port (2a) and an exhaust port (2b), respectively, the intake port (2a) and the exhaust port (2b) opening to the combustion chamber, and the intake valve (5) and an exhaust valve (6) each having an umbrella part (5b, 6b) formed on a shaft end side. The exhaust valve (6) is a coolant-filled hollow valve having water (10) enclosed as the coolant in a hollow section (9) that extends from the umbrella part (6b) to the shaft end side. The intake valve (5) is a solid valve having, on the entire bottom surface (5b4) of the umbrella part thereof, protrusions (11) that are arranged in a lattice shape in a plan view and that are demarcated by numerous parallel intersecting grooves (12).

Description

Cylinder head of internal combustion engine and internal combustion engine

[0001] The present invention relates to a cylinder head for an internal combustion engine and an internal combustion engine having the cylinder head, and more particularly to a cylinder head for an internal combustion engine and an internal combustion engine that uses a non-fossil fuel containing hydrogen.

[0002] Patent Document 1 discloses an internal combustion engine having an intake valve with a hollow portion inside, and an exhaust valve in a cylinder head, which has a refrigerant in the hollow portion inside, and when the internal combustion engine is running, the refrigerant absorbs heat on the head side, which is at a higher temperature, and repeatedly moves back and forth between the head side, which is at a lower temperature, and the shaft side, which is at a lower temperature, to transfer heat to the shaft side, thereby reducing temperature.

[0003] Patent No. 6356361

[0004] In the area of ​​internal combustion engines, a transition from traditionally used fossil fuels such as gasoline and diesel to decarbonized fuels including hydrogen is predicted, with the aim of reducing greenhouse gas emissions. Marine engines are also expected to transition from heavy oil to decarbonized fuels including hydrogen.

[0005] However, decarbonized fuels containing hydrogen have a faster combustion rate than fossil fuels, leading to knocking due to pre-ignition (ignition occurring much earlier than the intended ignition timing). Such pre-ignition is believed to occur in hot spots within the combustion chamber, where temperatures are significantly higher than in other areas due to temperature variations. In conventional internal combustion engines, intake valves are often forcibly cooled by vaporized fuel mixtures, particularly air-fuel mixtures cooled by intercoolers. However, exhaust valves, even if cooled by refrigerants, are exposed to high-temperature exhaust gases and therefore reach much higher temperatures than the intake valves. As a result, the area near the front side of the exhaust valve head (hereinafter simply referred to as the "head surface area") remains much hotter than the area near the intake valve head. This temperature difference between the areas near the heads of the intake and exhaust valves in the combustion chamber can create hot spots near the front side of the exhaust valve head, potentially leading to knocking.

[0006] On the other hand, unlike internal combustion engines used at medium to high speeds (several thousand rpm) such as automotive internal combustion engines, internal combustion engines used at low speeds (several hundred rpm) such as marine engines have the problem that even if sodium, as used in automotive internal combustion engines, is used as a refrigerant for the hollow exhaust valve, it does not have sufficient fluidity due to the insufficient rotation speed, and therefore does not provide a sufficient cooling effect.

[0007] In view of the above problems, the present invention provides a cylinder head and an internal combustion engine that can prevent knocking due to pre-ignition by reducing the temperature difference in the areas near the umbrella surfaces of both the intake valve and the exhaust valve in the combustion chamber of an internal combustion engine that uses decarbonized fuel containing hydrogen.

[0008] The inventors conducted a dynamic heating test to verify the heat dissipation effect of exhaust valves using a hollow exhaust valve (conventional technology) with metallic sodium filled in the hollow portion and a heat-pipe-cooled hollow exhaust valve with water filled in the hollow portion as a coolant, while setting the engine speed from low to high at various rotational speeds. As a result, it was confirmed that the latter (water-filled heat-pipe-cooled hollow exhaust valve) had a superior heat dissipation effect to the former (metallic sodium-filled hollow exhaust valve) at all rotational speeds, as shown in Figure 2A. Therefore, the inventors believed that if a heat-pipe-cooled hollow exhaust valve with water filled in the hollow portion were used as an exhaust valve in the cylinder head of an internal combustion engine equipped with intake and exhaust valves and using a decarbonized fuel containing hydrogen, the temperature of the exhaust valve head surface could be significantly reduced, thereby reducing the temperature difference in the combustion chamber near the heads of both the intake and exhaust valves.

[0009] However, simply using a heat pipe-cooled hollow valve as the exhaust valve has its limits in terms of cooling the exhaust valve head surface (improving heat dissipation), so the idea was to combine it with a structure that suppresses the temperature drop of the intake valve (head surface) made of a solid body, thereby effectively reducing the temperature difference in the areas near the heads of both the intake and exhaust valves in the combustion chamber (preventing knocking).

[0010] That is, if the surface area of ​​the intake valve head bottom (umbrella front) is increased by forming uniform irregularities across the entire bottom surface (umbrella front) of a solid intake valve or by forming concentric corrugated ridges (grooves) in a longitudinal cross section, the heat-receiving area of ​​the umbrella front will be larger, and the temperature of the umbrella front facing the combustion chamber will be higher than when the umbrella front bottom (umbrella front) is flat (conventional structure). Also, while the intake and exhaust valve heads have the same thickness in conventional structures, if the thickness of the intake valve head is made thinner than that of the exhaust valve head (= the thickness of the conventional intake valve head), thereby reducing the heat capacity of the intake valve head (less than that of the conventional intake valve head), the temperature of the umbrella front facing the combustion chamber will be higher.

[0011] In this way, the inventors thought that by adopting a new configuration in which "in the cylinder head of an internal combustion engine, a heat pipe-cooled hollow valve with water filled in the hollow portion is used as the exhaust valve, and the entire bottom surface (front surface) of the intake valve head, which is made of a solid body, is uniformly uneven, or has concentric circular wavy convex (concave) stripes in the longitudinal cross section, or the thickness of the intake valve head is made thinner than the thickness of the exhaust valve head (= the thickness of the intake valve head of a conventional intake valve)," they could reduce the temperature difference in the areas near the intake and exhaust valve heads within the combustion chamber.

[0012] That is, in order to solve the above-mentioned problems, in a first aspect of the invention, a cylinder head for an internal combustion engine is provided with poppet-type intake valves and exhaust valves with umbrella portions formed on the axial end side that open and close the intake port and exhaust port that open to the combustion chamber, respectively, and that uses a decarbonized fuel containing hydrogen, wherein the exhaust valve is preferably a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the umbrella portion to the axial end side, and the intake valve is preferably a solid valve in which a lattice-shaped protrusion portion defined by a number of intersecting grooves is provided on the entire bottom surface of the umbrella portion.

[0013] (Operation) The exhaust valve is a heat-pipe-cooled hollow valve with excellent heat dissipation properties. The coolant (water) in the hollow portion changes phase between liquid and gas to transfer heat from the head portion to the stem portion. The heat transferred to the stem portion is then transferred (dissipated) to the cylinder head, thereby suppressing the temperature rise of the exhaust valve head surface. As shown in Figure 2A, the heat-pipe-cooled exhaust valve has a superior heat dissipation property compared to a conventional hollow valve with a metallic sodium-filled coolant in the hollow portion, thereby reducing the temperature of the head surface. In particular, the engine speeds of automobiles running in urban areas tend to be in the low RPM range, and ship engines are also assumed to operate in the low RPM range. As is clear from Figure 2A, when the internal combustion engine is operating in the low RPM range (e.g., below 3000 rpm), the heat-dissipation effect of the intake valve is significantly better with a water-filled heat-pipe-cooled hollow valve than with a metallic sodium-filled hollow valve.

[0014] On the other hand, the intake valve has a grid-like protrusion formed on the bottom surface of the head portion, i.e., the entire head surface, in a plan view, which increases the surface area of ​​the head portion (the heat-receiving area facing the combustion chamber), making the head portion more susceptible to heating. As a result, the temperature in the area near the head surface of the intake valve in the combustion chamber rises, while the temperature in the area near the head surface of the exhaust valve is sufficiently reduced, reliably reducing the temperature difference between the areas near the head surfaces of the intake and exhaust valves.

[0015] Furthermore, a second aspect of the invention of a cylinder head for an internal combustion engine is a cylinder head for an internal combustion engine that is equipped with poppet-type intake valves and exhaust valves with umbrella portions formed on the axial end side, which respectively open and close the intake port and exhaust port that open to the combustion chamber, and that uses a decarbonized fuel containing hydrogen.It is desirable that the exhaust valve be a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the umbrella portion toward the axial end, and that the intake valve be a solid valve with a concentrically continuous, wavy convex ridge portion in vertical cross section provided on the entire bottom surface of the umbrella portion.

[0016] (Function) The function of the exhaust valve is the same as that of the "Function of the Exhaust Valve" in the cylinder of an internal combustion engine according to one embodiment of the present invention, and therefore a redundant explanation will be omitted. Meanwhile, the bottom surface (surface) of the head portion of the intake valve has a continuous, concentrically shaped, corrugated ridge in vertical cross section throughout. This increases the surface area (heat-receiving area facing the combustion chamber) of the head portion compared to conventional intake valves, which have a flat bottom surface (surface), making the head portion more susceptible to heating. As a result, the temperature in the combustion chamber near the head surface of the intake valve rises, while the temperature in the exhaust valve near the head surface is sufficiently reduced, thereby reliably reducing the temperature difference between the areas near the head surfaces of the intake and exhaust valves.

[0017] Furthermore, a third aspect of the invention of a cylinder head for an internal combustion engine is a cylinder head for an internal combustion engine that is equipped with poppet-type intake valves and exhaust valves with head portions formed on the axial end side, which respectively open and close the intake port and exhaust port that open to the combustion chamber, and that uses a decarbonized fuel containing hydrogen. It is desirable that the exhaust valve be a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the head portion to the axial end side, and that the intake valve be a solid valve whose head portion is formed thinner than the head portion of the exhaust valve.

[0018] (Operation) The operation of the exhaust valve is the same as the "Operation of the Exhaust Valve" in the cylinder of an internal combustion engine according to one embodiment of the present invention, and a redundant explanation will be omitted. Meanwhile, unlike conventional structures in which the intake valve head is formed to the same thickness as the exhaust valve head, the intake valve head is thinner than the heads of conventional intake and exhaust valves. As a result, the intake valve head has a smaller heat capacity than the intake valve head of a conventional intake valve formed to the same thickness as the exhaust valve head, thereby accelerating the temperature rise of the head surface, and therefore heats up more easily than the intake valve head of a conventional intake valve. As a result, the temperature in the region near the intake valve head surface in the combustion chamber rises, while the temperature in the region near the exhaust valve head surface is sufficiently reduced, thereby reducing the temperature difference between the regions near the intake and exhaust valve head surfaces.

[0019] In addition, a fourth aspect of the invention of the cylinder head for an internal combustion engine is the third aspect of the invention, wherein the entire bottom surface of the head portion of the intake valve is provided with lattice-like projections in plan view defined by a number of intersecting grooves or concentrically continuous corrugated convex streaks in vertical cross section.

[0020] (Function) By providing the entire bottom surface of the intake valve head with a grid-like projection defined by numerous intersecting grooves in plan view or a continuous, concentrically corrugated ridge in vertical cross section, the heat capacity of the head is reduced by the thinner wall, and the surface area of ​​the bottom surface of the intake valve head (the heat-receiving area facing the combustion chamber) is increased, making the head more susceptible to heating. As a result, the temperature in the combustion chamber near the intake valve head surface rises, while the temperature in the exhaust valve head surface is sufficiently reduced, further reducing the temperature difference between the intake and exhaust valve head surfaces.

[0021] In addition, a fifth aspect of the invention of the cylinder head for an internal combustion engine is any one of the first to fourth aspects of the cylinder head for an internal combustion engine, wherein the bottom surface of the head portion of the exhaust valve is preferably formed as a mirror surface.

[0022] (Function) The mirror-finished bottom surface of the exhaust valve head reflects infrared rays, reducing the amount of radiant heat transferred from the combustion chamber to the head bottom, suppressing temperature rise and making it easier for the exhaust valve head to cool, lowering the temperature in the area near the exhaust valve head surface in the combustion chamber. By bringing the temperature of the exhaust valve head closer to the temperature of the intake valve head, which is cooled by an intercooler or the like, the temperature difference between the areas near the head surfaces of the intake and exhaust valves is reduced.

[0023] A sixth aspect of the invention of the cylinder head for an internal combustion engine is any one of the first to fifth aspects of the invention, and it is desirable that the internal combustion engine is a marine engine.

[0024] (Operation) Even in a marine engine with a low rotational speed when driven, the head portion of the exhaust valve is sufficiently cooled, and the temperature difference between the areas near the head surfaces of the intake and exhaust valves in the combustion chamber is reduced.

[0025] Furthermore, it is desirable that the internal combustion engine have any of the first to sixth aspects of the invention of a cylinder head for an internal combustion engine, which includes a cylinder block having, inside thereof, pistons held in cylinders so as to be able to reciprocate freely, a crankshaft held so as to be able to rotate freely, and connecting rods rotatably connected to both the pistons and the crankshaft and converting the reciprocating motion of the pistons into rotational motion, and which is fixed to the cylinder block and forms a combustion chamber between the inside of the cylinder and the cylinder head.

[0026] (Operation) In an internal combustion engine having a cylinder head as described in each claim of the present application, the temperature in the combustion chamber near the intake valve head surface rises, while the temperature in the combustion chamber near the exhaust valve head surface is sufficiently reduced, thereby reducing the temperature difference between the intake and exhaust valve head surface areas in the combustion chamber.

[0027] According to this cylinder head, the surface area of ​​the bottom of the intake valve head is increased compared to the exhaust valve head by the use of protrusions such as a grid or wave pattern, or the intake valve head is made thinner than the exhaust valve head, and the intake valve head is made thinner than the exhaust valve head. This reduces the heat capacity of the intake valve head, making it easier to heat than conventional intake valve heads. This reduces the temperature difference in the areas near the intake and exhaust valve head surfaces in the combustion chamber, making it less likely for hot spots to occur in the combustion chamber, thereby reducing knocking due to pre-ignition even when using decarbonized fuel containing hydrogen. Furthermore, the water filled in the hollow portion of the exhaust valve is a safer cooling medium than metallic sodium, and using decarbonized fuel containing hydrogen for internal combustion engines is also significant as a measure against global warming.

[0028] Furthermore, with this cylinder head, the temperature of the exhaust valve head is brought closer to the temperature of the intake valve head, which is cooled by an intercooler or the like, thereby further reducing the temperature difference between the areas near the intake and exhaust valve head surfaces. This makes it less likely for hot spots to occur in the combustion chamber, thereby reducing knocking due to pre-ignition even when using decarbonized fuel containing hydrogen.

[0029] Furthermore, with this cylinder head, knocking due to pre-ignition is sufficiently reduced even when decarbonized fuel containing hydrogen is used in a marine engine.

[0030] Furthermore, with this internal combustion engine, the temperature difference in the areas near the valve head surfaces of the intake and exhaust valves in the combustion chamber is reduced, making it less likely that hot spots will occur in the combustion chamber, thereby reducing knocking due to pre-ignition even when using decarbonized fuel containing hydrogen.By reducing knocking when using decarbonized fuel containing hydrogen, this internal combustion engine improves torque and fuel efficiency based on ignition advance (slightly advancing the ignition timing beyond the time the piston reaches top dead center).

[0031] 5A is a longitudinal cross-sectional view showing an embodiment of an internal combustion engine having a cylinder head of the present application. FIG. 5B is an explanatory diagram of a valve train including an exhaust valve of a marine internal combustion engine having the cylinder head of the present application. (a) A longitudinal cross-sectional view of an intake valve used in a cylinder head. (b) A longitudinal cross-sectional view of an exhaust valve used in a cylinder head. Graphs showing the temperature of a refrigerant-filled hollow valve used in an automobile engine measured at various engine speeds in a dynamic heating test, with (a) being at 750 rpm, (b) being at 1800 rpm, and (c) being at 5200 rpm. FIG. 5B is an enlarged view of the bottom surface of an intake valve head provided with lattice-shaped protrusions in a plan view, as viewed in the direction of arrow A in FIG. 2. FIG. 5C is an explanatory diagram showing a modified example of the bottom surface of an intake valve head provided with lattice-shaped protrusions in a plan view. (a) An enlarged longitudinal cross-sectional view showing a modified example of the bottom surface of an intake valve head provided with a wavy ridge in a longitudinal cross section. (b) A view viewed in the direction of arrow B in FIG. 5A, showing the bottom surface of an intake valve head provided with wave-shaped protrusions.

[0032] A preferred embodiment of an internal combustion engine having a cylinder head according to the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the internal combustion engine 1 is configured by mounting a cylinder head 2 on a cylinder block 3. The cylinder block 3 has a cylindrical cylinder 3a at its upper portion and a crankshaft 3b at its lower portion. A piston 3c is provided inside the cylinder 3a so as to be able to slide back and forth. A connecting rod 3e is rotatably attached to both the cylinder 3a and the crankshaft 3b via a first connecting shaft 3f and a second connecting shaft 3g. As a result, the reciprocating motion of the cylinder 3a is converted into the rotational motion of the crankshaft 3b by the connecting rod 3e.

[0033] 1 is connected and fixed to the cylinder block 3 in a position facing the cylinder 3a and piston 3c. A combustion chamber 4 is provided inside both the cylinder head 2 and the cylinder 3a, above the top surface of the cylinder 3a. The cylinder head 2 has an intake port 2a and an exhaust port 2b that open toward the combustion chamber 4, and is provided with a spark plug 2g that generates a spark in the combustion chamber. Note that, while the spark plug 2g is provided in gasoline internal combustion engines for automobiles, if the internal combustion engine 1 is a diesel internal combustion engine for a ship, the spark plug 2g is not provided.

[0034] In the cylinder head 2 shown in Figure 1, the intake port 2a communicates with the intake passage 2c, and the exhaust port 2b communicates with the exhaust passage 2d. The cylinder head 2 has an intake valve 5 and an exhaust valve 6. The intake valve 5 and the exhaust valve 6 are held reciprocally by valve guides 2e and 2f, respectively, attached to the cylinder head 2. The intake valve 5 and the exhaust valve 6 have shafts 5a and 6a, each with a gradually increasing diameter provided at one end with a head portion 5b or 6b. Hereinafter, in this specification, the shafts 5a and 6a of the intake valve 5 and the exhaust valve 6 will be referred to as the upper side, and the head portions 5b and 6b will be referred to as the lower side. The intake port 2a and the exhaust port 2b are opened and closed by the head portions 5b and 6b, respectively.

[0035] 1, the intake valve 5 and the exhaust valve 6 have upper seats 5c, 6c attached to the base ends of their shafts 5a, 6a. Lower seats 5d, 6d are provided in the cylinder head 2 opposite the upper seats 5c, 6c, and compression valve springs 5e, 6e are provided between the upper seats 5c, 6c and the lower seats 5d, 6d. When the intake valve 5 and the exhaust valve 6 are pressed by cams 7b, 8b rotated by camshafts 7a, 8a, respectively, the head portions 5b, 6b descend, opening the intake port 2a and the exhaust port 2b, respectively. When the pressure from the cams 7b, 8b is released based on the rotational position, the head portions 5b, 6b ascend due to the biasing force of the valve springs 5e, 6e, closing the intake port 2a and the exhaust port 2b. This allows the following operations to be performed: "intake" with only the intake port 2a open, "compression" and "combustion" with both the intake port 2a and the exhaust port 2b closed, and "exhaust" with only the exhaust port 2b open.

[0036] A fuel injection device (not shown) is provided in the cylinder head 2, and this fuel injection device injects an atomized fuel mixture from the intake passage 2c into the combustion chamber 4 at the timing of "intake." During the "compression" stroke, the mixture in the combustion chamber 4 is compressed and explodes due to the ignition of the spark plug 301 (in the case of a marine diesel internal combustion engine, due to spontaneous combustion caused by the high temperature inside the combustion chamber 4), thereby executing the "combustion" stroke, and during the exhaust stroke, exhaust gas is discharged from the exhaust passage 2d.

[0037] Next, a valve train for a marine internal combustion engine including exhaust valves, a characteristic feature of the present application, in a cylinder block will be described with reference to FIG. 1A . In FIG. 1A , the symbols used represent up, down, left, and right, respectively, in the following order: Up, Lo, Le, Ri. FIG. 1A shows an exhaust valve train 21 for a marine internal combustion engine. The exhaust valve train 21 includes a camshaft 22 having a cam 22a, a push rod 23, a rocker arm 24, a bridge arm 25, a pair of exhaust valves (26a, 26b), and a pair of compression coil springs (27a, 27b). An intake valve train (not shown) is provided in the depth direction of FIG. 1A . The intake valve train (not shown) includes a pair of intake valves instead of the pair of exhaust valves (26a, 26b), and has a common configuration with the exhaust valve train 21, except that the installation angle of the cam on the camshaft 22 is different from that of the cam 22a.

[0038] The exhaust valve train 21 and intake valve train (not shown) shown in FIG. 1A are provided in a cylinder head 35, which is mounted on a cylinder block (not shown) similarly to the internal combustion engine of FIG. 1 to form a marine diesel internal combustion engine. Similar to the internal combustion engine of FIG. 1, the cylinder block (not shown) has a cylindrical cylinder with a piston connected to a connecting rod that slides back and forth as the crankshaft rotates. The cylinder head 35 has exhaust ports (28a, 28b) and intake ports (not shown) that open toward the combustion chamber 36. The exhaust ports (28a, 28b) have seats (29a, 29b) around their opening edges and communicate with an exhaust passage 30, and the intake ports (not shown) communicate with an intake passage (not shown).

[0039] As shown in FIG. 1A , the rocker arm 24 is attached to the cylinder head 35 so as to be able to swing about the rocker shaft 24a. The rocker arm 24 swings about the rocker shaft 24a by connecting a pivot portion 24c at the base end 24b to a push rod 23 that moves up and down based on the rotation of the cam 22a of the camshaft 22. The tip end 24d of the rocker arm 24 abuts against a bridge arm 25 that is attached to the cylinder head 35 so as to be able to move up and down. The bridge arm 25 is connected to the base ends (26a1, 26b1) of the exhaust valves (26a, 26b) on the left and right, and is biased toward the tip end 24d of the upper rocker arm 24 by compression coil springs (27a, 27b). The exhaust valves (26a, 26b) are slidably held within valve insertion pipes (31a, 31b) of the cylinder head 35. The exhaust valves (26a, 26b) open the exhaust ports (28a, 28b) when the tip end 24d of the rocker arm 24 descends based on the rotational state of the cam 22a.

[0040] Furthermore, when the tip end 24d of the rocker arm 24 receives an upward biasing force from the compression coil spring (27a, 27b) from the bridge arm 25 based on the rotational mode of the cam 22a, the exhaust valves (26a, 26b) close the exhaust ports (28a, 28b) with their faces (26a2, 26b2) in contact with the seats (29a, 29b) of the cylinder head 35. The intake valves (not shown) open and close their intake ports (not shown) at timings different from those of the exhaust valves (26a, 26b) based on the rotational mode of an intake cam (not shown) that has a different installation angle from the exhaust cam 22a of the camshaft 22.

[0041] Next, the intake valve 5 and exhaust valve 6 used in the cylinder head 2 of Fig. 1 and the cylinder head 35 of Fig. 1A will be described with reference to Fig. 2(a) and Fig. 2(b). In the description, the shaft portions 5a, 6a are referred to as the base end side, and the head portions 5b, 6b are referred to as the tip end side. The exhaust valves (26a, 26b) of Fig. 1A and the intake valve not shown in Fig. 1A have substantially the same shape as the intake valve 5.

[0042] 2(a) shows an intake valve 5 used in a cylinder head 2. The intake valve 5 is a solid metal internal combustion engine valve formed by a stem 5a having a constant outer diameter and an umbrella portion 5b integrally formed at the tip of the stem 5a. The umbrella portion 5b has a poppet-like configuration, with a neck 5b1 having a concave curved shape that increases in diameter toward the tip, a notched face portion 5b2 integrally formed at the tip of the neck and contacting the periphery of the opening of the intake port 2a shown in FIG. 1 when the valve is closed to close the intake port 2a, and an umbrella outer portion 5b3 having a constant outer diameter integrally formed at the tip of the face portion 5b2.

[0043] 2(b) shows an exhaust valve 6 used in the cylinder head 2. The exhaust valve 6 is a hollow internal combustion engine valve made of a highly heat-resistant metal. It is composed of a stem 6a with a constant outer diameter and a head 6b integrally formed at the tip of the stem 6a. The stem 6a is composed of a stem tip 6a1 with a central hollow 9 extending in the axial direction and a stem base 6a2 joined to the base end of the stem tip 6a1. The head 6b is composed of a neck 6b1 formed integrally at the tip of the stem tip 6a1 and having a concave curved shape that increases in diameter toward the tip; a notched face 6b2 formed integrally at the tip of the neck and contacting the periphery of the opening of the exhaust port 2b shown in FIG. 1 when the valve is closed to close the exhaust port 2b; and a head outer portion 6b3 with a constant outer diameter that is integrally formed at the tip of the face 6b2, forming a poppet-like shape.

[0044] As shown in Figure 2(b), the hollow portion 9 extends from the inside of the center of the shaft tip portion 6a1 of the shaft portion 6a to the vicinity of the base ends of the neck portion 6b1 and the face portion 6b2. The shaft tip portion 6a1 is joined to the shaft base end portion 6a2 by friction welding or the like, with water (purified water 10) serving as a refrigerant charged into a partial region of the hollow portion 9. The exhaust valve 6 is a heat-pipe-cooled hollow valve. When the valve 6 reciprocates in the axial direction in conjunction with the engine drive, the coolant (water) in the hollow portion changes phase between liquid and gas, transferring heat from the umbrella portion 6b to the shaft portion 6a. In other words, the high heat imparted to the umbrella portion 6b by the exhaust gas can be released to the cooler shaft portion 6a.

[0045] The inventors conducted dynamic heating tests to examine the heat dissipation effects of exhaust valves at automobile engine speeds of 750, 1800, and 5200 rpm using two types of exhaust valves: a hollow valve (conventional technology) filled with metallic sodium and a heat-pipe-cooled hollow valve filled with water as a coolant (see Figure 2A).The results showed that the latter (water-filled heat-pipe-cooled hollow valve) had a superior heat dissipation effect to the former (metallic sodium-filled hollow valve) at all speeds. Specifically, the dynamic heating tests were conducted on three types of valves: a solid valve, a hollow valve filled with metallic sodium (60% of the hollow volume was sodium), and a heat-pipe-cooled hollow valve filled with water (24% of the hollow volume was purified water).

[0046] As a result, at a rotation speed of 5200 rpm, the umbrella surface temperature of the latter (water-filled heat pipe-cooled hollow valve) was 98°C lower than that of the solid valve, but this was not significantly different from the reduction in umbrella surface temperature of the former (metallic sodium-filled hollow valve) (relative to the solid valve). On the other hand, at a rotation speed of 750 rpm (1800 rpm), the umbrella surface temperature of the latter (water-filled heat pipe-cooled hollow valve) was significantly lower by 219°C (227°C) than that of the solid valve. These reductions are significantly greater than the approximately 50°C reduction in umbrella surface temperature of the former (metallic sodium-filled hollow valve) (relative to the solid valve).

[0047] That is, at the high revolutions (5200 rpm) expected for use in an automobile engine, as shown in Figure 2A(c), there is not a large difference in the umbrella surface temperature between the former and latter, but at the low revolutions (750 rpm, 1800 rpm) expected for use in an automobile engine or marine engine traveling at low speeds, as shown in Figures 2A(a) and (b), there is a difference of just under 200°C in the umbrella surface temperature between the former and latter (the latter valve has a superior heat dissipation effect). Thus, heat pipe-cooled exhaust valves exhibit excellent heat dissipation effects, especially in internal combustion engines operated at low revolutions, such as automobile engines or marine engines traveling at low speeds in urban areas.

[0048] In this embodiment, a hollow portion 9 is formed inside the shaft tip portion 6a1 formed integrally with the neck portion 6b1, and after the hollow portion 9 is charged with water 10 as a refrigerant, the shaft base end 6a2 is joined to hermetically seal the hollow portion 9. However, in an exhaust valve, the shaft tip portion 6a1, the shaft base end 6a2, and the umbrella portion may be integrally formed, and a hole (hollow portion) extending from the umbrella front surface 6b4 to the shaft end may be drilled. After the refrigerant water 10 is charged into the hole, a cap may be welded to the opening of the hole (hollow portion) to seal the hole (hollow portion). Furthermore, the tip portion of the hollow portion 9 shown in FIG. 2(b) may be an umbrella hollow portion whose inner diameter gradually increases toward the tip inside the umbrella portion 6b.

[0049] 2(a) and 2(b), the axial lengths of the intake valve 5 and the exhaust valve 6 (the dimensions from the back surfaces Jr1, jr2 of each end to the umbrella front surfaces 5b4, 6b4, which are the bottom surfaces of the umbrella portions (5, 6)) are L1 and L1+Δ. The outer diameters of the stem 5a, neck 5b1, and face 5b2 of the intake valve 5 are the same as those of the stem 6a, neck 6b1, and face 6b2 of the exhaust valve 6, and the outer diameters of the umbrella outer portions 5b3 and 6b3 are the same, d1.

[0050] Furthermore, in the cylinder head of the internal combustion engine of this embodiment, the use of a heat pipe-cooled hollow exhaust valve that uses water as a refrigerant can significantly reduce the temperature of the exhaust valve head surface. However, there is a limit to how much the exhaust valve head surface can be cooled (improving the heat dissipation effect). Therefore, by also using a structure that suppresses the temperature drop of the intake valve (head surface) made of a solid body, the temperature difference in the areas near the heads of both the intake and exhaust valves in the combustion chamber can be effectively reduced (preventing knocking).

[0051] The umbrella outer portions (5b3, 6b3) of the intake valves (5, 6) shown in Figures 2(a) and 2(b) are exposed to the combustion chamber 4 when the valves are closed. The intake valve 5 shown in Figure 2(a) has a thinner axial thickness of the umbrella outer portion 5b3 than a conventional intake valve, and is also thinner by an axial length Δ than the umbrella outer portion 6b3 of the exhaust valve 6 shown in Figure 2(b). However, the shape (area) of the faces 5b2, 6b2 remains unchanged. As a result, the total length L1 of the intake valve 5 and the axial length J1 from the upper end of the face portion 5b2 to the umbrella front surface 5b4 are shorter than the total length L1 + Δ of the exhaust valve 6 and the axial length J2 from the upper end of the face portion 6b2 to the umbrella front surface 6b4. In this way, the head portion 5b of the intake valve 5 has a thinner head outer portion 5b3 than the head portion 6b of the exhaust valve 6. This reduces the heat capacity of the intake valve compared to conventional intake valves, thereby accelerating the temperature rise of the head surface 5b4. That is, the head portion 5b of the intake valve 5 heats up more easily than the head portion of conventional intake valves, so that the temperature of the region near the head surface 5b4 of the intake valve 5 in the combustion chamber 4 rises, while the temperature of the region near the head surface 6b4 of the exhaust valve 6 is sufficiently reduced, thereby reducing the temperature difference between the regions near the head surfaces of the intake valve 5 and the exhaust valve 6. As a result, the cylinder head 2 of this embodiment, even when used in an automobile engine or a marine engine that uses decarbonized fuels including hydrogen, is less likely to have a large temperature difference in the combustion chamber 4 when operated at low revolutions, thereby preventing knocking due to pre-ignition. Due to the reduction in knocking when using decarbonized fuel containing hydrogen, automobile engines and marine engines that use the cylinder head 2 can improve torque and fuel efficiency based on ignition advance (slightly advancing the ignition timing beyond the time when the piston reaches top dead center).

[0052] The umbrella surface 6b4 of the exhaust valve 6 shown in FIG. 2(b) is mirror-finished, while the umbrella surface 5b4, which is the bottom surface of the intake valve 5 shown in FIG. 2(a), is provided with numerous tiny lattice-shaped protrusions 11 formed from numerous intersecting grooves 12 (see FIG. 3) throughout the umbrella surface 5b4. The lattice-shaped protrusions 11 (white portions) in FIG. 3 are formed in areas surrounded by four of the numerous intersecting grooves 12 (filled in black) formed in a concave shape on the umbrella surface 5b4. The mirror-finished umbrella surface 6b4 of the exhaust valve 6 reflects infrared rays, thereby reducing the amount of radiant heat transferred from the combustion chamber 4 shown in FIG. 1 to the umbrella surface 6b4, thereby suppressing temperature increases. It is desirable to form as many protrusions 11 as possible by providing as many intersecting grooves 12 as possible.

[0053] 3, the bottom surface of the head portion 5b of the intake valve 5, i.e., the head surface 5b4, has more lattice-shaped protrusions 11 formed from multiple intersecting grooves 12, which increases the surface area of ​​the head surface 5b4 and makes the head portion of the intake valve 5 more susceptible to heat from the high-temperature exhaust gas in the combustion chamber 4. This makes the head portion 5b of the intake valve 5 more susceptible to heating, thereby reducing the temperature difference in the areas near the head surfaces 5b4, 6b4 of both the intake valve 5 and the exhaust valve in the combustion chamber 4 and making it less likely for hot spots to occur in the combustion chamber 4, thereby reducing knocking due to pre-ignition even when using decarbonized fuel containing hydrogen.

[0054] 4 shows a modified example of the umbrella surface (bottom surface of the umbrella portion) of an intake valve, which is provided with a large number of tiny lattice-shaped protrusions 13. Instead of the multiple orthogonal concave-shaped intersecting grooves 12 shown in FIG. 3, the umbrella surface of the intake valve has multiple concave-shaped intersecting grooves 14 formed at acute or obtuse angles, as shown in FIG. 4, thereby forming a plurality of diamond-shaped lattice-shaped protrusions 13. It is also desirable to form as many protrusions 13 as possible by providing as many intersecting grooves 14 as possible. The multiple lattice-shaped protrusions formed on the umbrella surface of the intake valve are not limited to rectangular or diamond shapes, as long as they are formed by a plurality of intersecting concave-shaped intersecting grooves.

[0055] In addition, in Figures 3 and 4, first grooves formed in parallel at equal intervals and second grooves formed in parallel at equal intervals extend on the umbrella surface of the intake valve 5 (bottom surface of the umbrella portion 5b) so that they intersect with each other, and minute protrusions (lattice-like protrusions) that are rectangular in plan view and defined by the first and second grooves run continuously along the grooves, and the minute protrusions are uniformly dispersed over the entire umbrella surface of the intake valve 5 (bottom surface of the umbrella portion 5b), but the groove depth, groove width, and spacing between grooves (groove pitch) are not limited to these.

[0056] 5(a) and 5(b) show an intake valve 5' in which a convex rib portion 37, consisting of a plurality of wavy convex ribs in longitudinal cross section, is provided across the entire bottom surface of the head surface 5b4 of the head portion 5b of the intake valve 5 shown in Fig. 2(a), instead of the lattice-shaped protrusions 11 formed from a plurality of intersecting grooves 12. The axial length from the upper end of the face portion 5b2' of the head portion 5b' to the lower end of the convex rib portion 37 is J1, the same as that of the intake valve 5.

[0057] As shown in Fig. 5(b), the convex ridge portion 37 is composed of multiple annular convex portions arranged concentrically. As shown in Fig. 5(a), the umbrella surface 5b4' of the umbrella portion 5b' has a wave-like shape in vertical cross section, with curved convex portions and curved concave portions alternately repeated. Like the umbrella surface 5b4, the umbrella surface 5b4' also has an enlarged surface area, making it more susceptible to heat from high-temperature exhaust gases, thereby reducing the temperature difference with the area of ​​the exhaust valve near the umbrella portion.

[0058] As shown in FIG. 5, the umbrella front surface 5b4 of the umbrella portion 5b of the intake valve 5 has a corrugated longitudinal cross section with continuous concentric circular recesses and protrusions. The depth (height) of the curved recesses (curved protrusions) and the pitch of the curved recesses (curved protrusions) are set to predetermined values ​​to increase the surface area (heat-receiving area) of the umbrella front surface 5b4'. However, the depth (height) of the curved recesses (curved protrusions) and the pitch of the curved recesses (curved protrusions) are not limited. In the intake valve 5 of this embodiment, the umbrella portion 5b is thinned as shown in FIG. 2(a) and the umbrella front surface 5b4 is provided with protrusions 11 (or protrusions 37 in FIG. 4) as shown in FIG. 3. However, the umbrella portion 5b of the intake valve 5 may be thinned without providing protrusions 11 (or protrusions 37) on the umbrella front surface 5b4, or the umbrella portion 5b may be provided with protrusions 11 (or protrusions 37) on the umbrella front surface 5b4 without thinning the umbrella portion 5b.

[0059] 1 Internal combustion engine 2 Cylinder head 2a Intake port 2b Exhaust port 3 Cylinder block 3b Crankshaft 3c Piston 3e Connecting rod 4 Combustion chamber 5 Intake valve 5b Umbrella portion 5b1 Neck portion 5b2 Face portion 5b4 Umbrella surface (bottom surface) of umbrella portion 5b 6 Exhaust valve 6b Umbrella portion 6b1 Neck portion 6b2 Face portion 6b4 Umbrella surface (bottom surface) of umbrella portion 6b 9 Hollow portion 10 Purified water J1 Axial length from the upper end of face portion 5b2 to umbrella surface 5b4 J2 Axial length from the upper end of face portion 6b2 to umbrella surface 6b4

Claims

1. A cylinder head for an internal combustion engine is provided with poppet-type intake valves and exhaust valves each having a head portion formed on an axial end side thereof, which respectively open and close an intake port and an exhaust port that open to a combustion chamber, and the engine uses a decarbonized fuel containing hydrogen, The exhaust valve is The valve is configured as a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the umbrella portion toward the shaft end, The intake valve is 1. A cylinder head for an internal combustion engine, comprising a solid valve having a plurality of projections, the projections being defined by a plurality of intersecting grooves and arranged over the entire bottom surface of the valve head.

2. A cylinder head for an internal combustion engine is provided with poppet-type intake valves and exhaust valves each having a head portion formed on an axial end side thereof, which respectively open and close an intake port and an exhaust port that open to a combustion chamber, and the engine uses a decarbonized fuel containing hydrogen, The exhaust valve is The valve is configured as a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the umbrella portion toward the shaft end, The intake valve is 1. A cylinder head for an internal combustion engine, characterized in that it is composed of a solid valve having a plurality of convex ridges, each of which has a corrugated vertical cross section and is concentrically continuous, provided over the entire bottom surface of its head portion.

3. A cylinder head for an internal combustion engine is provided with poppet-type intake valves and exhaust valves each having a head portion formed on an axial end side thereof, which respectively open and close an intake port and an exhaust port that open to a combustion chamber, and the engine uses a decarbonized fuel containing hydrogen, The exhaust valve is The valve is configured as a refrigerant-filled hollow valve in which water is sealed as a refrigerant in a hollow portion extending from the umbrella portion toward the shaft end, The intake valve is 1. A cylinder head for an internal combustion engine, comprising a solid valve having a head portion thinner than the head portion of said exhaust valve.

4. 4. The cylinder head for an internal combustion engine according to claim 3, characterized in that the entire bottom surface of the head portion of the intake valve is provided with a lattice-like protrusion portion in a plan view defined by a number of intersecting grooves or a corrugated convex streak portion in a vertical cross section which is continuous in a concentric pattern.

5. 5. The cylinder head for an internal combustion engine according to claim 1, wherein a bottom surface of the exhaust valve is formed as a mirror surface.

6. 6. The cylinder head for an internal combustion engine according to claim 1, wherein the internal combustion engine is a marine engine.

7. a cylinder block having therein pistons held reciprocally within cylinders, a crankshaft held rotatably, and a connecting rod rotatably connected to both the pistons and the crankshaft for converting the reciprocating motion of the pistons into rotational motion; 7. An internal combustion engine comprising: a cylinder head according to claim 1, said cylinder head being fixed to said cylinder block and defining a combustion chamber between said cylinder head and an inside of said cylinder.