Title of Invention

AN INTERNAL COMBUSTION ENGINE

Abstract

The invention provides an internal combustion engine which has intake passages defined independently in a cylinder head and optimized in shape. An engine 1 has at least one combustion chamber 11, at least two intake passages (first and second passageways 33b, 33c defined in an inlet pipe 33 and first and second intake ports 12, ,13 defined in a cylinder head 3) communicating with the combustion chamber 11, and an SCV 35 disposed in the first passageway 33b for opening and closing the intake passage. The SCV 35 is closed when the engine operates under a low load. The combustion chamber 11 is defmed in a cylinder head 3, and the intake passages (first and second intake ports 12, 13) are independently defined in the cylinder head 3.

Full Text

[Name of Document] Specification [Title of the Invention] Internal Combustion Engine [Technical Field] [0001] The present invention relates to an internal combustion engine for generating and efficiently-combusting a swirling flow of an air-fuel mixture in a combustion chamber when the internal combustion engine is under a low load. [Background Art] [0002] When a swirling flow of an air-fuel mixture is produced in a combustion chamber, the efficiency of combustion in the combustion chamber under a low load increases. When under a high load, however, an intake resistance increases and a charging efficiency decreases. There is known an internal combustion engine having two intake ports. Under a low load, an air-fuel mixture is supplied only from one of the intake ports into the combustion chamber to produce a swirling flow therein. Under a high load, an air-fuel mixture or air is supplied from both the intake ports into the combustion chamber to cancel out a swirling flow therein (see, for example, Patent Document 1). [0003] [Patent Document 1] Japanese Patent Laid-Open No. Sho 62-102856 [Disclosure of the Invention] [Problems to be Solved by the Invention] [0004] However, if the intake ports are branched in a cylinder head, then, in small-displacement engines, the distance from the position where the intake ports are branched to the combustion chamber is small, the cross-sectional areas of the ports change largely, and the radii of curvature of the ports are partly reduced, tending to lead to performance reductions and poor fuel economy. [0005] The present invention has been made in view of the above problems. It is an object of the present invention to provide an internal combustion engine which has intake passages defined independently in a cylinder head and optimized in shape. [Means for Solving the Problems] [0006] To solve the above problems, an internal combustion engine according to the present invention has at least one combustion chamber, at least two intake passages (e.g., first and second passageways 33b, 33c and first and second intake ports 12, 13 in the embodiment) communicating with the combustion chamber, and an opening and closing valve (e.g., SCV 35 in the embodiment) disposed in either one of the intake passages for opening and closing the intake passage, the opening and closing valve being closed when the internal combustion engine operates under a low load. The combustion chamber is defined in a cylinder head, and the intake passages are independently defined in the cylinder head. [0007] In the internal combustion engine according to the present invention, preferably, the intake passages include a first intake port and a second intake port which are defined in the cylinder head and have ends communicating with the combustion chamber and other ends communicating with the exterior, and an intake passageway defined in an inlet pipe connected to the cylinder head and a first passageway and a second passageway which are branched from the intake passageway toward the cylinder head. The first passageway communicates with the other end of the first intake port, the second passageway communicating with the other end of the second intake port. The intake passageway is branched in the inlet pipe. The opening and closing valve is disposed in the first passageway in the inlet pipe. [Effect of the Invention] [0008] With the internal combustion engine according to the present invention being constructed as described above, since the passage length of the intake passages in the cylinder head is sufficiently large, changes in the cross-sectional areas of the intake passages are small, and the radii of curvature of the intake passages are large, allowing an air-fuel mixture to be smoothly guided into the combustion chamber. [0009] If the intake passages are branched in the cylinder head, then the passage length of the intake passages (the first and second intake ports) in the cylinder head is sufficiently large. [Best Mode for Carrying out the Invention] [0010] A preferred embodiment of the present invention will be described below with reference to the drawings. First, an air-cooled internal combustion engine (engine 1) for use on a motorcycle will be described below with reference to Figs. 1 through 5. The engine 1 includes a cylinder head cover 2, a cylinder head 3, a cylinder block 4, and a crankcase 5. Since the engine 1 is mounted on a motorcycle with the cylinder head 3 extending forwardly, the direction indicated by the arrow U in Fig. 1 will be described as an upward direction, and the direction indicated by the arrow F as a forward direction. [0011] A cylinder sleeve 6 in the form of a hollow cylinder is fitted in the cylinder block 4 and defines therein a cylinder chamber 7 in which a piston 8 is slidably disposed. The piston 8 is connected to a crankshaft 10 that is rotatably supported in the crankcase 5 . A combustion chamber 11 is defined by being surrounded by the cylinder sleeve 6, the cylinder head 3, and the piston 8. [0012] The cylinder head 3 has two intake ports (a first intake port 12 and a second intake port 13) and an exhaust port 14 which are defined therein. The first and second intake ports 12, 13 extend upwardly in the cylinder head 3. The first intake port 12 has an end communicating with the combustion chamber 11 through a first intake opening 15 and the other end communicating with the exterior through an upper first intake joint opening 19. The second intake port 13 has an end communicating with the combustion chamber 11 through a second intake opening 16 and the other end communicating with the exterior through an upper second intake joint opening 20. The first and second intake ports 12, 13 are thus defined independently in the cylinder head 3, and are juxtaposed laterally as viewed in front elevation. The exhaust port 14 has an end branched in the cylinder head 3 into a Y-shaped exhaust port extending downwardly. The exhaust port 14 includes a first exhaust port 14a communicating with the combustion chamber 11 through a first exhaust opening 17 and a second exhaust port 14b communicating with the combustion chamber 11 through a second exhaust opening 18. The other end of the exhaust port 14 communicates with the exterior through an exhaust joint opening 21. [0013] The cylinder head 3 has mushroom-shaped first and second intake valves 22, 23 and mushroom-shaped first and second exhaust valves 24, 25. These valves 22 through 25 have ends mounted on respective valve stems supported by respective retainers. The other ends of the valves 22 through 25 are normally urged to move in a direction to close the first and second intake openings 15, 16 and the first and second exhaust openings 17, 18 by valve springs 26 through 29 supported by the cylinder head 3 (the valve spring 29 acting on the second exhaust valve 25 is not shown). [0014] A camshaft 30 is rotatably supported on the cylinder head 3 for opening and closing the first and second intake valves 22, 23 and the first and second exhaust valves 24, 25. Rotation of the crankshaft 10 is transmitted to the camshaft 30 by a chain mechanism (timing chain), not shown. The camshaft 30 has cams 31 associated respectively with the first and second intake valves 22, 23 and the first and second exhaust valves 24, 25. When the cams 31 lift rocker arms 32, the respective valves 22 through 25 are lowered to open and close the first and second intake openings 15, 16 and the first and second exhaust openings 17, 18. [0015] An inlet pipe 33 is connected to the first and second intake joint openings 19, 20 of the first and second intake ports 12, 13. A throttle valve 34 is mounted on the inlet pipe 33. The inlet pipe 33 has a passage defined therein which includes an intake passageway 33a communicating with the throttle valve 34 and a first passageway 33b and a second passageway 33c which are branched from the intake passageway 33a toward the cylinder head 3. The first passageway 33b is connected to the first intake joint opening 19, and the second passageway 33c is connected to the second intake joint opening 20. Therefore, air supplied from the carburetor 34 is branched from the intake passageway 33a into the first passageway 33b and the second passageway 33c, and supplied through the first and second passageways 33b, 33c into the combustion chamber 11 from the first and second intake openings 15, 16. [0016] A swirl control valve (hereinafter referred to as “SCV”) 35 is disposed in the first passageway 33b in the inlet pipe 33 for opening and closing the first passageway 33b. When the engine 1 operates under a low load, the SCV 35 is closed to supply air (an air-fuel mixture) only through the second passageway 33c (intake opening 16) to form a swirl in the combustion chamber 11. [0017] As shown in Fig. 5, an injector 46 is mounted in a lower portion of the inlet pipe 33 for producing fine particles of fuel (atomizing fuel) and injecting them into air flowing from the second passageway 33c to the second intake port 13, thereby supplying an air-fuel mixture to the combustion chamber 11. Since the fuel is supplied as an air-fuel mixture from the second intake port 13 which supplies air at all times, the injector 46 can keep its atomizing capability. [0018] A process of opening and closing the SCV 35 will be described below with reference to Fig. 6. The SCV 35 includes a rotary valve having a valve member 3 5a for opening and closing the first passageway 33b and an arm 35b linked to the valve member 35a. When the arm 35b is rotated, the valve member 35a is opened and closed. A diaphragm 37 is connected to the arm 35b through a link 36. The diaphragm 37 has an operating chamber 37a defined therein which is connected to an opening and closing valve 39 through a first intake passage 38. Though the SCV 35 is illustrated as including a rotary valve, the SCV 3 5 may include a butterfly valve as shown in Figs. 1 and 9 . [0019] An air passage pipe 40 which communicates with the exterior is connected to the tip end of the second passageway 33c in the inlet pipe 33 (near the second intake joint opening 20). The air passage pipe 40 is connected to a vacuum tank 4 2 through a second intake passageway 41. A check valve 43 is disposed between the second intake passageway 41 and the vacuum tank 42 for preventing air from flowing from the vacuum tank 42 into the second passageway 33c. The vacuum tank 4 2 is connected to the opening and closing valve 3 9 through a third intake passageway 44. With this structure, when air is supplied to the combustion chamber 11 through the inlet pipe 33, a negative pressure with respect to the atmospheric pressure is developed in the second passageway 33c, and hence a negative pressure is developed in the vacuum tank 42. [0020] The opening and closing valve 3 9 is controlled by an engine control unit (ECU) 45 to selectively apply the pressure in the vacuum tank 42 and the atmospheric pressure to the operating chamber 37a of the diaphragm 37. When the ECU 45 determines that the engine 1 is operating under a load equal to or greater than a predetermined load, the ECU 45 controls the opening and closing valve 3 9 to bring the vacuum tank 42 and the operating chamber 37a into communication with each other, developing a negative pressure in the operating chamber 37a. The link 36 is now pulled to turn the arm 35b, opening the valve member 3 5a to supply air from the first passageway 33b to the combustion chamber 11. When the ECU 45 determines that the engine 1 is operating under a load smaller than the predetermined load, the ECU 45 controls the opening and closing valve 3 9 to apply the atmospheric pressure to the operating chamber 37a, allowing the spring 37b to push back the link 36 to turn the arm 35b, closing the valve member 35a. [0021] Since a negative pressure is extracted through the air passage pipe 4 0 from the second passageway 33c, which is open at all times, near the cylinder head 1, the drive power for opening the SCV 35 can easily be provided, and the stable negative pressure can be provided. [0022] As shown in Fig. 7, the SCV 3 5 may be opened and closed in ganged relation to operation of a throttle valve 34. Specifically, the link 36 coupled to the arm 35b of the SCV 35 is connected to a throttle member of the throttle valve 34. The link 36 is connected to the throttle valve 34 such that the link 36 is not pulled until the throttle valve 34 is opened to a predetermined degree or more. When the throttle valve 34 is opened to the predetermined degree or more, the link 3 6 is pulled to turn the arm 35b, opening the valve member 35a. Since the SCV 35 is opened and closed in response to the opening and closing of the throttle valve 34, the SCV 35 is highly ganged with the throttle valve 34. When the throttle valve 34 is opened to a small degree and the engine 1 operates under a low load, the first passageway 33b is closed, producing a swirling flow in the combustion chamber 11. [0023] In the engine 1 thus constructed, when the SCV 3 5 is closed, air that has been brought into a normal state by an air cleaner, not shown, flows from the throttle valve 34 into the inlet pipe 33, and then flows from the second passageway 33c into the second intake port 13, where the air is mixed with fuel to produce an air-fuel mixture that is supplied from the second intake opening 16 to the combustion chamber 11. Therefore, an intensive oblique swirling flow of the air-fuel mixture is formed in the combustion chamber 11, making it possible to combust the fuel efficiently. When the SCV 35 is opened, air that flows into the inlet pipe 33 flows from the first and second passageways 33b, 33c into the first and second intake ports 12, 13. The air is supplied from the first intake opening 15 to the combustion chamber 11, and the air-fuel mixture is supplied from the second intake opening 16 to the combustion chamber 11. The air and the air-fuel mixture which flow in from the first and second intake openings 15, 16, respectively, impinge upon each other, attenuating a swirling flow and also attenuating a tumbling flow. Therefore, an unwanted quick combustion pressure buildup is reduced, allowing the engine to operate with low noise. [0024] The air and the air-fuel mixture that are supplied to the combustion chamber 11 as described above are compressed by the piston 8, after which it is ignited and combusted by an ignition plug 4 7 to generate energy for rotating the crankshaft 10 through the piston 8. Thereafter, an exhaust gas flows from the first and second exhaust openings 17, 18 into the exhaust port 14, from which the exhaust gas is discharged out of the engine.( [0025] In the engine 1/ the first and second passageways 33b, 33c defined in the inlet pipe 33 and the first and second intake ports 12, 13 defined in the cylinder head 3 •which are connected to the first and second passageways 33b, 33c are arranged such that the intake passage made up of the first passageway 33b and the first intake port 12 is positioned forwardly of the intake passage made up of the second passageway 3 3c and the second intake port 13 with respect to the engine 1 as viewed in side elevation in Fig, 8. Specifically, as shown in Fig. 8, the angle formed between the second intake port 13 which is supplied with air at all times and the second intake opening 16 (the seat surface for the second intake valve 23) is sharper in the cylinder head 3 than the angle formed between the first intake port 12 to which the SCV 3 5 is connected and the first intake opening 15 (the seat surface for the first intake valve 22) . The angle at which the air-fuel mixture flows from the second intake opening 16 into the combustion chamber 11 is smaller than the angle at which the air-fuel mixture flows from the first intake opening 15 into the combustion chamber 11. Therefore, the second intake port 13 has a jaw shape 13a in the form of a sharp edge for intensifying an oblique swirling component of the air-fuel mixture in the combustion chamber 11. The first intake port 12 has a jaw shape 12a of a large radius of curvature for reducing the resistance to the air-fuel mixture flow. Consequently, the air-fuel mixture smoothly flows from the first intake opening 15 into the combustion chamber 11 for increased intake efficiency. [0026] As described above, the first and second intake ports 12, 13 which communicate with the first and second intake openings 15, 16 are independently defined in the cylinder head 3, and air flowing out of the throttle valve 34 is branched into the first and second passageways 33b, 33c in the inlet pipe 33. Therefore, the freedom with which to lay out the first and second intake ports 12, 13 can be increased for optimizing the intake passages connected to the combustion chamber 11, and the space around these ports 12, 13 can be reduced for reducing the size of the cylinder head 3. The first and second intake ports 12, 13 which are connected to the first and second intake openings 15, 16 are branched in the inlet pipe 33, rather than the cylinder head 3, so that the passage length of the branched intake port portions is longer than with the conventional structure. Accordingly, changes in the cross-sectional areas of the first and second intake ports 12, 13 are small, and the radii of curvature of portions thereof are large, allowing the air-furl mixture to be smoothly guided into the combustion chamber 11. [0027] Since the throttle valve 34 is positioned upwardly and forwardly of the cylinder head 3, the first and second passageways 33b, 33c in the inlet pipe 33 have curved portions 33d in order to allow themselves to be curved downwardly from the forward position and installed in position. The SCV 35 is mounted in a vertically extending portion of the first passageway 33b. Therefore, as indicated by the arrow A in Fig. 8, air flowing out of the throttle valve 34 flows into the SCV 35 while being displaced along an outer wall surface in the passages in the curved portions 33d of the inlet pipe 33 (the first and second passageways 33b, 33c), i.e., while being displaced rearwardly in the longitudinal direction of the motorcycle on which the engine 1 is mounted. If the valve member 35a of the SCV 35 is rotated in the direction indicated by the arrow B in Fig. 8 to open itself, then the valve member 35a is opened so as to interconnect a rear portion of the first passageway 33b which is closer to the throttle valve 34 and a front portion of the first passageway 33b which is closer to the combustion chamber 11. Accordingly, the valve member 35a is progressively opened from the side where the air flowing from the throttle valve 34 is displaced and flows into the valve member 35a, and allows the air to flow into the first intake opening 15 without interrupting the air flow. Therefore, the total amount of air flowing into the combustion chamber 11 and the swirling ratio are increased. [0028] The SCV 35 has its shaft inclined with respect to the first intake port 12 and extending parallel to the ground level. Consequently, the shaft of the SCV 35 does not need to extend through the second passageway 33c which supplies air to the combustion chamber 11 at all times, does not obstruct the air flow in the second passageway 33c, and can be reduced in diameter. This structure makes it possible to make the bearing structure durable. [0029] The inlet pipe 33 is connected to the first and second intake joint openings 19, 2 0 defined in the cylinder head 3 with an insulator 48 interposed therebetween. The insulator 48 has a first joint passage 4 8a which provides communication between the first passageway 3 3b and the first intake port 12 and a second joint passage 4 8b which provides communication between the second passageway 33c and the second intake port 13. The second passageway 33c, the second intake port 13, and the second joint passage 48b have the same diameter, as shown in Fig. 2. As the inside diameter X of the first passageway 33b in which the SCV 35 is mounted is greater than the inside diameter Y of the first intake port 12, the inside diameter of a portion of the first joint passage 48a which is closer to the SCV 35 is made greater to match the inside diameter X of the first passageway 33b. [0030] Because the intake passage in which the SCV 3 5 is mounted is restricted in diameter by the diameter of the first joint passage 48a of the insulator 48, the cross-sectional area of the passage through the SCV 35 is rendered equivalent. Accordingly, when the SCV 35 is opened to supply air from the first and second intake ports 12, 13 to the combustion chamber 11, the flow rates of the air are held in balance. [0031] The engine 1 is air-cooled, and the cooling is performed by a lubricating oil used for lubricating components in the engine 1. The lubricating oil that has cooled the cylinder head 3 flows downwardly into the crankcase 5. The crankcase 5 has an oil pool 49 defined in a front lower portion thereof. The lubricating oil that has cooled and flowed out of the cylinder head 3, etc. is pooled in the oil pool 49. When the level of the pooled lubricating oil exceeds the height of the wall that defines the oil pool 4 9, the lubricating oil returns to an oil reservoir, not shown, defined in a lower portion of the crankcase 5. As can be seen from Fig. 1, inasmuch as the oil pool 4 9 is defined in the front lower portion of the crankcase 5 rearwardly of the cylinder block 4, the lubricating oil returning from the cylinder head 3 through the cylinder block 4 is pooled in the oil pool 49 without being mixed with other lubricating oil that has returned from other components in the engine 1. [0032] The oil pool 49 has an oil temperature sensor 50 for measuring the temperature of the lubricating oil returning from the cylinder head 3 to detect an increase in the temperature of the cylinder head 3. As shown in Fig. 1, the oil pool 49 has an inlet 49a having a cross-sectional area that is greater than the cross-sectional area of a bottom 49b thereof, as viewed in side elevation. Therefore, even if the motorcycle is tilted while in movement, the oil pool 49 can retain a sufficient amount of lubricating oil therein, allowing the temperature of the lubricating oil to be measured reliably. With the oil pool 49 being thus constructed, the temperature of the lubricating oil returning from the cylinder head 3 can be measured stably at all times without being affected by the rotational speed of the engine 1 and changes in the attitude thereof. After the temperature of the lubricating oil has once increased, it can stably be measured without being affected by external factors such as water applied to the crankcase. [0033] As shown in Fig. 10, the oil temperature sensor 50 extends horizontally from a side surface of the crankcase 5. As shown in Fig. 11, the oil temperature sensor 50 has a portion projecting outside of the crankcase 5 and covered with a cover 51 that is integrally formed with the crankcase 5. With the oil temperature sensor 50 being thus installed, the oil temperature sensor 50 is located within the profile of the crankcase 5 as viewed in side elevation, and will be free of direct impacts and less liable to suffer damage even when the motorcycle hits road steps, etc. Since the oil temperature sensor 50 is covered with the cover 51 integrally formed with the crankcase 5, it is protected against being directly hit by pebbles or the like that are flipped up while the motorcycle is running. [0034] As the oil pool 49 is constructed of the wall integrally formed with the crankcase 5, it does not need to be machined, and hence the manufacturing cost is prevented from increasing. Since the cover 51 is integrally formed with the crankcase 5, it does not need to be provided as a separator component and gives a good appearance, and the manufacturing cost is prevented from increasing. [Brief Description of the Drawings] [0035] [Fig. 1] Fig. 1 is a right-hand side elevational view of an engine according to the present invention, with a cylinder head and related components being shown in cross section. [Fig. 2] Fig. 2 is a right-hand side elevational view showing a second intake port. [Fig. 3] Fig. 3 is a right-hand side elevational view of the engine. [Fig. 4] Fig. 4 is a front elevational view showing a structure of a cylinder head and an inlet pipe. [Fig. 5] Fig. 5 is side elevational view showing a structure of the cylinder head and an injector. [Fig. 6] Fig. 6 is a block diagram showing an opening and closing mechanism for opening and closing an SCV with a negative pressure from an intake port. [Fig. 7] Fig. 7 is a block diagram showing an opening and closing mechanism for opening and closing an SCV in ganged relation to a throttle valve. [Fig. 8] Fig. 8 is a side elevational view showing the layout of first and second passageways defined in the inlet pipe and first and second intake ports. [Fig. 9] Fig. 9 is a side elevational view showing a structure of an insulator disposed in a joint between the cylinder head and the inlet pipe. [Fig. 10] Fig. 10 is a cross-sectional view of an oil pool in a crankcase and nearby components. [Fig. 11] Fig. 11 is a left-hand side elevational view of the engine. [Description of Reference Symbols] [0036] 1: engine (internal combustion engine) 3: cylinder head 11: combustion chamber 12: first intake port (intake passage) 13: second intake port (intake passage) 33: inlet pipe 33a: intake passageway (intake passage) 33b: first passageway (intake passage) 33c: second passageway (intake passage) 35: SCV (opening and closing valve) [Name of Document] Claims [Claim 1] An internal combustion engine having at least one combustion chamber, at least two intake passages communicating with said combustion chamber, and an opening and closing valve disposed in either one of the intake passages for opening and closing the intake passage, said opening and closing valve being closed when the internal combustion engine operates under a low load, wherein said combustion chamber is defined in a cylinder head, and said intake passages are independently defined in said cylinder head. [Claim 2] The internal combustion engine according to claim 1, wherein said intake passages comprise: a first intake port and a second intake port which are defined in said cylinder head and have ends communicating with said combustion chamber and other ends communicating with the exterior; and an intake passageway defined in an inlet pipe connected to said cylinder head and a first passageway and a second passageway which are branched from said intake passageway toward said cylinder head; said first passageway communicating with the other end of said first intake port, said second passageway communicating with the other end of said second intake port, said intake passageway being branched in said inlet pipe; said opening and closing valve being disposed in said first passageway in said inlet pipe.

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