Outboard motor

Abstract: An outboard motor comprising an engine, a vertically disposed crankshaft, an exhaust gas inlet being formed in an exhaust guide supporting the engine, and a catalytic system, wherein the catalytic system is disposed below a cylinder head and above said exhaust gas inlet.

Description: This invention relates to an outboard motor comprising an engine, a vertically disposed crankshaft, an exhaust gas inlet being formed in an exhaust guide supporting the engine, and a catalytic system. An outboard motor mounted on a small marine vessel is generally configured such that an upper case and an exhaust guide are connected with the upper side of a lower case, an engine is supported on the exhaust guide and secured thereto, the engine is covered with a cowling which in turn drives a propulsion unit to rotate and the exhaust from the engine is passed through an exhaust passage formed vertically in the side wall of the engine body, via an exhaust guide, an upper case and a lower case, and then discharged into sea water. Recently, in such an engine for an outboard motor, it is proposed that a catalyst is provided in the exhaust passage, in view of clarification of exhaust gas. In JP-A-7-189671, for example, it is disclosed that a catalyst is disposed in an upper case below an engine, and in JP-A-4-260893 an catalyst provided in an exhaust passage in the side surface of the engine body. Moreover, in US 5,556,311, a catalyst bed is mounted on the underside of an exhaust guide plate and receives exhaust gases after the exhaust gases have flown through said exhaust guide. Still another aspect is shown in DE 4234682 A1, wherein the catalytic converter is an integral element of an exhaust gas outlet frame that is mounted on the underside of an exhaust guide plate supporting the engine. However, in such a way above as the catalytic converter being disposed in the upper case below the engine, a bypass must be employed in order to locate the exhaust passage above the sea level for avoiding the catalytic converter from contacting seawater. In this case, it will be difficult to provide the bypass within a limited space of the cowling. Particularly, in 4-stroke cycle engines it is difficult to provide a bypass due to the large volume of the cylinder head having a valve actuating mechanism. In a manner such that a catalytic device is provided in the exhaust passage on the side wall of the engine body to overcome this problem, the volume of the catalytic device is limited due to the space limitation for mounting the catalytic device, resulting in the problems of increase of total size, particularly in total height, and fusion of support member for supporting the catalyst due to the increase in the temperature of the catalytic system located close to the exhaust gas outlet. Accordingly, it is an objective of the present invention to provide an outboard motor allowing the catalytic system to be compact and to be mounted without any alteration of engine components. According to the present invention this objective is solved for outboard motor as indicated above in that the catalytic system is disposed below a cylinder head and above said exhaust gas inlet. Preferred embodiments of the present invention are laid down in the dependent claims. According to the invention, it is possible that an exhaust gas inlet is formed in an exhaust guide supporting an engine, and that a catalytic device is disposed below a cylinder head and above said exhaust gas inlet. Further, it is advantageous when an exhaust delivery passage and an a exhaust return passage are formed in the side wall of said exhaust guide supporting the engine. In that case, it is possible that an exhaust delivery pipe and an exhaust return pipe are connected with said exhaust delivery passage and exhaust return passage, and that an cooling water passage is formed in the surface wall of said exhaust delivery pipe and exhaust return pipe. Moreover, said catalytic device can be located below the ignition plug of the lowest cylinder. Preferably said engine is a 4-stroke cycle engine. Any reference numerals added in the configuration above are only for easily understanding the invention with reference to the accompanying drawings, and never limit the scope of the invention. Other preferred embodiments of the present invention are laid down in further dependent claims. In the following, the present invention is explained in greater detail with respect to several embodiments thereof in conjunction with the accompanying drawings, wherein: Fig. 1 is a side elevational view of an outboard motor applied with the invention; Fig. 2 is a plan view of the engine in Fig. 1; Fig. 3 is a vertically sectional view around the exhaust camshaft 22 and crankshaft 21, showing first embodiment of the catalytic system of an engine for an outboard motor; Fig. 4(A) is a plan view, showing the exhaust guide 12 in Fig. 3, from which the engine body 20 is removed. Fig. 4 (B) is a cross sectional view, along the line B-B of Fig. 4(A); Fig. 5 is a side elevational view, showing another embodiment of the engine according to the invention. Now, referring to the drawings the embodiments of the invention is described hereinafter. Figs. 1 and 2 show an example of an outboard motor applied with this invention. Fig. 1 is a side elevational view and Fig. 2 is a plan view of the engine in Fig. 1. In the following description same reference numerals are used in the same structures in both drawings and the description therefor may be omitted. Referring to Fig. 1, an outboard motor 1 comprises a clamp bracket 3 detachably mounted on the rear end R (relative to advance direction) of a hull 2, a swivel bracket 5 pivoted up and down about a pivot axis 4 and supported by the clamp bracket 3, a steering bracket 6 allowing the swivel bracket 5 to rotate horizontally about its axis, and a propulsion unit 9 supported on the steering bracket 6 through a mount bracket 7. The propulsion unit 9 has an upper case 10 supported on the steering bracket 6. On the upper part of the upper case 10 are mounted an exhaust guide 12 which is a support member for supporting an engine 11, and a lower cowling 13 enclosing the lower part of the engine. An upper cowling (engine cover) 14 covering the upper part of the engine 11 is removably attached to the lower cowling 13. At the lower part of the upper case 10 is mounted a lower case 15, thereby, as a whole, a casing is configured. A cover member 16 is detachably mounted to the front part F of the engine cover 14. On both right and left sides of the cover member 16, air inlets 17 are opened, an air inlet 19 is also formed at the rear part R of the engine cover 14. In Fig. 2, the engine 11 is a 4-cylinder, 4-stroke cycle engine of water cooled type, in which a crankshaft 21, an exhaust camshaft 22, an intake camshaft 23 are disposed in an engine body 20 so as to pass through it vertically. A drive pulley 24 and a flywheel 25 are fixed on the upper part of the crankshaft 21, and driven pulleys 26, 27 are fixed on the camshafts 22, 23. The rotating movement of the drive pulley 24 is therefore transmitted to the driven pulleys 26, 27 through a belt 29. Four cylinders are vertically juxtaposed in the engine body 20. Four intake pipes 30 are connected with the cylinders, respectively and are extended, with throttle bodies 31 provided at their intermediate positions, respectively, to a silencer 32 disposed in front of the engine 11, where they are gathered to connect each other. There are provided fuel injection valves 33, a fuel pump 35, a thermostat 36, a starting motor 37, and a flywheel cover 38. Now, referring to Figs. 3 and 4, first embodiment according to the invention is described. Fig. 3 is a vertically sectional view around the exhaust camshaft 22 and crankshaft 21. In the engine body 20 four cylinders 20a are formed and exhaust valves 40 are disposed opposite to each cylinder 20a. An exhaust passage (not shown) in communication with each exhaust valve 40 passes vertically through the engine body 20, and is connected with an exhaust delivery passage (exhaust inlet port) 41. An exhaust delivery pipe 42 is connected with the exhaust delivery passage 41 and located in the dead space defined at the lower part of the cylinder head 20b. In this exhaust delivery pipe 42 is disposed a catalytic device 43 which is positioned above the outlet of the exhaust delivery passage 41. Fig. 4(A) is a plan view, showing the exhaust guide 12 in Fig. 3, from which the engine body 20 is removed. Fig. 4(B) is a cross sectional view, along the line B-B of Fig. 4(A). The exhaust guide 12 is connected with the exhaust delivery passage 41 formed so as to extend downward and then horizontally extend, and the exhaust return passage 44 formed so as to extend horizontally and then vertically. The catalytic device 43 is secured at the interconnection of the exhaust return pipe 45 and the exhaust delivery pipe 42. In the walls of the exhaust delivery passage 41, the catalytic device 43 and the exhaust return pipe 45, cooling water passages 42a, 45a and 43a are formed and they are connected with a cooling water passage 46. The operation of the embodiment having the configuration described above is now explained. The exhaust from respective cylinder 20a flows through downward in the exhaust passage formed in the engine body 20, and passes through the exhaust delivery passage 41 of the exhaust guide 12 and the exhaust delivery pipe 42, to the catalytic device 43. Further, the exhaust is discharged downward, via the exhaust return passage 44 and the exhaust return pipe 45. During this operation, as the catalyst 43 is arranged in parallel to the exhaust gas stream, all of the exhaust can flow within the catalyst 43 and thus clarified by those catalysts. Fig. 5 is a side elevational view of another embodiment of the invention. For the same structure as in the previous embodiment, same reference numerals are used and those description are omitted. In this embodiment, a catalytic device 43 is located in the dead space between the rear and lower part of a cylinder head 20b and the lower cowling 13. In this arrangement, the upper part of the catalytic device 43 is positioned below the ignition plug of the bottom cylinder. Although the embodiments of the invention have been described, the scope of the invention shall not be limited to it and can be changed or modified variously. For example, the invention may be also applied to 4 stroke cycle engines other than 2-stroke cycle engines referred in the embodiments heretofore. It is apparent from the description above that: according to the invention, a dead space defined below the cylinder head can be utilized to mount a catalytic device compactly, and the catalytic device can be made compact; the catalytic device can be disposed compactly without any alteration of engine components, as the exhaust system is together in the exhaust guide; cooling performance of the catalytic device is improved; the ignition plug is more easily removed; and that the invention is applied effectively to the 4-stroke cycle engine.

Claims: An outboard motor (1) comprising an engine (11), a vertically disposed crankshaft (21), an exhaust gas inlet being formed in an exhaust guide (12) supporting the engine (11), and a catalytic system (43), characterized in that the catalytic system (43) is disposed below a cylinder head (20b) and above said exhaust gas inlet. An outboard motor (1) according to claim 1, characterized in that an exhaust delivery passage (41) and an exhaust return passage (44) are formed in a side wall of said exhaust guide (12) supporting the engine (11). An outboard motor (1) according to claim 2, characterized in that an exhaust delivery pipe (42) and an exhaust return pipe (45) are connected with said exhaust delivery passage (41) and exhaust return passage (44), and that a cooling water passage (46) is formed in the surface wall of said exhaust deliver pipe (42) and exhaust return pipe (45). An outboard motor (1) according to at least one of the claims 1 to 3, characterized in that said catalytic system (43) is located below the ignition plug of the lowest cylinder (20a). An outboard motor (1) according to claims 3 or 4, characterized in that in the exhaust delivery pipe (42) there is disposed said catalytic system (43), which is positioned above the outlet of the exhaust delivery passage (41). An outboard motor (1) according to one of the claims 2 to 5, characterized in that the exhaust guide (12) is connected with the exhaust delivery passage (41) formed so as to extend downward and then horizontally extend, and the exhaust return passage (44) is formed so as to extend horizontally and then vertically. An outboard motor (1) according to one of the claims 1 to 6, characterized in that the catalytic system (43) is secured at an interconnection of the or an exhaust return pipe (45) and the or an exhaust delivery pipe (42). An outboard motor (1) according to one of the claims 1 to 7, characterized in that in walls of the or an exhaust delivery passage (41), the catalytic system (43) and the exhaust return pipe (45) there are formed cooling water passages (42a, 45a, 43a) and that they are connected with the or a cooling water passage (46). An outboard motor (1) according to one of the claims 1 to 8, characterized in that the catalytic system (43) is located in the dead space between the rear and lower part of the cylinder head (20b) and a lower cowling (13). An outboard motor (1) according to one of the claims 1 to 9, characterized in that said engine is a 4-stroke cycle engine (11).

Inventors: ISHII YASUSHI, ISHII, YASUSHI, Ishii, Yasushi, Sanshin Kogyo Kabushiki Kaisha
Applicants: YAMAHA MARINE KK, YAMAHA MARINE KABUSHIKI KAISHA
Application year: 2000
Main classification: F02B61
IPC codes: F01N7, F02B75, B63H20, F01N3, F02B61