Abstract: An internal combustion engine includes a structure that increases the velocity of exhaust gas. The internal combustion engine includes a branch section arranged to branch a shock wave propagating at a higher velocity than exhaust gas and to guide the branched shock wave, and a reflecting section provided in the branch section. The reflecting section is arranged to reflect and return the shock wave back to an exhaust path and cause the shock wave to collide against the exhaust gas, thereby increasing the pressure of the exhaust gas. In accompaniment with the exhaust gas passing a divergent section of a convergent-divergent nozzle, a new shock wave propagating in a downstream direction in the exhaust path is generated, and the temperature and pressure of the exhaust gas are decreased.

Abstract: An outboard motor that is capable of reducing a trolling noise includes an engine which has a crank shaft extending in an up-down direction; a drive shaft extending downward from the crank shaft and including a torsion bar spring; a propeller shaft; a propeller provided in the propeller shaft; a forward/backward switching mechanism arranged to connect the drive shaft and the propeller shaft with each other; and a vibration damper which includes a first cylindrical body and a second cylindrical body which are penetrated by the torsion bar spring. The first cylindrical body and the second cylindrical body are coaxial with each other. The first cylindrical body has its upper end portion connected with an upper end portion of the torsion bar spring whereas the second cylindrical body has its lower end portion connected with a lower end portion of the torsion bar spring. A viscous fluid is filled between the first cylindrical body and the second cylindrical body.

Abstract: An outboard motor includes an engine, an engine cover, a partitioning member, an intake device, and a fan. The engine is arranged to support a crankshaft extending along an up-down direction. The partitioning member is arranged to partition the inside of the engine cover into a lower chamber accommodating the engine and an upper chamber. In the partitioning member, a communication hole which is arranged to cause the upper chamber to communicate with the lower chamber is provided. Also, the engine cover has an air inlet arranged to cause the upper chamber to communicate with the atmosphere, and an air outlet arranged to cause the lower chamber to communicate with the atmosphere. The air inlet is arranged in an upper portion of the engine cover. The air outlet is arranged at a lower end portion of the engine cover. The intake device is connected to the engine. The intake device has an air suction port arranged to communicate with the upper chamber. The fan is arranged inside the engine cover.

Abstract: An outboard motor includes an engine, a first exhaust passage, a partition, a communication portion, an exhaust gas concentration sensor, and a catalyst. The engine is arranged to support a crankshaft extending along an up-down direction. The first exhaust passage is connected to the engine and is arranged to exhaust exhaust gas of the engine into water. The partition is arranged to partition an inside of the first exhaust passage into an upstream side and a downstream side. The communication portion is arranged to make the upstream side communicate with the downstream side of the partition in the first exhaust passage. The exhaust gas concentration sensor is arranged on the upstream side of the partition in the first exhaust passage. The catalyst is arranged on an upstream side of the exhaust gas concentration sensor in the first exhaust passage.

Abstract: An exhaust device for an outboard motor engine includes an exhaust passage, a catalyst an air inlet, and an air pump. The exhaust passage is connected to the engine arranged to support a crankshaft extending along an up-down direction. The catalyst is arranged in the exhaust passage. The air inlet is arranged at a position higher than the engine inside an engine cover covering the engine. The air pump is supported by the engine. Further, the air pump is arranged to supply air taken through the air inlet to an upstream side of the catalyst in the exhaust passage.

Abstract: An exhaust device for an outboard motor multi-cylinder engine includes an exhaust passage having a first end connected to the multi-cylinder engine, a catalyst provided in the exhaust passage, and an exhaust chamber connected to a second end of the exhaust passage as well as to a main exhaust passage positioned below the engine. The exhaust passage includes upstream portions for cylinders which have inlet ends respectively connected to exhaust gas outlets of a plurality of cylinders whose exhaust valve opening periods are different, a collecting portion arranged to connect the outlet ends of these upstream portions to each other, and a plurality of downstream portions which are branched from the collecting portion and connected commonly to the exhaust chamber. The catalyst is provided in each of the plurality of downstream portions.

Abstract: An outboard motor includes an engine and an exhaust pipe. The engine has a crank case, a cylinder body, and a cylinder head aligned along the front-rear direction of the outboard motor, and arranged to support a crankshaft so as to extend along an up-down direction. The exhaust pipe is arranged to lead an exhaust gas of the engine to a main exhaust passage positioned below the engine. The cylinder head has an exhaust gas outlet opened in the side portion on one side of the cylinder head in the left-right direction of the outboard motor. The exhaust pipe has a bypass exhaust pipe which, in a plan view, extends from the exhaust gas outlet, bypasses the engine along the crank case, and reaches the other side in the left-right direction of the engine.

Abstract: An injector bracket 10 is provided inside an air cleaner 5. The injector bracket 10 comprises a rectifying wall 10a bulging into a main chamber 5b, and a stream-line guide wall 10b in opposition to an air current M having passed through an element 8. The injector bracket 10 functions as a partition and forms a separate chamber 10e partitioned from the main chamber 5b in the air cleaner 5. An upstream injector unit 7 is arranged in the separate chamber 10e. The rectifying wall 10a is in the form of a symmetric blade.

Abstract: A fuel supply system has an air chamber that contains a fuel injector. At least one aperture is formed in a substantially lowermost portion of a lower surface of the air chamber. The aperture and the lower surface have a generally uninterrupted or smooth transition or interface.

Abstract: An engine control system enables engine control to cause ignition timing to approximate MBT without necessarily measuring torque and combustion pressure. The negative ion current in an engine combustion chamber is measured and a first crank angle B corresponding to a first rate in change of the negative ion current curve E is identified. A second crank angle C corresponding to a second rate in change of the negative ion current curve E also is identified. The ignition timing is controlled based upon a third crank angle G that generally is a midpoint between the first crank angle B and the second crank angle C. The third crank angle G becomes a specified target crank angle.

Abstract: An outboard motor includes a prime mover, a marine propulsion unit having a propeller arranged to be driven by a rotational force of the prime mover to generate a thrust force, a shift position changing mechanism, a shift position changing mechanism actuator, and a control unit arranged to control the shift position changing mechanism actuator. When the shift position is changed to one of the first shift position and the second shift position from the neutral position, the control unit inhibits a change in the shift position to the other one of the first shift position and the second shift position until a predetermined time period elapses. The above arrangement improves the controllability of a boat propulsion system having an electronically controlled shift mechanism.

Abstract: A boat propulsion system includes a power source, a propulsion unit, a propeller rotational speed detection section, a shift mechanism, an actuator, a control lever, a shift position detection section, an accelerator opening detection section, and a control unit. When the control lever is operated such that a shift position is changed from a first shift position to a second shift position, while the absolute value of accelerator opening varying speed becomes equal to or larger than a predetermined value, the control unit enables the actuator to maintain the first shift position until the rotational speed of a propeller becomes equal to or lower than a predetermined rotational speed and then to change to the second shift position. This minimizes a load generated on the power source, the power transmission mechanism, and other components of the boat propulsion system.

Abstract: A boat propulsion system includes a power source, a propulsion section, a shift position switching mechanism arranged to switch among a first shift position, a second shift position, and a neutral position, a gear ratio switching mechanism, an actuator, and a control section. When switching is to be performed from the neutral position to the first shift position and the high-speed gear ratio, the control section is arranged to cause the actuator to, maintain the low-speed gear ratio, switch to the first shift position, and then establish the high-speed gear ratio when the current gear ratio of the gear ratio switching mechanism is the low-speed gear ratio, and cause the actuator to establish the low-speed gear ratio before switching to the first shift position, switch to the first shift position, and then establish the high-speed gear ratio when the current gear ratio of the gear ratio switching mechanism is the high-speed gear ratio.

Abstract: An outboard motor includes a power source, a boat propulsion section, a shift position switching mechanism, a clutch actuator, and a control device. The shift position switching mechanism switches among a first shift position in which a first clutch is engaged and a second clutch is disengaged, a second shift position in which the first clutch is disengaged and the second clutch is engaged, and a neutral position in which both the first clutch and the second clutch are disengaged. When a gear shift is to be made from the first shift position to the second shift position, the control section causes the clutch actuator to gradually increase an engagement force of the second clutch. The outboard motor reduces the load to be applied to the power source and the power transmission mechanism at the time of a gear shift in a boat propulsion system including an electronically controlled shift mechanism.

Abstract: An exhaust device for an outboard motor includes an engine having a plurality of cylinders, a first expansion chamber case for collecting exhaust from a first part of the plurality of cylinders and a second expansion chamber case for collecting therein exhaust from a second part of the plurality of cylinders. First and second exhaust passages can extend individually from the first and second expansion chamber cases, respectively, and can communicate with water at the downstream end openings.

Abstract: An exhaust manifold includes first to eighth upstream exhaust pipes extending respectively from first to eighth cylinders ignited in that order; first to fourth midway exhaust pipes extending respectively from a joint of extended ends of the first and fifth upstream exhaust pipes, a joint of extended ends of the second and sixth upstream exhaust pipes, a joint of extended ends of the third and seventh upstream exhaust pipes, and a joint of extended ends of the fourth and eighth upstream exhaust pipes; and first and second downstream exhaust pipes extending respectively from a joint of extended ends of the first and third midway exhaust pipes and a joint of extended ends of the second and fourth midway exhaust pipes for communicating the respective joints to the ambient atmosphere.

Abstract: An engine control system enables engine control to cause ignition timing to approximate MBT without necessarily measuring torque and combustion pressure. The negative ion current in an engine combustion chamber is measured and a first crank angle B corresponding to a first rate in change of the negative ion current curve E is identified. A second crank angle C corresponding to a second rate in change of the negative ion current curve E also is identified. The ignition timing is controlled based upon a third crank angle G that generally is a midpoint between the first crank angle B and the second crank angle C. The third crank angle G becomes a specified target crank angle.

Abstract: An exhaust device for an outboard motor includes an engine having a plurality of cylinders, a first expansion chamber case for collecting exhaust from a first part of the plurality of cylinders and a second expansion chamber case for collecting therein exhaust from a second part of the plurality of cylinders. First and second exhaust passages can extend individually from the first and second expansion chamber cases, respectively, and can communicate with water at the downstream end openings.

Abstract: An exhaust device of an eight-cylinder engine can include first to eighth cylinders and a manifold. The first to eighth cylinders are ignited in that order. The exhaust manifold includes first to eighth upstream exhaust pipes extending respectively from the first to eighth cylinders. The first to fourth midway exhaust pipes can extend respectively from a joined portion of the first and fifth upstream exhaust pipes, a joined portion of the second and sixth upstream exhaust pipes, a joined portion of the third and seventh upstream exhaust pipes, and a joined portion of the fourth and eighth upstream exhaust pipes. A downstream exhaust pipe can connect extended ends of the first to fourth midway exhaust pipes to the ambient atmosphere.

Abstract: An exhaust device of a six-cylinder engine includes first to sixth cylinders and a manifold extending from the first to sixth cylinders. The first to sixth cylinders are ignited in that order. The exhaust manifold can include first to sixth upstream exhaust pipes extending respectively from the first to sixth cylinders, first to third midway exhaust pipes extending respectively from a joined portion of extended ends of the first and fourth upstream exhaust pipes, a joined portion of extended ends of the second and fifth upstream exhaust pipes, and a joined portion of extended ends of the third and sixth upstream exhaust pipes, and a downstream exhaust pipe connecting extended ends of the first to third midway exhaust pipes to the ambient atmosphere.