Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2001-06-11
2004-01-06
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S406590, C123S090500
Reexamination Certificate
active
06672283
ABSTRACT:
PRIORITY INFORMATION
This application is based on and claims priority to Japanese Patent Applications No.2000-173894, filed Jun. 9, 2000, No.2000-173903, filed Jun. 9, 2000, and No.2000-173928, filed Jun. 9, 2000, the entire contents of which are hereby expressly incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four-cycle engine for a marine drive, and more particularly relates to a four-cycle engine for a marine drive that includes a variable valve timing mechanism.
2. Description of Related Art
A typical outboard motor comprises a power head and a housing unit depending from the power head. The power head includes an internal combustion engine that drives a marine propulsion device such as a propeller with a driveshaft and a propulsion shaft that both are journaled within the housing unit. The marine propulsion device is attached to the end of the propulsion shaft extending out of the housing unit and is placed in a submerged position.
Recently, many outboard motors are powered by a four-cycle internal combustion engine because of the better emission control capability of four-cycle technology when compared to two-stroke technology. Generally, a four-cycle engine includes at least one intake port and at least one exhaust port that are in communication with a combustion chamber. One or more camshafts can be provided to actuate valves associated with the ports such that flow can be controlled through the ports. The valve movement is timed so that air can be introduced into the combustion chamber, compressed in the combustion chamber, combusted in the combustion chamber and the resulting exhaust gases then can be discharged from the combustion chamber.
Typical automobile engines include a variable valve timing mechanism that can advantageously change the timing of the opening and closing of the valves. Such variable valve timing mechanisms can adjust the timing of the valves such that a first valve timing is used at higher engine speeds and a second valve timing is used as low engine speeds. The valve timing usually is advanced in the high engine speed range to ensure high charging efficiency and high performance. Similarly, the valve timing can be delayed in the low engine speed to ensure high combustion efficiency, fuel economy and good emission control. Thus, generally speaking, the valve timing is adjusted to either an advanced first valve timing for higher engine speed ranges or a delayed second valve timing lower engine speed ranges.
Typically, adjusting the valve timing and configuring at least the intake system result in higher performance only in a particular desired power range. Because of this design characteristic, engine torque in a range of low and medium engine speed is likely to be neglected in favor of optimizing performance in a higher engine speed range.
While adjusting the valve timing of an automotive engine in this manner can satisfactorily improve the performance of the engine in a desired power range, such a technique does not readily transfer to marine applications. A marine drive, such as a propeller, accelerates quickly to a high speed rotation because of the low viscosity of water. Thus, a relatively large engine torque generally is necessary in the low and medium engine speed ranges. For instance, the sudden acceleration of a propeller from a slower rotation, or a standstill, to a suitable operating speed requires a very large engine torque.
A need therefore exists for an improved four-cycle engine for a marine drive that can generate relatively large torques while accelerating in low and medium engine speed ranges.
Another problem (i.e., over-revolution of the engine or “redlining the engine”) may arise also with marine drives. Automobile engines usually cut the supply of fuel (i.e., interrupted fuel injection, for instance) when the engine is revved to a high enough speed. By cutting the fuel, then engine returns to a suitable rotational speed or a normal operating condition. This method of engine speed control, however, generally is not suitable for marine drives due to the relatively high loads incurred while the watercraft is moving. In other words, reducing the amount of fuel in the air-fuel mixture still allows a low energy power stroke, which can cause swings in the engine speed. If the fuel-cut method were used, the engine speed might abruptly lower such that relatively large fluctuations in the engine speed would result during the over-rev control.
Outboard engines, thus, generally employ another method in which ignitions are cut if the over-revving occurs. While the method is effective against over-rev situations, unburned fuel can be discharged to the atmosphere when the ignition is cut. If the engine includes a catalyst within the associated exhaust system, the unburned fuel can foul the catalyst under extreme conditions.
Another need thus exists for an improved four-cycle engine for a marine drive that can prevent over-revving from occurring without causing major fluctuations in engine speed.
Some engines for marine drives also employ an idle air delivery device that bypasses a throttle valve in a main intake passage. An idle valve is provided within the delivery device to measure an amount of idle air passing therethrough. Changing a position of the idle valve can control the idle speed of the associated motor. Although idle air is delivered to the combustion chamber through the idle air delivery device, the throttle valve desirably is slightly opened to allow a light air flow through the main intake passage such that the idle speed can be substantially stabilized. The light flow of air also works to prevent sticking of the throttle valve when higher engine speed operation is desired.
Under certain circumstances, the idle speed may unexpectedly and unintentionally increase. More specifically, because the poorly regulated light flow of air through the main intake passage, air amounts delivered to the combustion chamber during idle can vary such that idle speed can exceed a desired objective idle speed. In some applications, delaying ignition timing can reduce the effects of this problem. This solution, however, may decrease fuel economy as well.
Hence, a further need exists for an improved four-cycle engine for a marine drive that can substantially maintain an actual idle speed at an objective idle speed without unwarranted decreases in fuel economy.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body and a member movable relative to the engine body. The engine body and the member together define a variable-volume combustion chamber. An air induction device is arranged to introduce air to the combustion chamber with the air induction device comprising an intake port that provides a connection between the air induction device and the combustion chamber. An intake valve is movable relative to the intake port between an open position and closed position such that the intake valve can selectively inhibit air flow into the combustion chamber. A valve actuator is rotatably journaled relative to the engine body. The valve actuator moves the intake valve at a preset angular position of the valve actuator. A valve actuator driving arrangement is adjustably connected to the valve actuator such that the preset angular position can be advanced or delayed through movement relative to the valve actuator driving arrangement. A setting mechanism is interposed between the valve actuator driving arrangement and the valve actuator. The setting mechanism is arranged to adjust the preset angular position of the valve actuator relative to the valve actuator driving arrangement. The setting mechanism is capable of adjusting the valve actuator between a first limit angular position and a second limit angular position with the first limit angular position being advanced relative to the second limit angular position. A sensor is arranged to sense an amount of the air within the induction devic
Knobbe Martens Olson & Bear LLP
Mohanty Bibhu
Yamaha Marine Kabushiki Kaisha
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