Internal-combustion engines – Poppet valve operating mechanism – Camshaft drive means
Reexamination Certificate
2002-12-10
2004-03-16
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Poppet valve operating mechanism
Camshaft drive means
C123S1950HC, C123S090380, C123S1960CP
Reexamination Certificate
active
06705263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to handheld type four-cycle engines which are mainly used as a power source for machines for portable operation such as trimmers. More particularly, it relates to improvement of a four-cycle engine that includes an engine main body, the engine main body including a crankcase having a crank chamber, a cylinder block having a cylinder bore and a cylinder head having an intake port and an exhaust port; a crankshaft supported in the crankcase and housed inside the crank chamber; a piston fitted in the cylinder bore and connected to the crankshaft; an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and exhaust valve being mounted in the cylinder head; a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and exhaust valve; and a power output or takeoff mechanism provided on one end of the crankshaft, the end projecting out of the engine main body.
2. Description of the Prior Art
Such a handheld type four-cycle engine is already known as disclosed in, for example, Japanese Patent Application Laid-open No. 10-288019.
Handheld type four-cycle engines are of course useful in terms of the prevention of environmental pollution as well as assuring the operators' health since the exhaust gas is comparatively clean. However, since the structure thereof is more complicated than that of two-cycle engines, there is a drawback that it is difficult to reduce the weight thereof. Weight reduction is an important issue for improvements particularly in the operability of handheld four-cycle engines.
However, in the handheld type four-cycle engine disclosed in the above-mentioned patent publication, a valve operation mechanism for opening and closing intake and exhaust valves provided in the upper part of a cylinder head is of a type that includes pushrods and rocker arms, and a valve operation chamber for housing the pushrods, a camshaft for driving the pushrods, etc. is formed in a side wall of the engine main body; the size of the engine main body therefore inevitably increases thus making it difficult to reduce the weight of the engine.
SUMMARY OF THE INVENTION
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to provide a lightweight handheld type four-cycle engine having good operability by making the engine main body compact.
In accordance with a first characteristic of the present invention in order to achieve the above-mentioned objective, there is proposed a handheld type four-cycle engine including an engine main body, the engine main body including a crankcase having a crank chamber, a cylinder block having a cylinder bore and a cylinder head having an intake port and an exhaust port; a crankshaft supported in the crankcase and housed inside the crank chamber; a piston fitted inside the cylinder bore and connected to the crankshaft; an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and the exhaust valve being mounted in the cylinder head; a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and the exhaust valve; and a power output mechanism provided on one end of the crankshaft projecting out of the engine main body, wherein the valve operation mechanism includes a camshaft rotatably supported in the cylinder head so as to open and close the intake valve and the exhaust valve, and a dry type timing transmission placed outside the engine main body on the side opposite the power output mechanism and providing association between the crankshaft and the camshaft.
The above-mentioned power output mechanism corresponds to the centrifugal clutch described in the embodiments below.
In accordance with the above-mentioned first characteristic, since the timing transmission and the power output mechanism are mounted on either side of the cylinder head on the two ends of the crankshaft, the weight balance at the two ends of the crankshaft is improved, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine. Furthermore, since the loads arising from the timing transmission and the drive shaft separately work on the two ends of the crankshaft during operation of the engine so avoiding the load on the crankshaft and its bearings from being localised, the durability thereof can be enhanced.
In accordance with a second characteristic of the present invention, in addition to the above-mentioned first characteristic, there is proposed a handheld type four-cycle engine wherein the timing transmission is made as a dry type and is separate from the crank chamber.
In accordance with the above-mentioned second characteristic, since it is unnecessary to provide the side wall of the engine main body with a special chamber for housing the timing transmission, the engine main body can be made thinner and more compact thus achieving a large reduction in the weight of the entire engine.
In accordance with a third characteristic of the present invention, in addition to the above-mentioned first or second characteristic, there is proposed a handheld type four-cycle engine wherein a flywheel is mounted on the crankshaft between the engine main body and the power output mechanism, the flywheel including cooling vanes for sending cooling air to the engine main body and having a diameter larger than that of the power output mechanism.
In accordance with the above-mentioned third characteristic, the cooling air can be supplied appropriately to the engine main body, without obstruction from the power output mechanism, by rotation of the cooling vanes while minimising any increase in the size of the engine due to the flywheel, and the cooling performance thereof can be enhanced.
In accordance with a fourth characteristic of the present invention, in addition to the above-mentioned first or second characteristic, there is proposed a handheld type four-cycle engine wherein an oil tank for storing a lubricating oil for lubricating the inside of the engine main body is placed outside the timing transmission so as to adjoin it and is supported on the engine main body.
In accordance with the above-mentioned fourth characteristic, since the oil tank covers at least one part of the timing transmission, the transmission can be protected. Moreover, since the oil tank and the flywheel are positioned opposite to each other, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible and the operability of the engine can be further enhanced.
In accordance with a fifth characteristic of the present invention, in addition to the above-mentioned first characteristic, there is proposed a handheld type four-cycle engine wherein the valve operation mechanism includes the timing transmission placed outside the engine main body and linked to one end of the crankshaft and a cam system for transmitting the rotational force of the driven side of the timing transmission to the intake and exhaust valves for opening and closing forces, a first valve mechanism chamber housing the timing transmission is provided integrally with an oil tank that is placed outside of the engine main body on the same side as the timing transmission, a second valve mechanism chamber housing at least one part of the cam system is formed in the cylinder head, and a pair of oil slingers for stirring and scattering the oil stored in the oil tank in order to generate an oil mist that is to be supplied to the second valve operation chamber and the crank chamber are fixed to the crankshaft so that the timing transmission is interposed between the pair of the slingers.
In accordance with the above-mentioned fifth characteristic, since the oil tank is placed on one
Ito Keita
Kasai Koji
Maeda Takeshi
Nishida Takao
Ryu Yasutake
Dolinar Andrew M.
Harris Katrina B.
Honda Giken Kogyo Kabushiki Kaisha
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Handheld type four-cycle engine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Handheld type four-cycle engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Handheld type four-cycle engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3192311