JPH05256114A - Rotary valve type four cycle gasoline engine - Google Patents

Abstract

PURPOSE:To provide a rotary valve type four cycle gasoline engine in which a rotary valve which is formed in a comparatively simple structure being provided in a cylinder head, in order to carry out intake/exhaust stroke is driven, enclosed tightness of a crank case can be maintained easily, the compression ratio of the crank case can be set highly, and axiety about strength of an extended crank shaft. CONSTITUTION:A bearing 32 is mounted through a bearing bracket 35 on a rotary valve shaft 15, while said bearing 32 being, deceleratedly driven in a half rotation from the first pulley 23 of a crank shaft 5 to the second pulley 22 of the rotary valve shaft 15 arranged in a cylinder head 3 through a timing velt 24 arranged outside a crank case 2 so as to carry out intake and exhaust stroke, and also ease bending stress of the crank shaft 5 caused by lateral component of pulling force of the timing velt 24 on the crank shaft 5 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crankcase compression type 4-cycle gasoline engine having a rotary valve shaft at the top of a cylinder.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to a crankcase compression type 4-cycle engine applied for a patent application No. 03-174812, which relates to a drive structure of a rotary valve shaft, and there is no conventional example corresponding to the present invention. FIG. 3 shows an example of the rotary valve type four-cycle engine. This is related to the drive structure of the rotary valve shaft of a four-cycle engine with a rotary valve at the top of the cylinder.
(Published by Maruzen Co., Ltd. in 1960).
In the figure, the piston 4 reciprocates along the cylinder 1 to change the volume of the combustion chamber formed between the piston 4 and the cylinder head 3. The rotary valve shaft 15 has an air supply port 26 and an exhaust port 25 which are independently formed. The combustion chamber communicates with the outside in synchronization with the movement of the piston 4 sliding in the cylinder. It is designed to configure compression, explosion, and exhaust strokes.

The movement of the piston 4 and the setting of the opening area of each port in the rotary valve are omitted since they are not directly related to the present invention, but the synchronization between the piston 4 and the rotary valve is a mechanical coupling mechanism as described below. Is done by. That is, the piston 4 is connected to the crankshaft via a connecting rod (not shown), and the rotation angle of the crankshaft 5 and the piston position have a fixed relationship. The rotation of the crankshaft is transmitted to the transmission shaft 10 by a pair of bevel gears provided in the crankcase,
Further, the rotation of the crankshaft is reduced to 1/2 and transmitted to the rotary valve shaft via the pair of bevel gears 27 and 28 on the rotary valve shaft side. Reference numeral 37 is a bearing that rotatably supports the transmission shaft.

[0004]

However, the conventional structure requires two sets of bevel gears and two bearings for the transmission shaft, so that the structure is complicated. In order to improve the performance of the crankcase compression type 4-cycle engine, it is necessary to reduce the volume of the crankcase as much as possible, and it becomes difficult to install a bevel gear for driving the rotary valve in the crankcase. Further, since the transmission shaft portion must be gas-sealed, there is a problem in that the structure is complicated from that point of view.

The object of the present invention is to solve the problems of the conventional device, to drive the rotary valve shaft in the cylinder head with a relatively simple, lightweight, and small structure, and to provide a pulley outside the crankcase. Maintains the tightness of the crankcase,
Moreover, it is possible to provide a rotary valve type four-cycle gasoline engine suitable for a hand-held work machine, which can set a high crankcase compression ratio.

[0006]

Both pulleys 22 and 23 for a timing belt 24 are provided outside the crankcase,
The crankshaft rotation is reduced to 1/2 by the timing belt 24, and the rotary valve inside the cylinder head is driven by the crankshaft. A bearing 32 is provided inside the pulley on the crankshaft side.

[0007]

Since the rotary valve rotates in synchronization with the crankshaft via the timing belt, it also synchronizes with the movement of the piston. The rotary valve communicates with the exhaust port during the exhaust stroke of the piston and the intake port during the intake stroke through the communication hole in the upper portion of the cylinder. Bearing 3 provided adjacent to first pulley 23 provided outside the crankcase by extending the crankshaft
2 has a function of relieving the bending stress of the extended crankshaft. Also, the second pulley and the belt 2 for driving the rotary valve.
Since 4 is provided outside the crankcase, the crankcase compression ratio of the crankcase compression type 4-cycle gasoline engine can be set high.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a structural schematic diagram of the first embodiment, and FIG. 2 is a structural schematic diagram of the second embodiment. In the first embodiment of FIG. 1, the piston 4 reciprocates along the cylinder 1, and the piston 4 slides in the cylinder in synchronization with the crankshaft 5 via the connecting rod. A combustion chamber is formed between the piston 4, the cylinder 1 and the cylinder head 3. The crankshaft 5 has main bearings 31a and 31b on both sides thereof and is closed by the crankcase 2 to form a crankcase chamber 8. The crankshaft 5 is extended leftward from the crankcase chamber 8 to provide a bearing 32 held by the crankcase via a bearing bracket 35, and the first pulley 23 and the output pulley 52 are attached to the outside thereof.

Further, the rotary valve shaft 1 is provided inside the cylinder head 3.
A bearing 33 for rotatably supporting the crankshaft 5 is installed. The rotary valve shaft is extended to the left to extend the first pulley 2 of the crankshaft.
A second pulley 22 is attached at a position corresponding to 3, and a timing belt 24 is attached between the pulleys 22 and 23. The outer diameter ratio of the first pulley 23 and the second pulley 22 is 1: 2, and the timing is set so that the rotary valve opens and closes the intake and exhaust ports in synchronization with the movement of the piston 4. A flywheel 40 also serving as a cooling fan and a magnet 41 is installed at an end of the crankshaft on the side opposite to the first pulley 23, and the flywheel 40 further includes a starting pulley 5
3 is attached, and a recoil starter 55 and a fan cover 61 are provided outside thereof. In the ignition coil 42, the magnet 4 embedded in the flywheel 40
A high voltage is generated from the electric power generated by No. 1 to cause the spark plug 57 provided in the combustion chamber to perform spark discharge.

FIG. 2 shows the second embodiment in which the crankshaft 5 is extended to the right in the direction of the cooling fan, contrary to the first embodiment of FIG. 1, and the first pulley 23 for driving the rotary valve shaft is provided outside the crankcase. It is provided. Rotary valve shaft 15, piston, cylinder,
The structure of the cylinder head is the same as in FIG. 1, and in this case as well, the bearing bracket 35 and the bearing 32 are provided outside the crankcase.
Is provided, and the first pulley 23 is further provided outside thereof. In the example of FIG. 2, a flywheel 4 that also functions as a cooling fan and a magnet ignition device is provided outside the first pulley 23.
0 and the starting pulley 53 are attached. In this case, cooling air is taken in from the recoil starter side, and a cooling air inlet 62 is provided on the outer circumference of the recoil starter.

Next, the operation of the above embodiment will be described.
The rotary valve shaft provided inside the cylinder head is decelerated to 1/2 rotation of the crank shaft via a timing belt 24 provided outside the crankcase, and the rotary valve passes through a communication hole in the upper part of the cylinder to exhaust the piston. Communicates with the exhaust port and with the intake port during the intake stroke. Even if the crankshaft is extended and the pulley is provided, the bending stress of the extended portion of the crankshaft can be relieved by the additional bearing 32 provided outside the crankcase. Further, in the present invention, since the rotary valve shaft 15 is driven from the crankshaft by the timing belt 24 provided outside the crankcase 2, the crankcase compression ratio is high even in the crankcase compression type 4-cycle gasoline engine. There is an advantage that can be set.

[0012]

Since the rotary valve type four-cycle gasoline engine of the present invention is constructed as described above, the crankshaft and the rotary valve shaft provided in the cylinder head are connected with a relatively simple structure and driven synchronously. Can be made so lightweight,
It is small in size and is suitable as an engine for hand-held work machines. Further, since the pulley is provided outside the crankcase, it is easy to maintain the airtightness of the crankcase and the crankcase compression ratio can be set high. Further, since the additional bearing 32 is provided outside the crankcase, bending stress of the crankshaft when the belt is driven can be relieved.

[Brief description of drawings]

FIG. 1 is a structural schematic diagram of a first embodiment according to the present invention.

FIG. 2 is a structural schematic diagram of a second embodiment according to the present invention.

FIG. 3 is an explanatory view of a rotary valve drive unit of a conventional example.

[Explanation of symbols]

3 ... Cylinder head, 5 ... Crank shaft, 15 ... Rotating valve shaft, 22 ... 2nd pulley, 23 ... 1st pulley, 24 ... Timing belt, 32 ... Bearing, 61 ... Fan cover.

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[Procedure amendment]

[Submission date] May 6, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (3)

[Claims] 1. A crankshaft compression type 4-cycle gasoline engine having a rotary valve shaft (15) in a cylinder head and driving the rotary valve shaft from a crankshaft (5) through a timing belt (24). In the above, a first pulley (23) for driving a timing belt, which is provided in a portion where the crankshaft (5) is extended to the outside of the crankcase (2), and a bearing (which is provided on the crankcase side of the first pulley ( 32) and a second valve disposed at the position of the rotary valve shaft (15) in the cylinder head corresponding to the first pulley.
A rotary valve type four-cycle gasoline engine having a pulley (22) and a timing belt (24) installed on both pulleys (22) and (23). 2. A bearing (32) for supporting a crankshaft extension is provided outside the crankcase (2).
The described rotary valve type 4-cycle gasoline engine. 3. The rotary valve type four-cycle gasoline engine according to claim 1, wherein the timing belt (24) is covered with a fan cover (61).