JPH0237102A - Four cycle engine - Google Patents

Abstract

PURPOSE:To reduce the blowby of air-fuel mixture and improve ignitability by providing three suction valves and making the degree between the intermediate suction valve and rocker arm be less than that between the suction valves on both sides and rocker arm. CONSTITUTION:Three suction valves 5 and two exhaust valves 6 are provided to one cylinder. The degree between the intermediate suction valve and a rocker arm 12 is made to be less than that between the suction valves on both sides and the rocker arm 12 and be approximately right angles. An ignition plug is provided to near the center of a combustion chamber 3. At the time when the suction valves are opened, the intermediate suction valve is opened at a rate larger than the suction valves on both sides, and a lot of in-take gas flows into the combustion chamber through the intermediate suction port. This makes it possible to improve ignitability as well as to reduce the blowby of air-fuel mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a four-stroke engine having three intake valves and a plurality of exhaust valves per cylinder.

[Prior Art] In order to improve the output performance of a four-stroke engine in its high-speed operating range, the number of intake valves and exhaust valves per cylinder has been increased.

And, while the spark plug faces approximately the center of the combustion chamber,
A four-stroke engine that has three intake valves and a plurality of exhaust valves per cylinder and opens and closes these valves via a rocker arm is disclosed in British Patent No. 687528, for example.
It is publicly known as shown in the specification of No.

[Problems to be Solved by the Invention] Incidentally, in the above-mentioned known engine, since the angles formed by the rocker arm and the three intake valves are the same,
The two intake valves operate approximately equally to supply an average mixture to the combustion chamber. In engines with three intake valves, the air-fuel mixture flows at high speeds under high loads.
At high engine speeds, there is a tendency for the air-fuel mixture that flows into the intake passages on both sides to blow directly into the exhaust passage. There was room.

This invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to make the middle intake valve open more quickly than the intake valves on both sides when the intake valves are opened. The engine is designed to be opened at a large ratio to supply a large amount of air-fuel mixture to the area around the spark plug from the middle intake boat, reducing blow-through of the air-fuel mixture at high loads and high speeds and improving ignition performance. This is what we are trying to provide.

[Means for Solving the Problems] In order to achieve the above object, the four-stroke engine of the present invention has the following features: The ignition plug is placed approximately in the middle of the combustion chamber, and one end of the rocker arm is brought into contact with the upper end of the intake valve. The rocker arm is extended downward to the outside of the engine, and the cam of the camshaft is brought into contact with the upper surface of the rocker arm. It is smaller than an angle and close to a right angle.

[Action] The angle between the middle intake valve and the rocker arm is smaller than the angle between the intake valves and the rocker arm on both sides, and is close to a right angle, so when the intake valve is opened, the middle intake valve and rocker arm is opened at a larger ratio than the intake valves on both sides, and a large amount of intake air flows into the combustion chamber from the middle intake boat, supplying a large amount of air-fuel mixture around the spark plug. The blow-through of the air-fuel mixture is reduced and the ignitability is improved.

[Example code] Embodiments of the invention will be described below with reference to the drawings.

The drawing shows one cylinder of a 4-cycle engine, where a is the cylinder, b is the cylinder head, 1 is the intake passage, and 2 is the cylinder head.
is the exhaust passage.

A combustion chamber 3 is formed on the lower surface of the cylinder head b, and an intake passage 1 and an exhaust passage 2 are open therein.

Reference numeral 4 denotes a screw hole for attaching a spark plug, which opens at the center of the upper surface of the combustion chamber 3.

5 is an intake valve that opens and closes the intake passage 1, and 6 is an exhaust valve that opens and closes the exhaust passage 2.

These intake valves 5 and exhaust valves 6 have umbrella portions at their lower ends facing the combustion chamber 3 and corresponding to the open ends of the intake passage 1 and exhaust passage 2, respectively, and intermediate portions thereof are connected to the cylinder head b via guides 5a and 6a. It is slidably supported on the wall.

7.8 is a spring that urges the valves 5 and 6 in the valve-closing direction.

A camshaft 9 drives the valve 5, and is rotatably supported between the upper end of the cylinder head b and the cam cap 10.

A cover 11 covers the camshaft 9 and the cam cap 10, and is connected to the upper end of the cylinder head b.

In order to improve its output performance, this four-stroke engine is provided with three intake valves 5 and two exhaust valves 6 per cylinder.

In addition, the arrangement structure of the three intake valves 5 is such that the middle intake valve is closer to the axis of cylinder a than the intake valves on both sides.
The combustion chamber 3 is faced to the combustion chamber 3 with a small inclination relative to the combustion chamber 1.

That is, if the inclination angle of the middle intake valve 5 is α1, and the inclination angle of the intake valves 5 on both sides is α2, α1 becomes α2.

Further, the three intake valves 5 are arranged such that their upper ends are located on substantially the same straight line 13 parallel to the axis 12 of the camshaft 9.

Therefore, as shown in FIG. 2, the intake valves 5 are arranged such that the middle valve is deviated outward from the valves on both sides with respect to the center line i4 that separates the intake side and the exhaust side in the combustion chamber 3. The valves 5 do not interfere with each other.

Further, each of the intake valves 5 is connected to a camshaft 9, and a rocker arm 12 is used as the connection means.

Each end of this rocker arm 12 is in contact with the upper end of each intake valve 5, and the other end is pivotally supported to the cylinder head b via a bearing 13, and a camshaft 9 is mounted on the upper surface of the intermediate portion thereof. The cam 9a is in contact with it.

As shown in FIGS. 1 and 3, the angle between the middle intake valve and the rocker arm is smaller than the angle between the intake valves on both sides and the rocker arm, and is close to a right angle.

In this way, since the angle between the middle intake valve and the rocker arm is smaller than the angle between the intake valves on both sides and the rocker arm and close to a right angle, when the intake valve 5 is opened, the middle intake valve is opened at a larger ratio than the intake valves on both sides, and a large amount of intake air flows into the combustion chamber 3 from the intermediate intake boat, supplying a large amount of air-fuel mixture around the spark plug, resulting in high load and high rotation speed. This reduces blow-by of the air-fuel mixture and improves ignitability.

On the other hand, two exhaust valves 6 are provided, and are arranged on a straight line 15 parallel to the center line 14 in the combustion chamber 3.

Further, the exhaust valves 6 are set to have the same inclination angle α3 with respect to the axis 11 of the cylinder a, and their upper ends are connected to a camshaft (not shown) via a rocker arm (not shown).

Since there are two exhaust valves 6, even if they are arranged in series within the combustion chamber 3, they will not interfere with each other.

In the above embodiment, the rocker arm 12 has independent arms and two exhaust valves 6 are provided. If the arrangement structure is similar to that of the intake valve 5, it is possible to provide three intake valves.

[Effects of the Invention] In this invention, when three intake valves are provided, the middle intake valve faces the combustion chamber with a smaller inclination to the axis of the cylinder than the intake valves on both sides.
The intermediate intake valve is offset outward from the intake valves on both sides on the intake side of the combustion chamber, so that three intake valves can be provided within the combustion chamber without interfering with each other. In addition, the angle between the middle intake valve and the rocker arm is smaller than the angle between the intake valves on both sides and the rocker arm, and is close to a right angle, so when the intake valve is opened, the middle intake valve on both sides It opens at a larger rate than the intake valve, and as a result, more intake air flows into the combustion chamber from the intermediate intake boat, supplying more air-fuel mixture around the spark plug, which is especially true at high loads and high rotation speeds. This reduces blow-by of the air-fuel mixture and improves ignitability.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of an engine according to the present invention;
Figure 2 is a sectional view taken along the ■-n line in Figure 1, and Figure 3 is a cross-sectional view taken along the ■-n line in Figure 2.
4 shows a sectional view taken along the line IV--IV in FIG. 3. a...Cylinder, b...Cylinder head, l...
Intake passage, 2...Exhaust passage, 3...Combustion chamber, 4...
・Spark plug, 5...Intake valve, 6...Exhaust valve, 9...Camshaft, 9a...Cam, 12...Rocker arm, lbi...Cylinder axis, α1... Inclination angle of the middle intake valve, α2...Inclination angle of the intake valves on both sides. Patent applicant Yamaha Motor Co., Ltd. agent Patent attorney Inner staff Mikio Diagram

Claims (1)

[Claims] A four-cycle engine in which each cylinder has three intake valves and a plurality of exhaust valves, and the middle intake valve faces the combustion chamber with a smaller inclination to the axis of the cylinder than the intake valves on both sides. In the engine,
A spark plug is positioned approximately in the center of the combustion chamber, one end of a rocker arm is brought into contact with the upper end of the intake valve, and the rocker arm is extended downward to the outside of the engine, and a cam of a camshaft is brought into contact with the upper surface of the rocker arm. The four-stroke engine is characterized in that the angle between the middle intake valve and the rocker arm is smaller than the angle between the intake valves on both sides and the rocker arm, and is close to a right angle.