JPH02125915A - Intake device for two cycle engine of crank pre-compression type - Google Patents

Abstract

PURPOSE:To improve a response property and the maximum output in the whole rotational range by opening or shutting a passage between a main intake port communicating to the inside of a crank chamber and an auxiliary intake port for connecting a main intake port to the inside of the crank chamber, by means of a rotary valve in response to the rotational speed of an engine. CONSTITUTION:When an engine is running in a load speed, a rotary valve 10 is opened so as to shut a passage between a main intake port 8 and an auxiliary intake port 9 by the wall part 11 of a rotary valve 10. And air-fuel mixture is led into the lower part of a cylinder 1 and a crank chamber, through only the main intake port 8. Thereby, combustion efficiency and a response property are improved in response to the state of comparatively low demand intake rate. On the other hand, when the engine is running in a high speed, the driving part such as a centrifugal governor or the like is operated, so that the rotary valve 10 is rotated by nearly 90 deg. through an arm 14 and a supporting shaft 13. Namely, the main intake port 8 and the auxiliary intake port 9 are connected to each other through the communication hole 12 of the rotary valve 10. Thereby, a large quantity of air-fuel mixture is fed into the combustion chamber side so as to increase the maximum output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an intake system for a crank precompression two-stroke engine.

[Prior Art] A cylinder of a typical two-stroke engine has one intake port formed therein. However, at high engine speeds, the required amount of intake air increases, making it difficult to increase the maximum output, so some engines have additional sub-intake ports.

[Problems to be Solved by the Invention] By the way, as in the above example, if the intake ports are made into primary and secondary intake ports, combustion efficiency will decrease and responsiveness will be impaired in the low rotational speed range of the engine where the required intake air amount is relatively small. The problem is that it becomes easier.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an intake system for a crank precompression type two-stroke engine that provides good response over the entire rotational range of the engine and facilitates obtaining maximum output.

[Means for Solving the Problems] In order to solve the above problems, an intake system for a crank precompression type two-stroke engine according to the present invention includes a main intake port that communicates with the crank chamber of the engine, and a main intake port that communicates with the crank chamber of the engine. It is equipped with a sub-intake port that communicates with the inside of the crank chamber, and is configured to shut off the main intake port and sub-intake port when the engine speed is below a predetermined speed, and to open communication when the speed exceeds a predetermined speed. It is characterized by being equipped with an on-off valve.

[Operation of the Invention] When the co-engine is running at a low speed below a predetermined rotational speed, the on-off valve closes the auxiliary intake port, so an amount of air-fuel mixture corresponding to the relatively small required intake air amount is supplied only from the main intake port, and the intake flow rate is reduced. This increases mixture atomization and improves engine combustion efficiency and responsiveness.

Also, when the engine is running at high speeds exceeding a certain number of revolutions,
Since the on-off valve opens the auxiliary intake port, the air-fuel mixture is supplied from the main and auxiliary intake ports, making it possible to supply an amount of intake air that can correspond to a relatively large amount of required supply, thereby improving maximum output.

[Example] An embodiment of the present invention is shown in FIGS. 1 to 4.

FIG. 1 is a diagram showing a crank precompression type two-stroke engine for a two-wheeled motor vehicle, with moving parts such as a piston, a connecting rod, and a crankshaft omitted. A water jacket 2 is formed around the cylinder 1, and a cylinder head 3 is attached to the upper part and a crankcase 4 is attached to the lower part. Inside the crankcase 4 is the crank chamber 5
It communicates with the combustion chamber 6 inside the cylinder 1. An intake passage 7 is provided on the side of the cylinder 1. The intake passage 7 is connected to a main intake port 8 that opens on the side surface of the cylinder 1, and as shown in FIG. A sub-intake port 9 is formed which communicates with the main intake port 8 and the sub-intake port 9, and a rotary valve 10 is provided at a connecting portion between the main intake port 8 and the sub-intake port 9 to enable communication or isolation between the two.

The rotary valve 10 is a specific example of an on-off valve in the present invention,
As shown in FIGS. 3 and 4, a communication hole 12 connecting the side surface and the bottom is formed by cutting out the side surface of a cylindrical member, leaving a wall section 11 that is approximately crescent-shaped in cross section. It is. The communication hole 12 forms a part of the sub-intake port 9. A support shaft 13 is formed to protrude from the center of the top of the rotary valve 10 and is rotatably supported by the cylinder 1 . The upper end of the support shaft 13 passes through the wall of the cylinder l and exits to the outside, where it is connected to one end of the arm 14. A driving member such as a centrifugal governor is connected to the other end of the arm 14. As is clear from FIG. 2, the lower end of the sub-intake port 9 communicates with the lower part of the scavenging port 15. The upper part of the scavenging port 15 and the exhaust port 16 are respectively formed on the inner surface of the cylinder 1, and the scavenging port 15 communicates with the crank chamber 5 through a passage formed vertically in the wall surface of the cylinder 1.

Next, the operation of this embodiment will be explained. Figure 4 shows the rotary valve 10.
The open or closed state of the rotary valve 10 is shown divided into upper and lower parts, with the upper half showing the open state of the rotary valve 10 and the lower half showing the closed state. When the engine is rotating at a low speed, the rotary valve 10 is in a closed state, as shown in the lower half of FIG. Therefore, the air-fuel mixture is introduced into the lower part of the cylinder 1 and the crank chamber 5 through only the main intake port 8. As a result, it is possible to cope with a relatively small required intake air amount state, and it is possible to improve combustion efficiency and responsiveness.

When the engine rotates at high speed and exceeds the specified rotation speed,
A drive unit such as a centrifugal governor is activated to rotate the rotary valve 10 by approximately 90 degrees via the arm 14.

As a result, the communication hole 12 allows the main intake port 8 and the sub-intake port 9 to communicate with each other, so that part of the air-fuel mixture is transferred to the sub-intake port 9.
It is introduced into the crank chamber 5 through. As a result, a sufficient amount of air-fuel mixture can be supplied to the combustion chamber to satisfy the relatively large amount of intake air required at high engine speeds, increasing the intake air flow velocity, promoting mixture atomization, and improving charging efficiency. As a result, the maximum output is improved. Therefore, it is possible to secure an appropriate amount of intake air over the entire engine speed range from low speed to high speed, resulting in good responsiveness and an increase in maximum output.

Note that the present invention is not limited to the above embodiments, and various applications and modifications are possible. For example, the on-off valve provided between the main intake port 8 and the auxiliary intake port 9 can be a slide valve that slides in the vertical direction of the cylinder l. Also,
The connecting portion between the auxiliary intake port 9 and the main intake port 8 may be opened and closed by rotating a plate-shaped valve.

Furthermore, the opening/closing control of the on-off valve can also be performed via electronic means, and in this case, various quantities such as throttle opening and intake negative pressure can be employed as sensor quantities for control.

[Effects of the Invention] The intake device according to the present invention is provided with a sub-intake port in addition to the main intake port, and an on-off valve for communicating or shutting off the two, so that the required intake air amount can be maintained throughout the rotational speed range. It is possible to secure an appropriate amount of intake air according to changes in air. Therefore, the combustion efficiency increases over the entire engine speed range, resulting in better response performance and an increase in maximum output.

[Brief explanation of drawings]

Figures 1 to 4 show examples, Figure 1 is a longitudinal sectional view of the engine, Figure 2 is a developed view of the inner surface of the cylinder, Figure 3 is an enlarged sectional view of the main parts, and Figure 4 shows the operation. It is an enlarged cross-sectional view of a cylinder for explanation. (Explanation of symbols) 1...Cylinder, 4...Crankcase, 5...
Crank chamber, 7...Intake passage, 8...Main intake port, 9...Sub-intake port, 10...Rotary valve (on/off valve)
. Patent applicant: Agent for Honda Motor Co., Ltd.
Patent Attorney Kiyoshi Komatsu

Claims (1)

[Claims] It is equipped with a main intake port that communicates with the inside of the engine crank chamber, and a sub-intake port that communicates the main intake port with the inside of the crank chamber. An intake system for a crank precompression type two-stroke engine, characterized in that an on-off valve is configured to shut off the gap between the two and open the air when the rotation speed exceeds a predetermined number of rotations.