JPH0486324A - Compression ratio varying mechanism for 2-cycle engine - Google Patents

Abstract

PURPOSE:To nearly uniform a thermal load of an inside circumferential surface of a cylinder in the circumferential direction so as to prevent seizure of a piston by arranging an auxiliary exhaust port being shifted in the circumferential direction with respect to a main exhaust port, in an engine where an auxiliary exhaust passage continuous with the auxiliary exhaust tort is opened/closed by an exhaust control valve so as to vary a compression ratio. CONSTITUTION:Scavenging passages 12, 13, a main exhaust passage 14 and an auxiliary exhaust passage 15 are formed for each cylinder in a cylinder body 2, and one side ends of those passages are opened in a cylinder 3 respectively as scavenging ports 16, 17, a main exhaust port 18 and an auxiliary exhaust port 19. The main exhaust passage 14 is formed to be directed more upward as it advances downstream (outlet) and the auxiliary exhaust passage 15 is formed above the main exhaust passage 14. The auxiliary exhaust port 19 is arranged being shifted in the circumferential direction of the cylinder 3 with respect to the main exhaust port 18. Accordingly, length l1 of a narrow width portion 3a between auxiliary exhaust ports 18, 19 is shortened than conventional so as to keep a thermal load on the inside circumferential surface of the cylinder 3 nearly uniform in the circumferential direction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a variable compression ratio mechanism for a two-stroke engine that changes the compression ratio depending on the rotational speed.

(Prior Art) For example, some two-stroke diesel engines are equipped with a variable compression ratio mechanism, and the variable compression ratio mechanism increases the compression ratio at startup and in low-load operating ranges. The aim is to improve startability and suppress the rise in cylinder internal pressure in high-load operating ranges.

By the way, the compression ratio variable mechanism includes a sub-exhaust passage (bypass passage) formed above the main exhaust passage formed in the cylinder body, which communicates with the main exhaust passage, and which opens and closes the sub-exhaust passage. It is known that an exhaust control valve is provided (see Japanese Patent Application Laid-Open No. 63-65121).According to this, the exhaust control valve is closed during startup and in a low-load operating range to reduce the compression ratio. Or enhanced.

(Problem to be solved by the invention) However, in the conventional variable compression ratio mechanism, the openings to the inner peripheral surface of the cylinder of the main exhaust passage and the sub-exhaust passage, respectively,
That is, the main exhaust port 118 and the sub-exhaust port 119 shown in FIG. 7 are opened at the same position in the circumferential direction of the cylinder 103.
] As a result, a narrow portion 103a is formed on the inner circumferential surface of the cylinder 103 that defines the main exhaust port 118 and the sub-exhaust port 119, and the heat load is concentrated on this portion 103a, causing piston seizure. There was a problem that it was more likely to occur.

The present invention has been made in view of the above problems, and its purpose is to prevent seizure of the piston by avoiding local concentration of heat load on the inner circumferential surface of the cylinder. The object of the present invention is to provide a variable compression ratio mechanism.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a main exhaust port that opens on the inner peripheral surface of the cylinder, and a sub-exhaust exhaust that opens on the second dead center side from the main exhaust port on the inner peripheral surface of the cylinder. In a compression ratio variable mechanism for a two-stroke engine that changes a compression ratio by opening and closing a sub-exhaust passage connected to the sub-exhaust port of a two-stroke engine with an exhaust control valve, the sub-exhaust port is connected to the main exhaust port. The feature is that the cylinders are arranged offset in the circumferential direction of the cylinder.

(Function) According to the present invention, since the length of the portion where the main exhaust port and the sub-exhaust port overlap in the circumferential direction of the cylinder is shortened, the width between the main exhaust port and the sub-exhaust port on the inner peripheral surface of the crank is shortened. The length of the narrow part, that is, the part where the heat load is concentrated, is shortened, and the heat load on the inner circumferential surface of the cylinder can be distributed approximately evenly in the circumferential direction, making it possible to effectively prevent seizure of the piston. .

(Example) An example of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a longitudinal cross-sectional view of a two-stroke day cell engine equipped with a variable compression ratio mechanism according to the present invention, FIG. 2 is an enlarged cross-sectional view of the vicinity of the exhaust passage of the engine when the exhaust control valve is open, and FIG. is a sectional view taken along the line ■-■ in Fig. 2, Fig. 4 is a view taken in the direction of arrow -■ in Fig. 2, Fig. 5 is a perspective view of the exhaust control valve, and Fig. 6 is a sectional view taken along the line ■-■ in Fig. 2.
The figure shows the performance characteristics of the engine.

The engine l shown in Fig. 1 is a three-cylinder two-stroke diesel engine, and as shown in Fig. 3, the cylinder body 2 has three cylinders 3 arranged in parallel. A cylinder head 4 is attached to the upper part of the cylinder. A piston 5 is fitted into each of the cylinders 3 so as to be movable.
is connected to the crankshaft 7 via a connecting rod 6.

Incidentally, the crankshaft 7 is arranged in the direction perpendicular to the plane of the paper in Fig. 1 (the cylinder 3
. . ), and is rotatably housed in a crank chamber 9 within a crankcase 8.

Further, the crank head 4 has a swirl chamber type sub-combustion chamber S formed for each cylinder, and the sub-combustion chamber S has a fuel injection valve 10 and a glow plug 1 screwed onto the cylinder head 4.
Each tip of 1 is facing.

Further, the cylinder body 2 is provided with a scavenging passage 1 for each cylinder.
2, 13, a main exhaust passage 14 and a sub-exhaust passage 15 are formed respectively, and these have scavenging ports 16, 17, a main exhaust port 18, and a sub-exhaust port 1 at one end or within the crank 3.
9 and 1 are respectively open, and the scavenging passages 12 and 13 are open.
The other end opens into the crank chamber 9.

By the way, as shown in detail in FIG. 2, the main exhaust passage 14 is formed to move upward as it goes downstream (outlet), and above the main exhaust passage 14 is the sub-exhaust passage 15. It is formed. As described above, each end of the main and sub exhaust passages 14.15 opens into the cylinder 3 through the main and sub exhaust ports 18.19, and the other end of the main exhaust passage 14 opens into the cylinder 3 through the main and sub exhaust ports 18.19. is connected to an exhaust pipe (not shown), and the other end of the sub-exhaust passage 15 opens into the main exhaust passage 14 as shown.

In this embodiment, as shown in FIG. The length of the narrow portion 3a between the main exhaust port 18 and the sub-exhaust port 19 on the surface is shorter than the length of the conventional one shown in FIG. There is.

Further, the sub-exhaust passage 15 connected to the sub-exhaust port 19 is formed in a straight line and perpendicular to the center edge of the crank 3 when viewed from the side as shown in FIG. 2, and in a straight line as shown in FIG. all have the same width in a straight line, and have an angle of ゛C with respect to the crankshaft center m.
It is formed at right angles, and a portion thereof overlaps the main exhaust passage 14. On the other hand, the main exhaust passage 14 is formed obliquely with respect to the crankshaft center m in order to avoid interference between the scavenging passages 12 and 13 of each cylinder and to keep the engine length small.

Furthermore, a circular hole 20 is provided at an intermediate position of the sub-exhaust passage 15 of the cylinder body 2 in the direction of the crankshaft (the cylinder 3...
In this circular hole 20, as shown in FIG. It is fitted,
The outer circumference of both ends of each exhaust control valve 21 and the inner circumference of the circular hole 20 are O
It is hermetically sealed by a ring 22°22.

As shown in FIG. 5, the exhaust control valve 21 is provided with a notched communication groove 21a, and the exhaust control valve 21 opens and closes the sub-exhaust passage 15 by its rotation.

The sub exhaust passage 15 is shifted in the same direction as the main exhaust passage 14 so that it is perpendicular to the crankshaft 7, so it is perpendicular to the exhaust control valve 21 which is parallel to the crankshaft 7, and the exhaust At an intermediate opening degree of the control valve 21, the cross-sectional shape of the sub-exhaust passage 15 becomes uniform in the width direction.

Thus, a total of three exhaust control valves 21 are provided for each cylinder.
As shown in Fig. 3, the cranks 3... are integrally and linearly connected by joints 23, 23 in the parallel direction of the cranks 3..., and the exhaust control valves 21... - One end is in contact with a plug 24 that closes one end opening of the circular hole 20, and the other end is in contact with these exhaust control valves 21...
It is connected by a coupling 26 to an output shaft 25a of a step motor 25, which rotates the motor 25 with a single weight. As shown in FIG. 3, data on the throttle opening and rotational speed of the engine 1 is sent to the controller 27, and the controller 27 adjusts the exhaust control valves 2 and 3 based on these data.
・A control signal for controlling the opening and closing of the step motor 25 is transmitted to the step motor 25.
to control the drive of the step motor 25.

Incidentally, the sub-exhaust passage 15, step motor 25, controller 27, etc. described in 1- below constitute the variable compression ratio mechanism according to the present invention.

By the way, as shown in FIG. 1, an intake passage 28 is formed in the side part of the cylinder body 2, and one end of the intake passage 28 opens into the crank chamber 9.
An intake pipe 29 is connected to the other end of 8. A slot valve 30 is provided in the intake passage 28 to allow air to flow only in the direction of the crank chamber 9.

Next, the operation of the two-stroke diesel engine 1 will be explained.

When the exhaust control valve 21 is closed as shown in FIG. 1, each sub-exhaust passage 15 is closed by the exhaust control valve 21. In this state, the piston 5 is moving inside the cylinder 3.
- When the engine rises, negative pressure is generated in the crank chamber 9, and intake air (air) is drawn into the crank chamber 9 from the intake pipe 29 through the riet valve 30. Then, this intake air is primarily compressed by the piston 5 that descends during the explosion/scavenging stroke, or the piston 5 opens the main exhaust port 18,
Next, when the scavenging port 16.17 is opened, this primary compressed intake air flows into the crank 3 from the scavenging port 16.17, and the exhaust gas produced by the combustion of fuel in the cylinder 3 is transferred to the main exhaust port. Push out to 18. Next, screw 1
When the scavenging ports 16, 17 and the main exhaust port 18 are closed, the intake air in the cylinder 3 rises by -L.
The compression stroke A (see FIG. 1) of the piston 5 at this time is large, and the compression ratio of the engine I at this time is increased.

When the piston 5 reaches near the top dead center, the intake air in the cylinder 3 becomes high temperature and high pressure, and an appropriate amount of fuel is injected from the fuel injection valve lO into the sub-combustion chamber S, and this fuel has a high temperature and a high pressure.
Ignition and combustion are caused by high-pressure intake air. and,
The piston 5 begins to descend as its head receives the pressure of the high-temperature, high-pressure exhaust gas generated by combustion, and when the piston 5 opens the main exhaust port 18 and the scavenging ports 16 and 17, the crank chamber is opened as described above. At step 9, the primary compressed intake air flows into the cylinder 3 from the scavenging ports 16 and 17, and from then on, the same action as described above is repeated, and the exhaust control valves 21...
・When operated at full load with fully closed, kerf a is shown in Figure 6.
The performance shown in can be obtained.

On the other hand, the step motor 25 rotates the exhaust control valves 21 .
When each auxiliary exhaust passage 15 is open, the compression stroke B of the piston 5 during the compression stroke is smaller than the stroke A (B<A) as shown in FIG. 1, so the compression ratio of the engine I is low. It can be suppressed.

Also, during the explosion and scavenging stroke in which the piston 5 descends,
First, the sub-exhaust port 19 is opened, and the exhaust gas in the cylinder 3 flows through the sub-exhaust passage 15 to the main exhaust passage 14.
The air is exhausted from the main exhaust passage 14 to the atmosphere through an exhaust pipe and a muffler (not shown). When the main exhaust port 18 is also opened, the exhaust gas flows through the main and auxiliary exhaust passages 14, 15 and is discharged into the atmosphere.

When the exhaust control valves 21 are fully opened and the engine is operated under full load, the performance shown by kerf b in FIG. 6 can be obtained.

For example, when operating at full load, the controller 27 controls the step motor 25 in a low speed range where the engine rotational speed N input thereto is less than or equal to N1 (N≦N) as shown in FIG. On the other hand, the exhaust control valve 21
Outputs a control signal to fully open the engine, and the engine rotation speed is N or more than N2 as shown in the figure (N, <N≦N2).
In the medium speed range, the step motor 25 is controlled to have an intermediate opening between fully closed and fully open depending on the opening of the exhaust control valve 21 or the engine speed at that time. Output a signal. Further, in a high speed range where the engine speed N exceeds N2 (N>N2), the controller 27 outputs a control signal to the step dryer 25 to fully open the exhaust control valves 21 .

As a result of the above, the solid line curve C is shown in Figure 6 during full load operation.
By controlling the exhaust control valves 21 to intermediate opening degrees, especially in the medium speed range, the performance shown in Figure 6 is improved compared to the case where this is not done. The torque direction I- can be achieved.

The exhaust control valves 21 are fully open in the area SA in FIG. 6, fully closed in the area SIl, and have an intermediate opening degree in the area Sc.

Hereinafter, in this embodiment, since the sub exhaust port 19 is disposed offset in the circumferential direction of the cylinder 3 with respect to the main exhaust port 18 as described above, the main exhaust port 18 and the main exhaust port 18 on the inner circumferential surface of the cylinder 3 Narrow portion 3 between sub-exhaust port 19
The length of a is shorter than the length of the conventional one shown in FIG. This makes it possible to avoid local concentration of heat load on the inner circumferential surface of the cylinder 3 and effectively prevent the piston 5 from continuing to move.

(Effects of the Invention) As is clear from the above description, according to the present invention, there is a main exhaust port that opens on the inner peripheral surface of the cylinder, and a sub-exhaust exhaust that opens on the top dead center side of the main exhaust port on the inner peripheral surface of the cylinder. In a compression ratio variable mechanism for a two-stroke engine that changes the compression ratio by opening and closing a sub-exhaust passage connected to the sub-exhaust port of the two-stroke engine with an exhaust control valve,
Since the sub-exhaust port is arranged offset from the main exhaust port in the circumferential direction of the cylinder, the narrow part between the main exhaust port and the sub-exhaust port on the inner peripheral surface of the cylinder, that is, the heat load is concentrated. The length of the piston portion is shortened, and the heat load on the inner circumferential surface of the cylinder can be kept approximately uniform in the circumferential direction, thereby preventing seizure of the piston.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of a two-stroke diesel engine equipped with a variable compression ratio mechanism according to the present invention, and Fig. 2 is an exhaust control diagram.
Fig. 3 is an enlarged cross-sectional view of the vicinity of the exhaust passage of the same engine in the open state, Fig. 3 is a cross-sectional view taken along line mm in Fig. 2, and Fig. 4 is a cross-sectional view taken along line mm in Fig.
Figure 5 is a perspective view of the exhaust control valve, Figure 6 is a diagram of engine performance characteristics, and Figure 7 is a diagram similar to Figure 4 showing the arrangement of conventional sub-exhaust ports. It is. 1...2-cycle engine, 3...Cylinder, 14
...Main exhaust passage, 15...Sub-exhaust passage, 18...
Main exhaust port, 19... Sub-exhaust port, 21... Exhaust control valve. Patent applicant: Yamaha Motor Co., Ltd. Agent
Patent Attorney Ryo Yamashita Figure 7 Figure 6 Engine speed N

Claims (1)

[Claims] An exhaust control valve connects a sub-exhaust passage connected to the sub-exhaust port of a two-cycle engine, which has a main exhaust port that opens on the inner circumferential surface of the cylinder, and an exhaust port that opens on the top dead center side of the main exhaust port on the inner circumferential surface of the cylinder. 2. A variable compression ratio mechanism for a two-stroke engine that changes the compression ratio by opening and closing the engine, characterized in that the auxiliary exhaust port is disposed offset in the circumferential direction of the cylinder with respect to the main exhaust port.
Variable compression ratio mechanism for cycle engines.