JPH0893483A - Exhaust control device for 2-cycle engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the assembling accuracy of an exhaust control valve and the sealing performance when the valve is closed in an exhaust control device of a two-cycle engine. A control valve shaft 6 is rotatably provided near the exhaust port and above an upper edge of the exhaust port, and an exhaust control valve 8 is directly fixed to a lower surface of the valve shaft 6. A contact surface 8b having a shape matching the upper inner peripheral surface of the exhaust port is formed on the upper surface of the exhaust control valve 8, and the cylinder center side portion of the exhaust control valve 8 covers the upper portion of the exhaust port and the inside of the cylinder. An arcuate surface 8c that matches the peripheral surface shape is formed. From the closed position where the contact surface 8b contacts the inner peripheral surface of the exhaust port and the arcuate surface 8c aligns with the inner peripheral surface of the cylinder, the exhaust control valve 8 is connected to the cylinder center side with the upper valve shaft center as the rotation center. Opens to the opposite side and fits into the storage recess 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust control system for a two-cycle engine, which has an exhaust control valve for changing exhaust timing and exhaust cross-sectional area in an exhaust passage.

[0002]

2. Description of the Related Art As this type of exhaust control device, there is a device disclosed in Japanese Patent Application Laid-Open No. 3-156122 or Japanese Utility Model Publication No. 47-36047, both of which are designed to open an exhaust control valve in a high speed rotation range. By increasing the timing and increasing the exhaust cross-sectional area, thereby achieving higher output, on the other hand, in the medium and low speed rotation range, by closing the exhaust control valve, the exhaust timing is delayed and the exhaust cross-sectional area is reduced. This prevents the fresh air from passing through and improves fuel efficiency.

As for the structure of the former exhaust control device, as shown in FIG. 5, an exhaust control valve 30 having a half-moon-shaped cross section is rotated around a rotation axis, and the upper part of the exhaust port 31 is exhaust controlled. It is a structure that is closed by the rotating peripheral surface of the valve 30.

The structure of the latter exhaust control device is, as shown in FIG. 6, an exhaust manifold 3 separated from the exhaust port 31.
3 (or valve mounting case) is provided with a valve shaft 35, and an arm 37 extending to the exhaust port side in the exhaust passage 36 is rotatably supported by the valve shaft 35, and a tip portion of the arm 37 is curved. The exhaust control valve 40 is configured by providing a blade (action portion) 38 in a shape of a circle. The blade 38 covers the upper portion of the exhaust port 31 and rotates downward to open the exhaust control valve 40. It has become.

[0005]

The former exhaust control valve of FIG. 5 has the following problems. (1) Since the rotating peripheral surface (sliding surface) of the valve 30 is used as the surface that covers the exhaust port 31, there is a gap between the piston 41 and the peripheral surface of the exhaust control valve 30 even when the valve is closed. Since there is a large gap, it is not possible to prevent the fresh air blow-through efficiently.

(2) Since the exhaust type exhaust control valve 30 having a half-moon-shaped cross section is provided and the exhaust port 31 is covered by the rotational sliding surface, the valve itself has a large diameter. Is difficult, and therefore the exhaust port 31
Is limited, and it is difficult to extremely delay the exhaust timing.

(3) Since the rotary sliding surface of the exhaust control valve 30 is the surface that covers the exhaust port 31 as it is, carbon and exhaust oil attached to the rotary surface when the valve is closed, and the fitting portion when the valve is opened. The exhaust control valve 30
May interfere with the smooth rotation of the.

The latter exhaust control valve of FIG. 6 has the following problems. (1) The valve shaft 35 of the exhaust control valve 40 is arranged at a position distant from the exhaust port 31, and a blade 38 is provided via an arm 37.
Since the upper part of 1 is closed, the arm 37
There is a high possibility that the closed position of the blade 38 is displaced and a gap is generated due to thermal expansion of the engine or vibration of the engine.

(2) The blade 38 is provided on the valve shaft 35 provided on the exhaust manifold 33 via the arm 37,
Since the exhaust control valve 40 is configured, the blade 38 must be provided in consideration of the mounting error of the exhaust manifold 33, etc., and it is very difficult to manufacture the blade 38 so as to ensure the accuracy in the closed position. Have difficulty.

(3) Further, the arm 37 is moved from the closed state of FIG.
Since the exhaust control valve 40 is opened by lowering, the arm 37 crosses the inside of the exhaust passage 36 when the valve is opened, which causes disturbance of the exhaust flow, and the blade 38 is positioned at the lower end of the exhaust passage 36. Because there is a blade 3
It is easy for carbon, oil drainage, etc. to adhere to the surface of 8.

[0011]

According to a first aspect of the present invention, a control valve shaft is rotatably provided near an exhaust port and above an upper end edge of the exhaust port, and a control valve shaft is provided on a lower surface of the valve shaft. The exhaust control valve is directly fixed, and the upper surface of the exhaust control valve is formed with a contact surface having a shape matching the upper inner peripheral surface of the exhaust port. An arcuate surface that covers the part and matches the inner peripheral surface of the cylinder is formed. Above the closed position where the contact surface abuts the inner peripheral surface of the exhaust port and the circular arc surface is aligned with the inner peripheral surface of the cylinder, The exhaust control device for a two-cycle engine is characterized in that the valve shaft core is opened to the side opposite to the cylinder center side with the valve shaft center as the rotation center.

According to a second aspect of the present invention, a recess for accommodating the valve is formed in the back of the valve shaft on the side opposite to the center of the cylinder so that the exhaust control valve is substantially completely retracted from the exhaust passage when the valve is opened. The exhaust control device for a two-cycle engine according to claim 1, wherein

[0013]

In the low and medium speed range where the engine speed reaches the set speed, the exhaust control valve is kept closed, which delays the exhaust timing and reduces the exhaust cross-sectional area to blow gas through. Prevent.

When the engine speed reaches the set speed,
The exhaust control valve is rotated around the valve core on the upper side by the drive actuator or the like, and reaches the open position of the storage recess on the back. As a result, the exhaust timing is advanced so as to be suitable for high-speed rotation, the exhaust cross-sectional area is expanded, and the output during high-speed rotation is improved.

[0015]

1 to 3 show an exhaust control device of a two-cylinder two-cycle engine to which the present invention is applied. In FIG. 1 showing a longitudinal sectional view, a cylinder liner 2 is provided inside a cylinder 1. The exhaust manifold 3 is fixed to the exhaust outlet side of the cylinder 1, and the exhaust port 4 provided in the cylinder liner 2 is opened and closed by the peripheral wall of the piston 7 as the piston 7 moves up and down. The exhaust port 4 communicates with an exhaust muffler or the like via an exhaust passage 5 in the cylinder 1 and the exhaust manifold 3. A cooling water jacket 39 is formed around the exhaust port 4.

A horizontal control valve shaft 6 is rotatably supported in the vicinity of the exhaust port and above the upper edge A1 of the exhaust port, that is, in the cylinder wall portion on the cylinder head side. An exhaust control valve 8 located in the exhaust passage 5 is directly fixed to the lower surface of the valve shaft 6, and the exhaust control valve 8 is rotated by the rotation of the valve shaft 6 so that the exhaust control valve 8 is closed in a solid line and open in a virtual line. Rotate around the valve axis O1 between the position and the position.

The structure of the exhaust control valve 8 will be described in detail. A horizontal valve mounting seat 6a is formed in the lower portion of the valve shaft 6, while a flat mounting surface 8a is formed in the upper end of the exhaust control valve 8, and a bolt is inserted in the lower portion of the exhaust control valve 8. A notch 12 for forming is formed. By contacting the upper mounting surface 8a of the exhaust control valve 8 with the valve mounting seat 6a and screwing the bolt 10 inserted into the bolt insertion hole 13 from the notch 12 of the valve 8 into the female screw hole 14 of the valve shaft 6. The valve 8 is fixed directly below the valve shaft 6.

A storage recess 17 for accommodating the entire exhaust control valve 8 when the valve is opened is formed on the back of the valve shaft 6, that is, on the side opposite to the center side of the cylinder. The valve 8 is rotated upward in the back portion and is housed in the recess 17 so that it does not project into the exhaust passage 5.

The shape of the portion of the exhaust control valve 8 on the cylinder center side will be described. As shown in FIG. 1, an upper end surface of the exhaust control valve 8 on the cylinder center line side has a constant width d in the horizontal direction, and a contact surface 8b having a shape matching the upper inner peripheral surface of the exhaust port 4 is formed. When the valve is closed, it fits snugly on the inner surface of the exhaust port.

The end surface of the exhaust control valve 8 on the cylinder center side covers the upper portion of the exhaust port and conforms to the circumferential shape of the cylinder inner peripheral surface (strictly, the liner inner peripheral surface) C as shown in FIG. An arcuate surface 8c is formed. In this embodiment, the diameter of the arcuate surface 8c is set to be slightly larger than the cylinder bore.

That is, the exhaust control valve 8 is located immediately below the valve shaft 6 when the valve is closed, the contact surface 8b contacts the upper inner peripheral surface of the exhaust port 4, and the arcuate surface 8c forms the cylinder. It has a shape that constitutes a part of the inner peripheral surface C.

In FIG. 2, the valve shaft 6 is provided in all cylinders (both single cylinder and multi-cylinder can pass through one shaft), and one common to all cylinders is provided, and a rotary actuator is provided at one end. 21 are interlockingly connected. The rotary actuator 21 is connected to an engine speed detection device, and the engine speed is set to a set speed (for example, 5000R).
When it is less than PM), the valve closed state is maintained, and when the rotational speed exceeds the set rotational speed, the valve shaft 6 is rotated in the arrow direction R of FIG. 1 to open the exhaust control valve 8.

The operation will be described. Figure 1 when the engine is stopped
The exhaust control valve 8 is maintained in the closed position shown by the solid line and covers the upper half of the exhaust port 4. At this time, the upper end contact surface 8b of the exhaust control valve 8 tightly adheres to the upper inner peripheral surface of the exhaust port 4 without a gap, and seals so that gas does not escape.

Further, as shown in FIG. 3, since the arcuate surface 8c forms a part of the cylinder inner peripheral surface C, the clearance between the arcuate surface 8c and the piston 5 is extremely small. That is, for example, it is possible to prevent the volume from changing rapidly in the piston expansion stroke.

After the engine is started, for example, the set speed is 500
In the low and medium speed range up to 0 RPM,
The exhaust control valve 8 keeps the closed state, thereby delaying the exhaust timing and reducing the exhaust cross-sectional area to prevent the blow-through of gas such as scavenging air. By the way, the exhaust timing is delayed by an amount corresponding to the piston stroke S1 as compared with the case of the valve open position.

The engine speed is the set speed (eg 50
(00 RPM), the drive actuator 21 operates to rotate the exhaust control valve 8 in the direction of arrow R in FIG. 1 to reach the open position in the recess 17. As a result, the exhaust timing is advanced so as to be suitable for high-speed rotation, the exhaust cross-sectional area is expanded, and the output during high-speed rotation is improved.

FIG. 4 shows the relationship between the engine output and the rotational speed. Graph X1 shows the case where the exhaust control valve 8 is closed, and graph X2 shows the case where the exhaust control valve 8 is opened. The engine speed of 5000 RPM, which substantially corresponds to the maximum output of the graph X1 when the valve is closed, is set as the set speed for switching the exhaust control valve 8, and is suitable for each speed from low speed rotation to high speed rotation range. It can be seen that excellent output characteristics are obtained.

That is, the engine output characteristic according to the present embodiment shows a change in the graph X1 at rotational speeds of 0 to 5000 RPM, and a change shown by a broken line near 5000 RPM, and thereafter changes in the graph X2. Show.

[0029]

[Another embodiment]

(1) Instead of directly detecting the engine speed by providing an engine rotation detection device, a medium whose pressure changes in proportion to the engine speed, such as water pressure in a jet pump of a water jet planing boat, is used. Alternatively, the drive actuator can be operated by utilizing the temperature of the lubricating oil. It is also possible to directly use the water pressure in the jet pump as the power source of the drive actuator.

[0030]

As described above, according to the first aspect of the present invention, the control valve shaft 6 is rotatably provided near the exhaust port and above the upper edge of the exhaust port. An exhaust control valve 8 is directly fixed to the lower surface of the exhaust control valve 8, and an upper surface of the exhaust control valve 8 is formed with a contact surface 8b having a shape matching the upper inner peripheral surface of the exhaust port 4. The center side portion has an arc-shaped surface 8c that covers the exhaust port upper side portion and conforms to the cylinder inner peripheral surface shape, and therefore has the following advantages.

(1) Since there is almost no gap between the piston 7 and the exhaust control valve 8 when the valve is closed, blow-through of fresh air can be efficiently prevented.

(2) It is possible to extremely delay the exhaust timing only by changing the height of the exhaust control valve 8.

(3) The exhaust control valve 8 is directly fixed to the lower surface of the valve shaft 6, and the valve shaft 6 is arranged near the exhaust port and above the upper edge of the exhaust port. As compared with the structure in which the valve is provided via the arm as shown in FIG. 6, it is less likely that the valve assembly accuracy will change due to thermal deformation or engine vibration, and good assembly accuracy can be maintained. That is, the sealing performance when the valve is closed is improved.

(4) Since the valve shaft 6 is arranged at a position where carbon does not adhere, the phenomenon that the rotation of the exhaust control valve 8 by the carbon is not obstructed does not occur. Further, even in the case of three cylinders or four cylinders, one valve shaft can be penetrated, so that the structure is simple.

According to the invention described in claim 2, the following effects are also obtained. When the valve is opened, the exhaust control valve 8 is housed in the housing recess 17 and substantially the entire exhaust passage 5 is retracted. Therefore, in the high-speed rotation range where a large exhaust cross-sectional area needs to be secured, as shown in FIG. In addition, compared to a valve structure in which an arm or the like is located in the exhaust passage when the valve is open, a sufficient exhaust cross-sectional area can be secured and the exhaust flow is not disturbed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an exhaust control device for a two-cycle engine to which the invention according to claims 1 and 2 of the present application is applied.

2 is an enlarged cross-sectional view taken along the line II-II of FIG.

3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a graph showing the relationship between engine output and rotation speed.

FIG. 5 is a vertical sectional view of a conventional example.

FIG. 6 is a vertical cross-sectional view of another conventional example.

[Explanation of symbols]

 1 Cylinder 4 Exhaust Port 5 Exhaust Passage 6 Valve Shaft 8 Exhaust Control Valve 8b Abutment Surface 8c Arc-Shaped Surface 17 Recess

Claims (2)

[Claims] 1. A control valve shaft is rotatably provided in the vicinity of the exhaust port and above an upper edge of the exhaust port, and the exhaust control valve is fixed directly to the lower surface of the valve shaft. On the upper surface, a contact surface having a shape that matches the upper inner peripheral surface of the exhaust port is formed, and on the cylinder center side portion of the exhaust control valve, a circle that covers the upper portion of the exhaust port and matches the inner peripheral surface shape of the cylinder. An arcuate surface is formed, and the abutment surface abuts the exhaust port inner peripheral surface and the arcuate surface aligns with the cylinder inner peripheral surface. Is an exhaust control device for a two-cycle engine, which is opened to the opposite side. 2. A recess for accommodating the exhaust control valve is formed on the back side of the valve shaft opposite to the center side of the cylinder so that the exhaust control valve retracts substantially completely from the exhaust passage when the valve is opened. The exhaust control device for a two-cycle engine according to claim 1.