JPH0658064B2 - 2-cycle engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-cycle engine in which an opening timing of an exhaust port is adjusted by a valve body rotatably provided on an upper exhaust passage side of the exhaust port.

[Prior Art] As a two-cycle engine of a motorcycle or the like, an exhaust port and a scavenging port are generally opened in an inner peripheral wall of a cylinder, and the timing of scavenging and exhausting is determined by their opening positions. As long as the burnt gas is sufficiently discharged, the lower the exhaust port, the longer the expansion stroke, which is advantageous for improving the thermal efficiency.

Therefore, as disclosed in Japanese Utility Model Laid-Open No. 54-9221, a valve element that forms the upper edge of the exhaust port is provided at the exhaust port of the cylinder, and the upper edge is raised when the engine rotates at high speed. A two-cycle engine has been developed in which the opening timing of the exhaust port is adjusted by lowering the upper edge of the exhaust port during low speed rotation to improve the output over the entire rotational speed of the engine.

[Problems to be solved by the invention]

However, in this type of conventional two-cycle engine, there is a problem that the noise at the time of medium / low speed rotation cannot be reduced as much as at the time of high speed rotation. this is,
It is considered that the exhaust silencer provided in the engine is set so as to most effectively reduce the exhaust noise at high speed rotation.

On the other hand, an engine of a motorcycle or the like is often used in a medium speed or low speed rotation range, and it is widely demanded to reduce noise at a medium or low speed rotation.

Therefore, in order to respond to this, it is conceivable that the shape of the exhaust port of the cylinder is opened at the time of medium / low speed rotation, but if this is done, the output may be reduced at high speed rotation.

[Means for solving problems]

The present invention has been made in view of the above circumstances, and provides a two-cycle engine capable of reducing exhaust noise during medium- and low-speed rotation without reducing output over the entire rotation speed. In the two-stroke engine according to the present invention, a concave portion for projecting the upper edge of the exhaust port toward the upper side of the cylinder is provided on the lower surface of the valve body for adjusting the exhaust timing by moving the upper edge of the exhaust port provided in the cylinder up and down. When provided, the exhaust port of the cylinder is formed in a substantially rectangular shape.

[Action]

In the present invention, the opening shape of the exhaust port at the time of medium / low speed rotation of the engine is made to have a small upper part so that the burned gas is gradually discharged to the exhaust passage, and at the time of high speed rotation, the exhaust port is made substantially rectangular. To increase the opening area.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a side view of the valve body, which is the main part of the present invention, as viewed from the direction indicated by arrow A in FIG. 3, FIG. 2 is a perspective view of the same, and FIG. 3 is a longitudinal sectional view showing a two-cycle engine. In these figures, the reference numeral 1 indicates a two-cycle engine. The engine 1 forms a combustion chamber 4 by covering a cylinder block 3 holding a piston 2 slidably and an upper portion of the cylinder block 3. And a cylinder head 5. Reference numeral 6 denotes an ignition plug which is attached to the cylinder head 5 and whose front end electrode faces the inside of the combustion chamber 4.

On one side surface of the cylinder 6a of the cylinder block 3,
The exhaust port 7 and the scavenging port 8 are opened. Exhaust port 7
Is formed in a substantially rectangular shape having arcuate corners that are long in the lateral direction when viewed from the direction of arrow A in order to increase the opening area, and the exhaust passage 9 extends obliquely downward from the exhaust port 7. It is open to the outside. On the other hand, the scavenging port 8 communicates with the crank chamber through the scavenging passage. Reference numeral 10 denotes an intake port opened on the cylinder peripheral wall on the opposite side of the exhaust port 7.

On the exhaust passage 9 side above the exhaust port 7 provided on the inner peripheral wall of the cylinder, the exhaust port 7 is advanced by advancing into the exhaust passage 9.
A valve body 11 that forms the upper edge of is provided. The valve body 11 is formed in a substantially drum shape and is rotatably supported by a bearing 12, and a part of the outer periphery thereof is cut off to form a part of the exhaust passage 9. An edge portion of the cut-off lower surface 11a of the valve body 11 advances into the exhaust passage 9 in accordance with an operating state of the engine such as a rotation speed and an output during operation of the engine to form an upper edge of the exhaust port 17, The opening timing of the exhaust port 7 is adjusted by moving the upper edge up and down. Reference numeral 15 is a drive wire for rotationally driving the valve body 11, which is interposed between, for example, a servo motor (not shown) mounted on the lower portion of the fuel tank and a pulley 16 provided at one end of the valve body 11 to drive the power of the servo motor. It is transmitted to the valve body 11. The valve body 11 increases the opening degree of the exhaust port 7 when the engine speed and the output are large,
As it lowers, it is driven within the range indicated by h in FIG. 3 so as to descend so as to advance into the exhaust passage 9 and decrease the opening of the exhaust port 7. Reference numeral 17 denotes an accommodation recess for accommodating the valve element 11, which is located on the upper back surface of the exhaust port 7 and faces the exhaust passage 9.

20 is provided on the lower surface 11a of the valve body 11, and the exhaust port 7
It is a groove-shaped recess that projects the upper edge toward the upper side of the cylinder 6a. The recess 20 corresponds to the center of the exhaust passage 9 and extends in the direction in which the burned gas flows. Also,
The depth is set so that the bottom of the valve body 11 faces the exhaust port 7 when the valve body 11 rotates clockwise in FIG. 3 during low-speed rotation.

In the two-stroke engine configured in this way,
When operating at low speed and medium speed rotation, the valve element 11 is connected to the exhaust passage 9 as shown by the one-dot chain line S and two-dot chain line M in the figure.
Advance in. Then, in the expansion stroke, the piston 2
Opens the exhaust port 7 from above and discharges the burned gas in the cylinder 6a to the exhaust passage 9. At this time, the opening shape of the exhaust port 7 at the beginning of opening is determined mainly by the piston 2 and the valve body 11, and the upper portion has a small shape.

Therefore, the exhaust port 7 can be gradually opened and the burned gas can be gradually discharged to the exhaust passage 9, so that the generation of noise due to the rapid flow of the burned gas can be suppressed.
Therefore, it is possible to suppress the pressure shock component from being transmitted to the exhaust pipe connected to the cylinder block 3, and it is possible to reduce wall vibration noise and discharge noise of the exhaust pipe. Further, by making the upper portion smaller, it is difficult for fresh air to blow through, so the output is improved as compared with the case where the opening shape is rectangular.

On the other hand, when operating at high speed rotation, the valve element 11 retracts from the exhaust port 7 as indicated by the broken line H in the figure. Therefore, the exhaust area 7 having a substantially rectangular shape can be entirely opened to increase the opening area, so that the output does not decrease. In this case, the exhaust port 7 is suddenly opened, but there is no problem because the exhaust silencer (not shown) is set at high speed rotation.

As described above, according to the present invention, the recess 20 provided on the lower surface 11a of the valve body 11 allows the opening shape of the exhaust port 7 at the time of middle- and low-speed rotation of the engine to have a small upper part,
The burned gas is gradually discharged to suppress the generation of sound due to the rapid flow of the burned gas, and at the time of high speed rotation, the opening shape of the exhaust port 7 is made substantially rectangular to increase the opening area. Since the above is the content thereof, the recess 20 is not limited to the groove-like one described in the above-mentioned embodiment, and as shown in FIG. 4 and FIG. It may be a recess 21 having a shape. In this embodiment, the concave portion 21 is set so as to become gradually deeper toward the central portion, and like the above-described embodiment, the valve element 11 is indicated by a chain line S in the figure at low speed and medium speed rotation. And, as shown by the chain double-dashed line M, it advances into the exhaust passage 9, and when it rotates at high speed, it retreats from the exhaust port 7 as shown by the broken line H.

〔The invention's effect〕

As described above, according to the present invention, the upper edge of the exhaust port is protruded toward the upper side of the cylinder on the lower surface of the valve body for adjusting the exhaust timing by moving the upper edge of the exhaust port provided in the cylinder up and down. Since the concave portion is provided, the opening shape of the exhaust port when the engine is rotating in the middle or low speed can be made to have a shape in which the upper portion becomes smaller.

Therefore, it is possible to suppress the generation of sound by gradually discharging the burnt gas to the exhaust passage and causing the burnt gas to rapidly flow, so that it is possible to reduce noise during the middle / low speed rotation.

Further, since the exhaust port of the cylinder is formed in a substantially rectangular shape, the opening area can be increased during high speed rotation, and the output during high speed rotation is not reduced.

[Brief description of drawings]

FIG. 1 is a side view of the valve body, which is an essential part of the present invention, as seen from the direction indicated by arrow A in FIG. 3, FIG. 2 is a perspective view of the same, and FIG. 3 is a longitudinal sectional view showing a two-cycle engine. 4 and 5 are a side view and a perspective view of a valve body showing another embodiment. 3 ... Cylinder block, 7 ... Exhaust port, 9 ... Exhaust passage, 11 ... Valve body, 11a ... Bottom surface, 20 ... Recessed portion, 2
1 ... recess.

Claims (1)

[Claims] 1. A substantially drum-shaped valve body, which advances into the exhaust passage and forms an upper edge of the exhaust opening, is rotatably provided on the upper exhaust passage side of the exhaust opening provided in the cylinder, and is used during engine operation. In a two-cycle engine configured to move the upper edge up and down to adjust the opening timing of the exhaust port, a recess is formed on the lower surface of the valve body so that the upper edge of the exhaust port projects toward the upper side of the cylinder. At the same time, a two-cycle engine in which the exhaust port of the cylinder is formed in a substantially rectangular shape.