JPH0635831B2 - Exhaust timing control device for 2-cycle engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust timing control device, and more particularly to an exhaust timing control device used in a two-cycle engine.

[Prior Art] Generally, an engine mounted on a vehicle has a low rotation type that emphasizes power characteristics at low speed running (low rotation range) and a power characteristics at high speed running (high rotation range). It is roughly divided into a high-speed type with emphasis on the former so that the peak of the engine output can be obtained in the low rotation range of the engine, and the latter can obtain the peak of the engine output in the high rotation range. It has become.

However, the former has a characteristic that the output in the high speed range reaches a peak, and the latter has the characteristic that the output in the low speed range becomes lower than that of the former. Therefore, it is considered to improve the output characteristics in the entire range from low speed running to high speed running by increasing the output in the low speed range while maintaining the high output in the high speed range. As a solution, it is mentioned that the exhaust timing of the engine is changed between low speed and high speed.

Then, as an example of a conventional structure in which such a solving means is applied to a two-cycle engine, for example, in Japanese Utility Model Laid-Open No. 51-3
The technique disclosed in Japanese Patent No. 9112 is known.

In this technique, a partition wall that divides the vicinity of the opening of the exhaust passage in the sliding direction of the piston is provided on the upper portion of the exhaust passage that communicates with the inside of the cylinder of the two-cycle engine, and the partition is positioned in the exhaust passage. A control valve for opening and closing a gap between the partition wall and the upper wall of the exhaust passage is provided. When the engine is in a low rotation state, the control valve closes the gap to exhaust the gas from the gap. By stopping the outflow of gas, the communication timing between the inside of the cylinder and the exhaust passage due to the sliding of the piston, that is, the exhaust timing, is controlled by the partition wall, and the exhaust timing at low engine speed is made appropriate. When the engine speed reaches a high speed range, the clearance is released to allow the exhaust gas to flow out from the clearance, thereby opening the communication timing between the inside of the cylinder and the exhaust passage. Earlier the exhaust timing is controlled at the edge, by which is to perform the appropriate exhaust at high rpm.

[Problems to be solved by the invention]

The present invention is intended to solve the following problems in the above-described conventional technique.

That is, in the above-mentioned technique, in the case where the gap is closed and the exhaust timing is controlled by the partition wall, in order to ensure the airtightness between the partition wall and the piston, the end surface on the cylinder side of the partition wall is secured. It is positioned at the same level as the inner peripheral surface of the cylinder so as to be as close as possible to the piston.However, by setting the position of the partition wall, when the piston slides, the piston, the piston ring or the oil ring and the partition wall are separated from each other. This is a problem in that they interfere with each other and hinder the smooth sliding of the piston.

Then, in order to solve such a problem, it is considered to chamfer the cylinder side corner of the partition wall to control the catch with the piston, the piston ring or the oil ring, like the corner of the opening. Has been done.

However, the following problems still remain in such measures.

That is, when chamfering the partition wall, the thickness of the partition wall must be increased in order to secure the strength of the partition wall. In order to cause such a new problem that the flow path resistance of the exhaust passage is increased and the exhaust efficiency is lowered, a countermeasure is required.

[Means for solving problems]

The present invention is intended to provide a two-cycle engine exhaust timing control device which can effectively solve the above-mentioned problems in the prior art, and the exhaust timing control device is provided especially in the upper part of the exhaust passage. A partition wall that divides the vicinity of the opening of the exhaust passage in the sliding direction of the piston is provided, and a control valve that is located in the exhaust passage and that opens and closes between the partition wall and the upper wall of the exhaust passage is provided, and It is characterized in that the end surface of the partition wall on the inner side of the cylinder is set back a minute distance to the downstream side of the exhaust passage from the inner peripheral surface of the cylinder.

[Work]

With the exhaust timing control device according to the present invention, by adopting the above-described configuration, the interference between the partition wall and the piston is suppressed to suppress the increase in the thickness of the partition wall, and thus the sliding resistance of the piston and the flow path of the exhaust passage. It reduces the resistance and improves the output characteristics of the engine as a whole.

〔Example〕

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. In the following description, the top dead center side of the piston will be the top and the bottom dead center side will be the bottom.

In FIG. 1, reference numeral 1 indicates a two-cycle engine to which the present embodiment is applied, and includes a cylinder 2, a piston 3 slidably fitted in the cylinder 2, and a space in the circumferential direction of the cylinder 2. And a plurality of scavenging passages 4 which are provided on the inner surface of the cylinder 2 and which are opened on the inner surface of the cylinder 2, and an opening 5 on the inner surface of the cylinder 2.
The exhaust timing control device 6 according to the present embodiment is provided on the upper wall of the exhaust passage 5.

The exhaust timing control device 6 is provided with a partition wall 7 in the upper part of the exhaust passage 5 that divides the vicinity of the opening 5a of the exhaust passage 5 in the sliding direction of the piston 3, that is, in the vertical direction. The partition wall 7 and the exhaust passage 5
A control valve 8 for opening and closing the upper wall is provided, and the end surface 7a of the partition wall 7 on the inner side of the cylinder 2 is retracted by a small distance g to the downstream side of the exhaust passage with respect to the inner peripheral surface 2a of the cylinder 2. It has a general configuration.

Next, these will be described in detail.
Is integrally provided with the cylinder 2 at a position spaced apart from the upper edge 5b of the opening 5a by a predetermined distance G, and forms a main passage 9 between the lower wall surface of the exhaust passage 5 and the exhaust gas. A sub-passage 10 is formed between the sub-passage 10 and the upper wall of the passage 5. And, the interval G is equal to
It is set based on the difference between the exhaust timing at the time of high rotation and the exhaust timing at the time of low rotation, which is set at the stage of setting the output characteristic of. Further, as shown in FIG. 2, the end surface 7a of the partition wall 7 on the inner side of the cylinder 2 extends along the inner peripheral surface 2a in a state of being retracted from the inner peripheral surface 2a of the cylinder 2 by the distance g described above. It is formed in a curved shape. The distance g is preferably set within the range of 0.5 to 1.0 mm.

The control valve 8 is formed in a cylindrical shape as a whole, and is rotatably attached to an upper wall of the exhaust passage 5 at a through height 11 formed so as to cross the exhaust passage 5. The middle portion of the control valve 8 in the lengthwise direction is exposed in the exhaust passage 5 so that it is overlapped with the downstream end of the sub passage 10 to close the sub passage 10. In addition, a communication hole 12 that connects the downstream end of the sub passage 10 to the main passage 9 when the control valve 8 is rotated by a predetermined angle is formed in the overlapping portion with the sub passage 10. ing. Further, as shown in FIG. 2, a swing arm 13 is integrally provided at one end of the control valve 8, and an operating rod 14 rotatably connected to the swing arm 13 is used. Drive means (not shown), such as a cabana, a servomotor, a fluid pressure cylinder, etc., are connected. Then, the drive means is adapted to rotate the control valve 8 to either one of fully open and fully closed based on the operating state of the engine 1.

On the other hand, the reference numeral 15 in FIGS. 1 and 2 is a water jacket, which extends from the wall of the crankcase 16 around the supporting portion of the control valve 8 of the cylinder 2, and further from the peripheral side wall of the cylinder 2. A cooling water circulation path is formed from the head 17 to a radiator (not shown), and the surroundings of the cylinder 2, the crankcase 15, the cylinder head 16, and the control valve 8 are cooled. Reference numeral 18 denotes a reinforcing rib that is provided from the opening 5a of the exhaust passage 5 toward the downstream side and divides the vicinity of the opening 5a of the exhaust passage 5 into two in the circumferential direction of the cylinder 2.

Thus, the exhaust timing control device 6 of this embodiment having such a configuration simultaneously molds the partition wall 7, the rib 18 and the through hole 11 at a predetermined position above the exhaust passage 5 when the cylinder 2 is cast. The control valve 8 is inserted into the through hole 11, and a drive means is connected to the control valve 8 via the swing arm 13 and the operating rod 14 so that the engine 1 is assembled.

Then, by rotating the control valve 8 in a predetermined direction based on the operating state of the engine 1, the output characteristic of the engine 1 can be enhanced in the entire rotation range.

That is, when the engine 1 is operated in the low rotation speed range, the control valve 8 is rotated in the closing direction by the driving means driven based on the information, as shown by the chain line in FIG. The sub passage 10 is closed.

When the sub-passage 10 is closed in this way, the outflow of exhaust gas from the sub-passage 10 is blocked, and the upper edge of the piston 3 in the downward stroke of the exhaust of the engine 1 is the partition wall 7. It starts from the time when it reaches the bottom. As a result, the exhaust timing of the engine 1 is delayed by an amount corresponding to the distance G between the upper edge 5b of the opening 5a and the partition wall 7, and proper exhaust at low engine speed is obtained. Improvement is achieved.

On the other hand, when the engine 1 reaches the high speed range,
By rotating the control valve 8 in the direction opposite to the direction described above, the sub passage 10 communicates with the main passage 9 through the communication hole 12 of the control valve 8 as shown by the solid line in FIG. To be In this state, the exhaust gas is discharged from the sub-passage 10, and the position of the piston 3 at which the exhaust is started is from the partition wall 7 to the upper edge 5b of the opening 5a.
Is raised, that is, the exhaust timing is advanced, so that appropriate exhaust is performed at the time of high rotation, and at the same time, the output of the engine in the high rotation range is improved.

Therefore, the characteristic improvement of the engine output can be obtained in the entire rotation range.

Since the end surface 7a of the partition wall 7 on the cylinder 2 side is retracted from the inner peripheral surface of the cylinder 2 to the downstream side of the exhaust passage 5 by a distance g, the piston 3 and the piston ring (oil The interference with the ring O is suppressed, the sliding resistance of the piston 3 is reduced, and the required strength for the partition wall 7 is reduced.
The partition wall 7 can be thinned and the flow path resistance of the exhaust passage 5 can be reduced.

On the other hand, although the airtightness between the partition wall 7 and the piston 3 may be reduced by retracting the end surface 7a of the partition wall 7, the retreat distance g is set to 0.5 as described above.
When it is set in the range of up to 1.0 mm, the effect is hardly seen, and the output improvement due to the reduction of both resistances described above is directly obtained as the output improvement of the engine 1.

It should be noted that the shapes, sizes, combinations and the like of the respective constituent members shown in the above embodiment are merely examples, and can be variously changed based on design requirements and the like.

〔The invention's effect〕

As described above, the exhaust timing control system for a two-cycle engine according to the present invention has, in the upper portion of the exhaust passage, a partition wall that divides the vicinity of the opening of the exhaust passage in the sliding direction of the piston, and And a control valve that opens and closes between the partition wall and the upper wall of the exhaust passage.
Moreover, the end surface of the partition wall on the inner side of the cylinder is retracted a minute distance to the downstream side of the exhaust passage from the inner peripheral surface of the cylinder. While suppressing the interference between the (oil ring) and the partition wall to reduce the sliding resistance of the piston,
By reducing the required strength for the partition wall, it is possible to reduce the wall thickness of the partition wall and reduce the flow path resistance of the exhaust passage, thereby reducing the horsepower loss due to the friction of moving parts and the reduction of exhaust efficiency to improve the engine output. It has excellent effects such as

[Brief description of drawings]

1 and 2 show an embodiment of the present invention.
FIG. 1 is a longitudinal sectional view of a two-cycle engine to which one embodiment is applied, and FIG. 2 is a sectional view taken along the line II-II of FIG. 1 ... (2-cycle) engine, 2 ... cylinder, 3 ...
… Piston, 5 …… Exhaust passage, 5a …… Opening, 5b ……
Upper edge, 6 ... Exhaust timing control device, 7 ... Partition, 8 ... Control valve, 9 ... Main passage, 10 ... Sub passage, 11 ...
Through hole, 12 ... Communication hole.

Claims (1)

[Claims] 1. A partition which divides the vicinity of the opening of the exhaust passage in the sliding direction of the piston is provided on the upper portion of the exhaust passage communicating with the inside of the cylinder of the two-cycle engine, and the partition is located in the exhaust passage. A control valve that opens and closes between the partition wall and the upper wall of the exhaust passage, and retracts the end face of the partition wall on the inner side of the cylinder toward the downstream side of the exhaust passage from the inner peripheral surface of the cylinder by a small distance. Characterized by that 2
Exhaust timing control device for cycle engine.