JPH0791987B2 - Two stroke engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an improvement of a two-stroke engine,
In particular, the present invention relates to a device that reduces as much as possible the reduction in output that occurs when the engine speed deviates from the increased output range due to the improvement of the exhaust system.

[Conventional technology]

It is generally known that the dimensions of the exhaust pipe greatly contribute to the performance of the two-stroke engine. That is, the exhaust passage 8
Is an appropriate size of the first inflating portion 8a extending from the exhaust port 7 in FIG. 1 over a predetermined length to gradually increase the cross-sectional area and the second inflating portion 8b relatively rapidly increasing in cross-sectional area. 4, the pressure in the vicinity of the exhaust port 7 is maintained at a negative pressure when the engine is in the scavenging stroke as shown by in FIG. 4, and after the piston closes the scavenging port 6, the second expansion section Straight pipe section 8c connected to 8b
By appropriately selecting the dimension up to the reflecting portion 8d from which the cross-sectional area is relatively sharply reduced, a positive pressure acts until the piston closes the exhaust port 7. That is, this improves the efficiency of scavenging by lowering the pressure in the combustion chamber during the scavenging stroke, while preventing the mixture introduced into the combustion chamber from flowing into the exhaust passage after the scavenging stroke, or Settings are made to improve the maximum output by reflowing what has flowed back into the combustion chamber.

[Problems to be Solved by the Invention]

However, even in such a setting, when the engine speed decreases, the pressure wave reflected and returned in the exhaust pipe becomes relatively fast, and as shown by in FIG. 4, the exhaust passage pressure during the scavenging stroke is increased. Rises to lower the scavenging efficiency, while lowering the exhaust passage pressure after closing the scavenging port to increase the blow-through of fresh air introduced into the combustion chamber. There is a problem that the combustion fuel component is increased.

[Means for Solving the Problems]

This invention reduces the blow-through of fresh air that occurs when the engine speed is greatly reduced from the maximum output speed while maintaining the performance when the engine speed is the maximum output speed, thereby reducing the efficiency. The purpose is to obtain a two-stroke engine that enables good driving. That is, performance deterioration due to attenuation of reflected waves does not occur during low-speed operation, exhaust pressure is raised overall to prevent blow-through of fresh air, and low-speed performance is improved, and engine speed is maximized. The purpose is to prevent performance degradation even at the output speed.

In the two-stroke engine according to the present invention, the exhaust passage communicating with the combustion chamber is formed to have a substantially U-shaped curve by an expansion part having a larger cross-sectional area and a reflection part having a smaller cross-sectional area downstream of the expansion part. The performance setting portion and an auxiliary portion that is connected to the performance setting portion and has an atmosphere open end, and the auxiliary portion is provided with a co-flow portion that divides the exhaust passage into a curved inner side and an outer side and allows the exhaust flow to flow in parallel. At the portion on the inner side of the curved portion of the parallel flow portion, there is arranged a resistance means composed of a butterfly valve for imparting flow path resistance, and the resistance means is provided with the output of the rotation speed detection means for detecting the rotation speed of the crankshaft. The resistance means driving device for driving the resistance means to increase the flow path resistance during low speed operation of the engine is connected.

[Action]

When the speed of the engine is reduced, the resistance means formed of a butterfly valve provided in the auxiliary portion of the exhaust passage increases the ventilation resistance of the exhaust passage, and as a result, the exhaust pressure in the exhaust passage is increased as shown by in FIG. Although it rises overall and the inflow efficiency of scavenging air into the combustion chamber decreases, the exhaust pressure near the exhaust port 7 increases immediately before the exhaust passage is closed, and as a result, blow-through of fresh air is prevented and fuel is used economically. can do.

Further, since the resistance means is arranged on the downstream side of the performance setting section, the reflected wave reflected by the performance setting section propagates into the exhaust passage without being blocked by the resistance means.

Further, since a negative reflected wave is also generated from the atmosphere open end of the auxiliary portion of the exhaust passage, by returning this reflected wave to the exhaust port at the beginning of the scavenging process, gas exchangeability is improved and output can be improved. In particular, the negative reflected wave returning from the open end of the atmosphere is not disturbed in the exhaust passage in which the resistance means is not interposed in the co-current part of the auxiliary portion, so this negative reflected wave is output more reliably. It can be used for improvement.

During high-speed operation, the average value of the pressure in the exhaust passage itself rises unless the resistance of the exhaust passage is decreased because the amount of exhaust gas per hour increases.Therefore, a negative reflected wave is generated in the scavenging process with the exhaust port open. Even if it is returned to the exhaust port at the initial timing, the negative pressure itself cannot be increased and the gas exchangeability cannot be improved. If the resistance means is composed of a butterfly valve, there is a limit to reducing the exhaust resistance in order to keep the internal pressure of the exhaust passage low because the valve element exists in the exhaust passage even when it is fully opened. By adopting a configuration in which the performance setting portion is curved in a substantially U shape and the resistance means is positioned in the exhaust passage inside the curved portion of the auxiliary portion, it is possible to increase the exhaust resistance by the resistance means during high speed operation. It can be suppressed as much as possible. This is because the exhaust gas has a high outflow speed during high-speed operation, and when it flows through the performance setting section, it is moved to the outside of the curve by centrifugal force and flows more along the outside of the curve. This is because a large amount of gas flows into the exhaust passage on the outside. That is, since the exhaust passage on the inside of the curve where the resistance means is present has a relatively small flow rate of the exhaust gas during high speed operation, the resistance means is less likely to become exhaust resistance and the pressure in the exhaust passage is less likely to rise. The gas exchangeability can be kept high and the performance will not be degraded.

〔Example〕

The present invention will be described below with reference to the illustrated embodiment. In FIG. 1, reference numeral 1 is a two-stroke engine used in a motorcycle, the combustion chamber 2 of which is composed of a cylinder 3, a piston 4, and a cylinder head 5. It is configured. Reference numeral 7 is an exhaust port that opens to the wall surface of the cylinder 3 that constitutes the combustion chamber.

As is well known, the exhaust passage 8 is composed of a performance setting portion P connected to the exhaust port 7, a tail pipe 8e connected to the performance setting portion P, and a muffler 8f attached to the rear end of the tail pipe 8e if necessary.

The performance setting section P includes a first expansion section 8a that extends from the exhaust port 7 over a predetermined length and gradually increases the cross-sectional area, a second expansion section 8b that relatively rapidly increases the cross-sectional area, and a second expansion section. It is composed of a straight pipe portion 8c connected to the portion 8b and a reflective portion 8d from which the cross-sectional area is relatively sharply reduced, and determines the basic performance of the engine. Then, the performance setting unit P is
As shown in the figure, it is formed so as to be curved in a substantially U shape in a side view.

In the present invention, the variable resistance means 9 for imparting the flow path resistance is provided in the auxiliary portion D formed by the tail pipe 8e, the silencer 8f and the like provided on the downstream side of the performance setting portion P.

As shown in the longitudinal sectional view of FIG. 2, the auxiliary portion D divides the tail pipe 8e into an upper exhaust passage 11 and a lower exhaust passage 12 by a partition wall 10, and the variable resistance means 9 is provided in the upper exhaust passage 11. Are arranged. The upper exhaust passage 11 is connected to the inside of the curved performance setting portion P, and the lower exhaust passage 12 is connected to the outside of the performance setting portion P. As a result, the portion of the auxiliary portion D where the partition wall 10 is provided constitutes the parallel flow portion according to the present invention.

The variable resistance means 9 is composed of a butterfly valve having a semicircular valve body 9a and a valve shaft 9b that completely close the upper exhaust passage 11, and closes about 1/2 of the cross-sectional area of the tail pipe 8e. It is configured. The variable resistance means 9 operates via a pulley 13 fixed to the valve shaft 9b and a flexible wire 14 connected to the pulley 13 to operate according to the engine speed, that is, the crankshaft speed. Connected to 15,
Opening / closing is controlled so that the opening is increased when the engine speed is high and is decreased when the engine speed is low. In addition, the pulley 13, the flexible wire 14, the pulse motor 15 and a computer 17 described later.
The resistance means drive device according to the present invention is constituted by the above.

Reference numeral 16 is a sensor that constitutes the rotational speed detecting means according to the present invention and detects the engine speed, and its output drives the pulse motor 15 via the computer 17.

In the two-stroke engine 1 configured as described above, when the exhaust port 7 is opened in the expansion stroke, the exhaust gas is discharged into the exhaust passage 8 and the pressure wave of the exhaust is propagated into the exhaust passage 8. This pressure wave propagates through the exhaust passage 8 at the speed of sound,
It is reflected as a negative reflected wave at a portion of the performance setting portion P where the passage cross-sectional area from the first inflating portion 8a to the second inflating portion 8b increases, and then is reflected as a positive reflected wave at the reflecting portion 8d. When the negative reflected wave reaches the engine 1, the pressure in the vicinity of the exhaust port 7 becomes a negative pressure. Therefore, when the negative reflected wave reaches the engine 1 at the beginning of the scavenging stroke, the gas exchange performance of the combustion chamber is improved. Will increase. Further, when the positive reflected wave reaches the engine 1, the pressure in the vicinity of the exhaust port 7 becomes high, so that the positive reflected wave is generated at the end of the scavenging stroke of the engine 1.
By arriving at, it is possible to prevent fresh air from passing through the combustion chamber. In this way, the reflected wave is the engine 1
High output can be obtained when it is adapted to the rotation speed.

When the time when the reflected wave reaches the engine 1 at low speed operation does not match the rotational speed of the engine 1, a fresh air blow-through phenomenon occurs. However, when the two-stroke engine 1 according to the present invention starts, the crankshaft When the speed is detected by the sensor 16 and it does not reach the predetermined speed, the computer 17 drives the pulse motor 15 to decrease the opening degree of the variable resistance means 9 to increase the ventilation resistance and increase the exhaust pressure. Let Therefore, the blow through that occurs through the exhaust port 7 is reduced. Even if the variable resistance means 9 is fully opened in this way, the negative reflected wave and the positive reflected wave described above are still in the exhaust passage 8.
It propagates through the variable resistance means 9 without being blocked and reaches the exhaust port 7. This is because the variable resistance means 9 is arranged in the auxiliary portion D of the exhaust passage 8. More specifically, when the variable resistance means is disposed between the second expanding portion 8b and the reflecting portion 8d, both the pressure wave reaching the reflecting portion 8d and the positive reflected wave reflected by the reflecting portion 8d are variable resistance means. Therefore, the positive reflected wave is attenuated by the resistance means, the ability to prevent blow-through is reduced, and the output is reduced. The variable resistance means is connected to the second expansion section 8b.
If it is arranged on the upstream side, not only the positive reflected wave but also the negative reflected wave is weakened, and the output is further reduced. However, by adopting the above configuration, the reflected wave is not attenuated due to the variable resistance means 9, so that it is possible to prevent the reflected wave from being attenuated and the performance from being deteriorated. On the contrary, when the speed of the crankshaft increases and reaches the predetermined speed, the opening degree of the variable resistance means 9 increases in the same manner as described above, the ventilation resistance is reduced, and the exhaust pressure is restored to the predetermined level.

At this time, the variable resistance means 9 is held in the fully opened state by the resistance means drive device including the computer 17, the pulse motor 15, and the like. When it is held in the fully open state like this,
The pressure wave is propagated to the atmosphere open end of the auxiliary portion D, and the positive pressure wave propagated from the engine 1 side is inverted at this atmosphere open end and becomes a negative reflected wave to return to the engine 1 side. Become. The negative reflected wave generated at the open end of the atmosphere reaches the exhaust port 7 with a time lag after the positive reflected wave reflected by the reflecting portion 8d, and the positive reflected wave reaches the exhaust port 7 at the end of the scavenging stroke.
After increasing the pressure in the vicinity, the pressure in the vicinity of the exhaust port 7 is reduced. The time when this pressure decreases depends on the passage length from the upstream end of the exhaust passage 8 to the atmosphere open end, and when the exhaust port 7 opens in the expansion stroke following the compression stroke, or
It is when the exhaust port 7 opens and the negative reflected wave, which is the pressure wave propagated from the combustion chamber to the exhaust passage 8 is inverted at the expansion section, reaches the exhaust port 7. That is, at the time of high-speed operation, in addition to the positive and negative reflected waves generated in the performance setting section P, negative reflected waves are generated even at the open end of the atmosphere, and all of these reflected waves can be used. The gas exchangeability is enhanced and the output can be improved. Particularly, since the negative reflected wave returning from the open end of the atmosphere is not disturbed in the lower exhaust passage 12 on the side where the variable resistance means 9 is not interposed in the co-current portion of the auxiliary portion D, this is more reliable. Negative reflected waves can be used to improve output.

In such a high-speed operation, since the amount of exhaust gas per unit time increases, unless the resistance of the exhaust passage 8 is reduced, the average value of the pressure inside the exhaust passage itself rises, so a negative reflected wave is generated in the exhaust port 7. Even if the gas is returned to the exhaust port 7 at the timing of the opening of the scavenging stroke, the negative pressure itself cannot be increased and the gas exchangeability cannot be improved. When the variable resistance means 9 is configured by a butterfly valve, the valve body 9a is present in the exhaust passage even when the variable resistance means 9 is fully opened. Therefore, the exhaust resistance is limited in order to keep the exhaust passage internal pressure low. There is a performance setting part P
Is curved substantially in a U shape, and the variable resistance means 9 is positioned in the upper exhaust passage 11 inside the curved portion of the auxiliary portion D, so that the variable resistance means 9 increases the exhaust resistance during high-speed operation. Can be suppressed as much as possible. This is because the exhaust gas has a high outflow speed during high-speed operation, so when flowing through the performance setting section P, it is moved toward the curve outer side by the centrifugal force and flows more along the curve outer side portion, and the auxiliary portion D continuous therewith. This is because a large amount of gas flows into the lower exhaust passage 12 on the outside of the curve. That is, in the upper exhaust passage 11 on the inner side of the curve where the variable resistance means 9 is present, the flow rate of exhaust gas is relatively small during high-speed operation. Therefore, the gas exchangeability during high-speed operation can be kept high, and the performance does not deteriorate.

The opening of the variable resistance means 9 is preferably adjusted steplessly according to the engine speed, but it may be of an open / close valve type that opens and closes temporarily.

〔The invention's effect〕

As described above, in the two-stroke engine according to the present invention, the exhaust passage communicating with the combustion chamber is formed in an approximately U-shape by the expansion portion increasing the cross-sectional area and the reflection portion decreasing the cross-sectional area on the downstream side of the expansion portion. It is composed of a curved performance setting portion and an auxiliary portion that is connected to the performance setting portion and has an atmosphere open end,
The auxiliary portion is provided with a parallel flow section that divides the exhaust passage into a curved inner side and an outer side to allow the exhaust flow to flow in parallel, and a portion that is the curved inner side of the parallel flow section is provided with a butterfly valve to provide flow path resistance. The resistance means for
When the speed of the engine decreases because a resistance drive device is connected to drive the resistance means to increase the flow path resistance during low speed operation of the engine according to the output of the rotation speed detection means for detecting the rotation speed of the crankshaft. Since the resistance means provided in the auxiliary portion of the exhaust passage increases the ventilation resistance of the exhaust passage, the exhaust pressure in the exhaust passage generally rises and the inflow efficiency of scavenging air into the combustion chamber decreases, but the exhaust passage By increasing the exhaust pressure in the vicinity of the exhaust port immediately before closing, blow-through of fresh air is prevented, and fuel can be used economically.

Further, since the resistance means is disposed on the downstream side of the performance setting section, the reflected wave reflected by the performance setting section propagates through the exhaust passage without being blocked by the resistance means.
Therefore, the reflected wave is not weakened even if the flow path resistance is increased during low speed operation.

Moreover, since the resistance means is driven by the resistance means drive device, it does not operate following the change in the exhaust pressure.

Further, since a negative reflected wave is also generated from the atmosphere open end of the auxiliary portion of the exhaust passage, by returning this reflected wave to the exhaust port at the beginning of the scavenging process, gas exchangeability is improved and output can be improved. In particular, the negative reflected wave returning from the open end of the atmosphere is not disturbed in the exhaust passage in which the resistance means is not interposed in the co-current part of the auxiliary portion, so this negative reflected wave is output more reliably. It can be used for improvement.

During high-speed operation, the average value of the pressure in the exhaust passage itself rises unless the resistance of the exhaust passage is decreased because the amount of exhaust gas per hour increases.Therefore, a negative reflected wave is generated in the scavenging process with the exhaust port open. Even if it is returned to the exhaust port at the initial timing, the negative pressure itself cannot be increased and the gas exchangeability cannot be improved. If the resistance means is composed of a butterfly valve, there is a limit to reducing the exhaust resistance in order to keep the internal pressure of the exhaust passage low because the valve element exists in the exhaust passage even when it is fully opened. By adopting a configuration in which the performance setting portion is curved in a substantially U shape and the resistance means is positioned in the exhaust passage inside the curved portion of the auxiliary portion, it is possible to increase the exhaust resistance by the resistance means during high speed operation. It can be suppressed as much as possible. This is because the exhaust gas has a high outflow speed during high-speed operation, and when it flows through the performance setting section, it is moved to the outside of the curve by centrifugal force and flows more along the outside of the curve. This is because a large amount of gas flows into the exhaust passage on the outside. That is, since the exhaust passage on the inside of the curve where the resistance means is present has a relatively small flow rate of the exhaust gas during high speed operation, the resistance means is less likely to become exhaust resistance and the pressure in the exhaust passage is less likely to rise. The gas exchangeability can be kept high and the performance will not be degraded.

In addition, since the resistance means is composed of a butterfly valve, there is an effect that it is easy to increase or decrease the resistance.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a side view in which a part of a two-stroke engine is cut away, FIG. 2 is a longitudinal sectional view of an auxiliary portion, and FIG. 3 shows a pulley portion of a resistance means. FIG. 5 is a plan view, FIG. 4 is a pressure diagram showing the exhaust pressure near the exhaust port, and FIG. 5 is a characteristic diagram showing the output characteristics of the engine. 8 ... Exhaust passage, P ... Performance setting part, D ... Auxiliary part,
8e ... Tail tube, 9 ... Variable resistance means, 10 ... Partition wall, 11 ...
Upper exhaust passage, 12 …… Lower exhaust passage, 13 …… Pulley, 14
…… Flexible wire, 15 …… Pulse motor.

Claims (1)

[Claims] 1. A performance setting section formed by bending an exhaust passage communicating with a combustion chamber into a substantially U shape, comprising an expansion section having an increased cross-sectional area and a reflection section having a cross-sectional area reduced on the downstream side of the expansion section. (P) and an auxiliary portion (D) that is connected to the auxiliary portion (D) and has an open end to the atmosphere, and the auxiliary portion (D) has an exhaust passage divided into a curved inner side and an outer side, and the exhaust flow flows in parallel. And a resistance means for providing a flow path resistance, which is formed of a butterfly valve, is arranged at a portion on the curved inner side of the parallel flow portion, and the rotation speed detection for detecting the rotation speed of the crankshaft is provided in the resistance means. A two-stroke engine, characterized in that a resistance means drive device is connected to drive the resistance means at a low speed operation of the engine according to the output of the means to increase the flow path resistance.