JPS62218616A - Two-cycle engine - Google Patents

Abstract

PURPOSE:To produce proper exhaust gas pulsation for an increased output power, by providing an exhaust gas pulsation forming space and an exhaust gas resistance control unit succeeding to it with the exhaust gas system of a two-cycle engine so that an exhaust gas resistance is changed according to the operating condition of an engine. CONSTITUTION:Exhaust gas from a two-cycle engine 1 is exhausted through an exhaust gas port 8, an enlarged chamber P, a throttle passage D and a muffler 8f. Since exhaust gas pulsation produced in an exhaust gas system is reflected by a pressure wave reflecting wall 8d and pressure wave is transmitted to the exhaust gas port 8 in agreement with the opening and closing timing of the exhaust gas port 8, the scavenging efficiency of an engine is improved. A vale 9 is disposed between the enlarged chamber P and the throttle passage D for controlling a flowing resistance of exhaust gas so that a control unit 17 operates an actuator 12 in accordance with an engine rotational speed 16 to provide the flow resistance of the exhaust gas in accordance with the engine rotational speed, whereby exhaust gas pulsation transmitted to the exhaust gas port 8 is changed.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to improvement of a two-stroke engine.
In particular, the present invention relates to a device that reduces as much as possible the decrease in output that occurs when the engine speed is out of the maximum output range due to improvements in the exhaust system.

[Conventional technology and its problems]

It is generally known that the dimensions of the exhaust pipe greatly contribute to the performance of a two-stroke engine. That is, the exhaust passage 8
In Fig. 1, the dimensions of the first expansion part 8a extending over a predetermined length from the exhaust lower and gradually increasing the cross-sectional area, and the second expansion part 8b whose cross-sectional area becomes gold layer relatively rapidly from there are appropriately determined. By selecting , the pressure near the exhaust port T is kept negative and positive when the engine is in the scavenging stroke, as shown by ■ in Fig. 6, and after the piston closes the scavenging port 6, the pressure is By appropriately selecting the dimensions of the straight pipe section 8c that continues to the section 8b and the reflecting section 8d''!1 whose cross-sectional area decreases relatively rapidly from there,
Positive pressure is applied until the piston closes the exhaust lower. That is, this K improves the efficiency of scavenging by lowering the pressure in the combustion chamber during the scavenging stroke, and on the other hand, prevents the air-fuel mixture introduced into the combustion chamber from escaping into the exhaust passage after the scavenging stroke is completed. Or ran away.

The settings are made to make the fuel flow back into the combustion chamber, thereby increasing the maximum output.

However, even with this setting, the engine force wave becomes relatively faster, and as shown by [F] in Fig. 6, the exhaust passage pressure increases during the scavenging stroke, reducing the scavenging efficiency. Some of them reduce the exhaust passage pressure after the scavenging port is closed and increase the blow-through of fresh air introduced into the combustion chamber. There is a problem that increases the number of

[゛Object and structure of the invention]

The purpose of this invention is to obtain a two-stroke engine that enables efficient operation by reducing as much as possible the blow-through that occurs when the engine is operated at a speed significantly lower than the maximum output speed. The exhaust passage leading to the combustion chamber is composed of a performance setting part P and an auxiliary part connected to the performance setting part P, and a resistance means t for imparting flow passage resistance to the auxiliary part during low speed operation of the engine is generally used. It has characteristics.

[For production]

When the engine speed decreases, the resistance means provided in the auxiliary part of the exhaust passage increases the ventilation resistance of the exhaust passage.
As shown by ■ in Figure 6, the exhaust pressure in the exhaust passage increases overall, and the inflow efficiency of scavenging air into the combustion chamber decreases\, and the exhaust pressure near the exhaust lower immediately before the exhaust passage closes increases. As a result, blow-by of fresh air is prevented and fuel can be used economically.

〔Example〕

Hereinafter, the present invention will be explained with reference to the illustrated embodiment. In FIG. It is configured. Reference numeral 7 denotes an exhaust port opening in the wall surface of the cylinder 3 constituting the combustion chamber.

As is well known, the exhaust passage 8 includes a performance setting part P connected to the exhaust lower, a tail pipe 8es connected to the performance setting part P, and a muffler 8f attached to the rear end as necessary.

The performance setting section P includes a first expansion section 8& that extends over a predetermined length from the exhaust port T and gradually increases in cross-sectional area, and a second expansion section 8BS that increases in cross-sectional area relatively rapidly from there. The straight pipe part 8c continues from the straight pipe part 8b to the reflecting part 8d whose cross-sectional area decreases relatively rapidly from there to the reflection part 8d, which determines the basic performance of the engine.

In this invention, a variable resistance means 9 for imparting flow path resistance is provided in an auxiliary part that is arranged downstream of the performance setting part P, such as the tail pipe 8e and the muffler 8f. . As shown in FIG. 2, an example of the variable resistance means 9 is a throttle valve 10 that closes approximately 1/2t of the cross-sectional area of the tail pipe 8e. This throttle valve 10 is connected by a flexible wire 11 to a pulse motor 12 that operates according to the engine speed, that is, the crankshaft speed, and is controlled to open and close so that when the engine speed is high, the opening degree is increased and when the engine speed is low, the opening degree is decreased. Ru.

13 is a pulley fixed to the valve shaft of the nine-throttle valve 10.

The throttle valve 10 is not limited to this example; for example, as shown in FIG. 4, a semicircular shape that is divided into upper and lower sections by a tail pipe 8et'' partition wall 14 and completely closes a part thereof may be used.

The variable resistance means 9 further includes a tail pipe 8e as shown in FIG.
This can also be done by changing the length of . That is, a bulge 8j'e is provided in a part of the tail pipe 8e, and this is partitioned by a partition wall 8k to provide a long passage and a short passage S that short-circuits this, and these can be switched by the switching valve 15. A short passage S is used when the engine speed is high, and a long passage S is used when the engine speed is low. Reference numeral 16 denotes a sensor for detecting the engine speed, and its output is sent to the computer 17 to drive the pulse motor 12t.

When it is detected that the speed has not reached the predetermined speed, the computer 17 drives the pulse motor 12 to reduce the opening degree of the variable resistance means 9, increasing the ventilation resistance and increasing the exhaust pressure. Therefore, blow-by air occurring through the exhaust lower t-hole is reduced. Conversely, when the speed of the crankshaft increases and reaches the scheduled speed, the variable resistance means 9 is operated in the same manner as above.
The degree of opening increases, reducing ventilation resistance and restoring the exhaust pressure to the expected level.

Although it is preferable that the opening degrees of the throttle valve 10 and the switching valve 15 be adjusted steplessly in accordance with the engine speed, they may be of an on-off valve type that open and close at once.

〔Effect of the invention〕

As described above, in this invention, the exhaust passage leading to the combustion chamber is made up of the performance setting part P and the auxiliary part connected thereto, and the auxiliary part is provided with resistance means for applying flow passage resistance during low speed operation of the engine. This has the effect of reducing the blow-through of fresh air that occurs when the engine is operated at a speed significantly lower than the maximum output speed, thereby enabling efficient operation.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; Fig. 1 is a partially cutaway side view of a two-row engine, and Fig. 2 is a side view of the engine.
3 is a plan view 1, FIG. 4 is a sectional view equivalent to FIG. 2 showing another embodiment, and FIG. 5 is a sectional view equivalent to FIG. 2 showing another embodiment. FIG. 6 is a pressure diagram showing the exhaust pressure near the exhaust port, and FIG. 7 is a characteristic chart showing the output characteristics of the engine. 8... Exhaust passage, P... Performance setting section, D...
- Auxiliary part, 8e...Tail pipe, 9...Variable resistance means, 12...Pulse motor. Patent applicant: Yamano Motor Co., Ltd. Agent: Masaki Yamakawa (and 2 others) Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) The exhaust passage leading to the combustion chamber is composed of a performance setting part (P) and an auxiliary part (D) connected thereto, and the auxiliary part (D) is connected to the performance setting part (P).
A two-stroke engine in which D) is provided with resistance means for applying flow path resistance during low-speed operation of the engine. (2) The two-stroke engine according to claim 1, wherein the resistance means is a throttle valve that adjusts the cross-sectional area of the flow path according to engine speed. (3) The two-stroke engine according to claim 1, wherein the resistance means is a switching valve that adjusts the length of the flow path according to engine speed.