JPH086586B2 - 2-cycle internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a cylinder head with a fresh air valve and an exhaust valve.
Cycle internal combustion engine.

[Conventional technology]

Japanese Patent Publication No. 60-5770 discloses an open chamber two-cycle internal combustion engine having an intake (fresh air) valve and an exhaust valve. In this two-cycle internal combustion engine, when the piston is at the bottom dead center, the intake valve and the exhaust valve are opened almost at the same time, and the fresh air flowing from the intake valve is directed downward and is inverted at the top surface of the piston to move inside the cylinder. To form a vertical U-shaped flow. The interface between the fresh air and the exhaust is first near the intake valve, then in the lower center of the cylinder, and then towards the exhaust valve, so that exhaust and fresh air replaces the entire cylinder. Has become.

However, although such a two-cycle internal combustion engine has no problem in the high load range, it has a problem in combustion at the idle time or in the light load range. At idle or in a light load area, the amount of fresh air supplied is small and a large amount of exhaust gas remains in the cylinder.Therefore, the fresh air is dispersed and thinned in the residual exhaust gas, and the fresh air is ignited by the cylinder head. Cannot be collected near the plug. That is, in the vertically U-shaped flow in the cylinder, the main stream of fresh air moves below the cylinder. For this reason, ignition due to the ignition plug provided in the cylinder head, the generation of flame kernels is hindered, and the flame propagation speed decreases, so that misfire or combustion fluctuation easily occurs.

Further, it has been publicly known to form a swirl around the cylinder axis in the intake air. For example, US Patent No.
No. 4543928 supplies air from two intake valves arranged opposite to each other to form a swirl around the cylinder axis. The exhaust valve is arranged in a sub chamber formed in the center of the top of the cylinder. Thus, the internal combustion engine disclosed in this patent is such that combustion is initiated in the subchamber and then spread into the swirling cylinder,
It does not generate swirl in the exhaust gas or stratify the residual exhaust gas and fresh air.

The applicant of the present application has previously described that when the load including the idle is low, a part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened is re-injected into the combustion chamber while being swirled around the cylinder axis, so that the piston We proposed a two-cycle internal combustion engine that can perform stratified combustion by collecting fresh air on the cylinder head side with respect to the residual exhaust gas on the engine side (Japanese Patent Publication No.
68608 publication). In this two-cycle internal combustion engine, stratification is performed as described above when the load is low, and transverse scavenging is performed when the load is medium and high.

[Problems to be solved by the invention]

In a two-cycle internal combustion engine, exhaust gas remains in the combustion chamber because it is exhausted by scavenging as described above, and the ratio of fresh air supplied to the residual exhaust gas in the combustion chamber decreases in the idle and light load regions, resulting in combustion failure. There was a problem of becoming stable. To solve this problem, in the prior application of the present application, a part of the exhaust gas discharged from the exhaust port is re-injected into the combustion chamber while swirling around the cylinder axis, thereby stratifying the fresh air and the residual exhaust gas. Achieved and solved by collecting fresh air in the vicinity of the cylinder head. However, in a two-cycle internal combustion engine having a fresh air valve and an exhaust valve in the cylinder head, when a swirl is formed around the cylinder axis at high load, both the fresh air and the exhaust will go around the cylinder, and There was a problem that the exhaust gas on the side could not be scavenged. Therefore, it is preferable to form a swirl at low load, but it is preferable to perform transverse exhaust without forming swirl at high load, and it is preferable to change the supply characteristic of fresh air according to the load of the engine. It was revealed. In this case, if the transverse scavenging efficiency under high load is not excellent, the possibility of high output, which is a characteristic of the two-cycle internal combustion engine, is reduced.

[Means for solving problems]

A two-cycle internal combustion engine according to the present invention is a fresh air supply system having a supercharging means and a fresh air driven in synchronization with a crank angle for opening and closing a fresh air port and an exhaust port provided in a cylinder head portion. In a two-cycle internal combustion engine having a valve and an exhaust valve, a valve drive mechanism that opens the exhaust valve earlier than the fresh air valve when the piston descending speed is fast, and one of the exhaust gas discharged from the exhaust port when the exhaust valve is opened. And a means for giving a swirl to the backflow exhaust gas around the cylinder axis when the part flows back into the combustion chamber, and the fresh air supplied from the fresh air valve is slowly on the exhaust swirl at idle and at low load. And two fresh air ports are provided so as to face both sides of the cylinder axis, and the two fresh air ports are high in fresh air supplied from the two fresh air ports to the combustion chamber. The flow resistance is formed to be substantially equal so as not to form a swirl around the cylinder axis in the combustion chamber during loading, and a fresh air valve is arranged in each of the two fresh air ports. To do.

[Work]

According to the present invention, stratification is achieved as follows in a low drag band including at least idle. That is,
If the exhaust valve opens during the downward stroke of the piston, a weak exhaust blowdown occurs and the exhaust port becomes positive pressure. The exhaust blowdown ends in a short time, and the piston continues to descend, so that the inside of the cylinder becomes a load on the exhaust port, and a part of the exhaust gas that has once been exhausted reflows into the combustion chamber. In the present invention, a means for swirling the re-inflowing exhaust gas around the cylinder axis is provided so that the exhaust gas swirls around the cylinder axis within the combustion chamber. After that, the fresh air valve opens. The amount of fresh air supplied is small at idle and in the light load region, and the fresh air flows in relatively slowly. Therefore, the slowly flowing fresh air slowly rides on the exhaust gas swirling around the cylinder axis, and the fresh air gathers near the cylinder head while riding on the exhaust swirl. Therefore, there is fresh air on the cylinder head side and residual exhaust gas on the piston side, and due to this stratification, a relatively rich air-fuel mixture is gathered in the vicinity of the spark plug, so it is possible to easily ignite and burn. Of. Then, at the time of high load, the fresh air flow rate increases, so that the effect of the exhaust swirl is no longer present, and cross scavenging is possible. At this time, if the flow resistances of both fresh air ports are different,
The swirl around the cylinder axis is again formed by the flow of fresh air from the fresh air port having the stronger flow, and the scavenging efficiency is reduced. In the present invention, since the two fresh air ports are formed so that their flow resistances are substantially equal to each other, swirl cannot occur due to the mutual flow relationship, and preferable scavenging can be performed.

〔Example〕

FIG. 1 is a diagram showing a six-cylinder two-cycle internal combustion engine 10 to which the present invention is applied, FIG. 2 is a diagram showing in detail the vicinity of the combustion chamber of one cylinder shown in FIG. 1, and FIG. 3 is a diagram showing FIG. It is a vertical sectional view which passes through a fresh air valve and an exhaust valve. Engine body 10 is cylinder block 12
And a cylinder head 14, and a combustion chamber 18 is formed above the piston 16. A fresh air port 20 and an exhaust port 22 are formed in the cylinder head 14 so as to face each other, and a fresh air valve 24 and an exhaust valve 24 each of which is a poppet valve are provided.

As shown in FIG. 2, two fresh air valves 24 and two exhaust valves 26 are provided, and a spark plug 28 is provided substantially in the center of the combustion chamber 18. The exhaust valve 26 is represented by Es and E, while the fresh air valve 24 is represented by FA and FB. This shows that the functions of the fresh air valve 24 are different from each other.
The fresh air valve represented by FA is called the low load fresh air valve, and the fresh air valve represented by FB is called the high load fresh air valve.

As shown in FIGS. 1 and 2, the cylinder head
Two fresh air manifolds 30 and 32 are mounted on the 14. Each branch pipe of one fresh air manifold 30 is a low-load fresh air valve.
It is connected to the fresh air port 20 on the side where the FA is arranged, and each branch pipe of the other fresh air manifold 32 is connected to the fresh air port 20 on the side where the high load fresh air valve FB is arranged. Both fresh air ports 20 extend substantially parallel to each other in a direction substantially perpendicular to the longitudinal axis of the engine,
Further, at least the fresh air ports 20 on both sides of the center line of the cylinder, which are substantially perpendicular to the longitudinal axis of the engine, and on which the low load fresh air valve FA is arranged, are open to the combustion chamber 18 in the connecting direction. A fuel injection valve 34 is arranged in each branch pipe of the fresh air port 20 or the fresh air manifolds 30, 32. A check valve 36, which is a reed valve, is arranged upstream of the fuel injection valve 34.

As shown in FIG. 1, the air is taken in from the air cleaner 38, the flow rate is controlled by the throttle valve 40, and the supercharger 42 is supercharged. An intercooler 44 is arranged downstream of the supercharger 42, and the two fresh air manifolds 30 and 32 are both connected to the intercooler 44. As the supercharger 42, a mechanical supercharger driven by the output of an engine such as a roots pump can be used. Also,
An air flow meter 46 is arranged upstream of the throttle valve 40.

A butterfly type fresh air control valve 48 is arranged at a gathering portion of the fresh air manifold 32 on the high load side. Fresh air valve 24 and exhaust valve 26
Is driven by a camshaft in synchronization with the crankshaft of the engine, whereas the fresh air control valve 48 is opened and closed according to the load and the rotational speed of the engine. The fresh air control valve 48 is closed at low load including at least when the engine is idle,
Therefore, at this time, air is supplied only from the fresh air manifold 30 on the low load side. The fresh air control valve 48 is opened at the time of high load in the engine, so that at this time, air is supplied through both the fresh air manifold 32 on the high load side and the fresh air manifold 30 on the low load side.

As shown in FIG. 1, two exhaust manifolds 50 are provided for six cylinders, and one exhaust manifold 50 is provided.
Is connected to the 1st, 2nd, and 3rd cylinders, and the other exhaust manifold 50
Is connected to cylinders 4, 5 and 6. A catalyst 52 is arranged in a collection portion of each exhaust manifold 50, and each exhaust manifold 50 further terminates independently through each other through a muffler 54. In this case, the ignition order is the order of the first, sixth, second, fourth, third and fifth cylinders. Each exhaust manifold 50 has three branch pipes,
Therefore, one branch pipe is connected to the exhaust port 22 for one cylinder.

FIG. 2 shows one such branch pipe 50a, which is mounted approximately perpendicular to the longitudinal axis of the engine. By the way, each cylinder has two exhaust ports 22, and these two exhaust ports 22 are merged into one port in the cylinder head 14. Exhaust valve indicated with Es
The exhaust port 22 on which 26 is arranged is formed substantially at right angles to the longitudinal axis of the engine so as to be aligned with the branch pipe 50a, and opens tangentially to the combustion chamber 18. The other exhaust port 22 is joined at an angle to the exhaust port 22 on the side formed substantially at right angles to the longitudinal axis of the engine. The configuration of the exhaust port 22 is that the exhaust gas exhaust rate can be increased by having two exhaust valves 26, and the exhaust gas is exhausted to the exhaust port 22 and the exhaust manifold 50, a part of which is exhausted. When re-entering the combustion chamber 18, there is almost no re-entry from the exhaust port 22 on the angled side due to the effect of inertia flowing in a straight line.
Exhaust port 22 with exhaust valve 26 attached to
Through which the re-inflow exhaust gas can form a swirl S around the cylinder axis.

This swirl S is the clockwise direction as seen in FIG.
The (Es side) exhaust port 22 forming the swirl S faces the fresh air port 20 having the high load side fresh air valve FB in a straight line, and the fresh air valve having the low load side fresh air valve FA. The port 20 and the port 20 face each other with a center line interposed therebetween. Therefore, the low load side fresh air valve FA
When the fresh air supplied from the fresh air port 20 having a swirl by itself produces the swirl, the swirl has the same clockwise direction as the swirl S of the re-inflow exhaust gas. When the load is low, the fresh air control valve 48 is closed, so there is no fresh air flow from the exhaust port 20 on the high load side facing the exhaust port 22 that forms the swirl S, and the swirl S of the re-inflow exhaust gas is blocked. Thus, the swirl S can be retained without disappearing.

As shown in FIG. 2, the inner wall of the cylinder head 14,
That is, the mask 56 is formed on the upper wall of the combustion chamber 18. The mask 56 traverses the combustion chamber 18 substantially parallel to the longitudinal axis of the engine, with the majority of the center being formed by a sharply rising plate-like ridge, with a gentle slope at the side edges. The spark plug 28 comes to the fresh air valve 24 side. The mask 56 helps to form the swirl S. That is, the re-injected exhaust gas from the exhaust valve (E) 26 is hardly present as described above, and even if there is an inflow, it is blocked by the mask 56. The re-injected exhaust gas from the exhaust valve Es tries to swirl by itself as described above, and further, if there is a flow away from the swirl toward the center of the combustion chamber 18, this also is blocked by the mask 56. Therefore, the re-injected exhaust gas from the exhaust valve Es passes through the gently sloped region of the side edge portion of the mask 56, and gradually flows along the combustion chamber 18 and the cylindrical surface of the cylinder. Further, at the time of high load, fresh air supplied in parallel from the two fresh air ports 20 hits the mask 56, is directed downward, and is prevented from blowing through the exhaust port 22. Spark plug 28
Is on the side of the fresh air valve 24, so it is possible to contact a richer air-fuel mixture even when the load is low.

Explaining the exhaust gas pressure here, when the engine load is low, there is a weak exhaust blowdown immediately after the exhaust valve 26 is opened and the exhaust port becomes a positive pressure, and the exhaust pressure of the combustion chamber 18 drops sharply. To do. When the pressure of the combustion chamber 18 becomes lower than the pressure of the exhaust port due to the downward movement of the piston 16, a part of the exhaust gas discharged from the combustion chamber by the exhaust blowdown is burned by the pressure difference between the exhaust port 22 and the combustion chamber 18. It comes to reflow (backflow) into the chamber 18.

Thus, when the engine load is low, there is a backflow of exhaust gas into the combustion chamber immediately after a weak exhaust blowdown. In the present invention, the exhaust gas that flows back into the combustion chamber is
As shown in the figure, a swirl S is formed in the combustion chamber 18 around the cylinder axis. Conventionally, it has been proposed to generate swirl in the intake air sucked from the intake port, but generating swirl in the backflowing exhaust gas is a major feature of the present invention.

FIG. 4 is a diagram showing the valve opening engine (FO) of the fresh air valve 24 and the valve opening engine (EO) of the exhaust valve 26 which are driven in synchronization with the crankshaft. In a two-cycle internal combustion engine, the piston 16
Is an expansion process in which TDC descends from top dead center TDC to bottom dead center BDC,
There are only two compression strokes that rise from bottom dead center BDC to top dead center TDC, and exhaust and intake are at bottom dead center between these two strokes.
It is performed near the BDC, and basically, the fresh air pushed in by the supercharger 42 includes scavenging for exchanging gas while pushing out exhaust gas. When the load is high, the amount of fresh air and the amount of fuel are large. Therefore, if the gas is scavenged and reliably performed, the amount of exhaust gas remaining in the cylinder is small, so there is little problem in combustion. However, scavenging must be done reliably and efficiently. Combustion must be performed when the amount of fresh air and fuel is small and the amount of residual exhaust gas is large at the time of idling and low load, and when fresh air and exhaust are mixed, the air-fuel ratio becomes thin, making ignition combustion extremely difficult. It will be.

In the present invention, the exhaust valve 26 opens at a time 80 degrees before the bottom dead center BDC, and at this time, the descending speed of the piston 16 is fast, so that the pressure of the combustion chamber 18 after idling and the weak exhaust blowdown at low load is The back pressure of the exhaust port 22 and the negative pressure of the combustion chamber 18 ensure that a reverse flow of exhaust gas occurs. The exhaust valve 26 closes at 40 degrees after the bottom dead center BDC where the compression stroke does not proceed so much. Further, the fresh air valve 24 is opened at a time when backflow of exhaust gas occurs after the exhaust valve 26 is opened, for example, at a point of 50 degrees before the bottom dead center BDC, and the bottom dead center after the exhaust valve 26 is closed. Closes at 70 degrees after BDC.

FIG. 5 is a diagram for explaining backflow of exhaust gas and swirl generation at idling time and low load, and stratification of fresh air and residual exhaust gas generated thereby. At this time,
The intake control valve 48 is closed, and fresh air is supplied only from the low load fresh air valve (FA) 20 side. The supply of this fresh air is slow because the amount itself is small and the boost pressure is also low. As shown in FIG. 5 (a), when the temperature reaches 80 degrees before the bottom dead center BDC, the exhaust valve 26 opens and an exhaust blowdown with a weak pressure P occurs. This exhaust blowdown is completed in a short time at idle and at low load. For example, the pressure of the exhaust port 22 at the time of idling and the weak exhaust blowdown at the time of low load momentarily becomes about ² to 3 kg / cm ² ,
Immediately drops to about 1.05kg / cm ² and stabilizes while maintaining a positive back pressure.

As the piston 16 descends, the inside of the combustion chamber 18 becomes negative pressure, and the exhaust gas re-enters as shown by the arrow Q as shown in FIG. 5 (b), and the structure of the exhaust port 22, the swirl formation of the mask 56, etc. By the means, a swirl S of exhaust gas is formed in the combustion chamber 18. At 60 degrees before bottom dead center BDC, the low load fresh air valve (FA20) opens. Fresh air is metered by the throttle valve 40, and the supercharging pressure of the supercharger 42 is also relatively low. In addition, since it takes time for the fresh air valve 24 to substantially fully open, fresh air does not immediately flow in, and exhaust gas backflow and swirl formation do not occur even when the low-load fresh air valve (FA20) is opened. in the process of. Thus, the formation of the exhaust swirl continues for a considerable time, and since the swirl is formed around the cylinder axis, it is maintained without disappearing until the end of the compression stroke.

Thereafter, as shown in FIGS. 5 (c) and 5 (d), when the fresh air valve 24 is substantially fully opened, fresh air comes in. At this time, the descending speed of the piston 16 is also small, so that almost no negative pressure is formed in the combustion chamber and the supercharging pressure is small as described above, so that the fresh air slowly flows into the combustion chamber.
Enter 18. Therefore, the inflowing fresh air slowly rides on the exhaust swirl and is supplied so as to rotate in the same direction as described above, and thus swirls together with the exhaust swirl on the exhaust swirl. In this way, the fresh air gathers at a portion of the cylinder head 14 side close to the spark plug 28 side,
That is, stratification of fresh air on the cylinder head 14 side and exhaust air on the piston 16 side is achieved. This stratification of the fresh air and the exhaust gas, as shown in FIG. 5 (e), the piston 16 descends to the bottom dead center, then rises slightly and the exhaust valve 26 closes, and the fresh air valve 24 closes. Is also maintained. Incidentally, even if the piston 16 goes up after passing through the bottom dead center, the movement speed is slow for a while, and the catalyst 52 provided in each exhaust manifold 50 prevents the pressures of the exhaust port 22 and the exhaust manifold 50 from decreasing. Outflow of fresh air from the combustion chamber 18 to the exhaust port 22,
So-called breath of fresh air hardly occurs. Also,
It has been confirmed that the catalyst 52 provided in each exhaust manifold 50 has a function of emitting a pressure at the time of exhaust blowdown, and this reflected pressure is after the piston 16 passes through the bottom dead center and starts to rise. A back pressure is applied to the combustion chamber 18 to effectively prevent blow-through of fresh air. In order to make full use of this effect, it is necessary to prevent the exhaust valve 26 from overlapping the valve opening timing, and thus, as shown in FIG. 1, the exhaust manifold 50 and the catalyst 52 are respectively provided. It is preferable to provide them. The fuel is injected while the fresh air valve 24 is open.

At the time of idling and at the time of light load, the air-fuel mixture gathers in the portion near the ignition plug 28 side of the cylinder head 14 side as described above, so that the air-fuel ratio does not become thin near the ignition plug 28, and the ignition plug 28 easily Ignition ensures that combustion is obtained. Then, this air-fuel mixture is placed on the exhaust gas, is activated by the high-temperature exhaust gas, forms an active heat atmosphere state containing radical fuel components, and burns in a state where ignitability is enhanced. It can be done.

Since the fresh air control valve 48 is opened during medium and high load, fresh air is supplied through both fresh air valves 24, and in particular, a large amount of air can pass through the fresh air port FB24 on the high load side. Like In this way, when the amount of fresh air increases, the swirl effect of the re-inflow exhaust gas disappears, and a large amount of fresh air is used for cross-scavenging. At this time, since the mask 56 crosses the center of the cylinder head 14, the fresh air supplied toward the exhaust port 22 hits the mask 56 and flows downward, and eventually the fresh air first flows downward and then the piston. It hits 16 and turned upward, and scavenging was performed with a U-shaped flow. At this time, if there is a difference in the flow strengths of the two fresh air ports 20, the swirl around the cylinder axis will be formed again by being pushed by the dominant direction. At high load, the scavenging efficiency cannot be enhanced by such a swirl around the cylinder axis, and in particular, the effect of the U-shaped transverse scavenging cannot be exhibited. Therefore, in the present invention, the two fresh air ports 20 are formed so that their flow resistances are substantially equal.

The first means for making the flow resistances approximately equal is to make the cross-sectional areas of both fresh air ports 20 approximately equal. This is not only preferable for increasing the transverse scavenging efficiency at high load, but also convenient for slowly supplying from the fresh air valve (FA) on the low load side at low load. In other words, when the load is low, the amount of air required is much smaller than that when the load is high. Therefore, it is preferable to form the fresh air valve (FA) and its fresh air port, which can be said to be dedicated to low load, to be small. By making it larger than it seems necessary (as much as the FB on the high load side), the cross-sectional area can be increased, thus helping to feed slowly. A second means for making the flow resistances substantially equal is to form the wall structure near the valve seat of the mask 56 and the fresh air valve 24 to be substantially equivalent to both fresh air ports 20. The means for making the flow resistances substantially equal is constituted by appropriately combining these first and second means and the like. However, it is preferable that the side edges of the mask 56 have the propeller blade-like upper and lower sides (Es side) and the lower side (E side) inclining to form an exhaust swirl, that is,
The part marked with an arrow S is a gentle slope, but the slope becomes steep when the ridgeline is crossed, whereas the lower side goes from FA to the ridgeline at a gentle slope and then descends at a steep slope. In such a case, the resistance of the fresh air flowing into the combustion chamber 18 from the fresh air port 20 on the high load side becomes larger, so the fresh air port on the low load side is made slightly smaller. Alternatively, the valve lift of the fresh air valve 24 may be slightly reduced.

〔The invention's effect〕

As described above, according to the present invention, it is possible to achieve the stratification between the fresh air and the residual exhaust gas at the time of idling and at the time of low load to perform the firing reliably, and to perform the transverse scavenging at the time of the high load. It is possible to obtain a two-cycle internal combustion engine that can obtain high output and can perform good combustion from low load to high load.

[Brief description of drawings]

FIG. 1 is a diagram showing a six-cylinder two-cycle internal combustion engine to which the present invention is applied, FIG. 2 is a diagram showing in detail the vicinity of the combustion chamber of one cylinder of FIG. 1, and FIG. 3 is a new diagram of FIG. FIG. 4 is a vertical sectional view passing through an air valve and an exhaust valve, FIG. 4 is a diagram showing valve timing, and FIG. 5 is an explanatory diagram for explaining stratification at low load. 14 ... Cylinder head, 16 ... Piston, 18 ... Combustion chamber, 20 ... Fresh air port, 22 ... Exhaust port, 24 ... Fresh air valve, 26 ... Exhaust valve, 42 ... Supercharger, 48: Fresh air control valve, 56: Mask.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tokuhiko Nakamura 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Corporation (56) Reference JP-A-56-44404 (JP, A) JP-A-62-291427 (JP, A) JP 60-5770 (JP, B2)

Claims (1)

[Claims] 1. A fresh air supply system having a supercharging means, and a fresh air valve and an exhaust valve driven in synchronization with a crank angle to open and close a fresh air port and an exhaust port provided in a cylinder head portion. And a valve drive mechanism that opens the exhaust valve earlier than the fresh air valve when the piston descending speed is fast, and a part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened in the combustion chamber. And a means for giving a swirl to the backflow exhaust gas around the cylinder axis when the air flows back to the exhaust gas so that the fresh air supplied from the fresh air valve slowly flows into the exhaust swirl at idle and at low load. And two fresh air ports are provided so as to face both sides of the cylinder axis.
The fresh air supplied from the two fresh air ports to the combustion chamber is formed to have almost equal flow resistance so as not to form a swirl around the cylinder axis in the combustion chamber under high load. A two-stroke internal combustion engine, characterized in that a fresh air valve is arranged in each of the.