JPH0491317A - Two stroke engine - Google Patents

Abstract

PURPOSE:To improve a scavenging effect and prevent blowby of fresh air and fuel by opening a first exhaust valve and a second scavenging valve which are opposite to each other on the diagonal line of a cylinder at the time of the first period of scavenging and exhaust processes, and by opening a second exhaust valve and a first scavenging valve which are opposite to each other on the diagonal line of the cylinder at the time of the latter period of the scavenging and exhaust processes. CONSTITUTION:A first and a second scavenging valves 2, 3 and a first and a second exhaust valves 4, 5 are provided opposing each other while holding the center line C1 of a cylinder line therebetween. The first exhaust valve 4 and the second scavenging valve 3 which are opposite to each other on the diagonal line C3 of a combustion chamber 8, are opened having the gap of a prescribed overlap O1 (not shown) at the time of first period of scavenging and exhaust processes. On the other hand, the second exhaust valve 5 and the first scavenging valve 2 are opened having the gap of a prescribe overlap O2 (not shown) at the time of the latter period of the scavenging and exhaust processes. It is thus possible to obtain an effect of loop scavenging for pushing combustion gas in the combustion chamber, while preventing blowby of fresh air from the combustion chamber toward and exhaust port, and also prevent knocking of an engine with an improved distribution condition of fresh air and fuel in the combustion chamber.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a two-stroke engine.

(Prior art and its problems) In the case of a two-stroke engine, the scavenging boat and exhaust port overlap each other and open for a long period of time.
There is a problem in that the fuel that flows into the shilling in the form of a mixture from the scavenging boat blows through to the exhaust port without undergoing a combustion process, resulting in deterioration of fuel efficiency or exhaust emissions.

Conventionally, as a countermeasure against this problem, a scavenging valve that opens and closes the scavenging boat in synchronization with the engine rotation, and an exhaust valve that opens and closes the exhaust port in synchronization with the engine are provided. A mask wall that closes the opening, or the opening between the peripheral edge of the exhaust valve located on the cylinder axis side and the valve seat when the scavenging valve or the amount of exhaust valve glue 7F is small, is made to protrude from the combustion chamber wall of the shilling head, and is removed from the combustion chamber. In addition to preventing fresh air from blowing through, loop scavenging is performed to push out the burnt gas in the combustion chamber (see Japanese Patent Laid-Open No. 1-273872).

However, the combustion chamber structure having such a mask wall has a problem in that the effective opening area of the scavenging boat or the exhaust port is reduced, thereby reducing the scavenging effect. Further, there are problems in that the distribution of fresh air and fuel in the combustion chamber becomes uneven, and the mask wall provided on the exhaust valve side becomes overheated, leading to knocking and the like in spark ignition engines.

The present invention aims to solve these conventional problems.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a pair of first and second scavenging valves that allow fresh air pumped from the supercharger to flow into one combustion chamber, and a pair of first and second scavenging valves that In a four-valve two-stroke engine equipped with a pair of first and second exhaust valves that allow burned gas to flow out from two combustion chambers, the first exhaust valve and the second scavenging valve are located diagonally opposite each other in the combustion chamber. The valve is opened with a predetermined overlap in the first half of the scavenging and exhaust stroke, and the second exhaust valve and the second sweeping air valve, which are also located diagonally opposite each other in the combustion chamber, are opened in the second half of the scavenging and exhaust stroke. The valve is configured to open after a predetermined overlap.

(Operation) In the first half of the scavenging stroke, when both the first exhaust valve and the second scavenging valve are open, the fresh air flowing in through the second scavenging valve flows in a loop along the diagonal of the combustion chamber. Since the flow is directed toward the first exhaust valve, a loop scavenging effect is obtained in which the burned gas in the combustion chamber is pushed out to the exhaust port.

Subsequently, in the latter half of the scavenging stroke, when both the second exhaust valve and the first sweeping air valve are open, the fresh air flowing in through the first sweeping air valve flows along the diagonal line of the combustion chamber. By creating a loop-shaped flow toward the second exhaust valve, a loop scavenging effect is obtained that pushes out the burned gas in the combustion chamber toward the exhaust port.

Since the overlap period during which the first scavenging air valve and the first exhaust valve, or the second scavenging air valve and the second exhaust valve, which are located adjacent to each other and face each other in the combustion chamber, open simultaneously can be set small, This prevents fresh air from blowing from the combustion chamber to the exhaust port.

In addition, by eliminating the mask wall protruding from the combustion chamber wall, the scavenging effect can be enhanced without reducing the effective opening area of the scavenging boat or exhaust port, and the distribution of fresh air and fuel in the combustion chamber can be improved. Improves engine knocking and prevents engine knocking.

(Example) Hereinafter, an example in which the present invention is applied to a diesel engine will be described based on the accompanying drawings.

As shown in Figures 1 and 2, 2-stroke ennon 1
A combustion chamber 8 is defined by the cylinder radius 6, cylinder 10, and piston 7. A fuel injection valve 9 is provided in the cylinder head 6 facing the center of the combustion chamber 8 . The fuel injection valve 9 injects and supplies an amount of fuel depending on the opening degree of the accelerator and the engine speed.

The cylinder head 6 is provided with first and second scavenging valves 2, 3 and first and second exhaust valves 4.5 facing one combustion chamber 8. A supercharger (not shown) is provided upstream of each scavenging boat 11 that is opened and closed by the first and second scavenging valves 2 and 3, and fresh air taken in from the air cleaner is fed under pressure. An exhaust pipe (not shown) is connected to each exhaust port 12 that is opened and closed by the first and second exhaust valves 4.5, and a three-way catalyst is interposed in the middle of the exhaust pipe.

First and second scavenging valves 2 and 3 and first and second exhaust valves 4 and 5
are provided facing each other across the cylinder row center line CI, and the first sweeping air valve 2 and the second exhaust valve 5 are diagonally opposite to each other across the cylinder row center line CI.
The second scavenging valve 3 is located opposite to the upper part of the
and the first exhaust valve 4 are in a positional relationship facing each other on the diagonal Jim Cs.

First and second scavenging valves 2 and 3 and first and second exhaust valves 4 and 5
are driven by cams (not shown) provided on the cylinder head 6, respectively, and are opened and closed at predetermined timings shown in FIG. 3 in synchronization with engine rotation.

The first exhaust valve 4 and the second scavenging valve 3, which face each other on the diagonal Nt CS of the combustion chamber 8, open with a predetermined opening O8 in the first half of the scavenging stroke, and also open the combustion chamber 7.
The second exhaust valves 5 facing each other on the diagonal #i C2 of
The first exhaust valve 4 and the first exhaust valve 2 are configured to open with a predetermined overlap 02 in the latter half of the scavenging stroke, that is, the first exhaust valve 4 opens while the piston 7 is descending, and the first exhaust valve 4 opens while the piston 7 is descending. The valve closes after exceeding the point (BDC) and starting to rise.

The second scavenging valve 3 opens following the first exhaust valve 4,
In the first half of the scavenging and exhausting stroke, the first exhaust valve 4 is opened and closed with a predetermined overlap period O3.

The second exhaust valve 5 opens before the piston 7 reaches the bottom dead center, and closes while the piston 7 is rising.

The first purge valve 2 opens following the second exhaust valve 5,
In the latter half of the exhaust stroke, the second exhaust valve 5 is opened and closed with a predetermined overlap period 02.

The first scavenging valve 2 and the second exhaust valve 5, the second exhaust valve 5 and the first exhaust valve 4 each have a predetermined overlap, and the first exhaust valve 4, the second scavenging valve 3, and the second exhaust valve 5 have a predetermined overlap. And the first purge valve 2 opens at the same time, sandwiching the bottom dead center of the piston 7. These four valves 2.3.4
．． The overlap period 03 during which the valves 5 and 5 are both open is different from the overlap period 0 between the first exhaust valve 4 and the second scavenging valve 3 or the overlap period 02 between the second exhaust valve 5 and the second scavenging valve 2. It is set as small as possible within a range of 173 or less.

Next, the effect will be explained.

In the two-stroke engine 1, an explosion occurs each time the piston 7 rises, and the strokes of scavenging, compression, explosion, and exhaust are performed each time the piston 7 reciprocates once by 1 degree.

In the first half of the scavenging stroke in which the piston 7 descends, when both the first exhaust valve 4 and the second scavenging valve 3 are open, fresh air flowing in through the second scavenging valve 3 flows as shown in FIG. As shown by the arrow in FIG.
This creates a loop scavenging effect that pushes air out.

In the latter half of the scavenging stroke in which the piston 7 rises, when both the second exhaust valve 5 and the second sweeping air valve 2 are open, the fresh air flowing in through the first sweeping air valve 2 is tjSS.
As shown by the arrow in the figure, a flow toward the second exhaust valve 5 is created in a loop along the diagonal line C2 of the combustion chamber 8, and this inflow of fresh air directs the burned gas in the combustion chamber 8 to the exhaust port 12. A loop scavenging effect can be obtained by pushing out air.

In this way, the fresh air flowing in with a phase difference from the second scavenging valve 3 and the second scavenging valve 2 is directed to the diagonal line C3. of the combustion chamber 8, respectively. Since the air flows in a loop along C2, scavenging is promoted and the distribution of fresh air in the combustion chamber 8 is made uniform, thereby improving combustibility.

In addition, the overlap period in which the four valves 2, 3, 4, and 5 open simultaneously is reduced, and the second scavenging valve 3 and the second exhaust valve 5, which are located adjacent to each other, open with a large phase difference. Therefore, fresh air that has flowed in through the second scavenging valve 3 can be prevented from blowing through the adjacent second exhaust valve 5 to the exhaust port 12 via a short path.

Similarly, the first purge valves 2 located adjacent to each other
Since the first exhaust valve 4 and the first exhaust valve 4 open with a large phase difference, the fresh air that has flowed in through the first sweeping air valve 2 can be blown through the adjacent first exhaust valve 4 to the exhaust port F12 in a short path. As a result, the filling efficiency of fresh air can be increased.

During one cycle, the first exhaust valve 4 and the second exhaust valve 5 have a slight overlap, and the second scavenging valve 3 and the second scavenging valve 2 have a slight overlap. Sufficient scavenging effect can be ensured without interruption of exhaust gas outflow or fresh air inflow.

Furthermore, since the combustion gas discharged through the first exhaust valve 4 contains almost no fresh air, if this exhaust gas is made to flow through the three-way catalyst, NOx in the exhaust gas can be reduced, and CO, H 2 C can be oxidized efficiently.

Note that the present invention can be applied not only to diesel engines but also to spark ignition engines.

In this case, it is possible to improve the distribution of fresh air and fuel in the combustion chamber, eliminate the mask wall in the conventional device, suppress local overheating of the combustion chamber wall, and prevent knocking.

(Effect of the invention) As described above, according to the present invention, 2 shillings
In a 4-valve 2X) Roke engine with a pair of scavenging and exhaust valves, the first and second scavenging valves, which face each other diagonally across the shilling, are opened with a predetermined overlap in the first half of the scavenging stroke. The second exhaust valve and the second sweeping air valve, which face each other on the diagonal line of the shilling, are configured to open with a predetermined overlap in the latter half of the scavenging stroke, thereby increasing the scavenging effect and improving the new By preventing air and fuel from flowing into the exhaust port, fuel consumption and exhaust emissions of a two-stroke engine can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view of a combustion chamber showing an embodiment of the present invention, lQ2
FIG. 3 is a cross-sectional view of the engine, FIG. 3 is an angle diagram showing valve opening/closing timing, and FIGS. 4 and 5 are explanatory diagrams showing gas flow. 2...Second scavenging valve, 3...Second scavenging valve, 4
...First exhaust valve, 5...Second exhaust valve, 6.
... Schilling, 7... Piston, 8... Combustion chamber, 9
... Fuel injection valve, 10... Schilling, 11... Scavenging boat, 12... Exhaust port.

Claims (1)

[Claims] A pair of first and second scavenging valves that allow fresh air pumped from a supercharger to flow into one combustion chamber, and a pair of first and second exhaust valves that also allow burned gas to flow out of one combustion chamber. In a four-valve two-stroke engine, the first exhaust valve and the second scavenging valve, which face each other on the diagonal of the combustion chamber, are opened with a predetermined overlap in the first half of the scavenging stroke, and A two-stroke engine characterized in that a second exhaust valve and a first sweeping air valve, which face each other, are opened with a predetermined overlap in the latter half of the scavenging and exhaust stroke.