JPH07116999B2 - Exhaust gas recirculation system for two-cycle internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas recirculation device for a two-cycle internal combustion engine.

[Conventional technology]

In a two-cycle diesel engine, an opening between the air intake valve peripheral portion located on the cylinder axis side and the valve seat and an opening between the exhaust valve peripheral portion located on the cylinder axis side and the valve seat in order to ensure good loop scavenging in the combustion chamber. A mask wall that closes when the lift amount of the air supply valve and the exhaust valve is small,
Further, there is known a two-cycle diesel engine in which an intake port and an exhaust port are extended upward in parallel with the cylinder axis (Japanese Patent Laid-Open No. 52-104613). In this two-cycle diesel engine, the supply air flowing in from the supply port heads to the piston top surface along the cylinder inner wall surface, then changes direction on the piston top surface and flows along the cylinder inner wall surface toward the exhaust port. Loop scavenging can be performed.

However, in this two-cycle diesel engine, when the lift amount of the intake valve and the exhaust valve becomes large, the opening formed between the intake valve and the valve seat opens in the combustion chamber over the entire circumference of the intake valve and becomes the exhaust valve. The opening formed between the valve seats opens in the combustion chamber over the entire circumference of the exhaust valve. As a result, the intake air that has flowed in from the opening of the air supply valve located on the cylinder axis side travels along the inner wall surface of the cylinder, and flows out into the exhaust port through the opening of the exhaust valve. Therefore, in this two-cycle diesel engine, since only a part of the intake air is used for performing the loop scavenging, there is a problem that a good loop scavenging cannot be secured.

Therefore, in order to obtain a strong loop scavenging, a mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between the intake valve and the exhaust valve, and the periphery of the intake valve located on the exhaust valve side by the mask wall. It has already been proposed by the applicant of the present invention of a two-cycle internal combustion engine in which the opening between the portion and the valve seat is closed over the full opening period of the air supply valve (see Japanese Patent Application No. 62-288390). In this two-cycle internal combustion engine, fresh air flows into the combustion chamber through the intake valve opening on the side opposite to the mask wall, then this fresh air descends along the cylinder inner wall surface below the intake valve and then reverses at the piston top surface. As a result, a strong loop scavenging can be obtained because it flows toward the exhaust valve.

However, when the strong loop scavenging is performed in this way, the combustion is improved, so that the combustion temperature rises, so that a large amount of NOx is generated. Therefore, a two-cycle internal combustion engine in which the exhaust gas engine is recirculated in the air supply passage to suppress the generation of NOx has already been proposed by the present applicant (see Japanese Patent Application No. 63-017017). This 2
In a cycle internal combustion engine, exhaust gas is recirculated in an operating region where a large amount of NOx is considered to be generated, for example, when the engine speed is above a certain level and the throttle valve opening is below a predetermined opening.

[Problems to be Solved by the Invention]

However, another problem has arisen when the combustion temperature is increased by performing strong loop scavenging, that is, the mixture is self-ignited by the high temperature residual gas.
NOx occurs when the combustion temperature rises in the presence of excess oxygen, but self-ignition occurs when the combustion temperature rises regardless of the presence of excess oxygen.Therefore, NOx generation conditions and occurrence of self-ignition The conditions are slightly different. In particular, when the air-fuel ratio is controlled to the stoichiometric air-fuel ratio, NOx can be purified by using a three-way catalyst, but the occurrence of self-ignition cannot be prevented. Therefore,
As described in No. 63-017017, even if the engine speed is equal to or higher than a certain value and the slot valve opening is equal to or lower than a predetermined opening, even if the exhaust gas is recirculated, the occurrence of self-ignition cannot always be prevented.

[Means for Solving the Problems]

In order to solve the above problems, according to the present invention, in a two-cycle internal combustion engine, an exhaust gas recirculation valve is provided in an exhaust gas recirculation passage that connects an engine air supply passage and an engine exhaust passage, and an engine load is preliminarily set. The exhaust gas recirculation valve is opened / closed to recirculate the exhaust gas into the air supply passage between the upper limit value and the lower limit value.

[Embodiment] Referring to FIG. 1, 1 is a two-cycle internal combustion engine body, 2
Is an air supply valve, 3 is an air supply port, 4 is a fuel injection valve for injecting fuel into the air supply port 3, 5 is a mechanical supercharger driven by an engine, 7 is an air supply duct, and 8 is Air supply duct 7
Throttle valve arranged inside, 9 is an air flow meter,
10 is an exhaust valve, 11 is an exhaust port, 12 is a three-way catalytic converter, 13 is an exhaust pipe, 14 is an oxygen concentration detector arranged in the exhaust pipe 13, 15 is a sub-muffler, 16 is a main muffler, 17 is an exhaust pipe Are shown respectively. A recirculation exhaust gas (hereinafter referred to as EGR) conduit 18 is branched from an exhaust pipe 17 downstream of the main muffler 16, and this EGR conduit 18 is an upstream air supply duct of the mechanical supercharger 5 and a downstream of the throttle valve 8. Connected to 7. A large number of annular cooling fins 19 are provided on the outer peripheral wall surface of the EGR conduit 18. An opening / closing valve 20 which is controlled to open / close by an output signal of the electronic control unit 30 is arranged in the EGR conduit 18.

The electronic control unit 30 includes a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, which are interconnected by a bidirectional bus 31.
It has an input port 35 and an output port 36. The output signals of the air flow meter 9 and the oxygen concentration detector 14 are input to the input port 35 via the corresponding AD converters 37 and 38, respectively. Further, the input port 35 is connected to a rotation speed sensor 21 that generates an output signal representing the engine rotation speed. Further, the output port 36 is connected to the fuel injection valve 4 and the on-off valve 20 via the corresponding drive circuits 39 and 40, respectively.

In the embodiment shown in FIG. 1, the fuel injection amount from the fuel injection valve 4 is adjusted so that the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes the stoichiometric air-fuel ratio based on the output signal of the oxygen concentration detector 14. Controlled. In a two-cycle internal combustion engine, the scavenging air flow may blow into the exhaust port 11, and in such a case, this air and exhaust gas are sufficiently mixed in the three-way catalytic converter 12, and oxygen in the air is reduced to three. Original catalytic converter 12
The oxygen concentration detector 14 is a three-way catalytic converter to detect the oxygen concentration in the exhaust gas after it has been used in the oxidation reaction in the
Located 12 downstream.

Next, the structure of the two-cycle internal combustion engine body 1 will be described with reference to FIGS. 2 and 3.

2 and 3, 50 is a cylinder block, 51 is a piston that reciprocates in the cylinder block 50,
Reference numeral 52 denotes a cylinder head fixed on the cylinder block 50, and 53 denotes a combustion chamber formed between the inner wall surface 52a of the cylinder head 52 and the top surface of the piston 51. A concave groove 54 is formed on the cylinder head inner wall surface 52a, and the air supply valve 2 is arranged on the cylinder head inner wall surface portion 52b forming the bottom wall surface of the groove 54. On the other hand, the cylinder head inner wall surface portion 52c excluding the groove 54 is substantially flat, and the exhaust valve 10 is arranged on the cylinder head inner wall surface portion 52c. The cylinder head inner wall surface portion 52b and the cylinder head inner wall surface portion 52c are connected to each other via a peripheral wall 55 of the groove 54. This groove circumferential wall 55
Is arranged very close to the periphery of the air supply valve 2 and the air supply valve 2
A mask wall 55a extending in an arc shape along the peripheral edge of the air intake valve, a fresh air guide wall 55b located between the air supply valves 2, and a fresh air guide wall located between the peripheral wall of the cylinder head inner wall surface 52a and the air supply valve 2. Five
5c and. Each mask wall 55a extends toward the combustion chamber 53 below the intake valve 2 in the maximum lift position, so that the opening between the peripheral edge of the intake valve 2 located on the exhaust valve 10 side and the valve seat 56 is small. The air supply valve 2 is closed by the mask wall 55a over the entire opening period. Further, the fresh air guide walls 55b, 55c are located in substantially the same plane, and these fresh air guide walls 55b, 55c extend substantially parallel to the line connecting the centers of both air supply valves 2. There is. The spark plug 57 is arranged on the cylinder head inner wall surface portion 52c so as to be located at the center of the cylinder head inner wall surface 52a.

FIG. 4 shows an example of the opening period of the intake valve 2 and the exhaust valve 10. In the example shown in FIG. 4, the exhaust valve 10 opens before the intake valve 2 and the exhaust valve 10 closes before the intake valve 2.

When the piston 51 descends and the exhaust valve 10 opens, the high-pressure burned gas in the combustion chamber 53 flows into the exhaust port 11. Next, when the air supply valve 2 is opened, fresh air containing fuel flows into the combustion chamber 53 from the air supply port 3, but since the mask wall 55a is provided to the opening of the air supply valve 2, the fresh air is supplied. And the fuel mainly flows from the opening of the intake valve 2 on the side opposite to the mask wall 55a to the combustion chamber 53.
Flows in. Next, this fresh air is indicated by arrow S in FIG.
The direction is changed at the top surface of the piston 51 toward the exhaust valve 10 as shown by. As a result, this scavenging air flow causes combustion chamber 53
The burnt gas inside is pushed out into the exhaust port 11, and thus loop scavenging is performed. By the way, in the embodiment shown in FIGS. 2 and 3, the mask wall 55 extending in an arc shape is formed.
The length of a is relatively long, and of the openings formed between the air supply valve 2 and its valve seat 56, approximately 1/3 of the openings located on the exhaust valve 10 side are closed by the mask wall 55a. Fresh air is supplied from approximately 2/3 of the openings located on the opposite side of 10. Further, in this embodiment, the fresh air flowing from the air supply valve 2 is the fresh air guide wall.
It is guided by 55b and 55c so as to face downward along the inner wall surface of the cylinder. Therefore, in this embodiment, when the air supply valve 2 is opened, most of the fresh air is directed to the top surface of the piston 51 along the inner wall surface of the cylinder, and thus good loop scavenging is performed.

However, if such good loop scavenging is performed, good combustion is performed, and thus the combustion temperature becomes high. As a result, the temperature of burnt gas remaining in the cylinder also rises,
Thus, the fresh air is heated by the residual burnt gas and self-ignites. When the amount of fresh air supplied to the engine cylinder is small, that is, when the engine is operating at low load, the residual gas amount is large but the residual gas temperature is relatively low, while the amount of fresh air supplied to the engine cylinder is large, that is, During high engine load operation, the residual gas temperature is high but the amount of residual gas is small. On the other hand, the temperature of the residual gas is relatively high during the medium load operation of the engine and the amount of the residual gas is relatively large, so that the temperature energy of the residual gas is the highest during the medium load operation of the engine. FIG. 6 shows the temperature T of the mixed gas of fresh air and residual gas. In FIG. 6, the horizontal axis represents the fresh air amount (intake air amount Q / engine speed N) supplied to the cylinder, that is, the load. Sixth
From the figure, it can be seen that the mixed gas temperature T is highest during the engine medium load operation. The mixed gas temperature T depends on the load Q / N, and when the mixed gas temperature T becomes higher than T ₀ , that is, the load Q / N
Is larger than the lower limit value A and smaller than the upper limit value B, self-ignition occurs. Therefore, when the load Q / N is larger than the lower limit value A and smaller than the upper limit value B, the on-off valve 20 is opened to supply the low temperature EGR gas into the air supply duct 7.

That is, as shown in FIG. 7, in step 60, the output signal of the air flow meter 9 representing the intake air amount Q and the output signal of the engine speed sensor 21 representing the engine speed N are read. Next, at step 61, it is judged if the load Q / N is larger than the lower limit value A and smaller than the upper limit value B.
If A <Q / N <B, the routine proceeds to step 62, where the on-off valve 20 is opened. If it is Q / NA or BQ / N, the routine proceeds to step 63, where the on-off valve 20 is opened.

As shown in FIG. 1, one end of the EGR conduit 18 is connected to the inside of the exhaust pipe 17 which has a substantially atmospheric pressure.
The other end of is connected to the air supply duct 7 in which negative pressure is generated. Therefore, when the opening / closing valve 20 opens, the EGR gas is recirculated in the air supply duct 7. Further, since the exhaust gas reaches the exhaust pipe 17 after passing through the sub-muffler 15 and the main muffler 16, the exhaust gas temperature in the exhaust pipe 17 is considerably lowered, and the EGR gas flows in the EGR conduit 18 having the cooling fins 19. When cooled down. Therefore, the air supply duct 7
Low temperature EGR gas will be supplied inside.

FIG. 8 (a) shows the gas composition in the cylinder when EGR gas is not supplied, and FIG. 8 (b) shows the gas composition in the cylinder when EGR gas is supplied under the same load Q / N conditions. Same load Q / N
Since the conditions are the same, the amount of fresh air is the same in FIGS. 8 (a) and 8 (b), and when EGR gas is supplied, as shown in FIG. 8 (b), part of the high temperature residual gas Is cold
Replaces EGR gas. Therefore, when the EGR gas is supplied, the mixed gas temperature T (FIG. 6) is lowered, and thus the occurrence of self-ignition can be prevented. In this embodiment, the on-off valve 20 is used as the exhaust gas recirculation valve, but a linear solenoid valve whose opening area of the valve continuously changes is used to change the EGR gas amount according to the size of the load. May be.

〔The invention's effect〕

The occurrence of auto-ignition can be prevented by recirculating EGR gas under load conditions where auto-ignition occurs.

[Brief description of drawings]

FIG. 1 is an overall view of a two-cycle internal combustion engine, FIG. 2 is a side sectional view of a two-cycle internal combustion engine body, FIG. 3 is a view showing an inner wall surface of a cylinder head, and FIG. FIG. 5, FIG. 5 is a side sectional view showing the position where the piston is lowered, FIG. 6 is a diagram showing the gas temperature in the cylinder, FIG. 7 is a flow chart for executing EGR control, and FIG. FIG. 4 is a diagram for explaining a gas composition in a cylinder. 2 ... Air supply valve, 7 ... Air supply duct, 10 ... Exhaust valve, 17 ... Exhaust pipe, 18 ... EGR conduit, 20 ... Open / close valve.

Claims (1)

[Claims] 1. In a two-cycle internal combustion engine, an exhaust gas recirculation valve is provided in an exhaust gas recirculation passage that connects an engine air supply passage and an engine exhaust passage, and an engine load has a predetermined upper and lower limit value. An exhaust gas recirculation apparatus for a two-cycle internal combustion engine, wherein the exhaust gas recirculation valve is opened during the period between so as to recirculate the exhaust gas into the supply passage.