JPH06101577A - Exhaust gas recirculation device of 2-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the NOx conversion efficiency of a three-way catalytic converter from being deteriorated by an increase in the air-fuel ratio of exhaust gas caused by the blowby of fresh air in a 2-cycle engine. CONSTITUTION:An EGR port 21 is provided near the exhaust valve 14 of an exhaust port 13 in a 2-cycle engine 1, and an EGR passage 25 for connecting the EGR port 21 to an intake passage 2 and a control valve 22 for opening and closing the EGR port 21 are provided. The control valve 22 is open during the open period of an intake valve 12 and recirculates to the intake side exhaust including a large amount of blowby fresh air. Therefore, the concentration of oxygen in the exhaust flowing through a three-way catalytic converter located downstream of an exhaust passage is reduced and the conversion efficiency of NOx can be kept good. Since the control valve 22 is closed while not in the above period, fresh air is not forced to flow into the exhaust side from the intake side by pressure fluctuation in the exhaust port 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for a two-cycle internal combustion engine, and more particularly to a timed EGR system for performing exhaust gas recirculation in synchronization with the stroke of each cylinder.

[0002]

2. Description of the Related Art In a two-cycle engine, the air supply valve is opened during the scavenging process after the exhaust valve is opened, and the supply air pressurized by the scavenging pump is introduced into the cylinder to exhaust the burned gas remaining in the cylinder. Pushing out to the port. For this reason, during the scavenging period, especially after the piston bottom dead center where the cylinder is filled with fresh air, the fresh air blows directly from the air supply valve to the exhaust valve, so a large amount of fresh air is mixed in the exhaust gas. The oxygen concentration in the exhaust gas rises. When the oxygen concentration in the exhaust gas rises, the NOx conversion efficiency of the exhaust purification system using a three-way catalyst decreases, which causes a problem of deterioration of exhaust emission. In consideration of this fresh air blow-through, the amount of fuel supplied so that the exhaust reaching the three-way catalyst is near the stoichiometric air-fuel ratio and the air-fuel ratio during combustion is set to the rich side in advance in order to improve NOx purification. However, if the fuel supply is increased, the air-fuel ratio at the time of combustion becomes excessive, which may result in deterioration of fuel efficiency and reduction of engine output.

In order to solve the above problem, the exhaust gas containing a large amount of fresh air during the scavenging period is recirculated to the air supply side to increase the air-fuel ratio in the three-way catalyst without increasing the fuel supply amount. Exhaust gas recirculation (EGR) devices have been devised to prevent this. An example of this type of EGR device is described in Japanese Utility Model Laid-Open No. 3-5961.
The EGR device of the same publication is provided with a first exhaust passage through which exhaust gas during exhaust blowdown containing almost no fresh air flows and a second exhaust passage through which exhaust gas containing a large amount of fresh air flows. The exhaust passage and the air supply passage are connected by the EGR passage, and only the exhaust gas containing a large amount of fresh air is recirculated to the air supply passage.

According to the device disclosed in the above publication, the effect of keeping the air-fuel ratio of the three-way catalyst near the stoichiometric air-fuel ratio without increasing the fuel supply amount and preventing the reduction of NOx conversion efficiency can be obtained. By recirculating the exhaust gas containing the fuel gas to the charge side, the combustion temperature can be lowered and the normal external EGR effect of reducing the generation of NOx can be obtained at the same time.

[0005]

However, in the apparatus disclosed in Japanese Utility Model Laid-Open No. 3-5961, EGR is performed during execution of EGR.
Since the passage is always open, fresh air may flow from the air supply passage to the exhaust side through the EGR passage, causing a problem that the exhaust air-fuel ratio in the three-way catalyst increases (becomes leaner). .

That is, the pressure in the exhaust passage is not constant and pulsates according to the opening / closing of the exhaust valve of each cylinder, and there is a period in which the pressure in the exhaust passage becomes lower than the pressure in the supply passage. Therefore, when the pressure in the exhaust passage decreases, exhaust containing a large amount of fresh air in the supply passage and fresh air in the EGR passage flows back to the exhaust passage side, increasing the exhaust air-fuel ratio in the exhaust passage. Of.

To solve this problem, for example, EGR
It is possible to install a check valve in the passage to prevent the reverse flow of fresh air. However, if a check valve is provided, the flow resistance of the EGR passage will increase significantly, so exhaust gas containing fresh air will be sufficient. There is a problem in that the air flow cannot be made to flow and the exhaust air-fuel ratio cannot be lowered sufficiently. In view of the above problems, the present invention can prevent the reverse flow of fresh air to the exhaust side and always maintain the exhaust air-fuel ratio in the three-way catalyst near the stoichiometric air-fuel ratio.
An object of the present invention is to provide an exhaust gas recirculation device for a cycle internal combustion engine.

[0008]

According to the present invention, in a two-cycle internal combustion engine in which exhaust gas is recirculated during a cylinder scavenging period, the vicinity of the exhaust valve of each cylinder exhaust port and the engine supply passage are communicated with each other. An exhaust gas recirculation passage and a control valve for opening and closing the respective exhaust gas recirculation passage are provided, and the control valve of each exhaust gas recirculation passage is opened during the opening period of the air supply valve of the corresponding cylinder. An exhaust gas recirculation system for a two-cycle internal combustion engine is provided.

It is also possible to further provide a means for stopping the exhaust gas recirculation in the exhaust gas recirculation device so as to stop the exhaust gas recirculation when the load is light.

[0010]

[Function] Since the control valve of each exhaust gas recirculation passage is opened during the air supply valve opening period of the corresponding cylinder, the exhaust port inside the exhaust port containing a large amount of fresh air during the scavenging period and immediately after the exhaust valve is closed. Exhaust gas is returned to the air supply passage. Also, since the control valve is closed during the period when the pressure of the exhaust port drops after the exhaust valve is closed, fresh air does not flow into the exhaust port from the air supply passage side. Further, by stopping the exhaust gas recirculation when the load is light, the combustion is stabilized when the load is light.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a first embodiment of the present invention. In the figure, 1 is a two-cycle engine, 2 is a supply passage, 3 is a throttle valve, and 4 is a supercharger provided downstream of the throttle valve 3 in the supply passage 2. Further, 11 is an air supply port of each cylinder of the engine 1, 12 is an air supply valve, 13 is an exhaust port of each cylinder, 14 is an exhaust valve, and 15 is an in-cylinder fuel injection valve for directly injecting fuel into each cylinder. is there.

An EGR port 21 for taking in exhaust gas is opened on a wall surface near the exhaust valve 14 of the exhaust port 13 of each cylinder, and each EGR port 21 has an exhaust rotary valve 22.
Through the EGR manifold 24. EGR
The manifold 24 is connected to a plurality of cylinder EGR ports 21, and the exhaust gas collected here is a single EG.
It is connected to the negative pressure portion downstream of the throttle valve 3 of the air supply passage 2 through the R passage 25.

2 and 3 are views showing the structure of the exhaust rotary valve 22. As shown in FIG. As shown in FIGS. 2 and 3, the exhaust rotary valve 22 includes an EGR port 21 and an EGR manifold 2 of each cylinder.
4 and across the communication passage 26 that communicates arranged to rotate at a _^1/2 of the speed of the crank shaft 31 in synchronization with the crankshaft rotation from an engine crankshaft 31 by a timing belt 32 or the like. The exhaust rotary valve 22, and gas passage 27 which extends in the diameter direction communicating channel 26 portion of each cylinder is provided, the communication passage 26 of each cylinder whenever the rotary valve 22 is rotated _^1/2 When opened, the EGR port 21 and the EGR manifold 24 communicate with each other.

FIG. 3 shows the arrangement of the exhaust rotary valve 22 and the EGR manifold 24. FIG. 3 shows an arrangement for a three-cylinder engine, in which each cylinder is provided with three exhaust valves 14,
Three EGR ports 21 are also provided near each exhaust valve 14 for each cylinder. In this embodiment, the exhaust rotary valve 2
Each of the gas passages 27 of No. 2 is a position that connects the EGR port 21 and the EGR manifold 24 between the opening of the intake valve and the closing of the exhaust valve in the intake valve opening period of the corresponding cylinder. It is provided in.

FIG. 4 is a timing chart for explaining the relationship between the opening / closing timing of the air supply valve and the exhaust valve of each cylinder and the opening / closing timing of the exhaust rotary valve 22. In the figure, TDC and BDC respectively indicate the piston top dead center and bottom dead center of each cylinder, and EXO,
EXC opens and closes the exhaust valve 14, and IN
O and INC represent the crank rotation angles of the intake valve opening and closing, respectively.

In the two-cycle engine, when the exhaust valve opens after the explosion stroke (EXO in FIG. 4), exhaust blowdown occurs in which high-pressure burned gas in the cylinder is discharged to the exhaust port (in FIG. 4, section I). ), Exhaust port pressure rises. Next, when the intake valve opens (Fig. 4, INO), fresh air pressurized by the supercharger flows in from the intake port, and burnt gas remaining in the cylinder is pushed out from the exhaust port. (Fig. 4, Section II) is performed. Exhaust valve closed (Fig. 4, EXC)
After that, fresh air continues to flow from the air supply port, and the cylinder is filled with fresh air until the air supply valve is closed (Fig. 4, INC) (Fig. 4, Section III), and compression is performed after the air supply valve is closed. ， Each stroke of explosion is performed and the cycle is completed.

Of the above, during the blowdown process (see FIG. 4,
The exhaust gas discharged to the exhaust port in the section I) is a burnt gas, and the residual oxygen concentration is low. On the other hand, the exhaust gas discharged to the exhaust port during the scavenging process contains a large amount of burned gas at the beginning of the scavenging process and has a low oxygen concentration, but fresh air is mixed with the burned gas that is scavenged as the scavenging process proceeds. Therefore, the oxygen concentration rises. In addition, since most of the burned gas in the cylinder is discharged to the exhaust port during the blowdown stroke when the engine is running at low speed, a large amount of fresh air may be mixed with the burned gas from the beginning of the scavenging stroke.

Further, after the piston is close to the bottom dead center (BCD), the fresh air is filled into the cylinder and the difference between the cylinder internal pressure and the air supply port becomes small. The velocity decreases and blow-through of fresh air flowing out from the air supply port directly to the exhaust port occurs, and the ratio of fresh air contained in the exhaust gas increases. In particular, after the bottom dead center, since the fresh air accumulated in the upper part of the cylinder is exhausted from the exhaust valve due to the rise of the piston, the piston bottom dead center (BD
The blow-through of fresh air increases most during the period from C) to the exhaust valve closing (EXC).

In this embodiment, the exhaust rotary valve is opened between the intake valve opening and the exhaust valve closing (see FIG. 4).
In the shaded area), the exhaust containing a large amount of fresh air is recirculated to the air supply side by the blow-by. As a result, the proportion of fresh air contained in the exhaust flowing through the three-way catalyst provided downstream of the exhaust passage is reduced, and an increase in the exhaust air-fuel ratio at the three-way catalyst is prevented. Further, since the exhaust rotary valve is closed near the piston top dead center where the exhaust port pressure drops after the exhaust valve is closed, it is possible to prevent fresh air from flowing into the exhaust port from the air supply side.

Next, FIG. 5 shows another example of setting the valve opening period of the exhaust rotary valve. In the example of FIG. 5 as well, the exhaust rotary valve is opened together with the intake valve opening, but the exhaust rotary valve is kept open even after the exhaust valve is closed and closed together with the intake valve closing. This is different from the case of FIG. As described above, a large amount of fresh air is blown into the exhaust port immediately before the exhaust valve is closed, but after the exhaust valve is closed, the flow of exhaust gas disappears, so the fresh air that has flowed into the exhaust port is exhausted immediately after the exhaust valve is closed. The gas stays in the vicinity of the exhaust valve of the port, and the oxygen concentration of the exhaust gas is increased near the exhaust valve. The fresh air staying in the vicinity of the exhaust valve diffuses with the passage of time, and the oxygen concentration of the exhaust gas in the exhaust port becomes uniform and the oxygen concentration in the vicinity of the exhaust valve also decreases. By delaying the valve closing timing to near the intake valve closing timing, in addition to fresh air due to blow-by during exhaust valve opening, exhaust gas with high oxygen concentration immediately after closing the exhaust valve is also supplied to the intake side. I try to bring it to reflux.

By delaying the closing timing of the exhaust rotary valve (that is, extending the opening period) in this way, even if the negative pressure in the air supply passage is small and the difference from the exhaust port pressure is small, fresh air is supplied. It is possible to recirculate a large amount of exhaust gas containing a large amount to the supply side. In particular, as shown in FIG.
When the supercharger 4 is arranged on the downstream side of the throttle valve 3, the downstream side negative pressure of the throttle valve 3 is set to be as small as possible in order to reduce the drive loss of the supercharger 4 and improve the fuel consumption. Therefore, there is a case where the differential pressure with the exhaust port 13 cannot be sufficiently large. Even in such a case, the exhaust gas recirculation amount is reduced by decreasing the differential pressure by extending the exhaust rotary valve opening period and recirculating exhaust gas with high oxygen concentration immediately after the exhaust valve is closed to the supply side. Can be prevented.

In the embodiment of FIG. 1, the air supply port of each cylinder is communicated with the common EGR manifold 24. However, since the EGR manifold 24 is provided, the exhaust gas from each cylinder is separated into a single gas. Since the air can be returned to the air supply passage 2 via the EGR passage 25, an individual EGR for each cylinder can be obtained.
There is a benefit of eliminating the passage. Further, since the EGR manifold 24 also functions as a surge tank, for example, even if the inside of the air supply port 11 momentarily becomes negative pressure due to a pressure wave generated in the exhaust air passage immediately after exhaust blowdown, the air supply passage is It is possible to prevent fresh air from flowing from 2 to the exhaust port 13 side. Further, since the residence time of the exhaust gas is increased by providing the EGR manifold 24, the cooling effect of the EGR gas is improved, the EGR gas temperature is reduced, the rise of the in-cylinder combustion temperature is prevented, and the NOx generation amount is reduced. The usual external EGR effect can be obtained.

Next, FIG. 6 shows the configuration of the second embodiment of the present invention. In this embodiment, the exhaust rotary valve (FIGS. 1 and 22) and the EGR manifold (24) of the above-described embodiment are not adopted, and the EGR port 21 of each cylinder and the downstream portion of the throttle valve 3 of the air supply passage 2 are connected. Connect with individual EGR piping 35,
The difference is that each EGR pipe 35 is opened and closed by using a high-speed EGR valve 36. A high-speed opening / closing solenoid valve is used as the high-speed EGR valve 36, and opens / closes the EGR pipe 35 in response to a signal from an engine control circuit (not shown). Also in this embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained by setting the opening / closing timing of each high speed EGR valve 36 to the timing of FIG. 4 or 5. Further, in this embodiment, since the opening / closing timing of the high speed EGR valve 36 can be changed by the signal from the control circuit, the opening time of the high speed EGR valve 36 is adjusted according to the negative pressure and the load condition downstream of the throttle valve 3. There is an effect that an optimum EGR amount can be set according to the operating state.

Next, FIG. 7 shows the configuration of the third embodiment of the present invention. The configuration of this embodiment is substantially the same as that of the embodiment of FIG. 1, but differs from that of FIG. 1 in that an electromagnetic valve 41 for closing the EGR passage 25 is provided. In this embodiment, the solenoid valve 41 operates in response to a signal from an engine control circuit (not shown), and closes the EGR passage 25 during light load operation such as idling to close the EG.
The recirculation of EGR gas passing through the R passage 25 is blocked.

The recirculation amount of EGR gas is determined by the exhaust rotary valve 22.
However, if the cylinder intake air amount fluctuates due to fluctuations in the EGR gas recirculation amount during idling, idle rotation may become unstable. Further, in the case of performing the stratified combustion by injecting the fuel from the in-cylinder injection valve 15 into the cylinder during the compression stroke during the light load operation or the like, in order to promote the atomization of the fuel and improve the combustion state. Although it is necessary to raise the mixture temperature, a large amount of external EGR is passed through the EGR passage 25.
When the gas is supplied into the cylinder, the amount of high temperature burnt gas (internal EGR amount) remaining in the cylinder decreases, and the mixture temperature cannot be kept high.

Therefore, in the present embodiment, the electromagnetic valve 41 is closed at the time of idling or at the time of light load for performing stratified charge combustion, and the EGR gas that recirculates through the EGR passage is shut off to stabilize idle rotation and at the time of light load. Combustion is improved.
Next, FIG. 8 shows a fourth embodiment of the present invention. In the present embodiment, an exhaust throttle valve 52 is arranged in the exhaust passage 51 downstream of the EGR port 21 in the configuration of the embodiment of FIG. The exhaust throttle valve 52 has a small pressure loss when fully opened, for example, a butterfly valve is used, and is opened / closed by an electromagnetic or negative pressure actuator 52a that operates according to a signal from an engine control circuit (not shown).

In the present embodiment, the exhaust throttle valve 52 is
In response to a signal from the engine control circuit, the engine is closed to a predetermined opening when the engine speed is low (for example, 1600 rpm or less), and the exhaust passage 51 is throttled. As a result, the exhaust port pressure rises when the engine is rotating at a low speed where the fresh air blow-through increases, so that the amount of EGR gas can be increased and the oxygen concentration of the exhaust gas flowing through the three-way catalyst can be greatly reduced. .

Further, when the engine speed increases, the exhaust throttle valve 52 is fully opened, so that there is no problem such as a decrease in output due to an increase in exhaust resistance. Further, according to the present embodiment, since the exhaust port pressure rises when the EGR amount is increased, it is not necessary to set the EGR passage 25 and the exhaust rotary valve 22 to large diameters in advance, so that each component is small. There is an advantage that can be realized.

In the third and fourth embodiments, the opening timing of the exhaust rotary valve 22 is set to the timing shown in FIG. 4 or 5. Further, in the second embodiment (FIG. 6), the same effect as that of the third embodiment can be obtained by keeping the high speed EGR valve 36 closed during a light load. Similarly, also in the second embodiment, if the throttle valve similar to that shown in FIG. 8 is provided in the exhaust passage, the same effect as in the fourth embodiment can be obtained.

[0030]

As described above, according to the present invention, exhaust gas containing a large amount of fresh air due to blow-through can be recirculated to the air supply side, and fresh air from the air supply side to the air exhaust side can be recirculated. Therefore, the exhaust air-fuel ratio at the three-way catalyst is always kept near the stoichiometric air-fuel ratio and NO
The purification efficiency of x can be favorably maintained. Further, if the exhaust gas recirculation is stopped at the time of idling or at the time of light load, there is an effect that the combustion at the time of idling and at the time of light load can be favorably maintained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an exhaust rotary valve.

FIG. 3 is a diagram showing a configuration of an exhaust rotary valve.

FIG. 4 is a timing chart showing the opening timing setting of the exhaust rotary valve.

FIG. 5 is a timing chart showing another example of setting the valve opening timing of the exhaust rotary valve.

FIG. 6 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

[Explanation of Codes] 1 ... Engine 2 ... Air Supply Passage 3 ... Throttle Valve 4 ... Supercharger 12 ... Air Supply Valve 13 ... Exhaust Port 14 ... Exhaust Valve 15 ... Cylinder Fuel Injection Valve 21 ... EGR Port 22 ... Exhaust Rotary Valve 24 ... EGR manifold 25 ... EGR passage 31 ... Crankshaft 32 ... Timing belt 35 ... EGR piping 36 ... High speed EGR valve 41 ... Electromagnetic valve 51 ... Exhaust passage 52 ... Exhaust throttle valve 52a ... Actuator

Claims (2)

[Claims] 1. In a two-cycle internal combustion engine that recirculates exhaust gas during a cylinder scavenging period, an exhaust gas recirculation passage that connects the vicinity of an exhaust valve of each cylinder exhaust port with an engine air supply passage, and the respective exhaust gas recirculation passages. A control valve for opening and closing the passage is provided, and the control valve of each exhaust gas recirculation passage is opened during the opening period of the air supply valve of the corresponding cylinder. apparatus. 2. The exhaust gas recirculation system according to claim 1, further comprising means for stopping the exhaust gas recirculation during engine light load operation.