JPH0615857B2 - Exhaust gas recirculation control device for engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas recirculation system that recirculates a part of exhaust gas into a cylinder during an intake stroke of an engine, in which exhaust gas recirculation timing is controlled. The present invention relates to a control device.

(Prior Art) Conventionally, as disclosed in, for example, Japanese Unexamined Patent Publication No. 56-148636, an engine equipped with a fuel injection device has a fuel injection valve in an intake passage communicating with a combustion chamber via an intake valve. In the low load region of the engine, by injecting fuel from the fuel injection valve in the latter half of the intake stroke, the air-fuel mixture is unevenly distributed in the upper part of the fuel chamber where the spark plug is located, and stratification is performed. There is known a technique in which a swirl is given to the intake air sucked into the air, and the swirl suppresses the diffusion of the stratified air-fuel mixture in the compression stroke to perform the stratified combustion in the explosive expansion stroke.

(Problems to be Solved by the Invention) In a fuel injection engine that performs such stratified combustion, part of the exhaust gas is recirculated into the cylinder during the intake stroke when the throttle valve opening is small and the load is low. In the case of performing so-called exhaust gas recirculation to reduce NOx in the exhaust gas, when the exhaust gas is supplied into the cylinder over the entire period of the intake stroke, as is usually done, the cylinder of the recirculated exhaust gas that has been thermally expanded Since the volume occupied in the intake air is large, the total amount of intake air is reduced and the engine output is reduced.To compensate for this, the opening of the throttle valve is corrected to the increase side. Negative pressure decreases and the cylinder pressure in the intake stroke approaches atmospheric pressure, which reduces engine pumping loss to improve output torque and reduce fuel consumption. You can

However, on the other hand, since the recirculated exhaust gas diffuses throughout the combustion chamber of the cylinder, the lower end portion of the region where the mixture of fuel and intake air is distributed and contributes to combustion, that is, the recirculated exhaust gas at the beginning of the intake stroke. The air-fuel mixture at the boundary with the recirculation exhaust region formed by the intake of the air becomes difficult to burn due to insufficient air, resulting in a problem that the generation of HC increases.

Further, since exhaust gas recirculation is performed during the entire intake stroke, the amount of exhaust gas recirculation also increases, and there is a problem that engine combustion becomes unstable.

The present invention has been made in view of the above points, and an object thereof is to appropriately set the timing of exhaust gas recirculation performed in the intake stroke of a fuel injection type engine that performs stratified charge combustion as described above, so that the air-fuel mixture is The recirculated exhaust gas is distributed between the upper part of the combustion chamber where the combustion temperature is high and the lower part of the combustion chamber that does not contribute to combustion, so that while suppressing the generation of HC, the pumping loss is effectively reduced and the engine torque is reduced. It is intended to improve NOx and reduce fuel consumption and to effectively reduce NOx with a minimum amount of recirculated exhaust gas.

(Means for Solving the Problems) In order to achieve the above object, the solution means of the present invention is such that an ignition plug and an opening of an intake passage are arranged in an upper portion of a cylinder and the spark plug is sucked into the cylinder. The swirl generating means for generating swirl in the intake air, the fuel injection control means for injecting the fuel necessary for combustion from the fuel injection valve after the middle stage of the intake stroke, and the exhaust gas supply means for supplying a part of the exhaust gas into the cylinder. In an exhaust gas recirculation control device for an engine equipped with
Exhaust gas supply control means for supplying exhaust gas by the exhaust gas supply means is provided at least during the early stage of the intake stroke when the engine is under a low load and during the period in which fuel is substantially injected by the fuel injection control means.

(Operation) With the above configuration, in the present invention, when the engine is at least under low load, the exhaust gas is supplied to the cylinder by the exhaust gas supply means at the beginning of the intake stroke and during the fuel injection period after the middle stage. , The exhaust gas is unevenly distributed in the region of the lower end of the combustion chamber in the cylinder that does not contribute to combustion and in the upper part of the combustion chamber where the air-fuel mixture is distributed, and the uneven distribution of the exhaust gas is generated in the cylinder by the swirl generating means. The throttle valve opening is increased to maintain the engine output by maintaining the intake air swirl and suppressing the filling amount of the intake air that is sucked into the combustion chamber due to the thermally expanded exhaust gas that is unevenly distributed at the lower end of the combustion chamber. To reduce the pumping loss of the engine and to reduce the combustion temperature of the air-fuel mixture by the exhaust gas unevenly distributed in the upper part of the combustion chamber to reduce NOx.
Is to reduce.

In addition, by performing exhaust gas recirculation in the intake stroke at intervals, an intake air layer is secured between the exhaust gas unevenly distributed between the lower end and the upper part of the combustion chamber, and the intake air creates a lower end of the mixture layer. The combustibility is enhanced to suppress the generation of HC.

(Example) Hereinafter, the Example of this invention is described in detail based on drawing.

In FIGS. 1 to 3, 1 is a cylinder block 2
And a cylinder 4 formed by the cylinder head 3.
An engine having 5; a piston that reciprocates in the cylinder 4; 6 a combustion chamber defined by the piston 5 in the cylinder 4; 7 an intake passage for supplying intake air into the combustion chamber 6; 8 a combustion chamber 6 are exhaust passages for exhausting the exhaust gas inside 6, and the openings 7a, 8a of the intake passage 7 and the exhaust passage 8 to the combustion chamber 6 are formed in the cylinder head 3, and the openings 7a of the intake passage 7 are Intake valve 9 that opens and closes the opening 7a
However, an exhaust valve 10 that opens and closes the opening 8a is provided in the opening 8a of the exhaust passage 8. Further, in the cylinder head 3, spark plugs 11 for igniting the air-fuel mixture in the combustion chamber 6 are attached to the side portions of the opening 7a of the intake passage 7 and the opening 8a of the exhaust passage 8, so that ignition is performed. The plug 11 and the opening 7a of the intake passage 7 are connected to the cylinder 4
It is arranged above the combustion chamber 6.

In the intake passage 7, an air flow meter 12 that detects the amount of intake air taken into the combustion chamber 6 in order from the upstream side,
The throttle valve 13 that controls the intake air amount
And a surge tank 14 that absorbs the pulsation of intake air are arranged, and the upstream end of the intake passage 7 is connected to an air cleaner 15.

Further, as shown in enlarged detail in FIGS. 2 and 3, the intake passage 7 downstream of the surge tank 14 is divided by a partition wall 16 into a primary-side intake passage 7b and a secondary-side intake passage 7c. The passage area of the secondary intake passage 7b is set smaller than that of the secondary intake passage 7c, and the primary intake passage 7b is provided.
Has a downstream end opened in the intake passage 7 slightly upstream of the intake valve 9 in the circumferential direction of the cylinder 4.
The swirl generating means 17 is configured to generate the swirl K of the intake air in the cylinder 4 by introducing the intake air flowing through the primary side intake passage 7b into the cylinder 4 in the circumferential direction while increasing the flow velocity. There is.

The downstream end of the secondary intake passage 7c opens in a direction substantially parallel to the center line of the cylinder 4, that is, toward the upper surface of the piston 5, and flows into the cylinder 4 through the secondary intake passage 7c. The swirl K is not added to the intake air. A swirl control valve 18 for controlling the strength of the swirl K by opening and closing the secondary intake passage 7c is disposed in the middle of the secondary intake passage 7c.
Is drive-coupled to an actuator (not shown), and the operation is controlled by the actuator according to the rotation speed and the load state of the engine 1. When the engine 1 is in the low speed and low load region, the swirl control valve 18 is closed,
The intake air is introduced from the primary intake passage 7b into the cylinder 4 to increase the strength of the swirl K, and the opening of the swirl control valve 18 increases as the engine 1 shifts to the high speed and high load region. The inflow ratio of the intake air from the secondary intake passage 7c is increased to weaken the strength of the swirl K in the cylinder 4.

In addition, the secondary side intake passage 7 downstream of the swirl control valve 18
A fuel injection valve 19 is disposed at c so as to inject fuel toward the combustion chamber 6, a constant fuel pressure is applied to the fuel injection valve 19, and the fuel injection valve 19 receives an input pulse. The valve opening time is changed according to the pulse width of the signal to change the fuel injection amount.

On the other hand, a catalyst 20 for purifying the exhaust gas is disposed in the middle of the exhaust passage 8, and an upstream end of an exhaust gas recirculation passage 21 is opened in the exhaust passage 8 upstream of the catalyst 20. The downstream end is opened to the primary side intake passage 7b of the intake passage 7. An exhaust gas recirculation valve 22 is disposed in the middle of the exhaust gas recirculation passage 21, and the exhaust gas recirculation valve 22 squeezes and opens the exhaust gas recirculation passage 21 and a diaphragm 24 drivingly connected to the valve body 23. And the diaphragm 2
4, the negative pressure chamber 25 defined by 4 and the negative pressure chamber 25
And a spring 26 for urging the diaphragm 24 in the valve closing direction of the valve body 23. The negative pressure chamber 25 is provided with a negative pressure source 28 via a negative pressure passage 28 provided with a duty valve 27. (Not shown). Thus, a part of the exhaust gas flowing through the exhaust passage 8 is made to flow into the primary side intake passage 7b of the intake passage 7 while the flow rate is controlled by the exhaust gas recirculation valve 22, and is supplied to the combustion chamber 6 of the cylinder 4. Supply means 29 is configured. Therefore, the swirl generating means 17 generates swirl K in the exhaust gas supplied to the combustion chamber 6 together with the intake air by the exhaust gas supply means 29.

Further, a rotary valve 30 that opens and closes the exhaust gas recirculation passage 21 is disposed in the exhaust gas recirculation passage 21 downstream of the exhaust gas recirculation valve 22. 4, the rotary valve 30 has an exhaust outlet 31a communicating with an exhaust gas recirculation passage 21 downstream of the rotary valve 30 (on the side of the primary intake passage 7b of the intake passage 7). A cylindrical valve casing 31 having the same is rotatably and airtightly fitted in the valve casing 31, and the inside thereof is communicated with an exhaust gas recirculation passage 21 upstream of the rotary valve 30 (exhaust gas recirculation valve 22nd speed). , The inside of the valve casing 3
No. 1 on the front side in the rotation direction to communicate with the exhaust outlet 31a
And a cylindrical valve body 32 having a communication hole 32a and a second communication hole 32b on the rear side thereof opened, the valve body 32 being a valve timing for adjusting the valve opening timing as shown in FIG. It is drivingly connected to the engine 1 through a variable mechanism 33, rotates the valve body 32 in synchronization with the rotation of the engine 1, and connects the first and second communication holes 32 a, 32 of the valve body 32.
The valve b is opened when the valve b matches the exhaust outlet 31a of the valve casing 31, and is opened in other states. The positional relationship between the first communication hole 32a on the front side in the rotational direction opened on the valve body 32 and the second communication hole 32b on the rear side is that the second communication hole 32b is in the middle or later of the intake stroke of the cylinder 4. Exhaust outlet 31a of valve casing 31
If it matches with the first communication hole 32a at the beginning of the intake stroke.
Is matched with the exhaust outlet 31a, in other words, both communication holes 32a and 32b are matched with the exhaust outlet 31a in the intake stroke so that the rotary valve 30 is opened twice.

The control system for controlling the operation of the combustion injection valve 19, the duty valve 27 for controlling the exhaust gas recirculation valve 22, and the variable mechanism 33 for controlling the rotary valve 30 will be described. 34 is the valve opening degree of the throttle valve 13. Is a crank angle sensor for detecting the crank angle of the engine 1 from the rotation angle of the distributor 36. The outputs of the throttle sensor 34, the crank angle sensor 35 and the air flow meter 12 are output signals thereof. Receive fuel injection valve 19,
C for controlling the duty valve 27 and the variable mechanism 33
It is input to a controller 37 having a built-in PU, and the controller 37 detects the rotational speed and load state of the engine 1 based on the crank angle signal from the crank angle sensor 35 and the airflow signal from the airflow meter 12, The basic fuel injection amount is determined by collating it with a preset fuel map, and the basic fuel injection amount is corrected according to the throttle signal from the throttle sensor 34 to determine the execution fuel injection amount, A fuel carrier control means 38 for outputting a signal of a pulse width corresponding to the execution fuel injection amount to the fuel injection valve 19 at a predetermined time after the middle stage of the intake stroke of the engine 1 to inject the fuel necessary for combustion. Is configured.

That is, the fuel injection timing is set by the fuel injection valve 19 in the opening curve of the intake valve 9 shown in FIG. 6 from the time IO when the intake valve 9 opens before the top dead center TDC to the BDC after bottom dead center.
The injection end timing θ _{E, INJ} is set around the timing at which the piston speed becomes maximum at a substantially intermediate portion of the intake stroke until the subsequent intake valve 9 is closed, and the injection end timing θ is set. _The injection start timing θ is the timing advanced by an injection angle θ _INJ corresponding to the fuel injection pulse width from _{E, INJ.
E, INJ,} and as the load of the engine 1 increases and the fuel injection pulse width increases, the injection angle θ _INJ corresponding to the pulse width increases and approximately the middle of the intake stroke. Injection start timing θ
_{E, INJ} and the injection end timing θ _{E, INJ} are changed.

Further, the controller 37 controls the valve opening degree of the exhaust gas recirculation valve 22 and the valve opening timing of the rotary valve 30 according to the load state of the engine 1, and when the engine 1 is in the low and medium load range, the exhaust gas recirculation valve 22 is controlled. And the first and second communication holes 32a and 32b of the valve element 32 of the rotary valve 30 are respectively connected to the exhaust outlet 31a at the beginning of the intake stroke and substantially during the fuel injection period by the fuel injection control means 38. By opening the rotary valve 30 in conformity with each other, the exhaust gas is supplied by the exhaust gas supply means 29 at the beginning of the intake stroke and the fuel injection timing after the middle period, while
Exhaust gas supply control means 39 is configured to stop the exhaust gas supply by opening the exhaust gas recirculation valve 22 when the engine 1 moves to the high load region.

Therefore, in the above embodiment, when the engine 1 is in the low and medium load range, the exhaust gas recirculation valve 22 is opened by the operation of the controller 37 by an opening degree corresponding to the engine load, and a part of the exhaust gas of the cylinder 4 is discharged. While being ready to be supplied into the combustion chamber 6, the first and second communication holes 32 of the valve body 32 of the rotary valve 30 are provided in the intake stroke of the cylinder 4.
a and 32b are the exhaust outlet 31a of the valve casing 31.
The rotary valve 30 is opened twice, and the exhaust gas whose flow rate is controlled by the exhaust gas recirculation valve 22 is opened by the opening of the rotary valve 30 and the fuel injection control is performed at the beginning of the intake stroke and after the middle stage. Fuel injection valve 19 by means 38
The fuel flows into the primary-side intake passage 7b of the intake passage 7 and is supplied into the combustion chamber 6 of the cylinder 4 within the fuel injection timing when the fuel is injected from. Therefore, at the end of the intake stroke, the combustion chamber 6
5, the exhaust layer Z ₁ containing the recirculated exhaust gas supplied in the early stage of the intake stroke and the fuel after the exhaust gas recirculation in the early stage of the intake stroke are sequentially provided from the lower side, as shown in FIG. Air layer Z consisting only of the intake air that was taken in before the injection was performed
₁ , an air-fuel mixture layer Z ₃ composed of a mixture of fuel injected from the fuel injection valve 19 and intake air, and an exhaust gas mixture layer Z ₄ containing recirculated exhaust gas supplied during the fuel injection period. Is formed and the inside of the combustion chamber 6 is stratified into four layers, and this stratification is strongly maintained under the swirl K generated in the combustion chamber 6 by the swirl generating means 17.

In this case, the temperature of the exhaust gas supplied to the region of the lower end of the combustion chamber 6 that does not contribute to combustion is higher than that of the intake air and is in the state of thermal expansion, so that the combustion chamber 6
The volume of the intake air is larger than that of intake air of the same mass, and the amount of intake air taken into the combustion chamber 6 after the exhaust gas recirculation in the early stage of the intake stroke is reduced, and the output of the engine 1 is reduced. The opening of the throttle valve 13 is corrected to increase so as to compensate for the decrease in the output of the engine 1. That is, in order to obtain the same engine output as in the normal case where air is sucked into the lower end of the combustion chamber 6, the throttle valve 1
3 is held open more than usual, and the correction of the opening of the throttle valve 13 lowers the intake negative pressure in the intake stroke to approach the atmospheric pressure. Becomes smaller, and the pumping loss of the engine 1 can be reduced. By reducing the pumping loss, it is possible to improve the output torque of the engine 1 and reduce the fuel consumption.

Exhaust gas is supplied during the fuel injection period after the middle of the intake stroke, and the exhaust gas has the highest combustion temperature of the air-fuel mixture in the region near the spark plug 11 located above the combustion chamber 6, that is, in the explosion expansion stroke. The combustion temperature in the above-mentioned region can be lowered by the inert exhaust gas, so that NOx can be reduced by the minimum amount of recirculation exhaust gas.
Can be effectively reduced.

Further, the exhaust gas recirculation to the combustion chamber 6 is performed in the early stage of the intake stroke and in the fuel injection period after the middle period, and the air is sucked in between the both periods, so that the air-fuel mixture in the intermediate portion in the combustion chamber 6 is sucked. Since the air layer Z ₂ containing only intake air is formed below the layer Z ₃ , the air-fuel mixture at the lower boundary of the air-fuel mixture layer Z ₃ can be completely burned under the air in the air layer Z _2. Therefore, the generation of HC can be suppressed.

When the engine 1 is in the high load range, the controller 37
The exhaust gas recirculation valve 22 is opened and the exhaust gas recirculation is stopped.

(Effects of the Invention) As described above, according to the present invention, in a fuel injection engine that performs stratified charge combustion, exhaust gas recirculation is performed at least during a low load at the beginning of the intake stroke and within the fuel injection time after the middle period. In this way, the exhaust gas is distributed to the region that does not contribute to combustion at the lower end of the combustion chamber in the cylinder and the region where the combustion temperature is the highest in the upper part of the combustion chamber. The air layer formed at the bottom enhances the combustibility of the air-fuel mixture at the lower end of the air-fuel mixture layer and suppresses the generation of HC, while the exhaust gas at the lower end of the combustion chamber suppresses the total intake air filling amount and opens the throttle valve. The engine's pumping loss can be reduced by increasing the degree of increase, and NOx can be reduced by lowering the combustion temperature of the air-fuel mixture due to the exhaust gas in the upper part of the combustion chamber, thus improving the engine torque. Further, it is possible to reduce fuel consumption and NOx at the same time.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is an overall schematic configuration diagram, FIG. 2 is a longitudinal sectional view of an essential part of an engine, FIG. 3 is a bottom view of a cylinder head, and FIG. 4 is a rotary valve. FIG. 5 is an enlarged sectional view, FIG. 5 is an explanatory view showing the gas composition in the cylinder at the end of the intake stroke, and FIG. 6 is an explanatory view showing the exhaust gas recirculation timing in the intake stroke. 1 ... Engine, 4 ... Cylinder, 6 ... Combustion chamber, 7 ...
... intake passage, 7a ... opening, 11 ... spark plug, 12 ...
… Air flow meter, 13… Throttle valve, 17
...... Swirl generating means, 19 ...... Combustion injection valve, 21 ......
Exhaust gas recirculation passage, 22 ... Exhaust gas recirculation valve, 29 ... Exhaust gas supply means, 30 ... Rotary valve, 34 ... Throttle sensor, 35 ... Crank angle sensor, 37 ... Controller, 38 ... Fuel injection control means, 39 ... Exhaust gas supply control means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Tanaka, Minoru Tanaka, No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture (56) References JP-A-56-156452 (JP, A) JP-A-52 -27903 (JP, A)

Claims (1)

[Claims] 1. A spark plug and an opening of an intake passage are provided in an upper part of a cylinder, and a swirl generating means for generating a swirl in intake air sucked into the cylinder, and an intake stroke at a low engine load. In the exhaust gas recirculation control device for an engine, which comprises fuel injection control means for injecting fuel necessary for combustion from the fuel injection valve after the middle period and exhaust gas supply means for supplying a part of exhaust gas into the cylinder, Exhaust gas recirculation control for an engine, characterized in that exhaust gas supply control means for supplying exhaust gas from the exhaust gas supply means is provided at the beginning of the intake stroke when the load is low, and substantially within the fuel injection period by the fuel injection control means. apparatus.