JP3477806B2 - Diesel engine exhaust purification system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine.

[0002]

2. Description of the Related Art The air-fuel ratio of inflowing exhaust gas is lean.
NO when_XAnd the air-fuel ratio of the inflowing exhaust gas is
NO absorbed when stoichiometric or rich_XEmit
NO _XPlace the absorbent in the engine exhaust passage and place it in the combustion chamber.
During normal operation when the average air-fuel ratio is lean
NO in the exhaust gas emitted from the engine_XNO_XAbsorbent
Absorbed by NO_XAbsorbent to NO_XWhen to release
Reduces the amount of intake air supplied to the combustion chamber and
The average air-fuel ratio in the combustion chamber is increased by increasing the fuel injection amount.
A diesel engine that has been switched from rich to rich
Known (see PCT International Publication WO93 / 07363)
See).

[0003]

By the way, if the intake air amount is decreased and the fuel injection amount is increased as in the diesel engine, the average air-fuel ratio in the combustion chamber can be made rich, but the intake air amount is simply changed. When the fuel injection amount is decreased and the fuel injection amount is increased, the output torque of the engine changes. That is, if the intake air amount is decreased, the output torque of the engine is reduced, and if the fuel injection amount is increased, the output torque of the engine is increased, but the decrease amount of the output torque and the increase amount of the output torque at this time are the same. Unless otherwise set, the output torque will fluctuate.

However, in the above-described diesel engine, the intake air amount is decreased and the fuel injection amount is increased at the same time for the purpose of merely switching the average air-fuel ratio in the combustion chamber from lean to rich. No consideration is given to fluctuations in output torque. As a result, in this diesel engine, the amount of intake air is reduced to release NO _X from the NO _X absorbent, and the output torque fluctuates when the fuel injection amount is increased.

[0005]

In order to solve the above problems, according to the present invention, when the air-fuel ratio of the inflowing exhaust gas is lean, NO _x is absorbed and the air-fuel ratio of the inflowing exhaust gas is increased. An NO _X absorbent that releases absorbed NO _X when it becomes stoichiometric or rich is placed in the engine exhaust passage, and the average air-fuel ratio in the combustion chamber is lean. In the exhaust gas discharged from the engine during normal operation NO _X is NO _X
Is absorbed in the absorber, in the diesel engine is switched from the average air-fuel ratio is lean to the stoichiometric air-fuel ratio or rich in the combustion chamber to when releasing the NO _X from _the NO _X absorbent, it should be released NO _X from _the NO _X absorbent An air amount reducing means for reducing the amount of air supplied to the combustion chamber at times, and a calculating means for calculating the additional fuel amount required to increase the engine output torque by the amount of decrease in the engine output torque due to the reduction of the air amount. , And a fuel amount increasing means for increasing the amount of fuel supplied into the combustion chamber by this additional fuel amount.

Further, according to the present invention, in order to solve the above problems, NO _X is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or rich. NO that releases the absorbed NO _x
The _X absorbent disposed in an engine exhaust passage, NO _X in the exhaust gas discharged from the engine during normal operation of the average air-fuel ratio has become lean in the combustion chamber is absorbed in the NO _X absorbent, NO _X absorption In a diesel engine in which the average air-fuel ratio in the combustion chamber is switched from lean to stoichiometric air-fuel ratio or rich when NO _X is to be released from the agent, NO _X absorbent is placed in the exhaust passage of each cylinder. one of NO and air amount decreasing means for reduction the amount of air from the _X absorbent is supplied to the combustion chamber of the linked cylinder to the one of NO _X absorbent when releasing the NO _X, engine according to reduction of the air amount Fuel amount increasing means for increasing the amount of fuel supplied to the combustion chambers of the remaining cylinders in order to increase the engine output torque by the amount of decrease in output torque is provided.

[0007]

In the first aspect of the invention, when the NO _X absorbent should release NO _X , the amount of air supplied to the combustion chamber is reduced, and at this time, the engine output torque is reduced by the amount of reduction in the engine output torque due to the reduction of the air amount. The engine output torque does not fluctuate because the fuel required to raise the temperature is additionally supplied.

In the second aspect of the invention, when NO _X is to be released from any one of the NO _X absorbents, the amount of air supplied to the combustion chamber of the cylinder connected to that NO _X absorbent is reduced. Since the amount of fuel supplied to the combustion chambers of the remaining cylinders is increased in order to increase the engine output torque by the amount of decrease in the engine output torque due to the decrease in the amount, the engine output torque does not fluctuate. Further, in the second aspect of the invention, the combustion deteriorates only in the cylinder in which the amount of air supplied to the combustion chamber is reduced, and good combustion is obtained in the remaining cylinders in which the amount of fuel is increased.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is a diesel engine body, 2 is a piston, 3 is a combustion chamber, 4 is a fuel injection valve, 5 is an intake valve, 6 is an intake port, 7 is an exhaust valve, 8 is an exhaust port. Are shown respectively. Intake port 6 corresponds to corresponding intake manifold 9
An intake control valve 12 is arranged in the intake duct 10 and is connected to the air cleaner 11 via the intake duct 10. The intake control valve 12 is opened / closed by an actuator 13 such as a step motor. On the other hand, the exhaust port 8 is connected via an exhaust manifold 14 and an exhaust pipe 15 to a casing 17 containing a NO _x absorbent 16, and an exhaust pipe 18 connected to the outlet side of the casing 17.
A temperature sensor 19 for detecting the exhaust gas temperature is arranged inside.

From the exhaust manifold 14, a recirculation exhaust gas (hereinafter referred to as EGR gas) conduit 20 is branched, and this E
The GR gas conduit 20 is the intake duct 1 downstream of the intake control valve 12.
Concatenated within 0. An EGR control valve 21 driven by, for example, a step motor is arranged in the EGR gas conduit 20. When the EGR control valve 21 is opened, the exhaust gas in the exhaust manifold 14 is supplied into the intake duct 10 via the EGR gas conduit 20, and the exhaust gas supplied into the intake duct 10, that is, EGR gas, flows through the intake manifold 9. It is distributed to each cylinder via.

The electronic control unit 30 comprises a digital computer, and a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 which are mutually connected by a bidirectional bus 31. And an output port 36. The temperature sensor 19 generates an output voltage proportional to the exhaust gas that has passed through the NO _X absorbent 16, and this output voltage is input to the input port 35 via the AD converter 37.
Further, a load sensor 41 that generates an output voltage proportional to the depression amount of the accelerator pedal 40 is provided, and the output voltage of the load sensor 41 is input to the input port 35 via the AD converter 38. Further, the input port 35 is connected to a rotation speed sensor 42 that generates an output pulse representing the engine rotation speed. On the other hand, the output port 36 is connected to the fuel injection valve 4, the actuator 13 and the EGR control valve 21 via the corresponding drive circuit 39.

The fuel injection amount Q from the fuel injection valve 4 is controlled based on the depression amount L of the accelerator pedal 40 and the engine speed N, as shown in FIG. Note that, in FIG. 2, the solid lines Q ₁ , Q ₂ , Q ₃ ... (Q ₁ <Q ₂ <Q ₃ ) represent equal injection amounts. Therefore, as can be seen from FIG. It increases as the depression amount L of the engine increases, and decreases as the engine speed N increases.
The relationship between the fuel injection amount Q, the depression amount L of the accelerator pedal 40, and the engine speed N shown in FIG. 2 is stored in the ROM 32 in advance.

On the other hand, the intake control valve 12 is normally kept fully open.
Therefore, the inside of the intake duct 10 is usually almost atmospheric air.
It is pressure. On the other hand, the average pressure in the exhaust manifold 14
The force is higher than atmospheric pressure and therefore the EGR control valve
When the valve 21 opens, the pressure in the exhaust manifold 14 and the intake
Due to the pressure difference from the pressure in
It is supplied into the ct 10. EGR as shown in FIG.
The opening degree S of the control valve 21 is the depression amount L of the accelerator pedal 40.
And is controlled based on the engine speed N, as shown in FIG.
In addition, this EGR control valve 21 is fully operated during engine low speed and low load operation.
When opened, the engine is under high load operation or high speed engine operation
Can be fully closed. In addition, these EGR control valves 21
The opening degree of the EGR control valve 21 is between the fully open region and the fully closed region.
S₁, S ₂, S₃Gradually increases from the fully open area to the fully closed area
Becomes smaller (S₁> S₂> S₃).

[0014] EGR induced to recycle into the combustion chamber 3 in order to suppress the generation of the NO _X in a diesel engine
It is preferable to increase the amount of gas as much as possible. However, if the EGR gas amount is increased too much, the excess air ratio becomes too small and combustion deteriorates. Therefore, the EGR gas amount is normally increased as much as possible within the range where combustion is not deteriorated. By the way, the excess air ratio is large during engine low speed and low load operation, and thus a large amount of EGR gas can be recirculated at this time. On the other hand, the average pressure in the exhaust manifold 14 is low during low-speed, low-load operation of the engine. Therefore, in order to recirculate as much EGR gas as possible at this time, as shown in FIG.
The GR control valve 21 is fully opened.

On the other hand, since the excess air ratio is small during engine high load operation, recirculation of EGR gas at this time deteriorates combustion. Therefore, as shown in FIG. 3, the EGR control valve 21 is fully closed during engine high load operation. Further, the average pressure in the exhaust manifold 14 becomes high during high-speed operation of the engine. Therefore, if the EGR control valve 21 is opened at this time, the recirculation amount of EGR gas becomes excessive. Therefore, when the engine is operating at high speed, as shown in FIG.
1 is fully closed. As can be seen from FIG. 3, the opening degree S of the EGR control valve 21 is decreased as the engine load increases or the engine speed increases during engine medium load operation or engine medium speed operation. Thus EG
The opening degree S of the R control valve 21 is controlled according to the depression amount L of the accelerator pedal 40, that is, the engine load and the engine speed N, but the excess air ratio is 1.0 regardless of the engine load and the engine speed. That is all. That is, the average air-fuel ratio in the combustion chamber 3 is lean regardless of the engine load and the engine speed.

Returning again to FIG. 1, the NO _x absorbent 16 contained in the casing 17 uses, for example, alumina as a carrier, and potassium K, sodium Na,
Lithium Li, cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, and one at least has rare earth such as yttrium Y, and a noble metal such as platinum Pt It is carried. Engine intake passage and NO _X ratio of the absorbent 16 the exhaust passage upstream of the supply air and fuel into the (hydrocarbon) of Toko called air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 16 _the NO _X absorbent 16 air-fuel ratio of the inflowing exhaust gas is absorbed NO _X when the lean, the oxygen concentration in the inflowing exhaust gas is performed to absorbing and releasing action of the NO _X that releases NO _X absorbed and decreases. In addition, when fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NO _x absorbent 16, the air-fuel ratio of the inflowing exhaust gas coincides with the average air-fuel ratio in the combustion chamber 3, and therefore in this case. The NO _X absorbent 16 is NO when the average air-fuel ratio in the combustion chamber 3 is lean.
_{When X} is absorbed and the oxygen concentration in the combustion chamber 3 decreases, the absorbed NO _X is released. In a diesel engine as shown in FIG. 1, the excess air ratio is usually 1.0 or more in all operating states, that is, the average air-fuel ratio in the combustion chamber 3 is burned in a lean state. Therefore, the NO _X discharged at this time is absorbed by the NO _X absorbent 16.

If the above-mentioned NO _X absorbent 16 is arranged in the engine exhaust passage, this NO _X absorbent 16 actually performs NO _X absorption and release, but the detailed mechanism of this absorption and release is not clear. There is also. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking the case where platinum Pt and barium Ba are supported on the carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, in a diesel engine, a large amount of oxygen exists in the exhaust gas, and these oxygen O ₂ adheres to the surface of platinum Pt in the form of O ₂ ⁻ or O ^{2 −} as shown in FIG. 4 (A). To do. On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O 2
₂ → 2NO ₂ ). Next, a part of NO ₂ produced is absorbed on the platinum Pt while being absorbed in the absorbent and combined with barium oxide BaO to be absorbed in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 4 (A). Diffuses in the agent. In this way, NO _X is absorbed in the NO _X absorbent 16.

The oxygen concentration in the inflowing exhaust gas is generated NO ₂ on the surface of as high as platinum Pt, as long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- Is generated. In contrast the reaction with the amount of NO ₂ oxygen concentration is lowered in the inflowing exhaust gas is lowered backward (NO ₃ ^- → NO ₂₎ proceeds to, thus nitrate ions to the absorber NO ₃ ^- Are released from the absorbent in the form of NO ₂ . That, NO _X from _the NO _X absorbent 16 when the oxygen concentration decreases in the inflowing exhaust gas is to be released. In this case, if the lean degree of the average air-fuel ratio in the combustion chamber 3 becomes low, the oxygen concentration in the inflowing exhaust gas decreases, so that if the lean degree of the average air-fuel ratio in the combustion chamber 3 becomes low, the average air-fuel ratio becomes the NO _X from _the NO _X absorbent 16 even lean is released within 3.

On the other hand, at this time, the average empty space in the combustion chamber 3
When the fuel ratio is made rich, a large amount of unburned HC, CO is emitted from the engine.
Are discharged, and these unburned HC and CO are oxygen on platinum Pt.
O₂ ^-Or O^2-It reacts with and is oxidized. Also burning
Exhaust gas when the average air-fuel ratio in the combustion chamber 3 becomes rich
NO from the absorbent due to the extremely low oxygen concentration in the ₂
Is released and this NO₂As shown in FIG.
It is reduced by reacting with unburned HC and CO. like this
NO on the surface of platinum Pt₂Sucks when no longer exists
NO from collecting agent to another₂Is released. Thus burning
If the average air-fuel ratio in chamber 3 is made rich, it will take a short time.
Later NO_XAbsorbent 16 to NO_XWill be released
It

That is, when the average air-fuel ratio in the combustion chamber 3 is made rich, first, unburned HC and CO immediately react with O ₂ ⁻ or O ^{2 −} on platinum Pt to be oxidized, and then on platinum Pt. or O ^2- is still unburned HC be consumed, CO remains if this unburned HC, NO _X discharged from the released NO _X and the engine from the absorbent by CO is allowed reduction ^- O ₂ of To be Therefore NO _X that is absorbed in the NO _X absorbent 16 in a short time if the average air-fuel ratio in the combustion chamber 3 rich is released, yet the atmosphere to the released NO _X is reduced To NO _X
Will be prevented from being discharged. Further, since the NO _X absorbent 16 has the function of a reduction catalyst, the NO _X released from the NO _X absorbent 16 can be reduced even if the average air-fuel ratio in the combustion chamber 3 is changed to the stoichiometric air-fuel ratio. However to release all NO _X that is absorbed in the NO _X absorbent 16 to NO _X from _the NO _X absorbent 16 is not only released gradually in the case where the average air-fuel ratio in the combustion chamber 3 to the stoichiometric air-fuel ratio Takes a little longer.

As described above, in the diesel engine, the average air-fuel ratio in the normal combustion chamber 3 is lean, so when the engine is operated, NO _X is absorbed by the NO _X absorbent 16. However there is a limit to the NO _X absorbing capacity of the NO _X absorbent 16, _the NO _X absorbent 16 when saturation NO _X absorbing capacity of the NO _X absorbent 16 is not E longer absorb NO _X. Therefore NO _X absorbing capacity of the NO _X absorbent 16 needs to release NO _X from _the NO _X absorbent 16 before saturation. Therefore, in the embodiment according to the present invention, when the NO _X absorbent 16 has absorbed a certain amount of NO _X , the average air-fuel ratio in the combustion chamber 3 is made rich, whereby NO _{X is} generated.
NO _X is released from the absorbent 16. Therefore, a method for increasing the average air-fuel ratio in the combustion chamber 3 in order to release NO _X from the NO _X absorbent 16 will be described next.

The opening S of the EGR control valve 21 when the depression amount L of the accelerator pedal 40 is changed during low speed operation of the engine.
Is shown by the broken line in FIG. As described above, the EGR control valve 21 is fully opened during the engine low load operation (region I in FIG. 5) and fully closed during the engine high load operation (region III in FIG. 5). It can be seen that at time (region II in FIG. 5), the opening degree S is decreased as the engine load increases. On the other hand, the intake control valve 12 is held in the fully open state regardless of the operating state of the engine as shown by the broken line in FIG.

On the other hand, the solid line in FIG. 5 indicates the NO _x absorbent 1.
6 shows a case where the average air-fuel ratio in the combustion chamber 3 is made rich in order to release NO _X from 6. As can be seen from FIG. 5, when the average air-fuel ratio in the combustion chamber 3 is made rich, the intake control valve 12 is closed by Δθ and the EGR control valve 21 is increased in opening S by ΔS.
Although not shown in FIG. 5, at the same time, the fuel injection amount Q is increased by ΔQ. That is, when the intake control valve 12 is closed, the amount of intake air supplied into the combustion chamber 3 decreases, so the average air-fuel ratio in the combustion chamber 3 decreases, and the opening S of the EGR control valve 21 increases. For example, since the EGR gas amount increases and the intake air amount decreases, the average air-fuel ratio in the combustion chamber 3 decreases, and if the fuel injection amount Q is increased, the average air-fuel ratio in the combustion chamber 3 will naturally be increased. Becomes smaller. Therefore, in the present invention, the average air-fuel ratio in the combustion chamber 3 is made rich by controlling the intake control valve 12, the EGR control valve 21, and the fuel injection amount Q.

In a diesel engine, when the intake air amount is reduced to make the average air-fuel ratio in the combustion chamber 3 rich, combustion deteriorates and the output torque of the engine decreases. Therefore, if the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich by reducing the intake air amount, a shock will occur. Therefore, in the embodiment according to the present invention, when the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich by reducing the intake air amount, the engine output torque is increased by the decrease amount of the engine output torque due to the reduction of the intake air amount. Is calculated, and the injected fuel amount is increased by this additional fuel amount ΔQ. In this way, even if the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich, the output torque of the engine does not change, and thus it is possible to prevent a shock from occurring.

Next, the rich control of the average air-fuel ratio will be described in more detail with reference to FIG. As shown in FIG. 5, during the engine low load operation I, the EGR control valve 21 is fully opened. Therefore, at this time, the EGR control valve 2 is opened.
The average air-fuel ratio in the combustion chamber 3 cannot be reduced by controlling 1. Therefore, at this time, the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich by decreasing the opening degree θ of the intake control valve 12 from the fully open state by Δθ and simultaneously increasing the fuel injection amount Q by ΔQ. The increase amount ΔQ of the fuel injection amount Q is an amount required to increase the engine output torque by the amount of decrease in the engine output torque due to the closing action of the intake control valve 12.
Therefore, as described above, no shock occurs even if the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich.

On the other hand, during engine high load operation III, the excess air ratio is small. Therefore, at this time, the average air-fuel ratio in the combustion chamber 3 can be switched from lean to rich by controlling only the EGR gas amount. Therefore, at this time, the intake control valve 12 is held in the fully open state and the EG
By opening the R control valve 21 and increasing the fuel injection amount Q by ΔQ, the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich. In addition,
At this time, the increase amount ΔQ of the fuel injection amount Q is equal to the EGR control valve 2
This is the amount required to increase the engine output torque by the amount of decrease in the engine output torque due to the valve opening action of No. 1.

On the other hand, during the engine medium load operation II, the intake control valve 12 is closed by Δθ, the opening degree S of the EGR control valve 21 is increased by ΔS, and the fuel injection amount Q is increased by ΔQ. . At this time, the increase amount ΔQ of the fuel injection amount Q is determined by the closing action of the intake control valve 12 and the EGR control valve 2
This is the amount required to increase the engine output torque by the amount of decrease in the engine output torque due to the valve opening action of No. 1.

The opening amount ΔS of the EGR control valve 21 when NO _X should be released from the NO _X absorbent 16 and the intake control valve 12
The valve closing amount Δθ and the increase amount ΔQ of the fuel injection amount Q are obtained by experiments in advance, and as a function of the depression amount L of the accelerator pedal 40 and the engine speed N, respectively, as shown in FIG.
It is stored in advance in the ROM 32 in the form of maps shown in (B) and (C).

By the way, as described above, the NO _X absorbent 16
It is necessary to release NO _X before the NO _X absorption capacity is saturated. For that purpose, it is necessary to estimate how much NO _X is absorbed in the NO _X absorbent 16,
Next, a method for estimating the NO _X absorption amount will be described. When the average air-fuel ratio in the combustion chamber 3 is lean, the higher the engine load, the larger the amount of NO _X discharged from the engine per unit time, so the NO _X absorbent 1 per unit time is increased.
6 _the amount of NO _X absorbed increases, the addition NO _X to NO _X amount exhausted from the more per unit time engine the engine speed increases is absorbed in a unit time between per _the NO _X absorbent 16 in order to increase Will increase. Thus _the amount of NO _X absorbed in unit time per _the NO _X absorbent 16 becomes a function of the engine load and the engine speed. In this case, the engine load is the accelerator pedal 40.
_The amount of NO _X can be represented with at amount of depression L absorbed in unit time per _the NO _X absorbent 16 since it of the amount of depression function of L and the engine rotational speed N of the accelerator pedal 40. Therefore, in the embodiment according to the present invention, NO _X per unit time
The NO _X amount NOXA absorbed by the absorbent 16 is previously obtained as a function of the depression amount L of the accelerator pedal 40 and the engine speed N, and this NO _X amount NOXA is a function of L and N of the map shown in FIG. ROM32 in the form
It is stored in. As described above, when the average air-fuel ratio in the combustion chamber 3 is lean, the NO _X absorption amount per unit time is expressed by NOXA, so the NO _X amount ΣNOX estimated to be absorbed by the NO _X absorbent 16 is estimated. Can be calculated using the following equation.

ΣNOX = ΣNOX + NOXA FIG. 8 shows a case where the engine medium speed / medium load operation is continuously performed. As shown in FIG. 8, while the engine is operating, the NO _X amount ΣNOX estimated to be absorbed by the NO _X absorbent 16 gradually increases. In the embodiment according to the present invention, when the NO _X amount ΣNO _X exceeds the predetermined allowable value MAX, the average air-fuel ratio in the combustion chamber 3 is temporarily switched from lean to rich, and is absorbed by the NO _X absorbent 16 during this period. All NO _x is NO _x absorbent 16
Emitted from. When the average air-fuel ratio in the combustion chamber 3 is switched from lean to rich during medium-speed / medium-load operation of the engine, the opening degree S of the EGR control valve 21 is increased by ΔS as shown in FIG. 8 as described above. The intake control valve 12 is closed by Δθ, and the fuel injection amount Q is increased by ΔQ.

9 and 10 show a fuel injection control routine, which is executed by interruption at regular time intervals. Referring to FIGS. 9 and 10, first, at step 100, it is judged if the NO _x releasing flag is set or not. Normally, the NO _x release flag is reset, so the routine proceeds to step 101,
It is determined whether or not the NO _X amount ΣNOX exceeds the allowable value MAX. When ΣNOX ≦ MAX, the routine proceeds to step 102, where the fuel injection amount Q is calculated from the relationship shown in FIG.
Next, at step 103, the opening degree S of the EGR control valve 21 is calculated from the relationship shown in FIG. 3, and then at step 104, the intake control valve 12 is fully opened. Next, at step 105, the NO _X absorption amount NOXA is calculated from the relationship shown in FIG. 7, and then at step 106, the NO _X amount ΣNOX.
(= ΣNOX + NOXA) is calculated. Therefore, at this time, that is, during normal operation, the amount Q of fuel shown in FIG. 2 is injected, and the EGR control valve 21 is set to the opening degree S shown in FIG.
The intake control valve 12 is held in the fully open state.

On the other hand, in step 101 ΣNOX>
When it is determined that the exhaust gas has reached MAX, the routine proceeds to step 107, where it is determined whether the exhaust gas detected by the temperature sensor 19 is higher than a predetermined temperature T ₀ , for example, 200 ° C. T <temperature of the NO _X absorbent 16 is considered to be low when T _0, at this time _the NO _X absorbent 16
Continue the air-fuel ratio of the exhaust gas flowing from _the NO _X absorbent 16 be rich in step 102 because NO _X is good NO _x is not released normal operation continues to. Since NO _X is released from _the NO _X absorbent 16 when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 16 rich when hand T> T a ₀ NO _X emission proceeds to step 108 Flag is set.

Next, at step 109, the NO _X amount ΣNO
A period C ₀ (= K · ΣN) in which the average air-fuel ratio in the combustion chamber 3 should be kept rich by multiplying X by a constant K
OX) is calculated. Then, it proceeds to step 110. Incidentally, when the NO _X release flag is set the next processing cycle after jumps from step 100 to step 110.

In step 110, the fuel injection amount Q is calculated from the relationship shown in FIG. 2, and the increased amount ΔQ is calculated from the relationship shown in FIG. 6 (C). Next, at step 111, Q is Δ
By adding Q, the final fuel injection amount Q (= Q
+ ΔQ) is calculated. Then, in step 112, FIG.
The opening degree S of the EGR control valve 21 is calculated from the relationship shown in
The valve opening amount ΔS is calculated from the relationship shown in FIG. Next, at step 113, the final opening S (= S + ΔS) of the EGR control valve 21 is calculated by adding ΔS to S. Next, at step 114, the valve closing amount Δθ of the intake control valve 12 is calculated from the relationship shown in FIG. 6 (B).
Therefore, at this time, the fuel injection amount Q is increased by ΔQ, the opening degree S of the EGR control valve 21 is opened by ΔS, and the intake control valve 12 is closed by Δθ.

Next, at step 115, the count value C is incremented by 1, and then at step 116, it is judged if the count value C has become larger than the period C ₀ calculated at step 109. When C> C ₀ , the routine proceeds to step 117, where the NO _x releasing flag is reset, and the routine proceeds to step 118, where ΣNO _x is made zero.
Next, at step 119, the count value C is made zero. Then, the normal operation state is restored.

11 and 12 show another embodiment.
In this embodiment, the same components as those in FIG. 1 are designated by the same reference numerals. Referring to FIG. 11 and FIG. 12, in this embodiment, each branch pipe of the intake manifold 9 is connected to each cylinder via corresponding intake ducts 22a, 22b, 22c, 22d, and each cylinder is connected to its corresponding exhaust pipe. 15a, 1
5b, 15c, 15d and corresponding casing 1 respectively
7a, 17b, 17c, NO _X absorbent 16a disposed within 17d, 16b, 16c, is connected to an exhaust manifold 23 through 16d. Each intake duct 22a, 22
Intake control valves 12a, 12b, 12c, and 12d, whose opening and closing are controlled by corresponding actuators 13a, 13b, 13c, and 13d, are arranged in b, 22c, and 22d, respectively. Exhaust pipes 15a, 15b, 15c, 15d of each cylinder
And the intake ducts 22a, 22b, 22c, 22d respectively correspond to the EGR gas conduits 20a, 20b, 20c, 20.
connected to each other via d, and each EGR gas conduit 20a,
EGR control valve 21 is provided in each of 20b, 20c and 20d.
a, 21b, 21c, 21d are arranged. That is, in this embodiment, the intake control valves 12a, 12b,
12c, 12d, NO _X absorbent 16a, 16b, 16
c, 16d, EGR gas conduits 20a, 20b, 20c,
20d and EGR control valves 21a, 21b, 21c, 2
1d is provided independently.

FIG. 13 shows changes in the NO _X amount ΣNOX, the opening degrees S of the EGR control valves 21a to 21d and the intake control valves 12a to 12 in each of the first cylinder # 1 to the fourth cylinder # 4.
The opening θ of d and the fuel injection amount Q are shown. Also in this embodiment, during normal operation, the EGR control valves 21a-2
1d is controlled based on FIG. 3, and each intake control valve 12a-1
2d is held in the fully open state, and the fuel injection amount Q is calculated based on FIG. It should be noted that FIG. 13 shows the case where the engine medium-speed / medium-load operation is continuously performed as in the case of FIG. 8.

As shown in FIG. 13, the NO _X amount ΣNOX
When the value exceeds the allowable value MAX, the E of the first cylinder # 1 is first
The opening degree S of the GR control valve 21a is increased by ΔS,
The intake control valve 12a is closed by Δθ. However, at this time, the fuel injection amount Q of the first cylinder # 1 is not increased. That is, in this embodiment, by increasing the opening degree of the EGR control valve 21a and closing the intake control valve 12a,
The average air-fuel ratio in the combustion chamber 3 of the # 1 cylinder # 1 is switched from lean to rich, whereby the N # of the # 1 cylinder # 1 is changed.
NO _X is released from the O _X absorbent 16a. Also in this embodiment, the values of ΔS and Δθ are stored in advance in the ROM 32 in the form of a map as shown in FIGS. 6A and 6B. 1 to a larger value than the case of the first embodiment shown in FIG.

Next, the NO _x absorbent 16a of the first cylinder # 1
NO _X releasing action from is completed when the EGR control valve 21a
The opening degree is returned to the original opening degree S, and the intake control valve 12a is fully opened. At the same time, this time, the opening degree S of the EGR control valve 21b of the second cylinder # 2 is increased by ΔS, and the intake control valve 12b is closed by Δθ. At this time, the average air-fuel ratio in the combustion chamber 3 of the second cylinder # 2 is switched from lean to rich, and thus NO _X is released from the NO _X absorbent 16b of the second cylinder # 2.

Next, the NO _x absorbent 16b of the second cylinder # 2
When the NO _x release action from the EGR control valve 21b is completed
The opening degree is returned to the original opening degree S, and the intake control valve 12b is fully opened. At the same time, this time, the opening degree S of the EGR control valve 21c of the third cylinder # 3 is increased by ΔS, and the intake control valve 12c is closed by Δθ. At this time, the average air-fuel ratio in the combustion chamber 3 of the third cylinder # 3 is switched from lean to rich, and thus NO _X is released from the NO _X absorbent 16c of the third cylinder # 3.

Next, the NO _x absorbent 16c of the third cylinder # 3
If NO _X release action is completed from the EGR control valve 21c
The opening degree of is returned to the original opening degree S, and the intake control valve 12c is fully opened. At the same time, this time, the opening degree S of the EGR control valve 21d of the fourth cylinder # 4 is increased by ΔS, and the intake control valve 12d is closed by Δθ. At this time, the average air-fuel ratio in the combustion chamber 3 of the fourth cylinder # 4 is switched from lean to rich, so that NO _X is released from the NO _X absorbent 16d of the fourth cylinder # 4.

When the opening S of the EGR control valve 21a of the first cylinder # 1 is increased by ΔS and the intake control valve 12a is closed by Δθ, combustion in the first cylinder # 1 deteriorates. The output torque of the engine will decrease. Therefore, in this embodiment, as shown in FIG.
If the intake control valve 12a is closed when the opening degree S of the EGR control valve 21a of the No. cylinder # 1 is increased, an addition necessary to increase the engine output torque by the decrease amount of the engine output torque at this time is added. The fuel ΔQ is supplied to all the cylinders other than the first cylinder # 1, that is, the second cylinder # 2, the third cylinder # 3, and the fourth cylinder # 4. That is, the fuel injection amount Q is increased by ΔQ in all cylinders except the first cylinder # 1. This ΔQ is also stored in advance in the ROM 32 in the form of a map as shown in FIG.

This also applies to the other cylinders.
When the opening degree S of the EGR control valve 21b of the No. cylinder # 2 is increased and the intake control valve 12b is closed, the fuel injection amount Q is increased by ΔQ in all the remaining cylinders. Opening S of the EGR control valve 21c of No. 3
Is increased and the intake control valve 12c is closed, the fuel injection amount Q is Δ in all remaining cylinders.
Increased by Q and EGR control valve 2 of # 4 cylinder # 4
When the opening degree S of 1d is increased and the intake control valve 12d is closed, the fuel injection amount Q is increased by ΔQ in all the remaining cylinders.

Therefore, in this embodiment, one of the four cylinders
Combustion deteriorates only in the cylinder of
Good combustion is obtained in the remaining three cylinders
Therefore, the amount of soot generated is smaller than that in the first embodiment, and
There is an advantage that the consumption of materials does not increase so much. 14
16 to 16 show the fuel injection control routine.
The routine is executed by interruption at regular time intervals.
Referring to FIGS. 14 to 16, first, step 2
NO in 00_XWhether the release flag is set
Is determined. Normally NO_XThe emission flag is reset
Yes, so proceed to step 201, and NO_XThe amount ΣNOX
It is determined whether the allowable value MAX has been exceeded. ΣNOX ≦
In case of MAX, the routine proceeds to step 202, where the fuel injection amount Q
Is calculated. Next, at step 203, each EGR control
The opening degree S of the valves 21a to 21d is calculated, and then the step
In 204, all intake control valves 12a-12d are fully opened.
Be done. Next, at step 205, from the relationship shown in FIG.
O _XThe absorption amount NOXA is calculated, and then step 206
Then NO_XThe amount ΣNOX (= ΣNOX + NOXA) is calculated
To be done. Therefore, at this time, normal operation is performed.

On the other hand, in step 201, ΣNOX>
When it is determined that it has become MAX, the process proceeds to step 207.
The exhaust gas detected by the temperature sensor 19 is
Specified temperature T₀, Whether it is higher than 200 ℃
Is determined. T <T₀When is NO_XAbsorbent 16
It is considered that the temperature of a to 16d is low, and at this time, NO
_XThe air-fuel ratio of the exhaust gas flowing into the absorbents 16a to 16d is
NO even if rich_XNO from absorbents 16a-16d_X
Is satisfactorily NO_XIs not released, proceed to step 202
Then normal operation is continued. On the other hand, T> T₀so
Sometimes NO_XExhaust flowing into the absorbents 16a to 16d
NO if the air-fuel ratio of air gas is made rich_XAbsorbent 16a-
16d to NO_XIs released, so proceed to step 208.
So no _XThe release flag is set.

Next, at step 209, the NO _X amount ΣNO.
A period C ₀ (= where the average air-fuel ratio in each combustion chamber 3 of each cylinder should be kept rich by multiplying X by a constant K
K · ΣNOX) is calculated. Then, it proceeds to step 210. Incidentally, when the NO _X release flag is set the next processing cycle after jumps from step 200 to step 210.

In step 210, the fuel injection amount Q for the Nth cylinder is calculated. It should be noted that N is set to 1 when the engine is started, and therefore, when the routine proceeds to step 210 for the first time after the engine is started, the fuel injection amount Q of the first cylinder is calculated. Next, at step 211, the opening degree S and the valve opening amount ΔS of the EGR control valves 21a to 21d for the Nth cylinder are calculated.
Next, at step 212, ΔS is added to S to obtain the final opening S (= S) of the EGR control valves 21a to 21d.
S + ΔS) is calculated. Next, at step 213, N
Valve closing amount Δθ of the intake control valves 12a to 12d for the No. cylinder
Is calculated.

Next, at step 214, the fuel injection amount Q and the increased amount ΔQ for all remaining cylinders other than the Nth cylinder are calculated. Next, at step 215, the final fuel injection amount Q (= Q + ΔQ) for all the remaining cylinders other than the Nth cylinder is calculated by adding ΔQ to Q. Next, at step 216, the opening degrees S of the EGR control valves 21a to 21d for all the remaining cylinders other than the Nth cylinder are calculated. Next, at step 217, the intake control valves 12a to 12d of all the remaining cylinders other than the Nth cylinder are fully opened, and then the routine proceeds to step 218.

Therefore, for example, when N = 1, the fuel injection amount Q in the first cylinder is maintained at the injection amount during normal operation,
The opening degree S of the EGR control valve 21a is increased by ΔS, and the intake control valve 12a is closed by Δθ. On the other hand, at this time, the fuel injection amount Q in all the remaining cylinders except the first cylinder, that is, the second cylinder, the third cylinder, and the fourth cylinder is Δ.
The amount is increased by Q, and the opening degree S of the EGR control valves 21b to 21d is increased.
Is maintained at the opening degree during normal operation, and the intake control valves 12b-1
2d is held in a fully opened state.

Next, at step 218, the count value C is incremented by 1, and then at step 219, it is judged if the count value C has become larger than the period C ₀ calculated at step 209. When C> C ₀ , the routine proceeds to step 220, where the count value C is made zero, and then at step 221, N is incremented by 1. Next, at step 222, it is judged if N has become 5. When N = 5, step 22
The routine proceeds to step 3, where the NO _x release flag is reset. Next, in step 224, ΣNOX is set to zero, and then in step 225, N is set to 1.

[0052]

[Effect of the Invention] is blocking the engine output torque when switching the mean air-fuel ratio from lean to stoichiometric or rich in the combustion chamber so as to release the NO _X in the diesel engine from _the NO _X absorbent is being changed Therefore, it is possible to prevent a shock from occurring at this time. Further, in particular, in the invention described in claim 2, the combustion is deteriorated only in the cylinder in which the amount of air supplied into the combustion chamber is reduced, and the good combustion is achieved in the remaining cylinders in which the amount of fuel is increased. Therefore, there is an advantage that the amount of soot generated is small and the fuel consumption does not increase so much.

[Brief description of drawings]

FIG. 1 is an overall view of a diesel engine.

FIG. 2 is a diagram showing a fuel injection amount Q.

FIG. 3 is a diagram showing an opening degree S of an EGR control valve.

FIG. 4 is a diagram for explaining the action of NO _X absorption and release.

FIG. 5 is a diagram showing an opening degree S of an EGR control valve and an opening degree θ of an intake control valve.

FIG. 6 is a diagram showing a map of opening degrees ΔS, Δθ and an increase amount ΔQ.

FIG. 7 is a diagram showing a map of a NO _X absorption amount NOXA.

FIG. 8 is a time chart of NO _X release control.

FIG. 9 is a flowchart for controlling fuel injection.

FIG. 10 is a flow chart for controlling fuel injection.

FIG. 11 is an overall view of a diesel engine showing another embodiment.

FIG. 12 is a plan view of FIG. 11.

FIG. 13 is a time chart of NO _X release control.

FIG. 14 is a flowchart for controlling fuel injection.

FIG. 15 is a flowchart for controlling fuel injection.

FIG. 16 is a flow chart for controlling fuel injection.

[Explanation of symbols]

4 ... Fuel injection valve 12, 12a, 12b, 12c, 12d ... Intake control valve 16, 16a, 16b, 16c, 16d ... NO _X absorbent 21, 21a, 21b, 21c, 21d ... EGR control valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/02 360 F02D 41/02 360 360 380 380E 41/38 41/38 C 43/00 301 43/00 301H 301N 45/00 364 45/00 364A F02M 25/07 550 F02M 25/07 550R (56) Reference JP-A-5-106479 (JP, A) International Publication 93/007363 (WO, A1) (58) Fields investigated (Int.Cl . ⁷ , DB name) F02D 41/00-45/00

Claims (2)

(57) [Claims] 1. The air-fuel ratio of the inflowing exhaust gas is lean.
NO when_XAnd the air-fuel ratio of the inflowing exhaust gas is
NO absorbed when stoichiometric or rich _XEmit
NO_XPlace the absorbent in the engine exhaust passage and place it in the combustion chamber.
During normal operation when the average air-fuel ratio is lean
NO in the exhaust gas emitted from the engine _XIs NO_XAbsorbent
Absorbed by NO_XAbsorbent to NO_XWhen to release
The average air-fuel ratio in the combustion chamber is from lean to theoretical air-fuel ratio.
In diesel engines that can be switched to ratio or rich,
NO_XAbsorbent to NO_XIn the combustion chamber when
An air amount reducing means for reducing the amount of air supplied,
The engine output is reduced by the decrease in the engine output torque due to the decrease in air volume.
Calculate the amount of additional fuel needed to increase force torque
The calculation means and the amount of fuel supplied to the combustion chamber are calculated as above
Dee equipped with fuel amount increasing means for increasing only the fuel amount
Exhaust gas purification device for diesel engines. 2. The air-fuel ratio of the inflowing exhaust gas is lean.
NO when_XAnd the air-fuel ratio of the inflowing exhaust gas is
NO absorbed when stoichiometric or rich _XEmit
NO_XPlace the absorbent in the engine exhaust passage and place it in the combustion chamber.
During normal operation when the average air-fuel ratio is lean
NO in the exhaust gas emitted from the engine _XIs NO_XAbsorbent
Absorbed by NO_XAbsorbent to NO_XWhen to release
The average air-fuel ratio in the combustion chamber is from lean to theoretical air-fuel ratio.
In diesel engines that can be switched to ratio or rich,
NO in the exhaust passage of each cylinder_XPlace the absorbent,
One or no_XAbsorbent to NO_XWhen to release
The one NO_XProvided in the combustion chamber of the cylinder connected to the absorbent.
An air amount reducing means for reducing the amount of supplied air, and
Engine output is equivalent to the decrease in engine output torque due to volume reduction
Supply into combustion chamber of remaining cylinders to increase torque
And a fuel amount increasing means for increasing the amount of fuel to be discharged.
Exhaust gas purification device for diesel engines.