JPH04246275A - Exhaust purifying device for internal combustion engine - Google Patents

Abstract

PURPOSE:To suppress the NOx discharge quantity of a lean burn internal combustion engine equipped with an air assisting injector. CONSTITUTION:An exhaust purifying device for an internal combustion engine which consists of an internal combustion engine 2 equipped with an air assisting injector 8, lean NOx catalyst 18 installed in the exhaust system 6 of the internal combustion engine, operation state detecting means for the engine, operation region judging means 104, 106, 216, and 218 for judging if the engine operation state is in the operation region in deficiency of HC or not, and assisting air control means 110 and 220 for suspending or reducing the supply of the air assistance in case of the shortage of HC. When the supply of the assisting air is suspended or reduced, the atomization of fuel is deteriorated, and the uncombusted HC in exhaust is increased, and the NOx purifying rate of the lean NOx catalyst 18 is improved.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an exhaust purification device for an internal combustion engine equipped with an air assist injector and having a zeolite-based NOx reduction catalyst in the exhaust system, in which assist air is controlled to improve the NOx purification rate of the catalyst. related to the equipment used.

0002

[Prior Art] Japanese Patent Application Laid-Open No. 63-283727 discloses that HC (hydrocarbons) is necessary for a zeolite catalyst supporting a transition metal to reduce NOx in a lean air-fuel ratio region, and that HC It is disclosed that a special HC supply device is provided to compensate for the shortage of HC. On the other hand, injecting air into the injected fuel flow to atomize the fuel,
Internal combustion engines equipped with air-assist type injectors (fuel injection valves) are also known.

0003

[Problems to be Solved by the Invention] However, in internal combustion engines equipped with air-assist injectors, the fuel is atomized well, so the amount of unburned HC emitted is small, and the amount of H in the exhaust gas is reduced.
The amount of C is low. Therefore, even if the exhaust system is equipped with a NOx reduction zeolite catalyst, HC will be insufficient in an operating range where a large amount of NOx is emitted, making it impossible to obtain a high NOx purification rate. In this case, it may be possible to provide a special HC supply device, but this would complicate the structure of the system and reduce reliability, making it impractical.

An object of the present invention is to provide an internal combustion engine equipped with an air assist injector and a NOx reduction zeolite catalyst in the exhaust system, which can be used in an operating range where the amount of HC is insufficient without the need for a special HC supply device. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that supplies a sufficient amount of HC and increases the NOx purification rate of a catalyst.

[0005]

[Means for Solving the Problems] The above object is achieved by providing an exhaust purification device for an internal combustion engine of the present invention with the following means. A lean-burn internal combustion engine equipped with an air-assist injector; a catalyst that is installed in the exhaust system of the internal combustion engine and is made of zeolite supported with a transition metal or a noble metal, and that reduces NOx in an oxidizing atmosphere in the presence of HC; (hereinafter referred to as lean NOx catalyst), an operating state detection means for detecting the operating state of the internal combustion engine, and the internal combustion engine operating state detected by the operating state detection means is in an operating range where the amount of HC to the lean NOx catalyst is insufficient. an operating region determining means for determining whether or not the amount of assist air supplied from the air assist injector is determined when the operating region determining means determines that the internal combustion engine operating state is in an operating region in which the amount of HC is insufficient; Assist air control means for reducing or stopping the supply of air.

[0006]

[Effect] Assist air is used in areas where the amount of HC is insufficient, that is, during medium load operation (high NOx emissions) and at high exhaust temperatures (a large amount of HC is required because the supplied HC is directly oxidized). Since it is reduced or stopped, the atomization (atomization) of the fuel deteriorates and the amount of unburned HC discharged increases. However, when the catalyst bed temperature (related to exhaust temperature) is high, NO
x Immediately stop the assist air when the exhaust amount reaches a large range, but when the catalyst bed temperature is low, the stop is delayed to achieve both atomization and HC supply. Thus,
Lean NOx without complicating the structure N to the catalyst
Ox purification rate improves.

[0007]

[Embodiments] Two embodiments according to the present invention will be described. 1 and 2 correspond to the first embodiment, FIGS. 3 and 4 correspond to the second embodiment, and FIGS. 5 to 11 show common configurations applied to both embodiments.

First, the common configuration will be explained. In FIG. 5, 2 is a lean-burn internal combustion engine, 4 is its intake system, and 6 is a lean-burn internal combustion engine.
indicates the exhaust system. The internal combustion engine 2 includes an air assist injector 8 that promotes atomization of fuel by injecting air. The air assist injector 8 has fuel and air injection controlled according to the output of an electronic control unit (ECU) 10. Assist air to the air assist injector 8 is supplied from upstream of the throttle valve 12 through a conduit 14. For example, an air pump 20 and a pressure regulator 22 are installed in the middle of the conduit 14.
, a control valve 16 is provided, and a pressure regulator 22 adjusts the air pressurized by the air pump 20 to a constant pressure.
Air is supplied to the air assist injector 8 when the power is N. To supply or stop the supply of assist air, turn on and off the control valve 16 according to the output of the ECU 10.
Do by doing.

FIG. 11 shows an example of the air assist injector 8. The air assist injector 8 includes a fuel injection section 82 and an air injection section 84. The air injection unit 84 includes a nozzle port 86, a needle 88 that opens and closes the nozzle port 86, a compression spring 90 that normally biases the needle 88 in the closing direction, a solenoid 92, and a solenoid 9.
The movable core 94 moves the needle 88 in the opening direction against the bias of the spring 90 when the needle 88 is energized. The fuel injection timing and assist air injection timing are controlled by the ECU 10.

[0010] The exhaust system 6 of the internal combustion engine 2 contains lean NOx.
A catalyst 18 is installed. Lean NOx catalyst 18
This reduces NOx in the exhaust and purifies the exhaust in the presence of HC in an oxidizing atmosphere (exhaust from combustion in a leaner range than stoichiometry). The NOx reduction mechanism of the lean NOx catalyst 18 is estimated to be a reaction between active species generated by partial oxidation of HC and NOx. Therefore, the larger the amount of HC in the exhaust gas, the more CO2 and H2 of HC.
The more the direct oxidation to O is suppressed and the partial oxidation to active species is promoted, the higher the NOx purification rate of the lean NOx catalyst 18 becomes.

In the present invention, the HC amount is controlled by suppressing the supply of assist air from the air assist injector 8 (turning the supply ON or OFF or the magnitude of the supply amount) without providing a special HC supply device. (Control in Figure 1-4). If the assist air supply is stopped or reduced,
The atomization of the fuel in the air assist injector 8 deteriorates and the combustibility in the engine decreases, the amount of unburned HC increases and the amount of HC in the exhaust increases, and conversely, if assist air is supplied or the supply amount is increased, The amount of HC in the exhaust gas decreases. However, stopping the supply of assist air or reducing the supply amount will worsen flammability, fuel efficiency, HC emissions, etc., so lean NO
x Control is performed only when the engine is operating in a state where HC is insufficient for NOx reduction in the catalyst 18. This assist air supply control is performed by controlling the control valve 16 by the ECU 10.

The ECU 10 is composed of a microcomputer, and as shown in FIG.
M) 66 and random access memory (RAM) 68
A storage unit consisting of a central processor unit (CP
U) 70 calculation units, which are connected to each other by a bidirectional bus 72. air flow meter 24,
Analog signals from the intake pressure sensor 26 and throttle opening sensor 28 are converted into analog/digital signals and input to an input port, and are connected to a crank angle sensor 30 and a crank angle reference sensor built into a distributor linked to the crankshaft. The digital signal from 32 is input as is to input port 62. The output port 64 includes a drive circuit 76a for driving the control valve, a drive circuit 76b for the fuel injection part 82 of the air assist injector 8, and a drive circuit 76c for the air injection part 84 of the air assist injector 8.
is connected. In the above, each sensor 24, 26
, 28, 30, and 32 constitute operating state detection means for detecting operating states of the internal combustion engine, such as engine rotational speed and engine load.

The ECU 10 stores the program means and map means shown in FIGS. 7-10 in the ROM 66, and these are read out by the CPU 70 and the following calculations are executed. Figure 7
shows a routine for calculating the operation timing of the air assist injector 8. This routine is executed by interrupts at regular intervals.

In FIG. 7, first, in step 302, the intake air amount Q (output of the air flow meter 24) and the engine rotational speed NE (calculated from the output of the crank angle sensor 30) are determined.
, and the throttle valve opening/closing speed ΔTA (calculated from the output of the throttle opening sensor 28) are read. Here, the throttle valve opening/closing speed ΔTA is the change in the opening degree of the throttle valve 12 per unit time, and when changing in the valve opening direction, ΔTA
TA takes a positive value. Next, in step 304, the valve opening time (fuel supply time) TAUF of the fuel injection section 82 is set to T
It is calculated by AUF=KQ/N. Here, K is a coefficient including various corrections. Next, in step 306, the fuel supply time TAUF is converted into a crank angle,
The fuel supply crank angle θf is determined. Next, in step 308, the nozzle opening 86 opening time, that is, the air injection time TAUA, is calculated from the map based on the throttle valve opening/closing speed ΔTA. The relationship between ΔTA and TAU is, for example, as shown in FIG. 8, when ΔTA is less than or equal to a predetermined throttle valve opening/closing speed ΔTAP (ΔTAP>O), TAUA is constant; when it exceeds ΔTAP, that is, during acceleration operation, TAUA increases almost linearly as ΔTA increases.

In FIG. 7, in step 310, the air injection time TAUA is converted to a crank angle, and the air injection crank angle θa is determined. Next, in step 312, the fuel supply start crank angle θ1 is calculated using the following equation. θ1 = θ2 −θf Here, θ2 is the fuel supply stop angle, which is a predetermined constant crank angle (see FIG. 9). Step 314
Then, the nozzle opening 86 valve opening crank angle θ3 is calculated by the following equation. θ3 = θ4 - θa Here, θ4 is the crank angle for closing the nozzle port 86, which is a predetermined constant crank angle (see FIG. 9).

FIG. 10 shows an air assist injector 8
A routine for controlling the operation of the air injection unit 84 (also referred to as an air blast valve) is shown. This routine is executed by interrupting every fixed crank angle (counted by the output from the crank angle reference position sensor 32). First, in step 402, it is determined whether or not the crank angle θ of the engine has reached the fuel supply start crank angle θ1. When θ=θ1, the process proceeds to step 404, where the fuel injection section 82 is opened. Next, in step 406, it is determined whether θ has reached the fuel supply stop crank angle θ2, and θ=θ2.
If so, the process advances to step 408, and the fuel injection section 82 is closed. Next, in step 410, it is determined whether the crank angle θ has reached the valve opening crank angle θ3 of the nozzle port 86, and if θ=θ3, the process proceeds to step 412.
The nozzle port 86 is opened to inject fuel and compressed air. Next, in step 414, it is determined whether θ has reached the valve closing crank angle θ4 of the nozzle port 86, and θ=θ4.
If so, the routine advances to step 416, where the nozzle port 86 is closed, and this routine ends.

Next, configurations specific to each embodiment will be explained. 1 and 2 relate to Embodiment 1 of the present invention, and show a routine for controlling the supply of assist air and a map used for calculating the routine.

The routine shown in FIG. 1 is interrupted at regular intervals, for example, every 50 milliseconds. In step 102, the engine load Q/N, the engine speed NE, the exhaust temperature T (
Q/N, NE (obtained from a map or provided with a temperature sensor in the exhaust system and read from its output), that is, read the current engine operating state.

Next, in step 104, it is determined whether or not the current engine operating state (the engine operating state read in step 102) is in a region where HC is insufficient for the NOx purification reaction in the lean NOx catalyst 18, for example, as shown in FIG. It is determined whether the Q/N vs. NE map (Map 1) is in the shaded area, that is, in the medium load, medium speed rotation area.

To explain Map 1 in more detail, the light load, low speed rotation region is a region where there is originally little NOx in the engine exhaust, and there is no shortage of HC. In the high-load, high-speed rotation region, the air-fuel ratio is set to the rich (but leaner than stoichiometric) side to achieve the output air-fuel ratio, so HC is relatively large. The remaining medium load and medium speed rotation range is a region where HC may be insufficient, and is a region where HC is desired to be increased.

If it is determined in step 104 that the current operating state of the internal combustion engine is in the shaded area in FIG.
If it is determined that the area is not in the shaded area, the process advances to step 106. In step 106, the exhaust temperature (lean NOx
It is determined whether the temperature of the gas entering the catalyst 18) T is higher than a predetermined exhaust gas temperature THI (for example, 550°C).

When the exhaust gas temperature T is higher than THI, direct oxidation of HC in the exhaust gas to H2O and CO2 progresses, the rate of partial oxidation decreases, and the amount of active species decreases. Therefore, even when T>THI, it should be included in the HC-deficient region. In the above, steps 104, 10
6 indicates that the current engine operating state is lean NOx catalyst 18
An operating region determining means is configured to determine whether or not the vehicle is in an operating region in which the amount of HC supplied to the vehicle is insufficient.

If it is determined in step 106 that T>THI, the process proceeds to step 110 and the control valve 16 is closed, and if T is less than THI, the process proceeds to step 108 and the control valve 16 is opened. Here, in step 110, when the operating region determining means determines that the internal combustion engine operating state is in an operating region in which the amount of HC is insufficient, the amount of air supplied to the air assist injector 8 is reduced or the supply of assist air is stopped. It constitutes a control means.

FIGS. 3 and 4 relate to a second embodiment of the present invention, and show a routine for controlling the supply of assist air and a map used for calculating the routine. In the second embodiment, when the engine operating state enters the shaded area of map 1 from the low load and low speed rotation side,
The closing of the control valve 16 is delayed for a certain period of time. This is because NOx is naturally low on the low load and low rotation side, so even if the area enters the shaded area of Map 1, NOx will not increase immediately due to the time lag, so do not close the control valve 16 immediately. This is to give priority to the combustibility and fuel efficiency of the engine.

The routine shown in FIG. 3 is interrupted at regular intervals, for example every 50 milliseconds. At step 202,
Read engine load Q/N and engine rotation speed NE. Then,
At step 204, a counter value CT corresponding to Q/N and NE is calculated from map 2. CT is a counter value that changes the temperature condition C, and CT is a counter value that changes the temperature condition C.
takes a large positive value, and the low load, low speed rotation range CT takes a large negative value in absolute value. Next, in step 206, the current CT obtained in step 204 is added to the previous C to obtain the current C. Therefore, the larger C is, the more the exhaust gas is in the high temperature region, and the smaller C is, the more the exhaust gas is in the lower temperature region.

Next, in steps 208-214, it is determined whether C is within a certain range, and if C is smaller than the lower limit of the certain range, the lower limit is changed to a value larger than the upper limit of the certain range. In the case of a value, set it to its upper limit and guard it so that the value of C does not diverge. That is, step 2
In step 08, it is determined whether C<0 or not, and if C<0, step 21
2, set C to 0, and if C is 0 or more in step 208, proceed to step 210, determine whether C>250, and set C
>250, the process proceeds to step 214 and sets C to 250, and if C is less than 250 in step 210, the process directly proceeds to the next step. When C is a value between 200 and 250, the value is left unchanged.

Next, the process proceeds to step 216. Steps 216-222 are steps for controlling the time for switching the control valve 16 to close. At step 216, C is 200.
It is determined whether or not the temperature is higher than that (when the exhaust gas temperature is high, when the catalyst bed temperature is high). When C is smaller than 200, it is determined that the exhaust gas is not at a high temperature, and normal air-assisted injection is performed. When C is 200 or more in step 216, it is determined that the exhaust gas is high temperature, and the process proceeds to step 218, where the current engine operating state (engine load
/N, engine rotational speed NE) is in the shaded area of map 1. If not, the process advances to step 222 to open the control valve 16; if so, the process advances to step 220 to open the control valve 1.
Close 6. Therefore, when entering the shaded area of map 1 from the high exhaust temperature side, steps 216, 218,
Step 220 immediately closes the control valve 16, but when entering the shaded area of map 1 from the low exhaust temperature side, step 2
Since the process proceeds from step 16 to step 222, the control valve 16 does not close until C becomes 200 or more, and the closing of the control valve 16 is delayed.

In the above, steps 216 and 218 constitute the operating region determining means in the second embodiment, which determines whether the current engine operating state is in an operating region in which the amount of HC is insufficient, and step 220 constitutes Embodiment 2 in which the supply amount of assist air is reduced or the supply is stopped when HC is insufficient
It constitutes an assist air control means in.

Next, the functions common to the first and second embodiments will be explained. When it is determined that the engine operating state is in an operating state where HC is insufficient, that is, the engine is in the middle load and middle rotation region, which is the shaded area on the map in Figure 1, or the exhaust temperature (catalyst bed temperature) is too high. When HC is almost directly oxidized, the control valve 16 is closed and the supply of assist air is stopped, or the opening degree of the control valve 16 is reduced to reduce the amount of assist air supplied. Ru.

When the supply of assist air is stopped or reduced, even if the air injection part 84 of the air assist injector 8 is set to open, the amount of air injected is small, so that the atomization and atomization of the fuel are reduced. Even if the fuel is not promoted and is drawn into the combustion chamber together with the intake air, complete combustion will be difficult, and a portion of the fuel will be discharged as unburned HC. Therefore, the amount of HC in the exhaust gas passing through the exhaust system 6 increases, which increases the lean NO.
x Used in the NOx reduction reaction in the catalyst 18,
Lean NOx improves the NOx purification rate of the catalyst 18.

When there is no shortage of HC, there is no need to take the trouble to worsen the combustion performance, so the control valve 16 is fully opened and air assist is performed as before. for example,
In low load and low speed rotation areas, NOx emitted from the engine
Since HC is naturally low and there is no shortage of HC, air assist can be performed and combustibility can be prioritized.

In Example 2, when the catalyst bed temperature is high, NO
x Immediately stop or reduce the assist air when the amount of emissions reaches a high area (shaded area in Map 1), but when the catalyst bed temperature is low, stop or reduce the assist air to achieve both fuel atomization and HC supply. be able to.

[0033]

[Effects of the Invention] According to the present invention, assist air is stopped or reduced in areas where the amount of HC is insufficient (during medium load, medium speed rotation, and high exhaust temperature), so fuel atomization is slightly sacrificed. This increases the amount of unburned HC produced, thereby improving the NOx purification rate of the lean NOx catalyst.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of an assist air supply control routine for an exhaust gas purification device for an internal combustion engine according to a first embodiment of the present invention.

[Figure 2] Engine load (Q/
N) Engine speed (NE) map.

FIG. 3 is a flowchart of an assist air supply control routine for an exhaust gas purification device for an internal combustion engine according to a second embodiment of the present invention.

[Figure 4] Count value CT used for calculation of the routine in Figure 3
This is a map to find.

FIG. 5 is an equipment system diagram of an exhaust purification device for an internal combustion engine according to the present invention.

FIG. 6 is a block diagram showing a system of the ECU and equipment connected to it in FIG. 5;

FIG. 7 is a flowchart for calculating the operation timing of air injection of the air assist injector.

8 is a map used to determine the air injection amount TAU from the accelerator opening/closing speed ΔTA in the calculation of FIG. 7; FIG.

FIG. 9 is a timing diagram showing the relationship between fuel injection timing, assist air injection timing, and crank angle in an air assist injector.

FIG. 10 is a flowchart of an execution routine for fuel injection and assist air injection of an air assist injector.

FIG. 11 is a sectional view of an assist air injection part of an example of an air assist injector.

[Explanation of symbols]

2 Internal combustion engine 6 Exhaust system 8 Air assist injector 10　ECU 12 Throttle valve 16 Control valve 18 Lean NOx catalyst 20 Air pump 24 Air flow meter 26 Intake pressure sensor 28 Throttle opening sensor 30 Crank angle sensor 32 Crank angle reference position sensor 82 Fuel injection part 84 Air injection part

Claims (1)

[Claims] Claim 1: An internal combustion engine capable of lean combustion equipped with an air assist injector, an exhaust system of the internal combustion engine,
It is made of zeolite supported with transition metals or noble metals, and in the presence of HC in an oxidizing atmosphere, NOx
a catalyst that reduces HC, an operating state detecting means for detecting an operating state of the internal combustion engine, and whether or not the operating state of the internal combustion engine detected by the operating state detecting means is in an operating range in which the amount of HC to the catalyst is insufficient. an operating region determining means for determining the amount of assist air supplied to the air assist injector when the operating region determining means determines that the internal combustion engine operating state is in an operating region in which the amount of HC is insufficient; An exhaust gas purification device for an internal combustion engine, comprising: an assist air control means for stopping supply.