JP2773341B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a lean burn engine having an exhaust system provided with a catalyst capable of purifying NOx in the presence of HC in an oxidizing atmosphere.

[Conventional technology]

Recently, in order to improve fuel efficiency, the development of a lean burn engine that burns at an air-fuel ratio in a lean or ultra-lean region has been promoted. In the lean air-fuel ratio range, conventional catalysts
Since x cannot be purified, reduction of NOx has become an issue for lean burn engines, and catalysts that can purify NOx even at a lean air-fuel ratio are attracting attention.

Japanese Patent Application Laid-Open No. 1-130735 and Japanese Patent Application No. 63-95026 are composed of a zeolite having a transition metal supported thereon in an oxidizing atmosphere (in an oxygen-excess atmosphere) and in the presence of HC (hydrocarbon in exhaust gas). It teaches a catalyst for reducing and purifying NOx (hereinafter referred to as a lean NOx catalyst).

[Problems to be solved by the invention]

NOx purification by the lean NOx catalyst is presumed to be a reaction between a part of HC (active species generated by partial oxidation) in the exhaust gas and NOx. If the exhaust gas lacks HC, the NOx purification rate decreases. In particular, when the catalyst temperature becomes high (about 300 ° C. or higher), direct oxidation of HC in the exhaust gas proceeds, the amount of active species generated decreases, and the NOx purification rate gradually decreases. Therefore, in the normal exhaust temperature range, the HC supply rate-determining (depending on the supplied HC amount)
NOx purification rate is determined), and increase of NOx becomes a problem.

The present invention controls the fuel injection timing in consideration of the fact that the fuel injection timing greatly influences the combustion in the combustion of the lean burn engine, and therefore the HC amount in the exhaust gas.
N in lean burn engines with lean NOx catalyst
The purpose is to improve the Ox purification rate.

[Means for solving the problem]

According to the present invention, according to the present invention, as shown in FIG. 1A, the exhaust system comprises a lean NOx catalyst (a zeolite carrying a transition metal or a noble metal, which purifies NOx in 2) is installed in the atmosphere (in the lean air-fuel ratio operating range), in the presence of HC, as a catalyst that reduces NOx in exhaust gas), and the injection timing of each cylinder is set to the best injection timing according to the operating state. An exhaust purification system for an individual-cylinder independent injection type internal combustion engine provided with fuel injection means for setting and executing a lean air-fuel ratio operation, wherein the amount of HC in exhaust flowing into the lean NOx catalyst 2 is controlled by a lean NOx catalyst. HC shortage judging means 4 for judging whether the required HC amount required for NOx purification by the HC 2 is insufficient, and in the cylinder when the HC amount shortage judging means 4 judges that the HC amount is insufficient. The rate at which the fuel Serial and fuel injection timing changing means 6 for changing the best injection timing fuel injection timing to be greater than the are achieved by an exhaust device of an internal combustion engine, characterized in that it comprises a.

[Action]

In the above description, the fuel injection timing changing means 6 includes, for example, any one of the following.

(I) Means for partially delaying the fuel injection timing from the intake stroke (first embodiment). ... Steps 108 to 111 in FIG. 3 (described later).

(Ii) Means for injecting part of the fuel before the intake stroke (second embodiment). ... Steps 131 to 138 in FIG. 6 (described later).

(Iii) Means for injecting fuel intermittently many times (third embodiment) Steps 148 to 152 in FIG. 7 (described later).

(Iv) Means for Simultaneous Injection or Group Injection of a Plurality of Fuel Injection Valves (Fourth Embodiment) Steps 172-1 in FIG.
76 (described below).

FIG. 1B shows the above fuel injection timings. However, (0) in FIG. 1B shows the fuel injection timing at normal time (when HC is not insufficient) (for example,
29733).

In the case of (i) (first embodiment), as shown in the column (I) of FIG. 1B, when HC is insufficient, the combustion injection is delayed from the injection timing at the normal time. Inside the cylinder in the next cycle. Some of the fuel that enters late is liquefied and enters the cylinder irregularly, so that incomplete combustion increases and the amount of HC in the exhaust increases, which is used for the catalytic reaction.

In the case of (ii) (second embodiment), as shown in column (II) of FIG. 1B, when HC is insufficient, some fuel is injected before the intake stroke to open the exhaust valve / intake valve. Since the fuel is put into the cylinder at the time of valve overlap, a part of the fuel flows through the cylinder to the exhaust port as unburned HC and is used for the catalytic reaction.

In the case of (iii) (third embodiment), (III) in FIG. 1B
As shown in the column, when HC is insufficient, multiple injections are performed intermittently to form a mixture layer vertically and intermittently separated by an air layer in the cylinder when the mixture flows into the cylinder. In the combustion process, a residue is formed in the lower gas mixture layer far from the spark plug. This increases the unburned HC in the exhaust, which is used for the catalytic reaction.

In case (iv) (fourth embodiment), as shown in column (IV) of FIG. 1B, when HC is insufficient, the normal independent injection in column (0) is switched to simultaneous injection or group injection. In this case, since 1/2 of the fuel injection is not synchronized with the intake stroke,
Air-fuel layers separated from each other by an air layer are formed in the upper and lower stages in the cylinder, and unburned air remains in the lower air-fuel mixture layer. The unburned HC in the exhaust gas thus increased is used for the catalytic reaction.

〔Example〕

First, the basic configuration and operation of each cylinder independent injection system during normal operation (when HC is not insufficient) will be described.

As shown in FIG. 2A, the intake system of the internal combustion engine 10 is an intake pipe.
12, a throttle body 14 having a throttle valve 16 therein, a surge tank 20, and an intake manifold 24. The opening of the throttle valve 16 is detected by a throttle sensor 18, and the intake pipe negative pressure is detected by an intake pipe pressure sensor 22. Each intake port is provided with an electromagnetically controlled injection valve 26 for independent injection of each cylinder. 10a is a cylinder (combustion chamber), and 28 is a spark plug. The exhaust system of the internal combustion engine 10 includes an exhaust manifold 30 and an exhaust pipe assembled together. The assembled exhaust pipe has an HC sensor 8, an exhaust temperature sensor 9, a lean NOx catalyst 2, and a three-way catalyst provided as necessary. Alternatively, an oxidation catalyst 3 is provided. However, the three-way catalyst or the oxidation catalyst 3 is not essential. Here, the lean NOx catalyst 2 is composed of a zeolite supporting a transition metal or a noble metal, and in an oxidizing atmosphere,
It is defined as a catalyst that reduces NOx in exhaust gas in the presence of HC.

Reference numeral 32 denotes a distributor, and the distributor shaft 32a makes one rotation with two rotations of the crankshaft. The distributor 32 includes a crank angle sensor 34 that outputs a crank angle signal at predetermined crank angles in accordance with the rotation of the distributor shaft 32a.

Reference numeral 36 denotes an electronic control unit (ECU) comprising a microcomputer. The ECU 36, as shown in detail in FIG. 2B, includes a central processor unit (CPU)
A / D converter 42 for converting analog signals from C sensor 8, exhaust temperature sensor 9, intake pipe pressure sensor 22 and throttle sensor 18 into digital signals, and converting signals from crank angle sensor 34 into engine speed signals An engine speed signal forming circuit 44 and a clock generating circuit 46
And a read-only memory (RO) of a read-only storage element for storing the arithmetic routines of FIGS. 3 and 6 to 8.
M) 48, a random access memory (RAM) 50 for temporarily storing data, and a calculation result in the CPU 40,
It comprises an output port 54 for outputting a valve opening time signal to a fuel injection valve (injector) 26 via a drive circuit 52, and a bus 56 for communicating these.

An arithmetic routine (routine of FIGS. 3 and 6 to 8) which is stored in the ROM 48 and read by the CPU 40 to execute fuel injection. Description will be made based on 101 to 105 and 109 to 111 (however, steps 106, 107, and 108 in FIG. 3).
Are steps unique to the first embodiment of the present invention, which will be described later).

In steps 101 and 102, the engine speed N,
The intake pipe pressure P is read. Proceeding to step 103, the basic injection time τ is determined, for example, from the NP map shown in FIG. Here, since the fuel pressure is fixed, the fuel injection amount is determined only by the injection time τ. Then steps
Proceeding to 104, the basic injection time τ is converted into the fuel injection crank angle θτ by the following equation.

Next, the routine proceeds to step 105, where the injection end crank angle θE corresponding to the fuel injection end timing predetermined between 30 ° and 120 ° ATDC (after top dead center) (θE includes the fuel transport period). Then, the best fuel injection start timing BIT (best injection time) is calculated by subtracting the fuel injection crank angle θτ from (BIT = θE−θτ). Then, the process proceeds to step 109 via steps 106 to 108 (described later), and the crank angle sensor 34
The angle θP is determined according to the crank angle signal from the controller. Incidentally, the routine proceeds to step 110, where the current crank angle θP is
It is determined whether or not the value matches the IT. If the value matches the value, the process proceeds to step 111 to start fuel injection. If not, the process returns by bypassing the fuel injection. In the fuel injection according to the above routine (normal fuel injection routine without steps 106, 107 and 108), fuel injection starts at BIT and ends at θE, as shown in FIG. The fuel injection in this case has the timing shown in white in the normal time column (0) in FIG. 1B, and the timing at which the injected fuel enters the cylinder is shown in black in the above (0) column in FIG. 1B. This is the timing shown. This timing is described in JP-A-59-2973.
The timing will be based on the one proposed in No. 3.

However, when fuel injection is performed only in accordance with the normal fuel injection timing described above, in a lean burn engine equipped with the lean NOx open medium 2, an effective NOx
Since the amount of HC in the exhaust gas for performing purification may be insufficient, it may be determined whether or not HC is insufficient, and when HC is insufficient, the fuel injection timing may be switched so as to increase the HC amount. It is a feature of the present invention that it becomes necessary and provides it.

 Next, the configuration of each embodiment will be described together with the operation.

In the first embodiment, in the fuel injection control calculation routine of FIG.
Insert 6, 107 and 108. For more information, see step 106
In read HC sensor 8 (Figure 1A, FIG. 2A reference) provided upstream of the lean NOx Hirakinakadachi 2 and the exhaust system output V _HC from. Next, the routine proceeds to step 107, where the present exhaust HC amount V
_HC is to lean NOx Hirakinakadachi required amount of HC V ₀ required in the NOx purification in 2 (however, the predetermined value V ₀ is changed by the exhaust gas temperature, etc.), determines whether the missing. V _HC > V
₀ if the do not lack, it is determined that the shortage if V _HC ≦ V _0. Therefore, step 107 constitutes the HC amount shortage determination means 4 in the first embodiment. However, the HC amount deficiency determining means 4 may be replaced with a means for determining the HC amount deficiency based on the exhaust gas temperature or the engine speed. For example, it may be determined whether or not the exhaust gas temperature detected by the exhaust gas temperature sensor 9 is higher than a predetermined temperature in a range of 400 ° C. to 500 ° C. If it is higher, it may be determined that the HC amount is insufficient, Alternatively, it may be determined whether or not the engine speed detected by the crank angle sensor 34 is higher than, for example, 3000 rpm, and if it is higher, it may be determined that the HC amount is insufficient. If it is determined in Step 107 that there is no shortage, the process proceeds to Step 109.If it is determined that the HC amount is insufficient, Step 108 is performed.
To delay the best fuel injection start timing BIT. Fifth
The figure shows the crank angle conversion, where BIT is θK
From the crank angle BITM delayed from BIT by θK, within the crank angle range of θτ,
This shows that fuel injection is performed. Therefore,
Steps 108 to 111 correspond to the fuel injection timing changing means 6 in the first embodiment.

Since the best fuel injection start timing BIT is delayed and the injection period τ does not change, as shown in column (I) of FIG. 1B, part of the injected fuel does not enter the cylinder in the injection cycle, and Etc. and enter the cylinder in the next injection cycle. Since such fuel is connected to the port wall to be in a liquid state and enters the cylinder, it is difficult to completely burn the fuel, and the amount of HC in the exhaust gas increases. That is, the amount of unburned HC in the exhaust gas is increased by intentionally preventing complete combustion only during the period of switching to step 108. As a result, the NOx purification rate of the lean NOx open medium 2 is increased only during the period of switching to step 108.

Next, a second embodiment will be described with reference to FIG. Steps 121 to 130 correspond to steps 101 to 107 and steps 109 to 111 of the first embodiment, and therefore description of those parts is omitted. In the second embodiment, step 108 of the first embodiment, which proceeds when V _HC > V ₀ , replaces steps 131 to 138. That is, when it is determined in step 126 that the HC amount is insufficient, the process proceeds to step 131. The fuel injection crank angle Shitatau at step 131 subtracts the crank angle Shitatau ₁ corresponding to the fuel injection time to be injected before the intake stroke, seek θτ _{2 =} θτ-θτ _1. Here, θτ ₂ is a crank angle corresponding to the fuel injection time of the fuel injected in the intake stroke. Then the process proceeds to step 132, determining a crank angle BIT corresponding to the start timing best fuel injection by subtracting the Shitatau ₂ from the crank angle corresponding to the predetermined fuel injection end timing determined in advance. Step 133
Go to, read the current crank angle CR _P. Then the process proceeds to step 134, reads a predetermined crank angle CR ₁ should start injection before the intake stroke. Crank angle CR ₁
Upon injection of fuel over crank angle Shitatau ₁ at this crank angle, the injected fuel just a predetermined angle to enter the cylinder during the intake / exhaust valve overlap. Then the process proceeds to step 135, determines whether the current crank angle has become CR _1, C
Proceed to R _P = CR _1's and step 136 executes the fuel injection only crank angle tau _1. CR _P in step 135 proceeds to step 137 be equal to CR _1, the current crank angle CR _P
There is judged whether equal to the best fuel injection BIT, proceeds only to step 138 if they are equal, executing the fuel injection only crank angle tau _2. Steps 131 to 138 constitute the fuel injection time changing means 6 in the second embodiment.

By the routine, first in Figure 1B (II) as shown in the column, the fuel is injected earlier before the intake stroke by crank angle tau _1, the fuel by the crank angle tau ₂ have over a certain time then injected, Shitatau The sum of the fuel injected at ₁ and the crank angle of θτ ₂ is the total fuel injection in one cycle. The fuel injected earlier enters the cylinder at the time of valve overlap when both the intake valve and the exhaust valve are open, passes through the cylinder, exits unburned to the exhaust port, and removes HC in the exhaust. increase. Therefore, the amount of HC supplied to the lean NOx catalyst 2 increases, and the NOx purification rate is improved. The fuel injected at τ ₂ later enters the cylinder during the expiration stroke, and good combustion is performed as in normal times.

Next, a third embodiment will be described with reference to FIG. In the third embodiment, Steps 141 to 147 and 153 to 155 correspond to Steps 101 to 107 and 109 to 111 in the first embodiment (FIG. 3), and thus the description is omitted. Step 14 of the third embodiment
In step 7, if the current HC amount V _HC is not larger than the required HC amount V ₀ , that is, if it is determined that the HC amount is insufficient, the process proceeds to step 148, and FIG. The normal injection is switched to the intermittent multiple injection in the column of FIG. 1B (III). More specifically, in step 148, the number of injections n is read, and the flow proceeds to step 149 to read the number of injections n. The flow then proceeds to step 149, where the crank angle θτ corresponding to the basic fuel injection amount τ
Into n equal parts, and the injection crank angle θ per one intermittent injection
Find τ _n . Go to step 150 and step 1
Current crank angle CR _P which had read at 45 it is determined whether the equal to the injection start crank CR ₁ of the first round of intermittent injection, the fuel is injected only crank angle tau _n proceeds to step 152 if equal If not equal, the routine proceeds to step 151, where the next injection start crank angle CR _n (n = 2, 3, 4,
.. N), and if so, step 15
Proceeding to 2, fuel is injected by τ _n . By repeating this n times, the intermittent fuel injection in one cycle is completed. Steps 148 to 152 constitute the fuel injection timing changing means 6 in the third embodiment.

Due to such intermittent injection, a rich air-fuel mixture layer is formed in the cylinder in the vertical direction in the n-th layer (lower fuel-air mixture layer of fuel injected earlier), and an air layer is formed between the air-fuel layers. State is generated. Then, it is burned in a combustion stroke through a compression stroke. However, although the upper layer air-fuel mixture near the ignition plug 28 is satisfactorily burned, the lower layer air-fuel mixture far from the ignition plug 28 is hardly burned (the propagation of combustion is prevented by the air layer between the air-fuel layers). , HC is generated and HC in exhaust
The amount increases, and the NOx purification rate of the lean NOx catalyst 2 is improved.
Note that the combustion stroke according to steps 153 to 155 in FIG.
This is a normal combustion stroke according to the column (0) in FIG. That is, the intermittent combustion injection is performed only when V _HC > V ₀ is not _satisfied in step 147.

Next, a fourth embodiment will be described with reference to FIG. In the fourth embodiment, steps 161 to 171 correspond to steps 101 to 107 and 109 to 111 of the first embodiment, and thus detailed description will be omitted. However, the step of determining the cylinder to be subjected to combustion injection in step 169 is inserted, but this is natural because normal injection performs independent injection. In step 166 of the fourth embodiment, the current HC amount of _VHC is required HC
If it is not larger than the amount V ₀ , that is, if the HC amount in the exhaust gas is insufficient for NOx purification, the routine proceeds to step 172, in which the normal injection shown in the column (0) of FIG. Switch to simultaneous injection for all cylinders. More specifically, at step 172, the combustion injection period τ is divided by 2 to obtain τ _S , and then at step 173
To read the injection start crank angles CR _S1 , CR _S2 (predetermined angles) of the fuel to be injected in each combustion injection period. Then the process proceeds to step 174, determines whether the current crank CR _P which had read in step 164 is equal to CR _S1, only the fuel injection willing all cylinders simultaneously τS time to step 176 if equal, not equal Step 17
Proceed to 5 CR _P is determined whether equal to CR _S2, willing to only the fuel injection all cylinders simultaneously tau _S time to step 176 when equal. Steps 172 to 176 constitute the combustion injection period changing means 6 in the fourth embodiment.

In the fuel injection according to such a routine, step 17
When the route is switched to the route of 2 to 176, when all the cylinders are simultaneously injected, as shown in the column (IV) of FIG. Enter cylinder in cycle. Therefore, an air-fuel mixture layer is formed in two stages in the cylinder, and there is an air layer between the air-fuel layers, which suppresses combustion propagation to the lower air-fuel mixture layer, increases the amount of unburned HC, and increases The amount of unburned HC also increases. Therefore, HC used for NOx purification of the lean NOx catalyst 2
And the NOx purification rate is improved. The combustion according to steps 161-171 is a normal good combustion according to the column (0) in FIG. 1B. Only when switched to steps 172-176, the above-mentioned NOx purification rate with sacrificing combustibility is reduced. An improvement is obtained.

As can be seen from the above, in the present invention, in any of the embodiments, it is determined whether or not the present HC amount V _{HC in} the exhaust gas is insufficient compared with the predetermined HC amount V ₀ required for NOx purification. Judge,
Only when the fuel injection time is insufficient, the fuel injection timing is changed from the normal good fuel injection timing (the one in the column (0) in FIG. 1B) to the first fuel injection timing.
Switching to any one of the fuel injection timing modes shown in the columns (I), (II), (III), and (IV) in the figure, and only during this switching time, the HC amount To increase the amount of active species (that react with NOx and detoxify NOx) required for NOx purification, thereby improving the NOx purification rate. Then, when V _HC > V _0, that is, when the HC amount is not insufficient, the fuel injection mode is returned to the normal good combustible fuel injection mode (column (0) in FIG. 1B), and the conventional good combustion is performed. Sex driving.

〔The invention's effect〕

According to the present invention, in the exhaust gas purification device of the internal combustion engine having the lean NOx catalyst in the exhaust system, the HC amount shortage determination unit and the fuel injection timing changing unit are provided. It is determined whether the HC amount V _HC is greater than a predetermined required HC amount V ₀ , and when it is not large, that is, when it is determined that the HC amount is insufficient, the fuel injection timing is changed by the fuel injection timing changing means so as to increase the unburned HC ( For example, the patterns in the column (0) of FIG. 1B are represented by (I), (II), (III), (I
V), the amount of HC in the exhaust gas is increased, and the NOx purification rate of the lean NOx catalyst can be improved. In addition, there is no need to mount a dedicated HC tank, and HC runs out. Further, the wood fuel is thermally decomposed by the heat in the cylinder, and HC having a small number of C in one molecule, which is particularly effective for improving the NOx purification rate of the lean NOx catalyst, can be automatically generated.

[Brief description of the drawings]

FIG. 1A is a basic block diagram of the exhaust gas purifying apparatus for an internal combustion engine of the present invention, and FIG. 1B is a diagram showing the normal fuel injection timing and the fuel injection timing at the time of switching (including the first to fourth embodiments) of the present invention. FIG. 2A is a system diagram of an exhaust gas purification device for an internal combustion engine according to the present invention, FIG. 2B is a configuration diagram of an electronic control device in FIG. 2A, and FIG. FIG. 4 is a control flowchart according to one embodiment, FIG. 4 is a relation diagram between a graph of the engine rotation speed N-intake pressure P used in the calculation of step 103 of the routine of FIG. 3 and the basic injection time τ, and FIG. FIG. 3 is a relational diagram converted into various quantities of crank angles expressed in each step in the routine of FIG. 3, FIG. 6 is a control flowchart according to the second embodiment of the present invention, and FIG. 7 is a control flowchart according to the third embodiment of the present invention. Control flowchart, FIG. Control flowchart according to the fourth embodiment of the light is. 2 ... lean NOx catalyst 4 ... HC amount determination means 6 ... fuel injection timing changing means 8 ... HC sensor 10 ... internal combustion engine 26 ... fuel injection valve (injector) 36 ... electronic control unit (ECU)

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (1)

(57) [Claims] (1) NO in exhaust gas in an exhaust system in a lean air-fuel ratio operation region.
Exhaust purification of each cylinder independent injection type internal combustion engine equipped with a lean NOx catalyst that purifies x and equipped with fuel injection means that sets and executes the injection timing of each cylinder to be the best injection timing according to the operating state An exhaust gas flowing into the lean NOx catalyst during a lean air-fuel ratio operation.
HC amount deficiency determining means for determining whether the amount of C is insufficient for the required HC amount required for NOx purification by the lean NOx catalyst, and HC amount deficiency determining means determine that the HC amount is insufficient. A fuel injection timing changing means for changing the fuel injection timing so that the rate at which the fuel in the cylinder flows out to the exhaust system while being unburned is sometimes larger than the best injection timing. Exhaust gas purification device for internal combustion engine