JPH03217640A - Exhaust gas purifier of internal combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides an exhaust system with NOx in the presence of HC in an oxidizing atmosphere.
This invention relates to an exhaust purification device for a lean burn engine equipped with a catalyst that can purify the exhaust gas. [Prior Art] Recently, in order to improve fuel efficiency, development of lean-harn engines that burn at a lean or ultra-lean air-fuel ratio has been progressing. In the lean air-fuel ratio region, conventional catalysts reduce NO
Since NOx cannot be purified, NOx reduction has become an issue for lean burn engines, and catalysts that can purify NOx even at lean air-fuel ratios are attracting attention.

Japanese Unexamined Patent Publication No. 1-130735, Patent Application No. 1983-950
No. 26 is a catalyst (hereinafter referred to as Lean NOx) that is made of zeolite that supports transition metals and reduces and purifies NOx in an oxidizing atmosphere (excessive oxygen atmosphere) and in the presence of HC (hydrocarbons in exhaust gas). catalysis).

[Problem to be solved by the invention]

It is estimated that NOx purification by a lean NOx catalyst is a reaction between a part of HC in the exhaust gas, active species generated by partial oxidation, and NOx, and when HC in the exhaust gas is insufficient, the NOx purification rate decreases. In particular, when the catalyst temperature becomes high (approximately 300° C. or higher), direct oxidation of HC in the exhaust gas progresses, the amount of active species produced decreases, and the NOx purification rate gradually decreases.

Therefore, in the normal exhaust gas temperature range, the HC supply becomes rate-limiting (the NOx purification rate is determined by the amount of HC supplied), and an increase in NOx becomes a problem.

The present invention takes into account that in combustion in a lean burn engine, the fuel injection timing greatly affects combustion and therefore the amount of HC in the exhaust gas, and by controlling the fuel injection timing,
The purpose is to improve the NOx purification rate in a lean burn engine equipped with a lean NOx catalyst.

[Means to solve the problem]

According to the present invention, the above object can be achieved as shown in FIG. 1A.
, Independent injection in each cylinder equipped with a lean NOx catalyst (defined as a catalyst made of zeolite supported with transition metals or noble metals, which reduces NOx in exhaust gas in an oxidizing atmosphere and in the presence of HC) 2 in the exhaust system. Internal combustion engine 10
And, the amount of HC in the exhaust gas flowing into the lean NOx catalyst 2 is the required H for NOx purification by the lean NOx catalyst 2.
A 1000-stage HC amount deficiency determination means 4 determines whether or not the amount of C is insufficient, and while the HC amount deficiency determination means 4 determines that the amount of HC is insufficient, fuel is This is achieved by an exhaust gas purification device for an internal combustion engine that includes a fuel injection timing changing means 6 that changes the injection timing.

[Effect]

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

(i) Means for partially delaying the fuel injection period from the intake stroke (first embodiment). ...Step 108 in Figure 3
~1l1 (described later).

(ii) Means for injecting part of the fuel before the intake stroke (second embodiment). ...Stethop 13 in Figure 6
1 to 138 (described later).

(iii) Means for intermittently injecting fuel multiple times (third
Example)... Stesops 148 to 152 in Fig. 7
(described later).

(1v) Means for simultaneous injection or group injection using a plurality of fuel injection valves (fourth embodiment) Steps 172 to 176 in FIG. 8 (described later).

The above fuel injection timings are illustrated in Fig. IB. However, (0) in FIG. IB indicates the fuel injection timing in normal conditions (when HC is not insufficient) (for example, as disclosed in Japanese Patent Laid-Open No. 59-29733).

In case (1) (first embodiment), as shown in column (i> in Figure IB), when HC is insufficient, fuel injection is delayed from the normal injection timing, so some of the fuel is injected into the cylinder during that cycle. Some of the fuel that enters later becomes liquid and enters the cylinder irregularly, increasing incomplete combustion and increasing the amount of HC in the exhaust. increase and use it for catalytic reactions.

In the case of (11) (second embodiment), (i
As shown in column i), when HC is insufficient, some fuel is injected before the intake stroke and is put into the cylinder at the time of valve overflow at the opening timing of the exhaust valve/intake valve, so some of the fuel is It passes through the cylinder and flows to the exhaust port as unburned HC, where it is used in the catalytic reaction.

In the case of (iii) (third embodiment), as shown in column (iii) of Fig. IB, when HC is insufficient, the cylinder is injected intermittently many times, and when the air-fuel mixture flows into the cylinder. A mixture layer is formed intermittently in the vertical direction separated by air layers, and during the combustion process, residual combustion is generated in the lower mixture layer far from the ignition plug. This increases unburned HC in the exhaust gas, which is used for the catalytic reaction.

In case (iv) (fourth embodiment), (
iv) As shown in lm, when HC is insufficient, normal independent injection in column (0) is switched to simultaneous injection or group injection. In this case, 1/2 of the fuel injection is not synchronized with the intake stroke, so two mixture layers are formed in the cylinder, upper and lower, separated by an air layer, and unburned remains are left in the lower mixture layer. arise. This increased unburned H in the exhaust gas.
C is used for catalytic reactions.

〔Example〕

First, the basic configuration and operation of the independent injection method for each cylinder during normal operation (when there is no shortage of HC) will be explained.

As shown in FIG. 2A, the intake system of the internal combustion engine 10 is composed of an intake pipe 12, a throttle body 14 containing a throttle valve 16, a surge tank 20, and an intake manifold 24. sensor 1
8. The intake pipe negative pressure is detected by the intake pipe pressure sensor 22. Each intake port is provided with an electromagnetically controlled fuel injection valve 26 for independent injection in each cylinder.

10a is a cylinder (combustion chamber), and 28 is a spark plug. The exhaust system of the internal combustion engine 10 consists of an exhaust manifold 30 and a collective exhaust pipe, and the collective exhaust pipe includes 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. The lean NOx catalyst 2 is defined as a catalyst made of zeolite on which a transition metal or a noble metal is supported, and which reduces NOx in exhaust gas in an oxidizing atmosphere and in the presence of HC.

32 is a distributor whose distributor shaft 32a rotates once for every two revolutions of the crankshaft.

The distributor 32 includes a distributor shaft 3.
A crank angle sensor 34 that outputs a crank angle signal at every predetermined crank angle in response to the rotation of the crankshaft 2a is installed inside the engine.

Reference numeral 36 denotes an electronic control unit (ECU) consisting of a microcomputer.The ECU 36 is a central processor (CP) that executes calculations, as shown in detail in Fig. 2B.
U) 4Q, an A/D converter 42 that converts analog signals from the HC sensor 8, exhaust temperature sensor 9, intake pipe pressure sensor 22, and throttle sensor 18 into digital signals, and a signal from the crank angle sensor 34 that converts the signals from the engine into digital signals. Engine rotation speed signal forming circuit 4 that converts into a rotation speed signal and takes it in
4, a cross signal generating circuit 46, a read-only memory (ROM) 4B which is a read-only storage element for storing the calculation routines shown in FIGS. Access memory (RAM)
50, an output port 54 for outputting a valve opening time signal to the fuel injection valve (injector) 26 via a drive circuit 52 according to the calculation result in the CPU 40, and a bus 56 for communicating these. has been done.

The normal fuel injection timing structure of the calculation routine (routines shown in FIGS. 3 and 6 to 8) that is stored in the ROM 4B and read out by the CPU 40 to execute fuel injection is explained by referring to the routine shown in FIG. 3, for example. Stenop 101 ~ 105
, 109 to 111 (however, the third
Stenops 106, 107, and 108 in the figure are stenops specific to the present invention, of which stenoprobe 108 is a step specific to the first embodiment of the present invention, which will be described later. ) The engine rotational speed N and intake pipe pressure P are read using the stenops 101 and 102, respectively. Proceeding to step 103, the basic injection time τ is determined from the NP map shown in FIG. 4, for example. Here, since the fuel pressure is constant, the fuel injection amount is determined only by the injection time τ. Next, the process proceeds to the steno knob 104, where the basic injection time τ is converted into a fuel injection crank angle θτ using the following equation.

60 x 10z -12X10-3X N
Subtract the fuel injection crank angle θτ from the injection end crank angle θE (θE includes the fuel transportation period) corresponding to the fuel injection end time predetermined between DC By this, the best fuel injection start timing BIT (Hest injection time) is calculated (BIT - θE - θ). Then, through steps 106 to 108 (described later), the steps 109
Then, the current crank angle θP is determined according to the crank angle signal from the crank angle sensor 34. Next, the process proceeds to Step 110, where it is determined whether the current crank angle θP matches BIT or not, and when it fails, the process proceeds to Step 111 to start fuel injection, and when they do not match, fuel injection is high-passed. and return. In the fuel injection according to the above routine (the normal fuel injection routine that does not involve the steps 106 and 107108), BIT7-fuel injection is started and ends at θE, as shown in FIG. In this case, the fuel injection is normal at (0) in Figure IB.
The timing shown in white is the timing when the injected fuel enters the cylinder.
The timing is shown in black at 41i11. This timing is similar to that devised in Japanese Patent Application Laid-Open No. 59-29733.

However, if fuel injection is performed only according to the above normal fuel injection timing, in a lean Hearn engine equipped with the lean NOx catalyst 2, depending on the operating conditions, the effective NOx
Since there may be cases where the amount of HC in the exhaust gas is insufficient to achieve x-purification, it is necessary to determine whether or not there is a shortage of HC, and if there is a shortage of HC, the fuel injection timing should be changed to increase the amount of HC. is required, and it is a feature of the present invention to provide it.

Next, the structure of each embodiment will be explained together with its operation.

In the first embodiment, staves 106, 107, and 108 are inserted between stenops 105 and 109 in the fuel injection control calculation routine shown in FIG. For more details, see Stenop 106, lean NOx in the exhaust system.
HC sensor 8 provided upstream of the catalyst 2 (Fig. IA, 2A)
Read the output VHC from (see figure). Next, the process advances to step 107, where the current amount of HC in the exhaust gas VHC is determined as lean N.
Necessary HC required for NOx purification in Ox catalyst 2
It is determined whether or not the amount VO is insufficient (where 0 is a predetermined value that changes depending on the exhaust temperature, etc.). VHC>
■If it is 0, it is determined that there is no shortage, and if VHC≦■0, it is determined that there is a shortage. Therefore, the steno knob 107 is
This constitutes 1,000 stages 4 for determining C amount shortage. However, the HC amount deficiency determining means 4 may be replaced with a means for determining HC amount deficiency based on exhaust temperature or engine rotational speed. For example, it may be determined whether the exhaust temperature detected by the exhaust temperature sensor 9 is higher than a predetermined temperature in the range of 400°C to 500°C, and if it is higher, it may be determined that the amount of HC is insufficient. Alternatively, it may be determined whether the engine rotation speed detected by the crank angle sensor 34 is greater than, for example, 300 rpm, and if so, it may be determined that the HCI is insufficient. Stenop 10
If it is determined in step 7 that there is no shortage, proceed to step 109, and if it is determined that the HC amount is insufficient, proceed to step 108, and the best fuel injection starts! Delay iIIIBIT. Fig. 5 shows the crank angle conversion, and shows the case where BIT is delayed by θK, and fuel injection is executed in the crank angle range of θτ from crank angle BITM delayed by θK from BIT. It is shown that. Therefore, steps 108 to 111 correspond to the fuel injection timing changing means 6 in the first embodiment.

Since the best fuel injection start time BIT is delayed and the injection period τ remains unchanged, a part of the injected fuel does not enter the cylinder during that injection cycle and flows into the intake boat wall, as shown in column (i) of Figure IB. etc., and enters the cylinder during the next injection cycle. Since such fuel flows through the port wall and enters the cylinder as a liquid, it is difficult to completely burn the fuel, which increases the amount of HC in the exhaust gas. That is, the amount of unburned HC in the exhaust gas is increased by intentionally preventing complete combustion only during the period when switching to Stesobu 108.

As a result, the NOx purification rate of the lean NOx catalyst 2 is
It is increased only during the period when switching to SteSob 108.

Next, a second embodiment will be described with reference to FIG. Steno knobs 121 to 130 are 101 to 107 in the first embodiment.
, and steps 109 to 111, so the explanation of that part will be omitted. In the second embodiment, V of the first embodiment is
Step 108, which proceeds if HC>V O, replaces the steno knobs 131-138. That is, when it is determined that HCfi is insufficient in the stenoprop 126,
Proceed to Stenop 131. The steno knob 131 subtracts the crank angle θτ1 corresponding to the fuel injection time of the fuel to be injected before the intake stroke from the fuel injection crank angle θτ to obtain θτ2−θτθτ1. Here, θτ2 is a crank angle corresponding to the fuel injection time of the fuel injected during the intake stroke. The process then proceeds to the steno knob 132, where θτ2 is subtracted from the crank angle corresponding to a predetermined fuel injection end time to obtain a crank angle BIT corresponding to the best injection start time.

Next, go to Steno Knob 133 and check the current crank angle C.
Load RP. The process then proceeds to step 134, where a predetermined crank angle CRI at which fuel injection should be started before the intake stroke is read. The crank angle CRI is a preset angle such that when fuel is injected over a crank angle of θτ1 at this crank angle, the injected fuel just enters the cylinder at the time of the intake/halve halving. Next, the process proceeds to step 135, where it is determined whether or not the current crank angle is CRI.
If RP=CR 1, the process proceeds to step 136 and fuel injection is performed by the crank angle τ1. C with Stenop 135
If RP is not equal to CRI, the process proceeds to step 137, and the current crank angle CRP is determined as the best fuel injection timing BIT.
, and only if they are equal, step 1
Proceeding to step 38, fuel injection is performed by the crank angle τ2. The stenops 131 to 138 constitute a fuel injection timing change stage 6 in the second embodiment.

According to the above routine, as shown in column (1l) of Fig. IB, fuel is injected by a crank angle τ1 before the intake stroke, and thereafter fuel is injected by a crank angle τ2 at a certain time interval, and θτl and θτ2 The sum of the fuel injected at the crank angle is the total fuel injection amount τ for one cycle. The fuel injected first enters the cylinder during valve overflow when both the intake and exhaust valves are open, passes through the cylinder, and exits unburned to the exhaust port, removing 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 later at τ2 enters the cylinder during the intake stroke, and good combustion occurs as in normal times.

Next, a third embodiment will be explained with reference to FIG. Third
In the embodiment, steps 141 to 147153 to 1
55 are steps 101 to 107 of the first embodiment (FIG. 3).
, 109 to 111, the explanation will be omitted.

In the steno knob 147 of the third embodiment, the current HC amount V
If HC is not larger than the required HC amount VQ, that is, HC
If it is determined that the amount is insufficient, the steno knob 14
Proceed to step 8 and change the normal injection in column (0) of Figure IB to Figure IB (
iii Switch to intermittent multiple injection in > column. More specifically, the number of injections n is read with the steno knob 14g, and the process proceeds to the stethoscope 149, where the crank angle θτ corresponding to the basic fuel injection amount τ is divided into n equal parts to obtain the injection crank angle θτn per intermittent injection. Next, the process proceeds to the steno knob 150, and it is determined whether the current crank angle CRP read by the steno knob 145 is equal to the injection start crank angle CRI of the first intermittent injection.
Proceeding to step 52, fuel is injected by the crank angle τn, and if they are not equal, the process proceeds to step 151 to determine whether or not it is equal to the next injection start crank angle CRn (n=2, 3, 4, . . . n). If they are equal, proceed to Stenop 152 and τn
Only inject fuel.

By repeating this n times, one cycle of intermittent fuel injection is completed. The stenops 148 to 152 constitute the fuel injection timing change stage 6 in the third embodiment.

Due to this intermittent injection, n thick mixture layers are formed in the vertical direction within the cylinder (the lower the layer, the mixture layer of the fuel injected earlier), and an air layer is formed between the mixture layers. state is generated. It then goes through a compression stroke and is combusted in a combustion stroke. However, although the mixture in the upper layer near the spark plug 28 is combusted well, the mixture in the lower layer far from the spark plug 28 is difficult to burn (propagation of combustion is blocked by the air layer between the mixture layers). HC is generated, the amount of HC in the exhaust gas increases, and the NOx purification rate of the lean NOx catalyst 2 is improved. In addition, steps 153 to 155 in FIG.
The combustion stroke according to this is the normal combustion stroke according to column (0) of FIG. 1B, and results in good combustion. That is, Stesop 1
The intermittent fuel injection described above is performed only when VHC>VO at step 47.

Next, a fourth embodiment will be described with reference to FIG. Fourth
In the embodiment, stenops 161 to 171 correspond to stenops 101 to 107 and 109 to 111 in the first embodiment, so detailed explanation will be omitted. However, Stesop 169
A stenop is inserted to determine which cylinder to inject fuel into, but this is natural since independent injection is performed during normal injection. In the steno knob 166 of the fourth embodiment,
If the VHC of the current HC amount is not greater than the required HC amount vO, that is, if the HC amount in the exhaust gas is insufficient for NOx purification, the process proceeds to the steno panel 172 and the normal injection shown in FIG. IB (0) 8 is performed. Figure IB (iv) f! Switch to ll1 simultaneous injection in all cylinders. More specifically, τS is obtained by dividing the fuel injection period τ by 2 using the stenop 172, and then step 17
3, the injection start crank angles CRS 1 and CRS 2 (predetermined angles) of the fuel to be injected in each fuel injection period are read. Next, the process proceeds to the stenoprop 174, and it is determined whether the current crank angle CRP read by the stenoprop 164 is equal to CRSl. If they are equal, the process proceeds to the stenoprop 176, where fuel is injected to all cylinders simultaneously for the time τS. Proceed to step 175 and C
It is determined whether or not R P fJ<C R S 2, and when they are equal, the process proceeds to the steno knob 176 and injects fuel into all cylinders simultaneously for S time.

The stenops 172 to 176 constitute a fuel injection timing change stage 6 in the fourth embodiment.

In fuel injection according to such a routine, step 17
When switching to routes 2 to 176, when all cylinders are injected simultaneously, fuel enters the cylinders as is in only half of the cylinders, and the remaining fuel enters the cylinders as shown in column (1v) of Figure IB. It enters the cylinder in cycles. Therefore, two air-fuel mixture layers are formed in the cylinder, and there is an air layer between the air-fuel mixture layers, suppressing combustion propagation to the lower air-fuel mixture layer, increasing the amount of unburned HC, and increasing the amount of unburned HC in the exhaust gas. The amount of unburned HC also increases. Therefore, the amount of HC used for NOx purification of the lean NOx catalyst 2 increases, and the NOx purification rate is improved. Combustion according to Stesob 161-171 is in accordance with No. IB
Normal combustion is good according to column (0) in the diagram, and only when switching to STEPs 172 to 176 can the above-mentioned improvement in NOx purification rate be achieved at the cost of combustibility. As can be seen from the above, in any of the embodiments of the present invention, it is determined whether or not the current H CIV H C in the exhaust gas is insufficient compared to the predetermined H CIIV Q required for NOx purification. However, only when there is insufficient fuel injection timing, change the fuel injection timing to the normal good fuel injection timing (Figure IB (Fig.
(0) column) to (1) in Figure IB, (ii >
, (mountain), or any of the fuel injection timings shown in columns (iv), and only during this switched period, the amount of HC is increased with a slight sacrifice in combustibility, and it is lean. The amount of active species necessary for NOx purification (those that react with NoX to make the NOx harmless) is increased by being guided to the NOx catalyst 2, thereby improving the NOx purification rate. And VH
When C>VO, that is, when the amount of HC is not insufficient, the fuel injection mode with good combustibility under normal conditions (
(column (0) in Figure IB) and continue to operate with good combustibility as before.

〔Effect of the invention〕

According to the present invention, in the exhaust gas purification device for an internal combustion engine in which a lean NOx catalyst is provided in the exhaust system, the HC amount deficiency determining means and the fuel injection timing changing means are provided, so that the HC amount insufficient determining means detects the current amount in the exhaust gas. HC amount VHC is the predetermined required HC amount V
Determine whether it is larger than Q, and if it is not larger, that is, HC
When it is objected that the amount is insufficient, the fuel injection timing is changed by the fuel injection timing changing means to increase the amount of unburned HC (Part I).
The pattern in column (0) of diagram B is (i) (ii
), (iii) (change to any of the patterns in iv >), increase the amount of HC in the exhaust gas, and
The NOx purification rate of the Ox catalyst can be improved.

[Brief explanation of drawings]

FIG. IA is a basic block diagram of the exhaust gas purification device for an internal combustion engine according to the present invention, and FIG. IB is a diagram showing the fuel injection timing during normal operation and during switching (including the first to fourth embodiments) according to the present invention. A fuel injection timing chart, FIG. 2A is an equipment 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 the electronic control device in FIG. 2A, and FIG. 3 is a first diagram of the present invention. A control flowchart according to the embodiment, FIG. 4 is a graph of the engine rotation rate N and intake pressure P used in the calculation of the steno valve 103 in the routine of FIG. 3, and a relationship between the basic injection time τ, and FIG. 6 is a control flowchart according to the second embodiment of the present invention, and FIG. 7 is a control according to the third embodiment of the present invention. Flowchart: FIG. 8 is a control flowchart according to a fourth embodiment of the present invention. 2... Lean NOx catalyst 4... HC amount determining means 6... Fuel injection timing changing means 8... HC sensor 10... Internal combustion Engine 26...Fuel injection valve (injector) 36...
...Electronic control unit (ECU) license Toyota Motor Corporation

Claims (1)

[Claims] 1. An exhaust purification device for an internal combustion engine with independent injection for each cylinder, in which a so-called lean NO_x catalyst is installed in the exhaust system, wherein the amount of HC in the exhaust gas flowing into the lean NO_x catalyst is lean. HC amount deficiency determining means for determining whether or not the required HC amount is insufficient for NO_x purification by the NO_x catalyst; and HC in the exhaust gas while the HC amount insufficient determining means determines that the HC amount is insufficient. An exhaust purification device for an internal combustion engine, comprising: fuel injection timing changing means for changing the fuel injection timing so as to increase the amount of fuel injection.