JP2669093B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is produced by partial oxidation of HC necessary for NOx purification by a lean NOx catalyst in an internal combustion engine having a so-called lean NOx catalyst in an exhaust system. The present invention relates to an exhaust gas purification device for an internal combustion engine, which produces a large amount of active species by injecting water into an intake system or a combustion chamber when the active species is insufficient, and promotes NOx purification by a lean NOx catalyst.

[Related Art] In recent years, in order to improve fuel efficiency, the development of a lean burn internal combustion engine that burns at an air-fuel ratio in a lean region has been promoted, and a part thereof has been put into practical use. In the lean air-fuel ratio range, NOx cannot be purified by conventional catalysts, so reduction of NOx has become a problem for lean-burn internal combustion engines, and catalysts that can purify NOx even at lean air-fuel ratios are drawing attention.

JP-A-1-130735 and Japanese Patent Application No. 63-95026 teach a catalyst (hereinafter, referred to as a lean NOx catalyst) which is composed of a zeolite supporting a transition metal and reduces NOx in the presence of HC in an oxidizing atmosphere. doing.

[Problems to be Solved by the Invention] However, even if a lean NOx catalyst is installed in the exhaust system of an internal combustion engine, the NOx purification rate decreases and the NOx emission amount increases depending on the operating state of the engine. There is a problem that the NOx amount cannot be suppressed within the regulation value.

On the other hand, the NOx reduction mechanism by lean NOx catalyst
As shown in Fig. 10, it is presumed that it is a reaction between NOx and a part of HC in exhaust gas, an active species generated by partial oxidation. Therefore, as shown in FIG. 9, as the HC concentration in the exhaust gas increases, the generation amount of the active species increases, and the NOx purification rate increases. As mentioned above, depending on the operating condition, NOx
It is considered that the purification rate decreases because the HC concentration in the exhaust gas decreases depending on the operating state of the internal combustion engine.

The present invention relates to a method for producing NOx depending on the operating state of an internal combustion engine.
It is an object of the present invention to solve a reduction in purification rate or a shortage of HC amount by controlling a combustion temperature of an internal combustion engine.

Means for Solving the Problems According to the present invention, the object is to provide a lean NOx catalyst (made of deolite supporting a transition metal or a noble metal, provided in an exhaust system of an internal combustion engine,
(Defined as a catalyst that reduces NOx in the presence of HC in an oxidizing atmosphere), and the active species generated by partial oxidation of HC are directly related to the amount of active species required for NOx reduction by lean NOx catalyst. Exhaust purification of the internal combustion engine, which comprises: HC shortage determination means that makes a dynamic judgment, and when the HC shortage determination means determines that the operating state is short of active species, and water injection means that injects water into the intake system or the combustion chamber. Achieved by the device.

[Action] The HC concentration of the exhaust gas, and thus the NOx purification rate,
As shown in the figure, it greatly depends on the air-fuel ratio and, as shown in FIG. 8, on the catalyst temperature. That is,
Regarding the air-fuel ratio, in the air-fuel ratio region leaner than the stoichiometric air-fuel ratio, the HC amount gradually decreases and the NOx purification rate decreases until the air-fuel ratio where the torque fluctuation starts to increase rapidly. Regarding the catalyst temperature, if the catalyst temperature exceeds a certain temperature, the NOx purification rate will suddenly decrease.

HC is insufficient in a high load or high speed range where the engine is operating in a lean air-fuel ratio range up to the air-fuel ratio where the torque fluctuation rises abruptly, or the catalyst temperature (correlation with exhaust temperature) exceeds a specified temperature. The determining means determines that the active species is insufficient, and the water injection means injects water into the intake system or the combustion chamber, so that the combustion temperature of the internal combustion engine is reduced. As a result, the quenching area in the combustion chamber wall is widened, part of the fuel is incompletely burned, unburned fuel is increased, and HC in the exhaust gas is increased. This HC flows to the lean NOx catalyst,
Improves Ox purification rate.

On the other hand, when the HC deficiency determination means determines that the operating state is not such that the active species is deficient, the water injection is stopped,
Combustion temperature is raised, almost complete combustion is performed, fuel efficiency is improved, and HC mission is also reduced.

EXAMPLES Hereinafter, desirable examples of the present invention will be described.

In FIG. 1, the exhaust system 4 of the internal combustion engine 2 has a lean
A NOx catalyst 6 is provided, and an air-fuel ratio sensor 8,
An exhaust temperature sensor 10 is provided.

An intake pipe pressure sensor 14 is provided in the intake system 12 of the internal combustion engine 2. In addition, the intake system 12 is provided with a water injection valve 18 that injects water into the intake gas when ON, and stops water injection when OFF. The water injection valve 18 may be provided so as to directly inject into the combustion chamber of each cylinder instead of the intake system 12. The pressurized water from the water pump 24 is guided to the water reflection valve 18 via the water supply pipe 22, and the water 20 is injected when the water injection valve is turned on.

A crank angle sensor 16 is provided in the distributor that is interlocked with the crankshaft of the internal combustion engine 2 so as to issue a signal for timing the interrupt of the calculation described later and to calculate the signal to obtain the engine rotation speed. It has become. Further, the internal combustion engine 2 is provided with a water temperature sensor 28 that detects the engine cooling water temperature.

A control device 30 is provided to control the operation of the internal combustion engine 2. The control device 30 is composed of a microcomputer, and executes a central processing unit (CP)
U) 30a, read-only read only memory (ROM) 30b,
A random access memory (RAM) 30c for temporary storage, an analog / digital converter 30d for converting an analog input into a digital quantity, an input interface 30e for receiving a digital input, an output interface 30f for outputting a calculation result as a command signal, and the like Has a path 30g that communicates each element of.

The output of the crank angle sensor 16 is an input interface
30e, the outputs of the air-fuel ratio sensor 8, the exhaust temperature sensor 10, the intake pipe pressure sensor 14, and the water temperature sensor 28 are input to the analog / digital converter 30d, respectively.
The command from 0f is sent to the water injection valve 18.

The routines of FIGS. 2 and 6 are water injection control routines for the internal combustion engine of the first and second embodiments of the present invention, respectively. The subroutine of FIG. 3 corresponds to the first and second embodiments. It is shared. The first embodiment corresponds to a case in which it is indirectly determined from an air-fuel ratio or an exhaust temperature whether or not an operating state in which active species generated by partial oxidation of HC is insufficient, and a second embodiment corresponds to a case where HC in the exhaust gas This corresponds to the case where the determination is made directly from the density. These routines are stored in the ROM 30b, read out to the CPU 30a, interrupted at every fixed crank angle, and executed.

First, the first embodiment will be described with reference to FIGS. In FIG. 2, in steps 101 and 102, the operating state of the internal combustion engine is read. In the illustrated example, at step 101, the air-fuel ratio ABF output from the air-fuel ratio sensor 8 is read, and at step 102, the exhaust temperature T
Read EX. Step 102 also includes an intake pipe pressure sensor 1
Intake pipe pressure PM, output from 4, crank angle sensor 1
The engine speed NE obtained by calculating the output of 6 is read and P
The exhaust gas temperature TEX may be estimated from M and NE.

Subsequently, the process proceeds to steps 103 and 104, where the lower air-fuel ratio ABF1 and the upper air-fuel ratio AB that determine the region where the air-fuel ratio ABF and HC are low are determined.
It is determined whether or not it is between F2, that is, whether it is in the region with a small amount of HC between ABF1 and ABF2 in FIG. 7, and when it is in the air-fuel ratio region with a small amount of HC, proceed to step 105, When it is in the air-fuel ratio region where the amount of HC is large, the process proceeds to step 106.

When proceeding to step 105, that is, when HC is insufficient,
In step 105, the target water injection time TW is calculated from the air-fuel ratio ABF and exhaust temperature TEX-target water injection time TW map of FIG. In FIG. 4, the larger the air-fuel ratio ABF, the larger the target water injection time TW, and the larger the exhaust gas temperature TEX, the larger the target water injection time TW.

On the other hand, when the routine proceeds to step 106, that is, when the amount of HC is comparatively large, the exhaust temperature TEX becomes NOx in FIG.
Exhaust gas temperature TE corresponding to catalyst temperature at which purification rate drops sharply
Judging whether or not it is larger than X1, and if TEX> TEX1, then even if the amount of HC is relatively large, the direct oxidation of Fig. 10 and the oxidation of active species to the CO ₂ side will proceed, and HC will run short. In step 107, the target water injection time TW is calculated from the exhaust temperature TEX-target water injection time TW map shown in FIG. Fifth
In the figure, the larger the exhaust temperature TEX, the larger the target water injection time TW.

Then, the process proceeds to steps 108 to 109, and water injection is executed for the target water injection time TW calculated in steps 103 to 107.
That is, in step 108, the water injection valve 18 is turned on to start water injection, and then proceeds to step 109, where the timer is set to the water injection end time calculated by adding the water injection time TW to the current time. To do. FIG. 3 is a subroutine for interrupting when the time counted by the timer coincides with the water injection end time. In step 301 of FIG. 3, the water injection valve 18 is turned off to terminate the water injection. During the water injection, a part of the heat is used for evaporating water, so that the combustion temperature decreases, the combustion is incomplete, and the amount of HC in the exhaust gas increases. Conversely, when water injection is stopped, the combustion temperature rises.

When the exhaust gas temperature TEX is equal to or lower than the predetermined temperature TEX1 in step 106, since the amount of HC is relatively large and the direct oxidation of HC does not proceed, it is not necessary to perform water injection, and the routine returns.

In the first embodiment, steps 101, 102, 103, 104, 106
And the air-fuel ratio sensor 8, the exhaust gas temperature sensor 10 (or the intake pipe pressure sensor 14 for estimating the exhaust gas temperature and the crank angle sensor 16 as the engine rotational speed sensor) are set to the amount that HC and thus the active species are required for NOx reduction. An HC shortage determination means for determining whether or not there is a shortage is configured. Steps 105, 107, 108, 109, the subroutine of FIG. 3, and the maps of FIGS. 4 and 5, the water injection valve 18 and the water supply devices 22 and 24 for the water injection valve 18 serve as water injection means. Configure.

Next, a second embodiment for directly determining the lack of the active species due to HC will be described with reference to FIG. However, in FIG. 1, an HC sensor 26 for detecting the concentration of HC in the exhaust gas is provided downstream or upstream of the lean NOx catalyst 6, and its output is input to an analog / digital converter 30d.

In FIG. 6, in step 201, the HC concentration VHC output from the HC sensor 26 is read. Then, it progresses to step 202 and it is judged whether present VHC is smaller than predetermined HC concentration V0. If VHC <V0, the flow proceeds to step 203 because the HC is insufficient for the active species, and the water injection valve 18 is turned on. Then, the flow proceeds to step 204 to set the water injection end timer. Steps 203 and 204 correspond to steps 108 and 109 of the first embodiment, and the subroutine of FIG. 3 is used for stopping the water injection according to the first embodiment. If VHC <V0 is not satisfied in step 202,
Since the HC concentration is relatively high, it is not necessary to execute water injection, and the flow returns as it is.

In the second embodiment, steps 201 and 202, the HC sensor
26 constitutes HC shortage determination means. Also, steps 203 and 2
04, the subroutine of FIG. 3, and the water injection valve 182 and the water supply devices 22 and 24 for the water injection valve 18 constitute water injection means.

 Next, the operation of the present invention will be described.

In the lean air-fuel ratio region, the air-fuel ratio ABF is ABF1 (for example, “1
6 ”) and ABF2 (for example,“ 19 ”), and even if the air-fuel ratio is ABF1 or less or ABF2 or more, exhaust temperature
When TEX is higher than the predetermined temperature TEX1, and when the HC concentration VHC is lower than the predetermined concentration V0, HC and therefore the active species is NOx.
It is judged to be insufficient in terms of reduction, and the water injection means executes water injection for a predetermined time. In cases other than the above, it is determined that HC and therefore the active species will not be insufficient for NOx reduction, and water injection is stopped.

When it is judged that HC is insufficient and water injection is executed, the combustion temperature of the internal combustion engine 2 becomes low, the combustion becomes partially incomplete combustion, and the amount of HC in the exhaust gas increases due to unburned fuel. To increase the NOx purification rate of the lean NOx catalyst 6.

If it is determined that HC is not insufficient and water injection is stopped,
The temperature of the internal combustion engine 2 rises, almost complete combustion is performed,
Good fuel economy and low HC emissions.

EFFECTS OF THE INVENTION According to the present invention, since the HC deficiency determination means and the water injection means are provided in the internal combustion engine in which the lean NOx catalyst is mounted in the exhaust system, the amount of active species generated by the partial oxidation of HC is reduced.
When it is determined that NOx reduction is insufficient, water injection is performed to lower the combustion temperature, and partially incomplete combustion can increase the amount of HC in exhaust gas, and thus the amount of active species, and increase the NOx purification rate. it can.

[Brief description of the drawings]

FIG. 1 is a system diagram of an exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention, FIG. 2 is a control flow diagram of the first embodiment of the present invention, and FIG. 3 is FIG. 2 or FIG. Control flow chart for stopping the water injection in the routine of FIG. 4, FIG. 4 is the air-fuel ratio ABF used in step 105 of FIG.
Exhaust temperature TEX-Target water injection time TW map diagram, Fig. 5 shows air-fuel ratio TEX used in step 107 of Fig. 2-
Target water injection time TW map diagram, FIG. 6 is a control flow diagram of the second embodiment of the present invention, FIG. 7 is an air-fuel ratio-torque fluctuation, HC, NOx characteristic diagram, and FIG. 8 is catalyst temperature-NOx purification rate. Fig. 9 is a characteristic diagram, Fig. 9 is a characteristic diagram of HC concentration-NOx purification rate, and Fig. 10 is a NOx reduction mechanism diagram. 2 …… Internal combustion engine 4 …… Exhaust system 6 …… Lean NOx catalyst 8 …… Air-fuel ratio sensor 10 …… Exhaust temperature sensor 12 …… Intake system 14 …… Intake pipe pressure sensor 16 …… Crank angle sensor 18 …… Water Injection valve 20 …… Injected water 26 …… HC sensor 28 …… Water temperature sensor 30 …… Control device

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F02D 45/00 301 F02D 45/00 312H 312 312 368G 368 F02M 25/02 K F02M 25/022 H B01D 53 / 36 101B

Claims (1)

(57) [Claims] 1. A catalyst for reducing NOx in the presence of HC in an oxidizing atmosphere, which is a so-called lean N, comprising a zeolite supporting a transition metal or a noble metal, provided in an exhaust system of an internal combustion engine.
It is indirectly or directly determined whether or not the Ox catalyst and the active species generated by the partial oxidation of HC are in an operating state in which the amount of the active species required for the reduction of NOx by the lean NOx catalyst is insufficient.
An HC deficiency determination means, and a water injection means for injecting water into the intake system or the combustion chamber when the HC deficiency determination means determines that the operating state is short of active species. Exhaust purification device.