JP3775547B2 - Exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device that purifies nitrogen oxides discharged from a diesel engine.
[0002]
[Prior art]
As a conventional exhaust gas purifying apparatus, for example, as disclosed in Japanese Patent Laid-Open No. 8-74561, a reducing agent is supplied from a common rail type injection system by POST injection from a catalyst inlet according to operating conditions of the internal combustion engine. There are things.
[0003]
[Problems to be solved by the invention]
However, in such a conventional exhaust gas purification device,
(1) The HC species that maximizes the NOx reduction ability of the catalyst varies depending on the catalyst. When a different HC species is given as the reducing agent, the NOx reduction effect is reduced.
(2) When the internal combustion engine is in the cold state, the ratio of light components increases because the ratio of unburned fuel is large, unlike the case where the HC species discharged from the engine is in the warm state.
(3) Since the temperature of the combustion chamber is low when the engine is cold, the HC species supplied to the catalyst is different from that during the warm-up at the same POST injection amount and POST injection timing as during the warm-up.
Therefore, when the reducing agent is supplied in the cold condition under the same conditions as in the warm-up condition, the HC species supplied to the catalyst is different from that in the warm-up condition. The problem arises that performance cannot be expected.
[0004]
The present invention has been made paying attention to such conventional problems, and detects the HC species and amount discharged from the engine when cold, and only the necessary amount of HC species from the reducing agent supply device is detected. It aims at solving the said problem by supplying to a catalyst.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention includes a catalyst that is disposed in an exhaust passage of an internal combustion engine and purifies exhaust gas, and supplies a reducing agent to the catalyst. In the exhaust gas purifying apparatus having the reducing agent supply means, means for determining whether or not to supply the reducing agent to the catalyst according to the temperature rise state of the catalyst, and whether the operating state of the internal combustion engine is a cold state The means for determining whether or not the engine is in a warm-up state and the reducing agent supply amount when it is determined to supply the reducing agent to the catalyst are increased in the cold state in comparison with the warm-up state according to the determination result of the operating state. It is characterized by controlling as follows.
[0007]
The invention described in Claim 2 is the exhaust gas purifying apparatus according to claim 1, a reducing agent supply to the catalyst and is characterized in that intends rows POST injection by common rail injection system.
[0009]
Furthermore, the invention according to claim 3 is the exhaust gas purification device according to claim 1 or 2 , further comprising an HC adsorbent upstream of the catalyst, the amount of HC adsorbed on the HC adsorbent and the operation. The supply start timing of the reducing agent is controlled based on the determination result of the state.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an exhaust gas purifying apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram showing a configuration of a first embodiment of an exhaust gas purifying apparatus according to the present invention.
[0011]
First, the configuration will be described with reference to FIG. 1. An engine 10 is provided, and an NOx catalyst 31 interposed in a catalyst case 30 located in the exhaust passage 20 is provided as an exhaust gas purification device. Further, upstream of the NOx catalyst 31, there is a common rail fuel injection device 40 as a reducing agent supply means, and an arbitrary amount of reducing agent can be supplied from the reducing agent tank 50.
In the figure, reference numeral 60 denotes an exhaust temperature sensor.
[0012]
Next, the operation of the first embodiment will be described.
(1) The catalyst contains an optimum HC species as a reducing agent, and the NOx reduction effect obtained by the supplied reducing agent is different (see FIG. 6).
(2) The HC type discharged from the engine when cold is different from that when warm. When cold, unburned HC increases and the content of light HC increases (see FIG. 7).
For the above two reasons, in the first embodiment, the effect of the NOx catalyst can be maximized by changing the amount of HC supplied during cold operation from that during warm-up.
[0013]
For example, when the HC species that is effective as a catalyst reducing agent is relatively light (HC with a small C number), the amount of light HC discharged from the engine when it is cold is large. Conversely, if the HC species effective for the catalyst is relatively heavy, the amount of heavy HC discharged from the engine when cold is reduced, so the amount of reducing agent to be supplied By increasing the number, it is possible to maximize the effect of the NOx catalyst when cold.
[0014]
Next, it demonstrates along the flowchart shown in FIG.
In step S101, the operating conditions (Q, intake air temperature, intake air amount) of the engine 10 are read.
[0015]
In step S102, the engine oil temperature is read.
[0016]
In step S103, it is determined by the catalyst activity determination means whether the NOx catalyst 31 is in the activation temperature range. If YES, the process proceeds to step S104.
In the first embodiment, the determination is made by the exhaust temperature sensor 60 provided upstream of the NOx catalyst 31, but the determination is made by calculating the exhaust temperature from the intake air temperature, the fuel injection amount, the EGR rate, and the intake air amount. It is also possible.
[0017]
In step S104, it is determined whether the engine 10 is in a cold state. If YES, the process proceeds to step S105, and if NO, the process proceeds to step S106.
[0018]
In step S105, since it is determined that the engine 10 is cold, the NOx catalyst activity during cold is improved by operating the following supply means.
(1) When the HC species effective for the catalyst is light, the supply amount of the reducing agent is reduced as compared with the warm-up time.
(2) When the HC species effective for the catalyst is heavy, the supply amount of the reducing agent is increased as compared with the warm-up time.
[0019]
In step S106, since it is determined that the engine 10 is warming up, a specified amount of reducing agent is supplied.
[0020]
(Second Embodiment)
FIG. 2 is a diagram showing the configuration of the second embodiment of the exhaust gas purifying apparatus according to the present invention.
The difference from the first embodiment is that the reducing agent tank 50 is eliminated, the reducing agent supply means into the exhaust is performed by the POST injection of the common rail fuel injection device 40, and the HC species effective for the catalyst is light. In the case of the HC type, the POST injection HC amount at the time of cooling is reduced.
[0021]
Next, the operation of the second embodiment will be described.
(1) The catalyst contains an optimum HC species as a reducing agent, and the NOx reduction effect obtained by the supplied reducing agent is different (see FIG. 6).
(2) The HC type discharged from the engine when cold is different from that when warm. When cold, unburned HC increases and the content of light HC increases (see FIG. 7).
For the above two reasons, in the first embodiment, the reducing agent is directly supplied from the reducing agent tank 50 to the exhaust system. However, in the second embodiment, the reduction is performed by the POST injection of the common rail fuel injection device 40. Supply the agent.
[0022]
When the HC species effective as a reducing agent for the catalyst is relatively light (HC having a small C number), the amount of light HC discharged from the engine at the time of cold operation is large. Therefore, the fuel supplied by POST injection at the time of cold operation By reducing the amount of NO, it is possible to minimize the deterioration of fuel consumption and maximize the effect of the NOx catalyst when cold.
[0023]
Next, it demonstrates along the flowchart shown in FIG.
In step S101, the operating conditions (Q, intake air temperature, intake air amount) of the engine 10 are read.
[0024]
In step S102, the engine oil temperature is read.
[0025]
In step S103, it is determined by the catalyst activity determination means whether the NOx catalyst 31 is in the activation temperature range. If YES, the process proceeds to step S104.
In the second embodiment, the determination is made by the exhaust temperature sensor 60 provided upstream of the NOx catalyst 31, but the exhaust temperature is calculated from the intake air temperature, the fuel injection amount, the EGR rate, and the intake air amount. It is also possible.
[0026]
In step S104, it is determined whether the engine 10 is in a cold state. If YES, the process proceeds to step S105, and if NO, the process proceeds to step S106.
[0027]
In step S105, it is determined that the engine 10 is cold. Therefore, when the HC species effective for the catalyst is light, the supply amount of the reducing agent is smaller than when the engine is warmed up (for example, the reducing agent supply amount on the map). If it has, it becomes as shown in FIG. 8), thereby improving the activity of the NOx catalyst when cold.
[0028]
In step S106, since it is determined that the engine 10 is warming up, a prescribed amount of reducing agent is supplied (for example, when the reducing agent supply amount is provided in the map, the result is as shown in FIG. 9).
[0029]
(Third embodiment)
The configuration of the third embodiment of the exhaust gas purifying apparatus according to the present invention is the same as that of the second embodiment (see FIG. 2).
The difference from the first embodiment is that the reducing agent tank 50 is eliminated, the reducing agent supply means into the exhaust is performed by the POST injection of the common rail fuel injection device 40, and the HC species effective for the catalyst is heavy. In the case of the HC type, the POST injection HC amount at the time of cooling is increased.
[0030]
Next, the operation of the third embodiment will be described.
In contrast to the second embodiment, when the HC species effective as a catalyst reducing agent is relatively heavy (HC having a large C number), the amount of heavy HC discharged from the engine when cold is small. Therefore, by increasing the amount of fuel supplied by POST injection when cold, it is possible to maximize the effect of the NOx catalyst when cold.
[0031]
Next, it demonstrates along the flowchart shown in FIG.
In step S101, the operating conditions (Q, intake air temperature, intake air amount) of the engine 10 are read.
[0032]
In step S102, the engine oil temperature is read.
[0033]
In step S103, it is determined by the catalyst activity determination means whether the NOx catalyst 31 is in the activation temperature range. If YES, the process proceeds to step S104.
In the third embodiment, the determination is made by the exhaust temperature sensor 60 provided upstream of the NOx catalyst 31, but the determination is made by calculating the exhaust temperature from the intake air temperature, the fuel injection amount, the EGR rate, and the intake air amount. It is also possible.
[0034]
In step S104, it is determined whether the engine 10 is in a cold state. If YES, the process proceeds to step S105, and if NO, the process proceeds to step S106.
[0035]
In step S105, since it is determined that the engine 10 is cold, when the HC species effective for the catalyst is heavy, the NOx catalyst during cold is increased by increasing the amount of reducing agent supplied compared to when warming up. Improve the activity.
[0036]
In step S106, since it is determined that the engine 10 is warming up, a specified amount of reducing agent is supplied.
[0037]
(Fourth embodiment)
The configuration of the fourth embodiment of the exhaust gas purifying apparatus according to the present invention is the same as that of the second embodiment (see FIG. 2).
[0038]
The operation of the fourth embodiment will be described.
In the fourth embodiment, in addition to the second embodiment, the following cooling characteristics are taken into consideration.
When the engine is cold, if the POST injection is performed at the same POST injection timing as that during warm-up, the temperature in the combustion chamber is lower than that during warm-up, so the HC type discharged from the cylinder is different from that during warm-up. For this reason, the optimum POST injection timing at the time of cool-down advances with respect to the optimum POST injection timing at the time of warm-up (see FIG. 10).
[0039]
For this reason, the effect of the NOx catalyst is maximized by advancing the POST injection timing at the time of cold operation from the time of warm-up.
[0040]
Next, it demonstrates along the flowchart shown in FIG.
In step S101, the operating conditions (Q, intake air temperature, intake air amount) of the engine 10 are read.
[0041]
In step S102, the engine oil temperature is read.
[0042]
In step S103, it is determined by the catalyst activity determination means whether the NOx catalyst 31 is in the activation temperature range. If YES, the process proceeds to step S104.
In the fourth embodiment, the determination is made by the exhaust temperature sensor 60 provided upstream of the NOx catalyst 31, but the determination is made by calculating the exhaust temperature from the intake air temperature, fuel injection amount, EGR rate, and intake air amount. It is also possible.
[0043]
In step S104, it is determined whether the engine 10 is in a cold state. If YES, the process proceeds to step S105, and if NO, the process proceeds to step S106.
[0044]
In step S105, since it is determined that the engine 10 is cold, the NOx catalyst activity during cold is improved by operating the following supply means.
{Circle around (1)} When the HC species effective for the catalyst is light, the supply amount of the reducing agent is decreased as compared with the warm-up time, or the POST injection timing is advanced as compared with the warm-up time without changing the POST injection amount.
(2) If the HC species effective for the catalyst is heavy, increase the supply amount of the reducing agent compared with the warm-up time, or advance the POST injection timing as compared with the warm-up time without changing the POST injection amount. (Naturally, the POST injection timing is different from that of a catalyst for which light HC is effective).
It is also effective to combine the advance angle of the POST injection timing and the supply / reduction amount of the reducing agent.
[0045]
In step S106, since it is determined that the engine 10 is warming up, a specified amount of reducing agent is supplied at a specified POST injection timing.
[0046]
(Fifth embodiment)
FIG. 3 is a diagram showing the configuration of the fifth embodiment of the exhaust gas purifying apparatus according to the present invention.
The difference from the first to fourth embodiments is that an HC adsorption catalyst 32 is provided upstream of the NOx catalyst 31 interposed in the catalyst case 30.
[0047]
The operation of the fifth embodiment will be described.
By providing the HC adsorption catalyst 32 upstream of the NOx catalyst 31, the following points are possible.
(1) HC discharged at low load can be adsorbed.
(2) At high load, the adsorbed HC can be desorbed and used as a reducing agent.
[0048]
When the engine is cold, more light HC species are discharged than when the engine is warm, and therefore, the HC adsorbed when the engine is cold contains a lot of light HC, so that the desorption temperature from the adsorption catalyst is also lowered. For this reason, since the time taken for all the adsorbed HC to be completely desorbed during transient operation such as acceleration is earlier than when warming up during cold operation, the supply of reducing agent by POST injection is started when warming up. It is necessary to do it earlier.
Other operations are the same as those of the third embodiment.
[0049]
Next, it demonstrates along the flowchart shown in FIG.
In step S201, the operating conditions (Q, intake air temperature, intake air amount) of the engine 10 are read.
[0050]
In step S202, the engine oil temperature is read.
[0051]
In step S203, the temperatures of the NOx catalyst 31 and the HC adsorption catalyst 32 are detected, and it is determined whether the temperature is within the HC desorption temperature range and whether the NOx catalyst 31 is within the activation temperature range.
In the fifth embodiment, the determination is made by the exhaust temperature sensor 60 provided upstream of the NOx catalyst 31, but the exhaust temperature is calculated from the intake air temperature, the fuel injection amount, the EGR rate, and the intake air amount. It is also possible.
[0052]
In step S204, it is determined from the catalyst temperature whether the NOx catalyst 31 is a desorption region or an adsorption region. If it is a desorption region, the process proceeds to step S205, and if it is an adsorption region, the process proceeds to step S218.
[0053]
In step S205, it is determined whether the engine 10 is in a cold state. If YES, the process proceeds to step S206, and if NO, the process proceeds to step S212.
[0054]
In step S206, in the case of the desorption region, the HC desorption amount per unit time corresponding to the operating state is calculated from the HC desorption map shown in FIG. However, since the HC adsorbed at the time of cooling is light, the desorption amount per unit time is d1 ′ larger than d1. Here, d1 ′ is obtained by multiplying d1 by a cooling coefficient (> 1).
[0055]
In step S207, the HC adsorption amount (remaining amount) of the NOx catalyst 31 is calculated.
[0056]
In steps S208 and S209, when the calculated HC adsorption amount becomes negative, it is determined that the adsorption amount is zero.
[0057]
In step S210, it is determined whether the catalyst is in the active temperature range. If YES, the process proceeds to step S211.
[0058]
In step S211, since it is determined that the desorbed HC from the adsorbent has disappeared and the engine 10 is in the cold state, the following reducing agent supply means is operated.
(1) When the HC species effective for the catalyst is light, the supply amount of the reducing agent is reduced as compared with the warm-up time.
(2) When the HC species effective for the catalyst is heavy, the supply amount of the reducing agent is increased as compared with the warm-up time, and the POST injection timing is advanced as compared with the warm-up time.
[0059]
In step S212, in the case of the desorption region, the HC desorption amount per unit time corresponding to the operating state is calculated from the HC desorption map shown in FIG.
[0060]
In step S213, the HC adsorption amount (remaining amount) of the NOx catalyst 31 is calculated.
[0061]
In steps S214 and S215, when the calculated HC adsorption amount becomes negative, it is determined that the adsorption amount is zero.
[0062]
In step S216, it is determined whether the catalyst is in the activation temperature range. If YES, the process proceeds to step S217.
[0063]
In step S217, since it is determined that the engine is warming up, a specified amount of reducing agent is supplied at a specified POST injection timing.
[0064]
In step S218, the adsorption amount a1 is detected from the HC adsorption amount map per unit time shown in FIG. 12, and the total adsorption amount a is calculated.
[0065]
【The invention's effect】
As described above in detail, according to the present invention, when the supply of the reducing agent in the cold state is performed under the same conditions as in the warm-up state, the HC species supplied to the catalyst is the warm-up state. Because it is different, the problem that NOx reduction performance similar to that at the time of warm-up cannot be expected is detected. HC type and amount discharged from the engine at the time of cold-down are detected, and only the necessary amount of HC type from the reducing agent supply device By supplying the catalyst, good NOx reduction performance can be obtained even when the engine is cold.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a first embodiment of an exhaust gas purifying apparatus according to the present invention.
FIG. 2 is a diagram showing a configuration of second to fourth embodiments.
FIG. 3 is a diagram showing a configuration of a fifth exemplary embodiment.
FIG. 4 is a flowchart for explaining the operation of the first to fourth embodiments.
FIG. 5 is a flowchart for explaining the operation of the fifth embodiment;
FIG. 6 is a graph showing the relationship between “engine oil / water temperature” and “NOx conversion rate”.
FIG. 7 is a diagram showing the relationship between “oil temperature” and “average C number of discharged HC”.
FIG. 8 is a diagram showing a relationship between “reducing agent supply amount” and “fuel injection amount” (at the time of warm-up).
FIG. 9 is a diagram showing the relationship between “reducing agent supply amount” and “fuel injection amount” (when cold).
FIG. 10 is a diagram showing the relationship between “in-cylinder temperature when performing POST injection” and “average C number of HC species supplied depending on POST injection amount”.
FIG. 11 is a diagram showing an HC desorption amount map.
FIG. 12 is a diagram showing an HC adsorption amount map.
[Explanation of symbols]
10 Engine 20 Exhaust passage 30 Catalyst case 31 NOx catalyst 32 HC adsorption catalyst 40 Common rail fuel injection device 50 Reductant tank 60 Waste temperature sensor

Claims (3)

In an exhaust gas purification apparatus having a catalyst for purifying exhaust gas interposed in an exhaust passage of an internal combustion engine, and having a reducing agent supply means for supplying a reducing agent to the catalyst,
Means for determining whether or not to supply a reducing agent to the catalyst according to a temperature rise state of the catalyst;
Means for determining whether the operating state of the internal combustion engine is a cold state or a warm-up state;
Exhaust gas characterized by controlling a reducing agent supply amount when it is determined to supply a reducing agent to the catalyst so as to increase more than when warming up in cold operation according to the determination result of the operating state Purification equipment. In the exhaust gas purifying apparatus according to claim 1, the exhaust gas purifying device, characterized in that intends row reducing agent supply to the catalyst in the POST injection by common rail injection system. 3. The exhaust gas purifying apparatus according to claim 1, wherein an HC adsorbent is provided upstream of the catalyst, and the reducing agent is based on an amount of HC adsorbed on the HC adsorbent and a determination result of the operating state. An exhaust gas purification device for controlling the supply start timing of the exhaust gas.

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