JP2018204495A - Exhaust emission control system and control device - Google Patents

Abstract

To provide an exhaust emission control system capable of improving NOelimination efficiency of an SCR.SOLUTION: An exhaust emission control system in one embodiment includes: an exhaust passage that is a passage of exhaust gas; an NOocclusion catalyst for occluding NOin exhaust gas guided in the exhaust passage; an SCR provided downstream of the NOocclusion catalyst in the exhaust passage and eliminating NOin the exhaust gas; a bypass passage that is in fluid communication with the exhaust passage and bypasses the NOocclusion catalyst; and a passage change-over section that guides exhaust gas to the NOocclusion catalyst while a temperature of the SCR is a predetermined temperature or lower and that guides the exhaust gas to the bypass passage without guiding the exhaust gas to the NOocclusion catalyst when the temperature of the SCR exceeds the predetermined temperature.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an exhaust gas purification system that purifies NO _x in exhaust gas from an internal combustion engine, and a control device related thereto.

Conventionally, as this type of exhaust purification system, an SCR (Selective Catalytic Reduction) is disposed in the exhaust passage, and an NO _x storage catalyst is disposed in the exhaust passage upstream of the SCR.

JP 2009-41442 A

To improve _the NO _x purification rate in the SCR, it is necessary to NO and NO ₂ are included in the appropriate in the exhaust gas.

However, _the NO _x storage catalyst from the time of the relatively low temperature at moderate temperatures, although it absorbs NO _x in the exhaust gas, to become substantially only NO at the outlet of the NO _x storage catalyst, in the conventional exhaust gas purification system, according to the SCR There was a problem that it was difficult to improve the NO _x purification rate.

An object of the present disclosure is to provide an exhaust purification system and a control device capable of improving the SCR NO _x purification rate.

A first form of the present disclosure includes an exhaust passage that is a passage for exhaust gas, a NO _x storage catalyst that stores NO _{x in} the exhaust gas guided through the exhaust passage, and a downstream of the NO _x storage catalyst in the exhaust passage. provided, the SCR to purify NO _x in the exhaust gas, said through exhaust passage in fluid communication with a bypass passage bypassing the _the NO _x storage catalyst, between the temperature of the SCR is equal to or less than a predetermined temperature, the _the NO _x storage The exhaust gas is directed to a catalyst, and when the temperature of the SCR exceeds a predetermined temperature, the exhaust gas purification system is provided with a passage switching unit that guides the exhaust gas to the bypass passage without guiding the exhaust gas to the NO _x storage catalyst. .

Second embodiment of the present disclosure, and _the NO _x storage catalyst for occluding NO _x in the exhaust gas which has been guided through the exhaust passage, wherein provided in the exhaust passage downstream of the _the NO _x storage catalyst, the NO _x in the exhaust gas A control device used in an exhaust system comprising an SCR to be purified and a bypass passage that is in fluid communication with the exhaust passage and bypasses the NO _x storage catalyst, wherein the temperature of the SCR is equal to or lower than a predetermined temperature, a first switching control unit for controlling so as to guide the exhaust gas to the _the NO _x storage catalyst, the temperature of the SCR reaches a predetermined temperature greater than the control to direct exhaust gas to the bypass passage not lead to exhaust gas to the _the NO _x storage catalyst And a second switching control unit.

According to each embodiment of the present disclosure, it is possible to provide an exhaust purification system and a control device that can improve the SCR NO _x purification rate.

Schematic diagram showing the configuration of the exhaust purification system of the present disclosure The flowchart which shows the process sequence of the control apparatus of FIG. Schematic diagram showing a configuration according to a modification of the exhaust purification system of the present disclosure

  Hereinafter, the exhaust purification system S and the control device 17 of the present disclosure will be described in detail with reference to the drawings.

<1. Definition>
Table 1 below shows the meanings of acronyms and abbreviations used in the present embodiment.

<2. Embodiment>
<2-1. Overall configuration of exhaust purification system>
In FIG. 1, an exhaust purification system S is mounted on a vehicle, and includes an exhaust passage 1, a three-way valve 3, a NO _x storage catalyst 5, a bypass passage 9, an oxidation catalyst 11, an injector 13, a urea SCR 15, And a control device 17.

  The exhaust passage 1 typically guides exhaust gas from an internal combustion engine (not shown) such as a diesel engine to the atmosphere (outside the vehicle). The internal combustion engine may be a gasoline engine.

In the exhaust passage 1, a three-way valve 3, a NO _x storage catalyst 5, an injector 13, and a urea SCR 15 are provided in order from the upstream side to the downstream side of the exhaust passage 1.

  The three-way valve is an example of a passage switching unit, and has a fluid inlet / outlet port in three directions.

  In particular, the three-way valve 3 has one inlet and two outlets. The inlet of the three-way valve 3 is connected to the upstream side of the exhaust passage 1 so as to be in fluid communication. One of the two outlets is connected to the downstream side of the exhaust passage 1 so as to be in fluid communication, and the other is connected to an upstream end of a bypass passage 9 described later so as to be in fluid communication. Opening and closing of each outlet of the three-way valve 3 is controlled by a control signal from the control device 17.

The NO _x storage catalyst 5 is provided in the exhaust passage 1 between the three-way valve 3 and the joining portion of the exhaust passage 1 and the bypass passage 9, and from a low temperature (about 200 ° C. or lower) to a middle temperature (400 ° C. or lower). occludes NO _x in the exhaust gas to the extent). However, at the outlet of the NO _x storage catalyst 5, the ratio of NO _{2 to} NO _x (hereinafter referred to as NO ₂ / NO _x ) is much smaller than the ratio of NO in NO _x (hereinafter referred to as NO / NO _x ). It is known.

As apparent from the above, the bypass passage 9 bypasses the NO _x storage catalyst 5 provided in the exhaust passage 1. Specifically, one end of the bypass passage 9 is connected to the other outlet of the three-way valve 3, and the other end is connected to a portion immediately downstream of the NOx storage catalyst 5 in the exhaust passage 1.

The oxidation catalyst 11 is provided in the middle of the bypass passage 9 and has, for example, a support made of cordierite honeycomb ceramic. A large number of cells are also formed in this carrier along the flow direction of the exhaust gas. In addition, the partition wall surrounding each cell is supported or coated with a catalyst such as a noble metal. Such an oxidation catalyst 11 oxidizes NO in the exhaust gas and converts it into NO ₂ . Here, the oxidation catalyst 11 converts NO into NO ₂ so that the NO ₂ / NO _x and the ratio of NO / NO _x approach the desired state (ie, both ratios are equal) at the outlet of the oxidation catalyst 11. To do.

  For example, when the temperature of the exhaust gas is equal to or higher than a predetermined temperature under the control of a DCU (not shown), the injector 13 has urea as a precursor inside the exhaust passage 1 and immediately upstream of the urea SCR 15. Water is injected and supplied to the exhaust gas guided through the exhaust passage 1. As a result, ammonia is generated immediately upstream of the urea SCR 15.

  Here, the DCU may be the control device 17 or another control device.

  The urea SCR 15 includes, for example, a support made of cordierite honeycomb ceramic. A large number of cells are also formed in this carrier along the flow direction of the exhaust gas. Moreover, the partition wall surrounding each cell is supported or coated with an SCR catalyst such as base metal oxide, zeolite, or noble metal.

Ammonia and exhaust gas from the exhaust passage 1 flows into the urea SCR 15. At that time, NO _x in the exhaust gas reacts with ammonia to be reduced to nitrogen and water. As a result, NO _x in the exhaust gas is rendered harmless. The water, nitrogen, carbon dioxide and the like thus generated are discharged into the atmosphere via a muffler (not shown).

  The control device 17 is realized by, for example, an ECM in which a microcomputer, a nonvolatile memory, a connector, a working memory, and the like are mounted on a substrate.

  For example, the connector is connected to a temperature sensor (not shown) that detects the temperature of the urea SCR 15. The microcomputer uses a working memory to execute a program stored in advance in a nonvolatile memory or the like.

<2-2. Operation of exhaust purification system>
Next, referring to FIG. 2 in addition to FIG. 1, the operation of the exhaust purification system S having the above configuration will be described focusing on the processing contents of the control device 17.

Immediately after starting the internal combustion engine, in the control device 17, the microcomputer outputs a control signal to the three-way valve 3, closes the outlet on the bypass passage 9 side of the three-way valve 3, and the exhaust gas in the exhaust passage 1 moves to the oxidation catalyst 11 side. Do not flow. As a result, the exhaust gas from the internal combustion engine flows into the NO _x storage catalyst 5 and NO _x is stored (step S001).

  After step S001, the microcomputer determines from the output signal of the temperature sensor whether the temperature of the urea SCR 15 exceeds a predetermined temperature and whether the ammonia adsorption amount in the urea SCR 15 exceeds a predetermined value (step S003). Here, the predetermined temperature is designed to be, for example, the activation temperature of the urea SCR 15 (about 200 ° C.), that is, the temperature at which the urea SCR 15 functions. A known technique is used for detecting the ammonia adsorption amount.

  If NO is determined in step S003, the microcomputer functions as a first switching control unit. In this case, the microcomputer closes the outlet on the bypass passage 9 side of the three-way valve 3 on the assumption that the exhaust gas does not need to flow into the oxidation catalyst 11 (step S005). For the first time, the state of the three-way valve 3 is maintained at the state set in step S001.

If YES is determined in step S003, the microcomputer functions as a second switching control unit because it is better to have the exhaust gas flow into the oxidation catalyst 11. In this case, the microcomputer outputs a control signal to the three-way valve 3 and closes the outlet of the three-way valve 3 on the exhaust passage 1 side (step S007). As a result, the exhaust gas in the exhaust passage 1 flows to the oxidation catalyst 11 side without flowing through the NO _x storage catalyst 5. Further, immediately after the execution of step S007 (or almost simultaneously), the injector 13 injects urea water into the exhaust passage 1.

As a result of step S007, in the exhaust gas flowing out from the oxidation catalyst 11, NO ₂ / NO _x and NO / NO _x approach each other equally, so the NO _x purification rate in the urea SCR 15 becomes a more preferable value.

  After step S005 or step S007, the microcomputer determines whether or not to end the operation of the internal combustion engine (step S009).

  If NO is determined in step S009, the process returns to step S001.

  On the other hand, if “YES” is determined in the step S009, the process of FIG.

<2-3. Effect of exhaust purification system>
As described above, the NO _x storage catalyst 5 can store NO _x from a low temperature to a medium temperature. Microcomputer, if the temperature of the urea SCR15 is below a predetermined temperature, since the urea SCR15 does not work, so as to occlude NO _x in _the NO _x storage catalyst 5, and controls the three-way valve 3.

In contrast, microcomputer, if the temperature is a predetermined temperature than the urea SCR 15, in order to optimize _the NO _x purification rate in the urea SCR 15, controls the three-way valve 3 so that exhaust gas passes through the oxidation catalyst 11.

As described above, according to the exhaust purification system S and the control device 17, if the temperature of the urea SCR 15 is equal to or lower than the predetermined temperature, the NO _x storage catalyst 5 stores NO _x , but if not, the urea SCR 15 NO to be optimized _x purification rate, it is possible to improve the NO _x purification rate of the urea SCR15 compared with the conventional exhaust purification system in.

<2-4. Addendum>
In the above description, the exhaust purification system S has been described as including the oxidation catalyst 11 provided on the bypass passage 9. However, the exhaust purification system S is not limited to this, but instead of the oxidation catalyst 11, as shown in FIG. 3, an oxidation catalyst is added to the so-called DPF to provide a PM filter function and an NO oxidation function in exhaust gas. You may have the CSF21 given.

In this case, the bypass passage 9 is simply a short circuit for the NO _x storage catalyst 5, and the CSF 21 is preferably provided immediately upstream of the injector 13 in the exhaust passage 1.

  In step S003, the microcomputer is described as obtaining the temperature of the urea SCR 15 from the output signal of the temperature sensor. However, the present invention is not limited thereto, and the microcomputer may estimate the temperature of the urea SCR 15 based on an output signal from the exhaust gas temperature sensor.

  In step S003, the microcomputer determines whether the temperature of the urea SCR 15 is higher than a predetermined temperature and whether the ammonia adsorption amount in the urea SCR 15 exceeds a predetermined value from the output signal of the temperature sensor. However, this is a preferable mode, and the microcomputer may merely determine whether or not the temperature of the urea SCR 15 exceeds the predetermined temperature from the output signal of the temperature sensor in step S003.

  Further, another three-way valve may be provided at the junction of the exhaust passage 1 and the bypass passage 9.

Exhaust gas purification system and a control device of the present disclosure can provide an exhaust gas purification system and a control device capable of improving _the NO _x purification rate of the SCR.

S Exhaust purification system 1 Exhaust passage 3 Passage switching part (three-way valve)
5 NO _x storage catalyst 9 Bypass passage 11 Oxidation catalyst 15 Urea SCR
17 Control device

Claims (4)

An exhaust passage which is a passage for exhaust gas;
A NO _x storage catalyst for storing NO _{x in} the exhaust gas guided through the exhaust passage;
An SCR provided downstream of the NO _x storage catalyst in the exhaust passage and purifying NO _x in the exhaust gas;
A bypass passage in fluid communication with the passage and bypassing the NO _x storage catalyst;
While the temperature of the SCR is equal to or lower than a predetermined temperature, exhaust gas is guided to the NO _x storage catalyst. When the temperature of the SCR exceeds a predetermined temperature, exhaust gas is guided to the bypass passage without introducing exhaust gas to the NO _x storage catalyst. A passage switching unit;
Exhaust gas purification system with The predetermined temperature is an activation temperature of the SCR.
The exhaust purification system according to claim 1. An oxidation catalyst that is provided in the bypass passage and oxidizes NO in the exhaust gas;
The passage switching unit guides exhaust gas to the oxidation catalyst provided in the bypass passage when the temperature of the SCR exceeds a predetermined temperature.
The exhaust purification system according to claim 1. An NO _x storage catalyst for storing NO _{x in} the exhaust gas guided through the exhaust passage, an SCR provided downstream of the NO _x storage catalyst in the exhaust passage, for purifying NO _x in the exhaust gas, and the exhaust passage A control device used in an exhaust system comprising a bypass passage that is in fluid communication with and bypasses the NO _x storage catalyst,
A first switching control unit configured to control exhaust gas to be guided to the NO _x storage catalyst while the temperature of the SCR is equal to or lower than a predetermined temperature;
A second switching control unit configured to control exhaust gas to the bypass passage without introducing exhaust gas to the NO _x storage catalyst when the temperature of the SCR exceeds a predetermined temperature;
A control device comprising:

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