KR100903338B1 - System for emission reduce line of diesel vehicle and method of monitoring thereof - Google Patents

Abstract

A post-treatment system of a diesel vehicle and a diagnostic method thereof are provided to simplify the system by diagnosing the malfunction of DFC(Diesel Fuel Cracking) and a secondary injection injector at the same time through one oxygen sensor. A diagnostic method of a post-treatment system of a diesel vehicle comprises: a step(S102,S103,S104) for detecting the signals of an NOx(Nitrogen Oxide) sensor in the active state of the post-treatment system and analyzing NOx purification rate of LNT(Lean NOx Trap); a step(S105) for determining that the NOx purification rate of the LNT reaches on the state in which the LNT regeneration is necessary; a step(S106) for supplying the diesel fuel to the DFC through a secondary injection injector in case the regeneration of LNT is necessary; and a step(S107,S108,S110,S122) for diagnosing the malfunction of the DFC and the secondary injection injector by analyzing the signal of the oxygen sensor installed at the downstream of the DFC in case of a fault detection mode of the DFC and the secondary injection injector.

Description

After-treatment system of diesel vehicle and its diagnostic method {SYSTEM FOR EMISSION REDUCE LINE OF DIESEL VEHICLE AND METHOD OF MONITORING THEREOF}

The present invention relates to a post-treatment system of a diesel vehicle, and more particularly, to improve fuel efficiency and improve the purification efficiency of particulate matter (hereinafter referred to as 'PM') and NOx contained in exhaust gas, and to improve fuel decomposition. After-treatment system of diesel vehicle that diagnoses abnormality of secondary injection injector and DFC catalyst by using information of oxygen sensor installed downstream of diesel fuel cracking (DFC), and its It is about a diagnosis method.

In general, the exhaust gas emitted from the engine is guided to a catalytic converter disposed in the middle of the exhaust pipe, purified, passed through a muffler, noise is attenuated, and discharged to the atmosphere through the tail exhaust pipe.

In the OBD regulation, not only the regulation of emission regulations, which is strengthened day by day, but also the improvement and improvement of the diagnostic ability to detect the failure and deterioration of exhaust components, and the standardization in the after service market It is required to satisfy several regulations.

NOx and PM are the main targets of exhaust gas regulation applied to diesel vehicles.

Since NOx is strongly dependent on the temperature of the combustion gas, a high concentration of NOx is produced in the high temperature range.

Therefore, in order to reduce NOx, the reduction of the combustion temperature by the EGR control is effective, but such a method may cause the oxidation efficiency of PM to deteriorate and thermal degradation.

For this reason, the problem of diesel engines is to simultaneously reduce NOx and PM while maintaining high thermal efficiency.

In order to satisfy the NOx and PM regulations among North American diesel Tier 2 BIN5 regulations or Euro 6 emission regulations, a separate aftertreatment system is applied.Diesel Oxidation Catalyst (DOC) and DPF ( DeNOx catalysts such as Diesel Particulate Filter (LNT), Lean NOx Trap (LNT), and Selective Catalytic Reduction (SCR) using Urea are applied.

The LNT is composed of a NOx storage catalyst and a DOC in one carrier, and adsorbs and stores NOx in a catalyst coat layer such as platinum oxide and barium oxide in a lean driving region. In the rich operating region, diesel fuel is used as a reducing agent to regenerate the catalyst by reducing NOx occluded in the catalyst.

The NOx purification efficiency of the LNT is approximately 70 to 90% or more, and the activation temperature is approximately 200 ° C to 500 ° C, and the purification of NOx is very good because of the correlation with the temperature range of the load of the diesel engine and the exhaust gas. High efficiency appears.

SCR catalyst uses ammonia (NH3) which is decomposed from urea as a reductant to purify NOx. It has excellent selectivity for NOx and promotes the reaction between NOx and ammonia even in the presence of oxygen. have.

Diesel vehicles monitor the after-treatment system according to the regulations of OBD-2 to detect catalyst failure. For this purpose, information of two oxygen sensors or two temperature sensors is typically used.

However, this method leads to a problem of complicated composition of the post-processing system and an increase in cost, and an analysis factor is too complicated for diagnosis of abnormality, thus degrading the performance of the process constituting the control means. There is a problem that a fault diagnosis cannot be provided.

The present invention has been made to solve the above problems, and an object thereof is to provide a post-treatment system for improving fuel efficiency and improving the purification efficiency of PM and NOx contained in exhaust gas in a diesel vehicle.

In addition, only one oxygen sensor is installed downstream of the DFC, and the information of this oxygen sensor is used to diagnose abnormality of the secondary injection injector and the DFC to provide monitoring that satisfies the regulations of the OBD-2. .

The present invention is to enable the simultaneous diagnosis of the abnormality of the DFC and the secondary injection injector by using the oxidation of the DFC and the cross reaction of the exhaust gas by using one oxygen sensor.

After-treatment system of a diesel vehicle according to a feature of the present invention for realizing the above object,

A DPF installed at an upstream side to which the engine is coupled in the exhaust pipe, a coating area having a DOC function is disposed, and a CPF collecting PM at a rear end of the coding area;

A differential pressure sensor provided on the upstream and downstream sides of the DPF to provide ECUs with differential pressure information that changes depending on the occlusion amount of the PM;

Disposed on the downstream side of the DPF, the NOx storage catalyst and the DOC are configured in one carrier to adsorb and store NOx in the catalyst in the lean operation region, and utilize NOx stored in the catalyst by using diesel fuel as a reducing agent in the rich operation region. Reducing LNT;

A second exhaust gas pipe branched from the exhaust pipe and connected to the LNT;

A secondary injection injector installed in the second exhaust gas pipe to inject diesel fuel;

A DFC installed at a downstream side of the secondary injection injector to pyrolyze the diesel fuel injected to generate a reducing agent in the form of CnHx (n = 1 to 5) molecules;

An oxygen sensor installed at a downstream side of the DFC to detect cross reaction of exhaust gas due to air-fuel ratio and pyrolysis of fuel;

And a control means for diagnosing the abnormality of the secondary injection injector and the DFC by comparing the cross-reaction of the air-fuel ratio and the exhaust gas detected by the oxygen sensor with a set measured value.

In addition, the diagnostic method of the after-treatment system of a diesel vehicle according to a feature of the present invention,

Analyzing the NOx purification rate of the LNT by detecting a signal of the NOx sensor in an activated state of the aftertreatment system;

Determining whether the NOx purification rate of the LNT is in a state requiring LNT regeneration;

If the LNT needs to be regenerated, injecting diesel fuel through a secondary injection injector to supply the DFC;

Determining whether the secondary injection injector and the DFC is a failure detection mode, and if the failure detection mode includes detecting and analyzing a signal of an oxygen sensor installed downstream of the DFC, diagnosing the failure of the secondary injection injector and the DFC.

According to the above configuration, the present invention provides a post-treatment system of a diesel vehicle that satisfies the diesel exhaust regulations of North America and Europe, which is strengthened, and simultaneously diagnoses an abnormality of a DFC and a secondary injection injector using one oxygen sensor. This is expected to provide the simplification of the system and the stabilization of the product.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

Since the present invention can be implemented in various different forms, the present invention is not limited to the exemplary embodiments described herein, and parts not related to the description are omitted in the drawings in order to clearly describe the present invention.

1 is a view showing the configuration of a post-processing system of a diesel vehicle according to an embodiment of the present invention.

In the present invention, a DPF (10) having a CPF (11) built in an upstream side to which an engine is coupled on an exhaust pipe (1) is installed, and a NOx storage catalyst (21) and a DOC (22) are built in series at a rear thereof. LNT 20 is installed.

The front end of the DPF 10 is provided with a coating area 11a for increasing the catalyst loading amount, and a CPF 11 for collecting PM at the rear end thereof is provided, and the coating area 11a with the catalyst loading amount increasing is Has the effect of DOC.

Differential pressure sensors 12 and 13 are installed on the upstream and downstream sides of the DPF 10 to be connected to the ECU 50, and information about the differential pressure that varies according to the occlusion amount of the PM collected by the DPF 10 is stored in the ECU ( 50), the regeneration time of the DPF 10 is determined.

The regeneration of the DPF 10 is performed after the fuel injection of the engine to regenerate the DPF 10 when the ECU 50 determines the regeneration time from the pressure difference ΔP detected by the differential pressure sensors 12 and 13. Run

The LNT 20 includes a NOx storage catalyst 21 and a DOC 22 in one carrier, and a catalyst coating layer such as an oxide catalyst such as platinum (Pt), a barium oxide, etc. in a lean operation region. ) NOx is adsorbed and stored, and diesel fuel is used as a reducing agent in a rich operating region to reduce NOx stored in the catalyst to regenerate the catalyst.

In addition, deterioration of fuel efficiency due to the regeneration of the NOx storage catalyst 21, deactivation of the catalyst by the secondary injection fuel of the NOx storage catalyst 21, and high temperature exhaust gas pass through the regeneration or desulfurization process of the CPF 11. In order to solve the problem that the catalyst may be damaged by abnormal combustion of the fuel, the secondary injection system and the DFC 30 may be installed in a separate exhaust gas path to regenerate the NOx storage catalyst 21. The fuel component decomposed by 30 is introduced into the NOx storage catalyst 21.

The DFC 30 is installed in a separate exhaust gas pipe 2 branched on the exhaust pipe 1 in front of the DPF 10, and the outlet 2a of the exhaust gas pipe 2 is NOx storage catalyst 21. ) Is inserted into and installed in the built-in LNT (20).

The outlet 2a of the exhaust gas pipe 2 is provided in a diffusion tube structure, and the outlet 2a of the diffusion tube structure is located in front of the NOx storage catalyst 21.

A secondary injection injector 41 capable of injecting diesel fuel is provided upstream of the DFC 30, and an exhaust gas distribution valve 42 is provided at an inlet of the exhaust gas pipe 2.

Therefore, when regenerating the NOx storage catalyst 21 constituting the LNT 20, the exhaust gas distribution valve 42 provided in front of the DFC 30 is opened, and the exhaust gas is distributed to the DFC 30 to flow. The exhaust gas acts as a heat source required for the DFC 30 reaction.

In addition, the fuel injected from the secondary injection injector 41 is cracked so as to easily react with the NOx storage catalyst 21 while passing through the DFC 30, and the NOx storage catalyst is passed through the outlet 2a of the diffusion tube structure. It is evenly distributed to 21.

The DFC 30 has alumina as a main component so that the activity is advantageous even at a low exhaust gas temperature and a low flow rate of 200 to 400 ° C, and rhodium or ruthenium or a mixture thereof is 1 to 10 g / g based on the total apparent volume of the carrier. Use prepared by supporting l.

The secondary injection injector 41 injects diesel fuel under the control of the ECU 50 to supply the reductant required for DeNOx from the LNT 20, and the DFC 30 uses the injected fuel as the reducing agent. (n = 1 ~ 5) Thermal decomposition in molecular form.

In addition, CO2 and H2 are generated through oxidation to be used as a reducing agent in the LNT 20.

In addition, one oxygen sensor 32 is installed downstream of the DFC 30 so that the concentration of oxygen contained in the exhaust gas passing through the DFC 30 is detected by the ECU 50, and the ECU 50. This monitors the failure of the secondary injector 41 and the DFC (30).

Oxygen sensor 32 is a sensor for measuring the air-fuel ratio in response to the partial pressure of oxygen in the exhaust gas or a specific gas that cross-reacts due to thermal decomposition in addition to oxygen affects the output signal.

2 is a diagram showing the output current (Ip) characteristics of the oxygen sensor 32 in the cross reaction according to the thermal decomposition of the DFC.

Gases that affect the output current characteristics of the oxygen sensor 32 and the cross reaction according to the thermal decomposition of the DFC 30 is determined as shown in Table 1 below.

GAS Response value (㎂ / vol%) H2 -226 CO -56 Ethlene (C2H4) -235 Propane (C3H8) -352 Methane (CH4) -148

As can be seen from Table 1, when these gases are included in the exhaust gas, the oxygen sensor 32 outputs a current value as small as the value shown in Table 1 per 1 vol%, and as a result, the air-fuel ratio of the actual exhaust gas Richer perception.

Gas of Table 1 is a gas generated by the cross-reaction in the DFC (30) can be utilized for the failure detection of the DFC (30) by using the above results.

 Downstream of the LNT 20, more specifically, behind the DOC 22, a NOx sensor 23 for determining the regeneration time of the NOX storage catalyst 21 is installed and connected to the ECU 50.

The ECU 50 monitors the amount of NOx contained in the exhaust gas through the signal of the NOx sensor 23 and determines that it is a regeneration time when NOx above the reference value is detected.

At this time, the ECU 50 outputs a control signal for opening the exhaust gas distribution valve 42 so that the exhaust gas flows into the exhaust gas pipe 2, and injects fuel through the secondary injection injector 41. .

Therefore, the exhaust gas acts as a heat source while passing through the DFC 30, and thermally decomposes the fuel injected through the secondary injection injector 41 to generate a reducing agent and then apply it to the LNT 20.

Therefore, the NOx storage catalyst 21 of the LNT 20 is regenerated by reducing the NOx stored using the reducing agent.

Referring to the operation of diagnosing the abnormality of the secondary injection injector and DFC in the after-treatment system of the diesel vehicle according to the present invention including the function as described above is as follows.

The air-fuel ratio and exhaust gas specification output from the oxygen sensor 32 according to the state of the secondary injection injector 41 and the DFC 30 installed in the exhaust gas pipe 2 in the after-treatment system of a diesel vehicle are shown in the following table. Same as 2.

Secondary injection injector normal broken DFC normal λ <1, DFC oxygen reduction detection, cross reaction detection λ> 1 broken λ <1, no DFC oxygen reduction, no cross reaction λ> 1

To summarize the results of Table 2, if the air-fuel ratio λ detected by the oxygen sensor 32 is greater than the reference value '1' when the secondary injection injector 41 is operated by the control of the ECU 50, the secondary The injection injector 41 is in a broken state.

In the state where the air-fuel ratio λ detected by the oxygen sensor 32 is smaller than the reference value '1', the amount of oxygen reduction and cross-reaction of the DFC 30 are detected and measured when the secondary injection injector 41 is normal. If it is in the range of the value, it is determined as normal with respect to the DFC 30.

However, when the secondary injection injector 41 is in a normal state and there is no reduction in the amount of oxygen in the DFC 30, and no cross reaction is detected, it is determined that the DFC 30 is broken.

In order to determine the amount of oxygen reduction and cross-reaction of the DFC 30, the secondary injection injector 41 and the oxygen sensor 32 according to the amount of fuel injected through the secondary injection injector 41 under the condition in which the DFC 30 is normal are used. Measure the output characteristics.

When the amount of oxygen decreases and cross-reaction occurs when the DFC 30 is normal, the output current Ip of the oxygen sensor 32 decreases, and the output value is moved in the rich direction as shown in FIG. 2.

However, if the secondary injection injector 41 is normal or the DFC 30 is broken, the air-fuel ratio λ output from the oxygen sensor 32 is detected to be smaller than the reference value '1', but the oxygen reduction and cross reaction are Since it does not occur, the output current Ip of the oxygen sensor 32 becomes large and moves in the lean direction.

Therefore, it is possible to diagnose whether or not the DFC 30 has failed by comparing the air-fuel ratio and the measured value measured by the oxygen sensor 32.

The operation thereof will be described in more detail with reference to FIG. 2 as follows.

The engine start of the diesel vehicle is kept on (S101), while the aftertreatment system is activated, the ECU 50 detects a signal from the NOx sensor 23 installed downstream of the LNT 20 (S103). It is determined whether the regeneration of (20), preferably the regeneration of the NOx storage catalyst 21 constituting the LNT 20 is necessary (S105).

If the regeneration of the LNT 20 is not necessary in the judgment of S105, the flow returns to the process of S103. If the regeneration of the LNT 20 is necessary, the exhaust gas distribution valve 42 is controlled to exhaust the gas. 30) to flow through.

Then, the secondary injection injector 41 is operated to inject diesel fuel upstream of the DFC 30 (S106).

At this time, the DFC 30 pyrolyzes the injected fuel in the form of CnHx molecules that can be used as a reducing agent, and generates CO 2 and H 2 through oxidation to supply the reducing agent for regeneration of the LNT 20.

As described above, the secondary injection injector 41 is operated to determine whether the failure detection mode has been entered in the state of injecting fuel upstream of the DFC 30 (107).

The failure detection mode is a condition in which the air-fuel ratio of the exhaust gas does not change, for example, an idle state, an overrun state, or an after run state.

If the state of entering the failure detection mode in the determination of S107 detects the signal of the oxygen sensor 32 installed downstream of the DFC (30) and then analyzes the concentration of the exhaust gas (S108).

It is determined whether the air-fuel ratio λ is less than the set reference value '1' in the analyzed exhaust gas concentration (S109).

If the air-fuel ratio λ detected by the oxygen sensor 32 is less than '1', which is a predetermined reference value in S109, the ECU 50 determines that fuel injection is not normally performed due to a failure of the secondary injection injector 41. (S110), the warning light is turned on accordingly (S111).

However, if the air-fuel ratio λ detected by the oxygen sensor 32 has a value larger than the set reference value '1' in the determination of S109, it is determined whether the air-fuel ratio is included in a range of previously measured values (S121).

When the air-fuel ratio detected in the determination of S121 is included in the range of the measured value, the secondary injection injector 41 and the DFC 30 determine that normal operation is maintained (S130).

However, if the air-fuel ratio is not within the range of the measured value, the ECU 50 determines that the cross reaction is not normally performed in the DFC 30 due to the failure of the DFC 30, and determines the failure of the DFC 30. (S122), turn on the warning light accordingly (S123).

According to the present invention, the LNT is mounted to the rear of the DPF, and adopting a structure in which a reducing agent component, that is, a decomposition component of the fuel is injected in the middle, has the advantage of simultaneously improving the NOx removal efficiency and fuel economy.

In addition, by installing only one oxygen sensor downstream of the DFC, the secondary injection injector and the DFC can be easily and reliably diagnosed using the measured values according to the air-fuel ratio of the exhaust gas discharged through the DFC and the cross reacting gas. There is an advantage.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It is included in the scope of rights.

1 is a view showing the configuration of a post-processing system of a diesel vehicle according to an embodiment of the present invention.

2 is a graph showing the cross-reaction characteristics of the exhaust gas according to the heat content of the DFC in the after-treatment system of a diesel vehicle according to an embodiment of the present invention.

3 is a flowchart illustrating a diagnosis procedure of the after-treatment system of a diesel vehicle according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: DPF 20: LNT

30: DFC 32: oxygen sensor

41: secondary injection injector

Claims (6)

A DPF installed at an upstream side to which the engine is coupled in the exhaust pipe, a coating area having a DOC function is disposed, and a CPF collecting PM at a rear end of the coding area; A differential pressure sensor provided on the upstream and downstream sides of the DPF to provide ECUs with differential pressure information that changes depending on the occlusion amount of the PM; Disposed on the downstream side of the DPF, the NOx storage catalyst and the DOC are configured in one carrier to adsorb and store NOx in the catalyst in the lean operation region, and utilize NOx stored in the catalyst by using diesel fuel as a reducing agent in the rich operation region. Reducing LNT; A second exhaust gas pipe branched from the exhaust pipe and connected to the LNT; A secondary injection injector installed in the second exhaust gas pipe to inject diesel fuel; A DFC installed at a downstream side of the secondary injection injector to pyrolyze the diesel fuel injected to generate a reducing agent in the form of CnHx (n = 1 to 5) molecules; An oxygen sensor installed at a downstream side of the DFC to detect cross reaction of exhaust gas according to an air-fuel ratio and fuel injection; Control means for diagnosing abnormality of the secondary injection injector and the DFC by comparing the cross-reaction of the air-fuel ratio and the exhaust gas detected by the oxygen sensor with a set measurement value; After-treatment system of a diesel vehicle comprising a. The method of claim 1, And the control means determines that the secondary injection injector has failed when the air-fuel ratio (λ) is larger than the reference value '1' while the secondary injection injector is operated. The method of claim 1, The control means determines that the DFC is normal when the cross-reaction value detected by the oxygen sensor in the state of the secondary injection injector is within the range of the set measurement amount, and determines the failure of the DFC if it is not within the range of the measured value. Aftertreatment system of diesel vehicle. Analyzing the NOx purification rate of the LNT by detecting a signal of the NOx sensor in an activated state of the aftertreatment system; Determining whether the NOx purification rate of the LNT is in a state requiring LNT regeneration; If the LNT needs to be regenerated, injecting diesel fuel through a secondary injection injector to supply the DFC; The diesel vehicle includes determining whether the secondary injection injector and the DFC are in a failure detection mode, and in the failure detection mode, detecting and analyzing a signal of an oxygen sensor installed downstream of the DFC to diagnose a failure of the secondary injection injector and the DFC. Method for Diagnosing Post-Processing System. The method of claim 4, wherein If the air-fuel ratio (λ) is less than the reference value '1' in the signal of the oxygen sensor installed on the downstream side of the DFC, it is determined that the secondary injection injector has a failure, and further comprising the step of turning on a warning light diesel vehicle after-treatment system diagnostic method . The method of claim 4, wherein In the normal state of the secondary injection injector whose air-fuel ratio (λ) exceeds the reference value '1' in the signal of the oxygen sensor installed downstream of the DFC, if the amount of gas cross reacted according to the thermal decomposition of the DFC falls within the range of the set measurement value A method for diagnosing the after-treatment system of a diesel vehicle in which the DFC is determined to be normal and the DFC is determined to be a failure if it is not within the range of the set measured value.

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