JP2020169609A - Diagnostic device for exhaust emission control device - Google Patents

Abstract

To provide a diagnostic device for an exhaust emission control device capable of avoiding a wrong diagnosis of an NOx elimination rate and improving accuracy of a purification diagnosis.SOLUTION: A diagnostic device for an exhaust emission control device includes: an urea injector capable of supplying urea water to an exhaust passage of an engine; an SCR catalyst eliminating NOx in exhaust gas through reduction action of ammonia generated from the supplied urea water; NOx concentration sensors provided on the upstream side and the downstream side of the SCR catalyst in the exhaust passage, respectively; and a controller diagnosing a purification ratio of the SCR catalyst on the basis of sensor outputs from the upstream side and downstream side NOx concentration sensors. A purification rate calculation section of the controller estimates current ammonia adsorption amount Qc adsorbed to the SCR catalyst, and restricts a diagnosis of the purification rate D of the SCR catalyst (S22) when the estimated current ammonia adsorption amount Qc is equal to or smaller than a predetermined threshold value La (NO in S13).SELECTED DRAWING: Figure 7

Description

The present invention diagnoses an exhaust gas purification device including a urea injector that supplies urea water into an exhaust passage and a selective reduction catalyst that purifies nitrogen oxides by the reducing action of ammonia generated from the supplied urea water. Regarding the device.

Conventionally, exhaust using a selective catalytic reduction catalyst (hereinafter referred to as SCR catalyst) that adds urea water as an exhaust gas purification device for removing nitrogen oxides (NOx) contained in vehicle exhaust gas. Purification systems are known.
In order to increase the NOx purification rate while suppressing the phenomenon of excess ammonia being discharged in the NOx reduction reaction, the so-called ammonia slip phenomenon, it is necessary to supply just enough urea water to the SCR catalyst. Therefore, deterioration (abnormality) diagnosis is performed on the purification performance of the SCR catalyst.

The diagnostic device of Patent Document 1 includes a urea injector capable of supplying urea water to the exhaust passage of the engine, an SCR catalyst provided in the exhaust passage on the downstream side of the urea injector, and upstream and downstream sides of the SCR catalyst. Purification that calculates the purification rate of the SCR catalyst based on the sensor outputs of the NOx sensors arranged in the exhaust passages, the ammonia sensor arranged in the upstream exhaust passages of the SCR catalyst, and the upstream and downstream NOx concentration sensors. A rate calculation unit, a diagnostic unit that diagnoses the SCR catalyst based on the calculated purification rate, and a diagnostic stop unit that stops the diagnosis of the SCR catalyst when the ammonia detection value detected by the ammonia sensor is larger than a predetermined threshold. The configuration with the above is disclosed.

Japanese Unexamined Patent Publication No. 2018-131995

The diagnostic apparatus of Patent Document 1 prevents erroneous detection of the NOx concentration sensor due to an increase in ammonia concentration, and avoids erroneous diagnosis of deterioration of the SCR catalyst.
However, in the technique of Patent Document 1, there is a risk of erroneously diagnosing a purification abnormality of the exhaust gas purification system even though the ammonia concentration has not increased.

Therefore, in order to clarify the cause of the above misdiagnosis, a verification experiment was conducted.
8 (a) to 8 (d) are graphs showing the speed of the traveling vehicle, the temperature of the SCR catalyst, the amount of ammonia adsorbed, and the NOx concentration before and after the SCR catalyst, respectively.
In the vehicle of this verification experiment, the engine was started from the state where the current amount of ammonia adsorbed on the SCR catalyst (hereinafter referred to as the actual amount of ammonia adsorbed) was zero, and 400 seconds after the start of running, the SCR catalyst was subjected to The injection of urea water has started.
The SCR catalyst used in the verification experiment is composed of copper ion exchange zeolite as a main component and has normal purification performance. In addition, the NOx concentration sensors arranged before and after the SCR catalyst also have normal functions.

As shown in FIG. 8C, after the start of injection of urea water, the actual adsorption amount adsorbed on the SCR catalyst increases in proportion to the elapsed time so as to gradually approach the target adsorption amount.
As shown in FIG. 8D, for a predetermined period (400 to 450 sec) immediately after the start of injection of urea water, the downstream NOx concentration was high even though each NOx concentration sensor was normal and the SCR catalyst was not deteriorated. It shows an abnormal value higher than the upstream NOx concentration, and then returns to the normal state.
As a result of this verification experiment, it was found that the downstream NOx concentration sensor outputs a higher sensor output (abnormal output) than the upstream NOx concentration sensor for a predetermined period immediately after the urea water is injected.

In addition, as a result of examination by the present inventor, the following NOx characteristics were confirmed.
As shown in FIG. 9, the NOx adsorbed on the SCR catalyst has a characteristic of drawing a parabola having a peak at a predetermined temperature (120 ° C.) depending on the temperature of the SCR catalyst. Further, as shown in FIG. 10, NOx adsorbed on the SCR catalyst has a property of decreasing as the gas contact property increases. Moreover, the amount of NO ₂ adsorbed tends to be larger than the amount of NO adsorbed regardless of the temperature of the SCR catalyst and the gas contactability.

The following verification experiments and examinations have revealed the following.
Copper can be present in zeolite in a monovalent state.
Further, NO ₂ can be present in the zeolite in the state of NO ₂ ions.
When one electron is supplied to NO ₂ from monovalent copper, NO ₂ becomes a NO ₂ ion, and copper and NO ₂ are coordinated, so that they are electrically bonded.
Therefore, in the absence of ammonia in the zeolite, NO ₂ is adsorbed to the zeolite by coordination bonds. In particular, when the engine is stopped immediately after the regeneration of the DPF (Diesel Particulate Filter) and the engine is restarted after the engine is cooled, the NOx adsorption tendency becomes strong. In this situation, when ammonia is supplied into the zeolite, the ammonia is preferentially coordinated to the zeolite and the previously adsorbed NO ₂ is released.

By detecting the NO ₂ released from the zeolite by desorption phenomena such NO ₂ is the downstream NOx concentration sensor, the reverse phenomenon of the sensor output of the upstream sensor output and the downstream NOx concentration sensor of the NOx concentration sensor Occurs.
That is, in a situation where the engine is started from a situation where ammonia is not adsorbed on the SCR catalyst, there is a risk that the NOx purification rate of the SCR catalyst will be erroneously diagnosed.

An object of the present invention is to provide a diagnostic device for an exhaust gas purification device that can avoid erroneous diagnosis of NOx purification rate and improve the accuracy of purification diagnosis.

The diagnostic device of the exhaust gas purification device according to claim 1 is a urea injector capable of supplying urea water to the exhaust passage of the engine, and urea water provided in the exhaust passage on the downstream side of the urea injector and supplied by the urea injector. A selective reduction catalyst that purifies NOx in the exhaust gas by the reducing action of ammonia generated from the exhaust gas, and upstream and downstream NOx concentration sensors disposed in the exhaust passages on the upstream and downstream sides of the selective reduction catalyst, respectively. In the diagnostic device of the exhaust gas purification device provided with the control means for diagnosing the purification rate of the selective reduction catalyst based on the sensor output of the upstream side and downstream side NOx concentration sensors, the control means is attached to the selective reduction catalyst. It is characterized in that the amount of adsorbed ammonia is estimated and the diagnosis of the purification rate of the selective reduction catalyst is limited when the estimated amount of adsorbed ammonia is equal to or less than a predetermined threshold value.

In the diagnostic device of this exhaust gas purification device, in order to estimate the amount of ammonia adsorbed by the selective reduction catalyst, the control means determines the adsorption state of NOx to the selective reduction catalyst using the amount of ammonia adsorption as a parameter. Can be done.
When the estimated amount of ammonia adsorbed is equal to or less than a predetermined threshold value, the control means is adsorbed by a coordination bond in the previous step and the selective reduction catalyst after supply of urea water in order to limit the diagnosis of the purification rate of the selective reduction catalyst. NOx released from can be excluded from the target for diagnosis of purification rate.
This makes it possible to avoid a false diagnosis of the NOx purification rate when the engine is started from a situation where ammonia is not adsorbed on the selective reduction catalyst.

The invention of claim 2 is the invention of claim 1, wherein in the control means, the amount of ammonia adsorbed by the selective reduction catalyst when the engine was stopped last time was equal to or less than the threshold value, and the temperature of the selective reduction catalyst when the engine was started was first. When the temperature is lower than the set temperature, the diagnosis of the purification rate of the selective reduction catalyst is limited.
According to this configuration, the parabolic NOx characteristic with the peak of the predetermined temperature can be considered, and the limited region of the purification rate diagnosis is minimized by setting the first set temperature to the predetermined temperature of the NOx characteristic. be able to.

The invention of claim 3 is the invention of claim 1 or 2, wherein the control means stops the supply of urea water by the urea injector when the temperature of the selective reduction catalyst is lower than the second set temperature. When the temperature of the selective reduction catalyst is lower than the second set temperature, it is characterized in that the diagnosis of the purification rate of the selective reduction catalyst is limited.
According to this configuration, after replacing NOx adsorbed on the selective reduction catalyst with ammonia, the purification rate diagnosis can be appropriately started.

The invention of claim 4 is the invention of any one of claims 1 to 3, wherein the control means controls the urea injector so that the amount of ammonia adsorbed by the selective reduction catalyst becomes the target adsorption amount. It is a feature.
According to this configuration, an appropriate amount of urea water can be supplied to the selective reduction catalyst, and the amount of ammonia adsorbed on the selective reduction catalyst can be easily estimated.

The invention of claim 5 is characterized in that, in the invention of claim 4, the target adsorption amount is set according to the temperature of the selective reduction catalyst.
According to this configuration, an appropriate amount of urea water can be supplied while preventing the ammonia slip phenomenon.

According to the diagnostic device of the exhaust gas purification device of the present invention, the accuracy of the purification diagnosis can be improved by avoiding the erroneous diagnosis of the NOx purification rate.

It is a system diagram which shows the preferable embodiment of the engine to which the exhaust gas purification apparatus of this invention is applied. It is a block diagram which shows the control system of an engine. It is a flowchart which shows the specific procedure of the dosing control. It is explanatory drawing which shows typically the procedure of estimating the temperature of the SCR catalyst. It is a graph which shows the relationship between the temperature of the SCR catalyst, the upper limit adsorption amount of ammonia, and the target adsorption amount. It is explanatory drawing which shows typically the procedure of determining the injection amount of urea water. It is a flowchart which shows an example of purification diagnosis control. In the verification experiment results, (a) is the vehicle speed, (b) is the SCR catalyst temperature, (c) is the target adsorption amount and the actual adsorption amount of ammonia, and (d) is the upstream NOx concentration and downstream. It is a time chart which shows each side NOx concentration. It is a graph which shows the relationship between the SCR catalyst temperature and the NOx adsorption amount. It is a graph which shows the relationship between a gas contact property and a NOx adsorption amount.

[Overall engine configuration]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
First, the overall configuration of the engine to which the exhaust gas purification device according to the present invention is applied will be described with reference to FIG.
The engine shown in FIG. 1 is a 4-cycle diesel in-vehicle engine mounted on a vehicle as a power source for traveling, and includes an engine body 1 and an intake system 3S that supplies air necessary for combustion in the engine body 1. , The exhaust system 4S (exhaust gas purification device) that purifies the exhaust gas discharged from the engine body 1 and discharges it to the outside, and the air (intake) supplied by the intake system 3S is compressed and sent out to the engine body 1. The supply device 50 and an EGR device 70 that circulate a part of the exhaust gas flowing through the exhaust system 4S to the intake system 3S are provided.

The engine body 1 is an in-line multi-cylinder type having a plurality of cylinders 2 arranged in a row (only one cylinder 2 is shown in FIG. 1), and the engine body 1 is a cylinder block 3 in which the plurality of cylinders 2 are formed inside. It has a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the upper opening of each cylinder 2, and a plurality of pistons 5 inserted into each cylinder 2 so as to be reciprocating. Since the structure of each cylinder 2 is the same, the description will be described below focusing on basically only one cylinder 2.

A combustion chamber 6 is partitioned above the piston 5. Fuel containing light oil as a main component is supplied to the combustion chamber 6 by injection from a fuel injection valve 15 described later. Then, the supplied fuel is burned by compression ignition (diffusion combustion), and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction.

Below the piston 5, a crankshaft 7, which is an output shaft of the engine body 1, is provided. The crankshaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in response to the reciprocating motion (vertical motion) of the piston 5.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the angle of the crankshaft 7 (crank angle) and the rotation speed of the crankshaft 7 (engine rotation speed). The cylinder head 4 is provided with a water temperature sensor SN2 that detects the temperature of the cooling water flowing inside the engine body 1 (cylinder block 3 and cylinder head 4).

The cylinder head 4 includes an intake port 9 and an exhaust port 10 that open into the combustion chamber 6, an intake valve 11 that opens and closes the intake port 9, an exhaust valve 12 that opens and closes the exhaust port 10, and an intake valve 11 and an exhaust valve 12. Valve mechanisms 13 and 14 are provided to open and close the engine in conjunction with the rotation of the crankshaft 7.

The cylinder head 4 is further provided with a fuel injection valve 15 for injecting fuel (light oil) into the combustion chamber 6. The fuel injection valve 15 is, for example, a multi-injection hole type injection valve that injects fuel radially from the central portion of the ceiling surface of the combustion chamber 6. Although not shown, a recess (cavity) for receiving the fuel injected from the fuel injection valve 15 is formed on the crown surface of the piston 5.

The intake system 3S includes an intake passage 30 through which intake air introduced into the engine body 1 flows. The downstream end (intake manifold) of the intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9. In the intake passage 30, an air cleaner 31 for removing foreign matter in the intake air, an intercooler 32 for cooling the intake air compressed by the supercharging device 50, an openable and closable throttle valve 33 for adjusting the intake air flow rate, and each cylinder. Surge tanks 34 for evenly taking in intake air are provided in this order from the upstream side (the side far from the engine body 1) of the intake air passage 30.

An air flow sensor SN3 for detecting the flow rate of air (fresh air) introduced into the engine body 1 through the intake passage 30 is provided in a portion of the intake passage 30 on the downstream side of the air cleaner 31. Further, the surge tank 34 is provided with an intake pressure sensor SN4 that detects the pressure of the intake air inside the surge tank 34.

The exhaust system 4S includes an exhaust passage 40 through which the exhaust gas discharged from the engine body 1 flows. The upstream end (exhaust manifold) of the exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10. The exhaust passage 40 is provided with a plurality of catalysts 41 to 44 for purifying various harmful components contained in the exhaust gas. In the present embodiment, the oxidation catalyst 41, the DPF (Diesel Particulate Filter) 42, the SCR catalyst (Selective Catalytic Reduction) 43 (selective reduction catalyst), and the slip catalyst 44 are located on the upstream side of the exhaust passage 40 (engine body 1). It is provided in this order from the side closest to).
Further, a urea injector 45 and a mixing plate 47 are provided in a portion of the exhaust passage 40 between the DPF 42 and the SCR catalyst 43.

The oxidation catalyst 41 is a catalyst for oxidizing CO and HC in the exhaust gas to make them harmless (converting them into CO2 and H2O). For example, a porous carrier and platinum supported on the carrier or the like. It has a catalytic substance such as palladium. The DPF 42 is a filter for collecting soot (soot) in the exhaust gas. The DPF 42 contains a catalytic substance such as platinum for burning the suit under high temperature conditions during filter regeneration. The DPF 42 is subjected to DPF regeneration for burning the suit, for example, on the condition that a predetermined amount of the suit is accumulated, the mileage, and the like, and when these conditions are satisfied.

The urea injector 45 is an injection valve that supplies urea water obtained by solubilizing high-purity urea with pure water into the exhaust passage 40. A downstream end of a supply pipe 46a for supplying urea water is connected to the urea injector 45. A urea tank 46 for storing urea water is connected to the upstream end of the supply pipe 46a. Further, the supply pipe 46a incorporates a pump 46P (pump device) that supplies urea water to the urea injector 45. When urea water is injected into the exhaust passage 40 from the urea injector 45, the urea contained in the urea water is converted to ammonia (NH3) by hydrolysis at a high temperature and adsorbed on the SCR catalyst 43 on the downstream side. Will be done.

The pump 46P is a pressurized pump, and by generating a pressing force, the urea water stored in the urea tank 46 is supplied to the urea injector 45 through the supply pipe 46a. When the pressing force is stopped, the urea water existing inside the urea injector 45 and in the supply pipe 46a is pulled back to the urea tank 46. That is, the pump 46P is a pump device capable of supplying urea water to the urea injector 45 and recovering the urea water once supplied to the urea injector 45 to the urea tank 46.

The mixing plate 47 is a plate-shaped member that partitions the exhaust passage 40 back and forth, and is provided at a portion between the urea injector 45 and the SCR catalyst 43 in the exhaust passage 40. The mixing plate 47 is formed with a plurality of openings for agitating the flow of exhaust gas. Such a mixing plate 47 plays a role of uniformly dispersing the urea contained in the urea water ejected from the urea injector 45 and delivering it to the downstream side (SCR catalyst 43).

The SCR catalyst 43 is provided in the exhaust passage 40 on the downstream side of the urea injector 45, and is a catalyst for reducing and purifying NOx in the exhaust gas (converting it to N2 or H2O).
The SCR catalyst 43 has, for example, a porous carrier and a catalyst substance such as vanadium, tungsten, or zeolite supported on the carrier. In this embodiment, copper ion exchange zeolite is used. As described above, the SCR catalyst 43 adsorbs ammonia generated from the urea water injected by the urea injector 45. The SCR catalyst 43 converts NOx in the exhaust gas into N2 and H2O by a chemical reaction (reducing action of ammonia) using this ammonia as a reducing agent.

The slip catalyst 44 is an oxidation catalyst for oxidizing ammonia that has slipped without being adsorbed by the SCR catalyst 43 (that is, has flowed out to the downstream side without being used for NOx reduction). As the slip catalyst 44, for example, one having the same structure as the oxidation catalyst 41 can be used.

A NOx concentration sensor SN5 (upstream NOx sensor) for detecting the concentration of NOx contained in the exhaust gas is provided in a portion of the exhaust passage 40 between the DPF 42 and the SCR catalyst 43. Further, the temperature of the exhaust gas is set in the exhaust passage 40 (the portion between the mixing plate 47 and the SCR catalyst 43) located on the downstream side of the NOx concentration sensor SN5 and directly upstream of the SCR catalyst 43. An exhaust temperature sensor SN6 for detecting is provided. Further, a NOx concentration sensor SN10 (downstream NOx sensor) for detecting the concentration of NOx contained in the exhaust gas is provided in a portion of the exhaust passage 40 between the SCR catalyst 43 and the slip catalyst 44.

The supercharger 50 is a so-called two-stage type supercharger, and has a first supercharger 51 and a second supercharger 52 arranged in series. The first supercharger 51 is a so-called turbocharger, which is rotatably provided with a turbine 61 that is rotationally driven by exhaust gas flowing through the exhaust passage 40 and a turbine 61 that flows through the intake passage 30. It has a first compressor 62 that compresses the intake air. The first compressor 62 is arranged in a portion of the intake passage 30 between the air cleaner 31 and the intercooler 32, and the turbine 61 is arranged in a portion of the exhaust passage 40 upstream of the oxidation catalyst 41. The exhaust passage 40 is provided with a bypass passage 63 for bypassing the turbine 61, and the bypass passage 63 is provided with a waist gate valve 64 that can be opened and closed.

The second supercharger 52 is a so-called electric supercharger, and has an electric drive motor 66 and a second compressor 67 that compresses intake air by being rotationally driven by the drive motor 66. The second compressor 67 is arranged in a portion of the intake passage 30 on the downstream side (between the first compressor 62 and the intercooler 32) of the first compressor 62. The intake passage 30 is provided with a bypass passage 68 for bypassing the second compressor 67. The bypass passage 68 is provided with a bypass valve 69 that can be opened and closed.

The EGR device 70 has an EGR passage 71 that connects the exhaust passage 40 and the intake passage 30, and an EGR cooler 72 and an EGR valve 73 provided in the EGR passage 71. The EGR passage 71 connects a portion of the exhaust passage 40 upstream of the turbine 61 and a portion of the intake passage 30 between the throttle valve 33 and the surge tank 34 to each other. The EGR cooler 72 is, for example, a heat exchanger that utilizes cooling water of an engine, and cools exhaust gas (EGR gas) that is returned from the exhaust passage 40 to the intake passage 30 through the EGR passage 71. The EGR valve 73 is provided in a portion of the EGR passage 71 on the downstream side (closer to the intake passage 30) of the EGR cooler 72, and adjusts the flow rate of the exhaust gas flowing through the EGR passage 71.

[Control system]
FIG. 2 is a block diagram showing a control system of the engine of the present embodiment. The vehicle on which the engine of the present embodiment is mounted includes a controller 100 (control means) that controls the engine in an integrated manner. The controller 100 is a microprocessor, and is composed of a well-known CPU, ROM, RAM, and the like. In the present embodiment, the controller 100 functions as a control unit that controls the operations of the urea injector 45 and the pump 46P.
The controller 100 does not have to be a single processor, and may include a plurality of electrically connected processors. For example, the controller 100 may include a first processor mainly for controlling the engine body 1 and a second processor for controlling dosing such as the urea injector 45 and the pump 46P.

Detection information from various sensors is input to the controller 100. Specifically, the controller 100 is electrically connected to the crank angle sensor SN1, water temperature sensor SN2, airflow sensor SN3, intake pressure sensor SN4, NOx concentration sensor SN5, exhaust temperature sensor SN6, and NOx concentration sensor SN10 described above. ing. Various information detected by these sensors, such as crank angle, engine rotation speed, engine water temperature, intake flow rate, intake pressure (supercharging pressure), NOx concentration in exhaust gas, and exhaust gas temperature, respectively. It is input to the controller 100.

In addition to the above, the vehicle includes a vehicle speed sensor SN7 that detects the traveling speed of the vehicle (hereinafter referred to as vehicle speed), an accelerator sensor SN8 that detects the opening degree of the accelerator pedal operated by the occupant who drives the vehicle, and outside. An outside air temperature sensor SN9 that detects the air temperature is provided. The detection information by the vehicle speed sensor SN7, the accelerator sensor SN8, and the outside air temperature sensor SN9 is also input to the controller 100.

The controller 100 controls each part of the engine while executing various determinations and calculations based on the input information from the sensors SN1 to SN10. That is, the controller 100 is electrically connected to the fuel injection valve 15, the throttle valve 33, the urea injector 45, the pump 46P, the waist gate valve 64, the drive motor 66, the bypass valve 69, the EGR valve 73, and the like. A command signal for control is output to each of these devices based on the result of calculation and the like.

As functional elements related to the control, the controller 100 has a main control unit 101, an SCR state estimation unit 102, a dosing control unit 103, a purification rate calculation unit 104, and a purification diagnosis unit 105. The purification rate calculation unit 104 and the purification diagnosis unit 105 are functional units for determining whether or not the NOx purification performance by the SCR catalyst 43 is functioning normally.

The main control unit 101 is a control module that controls combustion in the engine body 1. For example, the main control unit 101 is detected by the engine rotation speed detected by the crank angle sensor SN1, the engine load (required torque) specified from the detection value (accelerator opening) of the accelerator sensor SN8, and the airflow sensor SN3. The fuel injection amount and injection timing from the fuel injection valve 15 are determined based on the intake flow rate, and the fuel injection valve 15 is controlled according to the determination.

Further, the main control unit 101 sets a target boost pressure based on the engine rotation speed / load and the like, and the intake pressure (supercharge pressure) detected by the intake pressure sensor SN4 matches the target boost pressure. As such, the opening degrees of the Westgate valve 64 and the bypass valve 69 and the rotation of the drive motor 66 are controlled. Further, the main control unit 101 sets a target EGR rate, which is a target value of the EGR rate (ratio of EGR gas to all gas introduced into the cylinder 2), based on the engine speed / load and the like, and sets the target EGR rate. Each opening degree of the throttle valve 33 and the EGR valve 73 is controlled so that the rate is realized.

The SCR state estimation unit 102 is a control module that controls the process of estimating the state of the SCR catalyst 43. For example, the SCR state estimation unit 102 determines the NOx concentration in the exhaust gas detected by the NOx concentration sensor SN5 and the NOx concentration sensor SN10, the temperature of the exhaust gas detected by the exhaust temperature sensor SN6, and the urea from the urea injector 45. The temperature of the SCR catalyst 43 and the amount of adsorbed ammonia are estimated based on the amount of water injected.

The dosing control unit 103 is a control module that controls the injection of urea water by the urea injector 45. For example, the dosing control unit 103 determines the injection amount of urea water based on the temperature of the SCR catalyst 43 estimated by the SCR state estimation unit 102, and controls the urea injector 45 according to the determination.

The purification rate calculation unit 104 calculates the NOx purification rate (hereinafter abbreviated as purification rate) D of the SCR catalyst 43 when all of the plurality of purification diagnosis execution conditions are satisfied.
The purification rate D is calculated by the following equation (1).
D = actual purification rate / theoretical purification rate ... (1)
The actual purification rate is obtained by differentiating the sensor output value of the NOx concentration sensor SN10 from the sensor output value of the NOx concentration sensor SN5, and the theoretical purification rate is the fuel injection amount from the fuel injection valve 15, the fuel injection timing, and so on. It is obtained based on the NOx concentration generated in the cylinder based on the engine rotation speed, the intake air amount related to the air-fuel ratio, and the like.

The purification diagnosis execution conditions have the following first and second execution conditions.
The first execution condition is that the actual adsorption amount Qc of ammonia adsorbed on the SCR catalyst 43 (hereinafter referred to as the current ammonia adsorption amount Qc) is greater than the determination threshold value La (for example, 0.1 g / l) corresponding to zero. It's a big thing.
When the current ammonia adsorption amount Qc is equal to or less than the determination threshold value La, NOx (NO ₂ ) is adsorbed to the SCR catalyst 43 (zeolite) by a coordination bond. After that, when ammonia is supplied, the ammonia is preferentially coordinated and bound to the SCR catalyst 43, and the previously adsorbed NOx is desorbed. Therefore, the NOx concentration sensor SN10 on the downstream side is accurate for purification. This is because the NOx concentration cannot be acquired, and an output reversal phenomenon occurs between the NOx concentration sensor SN5 on the upstream side and the NOx concentration sensor SN10 on the downstream side.

The second execution condition is the following three items.
(A) The outputs of the NOx concentration sensors SN5 and SN10 are all set values (for example, 100 ppm) or more (b) The temperature of the SCR catalyst 43 is the first set temperature (120 ° C.) or more (c) The exhaust gas flow rate is the set flow rate or more. In addition to the above three items, the following items can be added to the second execution condition.
(D) Elapsed more than a predetermined time from the supply of urea water (e) Within a predetermined time from the regeneration of DPF42 (f) The abundance ratio of NO ₂ is approximately 50%.

The purification diagnosis unit 105 diagnoses the NOx purification performance including the degree of deterioration and functional abnormality of the SCR catalyst 43 based on the purification rate D calculated by the purification rate calculation unit 104.
When the purification rate D is equal to or higher than the preset determination threshold value Ld, the SCR catalyst 43 is functioning normally, so that the determination is normal. When the purification rate D is less than the determination threshold value Ld, the SCR catalyst 43 has a functional abnormality due to factors such as deterioration, so that the abnormality is determined.
When the purification diagnosis unit 105 determines an abnormality, the purification diagnosis unit 105 notifies the occupant by a notification means (not shown) such as a lamp provided on the meter panel.

[About dosing control]
Next, with reference to FIGS. 3 to 6, regarding the dosing control which is the control of the injection operation of the urea water from the urea injector 45, the basic dosing control which the dosing control unit 103 executes during the normal operation of the engine or the like. explain. In this dosing control during normal operation, a target adsorption amount of ammonia (Qa in FIG. 5) is set according to the temperature of the SCR catalyst 43, and an amount of urea water corresponding to the target adsorption amount is injected from the urea injector 45. Control is executed.
Further, the injection of urea water from the urea injector 45 is executed when the temperature of the SCR catalyst 43 is equal to or higher than the second set temperature (for example, 180 ° C.).
The target adsorption amount is predetermined based on the amount of ammonia that can be adsorbed by the SCR catalyst 43.

FIG. 3 is a flowchart showing a specific procedure of dosing control during normal operation.
When the control starts, the controller 100 (dosing control unit 103) estimates the temperature Ts of the SCR catalyst 43 (S1). In the figure, Si (i = 1, 2, ...) Indicates each step. Further, the temperature Ts of the SCR catalyst 43 is typically the temperature of the carrier of the SCR catalyst 43, that is, the floor temperature.

FIG. 4 is a diagram schematically showing a procedure for estimating the temperature Ts of the SCR catalyst 43 in S1 (in the figure, the SCR catalyst is simply abbreviated as SCR).
First, the controller 100 calculates the amount of heat input to the SCR catalyst 43 based on the temperature of the exhaust gas immediately before the SCR catalyst 43 detected by the exhaust temperature sensor SN6 and the flow rate of the exhaust gas. As described above, the flow rate of the exhaust gas can be estimated from the intake flow rate detected by the air flow sensor SN3, the opening degree of the EGR valve 73, and the like.

Next, the controller 100 calculates the amount of heat radiated from the SCR catalyst 43 based on the vehicle speed detected by the vehicle speed sensor SN7 and the outside air temperature detected by the outside air temperature sensor SN9. The controller 100 calculates the temperature Ts of the SCR catalyst 43 based on the calculated heat input amount and heat dissipation amount of the SCR catalyst 43 and the heat capacity of the SCR catalyst 43 stored in advance. The temperature Ts of the SCR catalyst 43 is calculated as a higher value as the amount of heat input is larger or the amount of heat radiation is smaller, and is calculated as a lower value as the amount of heat input is smaller or the amount of heat radiation is larger.
Here, the amount of heat radiated from the SCR catalyst 43 can be treated as being larger as the vehicle speed is higher. This is because the higher the vehicle speed, the more the traveling wind blowing on the SCR catalyst 43 increases and the heat dissipation is promoted. On the contrary, since the amount of heat radiation decreases as the vehicle speed decreases, it is estimated that the temperature Ts of the SCR catalyst 43 increases as the vehicle speed decreases.

Next, the controller 100 determines the target adsorption amount Qa of ammonia to be adsorbed on the SCR catalyst 43 (S2). FIG. 5 is a graph showing the relationship between the temperature of the SCR catalyst 43, the upper limit adsorption amount Qx of ammonia, and the target adsorption amount Qa. The target adsorption amount Qa is an appropriate ammonia adsorption amount capable of performing the required NOx purification in the SCR catalyst 43, and as shown in the graph of FIG. 5, the temperature of the SCR catalyst 43 in a region smaller than the upper limit adsorption amount Qx. (SCR temperature) It is variably set according to Ts. The controller 100 stores in advance a map that defines the relationship between the temperature Ts of the SCR catalyst 43 and the target adsorption amount Qa, and by collating the temperature Ts of the SCR catalyst 43 estimated in S1 above with this map, Determine the target adsorption amount Qa.

The target adsorption amount Qa of ammonia is set to a value smaller than the upper limit adsorption amount Qx. The upper limit adsorption amount Qx is the upper limit adsorption amount of ammonia that can be adsorbed on the SCR catalyst 43, and is also called a saturated adsorption amount. The SCR catalyst 43 has a property that the higher the internal temperature, the more difficult it is to adsorb ammonia. Therefore, the line of the upper limit adsorption amount Qx in FIG. 5 tends to have a smaller adsorption amount (downward to the right) toward the higher temperature side (right side) as a whole. The region exceeding the upper limit adsorption amount Qx is an ammonia slip region in which ammonia slips through the SCR catalyst 43 and flows out to the downstream side of the exhaust passage 40.

The target adsorption amount Qa of ammonia is also set to a variable value that decreases as the temperature Ts of the SCR catalyst 43 increases (conversely, increases as the temperature Ts decreases) in accordance with the tendency of the upper limit adsorption amount Qx as described above. Will be done. The controller 100 controls the operation of the urea injector 45 and the pump 46P according to such a variable target adsorption amount Qa. However, the target adsorption amount Qa changes depending on the temperature only in the range in which the temperature Ts of the SCR catalyst 43 belongs to a constant high temperature region (Ts = T1 to T2). In the low temperature range where the temperature is T1 or lower, the target adsorption amount Qa is set to a constant value Q1, and in the high temperature range where the temperature is T2 or higher, the target adsorption amount Qa is uniformly set to zero. The target adsorption amount Qa is set to a constant value Q1 on the low temperature side (Ts ≦ T1) because the NOx purification performance is sufficiently good if ammonia of about Q1 is adsorbed, so that it is further than Q1. This is because there is no point in increasing the amount of adsorption.

Next, the controller 100 estimates the actual adsorption amount of ammonia adsorbed on the SCR catalyst 43 at present, that is, the so-called current ammonia adsorption amount Qc (S3). As will be described in detail in step S5 described later, the current ammonia adsorption amount Qc is a parameter used in the process of determining the injection amount of urea water from the urea injector 45. Therefore, the current amount of ammonia adsorbed Qc can be obtained by back calculation from the history of the amount of urea water injected so far. That is, the amount obtained by subtracting the ammonia consumption at each time point (calculated in S4 described below) from the ammonia supply amount at each time point obtained from the history of the injection amount of urea water is added to the SCR catalyst 43 each time. Since it will be accumulated, it is possible to calculate the current ammonia adsorption amount Qc by accumulating this accumulated amount for each hour.

Next, the controller 100 estimates the ammonia consumption W, which is the amount of ammonia consumed in the SCR catalyst 43 (S4). The controller 100 determines the NOx concentration in the exhaust gas detected by the NOx concentration sensor SN5 and the flow rate of the exhaust gas estimated by calculation (a value obtained from the detected value of the intake air flow rate, the opening degree of the EGR valve 73, etc.). Based on this, the amount of NOx flowing into the SCR catalyst 43 is calculated. Based on the calculated NOx inflow amount, the controller 100 calculates the amount of ammonia consumed for NOx reduction in the SCR catalyst 43, that is, the ammonia consumption amount W (see a part of FIG. 6 described later).

Next, the controller 100 determines the injection amount U of urea water to be injected from the urea injector 45 (S5), and the urea injector 45 and the pump so as to inject urea corresponding to the determined injection amount U from the urea injector 45. The operation of 46P is controlled (S6).

FIG. 6 is a diagram schematically showing a procedure for determining the injection amount U in S5.
The controller 100 calculates the injection amount U of urea water based on the ammonia consumption amount W obtained in S4 and the required surplus supply amount Qd of ammonia. Here, the required surplus supply amount of ammonia Qd is the surplus supply amount of ammonia required to increase the current adsorption amount Qc of ammonia to the target adsorption amount Qa in the SCR catalyst 43, and the ammonia determined in S2 above. It is a value obtained by subtracting the current ammonia adsorption amount Qc calculated in S3 above from the target adsorption amount Qa of. The urea water injection amount U is calculated as a larger value as the required surplus supply amount Qd increases and the ammonia consumption amount W increases.

[Purification diagnosis control]
The above is the basic operation of dosing control. Subsequently, the purification diagnostic control for diagnosing whether the purification performance of the SCR catalyst 43 is functioning normally will be described.
This purification diagnosis control is intended to avoid erroneous diagnosis of NOx purification rate and improve the accuracy of purification diagnosis, and is mainly executed by the purification rate calculation unit 104 and the purification diagnosis unit 105.

An example of the purification diagnosis control operation by the controller 100 will be described with reference to the flowchart shown in FIG. In the figure, Si (i = 11, 12, ...) Indicates each step. Purification diagnosis control is executed in parallel under the situation where the dosing control shown in FIG. 3 is being executed by the dosing control unit 103 of the controller 100.

As shown in the flowchart of FIG. 7, in S11, the output signals and various information from the sensors SN1 to SN10 and the like are read, and the process proceeds to S12.
In S12, the current amount of ammonia adsorbed Qc is estimated, and the process shifts to S13.
Similar to the dosing control (S3) described above, the accumulated amount obtained by subtracting the ammonia consumption at each time point in the SCR catalyst 43 from the ammonia supply amount is integrated every hour to estimate the current ammonia adsorption amount Qc.

In S13, it is determined whether or not the current ammonia adsorption amount Qc, which is the first execution condition, is larger than the threshold value La.
As a result of the determination in S13, when the current ammonia adsorption amount Qc is larger than the threshold value La, the first execution condition is satisfied, and the process proceeds to S14.
In S14, it is determined whether or not the second execution conditions (a) to (c) are satisfied.
When the second execution conditions (a) to (c) are satisfied as a result of the determination in S14, the process proceeds to S15 in order to satisfy the condition for performing the purification diagnosis. If the second execution conditions (a) to (c) are not satisfied as a result of the determination in S14, it returns because it is not in a state where an accurate purification diagnosis can be performed.

In S15, the purification rate D is calculated using the equation (1), and the process proceeds to S16.
In S16, it is determined whether or not the purification rate D is equal to or greater than the threshold value Ld.
As a result of the determination in S16, when the purification rate D is equal to or greater than the threshold value Ld, the purification performance of the SCR catalyst 43 is sufficiently functioning, so that a normal determination is performed (S17) and the process returns.
As a result of the determination in S16, when the purification rate D is less than the threshold value Ld, the purification performance of the SCR catalyst 43 is not sufficiently functioning, so that an abnormality determination is performed (S18) and the process returns.

As a result of the determination in S13, when the current ammonia adsorption amount Qc is equal to or less than the threshold value La, a NOx desorption phenomenon may occur, so the process proceeds to S19.
When the current amount of ammonia adsorbed Qc is equal to or less than the threshold La, NOx in the exhaust gas is adsorbed on the SCR catalyst 43, and NOx is desorbed by the supply of ammonia. Therefore, NOx that should not originally exist is downstream of the SCR catalyst 43. It is released. This is because when the released NOx is detected by the NOx concentration sensor SN10, an accurate purification rate D cannot be obtained.

In S19, it is determined whether or not urea water can be injected from the urea injector 45.
As a result of the determination of S19, when urea water can be injected from the urea injector 45, that is, when the SCR catalyst 43 temperature Ts is equal to or higher than the second set temperature (180 ° C), even if the current ammonia adsorption amount Qc is equal to or lower than the threshold La. , Ammonia is adsorbed on the SCR catalyst 43, and the NOx desorption phenomenon does not occur, so that the process proceeds to S14. As a result of the determination in S19, if it is not possible to inject urea water from the urea injector 45, the process proceeds to S20.

In S20, it is determined whether or not NOx has flowed into the SCR catalyst 43.
The inflow of NOx into the SCR catalyst 43 is determined based on the sensor output of the upstream NOx concentration sensor SN5. As a result of the determination in S20, when NOx flows into the SCR catalyst 43, the NOx in the exhaust gas has already been adsorbed by the SCR catalyst 43, so that the process proceeds to S21.
As a result of the determination in S20, when NOx has not flowed into the SCR catalyst 43, NOx in the exhaust gas has not yet been adsorbed by the SCR catalyst 43, so that the process proceeds to S19.

In S21, it is determined whether or not the condition for discontinuing the purification diagnosis is not satisfied.
As a result of the determination in S21, if the condition for discontinuing the purification diagnosis is not satisfied, a return is made.
The conditions for discontinuing the purification diagnosis are, for example, that the current ammonia adsorption amount Qc is equal to or less than the threshold value La, or the temperature Ts of the SCR catalyst 43 is less than the first set temperature (120 ° C.).
When the current ammonia adsorption amount Qc exceeds the threshold La, NOx is difficult to be adsorbed by the SCR catalyst 43, and when the temperature Ts is equal to or higher than the first set temperature, NOx desorbed from the SCR catalyst 43 decreases due to the NOx characteristics. Because.

As a result of the determination in S21, if the purification diagnosis discontinuation condition is not unsatisfied, that is, if it is satisfied, the purification diagnosis is discontinued (S22), and the purification diagnosis discontinuation condition is continuously determined.
For example, when the current ammonia adsorption amount Qc is equal to or less than the threshold La (S13: No) when the engine was stopped last time, and the temperature Ts of the SCR catalyst 43 at the time of starting the engine this time is lower than the first set temperature (S19: No, S20: Yes). ), Due to the NOx characteristics, the amount of NOx adsorbed increases in proportion to the increase in the temperature Ts of the SCR catalyst 43, and the amount of NOx desorbed from the SCR catalyst 43 also increases, so that the purification diagnosis is stopped. The suspension of the purification diagnosis is continued after the engine is started until the current ammonia adsorption amount Qc increases and the temperature Ts of the SCR catalyst 43 rises and the purification diagnosis discontinuation condition is not satisfied.

Next, the operation and effect of the diagnostic device of the exhaust gas purification device according to the embodiment of the present invention will be described.
According to the present embodiment, in order for the controller 100 (SCR state estimation unit 102) to estimate the current ammonia adsorption amount Qc adsorbed on the SCR catalyst 43, the current ammonia adsorption amount Qc is used as a parameter for the NOx SCR catalyst 43. The adsorption state, so-called easiness of adsorption, can be determined. When the estimated current ammonia adsorption amount Qc is equal to or less than the predetermined threshold La, the controller 100 (purification rate calculation unit 104) is adsorbed by coordination bonds in the previous step in order to limit the diagnosis of the purification rate D of the SCR catalyst 43. Moreover, NOx released from the SCR catalyst 43 after the supply of urea water can be excluded from the diagnosis target of the purification rate D.
As a result, when the engine is started from a situation where ammonia is not adsorbed on the SCR catalyst 43, an erroneous diagnosis of the NOx purification rate D can be avoided.

When the current ammonia adsorption amount Qc of the SCR catalyst 43 when the engine is stopped last time is equal to or less than the threshold La and the temperature Ts of the SCR catalyst 43 when the engine is started is lower than the first set temperature, the controller 100 (purification rate calculation unit 104) is used. It limits the diagnosis of the purification rate D of the SCR catalyst 43. As a result, the parabolic NOx characteristic with the peak of the predetermined temperature can be considered, and the limited region of the purification rate diagnosis can be minimized by setting the first set temperature to the predetermined temperature of the NOx characteristic. ..

When the temperature Ts of the SCR catalyst 43 is lower than the second set temperature, the controller 100 (dosing control unit 103) stops the supply of urea water by the urea injector 45, and the temperature Ts of the SCR catalyst 43 is the second set temperature. When it is lower than, it limits the diagnosis of the purification rate D of the SCR catalyst 43. As a result, after replacing the NOx adsorbed on the SCR catalyst 43 with ammonia, the purification rate diagnosis can be appropriately started.

Since the controller 100 (dosing control unit 103) controls the urea injector 45 so that the ammonia adsorption amount of the SCR catalyst 43 becomes the target adsorption amount Qa, an appropriate amount of urea water can be supplied to the SCR catalyst 43. The current amount of ammonia adsorbed Qc adsorbed on the SCR catalyst 43 can be easily estimated.

Since the target adsorption amount Qa is set according to the temperature Ts of the SCR catalyst 43, it is possible to supply an appropriate amount of urea water while preventing ammonia slip.

Next, a modified example in which the embodiment is partially modified will be described.
1] In the above embodiment, an example in which the exhaust gas purification device of the present invention is applied to a diesel engine that crimps and ignites a fuel containing light oil as a main component has been described. The engine to which the present invention can be applied may be an engine that needs to be provided with an SCR catalyst in order to purify NOx, for example, a lean burn gasoline engine that burns a fuel containing gasoline as a main component under a lean air-fuel ratio. The present invention may be applied.

2] In the above embodiment, when the current ammonia adsorption amount Qc is equal to or less than the threshold value La and NOx flows into the SCR catalyst 43, the purification diagnosis is stopped (S23), but the purification diagnosis may be stopped. You may limit it without. Specifically, the sensor output value of the downstream NOx concentration sensor SN10 is corrected for a decrease equivalent to the desorption NOx, and the sensor output value of the upstream NOx concentration sensor SN5 and the correction sensor output value of the downstream NOx concentration sensor SN10 are used for purification. It is also possible to calculate the rate D.

3] In the above embodiment, when NOx flows into the SCR catalyst 43, an example of canceling the purification diagnosis stop by the regeneration execution determination (S21) of the DPF 42 has been described, but the NOx adsorbed on the SCR catalyst 43 is eliminated. It suffices if it can be determined, and it is possible to cancel the suspension of the purification diagnosis at the temperature Ts of the SCR catalyst 43, for example, 160 ° C. or higher.

4] In the above embodiment, as the first execution condition, an example of limiting the purification diagnosis of the SCR catalyst 43 when the current ammonia adsorption amount Qc is 0.1 g / l or less corresponding to zero has been described, but at least the SCR catalyst It suffices if the possibility of NOx binding to 43 can be determined, and the determination threshold La can be appropriately set according to the specifications of the exhaust gas purification device.

5] In addition, a person skilled in the art can carry out the present invention in a form in which various modifications are added to the above-described embodiment or in a combination of the respective embodiments without departing from the spirit of the present invention. It also includes various modified forms.

40 Exhaust passage 43 SCR catalyst 45 Urea injector 100 Controller 4S Exhaust system SN5 (upstream side) NOx concentration sensor SN10 (downstream side) NOx concentration sensor

Claims (5)

A urea injector capable of supplying urea water to the exhaust passage of the engine and an ammonia in the exhaust gas provided in the exhaust passage on the downstream side of the urea injector and generated from the urea water supplied by the urea injector. The sensor outputs of the selective reduction catalyst that purifies NOx, the upstream and downstream NOx concentration sensors arranged in the exhaust passages on the upstream and downstream sides of the selective reduction catalyst, and the upstream and downstream NOx concentration sensors, respectively. In the diagnostic device of the exhaust gas purification device provided with the control means for diagnosing the purification rate of the selective reduction catalyst based on
The control means estimates the amount of ammonia adsorbed on the selective reduction catalyst, and limits the diagnosis of the purification rate of the selective reduction catalyst when the estimated amount of ammonia adsorption is equal to or less than a predetermined threshold value. Diagnostic device for exhaust gas purification equipment. When the amount of ammonia adsorbed by the selective reduction catalyst when the engine is stopped last time is equal to or less than the threshold value and the temperature of the selective reduction catalyst when the engine is started is lower than the first set temperature, the control means purifies the selective reduction catalyst. The diagnostic device for an exhaust gas purification device according to claim 1, wherein the diagnosis of the exhaust gas purifying device is restricted. When the temperature of the selective reduction catalyst is lower than the second set temperature, the control means stops the supply of urea water by the urea injector, and when the temperature of the selective reduction catalyst is lower than the second set temperature. The diagnostic device for an exhaust gas purification device according to claim 1 or 2, wherein the diagnosis of the purification rate of the selective reduction catalyst is limited. The exhaust gas purification device according to any one of claims 1 to 3, wherein the control means controls the urea injector so that the amount of ammonia adsorbed by the selective reduction catalyst becomes the target adsorption amount. Diagnostic device. The diagnostic device for an exhaust gas purification device according to claim 4, wherein the target adsorption amount is set according to the temperature of the selective reduction catalyst.