JP6079567B2 - Exhaust purification device control method - Google Patents

Description

The present invention relates to a control method for an exhaust purification apparatus arranged NO _X sensor in the exhaust passage upstream of the selective catalytic reduction filter.

2. Description of the Related Art An exhaust emission control device incorporating a catalyst device that captures or adsorbs harmful components contained in exhaust gas or renders them harmless is known in order to minimize the environmental impact on exhaust gas discharged from an internal combustion engine. For example, particulate matter and nitrogen oxides in the exhaust, that is selective catalytic reduction filter for detoxifying NO _X, that is, an exhaust gas purification apparatus using the SCRF (S elective C atalytic R eduction F ilter) are known . In this method, a reducing agent containing urea is continuously supplied into an exhaust passage upstream of SCRF, and NO _X is reduced by SCRF to be decomposed into harmless nitrogen and water. In this case, since it is necessary to supply an appropriate amount of reducing agent to the exhaust passage, NO _X sensor for detecting the amount of NO _X contained in the exhaust flowing through the exhaust passage is built, detection information from the NO _X sensor Based on the above, the supply amount of the reducing agent is controlled. Further, in this SCRF, particulate matter containing carbonaceous or hydrocarbon components in the exhaust, i.e. PM for (P articulate M atter) also captured simultaneously regularly by burning captured PM with CO It is necessary to regenerate SCRF by decomposing it into water and water.

In the conventional exhaust gas purifying apparatus described above, the NO _X sensor SCRF types other than those than catalytic converter disposed downstream of the exhaust passage, the NO _X sensor as described in Patent Document 1 of the exhaust passage than SCRF The one arranged upstream is also known.

JP 2007-170383 A

As disclosed in Patent Document 1, in the exhaust purification apparatus arranged on the upstream side of the exhaust passage than SCRF the NO _X sensor, NO _X sensor exposed to exhaust gas containing a large amount of HC by driving condition of the vehicle May end up. For example, when the regeneration process of SCRF is started at the time of cold start of the internal combustion engine in which the NO _X sensor is not activated, a large amount of HC component flows from the internal combustion engine to the exhaust passage where the NO _X sensor is arranged. Similarly, when the operation of the internal combustion engine is stopped during the addition of fuel for regenerating the SCRF, a large amount of HC component remains in the exhaust passage.

When the NO _X sensor is activated in such a situation, there is a possibility that an abnormal output of the NO _X sensor may occur due to a large amount of HC components present around the NO _X sensor, or this may cause abnormal heat generation. As a result, in addition to the malfunction of the NO _X sensor, in the worst case which leads to failure of the NO _X sensor.

An object of the present invention is to provide an exhaust purification device arranged NO _X sensor upstream of the exhaust passage than SCRF, always control how high NO _X concentration reliable and can be detected.

The present invention, exhaust gas flowing through the SCRF for purifying NO _X contained in the exhaust from the internal combustion engine is incorporated in the middle of the exhaust passage, the exhaust passage from the upstream side of the SCRF to play this SCRF in the fuel addition means for adding fuel, control of the exhaust gas purifier and a NO _X sensor for detecting the concentration of NO _X contained in the exhaust flowing through the exhaust passage between the this fuel addition means SCRF A method for determining whether or not it is necessary to add fuel from the fuel addition means; and if it is determined that there is a need to add fuel from the fuel addition means, add fuel from the fuel addition means a step of, determining whether nO _X sensor is active, if the nO _X sensor is determined not in the activated state, the fuel added hand Even if it is determined that there is a need to add fuel, until the NO _X sensor is determined to be in the active state, and stopping the step of adding fuel from the fuel adding means comprises a It is characterized by that.

In the present invention, for example, even if there is a need for adding fuel from the fuel adding means immediately after the start of the internal combustion engine, NO _X sensor addition of fuel is not performed until the active state. The need to add fuel from the fuel addition means generally corresponds to the SCRF regeneration process. In addition, when an independent fuel addition valve is used as the fuel addition means, periodic fuel addition processing for maintaining the function of the fuel addition valve is also included.

  In the control method of the exhaust emission control device according to the present invention, when the ignition key switch is turned off during the step of adding fuel from the fuel addition means, the step of adding fuel from the fuel addition means is stopped, and thereafter The method may further comprise stopping the operation of the internal combustion engine.

Further, when the ignition key switch is turned off during the step of adding fuel from the fuel addition means, the method further includes the step of stopping energization of the NO _X sensor after maintaining the energization of the NO _X sensor for a certain time. be able to.

In addition to the independent fuel addition valve, the fuel addition means may include a fuel injection valve for injecting fuel into the combustion chamber during the exhaust stroke of the internal combustion engine. Can exhaust purification device further comprises an oxidation catalytic converter incorporated in the middle of the exhaust passage between the fuel addition means and the NO _X sensor. Further, the exhaust purification device can include a reducing agent addition valve for adding a reducing agent to the exhaust passage between the NO _X sensor and the selective reduction catalyst filter.

According to the control method of the exhaust gas purifying apparatus of the present invention, even if the need for adding fuel from the fuel addition means, until NO _X sensor is activated by stopping the fuel addition, the surrounding of the NO _X sensor Can be maintained in a state substantially free of HC components. As a result, it is possible to have high reliability to the NO _X concentration detected after activation of the NO _X sensor, it is possible to prevent NO _X sensor failure or the like in advance.

1 is a system conceptual diagram of an embodiment in which the present invention is applied to a vehicle equipped with a compression ignition type multi-cylinder internal combustion engine. It is a control block diagram of the principal part in embodiment shown in FIG. In the embodiment shown in FIG. 1, it is the time chart which represents typically the change of the principal part after an ignition key switch switches on. In the embodiment shown in FIG. 1, it is a time chart which shows typically the change of the principal part after an ignition key switch switches to OFF. In the embodiment shown in FIG. 1, it is a time chart which shows typically the change of the principal part after an ignition key switch switches to OFF. 2 is a flowchart showing a control procedure after an ignition key switch is turned on in the embodiment shown in FIG. 1. 2 is a flowchart showing a control procedure after an ignition key switch is turned off in the embodiment shown in FIG. 1.

  An embodiment in which the present invention is applied to a vehicle equipped with a compression ignition type multi-cylinder internal combustion engine will be described in detail with reference to FIGS. However, the present invention is not limited to such an embodiment, and the configuration can be freely changed according to required characteristics. For example, the present invention is also effective for a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (liquefied natural gas) or the like is used as fuel and is ignited by a spark plug.

  A main part of the engine system in the present embodiment is schematically shown in FIG. 1, and a control block of the main part is schematically shown in FIG. In FIG. 1, in addition to a valve mechanism and a silencer for intake and exhaust of the engine 10, a general exhaust turbo supercharger, an EGR device, and the like are omitted as auxiliary equipment of the engine 10. It should be noted that some of the various sensors required for smooth operation of the engine 10 are omitted for convenience.

  The engine 10 according to the present embodiment is a self-ignition system that spontaneously ignites, that is, compression, by directly injecting fuel such as light oil or biofuel or a mixed fuel thereof into the combustion chamber 10a in a compressed state from the fuel injection valve 11. This is an ignition type multi-cylinder internal combustion engine. However, a single cylinder internal combustion engine may be used due to the characteristics of the present invention.

The cylinder head 12 formed with the intake port 12a and the exhaust port 12b facing the combustion chamber 10a has a valve operating mechanism (not shown) including an intake valve 13a for opening and closing the intake port 12a and an exhaust valve 13b for opening and closing the exhaust port 12b. It has been incorporated. The previous fuel injection valve 11 facing the center of the upper end of the combustion chamber 10a is also assembled to the cylinder head 12 so as to be sandwiched between the intake valve 13a and the exhaust valve 13b. The amount and injection timing of fuel supplied to the combustion chamber 10a from the fuel injection valve 11, the ECU (E lectronic C ontrol U nit ) 15 based on operating conditions of the vehicle including the depression amount of the accelerator pedal 14 by the driver Be controlled. The amount of depression of the accelerator pedal 14 is detected by the accelerator opening sensor 16, and the detection information is output to the ECU 15.

  The ECU 15 is a well-known one-chip microprocessor, and includes a CPU, ROM, RAM, non-volatile memory, input / output interface and the like interconnected by a data bus (not shown). The ECU 15 in this embodiment is based on information from the accelerator opening sensor 16 and various sensors described later, an operation state determination unit 15a that determines the operation state of the vehicle, a fuel injection setting unit 15b, and a fuel injection valve drive. Part 15c. The fuel injection setting unit 15b sets the fuel injection amount and the injection timing from the fuel injection valve 11 based on the determination result in the operation state determination unit 15a. The fuel injection valve drive unit 15c controls the operation of the fuel injection valve 11 so that the amount of fuel set by the fuel injection setting unit 15b is injected from the fuel injection valve 11 at the set time.

  The intake pipe 17 connected to the intake port 12a of the cylinder head 12 defines an intake passage 17a together with the intake port 12a. An air flow meter 18 is attached on the upstream side of the intake pipe 17, and information relating to the detected intake flow rate is output to the ECU 15. The ECU 15 corrects the fuel injection amount from the fuel injection valve 11 based on detection information from the air flow meter 18 and the like. The intake pipe 17 on the downstream side of the air flow meter 18 is provided with a throttle valve 19 for adjusting the opening degree of the intake passage 17a and a throttle actuator 20 for driving the throttle valve 19.

  The previous ECU 15 further includes a throttle opening setting unit 15d and an actuator driving unit 15e. The throttle opening setting unit 15d sets the opening of the throttle valve 19 based on the determination result of the previous driving state determination unit 15a in addition to the depression amount of the accelerator pedal 14. The actuator driving unit 15e controls the operation of the throttle actuator 20 so that the throttle valve 19 has the opening set by the throttle opening setting unit 15d.

  A crank angle sensor 22 that detects the rotational phase of the crankshaft 21c to which the piston 21a is coupled via the connecting rod 21b, that is, the crank angle, and outputs the detected crank angle to the ECU 15 is attached to the cylinder block 21 in which the piston 21a reciprocates. It has been. Based on the information from the crank angle sensor 22, the driving state determination unit 15a of the ECU 15 grasps the running speed of the vehicle in addition to the rotation phase of the crankshaft 21c and the engine speed in real time.

The exhaust pipe 23 connected to the cylinder head 12 so as to communicate with the exhaust port 12b defines an exhaust passage 23a together with the exhaust port 12b. An exhaust gas purification device 24 for detoxifying harmful substances generated by combustion of the air-fuel mixture in the combustion chamber 10a is attached to the exhaust pipe 23 upstream of the silencer (not shown) attached to the downstream end side. ing. Exhaust purification apparatus 24 of this embodiment includes a SCRF24a, a reducing agent addition valve 24b, diesel oxidation catalytic converter, i.e. a DOC (D iesel O xidation C atalyst ) 24c, and a fuel addition valve 24d. These are arranged in order from the downstream side of the exhaust passage 23a. However, a catalytic converter other than the DOC 24c and the SCRF 24a can be further incorporated into the exhaust purification device 24 as an exhaust purification element.

SCRF24a has a function to detoxify by reducing NO _X in the exhaust gas while capturing the PM in the exhaust as well known. The reducing agent addition valve 24b continuously supplies urea-containing water for reducing NO _X toward the SCRF 24a. The DOC 24c generates combustion gas and maintains the SCRF 24a disposed on the downstream side at an appropriate reaction temperature, and periodically burns the PM trapped and deposited by the SCRF 24a, thereby performing the regeneration process of the SCRF 24a. belongs to.

  The fuel addition valve 24d is for supplying fuel toward the DOC 24c and for combusting the fuel using the catalytic reaction in the DOC 24c. In the present invention for adding fuel to the exhaust gas flowing through the exhaust passage 23a. It functions as a fuel addition means. As the fuel addition means of the present invention, the fuel injection valve 11 of the engine 10 can be used. In this case, it is necessary to inject fuel from the fuel injection valve 11 into the combustion chamber 10a during the exhaust stroke of the engine 10. is there. When the fuel injection valve 11 of the engine 10 is used as the fuel addition means of the present invention, the fuel addition valve 24d can be omitted. This fuel addition valve 24d has the same basic structure as the normal fuel injection valve 11, and controls the energization time to pulse an arbitrary amount of fuel into the exhaust passage 23a at an arbitrary time interval. It can be supplied. The amount of fuel per one time supplied from the fuel addition valve 24d to the exhaust passage 23a is based on the operating state of the vehicle including the intake air amount and air-fuel ratio detected by the air flow meter 18, and the fuel addition setting unit of the ECU 15 It is set by 15f. The fuel addition valve drive unit 15g of the ECU 15 controls the operation of the fuel addition valve 24d so that the amount of fuel set by the fuel addition setting unit 15f is injected from the fuel addition valve 24d at a set cycle.

  The operating state determination unit 15a of the ECU 15 also determines whether fuel needs to be added from the fuel addition valve 24d to the exhaust passage 23a. More specifically, in the following three cases, the operation state determination unit 15a of the ECU 15 determines that it is necessary to add fuel from the fuel addition valve 24d to the exhaust passage 23a. That is, the case where the bed temperature of the DOC 24c is maintained within a certain range, the case where the regeneration process of the SCRF 24a is performed, and the case where the fuel addition valve 24d itself is regularly maintained.

The basic configuration of the reducing agent addition valve 24b is the same as that of the normal fuel injection valve 11 in the same manner as the previous fuel addition valve 24d. By controlling the energization time, an arbitrary amount of reducing agent can be added at an arbitrary time interval. Thus, it can be supplied to the exhaust passage 23a in pulses. The amount of reducing agent per one time supplied from the reducing agent addition valve 24b to the exhaust passage 23a is set by the reducing agent addition setting unit 15h of the ECU 15. This is set based on the operation state of the vehicle including the intake air amount and air-fuel ratio detected by the air flow meter 18 in addition to detection information from the NO _X sensor 25 described later. The reducing agent addition valve drive unit 15i of the ECU 15 controls the reducing agent addition valve 24b so that the amount of reducing agent set by the reducing agent addition setting unit 15h is injected from the reducing agent addition valve 24b at a set cycle. Control the operation.

In the exhaust passage 23a between the DOC 24c and the reducing agent addition valve 24b, a NO _X sensor 25 that detects the concentration of NO _{X in} the exhaust flowing through the exhaust passage 23a and outputs this to the ECU 15 is disposed. Reducing agent addition setting unit 15h of the ECU15 can this NO _X based on the concentration of NO _X in the exhaust gas detected by the sensor 25, to more accurately feedback-control the amount of the reducing agent from the reducing agent addition valve 24b .

The NO _X sensor driving unit 15 j of the ECU 15 controls on / off of energization to the NO _X sensor 25 in conjunction with the on / off operation of the ignition key switch 26. However, as shown in FIG. 5, when the ignition key switch 26 is turned off at time t ₄ while fuel is being added from the fuel addition valve 24 d to the exhaust passage 23 a, the time t ₆ after a certain time has elapsed. and so as to stop the power supply to the NO _X sensor 25 at. Thereby, it is possible to prevent the malfunction when the NO _X sensor 25 is reactivated by thermally decomposing the HC component in the exhaust intervening around the detection element of the NO _X sensor 25 in the active state. .

5, the engine speed, the HC concentration around of the NO _X sensor 25, and the temperature of the NO _X sensor 25, and the addition conditions of the fuel, the energization conditions of NO _X sensor 25, the ignition key switch 26 ON / The relationship with an OFF state is shown typically. The ignition key switch 26 is turned off at time t _4, it shows a case where immediately stop the operation of the engine 10 by the broken line stops the fuel addition to the exhaust passage 23a accordingly. In contrast, in the present embodiment it indicates that it is de-energized for NO _X sensor 25 at time t _6, during which it will be understood that the NO _X sensor 25 is maintained in an active state.

NO _X sensor activation determination part 15k of the ECU15 is, NO _X sensor driver information from 15j, i.e. based on the conduction start of the information for the NO _X sensor 25, NO _X sensor 25 is activated, i.e. its lowest activation temperature _{T R} It is determined whether or not the temperature has been increased. This determination operation is performed based on the amount of power supplied to the NO _X sensor 25 and taking into account the exhaust temperature, the exhaust flow velocity, and the like. The determination result by the NO _X sensor activation determination unit 15k is output to the fuel addition valve drive unit 15g. The fuel addition valve drive unit 15g does not operate the fuel addition valve 24d when the NO _X sensor activation determination unit 15k determines that the NO _X sensor 25 is not in the active state. More specifically, even when it is determined that it is necessary to add the fuel at the time t ₂ shown in FIG. 3, the fuel addition valve driving unit 15g is the NO _X sensor 25 is active NO _X until the sensor activation determination unit 15k determines the time t ₃ has not operated the fuel addition valve 24d. Thus, NO _X concentration detected by the NO _X sensor 25 is always after NO _X sensor 25 is activated, it is possible to obtain the detection information of high reliability.

3, an exhaust temperature, a temperature of the NO _X sensor 25, and the addition conditions of the fuel, and the presence or absence of the need for fuel addition, the relationship between the energization conditions of NO _X sensor 25 is schematically shown. At time t ₁ becomes the ignition key switch 26 ON, NO _X energization to the sensor 25 is started, if the need for added fuel occurs at time t _2, the time t exhaust gas temperature is raised to T _EL in conventional Fuel addition is started at ₃ '. In contrast, in the present embodiment, it shows that the NO _X sensor 25 starts adding fuel at the lowest activation temperature T time reached _R t _3.

  The operation state determination unit 15a of the previous ECU 15 calculates the PM accumulation amount captured by the SCRF 24a based on the continuous operation state of the engine 10, and the ECU 15 performs the SCRF 24a when the PM accumulation amount reaches a predetermined value. The playback process is started. Specifically, the amount of fuel added per unit time from the fuel addition valve 24d according to the exhaust flow rate passing through the SCRF 24a is such that high-temperature exhaust gas is supplied from the DOC 24c to the SCRF 24a according to the PM accumulation amount. It is set by the fuel addition setting unit 15f. The exhaust flow rate described above can be substituted with the intake flow rate from the air flow meter 18. It is also possible to arrange pressure sensors in the exhaust passages 23a upstream and downstream of the SCRF 24a, and to control the regeneration process of the SCRF 24a based on the differential pressure detected by these pressure sensors.

Next, the control procedure of the exhaust emission control device 24 in this embodiment will be described with reference to FIGS. 6 and 7. When the ignition key switch 26 is turned on in step S11, the engine 10 is started. A series of processing is started. That is, to start the energization of the NO _X sensor 25 at step S12, it is determined whether the necessity of added fuel in S13 step, the step in S13 until it is determined that where there is a need for added fuel Is repeated. If it is determined in step S13 that fuel needs to be added, the process proceeds to step S14. Then, NO temperature TS of _X sensor 25 determines whether the minimum activation temperature _T or is _R or, where NO _X temperature TS of the sensor 25 is repeated steps in S14 until the minimum activation temperature _{T R} or It is. Temperature TS of the NO _X sensor 25 at this step S14 is minimum activation temperature _{T R} above, that is, when the NO _X sensor 25 is determined to be activated, the process proceeds to step S15. Then, addition of fuel from the fuel addition valve 24d to the exhaust passage 23a is started, and a fuel addition flag is set. Thus, by initiating the addition of the fuel after activating the NO _X sensor 25, it is possible to ensure the reliability of the NO _X concentration detected by the NO _X sensor 25.

  Following the step of S15, it is determined whether or not the need for fuel addition has been eliminated in the step of S16. Here, the step of S16 is repeated until it is determined that there is no need for fuel addition. If it is determined in step S16 that there is no need for fuel addition, that is, there is no need for regeneration processing of the SCRF 24a, periodic operation of the fuel addition valve 24d, and bed temperature control of the DOC 24c, SCRF 24a, S17 Move to the step. Then, after stopping the addition of fuel from the fuel addition valve 24d and resetting the fuel addition flag, the steps after S13 are repeated until the ignition key switch 26 is turned off.

  On the other hand, after the ON operation of the ignition key switch 26 in step S11, the process shown in FIG. 7 is performed in parallel with the process of FIG. That is, it is determined in step S21 whether or not the ignition key switch 26 has been turned off, and step S21 is repeated until the ignition key switch 26 is turned off. If the ignition key switch 26 is turned off in step S21, that is, if it is determined that the driver wants to stop the engine 10, the process proceeds to step S22 and the fuel addition flag is set. It is determined whether or not. Here, if it is determined that the fuel addition flag is not set, that is, it is determined that fuel is not being added from the fuel addition valve 24d to the exhaust passage 23a, the process is terminated as it is, and a normal engine stop process is executed. .

If it is determined in step S22 that the fuel addition flag has been set, that is, fuel is being added from the fuel addition valve 24d to the exhaust passage 23a, the process proceeds to step S23. Then, immediately after stopping the fuel addition process from the fuel addition valve 24d and resetting the fuel addition flag, the timer is counted up in step S24, and the process proceeds to step S25. Count value C _n of the timer at this step S25 is determines whether a threshold C _E above a preset, the threshold C _E is the period from time t ₄ in FIG. 5 to time t ₆ Correspond. At first, since the count value C _n of the timer is smaller than the threshold value _CE , the process proceeds to step S26. Then, the count value C _n of the timer is equal to or threshold C _F over a preset, the threshold C _F corresponds to the time from the time t ₄ in FIG. 4 to time t _5. In any case, initially the count value C _n of the timer is smaller than the threshold value C _F, returns to step S24,, S25 described above by performing a count-up timer, S26 steps are repeated. Thus, the fuel injected into the exhaust passage 23a of the operating state from to continue the fuel addition valve 24d of the engine 10 than the NO _X sensor 25 caused to flow down on the downstream side, the atmosphere of the exhaust passage 23a of the periphery of the NO _X sensor 25 Can be reduced to a state with less HC component.

4, the engine speed, the HC concentration around of the NO _X sensor 25, and the temperature of the NO _X sensor 25, and the addition conditions of the fuel, the energization conditions of NO _X sensor 25, the ignition key switch 26 ON / The relationship with an OFF state is shown typically. The ignition key switch 26 is turned off at time t _4, which respectively stops fuel addition to the conduction and the exhaust passage 23a for NO _X sensor 25 along with the, shows the case of immediately stopping the operation of the engine 10 by a broken line ing. In contrast, in the present embodiment since the stopping of the engine at time t _5, it will appreciate that HC concentration is reduced sufficiently.

In this way, if the count value C _n steps at the timer of S26 is determined to be the threshold value C _F above, it determines whether or not the engine flag shifts is set in step S27. Initially, since the engine flag is not set, the routine proceeds to step S28, where the fuel injection from the fuel injection valve 11 is stopped to stop the engine 10, the engine flag is set, and then the routine returns to step S24. Therefore, when the timer count value C _n is between the threshold value _CF and the threshold value _CE , the steps S24, S26, and S27 are repeated. As a result, the continuation of the energization of NO _X sensor 25, HC components interposed around the sensing element of the NO _X sensor 25 is thermally decomposed into carbon dioxide and water (refer to FIG. 5).

In this way, if it is determined in step S25 that the timer count value C _n is _equal to or greater than the threshold value _CE , that is, no HC component remains around the NO _X sensor 25, the process proceeds to step S29. . Then, energization to the NO _X sensor 25 is stopped and the engine flag is reset, and the count value C _{n of the} timer is reset to 0 to finish a series of control. Therefore, the atmosphere around the NO _X sensor 25 can be maintained in a state where there is almost no HC component that adversely affects the detection, and the reliability of the value when the NO _X concentration is detected again after being activated. Can be kept high.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

10 engine 15 ECU
15a Operation state determination unit 15f Fuel addition setting unit 15g Fuel addition valve drive unit 15k NO _X sensor activation determination unit 23a Exhaust passage 24 Exhaust purification device 24a SCRF
24d Fuel addition valve 25 NO _X sensor

Claims (1)

A selective catalytic reduction filter that is incorporated in the middle of the exhaust passage to purify nitrogen oxides contained in the exhaust from the internal combustion engine, and from the upstream side of the selective catalytic reduction filter to regenerate the selective catalytic reduction filter Fuel addition means for adding fuel to the exhaust flowing through the exhaust passage, and NO for detecting the concentration of nitrogen oxides contained in the exhaust flowing through the exhaust passage between the fuel addition means and the selective catalytic reduction filter A control method of an exhaust emission control device having an _X sensor,
Determining the necessity of adding fuel from the fuel addition means;
If it is determined that there is a need to add fuel from the fuel addition means, adding fuel from the fuel addition means;
Determining whether the NO _X sensor is in an active state;
If NO _X sensor is determined not in the activated state, even if it is determined that there is a need to add fuel from the fuel addition means, to said NO _X sensor is determined to be in the active state, And a step of stopping the step of adding fuel from the fuel addition means.

Images