JP2013108419A - Failure diagnosis method for nox sensor, failure diagnosis system for nox sensor, and internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a failure diagnosis method for a NOx sensor and a failure diagnosis system for the NOx sensor capable of continuously performing failure diagnosis of the NOx sensor, by comparing a calculation value of a NOx concentration with a detection value of the NOx sensor, and to provide an internal combustion engine.SOLUTION: A NOx concentration NOx_cyl is calculated on the basis of a detection value m_air of an intake amount sensor 31 disposed at an intake passage 12 of an internal combustion engine 10, a detection value Ti of a temperature sensor 32 disposed at an intake manifold 11a, a detection value Pi of a pressure sensor 33 disposed at the intake manifold 11a, and a fuel injection amount q. The calculated NOx concentration NOx_cyl is compared with a detection value NOx_m of the NOx sensor to perform diagnosis whether the NOx sensor 34 disposed at an exhaust passage 18 is abnormal.

Description

  The present invention relates to an NOx sensor abnormality diagnosis method, a NOx sensor abnormality diagnosis system, and an internal combustion engine that can continuously diagnose abnormality of a NOx sensor without taking a large number of experimental steps.

In vehicles such as trucks and buses, in order to reduce the amount of NOx (nitrogen oxides) discharged from the internal combustion engine mounted on the vehicle, it is reduced to nitrogen (N ₂ ) using an exhaust gas purification treatment device. In the atmosphere. In order to perform this NOx purification efficiently, it is necessary to accurately measure the NOx concentration and the NOx amount in the exhaust gas. For this purpose, a NOx sensor is used.

  Since a reducing agent such as urea necessary for reducing NOx in the exhaust gas is supplied based on the detected value of the NOx sensor, the NOx sensor is in a normal state or in an abnormal state such as a failure. It is important whether there is. If the NOx sensor is abnormal, the amount of reducing agent supplied cannot be made appropriate, and if the reducing agent is insufficient, the reduction and purification of NOx in the exhaust gas becomes insufficient. If NOx above the standard is released into the atmosphere and the reducing agent is excessive, the reducing agent that was not consumed by the reduction of NOx is released into the atmosphere and the reducing agent is consumed wastefully. Become.

  For this reason, abnormality diagnosis of the NOx sensor is important. For example, the NOx sensor is provided with an exhaust NOx flow rate calculation storage means and a detected NOx concentration storage means, and is detected by the NOx sensor with a reference pattern as a reference for the temporal change of the exhaust NOx flow rate. A follow-up pattern is defined as a reference for the temporal change in the detected NOx concentration, and when the internal combustion engine is in the normal operation mode, the detected NOx concentration follows when the exhaust NOx flow changes with a predetermined relationship with respect to the reference pattern. There has been proposed a NOx sensor failure diagnosis device including failure determination means for determining the responsiveness of the NOx sensor by determining whether or not the pattern has changed with a predetermined relationship (for example, Patent Document 1). reference).

  In this NOx sensor diagnosis method, a reference pattern as a reference for the temporal change of the NOx flow rate discharged from the internal combustion engine and a follow-up pattern as a reference for the temporal change of the detected NOx concentration detected by the NOx sensor are set in advance. Although it is necessary, since the flow rate of exhausted NOx varies greatly depending on environmental conditions such as the operating state of the internal combustion engine, it is necessary to set a large number of reference patterns, and there is a problem that it takes a lot of man-hours.

  On the other hand, whether the NOx sensor is responding to the peak appearing in the transition of the NOx amount on the upstream side, the upstream NOx amount calculating unit and the NOx sensor value detecting unit for calculating the NOx amount on the upstream side of the reduction catalyst A rationality determination unit that determines the rationality of the NOx sensor by determining whether or not, and an exhaust gas amount calculation unit that calculates the amount of exhaust gas discharged from the internal combustion engine. When the NOx sensor rationality diagnosis device (see, for example, Patent Document 2) that recognizes the occurrence of a peak in accordance with the amount and determines the rationality of the NOx sensor or the internal combustion engine reaches a preset reference operating condition, A NOx correction system comprising first correction means for correcting the output of the NOx sensor based on the deviation between the output value of the NOx sensor and a reference output value preset in accordance with the reference operating condition (for example, a patent document) 3 reference) has been proposed.

  Further, the NOx concentration in the exhaust gas reaching the NOx sensor is forcibly changed, and the output value output from the NOx sensor at this time deviates from the change that can be taken when the NOx sensor is normal. In addition, a NOx sensor failure diagnosis device (see, for example, Patent Document 4) provided with a failure determination means that determines that the NOx sensor is abnormal or reaches the NOx sensor during an abnormality determination mode in a predetermined operating state of the internal combustion engine. NOx concentration increase / decrease changing means for once increasing and decreasing the NOx concentration in the exhaust gas to be emitted, and when the NOx concentration is increased / decreased, the NOx sensor detects from the output state of the predetermined first output value of the NOx sensor. Based on the elapsed time measuring means for measuring the elapsed time until the predetermined second output value is output, the measured elapsed time and the reference elapsed time, With a determination means for determining normality or abnormality of the support, the exhaust gas purification system has been proposed (e.g., see Patent Document 5).

  However, in the abnormality diagnosis of these NOx sensors, the operation state of the internal combustion engine is performed when the peak of the NOx concentration occurs or in a specific state created by forcibly changing the NOx concentration. There is a problem that diagnosis can be performed only under conditions under conditions, and abnormality diagnosis cannot be performed continuously.

JP 2008-190383 A JP 2010-255781 A JP 2009-127552 A JP 2003-120399 A JP 2009-181550 A

  The present invention has been made in view of the above-described situation, and an object of the present invention is to continuously perform abnormality diagnosis of the NOx sensor by comparing the calculated value of the NOx concentration with the detected value of the NOx sensor. An object of the present invention is to provide a NOx sensor abnormality diagnosis method, a NOx sensor abnormality diagnosis system, and an internal combustion engine.

  The NOx sensor abnormality diagnosis method of the present invention for achieving the above object is a NOx sensor abnormality diagnosis method disposed in an exhaust passage of an internal combustion engine, and is disposed in an intake passage of the internal combustion engine. Detection value (m_air) of the intake air amount sensor, detection value (Ti) of the temperature sensor arranged in the intake manifold, detection value (Pi) of the pressure sensor arranged in the intake manifold, and fuel injection amount (q) The NOx concentration (NOx_cyl) is calculated from the above, and the calculated NOx concentration (NOx_cyl) is compared with the detected value (NOx_m) of the NOx sensor to diagnose whether the NOx sensor is abnormal. It is the method characterized by this.

  According to this method, by determining the NOx concentration in the exhaust gas by calculation, the abnormality diagnosis of the NOx sensor can be performed without taking a lot of experiment man-hours, and the NOx concentration is always calculated. It is not necessary to limit the timing for performing abnormality diagnosis of the NOx sensor when the operating state of the internal combustion engine is in a special condition, and it can be performed continuously.

前記吸気量センサで検出した吸入空気の質量流量（ｍ＿ａｉｒ）と前記燃料噴射量（ｑ）とから、（２）式により、排気空気過剰率（λ）を算出する第２演算ステップと、

前記排気空気過剰率（λ）からＥＧＲガスの時間遅れを考慮して算出したＥＧＲ空気過剰率（λ＿ｅｇｒ）と、大気中の酸素濃度（Ｏ２＿ａｉｒ）と、理論空燃比（Ｌ＿ｓｔ）とから、（３）式によりＥＧＲガス中の酸素濃度（Ｏ２＿ｅｇｒ）を算出する第３演算ステップと、

（４）式より、シリンダ内の酸素濃度（Ｏ２＿ｃｙｌ）を算出する第４演算ステップと、

定常時のシリンダ内の酸素濃度（Ｏ２＿ｒｅｆ）と定常時のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｒｅｆ）と、指数ｉとが予め設定されている（５）式の、シリンダ内の酸素濃度（Ｏ２＿ｃｙｌ）とシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）の関係から、現在のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）を算出する第５演算ステップと、

前記（５）式から算出された現在のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）と前記ＮＯｘセンサの検出値（ＮＯｘ＿ｍ）とを比較して、前記ＮＯｘセンサが異常であるか否かの診断を行う第５演算ステップとを備えて構成すると、排気ガス中のＮＯｘ濃度を容易に計算できる。 Further, in the abnormality diagnosis method for the NOx sensor, the calculation step for calculating the NOx concentration (NOx_cyl) includes a mass flow rate of the intake air (new air flow rate: m_air) detected by the intake air amount sensor and the temperature sensor. The mass flow rate (m_egr) of the EGR gas is calculated by the equation (1) from the mass flow rate (m_cyl) in the cylinder calculated from the detection value (Ti) detected by the pressure sensor and the detection value (Pi) detected by the pressure sensor. A first computing step to:

A second calculation step of calculating an exhaust air excess ratio (λ) by the equation (2) from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor and the fuel injection amount (q);

From the EGR air excess rate (λ_egr) calculated from the exhaust air excess rate (λ) in consideration of the time delay of EGR gas, the oxygen concentration (O2_air) in the atmosphere, and the theoretical air-fuel ratio (L_st), (3 ) Equation to calculate the oxygen concentration (O2_egr) in the EGR gas,

A fourth calculation step for calculating the oxygen concentration (O2_cyl) in the cylinder from the equation (4);

The oxygen concentration (O2_ref) in the cylinder in the formula (5) in which the oxygen concentration (O2_ref) in the cylinder at a constant time, the NOx concentration discharged from the cylinder at the steady state (NOx_ref), and the index i are set in advance. A NOx concentration (NOx_cyl) discharged from the current cylinder from the relationship between the NOx concentration discharged from the cylinder (NOx_cyl),

The NOx concentration (NOx_cyl) discharged from the current cylinder calculated from the equation (5) is compared with the detected value (NOx_m) of the NOx sensor to diagnose whether the NOx sensor is abnormal. When configured to include the fifth calculation step to be performed, the NOx concentration in the exhaust gas can be easily calculated.

  A NOx sensor abnormality diagnosis system for achieving the above object is a NOx sensor abnormality diagnosis system comprising a control device for performing abnormality diagnosis of a NOx sensor disposed in an exhaust passage of an internal combustion engine, The control device detects a detected value (m_air) of an intake air amount sensor disposed in the intake passage of the internal combustion engine, a detected value (Ti) of a temperature sensor disposed in the intake manifold, and a detection of a pressure sensor disposed in the intake manifold. The NOx concentration calculating means for calculating the NOx concentration (NOx_cyl) from the value (Pi) and the fuel injection amount (q), and the calculated NOx concentration (NOx_cyl) and the detected value (NOx_m) of the NOx sensor are compared. And it comprises a comparative diagnosis means for diagnosing whether or not the NOx sensor is abnormal.

  According to this configuration, by calculating the NOx concentration in the exhaust gas by calculation, the abnormality diagnosis of the NOx sensor can be performed without taking a lot of experiment man-hours, and the NOx concentration is always calculated. It is not necessary to limit the timing for performing abnormality diagnosis of the NOx sensor when the operating state of the internal combustion engine is in a special condition, and it can be performed continuously.

前記吸気量センサで検出した吸入空気の質量流量（ｍ＿ａｉｒ）と前記燃料噴射量（ｑ）とから、（２）式により、排気空気過剰率（λ）を算出する第２演算手段と、

前記排気空気過剰率（λ）からＥＧＲガスの時間遅れを考慮して算出したＥＧＲ空気過剰率（λ＿ｅｇｒ）と、大気中の酸素濃度（Ｏ２＿ａｉｒ）と、理論空燃比（Ｌ＿ｓｔ）とから、（３）式によりＥＧＲガス中の酸素濃度（Ｏ２＿ｅｇｒ）を算出する第３演算手段と、

（４）式より、シリンダ内の酸素濃度（Ｏ２＿ｃｙｌ）を算出する第４演算手段と、

定常時のシリンダ内の酸素濃度（Ｏ２＿ｒｅｆ）と定常時のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｒｅｆ）と、指数ｉとが予め設定されている（５）式のシリンダ内の酸素濃度（Ｏ２＿ｃｙｌ）とシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）の関係から、現在のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）を算出する第５演算手段とを備え、

前記比較診断手段が、前記算出された現在のシリンダから排出されるＮＯｘ濃度（ＮＯｘ＿ｃｙｌ）と前記ＮＯｘセンサの検出値（ＮＯｘ＿ｍ）とを比較して、前記ＮＯｘセンサが異常であるか否かの診断を行う第６演算手段を備えて構成されると、排気ガス中のＮＯｘ濃度を容易に計算できる。 In the above NOx sensor abnormality diagnosis system, the NOx concentration calculating means includes a mass flow rate of intake air (new air flow rate: m_air) detected by the intake air amount sensor, a detection value (Ti) detected by the temperature sensor, and the A first calculating means for calculating a mass flow rate (m_egr) of EGR gas from the mass flow rate (m_cyl) in the cylinder calculated from the detection value (Pi) detected by the pressure sensor;

A second calculating means for calculating an exhaust air excess ratio (λ) from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor and the fuel injection amount (q) by the equation (2);

From the EGR air excess rate (λ_egr) calculated from the exhaust air excess rate (λ) in consideration of the time delay of EGR gas, the oxygen concentration (O2_air) in the atmosphere, and the theoretical air-fuel ratio (L_st), (3 ) The third calculating means for calculating the oxygen concentration (O2_egr) in the EGR gas by the equation;

A fourth calculation means for calculating the oxygen concentration (O2_cyl) in the cylinder from the equation (4);

The oxygen concentration (O2_ref) in the cylinder at the constant time, the NOx concentration (NOx_ref) discharged from the cylinder at the steady state, and the index i are set in advance. Fifth calculating means for calculating the NOx concentration (NOx_cyl) discharged from the current cylinder from the relationship of the NOx concentration (NOx_cyl) discharged from the cylinder;

The comparison diagnosis means compares the calculated NOx concentration (NOx_cyl) discharged from the current cylinder with the detected value (NOx_m) of the NOx sensor to diagnose whether the NOx sensor is abnormal. If it comprises the 6th calculating means which performs this, the NOx density | concentration in exhaust gas can be calculated easily.

  An internal combustion engine for achieving the above object includes the above NOx sensor abnormality diagnosis system, and can achieve the same effects as the above NOx sensor abnormality diagnosis system.

  According to the NOx sensor abnormality diagnosis method, the NOx sensor abnormality diagnosis system, and the internal combustion engine according to the present invention, the NOx concentration in the exhaust gas is obtained by calculation, and the calculated NOx concentration and the NOx detected by the NOx sensor are calculated. By comparing the concentration, the abnormality diagnosis of the NOx sensor can be performed without taking a lot of experiment man-hours. In addition, since the operating state of the internal combustion engine is not in a special condition and the value of the NOx concentration can always be calculated and compared, the abnormality diagnosis of the NOx sensor can be performed continuously.

It is a figure which shows the structure of the abnormality diagnosis system of the NOx sensor of embodiment of this invention, and an internal combustion engine. It is a figure which shows the structure of the control apparatus of the abnormality diagnosis system of the NOx sensor of embodiment of this invention.

  Hereinafter, an NOx sensor abnormality diagnosis method, a NOx sensor abnormality diagnosis system, and an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the internal combustion engine 10 includes an engine body 11, an intake passage 12 connected to the intake manifold 11a, and an exhaust passage 18 connected to the exhaust manifold 11b.

  The intake passage 12 is provided with an air cleaner 13, a compressor 14 a of a turbocharger (turbo turbocharger) 14, an intercooler 15, and an intake throttle (intake valve) 16 in order from the upstream side. The exhaust passage 18 is provided with a turbine 14b of the turbocharger 14 and an exhaust gas purification device 19.

  In the configuration of FIG. 1, the exhaust gas purification device 19 includes an upstream DPF (diesel particulate filter) 19a and a downstream SCR catalyst (selective reduction catalyst) 19b. On the upstream side of the SCR catalyst 19b, a reducing agent injection device (not shown) that sprays an ammonia-based solution (a solution that generates ammonia or ammonia water) such as urea water serving as a NOx reducing agent into the exhaust passage 18. Is provided.

  Further, for EGR (exhaust gas recirculation), an EGR passage 20 that connects the exhaust passage 18 and the intake passage 12 is provided, and an EGR cooler 21 and an EGR valve 22 are provided in the EGR passage 20. . Further, in order to prevent overcooling of the EGR gas Ge by the EGR cooler 21, an exhaust return passage 23 provided with a flow rate adjusting valve 24 is provided connecting the outlet of the EGR cooler 21 and the exhaust passage 18.

  The air A is dust-removed by the air cleaner 13 in the intake passage 12, is supercharged by the compressor 14 a, rises in pressure and temperature, is cooled by the intake cooler 15, and then is flowed by the intake throttle 16. And is mixed with EGR gas Ge as required and enters each cylinder (cylinder) 17 of the engine body 11 from the intake manifold 11a. The EGR gas Ge is branched from the exhaust passage 18 to the EGR passage 20 and the exhaust return passage 23, and is appropriately cooled by the EGR cooler 21, and the flow rate is adjusted by the EGR valve 22 and the flow rate adjusting valve 24, and the intake passage. 12 is supplied.

  In the cylinder 17, the fuel injected from a fuel injection valve (not shown) and air A are mixed and burned to generate exhaust gas G. The generated exhaust gas G is discharged from the exhaust manifold 11 b to the exhaust passage 18, and after driving the turbine 14 a, PM (particulate matter) and the like are removed by the DPF 19 a, and then the SCR is used by the reducing agent supplied to the exhaust passage 18. NOx is reduced to nitrogen by the catalyst 19b, and then released into the atmosphere through a silencer (not shown) or the like. A part of the exhaust gas G is branched into the EGR passage 20 and recirculated as the EGR gas Ge.

  In order to perform the operation control of the internal combustion engine 10, the regeneration control of the DPF 19a, the reducing agent supply control for NOx purification in the SCR catalyst 19b, etc., in the intake system, the intake air is interposed between the air cleaner 13 and the compressor 14a. An airflow sensor (intake air amount sensor) 31 for measuring the amount m_air includes a temperature sensor (intake manifold temperature sensor) 32 for measuring the intake air temperature Ti in the intake manifold 11a and a pressure sensor (for measuring the intake air pressure Pi). An intake pressure sensor (boost pressure sensor) 33 is provided. In the exhaust system, a NOx sensor 34 that measures the NOx concentration NOx_m is disposed between the DPF 19a and the SCR catalyst 19b.

  It is called an ECU (engine control unit) that inputs the detection values of these sensors 31 to 34 and performs operation control of the internal combustion engine 10, regeneration control of the DPF 19a, reductant supply control for NOx purification in the SCR catalyst 19b, and the like. A control device (ECU) 30 is provided.

  The internal combustion engine 10 is provided with a NOx sensor abnormality diagnosis system for abnormality diagnosis of the NOx sensor 34 disposed in the exhaust passage 18 of the internal combustion engine 10, and a control device 40 of the NOx sensor abnormality diagnosis system is provided. A control unit (ECU) 30 is built in and configured.

  The control device 40 calculates the NOx concentration NOx_cyl from the detection value m_air of the intake air amount sensor 31, the detection value (intake air temperature) Ti of the temperature sensor 32, the detection value (intake air pressure) Pi of the pressure sensor 33, and the fuel injection amount q. A NOx concentration calculating means 41 for calculating, and a comparison diagnosis means 42 for comparing the calculated NOx concentration NOx_cyl and the detected value NOx_m of the NOx sensor 34 to diagnose whether or not the NOx sensor 34 is abnormal are provided. Configured. The fuel injection amount q can be easily set to the value of the commanded fuel injection amount in the control unit (ECU) 30, but when the actual fuel injection amount is measured, the value of the measured actual fuel injection amount It is good.

As shown in FIG. 2, the NOx concentration calculating means 41 includes first to fifth calculating means 41a to 41e, and the intake air detected by the intake air amount sensor 31 by the first calculating means 41a in the first calculating step. The mass flow rate m_egr of the EGR gas Ge is calculated from the mass flow rate (new air flow rate) m_air of A and the mass flow rate m_cyl in the cylinder 17 by the equation (1). That is, “(mass flow rate of EGR gas: m_egr) = (mass flow rate of cylinder m_cyl) − (mass flow rate of intake air: m_air)”. The mass flow rate m_cyl in the cylinder is calculated from the temperature Ti detected by the temperature sensor 32 and the pressure Pi detected by the pressure sensor 33.

  Here, the measured value detected by the intake air amount sensor 31 is used for the mass flow rate (new air flow rate) m_air of the intake air A, and the mass flow rate m_cyl in the cylinder 17 is set such that V is the cylinder volume and R is the gas constant. , Η is volume efficiency, a calculated value calculated by “m_cyl = [(Pi × V) / (R × Ti)] × η” is used.

Further, in the second calculation step, the exhaust air excess ratio λ is calculated by the second calculation means 41b from the intake air mass flow rate m_air detected by the intake air amount sensor 31 and the fuel injection amount q by the equation (2). . The theoretical air-fuel ratio L_st varies slightly depending on the fuel, but is 14.6 in the case of light oil used in a diesel engine, and 14.5 to 14 in the case of gasoline used in a gasoline engine. 7

Next, in the third calculation step, the third calculation means 41c calculates the oxygen concentration O2_egr of the EGR gas G_egr. The oxygen concentration O2_egr in the EGR gas Ge is calculated from the oxygen concentration O2_air in the atmosphere, the excess EGR air ratio λ_egr, and the theoretical air-fuel ratio L_st by the equation (3). As the EGR excess air ratio λ_egr, a value taking into account the time delay of the EGR gas Ge from the exhaust air excess ratio λ is used.

In the fourth calculation step, the fourth calculation means 41d calculates the oxygen concentration O2_cyl in the cylinder 17 from the equation (4).

  In the fifth calculation step, the fifth calculation means 41e converts the oxygen concentration O2_cyl in the cylinder 17 to calculate the NOx concentration NOx_cyl in the cylinder 17. Here, the oxygen concentration O2_ref in the cylinder 17 at the normal time, the NOx concentration NOx_ref discharged from the cylinder 17 at the normal time, and the index i are set in advance in the cylinder 17 of the equations (5) and (6). The NOx concentration NOx_cyl discharged from the current cylinder 17 is calculated from the relationship between the oxygen concentration O2_cyl of NO2 and the NOx concentration NOx_cyl discharged from the cylinder 17.

The oxygen concentration O2_ref, the NOx concentration NOx_ref, and the index i are previously determined and set in advance through steady-state engine experiments.

  Then, the comparison diagnosis means 42 compares the calculated NOx concentration NOx_cyl discharged from the current cylinder 17 with the detected value NOx_m of the NOx sensor 34 to diagnose whether the NOx sensor 34 is abnormal. A sixth calculating means 42a is provided.

  In the sixth calculation step, the sixth calculation means 42a diagnoses whether or not the NOx sensor 34 is abnormal. In the diagnosis of whether or not the NOx sensor 34 is abnormal, the NOx sensor 34 is normal. If this is the case, the absolute value of the difference between the calculated NOx concentration NOx_cyl and the detected value NOx_m of the NOx sensor 34 should be equal to or less than the determination value NOx_jud set to an appropriate value. Conversely, the NOx sensor 34 is abnormal. In such a state, the absolute value of the difference should exceed the determination value NOx_jud. Accordingly, when the absolute value of the difference exceeds the determination value NOx_jud, it is determined that the NOx sensor 34 is abnormal.

  That is, it is determined that | NOx_cyl-NOx_m | ≦ NOx_jud is normal and | NOx_cyl-NOx_m |> NOx_jud is abnormal. Accordingly, the NOx sensor 34 can be diagnosed for abnormality by comparing the calculated NOx concentration NOx_cyl with the detected value NOx_m of the NOx sensor 34.

  According to the NOx sensor abnormality diagnosis method, the NOx sensor abnormality diagnosis system, and the internal combustion engine 10 described above, the NOx concentration in the exhaust gas G NOx_cyl is obtained by calculation, so that the NOx sensor 34 does not require much experimentation. In addition, since the NOx concentration NOx_cyl is always calculated, it is not necessary to limit the timing for performing the abnormality diagnosis of the NOx sensor 34 when the operating state of the internal combustion engine 10 is in a special condition. Can be done continuously.

  According to the NOx sensor abnormality diagnosis method, the NOx sensor abnormality diagnosis system, and the internal combustion engine of the present invention, the NOx sensor abnormality diagnosis is continuously performed by comparing the calculated value of the NOx concentration with the detected value of the NOx sensor. This can be used for many internal combustion engines that are mounted on vehicles.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Engine main body 11a Intake manifold 12 Intake passage 17 Cylinder
18 Exhaust passage 19 Exhaust gas purification device 19a DPF
19b SCR catalyst (selective reduction catalyst)
20 EGR passage 30 control unit (ECU)
31 Intake air volume sensor (air flow sensor)
32 Temperature sensor (Intake manifold temperature sensor)
33 Pressure sensor (Intake pressure sensor: Boost pressure sensor)
34 NOx sensor 40 control device (control device for abnormality diagnosis system of NOx sensor)
41 NOx concentration calculating means 41a 1st calculating means 41b 2nd calculating means 41c 3rd calculating means 41d 4th calculating means 41e 5th calculating means 42 Comparative diagnostic means 42a 6th calculating means A Air G Exhaust gas Ge EGR gas L_st Theoretical sky Fuel ratio NOx_cyl Calculated value of NOx concentration NOx_jud Determination value NOx_m Measured value of NOx concentration m_air Detected value of intake air sensor m_cyl Mass flow rate m_egr in cylinder Mass flow rate of EGR gas O2_air Oxygen concentration O2_egr EGR air excess pressure P in air Intake air temperature q Fuel injection amount λ Exhaust air excess ratio λ_egr EGR gas excess air ratio

Claims (5)

An abnormality diagnosis method for a NOx sensor disposed in an exhaust passage of an internal combustion engine,
A detection value (m_air) of an intake air amount sensor arranged in the intake passage of the internal combustion engine, a detection value (Ti) of a temperature sensor arranged in the intake manifold, and a detection value (Ti) of a pressure sensor arranged in the intake manifold ( Pi) and the fuel injection amount (q) to calculate the NOx concentration (NOx_cyl),
Comparing the calculated NOx concentration (NOx_cyl) with the detected value (NOx_m) of the NOx sensor, a diagnosis is made as to whether or not the NOx sensor is abnormal. . An arithmetic step for calculating the NOx concentration (NOx_cyl)
Mass flow rate in the cylinder calculated from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor, the detection value (Ti) detected by the temperature sensor, and the detection value (Pi) detected by the pressure sensor ( m_cyl), a first calculation step for calculating the mass flow rate (m_egr) of the EGR gas by the equation (1),

A second calculation step of calculating an exhaust air excess ratio (λ) by the equation (2) from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor and the fuel injection amount (q);

From the EGR air excess rate (λ_egr) calculated from the exhaust air excess rate (λ) in consideration of the time delay of EGR gas, the oxygen concentration (O2_air) in the atmosphere, and the theoretical air-fuel ratio (L_st), (3 ) Equation to calculate the oxygen concentration (O2_egr) in the EGR gas,

A fourth calculation step for calculating the oxygen concentration (O2_cyl) in the cylinder from the equation (4);

The oxygen concentration (O2_ref) in the cylinder in the formula (5) in which the oxygen concentration (O2_ref) in the cylinder at a constant time, the NOx concentration discharged from the cylinder at the steady state (NOx_ref), and the index i are set in advance. A NOx concentration (NOx_cyl) discharged from the current cylinder from the relationship between the NOx concentration discharged from the cylinder (NOx_cyl),

The NOx concentration (NOx_cyl) discharged from the current cylinder calculated from the equation (5) is compared with the detected value (NOx_m) of the NOx sensor to diagnose whether the NOx sensor is abnormal. A NOx sensor abnormality diagnosis method, comprising: a sixth calculation step. A NOx sensor abnormality diagnosis system comprising a control device for performing abnormality diagnosis of a NOx sensor disposed in an exhaust passage of an internal combustion engine,
The control device is
A detection value (m_air) of an intake air amount sensor arranged in the intake passage of the internal combustion engine, a detection value (Ti) of a temperature sensor arranged in the intake manifold, and a detection value (Pi) of a pressure sensor arranged in the intake manifold And NOx concentration calculating means for calculating the NOx concentration (NOx_cyl) from the fuel injection amount (q),
Comparing the calculated NOx concentration (NOx_cyl) with the detected value (NOx_m) of the NOx sensor, a comparison diagnosis means for diagnosing whether or not the NOx sensor is abnormal is provided. NOx sensor abnormality diagnosis system. The NOx concentration calculating means
The mass flow rate (m_cyl) in the cylinder calculated from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor, the detection value (Ti) detected by the temperature sensor, and the detection value (Pi) detected by the pressure sensor. ) From the first calculation means for calculating the mass flow rate (m_egr) of the EGR gas by the equation (1),

A second calculating means for calculating an exhaust air excess ratio (λ) from the mass flow rate (m_air) of the intake air detected by the intake air amount sensor and the fuel injection amount (q) by the equation (2);

From the EGR air excess rate (λ_egr) calculated from the exhaust air excess rate (λ) in consideration of the time delay of EGR gas, the oxygen concentration (O2_air) in the atmosphere, and the theoretical air-fuel ratio (L_st), (3 ) The third calculating means for calculating the oxygen concentration (O2_egr) in the EGR gas by the equation;

A fourth calculation means for calculating the oxygen concentration (O2_cyl) in the cylinder from the equation (4);

The oxygen concentration (O2_ref) in the cylinder at the constant time, the NOx concentration (NOx_ref) discharged from the cylinder at the steady state, and the index i are set in advance. Fifth calculating means for calculating the NOx concentration (NOx_cyl) discharged from the current cylinder from the relationship of the NOx concentration (NOx_cyl) discharged from the cylinder;

The comparison diagnosis means compares the calculated NOx concentration (NOx_cyl) discharged from the current cylinder with the detected value (NOx_m) of the NOx sensor to diagnose whether the NOx sensor is abnormal. An NOx sensor abnormality diagnosis system comprising: sixth arithmetic means for performing   An internal combustion engine comprising the NOx sensor abnormality diagnosis system according to claim 3 or 4.

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