SCR (Selective Catalytic Reduction) system with calibrator and nitrogen-oxygen sensor fault detection, calibration and protection method thereof

Abstract

The invention provides an SCR system with a calibrator and a nitrogen oxygen sensor fault detection, calibration and protection method thereof, the calibrator (285) is arranged in the SCR system and comprises a hollow cavity, the hollow cavity is provided with an air inlet hole and an air inlet and outlet hole, the air inlet hole is used for receiving upstream tail gas of an SCR catalytic device (105) in the SCR system, and the air outlet hole is used for receiving downstream tail gas of the SCR catalytic device (105) in the SCR system; the air inlet and outlet hole is communicated with an air outlet part at the tail end of the SCR catalytic device (105); a nitrogen and oxygen sensor (205) is arranged in the hollow cavity and used for detecting the nitrogen and oxygen content in the hollow cavity; a gas outlet (206) is also formed in the hollow cavity and is used for exhausting tail gas; a gas flow control device is arranged between the gas inlet hole of the calibrator (285) and upstream tail gas of the SCR catalytic device (105) and is used for controlling the upstream tail gas to enter the hollow cavity through the gas inlet hole; the method is used for carrying out fault detection, calibration and protection on the nitrogen-oxygen sensor.

Description

Technical Field

[0001] The invention relates to an SCR system and a nitrogen oxygen sensor fault detection, calibration and protection method thereof, in particular to an SCR system with a calibrator and a nitrogen oxygen sensor fault detection, calibration and protection method thereof. Background Art

[0002] This section merely provides background information related to the present disclosure and is not necessarily prior art.

[0003] Selective catalytic reduction (SCR) technology is an advanced emission control technology widely used to reduce nitrogen oxide (NOx) emissions from diesel engines. In this process, a chemical called a reductant (usually urea solution or ammonia) is introduced into the emission system. Under the action of high temperature and catalyst, the reductant will chemically react with nitrogen oxides and convert them into nitrogen and water vapor, both of which are harmless gases, thereby significantly reducing NOx emissions.

[0004] The key components of SCR technology include a catalytic reactor, an injection system for supplying reductant and a control unit for monitoring emissions and regulating the amount of reductant injected. This technology is highly efficient and can reduce NOx emissions by up to 90%, which is essential for meeting increasingly stringent environmental regulations.

[0005] In diesel engine systems, SCR technology has become one of the standard configurations. It not only helps protect the environment, but also improves engine performance and fuel economy. By using SCR technology, automakers are able to produce cleaner and more efficient vehicles while also meeting stringent global requirements for vehicle emissions. In addition, the SCR system can be used in combination with other emission control technologies such as particulate filters (DPF) and oxidation catalysts (DOC) to further optimize overall emission performance.

[0006] The On-Board Diagnostics (OBD) system is an integral part of modern cars. It can monitor and diagnose the performance of the vehicle's engine and other important systems. The main function of the OBD system is to continuously detect the operating status of the vehicle's emission control system, ensure that all environmental protection related components are working properly, detect faults in a timely manner, and warn the driver through the fault indicator lights in the cockpit (such as the engine warning light).

[0007] In the diesel engine aftertreatment system, OBD plays a particularly important role. Due to the characteristics of diesel engines, their emission control systems such as SCR (Selective Catalytic Reduction) and DPF (Diesel Particulate Filter) need special monitoring to ensure that they effectively reduce emission pollutants such as nitrogen oxides and particulate matter. The OBD system monitors the functionality and efficiency of these components, such as detecting the correctness of urea injection in the SCR system, the activity of the catalyst, and the clogging of the DPF.

[0008] In addition, as environmental standards become increasingly stringent, the OBD system of diesel engines must also monitor and report emission-related data more accurately. Regulations require that the OBD system be able to detect and record any performance degradation or failure of the emission control system and store related fault codes, which can be read by dedicated equipment for maintenance and repair. OBD in diesel engine aftertreatment systems is not only a regulatory requirement, but also a key technology to ensure efficient and clean operation of the engine and emission system.

[0009] As OBD standards become stricter, OBD diagnosis of nitrogen oxide sensors in SCR systems becomes increasingly difficult. Usually, an SCR system includes two nitrogen oxide sensors: one is arranged upstream of the SCR, called the SCR upstream nitrogen oxide sensor (upstream NOx sensor), or the engine original nitrogen oxide sensor (hereinafter referred to as the upstream NOx sensor), and the other is arranged downstream of the SCR, called the SCR downstream nitrogen oxide sensor, or the engine tail exhaust nitrogen oxide sensor (hereinafter referred to as the downstream NOx sensor). In OBD, in addition to the need to diagnose the circuit fault of the nitrogen oxide sensor, it is also necessary to judge the rationality of the reading of the nitrogen oxide sensor. This type of diagnosis is usually called rationality (In-Range) diagnosis, including high reading (In-Range-High), low reading (In-Range-Low), and unchanged reading (Stuck-In-Rage) faults. In addition, if the nitrogen oxide sensor is used for SCR control, OBD also has requirements for the response time of the nitrogen oxide sensor, and an alarm is also required if the response time exceeds the allowable range.

[0010] The diagnosis method of NOx sensor is currently mainly realized by comparing the virtual prediction value with the sensing value of NOx sensor, and comparing the sensing value of upstream and downstream NOx sensor. For the comparison of upstream and downstream NOx sensors, due to the influence of urea injection and SCR catalyst ammonia storage, it is necessary to select appropriate comparison conditions. This comparison condition includes stopping urea injection, high exhaust temperature to remove ammonia storage, and stable exhaust gas flow and temperature. These conditions limit the opportunity of OBD operation, which may cause the sensor to have problems but not be detected and repaired for a long time, causing emission problems.

[0011] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0012] Purpose of the invention: The technical problem to be solved by the present invention is to provide an SCR system with a calibrator and a method for fault detection, calibration and protection of its nitrogen and oxygen sensor in view of the deficiencies in the prior art.

[0013] In order to solve the above technical problems, the present invention discloses an SCR system with a calibrator and a nitrogen oxygen sensor fault detection, calibration and protection method thereof, wherein the calibrator is arranged in the SCR system and comprises:

[0014] A hollow cavity is provided with an air inlet and an air inlet and outlet, wherein:

[0015] An air inlet hole is used to receive the upstream exhaust gas of the SCR catalytic device in the SCR system;

[0016] Inlet and outlet holes are connected to the outlet of the SCR catalytic device;

[0017] A nitrogen and oxygen sensor is provided in the hollow cavity to detect the nitrogen and oxygen content in the hollow cavity;

[0018] The hollow cavity is also provided with an air outlet for discharging exhaust gas;

[0019] An airflow control device is provided between the air inlet hole of the calibrator and the upstream exhaust gas of the SCR catalytic device, for controlling the upstream exhaust gas to enter the hollow cavity through the air inlet hole.

[0020] Furthermore, a conical hole is provided in the hollow cavity between the air inlet hole and the air inlet and outlet holes, and the conical hole is used to prevent the exhaust gas downstream of the SCR catalytic device from flowing into the hollow cavity through the air inlet and outlet holes when the air is taken in by the air inlet hole.

[0021] Furthermore, the air outlet faces away from the catalytic device.

[0022] Furthermore, the inlet and outlet holes are evenly distributed in the exhaust gas downstream of the SCR catalytic device.

[0023] Furthermore, the inlet and outlet holes are distributed in a cross shape and are arranged facing the catalytic device of the SCR.

[0024] Furthermore, the system comprises:

[0025] An upstream exhaust pipe for receiving exhaust gas, wherein an upstream exhaust temperature sensor is provided on the upstream exhaust pipe, and a urea mixing device is provided downstream of the upstream exhaust pipe;

[0026] The urea mixing device comprises: a urea nozzle and a mixer;

[0027] The SCR catalytic device is arranged downstream of the urea mixing device;

[0028] The calibrator is arranged downstream of the SCR catalytic device;

[0029] A downstream exhaust temperature sensor is provided downstream of the SCR catalytic device;

[0030] The upstream exhaust temperature sensor, the urea nozzle, the downstream exhaust temperature sensor, the nitrogen oxide sensor in the calibrator and the airflow control device are all electrically connected to the controller. The controller receives signals from each sensor and controls the urea nozzle and the airflow control device.

[0031] Furthermore, the airflow control device comprises:

[0032] An upper drainage pipe is connected to the upstream exhaust pipe, the other end of the upper drainage pipe is connected to one end of the control valve, the other end of the control valve is connected to the lower drainage pipe, and the other end of the lower drainage pipe is connected to the air inlet; the control valve is electrically connected to the controller.

[0033] The present invention also provides a nitrogen oxide sensor fault detection method, which is implemented using the above system and is used to detect a fault of a downstream nitrogen oxide sensor. The method comprises:

[0034] Step a1, installing an upstream nitrogen oxide sensor upstream of the SCR catalyst device;

[0035] Step a2, turning on the airflow control device and waiting for Tsmin seconds, wherein the minimum value of Tsmin is not less than the flow time of the airflow from the upstream nitrogen oxide sensor of the SCR catalyst device to the downstream nitrogen oxide sensor plus the response time of the nitrogen oxide sensor;

[0036] Step a3, set the judgment conditions:

[0037] dMf <MFR_Thd

[0038] dNOx_D <NDR_Thd

[0039] Among them, dMf is the rate of change of the engine exhaust mass flow rate, dNOx_D is the absolute value of the rate of change of the nitrogen oxide sensor sensing value; MFR_Thd and NDR_Thd are two judgment thresholds;

[0040] According to the above judgment conditions, if the conditions are met, execute step a4, otherwise execute step a5;

[0041] Step a4, calculating the difference Vd between the sensing value of the nitrogen oxide sensor and the upstream nitrogen oxide sensor, wherein the sensing value of the upstream nitrogen oxide sensor is related to the nitrogen oxide concentration of the exhaust gas upstream of the SCR catalytic device, as follows:

[0042] Vd=NOx_D–NOx_U

[0043] Wherein, NOx_D is the nitrogen oxide concentration sensing value obtained from the nitrogen oxide sensor, and NOx_U is the nitrogen oxide concentration sensing value obtained from the upstream nitrogen oxide sensor;

[0044] If the value of the reading difference Vd is greater than or equal to the first threshold value VD_Max, the error flag IRH_Err is set to 1, and a first type of alarm is triggered;

[0045] If the over-reading difference Vd value is less than the first threshold value VD_max, the Vd value is compared with the second threshold value VD_Min. If it is less than the second threshold value VD_Min, the error flag IRL_Err is set to 1, and the second type of alarm is triggered;

[0046] Step a5, calculate the absolute value dNOx_U of the rate of change of the nitrogen oxide concentration sensing value NOx_U, and determine whether it is greater than the threshold R_min. If not, end the fault detection. Otherwise, calculate the cumulative amount AC_NOxU of the absolute value dNOx_U, and calculate the cumulative amount AC_NOxD through the rate of change deNOx_D of the nitrogen oxide concentration sensing value NOx_D, as follows:

[0047] AC_NOxU=sigma(dNOx_U*T)

[0048] AC_NOxD=sigma(dNOx_D*T)

[0049] Wherein, sigma() represents cumulative calculation, and T is the calculation period of the downstream nitrogen oxide sensor fault detection method;

[0050] Compare the accumulated amount AC_NOxU with the threshold value Calc_Thd, and if the accumulated amount AC_NOxU is less than or equal to the threshold value Calc_Thd, then end the fault detection;

[0051] Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd1. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd1, the error flag SIR_Err is set to 1 and the third type alarm is triggered. Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd2.

[0052] If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd2, the error flag SRP_Err is set to 1 and the fourth type alarm is triggered.

[0053] The present invention also proposes a nitrogen oxide sensor calibration method, which is implemented using the above system and is used to calibrate the nitrogen oxide sensor upstream of the SCR catalyst device. The method comprises:

[0054] Step b1, an upstream nitrogen oxide sensor is arranged upstream of the SCR catalyst device, and calibration conditions are set, as follows:

[0055] Condition 1: the NOx sensor is not used to diagnose SCR efficiency;

[0056] Condition 2, the NOx sensor is not used for feedback control of SCR urea injection;

[0057] Condition 3, the NOx sensor has no fault;

[0058] Condition 4: the upstream nitrogen oxide sensor has no fault;

[0059] Condition 5: the calibration time exceeds the preset time interval;

[0060] Step b2, determine whether the above calibration conditions are met, if so, execute step b3, otherwise end the calibration;

[0061] Step b3, turn on the airflow control device, wait for Tsmin seconds, and set the judgment conditions as follows:

[0062] dMf <MFR_Thd

[0063] dNOx_UI <NDRI_Thd

[0064] Among them, dMf is the rate of change of the engine exhaust mass flow, dNOx_UI is the absolute value of the rate of change of the nitrogen oxide concentration obtained by the upstream nitrogen oxide sensor, and MFR_Thd and NDRI_Thd are the judgment thresholds;

[0065] Step b4, make a judgment according to the above judgment conditions. If the above conditions are met, execute step b5; otherwise, execute step b6;

[0066] Step b5, calculating the reading difference Vdi between the downstream nitrogen oxide sensor and the upstream nitrogen oxide sensor, as follows:

[0067] Vdi=NOx_D–NOx_UI

[0068] Wherein, NOx_UI is the nitrogen oxygen concentration sensing value obtained from the upstream nitrogen oxygen sensor;

[0069] If the value of the reading difference Vdi is greater than or equal to the threshold value VDI_Max, the error flag IRH_Err of the downstream reading difference sensor is set to 1, otherwise the reading difference Vdi is compared with the threshold value VDI_Min, if it is less than the threshold value VDI_Min, the error flag IRL_Err of the downstream nitrogen oxide sensor is set to 1;

[0070] If the value of the reading difference Vdi is greater than or equal to the threshold value VDI_Min and less than the threshold value VDI_Max, use the single-point calibration or table calibration method to calculate the calibration parameters;

[0071] Step b6, determining whether the absolute value dNOx_Ui of the rate of change of the nitrogen oxide concentration sensing value NOx_UI is greater than the threshold R_min, or whether the absolute value ddNOx_Ui of the rate of change within a period of time Tdsmin seconds is greater than the threshold dR_min;

[0072] If neither of the above two conditions is met, the calibration is terminated. Otherwise, the cumulative amount AC_NOxUi of the absolute value dNOx_Ui of the nitrogen oxygen concentration change rate is calculated, and the cumulative amount AC_NOxD is calculated by the change rate deNOx_D of the nitrogen oxygen concentration sensing value NOx_D. The calculation method of the cumulative amount AC_NOxUi is as follows:

[0073] AC_NOxUi=sigma(dNOx_Ui*T)

[0074] Wherein, sigma() represents cumulative calculation, and T is the calculation period of the method for calibrating the nitrogen oxide sensor upstream of the SCR catalyst device (105);

[0075] Compare the accumulated amount AC_NOxUi with the threshold Calci_Thd. If the accumulated amount AC_NOxUi is less than or equal to the threshold Calci_Thd, the calibration is terminated.

[0076] Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd1. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd1, the error flag SIR_Err of the downstream nitrogen oxygen sensor is set to 1. Otherwise, AC_NOxD is compared with the threshold AVmin_Thd2.

[0077] If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd2, the error flag SRP_Err of the downstream nitrogen oxygen sensor is set to 1.

[0078] The present invention also proposes a nitrogen oxygen sensor protection method, which is implemented using the above system, and the method includes:

[0079] Step c1, before the nitrogen oxygen sensor is turned on, the control valve is opened;

[0080] Step c2, obtaining the reading T121 of the upstream exhaust temperature sensor. If the reading T121 is greater than the dew point threshold T_DPThd for a period exceeding the threshold DPT_Thd, the control valve is closed and the cleaning completion flag PFLAG is set to 1;

[0081] Step c3, setting the cleaning completion flag PFLAG to 1 as one of the starting conditions of the nitrogen oxide sensor.

[0082] Beneficial effects:

[0083] 1. The calibrator designed by the present invention can be used to perform comparison diagnosis on upstream and downstream NOx sensors. For a system using an upstream indirect NOx sensor, the calibrator can also be used to calibrate the upstream indirect NOx sensor.

[0084] 2. The SCR system with calibrator proposed in the present invention adds more upstream and downstream NOx sensor comparison conditions, obtains more OBD diagnosis opportunities, and can also calibrate the upstream indirect NOx sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0086] Figure 1 It is a general schematic diagram of the SCR system using a calibrator.

[0087] Figure 2 is a schematic diagram of the structure of a calibrator in an embodiment.

[0088] Figure 3 FIG. 1 is a schematic diagram of a calibrator measuring downstream exhaust gas in an embodiment.

[0089] Figure 4 FIG. 1 is a schematic diagram of a calibrator measuring upstream exhaust gas in an embodiment.

[0090] Figure 5 The figure is a schematic diagram of a pipeline purging method in an embodiment.

[0091] Figure 6 The figure is a schematic diagram of the NOx sensor fault diagnosis process in an embodiment.

[0092] Figure 7 The figure is a schematic diagram of a calibration process for an indirect nitrogen oxide sensor in an embodiment. DETAILED DESCRIPTION

[0093] In an SCR (Selective Catalytic Reduction) system, the engine exhaust can also be calculated indirectly. In the indirect measurement method, the engine exhaust nitrogen oxide concentration can be calculated by physical quantities such as the engine's air-fuel ratio, the engine's intake flow, the EGR state, and the ambient humidity. The engine exhaust nitrogen oxide content calculated by the indirect method will be affected by factors such as engine component deviation and engine aging, and calibration is required to maintain accuracy. The indirect measurement device of the engine exhaust is also called an upstream indirect NOx sensor.

[0094] In order to add more upstream and downstream NOx sensor comparison conditions to obtain more OBD diagnosis opportunities, and also to be able to calibrate the upstream indirect NOx sensor, the present invention proposes a calibrator, which includes a sampling tube and an airflow cone arranged at its upper end. At the upper part of the cone is an air cavity, in which the probe of the downstream NOx sensor is arranged. In an SCR system using a calibrator, the calibrator is arranged downstream of the SCR catalyst and fluidically connected to the upstream of the SCR catalyst through a pipeline with an airflow control valve. When the control valve is in a closed state, the downstream NOx sensor reads the nitrogen oxide concentration downstream of the SCR, and when the control valve is in an open state, the downstream NOx sensor reads the nitrogen oxide concentration upstream of the SCR. Through the calibrator, the upstream and downstream NOx sensors can be compared and diagnosed. For systems using upstream indirect NOx sensors, the calibrator can also be used to calibrate the upstream indirect NOx sensor.

[0095] SCR systems using calibrators such as Figure 1 As shown, in the system, the upstream exhaust temperature sensor 121 is installed on the upstream exhaust pipe of the system, and the exhaust pipe is connected to the decomposition pipe through a transition end cone. The decomposition pipe is equipped with a urea nozzle 125 and a mixer 104. The urea solution sprayed by the urea nozzle 125 is further broken into smaller particles in the mixer 104 and fully mixed with the exhaust gas flowing therethrough. The SCR catalyst 105 is connected downstream of the mixer 104. The mixed exhaust gas undergoes an oxidation-reduction reaction in the SCR catalyst 105, and the nitrogen oxides therein are decomposed into nitrogen and water. After passing through the SCR catalyst 105, the exhaust gas flows out through the downstream exhaust pipe. The downstream exhaust temperature sensor 122 and the calibrator 285 are arranged on the downstream exhaust pipe. The calibrator 285 is connected to the downstream end of the solenoid valve (control valve) 130 through the lower drainage pipe 102, and the upstream end of the solenoid valve 130 is connected to the upstream exhaust pipe through the upper drainage pipe 101. The upstream exhaust temperature sensor 121 and the downstream exhaust temperature sensor 122 are electrically connected to the controller 110 through signal lines 111 and 114 respectively. At the same time, the controller 110 controls the urea nozzle 125 and the solenoid valve 130 through signal lines 112 and 113 respectively. The calibrator 285 is equipped with a downstream NOx sensor and is connected to the controller 110 through a signal line 115.

[0096] One implementation of the calibrator 285 is as follows Figure 2 The calibrator is installed on the pipeline 210 (the pipeline 210 can be Figure 1 The downstream exhaust pipe in the vertical pipe includes a cross-shaped sampling pipe 215 and an airflow cone nozzle 202 arranged at the upper end of the vertical pipe. The upper part of the cone nozzle 202 is an air cavity 203 and a downstream NOx sensor probe 205. The air inlet end of the probe is fluidically connected to the root of the cone nozzle 202. The side wall of the air cavity 203 has an interface 201. Figure 1 In the system, the interface is connected to the lower pipe 102. A plurality of inlet and outlet air holes 204 are arranged on the side of the sampling pipe 215 facing the exhaust gas outflow from the SCR, and the air holes 204 are evenly arranged in the exhaust gas flow. Figure 3 and Figure 4 As shown, an air outlet 206 is arranged at the upper end of the vertical pipe, and air only flows out of the air outlet but not in.

[0097] exist Figure 1 In the system shown in FIG. 1 , after the solenoid valve 130 is opened, the upstream exhaust gas enters the calibrator 285 through the upper and lower drainage pipes 101 and 102. Due to the special structure of the calibrator 285, Figure 4 As shown, under the action of the upstream air pressure, the upstream exhaust gas passes through the cone nozzle 202 and flows through the inlet and outlet holes 204 and the outlet hole 206, so that the downstream NOx sensor 205 only contacts the upstream exhaust gas, so that its reading is actually the upstream nitrogen oxygen value. Figure 3 As shown, the exhaust gas downstream of the SCR flows into the sampling tube 215 from the air inlet and outlet holes 204, and then flows out from the air outlet hole 206. At this time, the NOx sensor only contacts the downstream exhaust gas, and its reading is the downstream nitrogen oxygen value.

[0098] After the solenoid valve 130 is opened, part of the exhaust gas flow upstream of the SCR catalyst 105 that has not been de-solidified will flow out through the upper and lower drainage 101, 102, the solenoid valve 130, the interface 201, the airflow cone nozzle 202, and the inlet and outlet air holes 204 and 206. This part of the airflow is called the calibration airflow, which will increase the emission of the system. At the same time, the calibration airflow flow rate cannot be too small. The airflow velocity of an airflow with too small a flow rate will be very slow, resulting in a longer reaction time of the nitrogen oxide sensor. The calibration airflow flow rate can be achieved by adjusting the opening size of the airflow cone nozzle 202. Generally speaking, the airflow flow rate needs to maintain the minimum flow rate (for example, the flow rate when the response speed of the nitrogen oxide sensor T33 is set to 5s from the measured value 33% to 66% response time) under the condition of the minimum working back pressure (for example, the back pressure selected at the idle condition is the minimum working back pressure); at the same time, under the condition of the designed maximum back pressure (for example, 12kPa), it is ensured that the maximum flow rate does not cause emission problems (for example, not more than 1% of the exhaust flow rate).

[0099] The calibrator operates under the control of the controller 110. The controller 110 may include a microprocessor that receives and processes signals from the exhaust temperature sensors 121, 122 and the downstream NOx sensor 205, and sends control signals to the urea nozzle 125 and the control valve 130. The microprocessor in the controller 110 may run a control program, as follows: Figure 1 The exemplary methods for implementing the functions of the illustrated system may all be implemented by a control program running in the controller 110 .

[0100] exist Figure 1 In the system, when the engine exhaust temperature drops below the dew point, the water vapor in the exhaust gas will condense into water droplets in the upper and lower drainage pipes 101 and 102 connected to the calibrator 285 and the solenoid valve 130. In order to prevent the accumulated water droplets from entering the nitrogen oxide sensor in the working state after the solenoid valve 130 is opened and damaging its heating and temperature control device, the pipeline consisting of the upper and lower drainage pipes 101 and 102 and the solenoid valve 130 needs to be purged before the nitrogen oxide sensor is started. Figure 5 The control method shown can be used to control the purge. In this method, the control valve 130 is first opened. At this time, under the action of the pressure difference between the upstream and downstream of the SCR catalyst 105, an airflow will flow into the calibrator 285 through the upper drainage pipe 101, the solenoid valve 130, and the lower drainage pipe 102. This airflow blows out the accumulated moisture therein. Then the program enters a waiting state until the reading T121 of the upstream exhaust temperature sensor 121 is greater than the dew point threshold T_DPThd for a time exceeding the threshold DPT_Thd. At this time, the airflow flowing through the upper and lower drainage pipes 101, 102, and the solenoid valve 130 will not condense, and at the same time take away the accumulated moisture therein. After that, the program closes the solenoid valve 130 and sets a purge completion flag PFLAG to 1. The purge completion flag is a condition for starting the downstream NOx sensor 205, that is, only when the flag is set to 1, the system allows the downstream NOx sensor 205 to start. Since the exhaust temperature upstream of SCR 105 rises faster than that downstream, after the engine is started, the time when PFLAG is set to 1 is shorter than the downstream dew point protection time (the same dew point protection logic also applies to the downstream NOx sensor. At this time, the reading of the downstream exhaust temperature sensor 122 can be used to determine the dew point condition). The cleaning of the calibrator 285 does not affect the normal use of the downstream NOx sensor 205.

[0101] exist Figure 1 In the system shown in the figure, if an upstream NOx sensor is used to measure the original exhaust nitrogen and oxygen concentration of the engine, the following method can be used: Figure 6The method shown in the flow chart is used to detect the IR fault of the downstream NOx sensor. In this procedure, the downstream NOx sensor is diagnosed by comparing the readings of the upstream and downstream NOx sensors. The application condition is that there is no fault in the upstream NOx sensor. Otherwise, it can only be determined that one of the upstream and downstream NOx sensors is faulty, and the fault cannot be isolated to the downstream NOx sensor. If an upstream NOx sensor is used, the diagnosis of the sensor can be achieved by comparing the original exhaust calculation value with the upstream NOx sensor reading. The diagnostic method can also refer to Figure 6 When the downstream NOx sensor is tested by OBD, the downstream NOx sensor cannot be used to diagnose the SCR efficiency and perform feedback control on the SCR.

[0102] exist Figure 1 In the system shown, Figure 6 The flowchart shown can be implemented by an interrupt service program with an interrupt period of T. After the program starts, the control valve 130 is first opened and a period of Tsmin seconds is waited. The minimum value of Tsmin is not less than the flow time of the air flow from the upstream air intake point of the SCR catalyst 105 to the calibrator 285 plus the response time of the downstream NOx sensor 205. Then, the program determines whether conditions C1 and C2 are met:

[0103] dMf <MFR_Thd(C1)

[0104] dNOx_D <NDR_Thd(C2)

[0105] Where dMf is the rate of change of the engine exhaust mass flow, dNOx_D is the absolute value of the rate of change of the upstream NOx sensor. MFR_Thd and NDR_Thd are two judgment thresholds that can be set (calibrated) through experiments.

[0106] If conditions C1 and C2 are met, the difference between the readings of the downstream NOx sensor and the upstream NOx sensor, Vd, is calculated.

[0107] Vd=NOx_D–NOx_U(F1)

[0108] Among them, NOx_D is the nitrogen oxygen concentration sensing value obtained from the downstream NOx sensor (205), and NOx_U is the nitrogen oxygen concentration sensing value obtained from the upstream NOx sensor.

[0109] If the value of Vd is greater than or equal to the threshold VD_Max, the error flag IRH_Err is set to 1, which triggers the In-Range-High alarm.

[0110] If the Vd value is less than VD_max, the Vd value is compared with another threshold value VD_Min. If it is less than VD_Min, the error flag IRL_Err is set, which will trigger the In-Range_Low alarm.

[0111] If the Vd value is less than VD_Max but greater than VD_Min, the flags IRL_Err and IRH_Err are reset and cleared to zero (in order to prevent frequent changes in the error flag when the error is near the threshold, a de-jitter function can also be added. The process for implementing this function is not described in the following sections). Figure 6 The program exits after setting or resetting the error flag. The thresholds VD_Max and VD_Min are limited by the error or uncertainty of the sensor itself and the emission requirements and can be calibrated according to the actual application.

[0112] Back to the judgment of conditions C1 and C2, if conditions C1 and C2 are not met, it is judged whether the absolute value of the change rate of the NOx_U value, dNOx_U, is greater than the threshold R_min. If not, the program ends. Otherwise, the cumulative amount of dNOx_U, AC_NOxU, is calculated, and another cumulative amount, AC_NOxD, is calculated through the change rate of the NOx_D value, deNOx_D. In the program, the calculation can be carried out by the following methods:

[0113] AC_NOxU=ACNOxU+dNOx_U*T(F2)

[0114] AC_NOxD=ACNOxD+dNOx_D*T(F3)

[0115] Then AC_NOxU is compared with the threshold Calc_Thd. If AC_NOxU is less than or equal to Calc_Thd, the program exits, otherwise AC_NOxD is compared with the threshold AVmin_Thd1. If AC_NOxD is less than AVmin_Thd1, the error flag SIR_Err is set to 1. This error flag will trigger the Stuck_In_Range alarm.

[0116] If AC_NOxD is greater than or equal to AVmin_Thd1, AC_NOxD is compared with another threshold AVmin_Thd2. If AC_NOxD is less than AVmin_Thd2, the error flag SRP_Err is set to 1, which will trigger the Slow_Response alarm.

[0117] If AC_NOxD is greater than or equal to AVmin_Thd2, the error flags SIR_Err and SRP_Err are cleared (in order to prevent frequent changes in the error flags when the error is near the threshold, a de-jitter function can also be added. The process for implementing this function is not described in Figure 6 The program exits after setting or clearing the error flag. The thresholds Calc_Thd, AVmin_Thd1, and AVmin_Thd2 can be calibrated according to the application.

[0118] The upstream NOx concentration can be measured indirectly. In indirect measurement, the engine exhaust NOx is not directly measured by the NOx sensor, but calculated using the engine cylinder operating parameters and environmental parameters. Affected by factors such as the deviation between engine parts and the aging of the engine body, in order to improve the accuracy of indirect measurement, the engine exhaust NOx concentration obtained by indirect measurement needs to be calibrated according to the individual differences and aging degree of the engine.

[0119] exist Figure 1 In the system shown, the indirect NOx sensor can be calibrated by using Figure 7 The program shown in the flowchart is implemented. This program can be used as an interrupt service program with an interrupt cycle of T. After the program starts, Figure 7 As shown, first determine whether the calibration conditions are met. If not, the program stops and exits. The calibration conditions can be selected from the following conditions:

[0120] Condition 1: The downstream NOx sensor is not used to diagnose the SCR efficiency. (When the SCR efficiency diagnosis enable condition is not met, the SCR efficiency diagnosis program is not started, or when the SCR in-use-ratio is already met, the SCR diagnosis program may not be started).

[0121] Condition 2: Downstream NOx sensor is not used for feedback control. Some SCR control systems use downstream NOx sensor for feedback control, which needs to be temporarily turned off when calibrating the upstream indirect NOx sensor.

[0122] Condition 3: The downstream NOx sensor has no fault;

[0123] Condition 4: There is no fault in the sensors involved and used in the upstream indirect sensor calculation;

[0124] Condition 5: The time between two calibrations exceeds a minimum time setting value, which determines the calibration frequency (minimum time interval).

[0125] If the calibration conditions are met, the control valve 130 is opened and Tsmin seconds are waited. Then it is determined whether the system meets conditions C1 and C3:

[0126] dNOx_UI <NDRI_Thd(C3)

[0127] Where dNOx_UI is the absolute value of the nitrogen oxide concentration change rate calculated by the upstream indirect nitrogen oxide sensor, and NDRI_Thd is the judgment threshold, which can be set (calibrated) through experiments. If conditions C1 and C3 are met, the reading difference between the downstream NOx sensor and the upstream indirect NOx sensor is calculated, Vdi,

[0128] Vdi=NOx_D–NOx_UI(F4)

[0129] Wherein, NOx_UI is the nitrogen oxygen concentration sensing value obtained from the upstream indirect NOx sensor. If the value of Vdi is greater than or equal to the threshold value VDI_Max, the error flag IRH_Err of the downstream NOx sensor is set to 1. If the value of Vdi is less than VDI_max, the value of Vdi is compared with another threshold value VDI_Min. If it is less than VDI_Min, the error flag IRL_Err of the downstream NOx sensor is set to 1. If the value of Vdi is less than VDI_Max but greater than VDI_Min, the flags IRL_Err and IRH_Err are reset to zero (in order to prevent frequent changes in the error flag when the error is near the threshold, a de-jitter function can also be added. The process of implementing this function is not shown in the figure). Figure 7 The calibration parameters are then calculated. There are two ways to calculate the calibration parameters:

[0130] Method 1: Single-point calibration

[0131] Single-point calibration is to calibrate one parameter, Gc., and calculate the calibrated upstream indirect nitrogen and oxygen concentration value, NOx_UIc, using the following formula:

[0132] NOx_UIc=NOx_UI*Gc+C0(F5)

[0133] Among them, C0 is a bias constant, which can be calibrated by some special working conditions (such as engine cylinder braking conditions). Gc can be calculated by the following formula:

[0134] Gc=(NOx_D–C0) / NOx_UI(F6)

[0135] Method 2: Table Calibration

[0136] Table calibration is to calibrate the compensation table Tbl() according to the current working conditions. Tbl() can be an xyz table, where xy is the input and z is the output. Commonly used compensation tables use engine speed and torque as x input and y input respectively. At this time, the NOx_UI value corresponding to the current working condition can be used to update the table value under similar x input and y input. After the update, the NOx_UIc value is calculated by the following formula:

[0137] NOx_UIc=NOx_UI*Tbl(x,y)(F7)

[0138] During calibration, if the calibration coefficient changes greatly, such as in single-point calibration, if the value of Gc changes by more than a certain amplitude, the calibration frequency can be increased (the minimum time setting value is reduced in condition 5) to reduce the impact of its change on the accuracy of the upstream indirect NOx sensor. The program exits after completing the error table value setting or calibration calculation. The thresholds VDI_Max and VDI_Min are limited by the sensor's own error or uncertainty and emission requirements, and can be calibrated according to the actual application.

[0139] Back to the judgment of conditions C1 and C3, if conditions C1 and C3 are not met, then determine whether the absolute value of the rate of change of the NOx_UI value, dNOx_Ui, is greater than the threshold R_min, or whether the absolute value of its rate of change within a period of time Tdsmin seconds, ddNOx_Ui, is greater than a threshold dR_min. If both conditions are not met, then end the program, otherwise calculate the cumulative amount of dNOx_Ui, AC_NOxUi, and calculate another cumulative amount, AC_NOxD, through the rate of change of the NOx_D value, deNOx_D. The threshold dR_min is determined by the difference in response time between the upstream indirect NOx sensor and the downstream NOx sensor, and can also be determined (calibrated) by experiment. AC_NOxUi is calculated by formula (F8):

[0140] AC_NOxUi=ACNOxUi+dNOx_Ui*T(F8)

[0141] Then AC_NOxUi is compared with the threshold Calci_Thd. If AC_NOxUi is less than or equal to Calci_Thd, the program exits. Otherwise, AC_NOxD is compared with the threshold AVmin_Thd1. If AC_NOxD is less than AVmin_Thd1, the error flag SIR_Err of the downstream NOx sensor is set to 1. If AC_NOxD is greater than or equal to AVmin_Thd1, AC_NOxD is compared with another threshold AVmin_Thd2. If AC_NOxD is less than AVmin_Thd2, the error flag SRP_Err of the downstream NOx sensor is set to 1. If AC_NOxD is greater than or equal to AVmin_Thd2, the error flag SIR_Err and SRP_Err are cleared (in order to prevent frequent changes in the error flag when the error is near the threshold, a de-jitter function can also be added. The process for implementing this function is not shown in the figure. Figure 7 The program exits after setting or clearing the error flag. The thresholds Calc_Thd, AVmin_Thd1, and AVmin_Thd2 can be calibrated according to the application.

[0142] In a specific implementation, the present application provides a computer storage medium and a corresponding data processing unit, wherein the computer storage medium can store a computer program, and when the computer program is executed by the data processing unit, the invention content of a SCR system with a calibrator and a method for detecting, calibrating and protecting a nitrogen and oxygen sensor fault provided by the present invention and some or all of the steps in each embodiment can be run. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0143] Those skilled in the art can clearly understand that the technical solutions in the embodiments of the present invention can be implemented by means of computer programs and their corresponding general hardware platforms. Based on such an understanding, the technical solutions in the embodiments of the present invention can be essentially or partly contributed to the prior art in the form of computer programs, i.e., software products, which can be stored in a storage medium and include several instructions for enabling a device including a data processing unit (which can be a personal computer, a server, a single-chip microcomputer, an MCU or a network device, etc.) to execute the methods described in various embodiments of the present invention or certain parts of the embodiments.

[0144] The present invention provides a method and idea for fault detection, calibration and protection of an SCR system with a calibrator and a nitrogen oxide sensor thereof. There are many methods and approaches to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. An SCR system with a calibrator, characterized in that: The calibrator (285) is arranged in the SCR system and comprises: A hollow cavity is provided with an air inlet and an air inlet and outlet, wherein: An air inlet hole for receiving upstream exhaust gas from an SCR catalytic device (105) in the SCR system; An air inlet and outlet hole, connected to the air outlet at the end of the SCR catalytic device (105); A nitrogen and oxygen sensor (205) is provided in the hollow cavity for detecting the nitrogen and oxygen content in the hollow cavity; The hollow cavity is also provided with an air outlet (206) for discharging exhaust gas; An airflow control device is provided between the air inlet hole of the calibrator (285) and the upstream exhaust gas of the SCR catalytic device (105), for controlling the upstream exhaust gas to enter the hollow cavity through the air inlet hole.

2. The SCR system with a calibrator according to claim 1, characterized in that: A conical hole is provided in the hollow cavity between the air inlet hole and the air inlet and outlet holes, and the conical hole is used to prevent the exhaust gas downstream of the SCR catalytic device (105) from flowing into the hollow cavity through the air inlet and outlet holes when the air is taken in through the air inlet hole.

3. The SCR system with a calibrator according to claim 1, characterized in that: The air outlet (206) faces away from the catalytic device (105).

4. The SCR system with a calibrator according to claim 1, characterized in that: The inlet and outlet holes are evenly distributed in the exhaust gas downstream of the SCR catalytic device (105).

5. The SCR system with a calibrator according to claim 4, characterized in that: The inlet and outlet holes are distributed in a cross shape and are arranged facing the SCR catalytic device (105).

6. The SCR system with a calibrator according to claim 1, characterized in that: The system comprises: An upstream exhaust pipe for receiving exhaust gas, wherein an upstream exhaust temperature sensor (121) is provided on the upstream exhaust pipe, and a urea mixing device is provided downstream of the upstream exhaust pipe; The urea mixing device comprises: a urea nozzle (125) and a mixer (104); The SCR catalytic device (105) is arranged downstream of the urea mixing device; The calibrator (285) is arranged downstream of the SCR catalytic device (105); A downstream exhaust temperature sensor (122) is provided downstream of the SCR catalytic device (105); The upstream exhaust temperature sensor (121), the urea nozzle (125), the downstream exhaust temperature sensor (122), the nitrogen oxide sensor in the calibrator (285), and the airflow control device are all electrically connected to the controller (110). The controller (110) receives signals from each sensor and controls the urea nozzle (125) and the airflow control device.

7. The SCR system with a calibrator according to claim 4, characterized in that: The airflow control device comprises: An upper drainage pipe (101) connected to an upstream exhaust pipe, the other end of the upper drainage pipe (101) is connected to one end of a control valve (130), the other end of the control valve (130) is connected to a lower drainage pipe (102), and the other end of the lower drainage pipe (102) is connected to the air inlet; the control valve (130) is electrically connected to the controller (110).

8. A method for detecting nitrogen oxide sensor failure, characterized in that: Using the system described in any one of claims 1 to 7, the method for detecting a fault in a downstream nitrogen oxide sensor (205) comprises: Step a1, arranging an upstream nitrogen oxide sensor upstream of the SCR catalyst device (105); Step a2, turning on the airflow control device and waiting for Tsmin seconds, wherein the minimum value of Tsmin is not less than the flow time of the airflow from the upstream nitrogen oxide sensor of the SCR catalytic device (105) to the downstream nitrogen oxide sensor (205) plus the response time of the nitrogen oxide sensor (205); Step a3, set the judgment conditions: dMf <MFR_Thd dNOx_D <NDR_Thd Wherein, dMf is the rate of change of the mass flow of the engine exhaust gas, dNOx_D is the absolute value of the rate of change of the sensing value of the nitrogen oxide sensor (205); MFR_Thd and NDR_Thd are two judgment thresholds; According to the above judgment conditions, if the conditions are met, execute step a4, otherwise execute step a5; Step a4, calculating the difference Vd between the sensing value of the nitrogen oxide sensor (205) and the upstream nitrogen oxide sensor, wherein the sensing value of the upstream nitrogen oxide sensor is related to the nitrogen oxide concentration of the exhaust gas upstream of the SCR catalyst device (105), as follows Vd=NOx_D–NOx_U Wherein, NOx_D is a nitrogen oxide concentration sensing value obtained from a nitrogen oxide sensor (205), and NOx_U is a nitrogen oxide concentration sensing value obtained from an upstream nitrogen oxide sensor; If the value of the reading difference Vd is greater than or equal to the first threshold value VD_Max, the error flag IRH_Err is set to 1, and a first type of alarm is triggered; If the over-reading difference Vd value is less than the first threshold value VD_max, the Vd value is compared with the second threshold value VD_Min. If it is less than the second threshold value VD_Min, the error flag IRL_Err is set to 1, and the second type of alarm is triggered; Step a5, calculate the absolute value dNOx_U of the rate of change of the nitrogen oxide concentration sensing value NOx_U, and determine whether it is greater than the threshold R_min. If not, end the fault detection. Otherwise, calculate the cumulative amount AC_NOxU of the absolute value dNOx_U, and calculate the cumulative amount AC_NOxD through the rate of change deNOx_D of the nitrogen oxide concentration sensing value NOx_D, as follows: AC_NOxU=sigma(dNOx_U*T) AC_NOxD=sigma(dNOx_D*T) Wherein, sigma() represents cumulative calculation, and T is the calculation period of the downstream nitrogen oxide sensor fault detection method; Compare the accumulated amount AC_NOxU with the threshold value Calc_Thd, and if the accumulated amount AC_NOxU is less than or equal to the threshold value Calc_Thd, then end the fault detection; Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd1. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd1, the error flag SIR_Err is set to 1 and the third type alarm is triggered. Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd2. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd2, the error flag SRP_Err is set to 1 and the fourth type alarm is triggered.

9. A method for calibrating a nitrogen oxygen sensor, characterized in that: The method is implemented by using the system described in any one of claims 1 to 7 to calibrate a nitrogen oxygen sensor upstream of an SCR catalyst device (105), the method comprising: Step b1, an upstream nitrogen oxide sensor is arranged upstream of the SCR catalyst device (105), and calibration conditions are set, specifically as follows: Condition 1, the nitrogen oxide sensor (205) is not used to diagnose the SCR efficiency; Condition 2, the nitrogen oxide sensor (205) is not used for feedback control of SCR urea injection; Condition 3, the nitrogen oxide sensor (205) has no fault; Condition 4: the upstream nitrogen oxide sensor has no fault; Condition 5: the calibration time exceeds the preset time interval; Step b2, determine whether the above calibration conditions are met, if so, execute step b3, otherwise end the calibration; Step b3, turn on the airflow control device, wait for Tsmin seconds, and set the judgment conditions as follows: dMf <MFR_Thd dNOx_UI <NDRI_Thd Among them, dMf is the rate of change of the engine exhaust mass flow, dNOx_UI is the absolute value of the rate of change of the nitrogen oxide concentration obtained by the upstream nitrogen oxide sensor, and MFR_Thd and NDRI_Thd are the judgment thresholds; Step b4, make a judgment according to the above judgment conditions. If the above conditions are met, execute step b5; otherwise, execute step b6; Step b5, calculating the reading difference Vdi between the downstream nitrogen oxide sensor and the upstream nitrogen oxide sensor, as follows: Vdi=NOx_D–NOx_UI Wherein, NOx_UI is the nitrogen oxygen concentration sensing value obtained from the upstream nitrogen oxygen sensor; If the value of the reading difference Vdi is greater than or equal to the threshold value VDI_Max, the error flag IRH_Err of the downstream reading difference sensor is set to 1, otherwise the reading difference Vdi is compared with the threshold value VDI_Min, if it is less than the threshold value VDI_Min, the error flag IRL_Err of the downstream nitrogen oxide sensor is set to 1; If the value of the reading difference Vdi is greater than or equal to the threshold value VDI_Min and less than the threshold value VDI_Max, use the single-point calibration or table calibration method to calculate the calibration parameters; Step b6, determining whether the absolute value dNOx_Ui of the rate of change of the nitrogen oxide concentration sensing value NOx_UI is greater than the threshold R_min, or whether the absolute value ddNOx_Ui of the rate of change within a period of time Tdsmin seconds is greater than the threshold dR_min; If neither of the above two conditions is met, the calibration is terminated. Otherwise, the cumulative amount AC_NOxUi of the absolute value dNOx_Ui of the nitrogen oxygen concentration change rate is calculated, and the cumulative amount AC_NOxD is calculated by the change rate deNOx_D of the nitrogen oxygen concentration sensing value NOx_D. The calculation method of the cumulative amount AC_NOxUi is as follows: AC_NOxUi=sigma(dNOx_Ui*T) Wherein, sigma() represents cumulative calculation, and T is the calculation period of the method for calibrating the nitrogen oxide sensor upstream of the SCR catalyst device (105); Compare the accumulated amount AC_NOxUi with the threshold Calci_Thd. If the accumulated amount AC_NOxUi is less than or equal to the threshold Calci_Thd, the calibration is terminated. Otherwise, the accumulated amount AC_NOxD is compared with the threshold AVmin_Thd1. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd1, the error flag SIR_Err of the downstream nitrogen oxygen sensor is set to 1. Otherwise, AC_NOxD is compared with the threshold AVmin_Thd2. If the accumulated amount AC_NOxD is less than the threshold AVmin_Thd2, the error flag SRP_Err of the downstream nitrogen oxygen sensor is set to 1.

10. A nitrogen oxygen sensor protection method, characterized in that: Implemented using the system described in any one of claims 6 to 7, the method comprises: Step c1, before the nitrogen oxygen sensor (205) is turned on, the control valve (130) is turned on; Step c2, obtaining the reading T121 of the upstream exhaust temperature sensor (121), if the reading T121 is greater than the dew point threshold T_DPThd for a period exceeding the threshold DPT_Thd, closing the control valve (130) and setting the cleaning completion flag PFLAG to 1; Step c3, setting the cleaning completion flag PFLAG to 1 as one of the start-up conditions of the nitrogen oxide sensor (205).

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