WO2021213093A1

WO2021213093A1 - Fault diagnosis method for scr urea injection apparatus

Info

Publication number: WO2021213093A1
Application number: PCT/CN2021/081603
Authority: WO
Inventors: 陈一平; 何家明; 蔡继业
Original assignee: 上海星融汽车科技有限公司
Priority date: 2020-09-10
Filing date: 2021-03-18
Publication date: 2021-10-28
Also published as: CN112031903A; CN112031903B; AU2021236547A1; CA3131581A1

Abstract

Provided is a fault diagnosis method for a selective catalytic reduction (SCR) urea injection apparatus, belonging to the technical field of vehicle-mounted device detection; when an automobile is moving, the method can monitor and extract the pressure of the urea solution in a liquid outlet pipe of an SCR urea spraying apparatus in real time, and compare in real time the deviation of the urea solution pressure interquartile range and the standard interquartile range in a certain detection period; by means of the statistical method, it is possible to achieve real-time fault diagnosis of the SCR urea spraying apparatus, and, in a fault state, prompt a driver of the diagnosis result in a timely manner, so as to prevent the urea solution from affecting the safety and stability of automotive travel due to the imbalance of the urea solution and the unstable pressure.

Description

A fault diagnosis method for SCR urea injection device

Technical field

The invention relates to a fault diagnosis method for an SCR urea spraying device, and belongs to the technical field of vehicle-mounted equipment detection.

Background technique

With the continuous development and growth of China's automobile industry, the market share of commercial vehicles is also increasing. As the main power source of commercial vehicles, the demand and delivery of diesel engines are also increasing year by year. Diesel engines have sufficient displacement, excellent power, and excellent fuel economy. At the same time, their pollution to the environment is also high. It has become an urgent problem to be solved in China's vehicle emissions management. China also began to spread the country on July 1, 2019. Within the scope, heavy-duty diesel engines are implemented with the National Phase VI emission standards. In order to reduce pollution during diesel engine operation, the SCR (Selective Catalytic Reduction) of the exhaust gas treatment system is usually used to reduce emissions.

The technical principle of SCR is to use a reducing agent to selectively reduce nitrogen oxides to nitrogen and water in an oxygen-rich environment under the action of a catalyst. The reducing agent currently used is urea solution (for example, a urea solution with a mass concentration of 32.5%). The urea solution decomposes into NH ₃ and CO ₂ _{at high temperature, and chemically reacts with NO and NO 2} in the exhaust gas of diesel vehicles to produce nitrogen. And water, meet the requirements of emission regulations.

In SCR, the reducing agent urea solution is sprayed after being pressurized by the urea pump and atomized by the urea nozzle. Specifically, when working, it will go through the three processes of building pressure, spraying and pumping in sequence. In the pressure building process, the urea pump builds pressure. At this time, the pressure in the urea tank is slowly increased and then maintained at about normal working pressure (the pressure is maintained at the normal working pressure after the device is built); when the injection conditions are met, The engine control unit or DCU issues a command to open the urea nozzle; when the engine is finished, the key switch is turned off, and the urea pump enters the reverse pumping phase. To prevent the pipeline from clogging the urea crystals, the pump will pump the remaining urea in the pipeline and nozzles back into the urea box.

In the spraying stage of the SCR urea spraying device, the opening of the nozzle periodically changes with time to realize the urea solution spraying cycle one after another. When the nozzle is opened, the urea solution is sprayed, and the pressure in the outlet pipe drops. At this time, the urea When the pump receives a signal that the pressure of the urea solution in the outlet pipe is insufficient, it will increase the duty cycle to supplement more urea solution into the outlet pipe to stabilize the pressure.

If problems such as aging of the urea pump and clogging of the inlet filter occur in its SCR urea spraying device, it will be more difficult for the urea pump to replenish the pressure in the outlet pipe, which will make it more difficult to replenish its outlet in time after the nozzle is opened. The pressure of the tube urea solution causes its pressure fluctuations to be more obvious, and the resulting imbalance and instability of the urea solution will also affect the operation of the SCR post-processing system, reduce the efficiency of vehicle operation, and may also affect the driving The safety and stability of the vehicle will affect the driving safety.

Therefore, the art hopes to provide a fault diagnosis method for the SCR urea spraying device.

Summary of the invention

In view of the above-mentioned and/or other problems of the related art, one aspect of the present invention provides a fault diagnosis method for SCR urea spraying device, wherein:

The fault diagnosis method includes the following steps:

Step 1): Obtain the pressure value of the urea solution in the outlet pipe of the SCR urea spraying device in real time;

Step 2): Define a detection period T, and divide one detection period T into n time intervals t _i (t ₁ , t ₂ ...... t _n ) according to time sequence; when the detection period T is initially The cumulative value of abnormal conditions is set to zero;

Step 3): t _i sequentially urea solution and the corresponding pressure values are plotted in FIG box, and the box plot analysis, it is determined whether the time interval t _i abnormal situation of the time interval; if abnormal In case, the cumulative value of abnormal conditions increases by 1, otherwise, the cumulative value of abnormal conditions does not increase;

In the step 3), the method for judging the abnormal situation is: obtaining the corresponding upper quartile and lower quartile according to the maximum pressure value and the minimum pressure value in the box chart, and calculating the The difference between the upper quartile and the lower quartile is counted as the interquartile difference of the time interval; the interquartile difference of the time interval is compared with the pre-measured standard interquartile difference, if If it is greater than the standard interquartile range, it is judged that there is an abnormal situation;

Step 4): If the abnormality cumulative value reaches a threshold value, a fault alarm, end detection; abnormality if the cumulative value does not reach the threshold value, the time interval T _i of the number i is incremented by one;

Step 5): If the value of the serial number i is less than or equal to n, return to step 3); if the value of the serial number i is greater than n, return to step 2) to enter the next detection cycle.

Preferably, the numerical value of the standard interquartile range and the threshold value are obtained in advance through simulation analysis in a laboratory.

Preferably, in the step 1), the pressure value of the urea solution in the outlet pipe of the SCR urea spraying device is obtained in real time through a pressure sensor arranged on the outlet pipe of the SCR urea spraying device, and the data Transfer to the controller.

The present invention provides a fault diagnosis method for the SCR urea spraying device; when the car is driving, the method can monitor and extract the pressure of the urea solution in the outlet pipe of the SCR urea spraying device in real time. Compare the deviation of the urea solution pressure interquartile range with the standard interquartile range within a certain detection period. Through scientific statistical methods, real-time fault diagnosis of the SCR urea spraying device can be realized, and under fault conditions, the The diagnosis results are promptly provided to the driver in order to prevent the unbalanced discharge of the urea solution and unstable pressure from affecting the safety and stability of driving.

Description of the drawings

FIG. 1 is a schematic flowchart of a specific embodiment of the fault diagnosis method for the SCR urea spraying device of the present invention;

Figure 2 is a schematic diagram of the simple structure of the SCR urea spraying device;

Figure 3 is a set of box diagrams in Example 1;

Figure 4 is another set of box diagrams in Example 1.

Detailed ways

The present invention will be further described below through specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and the features in the embodiments can be combined with each other if there is no conflict.

Regarding the composition of the SCR urea spraying device, see Fig. 2, which mainly includes a urea tank 1, a urea pump 2, a liquid outlet pipe 3, a liquid outlet 4, a nozzle 5, a pressure sensor 6 and a controller 7.

Among them, the urea tank 1 stores the urea solution; the urea pump 2 draws or pours the urea solution from the urea tank 1. The urea tank 1 and the urea pump 2 are connected through the extraction pipeline 12 and the return pipeline 21, and the extraction pipeline 12 is provided with The liquid inlet 120 and its filtering, and the return pipe 21 is provided with a liquid return port 210; the urea solution drawn from the urea tank 1 by the urea pump 2 through the extraction pipe 12 enters the liquid outlet pipe 3, and then passes through the liquid outlet 4 Reaching the nozzle 5, when the switch on the nozzle 5 is turned on, the urea solution is sprayed from the nozzle 5.

The outlet pipe 3 is provided with a pressure sensor 6 that monitors the pressure of the urea solution in the outlet pipe 3 in real time, and the pressure sensor 6 transmits the pressure value of the urea solution obtained in real time to the controller 7. The controller 7 controls the operation of the urea pump 2, the pressure sensor 6 and the nozzle 5.

As explained in the background art, when the nozzle 5 is opened, the urea solution is sprayed, the pressure in the outlet pipe 3 drops, the pressure sensor 6 transmits the pressure value of the urea solution to the controller 7, and the controller 7 analyzes and obtains the inside of the outlet pipe 3. A signal of insufficient pressure of the urea solution, and at the same time instructs the urea pump 2 to draw the urea solution into the outlet pipe 3 to stabilize the pressure.

And if the urea pump 2 is aging in its SCR urea spraying device, the inlet 120 and its filter are blocked, it will be difficult for the urea pump 2 to replenish the pressure in the outlet pipe 3, which will cause the nozzle 5 to open after the nozzle 5 is turned on. It is more difficult to replenish the pressure of the urea solution in the liquid outlet pipe 3 in time, resulting in more obvious pressure fluctuations, and the resulting imbalance and instability of the urea solution will also affect the operation of the SCR post-processing system.

Therefore, in a specific embodiment of the present invention, a fault diagnosis method for SCR urea spraying device is provided, which includes the following steps:

Step 1): Obtain the pressure value of the urea solution in the outlet pipe of the SCR urea spraying device in real time.

Specifically, referring to FIG. 2, the pressure sensor 6 on the liquid outlet pipe 3 in the device obtains the pressure value of the urea solution in the liquid outlet pipe 3 in real time, and transmits the data to the controller 7.

Step 2): Define the detection period T, and divide a detection period T into n time intervals t _i (t ₁ , t ₂ ......t _n ) according to the time sequence; the abnormal situation at the beginning of the detection period T is accumulated The value is set to zero;

Step 3): sequentially time interval t _i corresponding to the urea solution and the pressure values are plotted in FIG box, and the box plot analysis, the time interval is determined whether the _i t abnormality occurs; if an abnormal condition occurs, The cumulative value of abnormal conditions increases by 1, otherwise, the cumulative value of abnormal conditions does not increase.

In step 2), the method of judging abnormal situations is: obtain the corresponding upper quartile and lower quartile according to the maximum pressure value and minimum pressure value in the box chart, and calculate the upper quartile and the lower quartile The difference of the quantile is counted as the interquartile difference of the time interval; the interquartile difference of the time interval is compared with the standard interquartile difference measured in advance, if it is greater than the standard interquartile difference, it is judged as An abnormal situation occurred.

Step 5): If the value of the sequence number i is less than or equal to n, return to step 3); if the value of the sequence number i is greater than n, then return to step 2) to enter the next detection cycle.

For ease of illustration, the technical terms in the above scheme are represented by symbols, and the specific interpretation of the symbols is described below in conjunction with the contents of the scheme:

T is the detection period.

A detection period T is divided into n time intervals t _i (t ₁ , t ₂ ......t _n ) according to time sequence; t _i is any one of the time intervals.

The detection period T is set by the user according to the current actual usage and requirements. Those skilled in the art can select an appropriate value according to the specific situation and give feedback on the state of the SCR urea spraying device, so as to efficiently and accurately identify its fault, and to meet the requirements of no false alarms or underreports.

P represents the pressure value of the urea solution in the liquid pipe 3.

Draw a box diagram for each time interval t _i and its corresponding urea solution pressure value. The maximum urea solution pressure value _{in this time interval t i} _{is expressed as P MAX} , and the minimum urea solution pressure value is expressed as P _MIN , According to P _MAX and P _MIN _{, the upper quartile P 1} , the median P ₂ and the lower quartile P ₃ between the two can be obtained (the scheme of the present invention only uses the upper four of the box-plot parameters quantile P ₁ P ₃ and the lower quartile); quartile computing the difference between P ₁ and P ₃ of the lower quartile, counted as the time interval of t interquartile △ _i P _i ( P ₁ -P ₃ =△P _i );

The standard interquartile range of the test cycle (expressed as △P0) is obtained in advance through simulation analysis in the laboratory; for example, the pressure value P of the urea solution in the outlet pipe 3 is used as the judgment data source, and a complete set of SCR is used in advance The system conducts the experiment, extracts the real-time urea solution pressure value P data and divides into groups according to the detection period T to make a box diagram and extracts the parameters to calculate the interquartile range. The interquartile range of multiple sets of standard data is averaged, which is the above The standard interquartile difference △P0.

Similarly, the following threshold C _{max of the} cumulative value of abnormal conditions, also called warning count, is also obtained in advance through simulation analysis in the laboratory.

Compare the interquartile difference △P _{i of} the time interval t _i with the pre-measured standard interquartile difference △P0. If it is greater than the standard interquartile difference △P0, the cumulative value of the abnormal situation (denoted as C) increases by 1 , Otherwise, the cumulative value C of abnormal conditions does not increase; that is, when ΔP _i _{> ΔP0 of the time interval t i} , the count C=C+1; otherwise, C does not increase, C=C+0. In other words, when ΔP _i _{≤ ΔP0 in the time interval t i} , C does not increase, C=C+0; otherwise, C=C+1.

If abnormality cumulative value reaches a threshold value (warning count C _max), the controller 7 sent to the system failure alarm, end detection; if abnormality accumulated value does not reach the threshold value, the time interval t number _i i is increased 1 (i = i +1).

If the value of sequence number i is less than or equal to n, then return to step 3), that is, analyze and judge the next time interval; if the value of sequence number i is greater than n, it means that the entire detection period T has ended, and the entire detection period T If the cumulative value of abnormal conditions is less than the threshold C _max , return to step 2) for the next detection cycle. The cumulative value of abnormal conditions in the next detection cycle is reset to zero (ie, C is cleared).

Example 1

For the urea spraying device of the SCR system of a diesel vehicle, fault diagnosis is carried out during the injection stage:

As shown in Figure 1:

S1: Obtain the pressure value P of the urea solution in the outlet pipe of the device in real time;

S2: Define the detection period T=1s, divide a detection period T into n (n=100) time intervals t _i (t ₁ , t ₂ ......t ₁₀₀ ) according to the time sequence, and each time interval has a duration Is 10ms;

The initial cumulative value C of abnormal conditions is set to zero (C=0);

The standard interquartile difference △P0=35kpa was determined in advance through simulation analysis in the laboratory, and the threshold value of the cumulative value of abnormal conditions _Cmax =3;

S3: Draw a box diagram for the time interval t _i and its corresponding urea solution pressure value P _{sequentially, extract the upper quartile P 1} and the lower quartile P ₃ in the box diagram, and calculate the time interval The interquartile difference of t _i _{△P i} , and compare △P _i with the standard interquartile difference △P0=35kpa;

As shown in Figure 1, if △P _i ≤△P0, it is a normal situation, the cumulative value C of abnormal situations does not increase, C=C+0;

As shown in Fig. 1, if ΔP _i > ΔP0 (ie, ΔP _i ≤ ΔP0 is judged as no), it is an abnormal situation, and the count of the cumulative value C of the abnormal situation increases by 1, and C=C+1.

For example, referring to Figure 3, _{the box plot of the first time interval t 1} , it can be seen that the difference between the upper quartile P ₁ and the lower quartile P _{3 of} the box plot does not exceed 200 hPa (20kpa ), that is, △P1<△P0=35kpa, which is the data of normal conditions, the cumulative value C of abnormal conditions does not increase, and remains the initial value 0;

For example, referring to Figure 4, _{the box plot of the 39th time interval t 39} , it can be seen that the difference between the upper quartile P ₁ and the lower quartile P _{3 of} the box plot is about 1000 hPa (100kpa ), that is, ΔP ₃₉ > ΔP0 = 35kpa, which is the data of the abnormal situation, the cumulative value C of the abnormal situation increases by 1, C=C+1.

S4: The cumulative value C of abnormal conditions does not reach the threshold, then _{the serial number i of the time interval t i} increases by 1, that is, i=i+1; if the cumulative value of abnormal conditions reaches the threshold, a fault alarm is issued and the detection ends;

S5: If the value of the sequence number i is less than or equal to n, return to step 3); if the value of the sequence number i is greater than n, then return to step 2) to enter the next detection cycle.

For example, the _{cumulative value C of the abnormal situation in the first time interval t 1} is 0, and the threshold is not reached, then the serial number i is increased by 1, and the serial number i=2; since the serial number i=2 is less than n(100), return to step 3) Analyze and judge the time interval t _2.

For example, the cumulative value C of abnormal conditions in the 39th time interval t ₃₉ is 1, and the threshold is not reached, then the serial number i is increased by 1, and the serial number i=40; since the serial number i=40 is less than n(100), return to step 3) Analyze and judge the time interval t _40.

For example, after the 69th time interval is detected sequentially, the cumulative value of abnormal conditions C=3, reaching the threshold C _max , and the controller 7 issues a fault alarm, for example, to remind the driver that the pressure of the urea solution in the SCR system fluctuates greatly. Failure; end of detection.

For example, in another embodiment, the time interval sequentially detected time interval t ₁ to t _100, the entire detection period T are all finished, and the abnormality detection period T is the entire accumulation value is smaller than the threshold value C _max, the increased index i 1. The serial number i=101; since the serial number i=101, which is greater than n(100), return to step 2) to enter the next detection cycle, and the cumulative value of abnormal conditions in the next detection cycle is reset to zero.

It should be understood that although this specification is described in accordance with the embodiments, not every embodiment only includes an independent technical solution. This narration in the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions of the feasible implementations of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementations or implementations made without departing from the technical spirit of the present invention All changes shall be included in the protection scope of the present invention.

Claims

A fault diagnosis method for SCR urea spraying device, which is characterized in that:

The fault diagnosis method includes the following steps:

Step 1): Obtain the pressure value of the urea solution in the outlet pipe of the SCR urea spraying device in real time;

Step 2): Define a detection period T, and divide one detection period T into n time intervals t i (t 1 , t 2 ...... t n ) according to time sequence; when the detection period T is initially The cumulative value of abnormal conditions is set to zero;

Step 3): t i sequentially urea solution and the corresponding pressure values are plotted in FIG box, and the box plot analysis, it is determined whether the time interval t i abnormal situation of the time interval; if abnormal In case, the cumulative value of abnormal conditions increases by 1, otherwise, the cumulative value of abnormal conditions does not increase;

In the step 3), the method for judging the abnormal situation is: obtaining the corresponding upper quartile and lower quartile according to the maximum pressure value and the minimum pressure value in the box chart, and calculating the The difference between the upper quartile and the lower quartile is counted as the interquartile difference of the time interval; the interquartile difference of the time interval is compared with the pre-measured standard interquartile difference, if If it is greater than the standard interquartile range, it is judged that there is an abnormal situation;

Step 4): If the abnormality cumulative value reaches a threshold value, a fault alarm, end detection; abnormality if the cumulative value does not reach the threshold value, the time interval T i of the number i is incremented by one;

Step 5): If the value of the serial number i is less than or equal to n, return to step 3); if the value of the serial number i is greater than n, return to step 2) to enter the next detection cycle.
The fault diagnosis method for SCR urea spraying device according to claim 1, characterized in that:

The numerical value of the standard interquartile range and the threshold value are obtained in advance through simulation analysis in the laboratory.
The fault diagnosis method for SCR urea spraying device according to claim 1, characterized in that:

In the step 1), the pressure value of the urea solution in the outlet pipe of the SCR urea spraying device is obtained in real time through a pressure sensor arranged on the outlet pipe of the SCR urea spraying device, and the data is transmitted to the control Device.