EGR (Exhaust Gas Recirculation) control method and system after failure of exhaust system

Abstract

The invention provides an EGR control method and system after an exhaust system breaks down, and belongs to the technical field of engine exhaust gas recirculation rate control. According to the method, after it is detected that a switch type oxygen sensor at the downstream of a catalyst of the exhaust system breaks down, different working conditions are divided, and target air and fuel gas and the corrected target EGR rate are determined based on the different working conditions; and EGR control is conducted according to the corrected target EGR rate. According to the method, the target EGR rate can be optimized based on improvement of emission and EGR rate control stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of engine exhaust gas recirculation rate control technology, and particularly relates to an EGR control method and system after exhaust system failure. BACKGROUND

[0002] Exhaust gas recirculation (EGR) takes exhaust gas from the exhaust system into the intake system. Studies have shown that the EGR system has certain advantages in improving emissions, reducing fuel consumption and improving anti-knock capacity. Low-pressure EGR takes gas after the turbine, so there is no loss of turbine efficiency, and it can use EGR under almost all working conditions, which is more significant for improving fuel efficiency. However, due to the low pressure difference, a large-diameter valve is needed to meet the flow requirements. In some working conditions, the opening of the mixing valve needs to be controlled to adjust the pressure at the outlet of the EGR valve, thereby improving the pressure difference on both sides of the EGR valve and improving the EGR rate. If the downstream switch-type oxygen sensor of the exhaust system catalyst fails, the target EGR rate before the failure is still controlled, which will cause the stability of the engine emissions and the EGR rate to deteriorate. SUMMARY

[0003] The present application aims to solve at least one of the technical problems existing in the prior art, and provides an EGR control method and system after exhaust system failure.

[0004] In a first aspect, the present application provides an EGR control method after exhaust system failure, including the following steps:

[0005] S100, after detecting that the switch-type oxygen sensor downstream of the exhaust system catalyst fails, different working conditions are divided, and the target air-fuel ratio and the corrected target EGR rate are determined based on different working conditions;

[0006] S200, EGR control is performed according to the corrected target EGR rate.

[0007] Further, the exhaust system includes components such as a switch oxygen sensor, a linear oxygen sensor, a catalyst, and a particulate filter.

[0008] Further, step S100 includes the following steps:

[0009] S110, before the end of the engine catalyst light-off air-fuel ratio control, the air-fuel ratio is maintained at the air-fuel ratio before the failure occurs; and after the end of the engine catalyst light-off air-fuel ratio control, the target air-fuel ratio is fixed unchanged, that is, the control target fuel equivalent ratio FEQR is 1;

[0010] S120, 1) in the first case, the corrected target EGR rate ;

[0011] 2) In the second case, the corrected target EGR rate wherein is a speed-load correction coefficient, is a correction coefficient based on an air-fuel ratio characteristic coefficient, is a target EGR rate self-learning correction coefficient;

[0012] 3) In other cases,

[0013] a) If transitioning from the second case to the first case, the corrected target EGR rate is:

[0014]

[0015] wherein is the target EGR rate of the previous sampling period, and the first value thereof is the target EGR rate at the last time of the second case; is the actual EGR rate of the previous sampling period, and the first value thereof is the actual EGR rate at the last time of the second case; is a decrement; is a first variation determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the previous sampling period;

[0016] b) If transitioning from the first case to the second case, the corrected target EGR rate is:

[0017]

[0018] wherein is an increment, = , is a default increment, is a target EGR rate self-learning correction coefficient of is a second variation determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the previous sampling period.

[0019] Further, the first case is that the linear oxygen sensor upstream of the catalyst is not activated, or the GPF requests active regeneration activation, or the engine requests to exit the engine idle closed-loop control.

[0020] Further, the second case is that all of the following conditions are met: a) not entering the scavenging working condition, b) the engine idle requests air path torque, c) the engine idle requests fire path torque, and d) the engine enters the idle closed-loop control.

[0021] Further, the updating method of the target EGR rate self-learning correction coefficient after the fault occurs is:

[0022] Air-fuel ratio characteristic coefficient The air-fuel ratio characteristic coefficient is accumulated to obtain an air-fuel ratio characteristic coefficient cumulative value wherein the time t=0 occurs at the first time when all the above conditions are satisfied, i.e., at each time when the conditions enter enable, the air-fuel ratio characteristic coefficient cumulative value is reset to zero The air-fuel ratio characteristic coefficient cumulative value is read in real time ,

[0023] (1) If the condition is not less than a first predetermined value A, wherein , is a first base value, and a correction coefficient is based on the mass flow rate of the intake air and the catalyst body temperature are jointly determined, then wherein is a target EGR rate self-learning correction coefficient updated last time.

[0024] Further, (2) if the condition is less than the first predetermined value A but not less than a second predetermined value B, wherein , is a second base value, then .

[0025] Further, (3) if the T1 time is less than the second predetermined value B but greater than 0, but is greater than a third predetermined value D, wherein , is a third base value, then .

[0026] Further, (4) if the T2 time is less than the second predetermined value B but greater than 0, but is greater than the third predetermined value D, then .

[0027] Further, (5) if the condition is less than the predetermined value -A, then .

[0028] Further, (6) if the condition is not less than the predetermined value -A but less than the predetermined value -B, then .

[0029] Further, (7) if the T1 time is not less than -B but less than 0, but is greater than the third predetermined value D, then .

[0030] Further, (8) if T2 time is not less than the second preset value B but less than 0, but is greater than the third preset value D, then .

[0031] Further, (9) in other cases, .

[0032] Further, the self-learning correction coefficient The self-learning method is as follows:

[0033] If the process of transitioning from the second case to the first case or if the process of transitioning from the first case to the second case:

[0034] (1) all appear greater than the preset value 0.1 within the continuous time T3, then , wherein is the self-learning correction coefficient updated last time ;

[0035] (2) all appear not greater than the preset value 0.01 within the continuous time T3, then ;

[0036] (3) in other cases, .

[0037] In a second aspect, an embodiment of the present application provides an EGR control system after exhaust system failure, comprising:

[0038] A determination module is configured to divide different working conditions after detecting that a switching oxygen sensor downstream of an exhaust system catalyst fails, and determine a target air-fuel ratio and a corrected target EGR rate based on different working conditions.

[0039] A control module is configured to perform EGR control according to the corrected target EGR rate.

[0040] The EGR control method and system provided by the present application can optimize the target EGR rate based on improving emissions and EGR rate control stability. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A flowchart of an exhaust system failure EGR control method provided by an embodiment of the present application is shown;

[0042] Figure 2 A structural diagram of an EGR control system after exhaust system failure is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0043] For those skilled in the art to better understand the technical solutions of the present application, the exemplary embodiments of the present application are described below in conjunction with the drawings, which include various details of the embodiments of the present application to help understanding, and should be considered only as exemplary. Therefore, those skilled in the art should realize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. Also, for the sake of clarity and conciseness, the description below omits the description of well-known functions and structures.

[0044] In the case of no conflict, each embodiment of the present application and each feature in the embodiments can be combined with each other.

[0045] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0046] The terms used herein are only used to describe specific embodiments, and are not intended to limit the present application. As used herein, the singular forms "a" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the terms "comprise" and / or "consist of, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The terms "connected" or "coupled" and / or similar terms are not limited to a physical or mechanical connection, but can include an electrical connection, whether direct or indirect.

[0047] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in a generally used dictionary should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present application, and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0048] The present application provides an EGR control method after exhaust system failure, i.e., target EGR rate setting after failure of a switching-type oxygen sensor downstream of an exhaust system catalyst. Figure 1 A flowchart of an EGR control method after exhaust system failure is provided for an embodiment of the present application, which includes the following steps:

[0049] S100, after detecting that the switch-type oxygen sensor downstream of the exhaust system catalyst fails, different working conditions are divided, and the target air-fuel ratio and the corrected target EGR rate are determined based on different working conditions.

[0050] In one embodiment, the exhaust system includes components: switch oxygen sensor, linear oxygen sensor, catalyst, GPF. Switch oxygen sensor: currently used for oxygen sensor after catalyst, can reflect the rich and lean degree of exhaust system, but cannot accurately reflect the rich and lean situation. Linear oxygen sensor: also known as wide-range oxygen sensor, accurately reflects the rich and lean situation of the exhaust system, as an oxygen sensor before the catalyst, as a key component of the closed-loop control of the fuel injection system. Catalyst: three-way catalyst converter (TWC) is an important component in modern engine management system, installed in the exhaust system of the vehicle, its working temperature reaches 300° or above, under the catalytic action of noble metals platinum, rhodium, palladium, cerium oxide can absorb and release oxygen in a specific environment, play the role of oxygen storage; can oxidize and reduce chemical reaction of CO, HC, NOx and other harmful gases generated by automobile combustion, convert into CO2, H2O, N2, thereby purifying automobile exhaust. GPF: particulate trap, a ceramic filter installed in the catalyst of the engine exhaust system, which can capture particulate emissions before they enter the atmosphere.

[0051] Assuming that the switch-type oxygen sensor downstream of the exhaust system catalyst fails, the target EGR rate before failure is , which can be determined by the prior art CN202011247319.6 "A method and system for calculating target EGR rate".

[0052] After the switch-type oxygen sensor detects a fault, since the switch-type oxygen sensor is arranged downstream of the catalyst, the main purpose is to control or estimate the catalyst oxygen storage capacity, and to diagnose the catalyst degradation. After the failure of the rear oxygen sensor, the accuracy of the catalyst oxygen storage capacity control or estimation and the catalyst degradation diagnosis cannot be performed. In order to avoid adverse effects on emissions, relevant control optimization is performed after the switch-type oxygen sensor detects a fault.

[0053] The oxygen concentration in the exhaust pipe is too low, which is called "over-concentration"; the oxygen concentration in the exhaust pipe is too high, which is called "over-dilution"; the concentration of air in the exhaust pipe is characterized by the inverse of the excess air coefficient , i.e. the fuel equivalence ratio .

[0054] The linear oxygen sensor reflects the actual , so setting the target air-fuel ratio can be achieved by setting the target , then the target , "actual fuel" refers to the actual amount of fuel entering the cylinder per unit time, "actual air" refers to the actual amount of fresh air entering the cylinder per unit time, "target fuel" refers to the target amount of fuel entering the cylinder per unit time, "target air" refers to the target amount of fresh air entering the cylinder per unit time, "ideal air" refers to the ideal amount of fresh air entering the cylinder per unit time, and "ideal fuel" refers to the ideal amount of fuel entering the cylinder per unit time. "Target" is not equal to "ideal", the target value can be actively changed according to the engine working condition, but the ideal value is determined by the oil product.

[0055] When the engine is cut off, 0; when "too rich", 1; when "too lean", 1; When equal to 1, the current ideal air-fuel ratio is equal to 1. When equal to 1, the ratio of the actual air quantity to the actual fuel quantity is equal to the ratio of the ideal air quantity to the ideal fuel quantity, and the ideal air-fuel ratio in the present example is 14.3.

[0056] In one embodiment, step S100 includes the following steps:

[0057] S110, before the end of the engine catalyst light-off air-fuel ratio control (see patent CN202010621851.3 for details ), the air-fuel ratio is maintained before the fault occurs; After the engine catalyst light-off air-fuel ratio control is over, the target air-fuel ratio is fixed and unchanged, that is, the control target fuel equivalent ratio FEQR is 1; Avoid causing the emission to deteriorate.

[0058] S120, 1) In the first case, the corrected target EGR rate ;

[0059] Specifically, the first case is that the linear oxygen sensor upstream of the catalyst is not activated, or the GPF requests active regeneration activation (as mentioned in the prior art patent CN201911303613.1 < Method for hierarchical control of active regeneration of particulate filter >) or the engine requests to exit the engine idle closed-loop control (as mentioned in the prior art patent CN202010584166.8 < Engine idle target speed control method >) after the idle closed-loop control.

[0060] 2) In the second case, the corrected target EGR rate , wherein is a speed-load correction coefficient, is a correction coefficient based on air-fuel ratio characteristics, is a target EGR rate self-learning correction coefficient;

[0061] Specifically, the second case is: a) not entering the scavenging working condition, i.e. the scavenging working condition mentioned in the patent CN202010484842.4 "Determination method of scavenging activation working condition of supercharged direct injection engine" is not allowed to be activated. b) The engine idle request air path torque (see CN202010266906.3 "Method for controlling engine idle control air path torque" for details) fluctuation range does not exceed the preset value, and the example takes ±10 Nm. c) The engine idle request fire path torque (see CN202010266419.7 "Method for controlling engine idle control fire path torque" for details) fluctuation range does not exceed the preset value, and the example takes ±10 Nm. d) The engine enters idle closed loop control.

[0062] After all the above conditions are met, the air-fuel ratio characteristic coefficient Optimize the target EGR rate, where is the target FEQR, is the actual FEQR. The greater, the less fuel in the cylinder, the more air, the easier to generate NOx, the greater the demand for EGR rate; on the contrary, the smaller the demand for EGR rate.

[0063] is the target EGR rate self-learning correction coefficient after the failure of the switching oxygen sensor occurs, and its default value is 0, which can be continuously self-learning and updated, and can be saved after the vehicle is powered off.

[0064] is a basic correction coefficient determined based on engine speed n and load rho (fresh air intake density into the cylinder), the higher the engine speed and the greater the engine load, the more likely the engine is to knock, in order to ensure that the engine can avoid real knock when the knock sensor fails, the basic correction coefficient determined based on speed and load is smaller, so the possibility of knock is lower. The purpose of reducing the EGR rate is to reserve space for the engine in the working condition prone to knock, and once the real knock occurs in the working condition prone to knock, the EGR rate can be increased to suppress the possibility of knock. The speed and load correction coefficient The corresponding values of engine speed n and load rho are determined by querying the following table.

[0065] Table 1 Corresponding relationship between speed and load correction coefficient and engine speed and load

[0066]

[0067] is based on the air-fuel ratio characteristic coefficient The determined correction coefficient. The correction coefficient based on the air-fuel ratio characteristic coefficient is determined by looking up the value corresponding to the air-fuel ratio characteristic coefficient in the following table.

[0068] Table 2 Correspondence between correction coefficient based on air-fuel ratio characteristic coefficient and air-fuel ratio characteristic coefficient

[0069] #timg# -0.2 -0.16 -0.12 -0.1 -0.05 0 0.05 0.1 0.12 0.16 0.2 #timg# 0.8 0.85 0.9 0.92 0.95 1 1.02 1.05 1.08 1.12 1.2

[0070] Target EGR rate self-learning correction coefficient after fault occurrence The updating method is:

[0071] The air-fuel ratio characteristic coefficient is accumulated to obtain an air-fuel ratio characteristic coefficient accumulated value , where the time t=0 occurs at the first time when all the above conditions are met, that is, at each time when the conditions enter to enable occurrence, the air-fuel ratio characteristic coefficient accumulated value is cleared to 0, and the air-fuel ratio characteristic coefficient accumulated value is read in real time ,

[0072] (1) If the following condition occurs is not less than a first preset value A, where , the first base value is 0.2 in this example, and the correction coefficient is determined based on the mass flow rate of the intake cylinder mixture and the catalyst body temperature together, which is mainly that the higher the mass flow rate of the intake cylinder mixture, the higher the catalyst body temperature, the more likely it is to produce NOx, in order to suppress emission deterioration and consider the control of EGR rate, therefore, when the mass flow rate of the intake cylinder mixture is higher and the catalyst body temperature is higher, the EGR rate needs to be improved to improve NOx. Based on the emission standard and the emission test result, the is calibrated so that it can still ensure that the emission meets the national emission standard after the switch oxygen sensor fails. Then , where is the target EGR rate self-learning correction coefficient updated last time.

[0073] (2) If the following condition occurs is less than the first preset value A but not less than a second preset value B, where . Where, the second base value is 0.1 in this example, then .

[0074] (3) If T1 time (0.1s in this example) is less than the second preset value B and greater than 0, but is greater than a third preset value D, where , the third base value​ The present example takes 0.1 s At this time, it is indicated that the air-fuel ratio fluctuation is large, and the generation of NOx is also avoided, and the EGR rate is appropriately increased.

[0075] (4) If the T2 time (the present example takes 0.2 s) is less than the second preset value B but greater than 0, but is greater than the third preset value D, wherein the third basic value The present example takes 0.1 s At this time, it is indicated that the air-fuel ratio fluctuation is large, and the generation of NOx is also avoided, and the EGR rate is appropriately increased.

[0076] (5) If the T1 time (the present example takes 0.1 s) is less than the preset value -A, then it is indicated that the air in the exhaust system is insufficient, and at this time, the EGR rate needs to be appropriately reduced to inhibit the generation of HC and other emissions.

[0077] (6) If the T1 time (the present example takes 0.1 s) is not less than the preset value -A but less than the preset value -B, then .

[0078] (7) If the T1 time (the present example takes 0.1 s) is not less than -B but less than 0, but is greater than the third preset value D, then At this time, it is indicated that the air-fuel ratio fluctuation is large, but the air-fuel ratio is still rich, and the EGR rate is appropriately reduced to avoid excessive generation of HC and other emissions in the exhaust system.

[0079] (8) If the T2 time (the present example takes 0.2 s) is not less than the second preset value B but less than 0, but is greater than the third preset value D, then At this time, it is indicated that the air-fuel ratio fluctuation is large, and the generation of NOx is also avoided, and the EGR rate is appropriately increased.

[0080] (9) In other cases, .

[0081] The above execution priorities are lower and lower, and each driving cycle is executed at most once.

[0082] 3) In other cases,

[0083] a) If it is transitioned from the second case to the first case, the corrected target EGR rate is:

[0084]

[0085] wherein is the target EGR rate of the last moment of the second case, and the first value of is the target EGR rate of the last moment of the second case; is the actual EGR rate of the last moment of the second case, and the first value of is the actual EGR rate of the last moment of the second case, is the decrement, and the value of the example is 0.03; is the first change amount determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period.

[0086] is the first change amount determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period is determined by querying the corresponding value of the difference between the target EGR rate and the actual EGR rate of the last sampling period through the following table.

[0087] Table 3 Corresponding relationship between the first change amount and the difference between the target EGR rate and the actual EGR rate of the last sampling period determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period

[0088] #timg# -0.1 -0.08 -0.06 -0.05 -0.03 -0.02 -0.01 #timg# 0.01 0.02 0.03 0.04 0.05 0.06 0.08

[0089] b) If the transition is from the first case to the second case, the corrected target EGR rate is:

[0090]

[0091] wherein is the increment, = , is the default increment, and the value of the example is 0.04, is the target EGR rate self-learning correction coefficient of , and the default value is 0, which can be continuously self-learned and updated, and can be saved after the vehicle is powered off; is the second change amount determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period.

[0092] is the second change amount determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period is determined by querying the corresponding value of the difference between the target EGR rate and the actual EGR rate of the last sampling period through the following table.

[0093] Table 4 Corresponding relationship between the second change amount and the difference between the target EGR rate and the actual EGR rate of the last sampling period determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate of the last sampling period

[0094] #timg# 0.01 0.02 0.03 0.05 0.08 0.08 0.1 #timg# 0.08 0.06 0.05 0.04 0.03 0.02 0.01

[0095] Self-learning correction coefficient The self-learning method is as follows:

[0096] If the process of transitioning from the second case to the first case or from the first case to the second case:

[0097] (1) If both of the following conditions are met within a continuous time T3 (0.5 in this example) greater than a preset value 0.1, then , wherein is the self-learning correction coefficient updated last time .

[0098] (2) If both of the following conditions are met within a continuous time T3, then .

[0099] (3) In other cases, .

[0100] After the update is completed, the new learning value is used again in the next driving cycle.

[0101] S200, EGR control is performed according to the corrected target EGR rate.

[0102] The embodiment of the application can optimize the target EGR rate based on improving emissions and EGR rate control stability.

[0103] The application also provides an EGR control system after exhaust system failure. Figure 2 The structure block diagram of an EGR control system after exhaust system failure provided by the embodiment of the application, the system comprises:

[0104] The determination module 11 is used for detecting that the switch-type oxygen sensor downstream of the exhaust system catalyst fails, dividing different working conditions, and determining the target air-fuel ratio and the corrected target EGR rate based on different working conditions;

[0105] The control module 12 performs EGR control according to the corrected target EGR rate.

[0106] Example embodiments have been disclosed herein and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. In some instances, it will be apparent to those skilled in the art that features, characteristics or / and elements described in connection with a particular embodiment can be used in conjunction with other embodiments unless otherwise explicitly stated. Accordingly, it will be understood that various changes in form and details can be made without departing from the scope of the present application as set forth in the appended claims.

Claims

1. A method for controlling EGR after an exhaust system failure, characterized in that: The following steps are involved: S100, after detecting a fault in a switch-type oxygen sensor downstream of a catalyst in the exhaust system, classifying different operating conditions and determining a target air / fuel ratio and a corrected target EGR rate based on the different operating conditions; S200: Perform EGR control according to the corrected target EGR rate.

2. The method according to claim 1, characterized in that The exhaust system includes the following components: switch oxygen sensor, linear oxygen sensor, catalyst, and particulate filter.

3. The method according to claim 2, characterized in that Step S100 includes the following steps: S110, before the engine catalyst light-off air-fuel ratio control ends, the air-fuel ratio is maintained at the air-fuel ratio before the fault occurs; after the engine catalyst light-off air-fuel ratio control ends, the target air-fuel ratio is fixed unchanged, that is, the target fuel equivalence ratio FEQR is controlled to 1; S120, 1) In the first case, the corrected target EGR rate ; 2) In the second case, the corrected target EGR rate ,in is the speed load correction factor, is the correction coefficient based on the air-fuel ratio characteristic coefficient, is the target EGR rate self-learning correction coefficient; 3) In other cases, a) If the transition from the second case to the first case occurs, the corrected target EGR rate is: in is the target EGR rate of the previous sampling period, and its first value is the target EGR rate at the last moment of the second case; is the actual EGR rate of the previous sampling period, and its first value is the actual EGR rate at the last moment of the second case; For reduction; Determining a first variation based on an absolute value of a difference between a target EGR rate and an actual EGR rate in a previous sampling period; b) If the transition from the first case to the second case occurs, the corrected target EGR rate is: in is the increment, = , is the default increment, for The target EGR rate self-learning correction coefficient, The second change amount is determined based on the absolute value of the difference between the target EGR rate and the actual EGR rate in the previous sampling period.

4. The method according to claim 3, characterized in that The first case is when the linear oxygen sensor upstream of the catalyst is not activated, or the GPF requests active regeneration activation or the engine requests to exit the engine idle closed-loop control.

5. The method according to claim 4, characterized in that The second case is when all of the following conditions are met: a) the engine does not enter the scavenging condition, b) the engine idle speed requests the gas circuit torque, c) the engine idle speed requests the fire circuit torque, and d) the engine enters the idle closed-loop control.

6. The method according to claim 5, characterized in that Target EGR rate self-learning correction coefficient after a fault occurs The update method is: Air-fuel ratio characteristic coefficient Accumulate and obtain the accumulated value of the air-fuel ratio characteristic coefficient , where t=0 occurs at the first moment when all the above conditions are met, that is, each time the condition enters the enable state, the air-fuel ratio characteristic coefficient is accumulated. Clear to 0 and read the accumulated value of the air-fuel ratio characteristic coefficient in real time , (1) If Not less than the first preset value A, where , is the first basic value, correction coefficient is based on the mass flow rate of the mixture entering the cylinder and catalyst body temperature Joint decision, ,in The target EGR rate self-learning correction coefficient updated in the last learning.

7. The method according to claim 6, characterized in that (2) If is less than the first preset value A but not less than the second preset value B, wherein , is the second basic value, then .

8. The method according to claim 7, characterized in that (3) If time T1 Less than the second preset value B is greater than 0, but is greater than a third preset value D, wherein , is the third basic value, then .

9. The method according to claim 8, characterized in that (4) If time T2 Less than the second preset value B is greater than 0, but is greater than the third preset value D, then .

10. The method according to claim 9, characterized in that (5) If Less than the preset value -A, then .

11. The method according to claim 10, characterized in that (6) If Not less than the preset value - A but less than the preset value - B, then .

12. The method according to claim 11, characterized in that (7) If time T1 Not less than -B but less than 0, but is greater than the third preset value D, then .

13. The method according to claim 12, characterized in that (8) If time T2 Not less than the second preset value B but less than 0, but is greater than the third preset value D, then .

14. The method according to claim 13, wherein: (9) In other cases, .

15. The method according to claim 14, characterized in that Self-learning correction coefficient The self-learning method is as follows: If there is a transition from the second situation to the first situation or if there is a transition from the first situation to the second situation: (1) If the value is greater than the preset value 0.1 for the continuous time T3, then ,in Self-learning correction coefficient updated for the last learning ; (2) If the value is not greater than the preset value 0.01 within the continuous time T3, then ; (3) In other cases, .

16. An EGR control system after an exhaust system failure, characterized in that: include: a determination module, configured to, upon detecting a fault in a switch-type oxygen sensor downstream of a catalyst in the exhaust system, classify different operating conditions and determine a target air / fuel ratio and a corrected target EGR rate based on the different operating conditions; The control module is configured to perform EGR control according to the corrected target EGR rate.

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