Method for operating exhaust gas recirculation system, engine and vehicle

Abstract

The present invention relates to a method for operating an exhaust gas recirculation system of an engine, the exhaust gas recirculation system comprising an actual EGR flow calculation module for calculating an actual EGR flow; the method comprises the steps that first EGR mass flow calculated in a first calculation mode is obtained; and a second EGR mass flow calculated in a second calculation mode is obtained, the deviation between the first EGR mass flow and the second EGR mass flow is obtained, and the actual EGR flow calculation module is diagnosed based on the deviation. The invention also relates to an engine and a vehicle comprising the engine.

Description

Technical Field

[0001] The present invention relates to a method for operating an exhaust gas recirculation (EGR) system of an engine, an engine having an exhaust gas recirculation system and a vehicle having an engine. Background Art

[0002] In recent years, with the improvement of environmental protection requirements, emission regulations have become increasingly stringent on nitrogen oxide emissions. In addition, the regulations have added mandatory requirements for emission supervision of vehicles or machinery, such as using a portable emission test system (PEMS) for emission supervision. The exhaust gas recirculation system is one of the effective means to control nitrogen oxide emissions. By fully mixing the recirculated exhaust gas with fresh air before entering the cylinder, the specific heat capacity of the gas in the cylinder can be reduced, thereby inhibiting the generation of nitrogen oxides.

[0003] In the prior art, an engine with an exhaust gas recirculation system performs direct or indirect closed-loop control or feedback control on the EGR flow rate (e.g., mass flow rate) or the EGR rate. The control accuracy of the EGR flow rate or the EGR rate directly determines the nitrogen oxide emission level and / or emission durability of the engine, and determines the consistency level of nitrogen oxide emissions between different engine products of the same model, etc.

[0004] As a prerequisite for EGR flow control or EGR rate closed-loop control, the actual EGR flow needs to be accurately determined. However, since the recirculated exhaust gas comes from the high-temperature gas generated by combustion in the engine cylinder, it is usually impossible to directly measure the EGR flow by installing a flow sensor in the EGR pipeline. Generally, the EGR flow is determined indirectly by calculation methods. Existing EGR flow calculation methods generally require determining the EGR passage area through the opening (or opening position) of the EGR valve (exhaust gas recirculation valve).

[0005] However, due to the inevitable dimensional deviations in the manufacturing process of the EGR valve, the flow capacity of different EGR valves will vary. It is difficult to adapt the unified EGR flow calculation method to the specific conditions of each mass-produced engine. The deviation between the calculated EGR flow and the actual EGR flow may vary from engine to engine, which in turn causes differences in the consistency of NOx emissions between mass-produced engines.

[0006] In addition, as the engine runs longer, the flow capacity (or passage area) of the EGR line decreases. The main reason is that dirt accumulates at the EGR valve. The main components of the dirt are engine combustion products, namely hydrocarbons and soot. In addition, some end users may mistakenly use high-sulfur fuel that does not meet the requirements, and the sulfides produced by its combustion will make the EGR valve more prone to dirt. The dirt accumulated at the EGR valve includes carbon deposits and coking, which is still a difficult problem to solve.

[0007] For example, the prior art knows methods for calculating EGR flow based on the compressible gas equation or the Venturi tube principle, and methods for calculating EGR flow using the MAF (intake air flow sensor) before the supercharger compressor or the PMF sensor after the supercharger intercooler. In these methods, sensors such as EGR pressure, temperature, and valve position are also used to calculate the EGR flow. However, the inaccurate identification of the EGR passage area caused by the above reasons, and the resulting deviation in EGR flow calculation, cannot be diagnosed or overcome, which will deteriorate the emission consistency and durability of the engine.

[0008] The present invention is directed to solving at least one of the above problems of the prior art as well as other problems. Summary of the invention

[0009] According to a first aspect of the invention, a method for operating an exhaust gas recirculation system of an engine is proposed,

[0010] The exhaust gas recirculation system includes an actual EGR flow calculation module, which is used to calculate the actual EGR flow;

[0011] The method comprises:

[0012] Obtaining a first EGR mass flow calculated in a first calculation manner;

[0013] The second EGR mass flow calculated by the second calculation method is obtained,

[0014] Obtain the deviation between the first EGR mass flow rate and the second EGR mass flow rate,

[0015] It is characterized in that

[0016] The actual EGR flow rate calculation module is diagnosed based on the deviation.

[0017] The above method achieves the following advantages: by providing redundant feedback for EGR flow closed-loop control through different EGR flow calculation methods, timely and effective diagnosis and adjustment of the actual EGR flow calculation module can be achieved. Therefore, the calculation accuracy of EGR mass flow can be maintained in a low-cost manner, thereby improving the consistency and durability of engine emissions. In addition, the influence of dirt on the control at the EGR valve is avoided through the calculation method, thereby extending the service life and maintenance cycle of the EGR valve.

[0018] The invention also relates to an engine and a vehicle comprising the engine. The engine has an exhaust gas recirculation system and a control device, which is configured to be able to perform the above method.

[0019] The vehicle according to the present invention should be understood as a vehicle in a broad sense, which may be a transportation vehicle, a construction machine, an agricultural machine, or other machine that can be equipped with an engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a first embodiment of an exhaust gas recirculation system is shown.

[0021] Figure 2 A schematic diagram of a second embodiment of an exhaust gas recirculation system is shown.

[0022] Figure 3 A flow chart of a method according to the present invention for operating an exhaust gas recirculation system is shown.

[0023] Figure 4 A flow chart showing a modification strategy subroutine according to the present invention.

[0024] Figure 5 A set of corresponding relationship collection data between the EGR valve opening and the corresponding EGR valve passage area is shown.

[0025] Reference numerals list

[0026] 1. Exhaust gas turbocharger compressor

[0027] 2. Charge air intercooler

[0028] 3. Intake throttle valve

[0029] 4. Engine cylinder

[0030] 5. Exhaust turbocharger turbine

[0031] 6. EGR cooler

[0032] 7. EGR valve

[0033] 8. Air Inlet

[0034] 9. Exhaust port

[0035] 11. Charge air intercooler outlet temperature sensor

[0036] 12. Intake duct temperature sensor

[0037] 13. Intake pressure sensor

[0038] 14. EGR valve inlet temperature sensor

[0039] 15. EGR valve inlet pressure sensor

[0040] 16. EGR valve outlet pressure sensor

[0041] 17. EGR valve position sensor

[0042] 18. EGR outlet temperature sensor DETAILED DESCRIPTION

[0043] The following will describe the method, engine and vehicle for operating the exhaust gas recirculation system of the engine according to the present invention with reference to the accompanying drawings and through specific embodiments. However, the exemplary embodiments can be implemented in various forms and should not be understood as being limited to the embodiments described herein; on the contrary, these embodiments are provided to make the present invention comprehensive and complete and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0044] Figure 1 A schematic diagram of a first embodiment of an exhaust gas recirculation system for an engine is shown. Figure 1 As shown, the engine includes a cylinder 4 for fuel combustion. Fresh air is delivered to the cylinder 4 through the compressor 1 of the exhaust turbocharger, the charge air intercooler 2, and the air intake port 8. An intake throttle valve 3 is provided in the intake duct, and the flow rate of fresh air entering the cylinder 4 is controlled by means of the opening of the intake throttle valve 3. The exhaust gas generated by the combustion in the engine cylinder 4 is discharged through the exhaust port 9. A part of the exhausted exhaust gas enters the exhaust after-treatment system (not shown) through the turbine 5 of the exhaust turbocharger, and is discharged into the atmosphere after exhaust after-treatment. The other part of the exhaust gas (EGR part) is sent back to the cylinder through the exhaust gas recirculation system. As shown Figure 1 As shown, the exhaust gas recirculation system includes an EGR pipeline, an EGR cooler 6 and an EGR valve 7. In this embodiment, the exhaust gas is introduced into the EGR pipeline upstream of the turbine 5, passes through the EGR valve 7 and the EGR cooler 6 in sequence into the intake passage, and then enters the cylinder 4 through the intake port 8 after merging with the fresh air. Here, the amount of exhaust gas to be recirculated is controlled by the opening of the EGR valve 7. Here, the EGR valve 7 is arranged upstream of the EGR cooler 6, so it is also called a hot end EGR valve.

[0045] like Figure 1 As shown, a charge air intercooler outlet temperature sensor 11 is arranged at the outlet of the charge air intercooler 2. An intake duct temperature sensor 12 and an intake duct pressure sensor 13 are arranged in the intake duct. Here, the intake duct temperature sensor 12 and the intake duct pressure sensor 13 are arranged downstream of the intake throttle valve 3 and downstream of the recirculation exhaust gas confluence point. Therefore, the intake duct temperature sensor 12 and the intake duct pressure sensor 13 measure the temperature and pressure of the recirculation exhaust gas and fresh air mixture. An EGR valve inlet temperature sensor 14 (for measuring the exhaust gas temperature T at the EGR valve inlet) is arranged at the inlet of the EGR valve 7. egrin) and the EGR valve inlet pressure sensor 15 (used to measure the exhaust pressure P at the EGR valve inlet egrin At the outlet of the EGR valve, an EGR valve outlet pressure sensor 16 is provided (for measuring the exhaust pressure P at the outlet of the EGR valve). egrout An EGR outlet temperature sensor 18 is provided at the outlet of the EGR cooler 6 (for measuring the temperature at the outlet of the EGR cooler 6, i.e., the EGR outlet temperature). In addition, an EGR valve position sensor 17 is provided to obtain the opening of the EGR valve.

[0046] Figure 2 A schematic diagram of a second embodiment of an exhaust gas recirculation system is shown. Figure 1 The difference of the first embodiment shown is that the EGR cooler 6 is arranged upstream, not downstream, of the EGR valve 7. Therefore, the EGR valve 7 is also called a cold-end EGR valve. Accordingly, the EGR valve outlet pressure sensor 16 and the EGR outlet temperature sensor 18 are both arranged at the outlet of the EGR valve 7. And the EGR valve inlet temperature sensor 14 and the EGR valve inlet pressure sensor 15 are arranged between the EGR cooler 6 and the EGR valve 7.

[0047] During the operation of the exhaust gas recirculation system, closed-loop control, i.e., feedback control, is performed. In this case, it is necessary to know the theoretical EGR flow rate and the actual EGR flow rate, and to perform feedback regulation, such as PID regulation, based on the deviation between the theoretical EGR flow rate and the actual EGR flow rate. As mentioned above, the actual EGR flow rate is generally obtained by calculation. Therefore, the exhaust gas recirculation system also includes an actual EGR flow rate calculation module for calculating the actual EGR flow rate.

[0048] As mentioned above, due to the size deviation and dirt of the EGR valve, there will be a deviation between the calculated EGR flow and the actual EGR flow. And this deviation may increase over time. Therefore, it is necessary to diagnose or monitor the actual EGR flow calculation module in the exhaust gas recirculation system control, and adjust or update the calculation module when the above deviation is too large.

[0049] Below, refer to Figure 3 A method for operating an exhaust gas recirculation system is described, wherein an actual EGR flow calculation module is diagnosed. First, in step S01, it is determined whether an enabling condition, or also called a triggering condition, is met. Under the enabling condition, the engine operates at a high speed and in a steady state. The enabling condition may include at least one of the following conditions:

[0050] The ambient pressure is greater than an ambient pressure threshold. Preferably, the ambient pressure threshold may be set to 81 kPa, for example;

[0051] The ambient temperature is lower than an ambient temperature threshold. Preferably, the ambient temperature threshold can be set to 38 degrees, for example;

[0052] The EGR valve opening is greater than an EGR valve opening threshold and / or the EGR valve is not stuck. Preferably, the EGR valve opening threshold can be set to 5%, for example;

[0053] The engine speed is higher than an engine speed threshold, preferably, the engine speed threshold may be set to 1300 rpm, for example;

[0054] During the measurement time of the engine speed fluctuation, the engine speed fluctuation amplitude does not exceed the engine speed fluctuation amplitude threshold, and the engine speed fluctuation measurement time exceeds the engine speed fluctuation measurement time threshold. Preferably, the engine speed fluctuation amplitude threshold can be set to 20 rpm, for example, and the engine speed fluctuation measurement time threshold can be set to 120 seconds, for example;

[0055] The engine fuel injection amount is higher than the engine fuel injection amount threshold. Preferably, the engine fuel injection amount threshold can be set to 40 mm 3 / str;

[0056] During the measurement time of the engine fuel injection amount fluctuation, the fluctuation amplitude of the engine fuel injection amount does not exceed the engine fuel injection amount fluctuation amplitude threshold, and the measurement time of the engine fuel injection amount fluctuation exceeds the engine fuel injection amount fluctuation measurement time threshold. Preferably, the engine fuel injection amount fluctuation amplitude threshold can be set to 2 mm, for example. 3 / str, the engine fuel injection amount fluctuation measurement time threshold can be set to 120 seconds, for example;

[0057] Especially during the measurement time when the engine fuel injection amount fluctuates, the intake throttle valve 3 is not in a working state; because when the intake throttle valve 3 is working, the temperature of the EGR of the supercharged air intercooler outlet temperature sensor 11, the intake duct temperature sensor 12 and the EGR outlet temperature sensor 18 is affected, and thus the deviation of the calculation results that depend on these temperature sensors increases.

[0058] During the measurement time of the temperature sensor fluctuation, the fluctuation amplitude of the temperature measurement values ​​of the charge air intercooler outlet temperature sensor 11, the intake duct temperature sensor 12, and the EGR outlet temperature sensor 18 is lower than the temperature measurement value fluctuation amplitude threshold, and the measurement time of the temperature sensor fluctuation exceeds the temperature sensor fluctuation measurement time threshold. Preferably, the temperature measurement value fluctuation amplitude threshold can be set to 1 degree Celsius, for example, and the temperature sensor fluctuation measurement time threshold can be set to 90 seconds, for example.

[0059] The difference between the temperature measurement value of the EGR outlet temperature sensor 18 and the temperature measurement value of the intake passage temperature sensor 12 is higher than the temperature difference threshold value. Preferably, the temperature difference threshold value can be set to 85 degrees Celsius, for example.

[0060] If it is determined in step S01 that the enabling condition is not satisfied, then the process returns to step S01 and the determination is repeated. Here, the process may return to step S01 after a certain time delay, or may return to step S01 again after a certain triggering event to start the determination.

[0061] If it is determined in step S01 that the method enabling condition is satisfied, then the first EGR mass flow M calculated in the first calculation method is obtained. egr1 (Step S02 ). Here, “obtain” should be understood to include: obtaining by calculation or directly obtaining by acquiring data from other devices.

[0062] In the first calculation method, the first EGR mass flow rate M is calculated based on the Bernoulli equation and the gas state equation. egr1 For example, the first EGR mass flow rate M is calculated based on the following formula: egr1 :

[0063]

[0064] in,

[0065] M egr1 represents a first EGR mass flow calculated by a first calculation method;

[0066] C represents a flow coefficient, which can be determined, for example, by experiments;

[0067] A represents the EGR passage area, and the EGR passage area is positively correlated with the EGR valve opening position. Preferably, corresponding relationship data for determining the EGR passage area based on the EGR valve opening position is stored. The corresponding relationship data is, for example, a functional relationship, a characteristic curve, or a lookup table. Here, based on the stored corresponding relationship data, the EGR passage area is determined using the EGR valve opening position obtained from the EGR valve position sensor 17. The corresponding relationship data is stored in a non-volatile memory, and the data will not be lost even if the engine loses power.

[0068] P egroin represents the EGR valve inlet pressure, for example, obtained by the measurement value of the EGR valve inlet pressure sensor 15;

[0069] P egrout represents the EGR valve outlet pressure, for example, obtained by the measurement value of the EGR valve outlet pressure sensor 16;

[0070] R represents the gas constant (also called the "universal or ideal gas constant");

[0071] T rgrin represents the EGR valve inlet temperature, which is obtained from, for example, a measurement value of the EGR valve inlet temperature sensor 14 .

[0072] Preferably, in the normal working state of the exhaust gas recirculation system, the first EGR mass flow calculated by the first calculation method is used as the actual EGR flow. Therefore, in this step, the first EGR mass flow can be obtained by calculation in the above manner, or the first EGR mass flow can be directly obtained from the actual EGR flow calculation module.

[0073] Then, in step S03, the second EGR mass flow M calculated by the second calculation method is obtained. egr2 Here, the following formula is used based on the fresh air gas temperature T 1 , the mixed gas temperature at the inlet duct T 2 , EGR outlet temperature T 8 And the total air intake volume M 总 To calculate M egr2 :

[0074]

[0075] in,

[0076] M egr2 represents a second EGR mass flow calculated by a second calculation method;

[0077] T 2 represents the mixed gas temperature at the intake duct, for example, obtained from the measurement value of the intake duct temperature sensor 12;

[0078] T 1 represents the fresh air gas temperature, which is obtained, for example, from a measurement value of the charge air intercooler outlet temperature sensor 11 .

[0079] T 8 represents the EGR outlet temperature, for example, obtained from the measurement value of the EGR outlet temperature sensor 18 (see Figure 1 and Figure 2 );

[0080] M 总 Indicates the total intake air volume, which is calculated based on the readings of the pressure and temperature sensors located at the engine intake duct. 总 The calculation method of is known in the prior art and will not be described in detail here.

[0081] Since the temperature sensor has poor transient response to the measured object, the second calculation method can only achieve high accuracy when the measured temperature is stable for a certain period of time. Therefore, when the exhaust gas recirculation system works normally, only the second EGR mass flow calculated by the second calculation method is used as an auxiliary parameter.

[0082] Then, in step S04, the first EGR mass flow rate M is obtained. egr1 and the second EGR mass flow rate M egr2 In this embodiment, the deviation can be, for example, the mass flow deviation rate ΔM egr1 (|M egr1 -M egr2 | / M egr1 In step S05, the mass flow deviation rate ΔM is obtained. egr1 The first deviation rate threshold is compared with the second deviation rate threshold, respectively. The first deviation rate threshold is smaller than the second deviation rate threshold.

[0083] If the mass flow deviation rate ΔM egr1 If the actual EGR flow rate is less than the first deviation rate threshold (S06), it is considered that the calculation method (ie, the first calculation method) in the actual EGR flow rate calculation module does not have excessive deviation, and thus it is determined that the actual EGR flow rate calculation module does not need to be adjusted. Here, the method routine ends.

[0084] If the mass flow deviation rate ΔM egr1 If the actual EGR rate is greater than or equal to the first deviation rate threshold but less than the second deviation rate threshold (S07), the first countermeasure is taken (S08). In the first countermeasure, the actual EGR rate is increased by continuously increasing the EGR valve opening until the second EGR mass flow rate M egr2 is equal to the theoretical EGR mass flow rate (i.e., the set EGR mass flow rate requirement value), and the second EGR mass flow rate M is adopted egr2 Instead of the first EGR mass flow M egr1 It is input into the EGR flow closed-loop control as the actual EGR mass flow. Here, M egr1 With M egr2 The relative size relationship between them is because the corresponding relationship between the EGR valve opening and the passage area is not corrected here.

[0085] If the mass flow deviation rate ΔM egr1If the error value is greater than the second deviation rate threshold (S07), it is considered that the main calculation method of the EGR mass flow has a large deviation and should be corrected. Here, the second countermeasure (S09-S10) is taken. In the second countermeasure, first, the count value fail_count of the error counter is increased, for example, the count value is increased by 1 in each ECU logic operation clock. When the count value fail_count of the error counter is greater than the threshold, the EGR flow low fault code is activated and the correction strategy is triggered. In this correction strategy, the correspondence between the EGR valve opening and the passage area is corrected. Generally, the correspondence between the original EGR valve opening and the passage area is covered by the updated correspondence between the EGR valve opening and the passage area. Preferably, the fail_count threshold can be set to 100,000, for example. The accumulated fail_count in a key cycle will be cleared only when the engine is stopped and the above fault code is not activated. If a new EGR valve is replaced during engine repair and maintenance, the engine diagnostic tool is used to restore the unified and default calibration value of the ECU. The above mentioned EGR flow low fault code is cancelled.

[0086] Refer to the following Figure 4 To illustrate the correction strategy for correcting the correspondence between the EGR valve opening and the passage area. In this correction strategy, a certain number of engine steady-state operating points are executed or found. Here, "finding" a certain number of engine steady-state operating points means: during the operation of the vehicle, randomly finding steady-state operating points that meet the conditions. That is to say, when the steady-state operating points appear, they are utilized. "Executing" a certain number of engine steady-state operating points means: controlling the parasitic load of the vehicle so that the engine works at a steady-state operating point that meets the conditions. In the case of "execution", the correction strategy is automatically activated after the engine is powered on again after shutdown. At this time, the machine cannot perform external work and is suitable for achieving the engine steady-state operating point. The "certain number" refers to a predetermined number, for example, it can be specified as "6" or more.

[0087] Here, each of the certain number of engine steady-state operating points may be a specifically specified operating point (e.g., a specific fuel injection amount, etc.), but may also be an operating point that is considered to meet the requirements as long as certain conditions are met. The "engine steady-state operating point" may be, for example, an operating point that meets the above-mentioned enabling conditions or triggering conditions.

[0088] In the specific implementation correction strategy, first, execute or find an engine steady-state operating point (S901). Then, for each engine steady-state operating point, continuously change the EGR valve opening, and obtain the corresponding EGR valve passage area for each EGR valve opening (S902). Here, the EGR valve position sensor 17 is used to obtain the EGR valve opening. The second EGR mass flow M is calculated using the above formula 2 egr2 Assuming the first EGR mass flow rate M egr1 Equal to the second EGR mass flow rate M egr2 , and based on the first EGR mass flow M egr1 , the EGR passage area A is calculated using the above formula 1. Thus, in other words, at each EGR valve opening, a data pair consisting of the EGR valve opening and the corresponding EGR valve passage area is obtained, and a data pair set is obtained for all EGR valve openings of an engine steady-state operating point. For all engine steady-state operating points, the same number of data pair sets as the operating points are obtained.

[0089] Then, it is determined whether the amount of data obtained is sufficient (S903), that is, whether the EGR valve opening has been continuously changed for sufficient engine steady-state operating points and the corresponding EGR valve passage area has been obtained. Here, for example, it can be determined whether the number of engine steady-state operating points that have been executed or found meets the quantity requirement, such as whether 6 operating points have been reached.

[0090] If it is determined in step S903 that the amount of data obtained is sufficient, data filtering is performed (S904). In data filtering, for example, the average value and standard deviation of the corresponding EGR valve passage area obtained at each EGR valve opening can be calculated. If the difference between the calculated value of the EGR valve passage area and the average value significantly exceeds the standard deviation, for example, greater than twice the standard deviation, the value is identified as an abnormal value and is filtered out. Of course, any data filtering method known in the prior art can also be used.

[0091] Then, for each EGR valve opening, the average value of the EGR valve passage area is calculated as the updated EGR valve passage area value (S905). Thus, a set of corresponding relationship collection data between the EGR valve opening and the corresponding EGR valve passage area can be obtained (see Figure 5 ). Each EGR valve opening (%) corresponds to an EGR valve passage area. Of course, the new corresponding relationship collection data may not be as follows. Figure 5 The diagram is not in the form of a look-up table as shown, but rather in the form of a functional relationship or a characteristic curve, for example.

[0092] Next, the corresponding relationship acquisition data is used to update (or overwrite) the stored relationship data for determining the EGR passage area based on the EGR valve opening position (S906).

[0093] Although the above steps are shown in a serial manner in the accompanying drawings, it will be appreciated by those skilled in the art that these steps do not necessarily have to be performed in a serial manner. Some of the steps may be performed in parallel, for example, steps S02 and S03 may be performed in parallel or in a reverse order. Based on the accompanying drawings and the methods shown, those skilled in the art may understand other embodiments not shown or described herein without departing from the scope of the present invention.

[0094] Industrial Applicability

[0095] The working method of the exhaust gas recirculation system is described below. When the exhaust gas recirculation system of the engine is working, the first EGR mass flow rate M is calculated by the first calculation method mentioned above. egr1 and use it as the actual EGR mass flow rate in EGR closed-loop control.

[0096] At this time, it is determined whether the method enabling condition is met. If the enabling condition is met, the first EGR mass flow M is obtained. egr1 And further obtain the second EGR mass flow M calculated by the second calculation method egr2 Then, the first EGR mass flow rate M is obtained egr1 and the second EGR mass flow M egr2 The mass flow rate deviation rate ΔM egr1 .

[0097] If the mass flow deviation rate ΔM egr1 If the mass flow rate deviation rate ΔM is less than the first deviation rate threshold, no countermeasures are required. egr1 If the actual EGR rate is greater than or equal to the first deviation rate threshold but less than the second deviation rate threshold (S07), the actual EGR rate is increased by continuously increasing the EGR valve opening until the second EGR mass flow rate M egr2 is equal to the set EGR mass flow demand value, and the second EGR mass flow M is adopted egr2 Instead of the first EGR mass flow M egr1 The actual EGR mass flow rate is input into the EGR flow closed-loop control. egr1 If it is greater than the second deviation rate threshold, the EGR flow low fault code will be activated after a certain counting time and the correction strategy will be triggered.

[0098] In the correction strategy, the corresponding relationship between the new EGR valve opening and the EGR valve passage area is obtained, and the data is collected and used to update the actual EGR calculation module.

[0099] The method according to the invention for operating an exhaust gas recirculation system has the following advantages:

[0100] 1. Different EGR flow calculation methods are used to realize different EGR flow virtual sensors, providing redundant feedback for EGR flow closed-loop control, such as PID control. Therefore, different methods can be used to diagnose and adjust the actual EGR flow calculation module, and the effectiveness and timeliness of diagnosis and adjustment are improved.

[0101] 2. Throughout the life cycle of the engine, the first and second calculation methods can be used to diagnose the actual EGR flow calculation module and make corrections when necessary. Thus, the calculation accuracy of the EGR mass flow can be maintained, thereby improving the engine emission consistency and durability.

[0102] 3. It is not necessary to add a compressor front air flow sensor in the fresh air intake pipeline, which is lower in cost.

[0103] 4. Through the diagnosis and update of the actual EGR flow calculation module, the influence of dirt on the control of the EGR valve is avoided through calculation, thus extending the service life and maintenance cycle of the EGR valve, thereby reducing user costs and improving product competitiveness.

[0104] It is obvious that various modifications and variations may be made to the embodiments disclosed above without departing from the scope or spirit of the invention for those skilled in the art. Other embodiments of the invention will be apparent to those skilled in the art from the practice of the invention disclosed in this specification. This specification and the examples disclosed therein should be considered to be illustrative only.

Claims

1. A method for operating an exhaust gas recirculation system of an engine, The exhaust gas recirculation system includes an actual EGR flow calculation module, which is used to calculate the actual EGR flow; The method comprises: Obtaining a first EGR mass flow calculated in a first calculation manner; The second EGR mass flow calculated by the second calculation method is obtained, Obtain the deviation between the first EGR mass flow rate and the second EGR mass flow rate, It is characterized in that The actual EGR flow rate calculation module is diagnosed based on the deviation.

2. The method according to claim 1, characterized in that The method further includes determining whether an enabling condition is met, The enabling condition includes at least one of the following conditions: The environmental pressure is greater than the environmental pressure threshold; The ambient temperature is lower than the ambient temperature threshold; The EGR valve opening is greater than the EGR valve opening threshold; EGR valve is not stuck; The engine speed is above the engine speed threshold; During the measurement time of the engine speed fluctuation, the engine speed fluctuation amplitude does not exceed the engine speed fluctuation amplitude threshold, and the engine speed fluctuation measurement time exceeds the engine speed fluctuation measurement time threshold; The engine fuel injection amount is higher than the engine fuel injection amount threshold; During the measurement time of the engine fuel injection amount fluctuation, the fluctuation amplitude of the engine fuel injection amount does not exceed the engine fuel injection amount fluctuation amplitude threshold, and the measurement time of the engine fuel injection amount fluctuation exceeds the engine fuel injection amount fluctuation measurement time threshold; The intake throttle valve is not in working condition; During the measurement time of the temperature sensor fluctuation, the fluctuation amplitudes of the temperature measurement values ​​of the charge air intercooler outlet temperature sensor, the intake duct temperature sensor, and the EGR outlet temperature sensor are respectively lower than the temperature measurement value fluctuation amplitude threshold, and the measurement time of the temperature sensor fluctuation exceeds the temperature sensor fluctuation measurement time threshold; The difference between the temperature measurement value of the EGR outlet temperature sensor and the temperature measurement value of the intake passage temperature sensor is greater than a temperature difference threshold.

3. The method according to claim 1, characterized in that: The obtaining of the first EGR mass flow rate calculated in the first calculation method includes: calculating the first EGR mass flow rate M based on the Bernoulli equation and the gas state equation egr1 .

4. The method according to claim 3, characterized in that The obtaining of the first EGR mass flow rate calculated in the first calculation method includes: calculating the first EGR mass flow rate M based on the following formula: egr1 : in, M egr1 represents the first EGR mass flow rate; C represents the flow coefficient; A represents the EGR passage area; P egrin Indicates the EGR valve inlet pressure; P egrout Indicates the EGR valve outlet pressure; R represents the gas constant; T egrin Indicates the EGR valve inlet temperature.

5. The method according to claim 4, characterized in that The EGR passage area A is obtained by the EGR valve opening position based on the stored corresponding relationship data, and the corresponding relationship data is a functional relationship or a characteristic curve or a lookup table that can determine the passage area A based on the EGR valve opening position.

6. The method according to claim 1, characterized in that The second EGR mass flow rate calculated in the second calculation method includes: calculating the second EGR mass flow rate M based on the fresh air gas temperature, the mixed gas temperature at the intake passage, the EGR outlet temperature and the total intake air volume. egr2 .

7. The method according to claim 6, characterized in that The obtaining of the second EGR mass flow rate calculated in the second calculation method includes: calculating the second EGR mass flow rate M based on the following formula: egr2 : M egr2 represents the second EGR mass flow rate; T2 represents the mixed gas temperature at the intake port; T1 represents the fresh air gas temperature; T8 represents the EGR outlet temperature; M 总 Indicates the total air intake.

8. The method according to claim 1, characterized in that The deviation between the first EGR mass flow rate and the second EGR mass flow rate is based on the first EGR mass flow rate M obtained by the following formula egr1 and the second EGR mass flow M egr2 The mass flow rate deviation rate ΔM egr1 : |M egr1 -M egr2 | / M egr1 Among them, ΔM egr1 Indicates the mass flow deviation rate; M egr1 represents the first EGR mass flow rate; M egr2 represents the second EGR mass flow rate.

9. The method according to claim 8, characterized in that Diagnosing the actual EGR flow calculation module based on the deviation includes: The mass flow deviation rate ΔM egr1 Compare with a first deviation rate threshold and a second deviation rate threshold respectively, wherein the first deviation rate threshold is less than the second deviation rate threshold; The mass flow rate deviation rate ΔM egr1 When the deviation rate is less than the first deviation rate threshold, it is determined that the actual EGR flow calculation module is operating normally and no countermeasures are taken; The mass flow rate deviation rate ΔM egr1 When the deviation rate is greater than or equal to the first deviation rate threshold but less than the second deviation rate threshold, it is determined to take the first response measure; The mass flow rate deviation rate ΔM egr1 When the deviation rate is greater than the second deviation rate threshold, it is determined to take the second countermeasure.

10. The method according to claim 9, characterized in that The first countermeasure includes: increasing the EGR valve opening until the second EGR mass flow M egr2 Equal to the theoretical EGR mass flow rate, the second EGR mass flow rate M egr2 Used as the actual EGR mass flow rate for closed-loop EGR control.

11. The method according to claim 9, characterized in that The second countermeasure includes: activating a fault code and / or triggering a correction strategy.

12. The method according to claim 11, characterized in that The second countermeasure includes: activating the fault code and / or triggering the correction strategy only when the count value of the error counter reaches the count threshold, wherein the mass flow deviation rate ΔM egr1 When the error rate is greater than the second deviation rate threshold, the count value of the error counter is increased by 1 in each ECU logic operation clock.

13. The method according to claim 11, characterized in that The correction strategies include: Execute or find a certain number of engine steady-state operating points; For each engine steady-state operating point, the EGR valve opening is continuously changed to obtain data on the corresponding relationship between the EGR valve opening and the corresponding EGR valve passage area; The actual EGR flow calculation module is corrected by collecting data using the corresponding relationship.

14. The method according to claim 13, characterized in that The data collected to obtain the corresponding relationship between the EGR valve opening and the corresponding EGR valve passage area include: Get the EGR valve opening; Obtaining a second EGR mass flow calculated in a second calculation manner; Assuming the first EGR mass flow rate M egr1 Equal to the second EGR mass flow rate M egr2 , and based on the first EGR mass flow M egr1 , use the first calculation method to infer the EGR passage area.

15. The method according to claim 13, characterized in that The correction strategies include: The engine steady-state operating point is the engine operating point that meets the enabling conditions. The enabling condition includes at least one of the following conditions: The environmental pressure is greater than the environmental pressure threshold; The ambient temperature is lower than the ambient temperature threshold; The EGR valve opening is greater than the EGR valve opening threshold; EGR valve is not stuck; The engine speed is above the engine speed threshold; During the measurement time of the engine speed fluctuation, the engine speed fluctuation amplitude does not exceed the engine speed fluctuation amplitude threshold, and the engine speed fluctuation measurement time exceeds the engine speed fluctuation measurement time threshold; The engine fuel injection amount is higher than the engine fuel injection amount threshold; During the measurement time of the engine fuel injection amount fluctuation, the fluctuation amplitude of the engine fuel injection amount does not exceed the engine fuel injection amount fluctuation amplitude threshold, and the measurement time of the engine fuel injection amount fluctuation exceeds the engine fuel injection amount fluctuation measurement time threshold; The intake throttle valve is not in working condition; During the measurement time of the temperature sensor fluctuation, the fluctuation amplitudes of the temperature measurement values ​​of the charge air intercooler outlet temperature sensor, the intake duct temperature sensor, and the EGR outlet temperature sensor are respectively lower than the temperature measurement value fluctuation amplitude threshold, and the measurement time of the temperature sensor fluctuation exceeds the temperature sensor fluctuation measurement time threshold; The difference between the temperature measurement value of the EGR outlet temperature sensor and the temperature measurement value of the intake passage temperature sensor is greater than a temperature difference threshold.

16. The method according to claim 13, characterized in that Using the corresponding relationship to collect data to correct the actual EGR flow calculation module includes: The stored corresponding relationship data is updated using the corresponding relationship acquisition data, wherein the corresponding relationship data is a functional relationship or a characteristic curve or a lookup table that can determine the passage area A based on the EGR valve opening position.

17. The method according to claim 16, characterized in that Updating the stored corresponding relationship data using the corresponding relationship acquisition data includes: The correspondence acquisition data is used to overwrite the stored correspondence data after filtering and / or averaging.

18. An engine having an exhaust gas recirculation system and a control device, the control device being configured to be able to perform the method according to any one of claims 1 to 17.

19. A vehicle having an engine according to claim 18.

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