Control System and Strategy for Target Compensation of Oxygen Storage Percentage in Air-Fuel Ratio of Natural Gas Engine

Abstract

The present invention discloses a control system and strategy for target compensation of the air-fuel ratio oxygen storage percentage of a natural gas engine, which is implemented by using the control system as described above. The control strategy includes: when the natural gas engine is running, measuring the air-fuel ratio at the inlet and outlet of the three-way catalytic converter through the front oxygen sensor and the rear oxygen sensor; feeding back the rich and lean conditions of the air-fuel ratio control of the engine body through the measured value of the rear oxygen sensor; using the average value of the continuously measured rear oxygen concentration for N times in real time to query the ROL target compensation curve calibrated in the ECU, so as to obtain a ROL target compensation value to correct and calculate the ROL target value; and then comparing the corrected and calculated ROL target value with the actual ROL value, calculating the correction amount of the front oxygen concentration, and finally obtaining the front oxygen concentration target value. Thereby, the closed-loop speed of the air-fuel ratio based on the control of the oxygen storage percentage (ROL) can be greatly improved, and finally the control accuracy of the air-fuel ratio at the inlet of the catalytic converter can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of emission control strategies for natural gas engines, and in particular to a control system and strategy for target compensation of air-fuel ratio and oxygen storage percentage of natural gas engines. Background Art

[0002] At present, the mainstream technical route of National VI natural gas engines is equivalent + EGR (Exhaust Gas Recirculation, exhaust gas recirculation system) + TWC + route. The engine emissions are processed by a three-way catalytic converter (TWC). The air-fuel ratio control of the engine is crucial to the efficiency of the catalyst. If the air-fuel ratio is controlled to be rich, CH 4 and NH 3 will increase significantly. If the air-fuel ratio is controlled lean, NO x It will be too high. Only when the air-fuel ratio is controlled within a certain range can the conversion efficiency of the catalyst be maximized. The existing method is that the current strategy is to compare the actual oxygen storage percentage with the calibrated target oxygen storage percentage to output the deviation, and then perform rich or lean PI closed-loop control based on the deviation, output the front oxygen correction amount, and thus obtain the final front oxygen closed-loop target. When the rear oxygen concentration switches between rich and lean frequently, the oxygen storage percentage calculation may be inaccurate, resulting in inaccurate correction of the front oxygen concentration, which is not conducive to high-precision control of the air-fuel ratio, and ultimately causes the air-fuel ratio control at the catalyst inlet to deviate from the optimal conversion window, and the conversion efficiency of various pollutants in the exhaust gas decreases.

[0003] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a control system and strategy for target compensation of oxygen storage percentage of air-fuel ratio of natural gas engine, which can use ECU to monitor the post-oxygen concentration of catalyst in real time, and inquire the compensation strategy of oxygen storage percentage (ROL) target compensation value by calculating the average value of post-oxygen concentration through N consecutive post-oxygen concentration measurements, thereby greatly improving the air-fuel ratio closed-loop speed based on oxygen storage percentage (ROL) control, and finally improving the air-fuel ratio control accuracy of catalyst inlet.

[0005] To achieve the above object, the present invention provides a control system for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine, including an engine body, an EGR, a supercharger, a three-way catalytic converter, a front oxygen sensor, and a rear oxygen sensor; the engine body includes an intake side and an exhaust side; the EGR is connected between the pipelines on the intake side and the exhaust side of the engine body; the supercharger is arranged at the intake port of the intake side and the exhaust port of the exhaust side; the three-way catalytic converter is arranged at the exhaust port of the supercharger; the front oxygen sensor and the rear oxygen sensor are respectively arranged at the inlet and outlet positions of the three-way catalytic converter.

[0006] In a preferred embodiment, the control system for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes an intercooler and a throttle valve; the intercooler is arranged behind the supercharger on the intake side of the engine body; the throttle valve is arranged behind the intercooler on the intake side of the engine body; wherein air enters the engine body through the intake end of the supercharger, the intercooler, the throttle valve, and the intake side, and the exhaust gas after combustion is discharged into the atmosphere through the exhaust side, the exhaust end of the supercharger, the front oxygen sensor, the three-way catalytic converter, and the rear oxygen sensor, and a part of the exhaust gas enters the engine body again for circulation after passing through the EGR and the intake side from the exhaust side.

[0007] To achieve the above object, the present invention also provides a control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine, which is implemented by using the control system as described above. The control strategy includes: when the natural gas engine is running, the air-fuel ratios at the inlet and outlet of the three-way catalytic converter are measured by the front oxygen sensor and the rear oxygen sensor; the lean and rich conditions of the air-fuel ratio control of the engine body are fed back through the measured value of the rear oxygen sensor; the average value of the continuously measured N times of the rear oxygen concentration is used to query the ROL target compensation curve calibrated in the ECU, so as to obtain a ROL target compensation value to correct and calculate the ROL target value; and then the corrected and calculated ROL target value is compared with the actual ROL value to calculate the correction amount of the front oxygen concentration, and finally the front oxygen concentration target value is obtained.

[0008] In a preferred embodiment, the control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes that the calculation of the average value of the continuously measured N times of the rear oxygen concentration includes the following formula:

[0009] EGOlam_avg=(EGOlamx_1+EGOlamx_2+EGOlamx_3···+EGOlamx_n) / n;

[0010] Where EGOlam is the real-time rear oxygen concentration value, EGOlam_avg is the average value of the rear oxygen concentration for n times, and n is a positive natural number.

[0011] In a preferred embodiment, the control strategy for target compensation of the oxygen storage percentage in the air-fuel ratio of a natural gas engine further includes the calculation of the ROL target value, which includes the following formula:

[0012] ROL_Tgt = ROL_T_Def + ROL_T_Offs;

[0013] Where ROL_Tgt is the ROL target value, ROL_T_Def is the initial set value of the ROL target, and ROL_T_Offs is the ROL target compensation value.

[0014] In a preferred embodiment, the control strategy for target compensation of the oxygen storage percentage in the air-fuel ratio of a natural gas engine further includes the calculation of the target value of the front oxygen concentration, which includes the following formula:

[0015] Lam_Tgt = Lam + Lam_T_Offs;

[0016] Where Lam_Tgt is the target value of the front oxygen concentration, Lam is the real-time front oxygen concentration value, and Lam_T_Offs is the front oxygen concentration correction amount.

[0017] In a preferred embodiment, the control strategy for target compensation of the oxygen storage percentage in the air-fuel ratio of a natural gas engine further includes the calculation of the front oxygen concentration correction amount, which includes the following formula:

[0018] Lam_T_Offs = (ROL_Tgt - ROL) * k;

[0019] Where ROL is the actual ROL value and k is the calculation correlation coefficient.

[0020] Compared with the prior art, the control system and strategy for target compensation of the oxygen storage percentage in the air-fuel ratio of the natural gas engine of the present invention have the following beneficial effects: This strategy uses the ECU to monitor the rear oxygen concentration of the catalytic converter in real time, and calculates the average value of the rear oxygen concentration through continuous measurement of N times of the rear oxygen concentration to query the compensation strategy of the oxygen storage percentage (ROL) target compensation value, thereby greatly improving the air-fuel ratio closed-loop speed based on the control of the oxygen storage percentage (ROL), and ultimately improving the control accuracy of the air-fuel ratio at the inlet of the catalytic converter. This strategy avoids the overly frequent switching of the front oxygen concentration correction when the rear oxygen concentration changes greatly between rich and lean under transient conditions, greatly improves the air-fuel ratio closed-loop speed based on ROL control, thereby improving the control accuracy of the air-fuel ratio at the inlet of the catalytic converter, making the air-fuel ratio control within the optimal conversion window of the catalytic converter, and ensuring that the catalytic converter is in a state of high conversion efficiency. Description of the Drawings

[0021] Figure 1 is a schematic diagram of the component layout of the control system according to an embodiment of the present invention;

[0022] Figure 2It is a schematic flow diagram of a control strategy according to an embodiment of the present invention.

[0023] Main reference numerals description:

[0024] 1 - Engine body, 2 - Intake side, 3 - Exhaust side, 4 - EGR, 5 - Throttle valve, 6 - Intercooler, 7 - Turbocharger, 8 - Three-way catalytic converter, 9 - Front oxygen sensor, 10 - Rear oxygen sensor. Specific embodiments

[0025] The following combines the accompanying drawings to describe in detail the specific embodiments of the present invention. However, it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0026] Unless otherwise clearly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "having" etc. will be understood to include the stated elements or components, without excluding other elements or other components.

[0027] As Figure 1 shown, a control system for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to a preferred embodiment of the present invention includes an engine body 1, an EGR 4, a turbocharger 7, a three-way catalytic converter 8, a front oxygen sensor 9, and a rear oxygen sensor 10; the engine body 1 includes an intake side 2 and an exhaust side 3; the EGR 4 is communicatively connected between the pipelines of the intake side 2 and the exhaust side 3 of the engine body 1; the turbocharger 7 is provided at the intake port of the intake side 2 and the exhaust port of the exhaust side 3; the three-way catalytic converter 8 is provided at the exhaust port of the turbocharger 7; the front oxygen sensor 9 and the rear oxygen sensor 10 are respectively provided at the inlet and outlet positions of the three-way catalytic converter 8.

[0028] In some embodiments, the control system for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes an intercooler 6 and a throttle valve 5; the intercooler 6 is provided at the rear of the turbocharger 7 on the intake side 2 of the engine body; the throttle valve 5 is provided at the rear of the intercooler 6 on the intake side 2 of the engine body; wherein air enters the engine body 1 through the intake end of the turbocharger 7, the intercooler 6, the throttle valve 5, and the intake side 2, and the burned exhaust gas is discharged into the atmosphere through the exhaust side 3, the exhaust end of the turbocharger 7, the front oxygen sensor 9, the three-way catalytic converter 8, and the rear oxygen sensor 10, and a part of the exhaust gas enters the engine body 1 for circulation after passing through the EGR 4 and the intake side 2 from the exhaust side 3.

[0029] As Figure 2As shown, a control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to a preferred embodiment of the present invention is implemented by using the control system as described above. The control strategy includes: when the natural gas engine is running, the air-fuel ratio at the inlet and outlet of the three-way catalytic converter 8 is measured by the front oxygen sensor 9 and the rear oxygen sensor 10; the richness and leaness of the air-fuel ratio control of the engine body 1 are fed back through the measured value of the rear oxygen sensor 10; the average value of the continuously measured rear oxygen concentration for N times is used to query the ROL target compensation curve calibrated in the ECU, so as to obtain a ROL target compensation value to correct and calculate the ROL target value; and then, according to the corrected and calculated ROL target value, it is compared with the actual ROL value, the correction amount of the front oxygen concentration is calculated, and finally the front oxygen concentration target value is obtained.

[0030] In some embodiments, the control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes that the calculation of the average value of the rear oxygen concentration for N times includes the following formula:

[0031] EGOlam_avg=(EGOlamx_1+EGOlamx_2+EGOlamx_3···+EGOlamx_n) / n;

[0032] Where EGOlam is the real-time rear oxygen concentration value, EGOlam_avg is the average value of the rear oxygen concentration for n times, and n is a positive natural number.

[0033] In some embodiments, the control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes that the calculation of the ROL target value includes the following formula:

[0034] ROL_Tgt=ROL_T_Def+ROL_T_Offs; where ROL_Tgt is the ROL target value, ROL_T_Def is the initial set value of the ROL target, and ROL_T_Offs is the ROL target compensation value.

[0035] In some embodiments, the control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes that the calculation of the front oxygen concentration target value includes the following formula:

[0036] Lam_Tgt=Lam+Lam_T_Offs; where Lam_Tgt is the front oxygen concentration target value, Lam is the real-time front oxygen concentration value, and Lam_T_Offs is the front oxygen concentration correction amount.

[0037] In some embodiments, the control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine further includes that the calculation of the front oxygen concentration correction amount includes the following formula:

[0038] Lam_T_Offs=(ROL_Tgt-ROL)*k; ROL is the actual ROL value and k is the calculated correlation coefficient.

[0039] In some embodiments, the principle of the control strategy of the target compensation of the air-fuel ratio oxygen storage percentage of the natural gas engine of the present invention is roughly as follows:

[0040] The present invention is a control strategy for target compensation of the air-fuel ratio oxygen storage percentage (hereinafter referred to as ROL) of a natural gas engine. Figure 1 As shown, it is the layout and working status of the natural gas engine. When the engine is operating normally, the exhaust gas generated by the combustion of the engine body 1 is purified by the catalyst and then discharged into the atmosphere. The conversion efficiency of TWC is the most important factor to ensure that the engine emissions meet the standards. The National VI gas engine after-treatment TWC has a high conversion efficiency for the main emissions. At the same time, the air-fuel ratio measured by the oxygen sensor 9 before the catalyst inlet is one of the most important factors affecting the TWC conversion efficiency. Therefore, ensuring high-precision control of the air-fuel ratio at the catalyst inlet plays a vital role in engine and vehicle emissions.

[0041] When the natural gas engine is running, the air-fuel ratio at the inlet and outlet of the catalyst is measured by the front oxygen sensor 9 and the rear oxygen sensor 10, and the rich and lean situation of the engine air-fuel ratio control is fed back through the measurement value of the rear oxygen sensor 10. This strategy uses the average value of the continuous N-time rear oxygen concentration measured in real time (N can be calibrated by itself) to query the ROL target compensation curve calibrated in the ECU, so as to obtain a ROL target compensation value to correct the calculated ROL target value, and then compare the corrected calculated ROL target value with the actual ROL value to calculate the front oxygen concentration correction amount, and finally obtain the front oxygen concentration target value.

[0042] In summary, the control system and strategy of the target compensation of the oxygen storage percentage of the air-fuel ratio of the natural gas engine of the present invention have the following advantages: This strategy uses the ECU to monitor the post-oxygen concentration of the catalyst in real time, and calculates the average value of the post-oxygen concentration through continuous measurement of N times to query the compensation strategy of the target compensation value of the oxygen storage percentage (ROL), thereby greatly improving the air-fuel ratio closed-loop speed based on the oxygen storage percentage (ROL) control, and finally improving the air-fuel ratio control accuracy at the inlet of the catalyst. This strategy avoids the excessively frequent switching of the pre-oxygen concentration concentration correction when the post-oxygen concentration changes greatly under transient conditions, greatly improves the air-fuel ratio closed-loop speed based on ROL control, thereby improving the air-fuel ratio control accuracy at the inlet of the catalyst, making the air-fuel ratio control within the optimal conversion window of the catalyst, and ensuring that the catalyst is in a state of high conversion efficiency.

[0043] The foregoing description of the specific exemplary embodiments of the present invention is for purposes of illustration and exemplification. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many modifications and variations are possible in light of the above teaching. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the invention and its practical applications, so that those skilled in the art can implement and utilize the various different exemplary embodiments of the invention, as well as various different selections and modifications. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine, which utilizes a control system for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine. Characterized in that, The control system includes: An engine body, which includes an intake side and an exhaust side; EGR, which is connected and arranged between the pipelines on the intake side and the exhaust side of the engine body; A supercharger, which is arranged at the intake port of the intake side and the exhaust port of the exhaust side; A three-way catalytic converter, which is arranged at the exhaust port of the supercharger; and A front oxygen sensor and a rear oxygen sensor, which are respectively arranged at the inlet and outlet positions of the three-way catalytic converter; The control strategy includes: When the natural gas engine is running, measure the air-fuel ratio at the inlet and outlet of the three-way catalytic converter through the front oxygen sensor and the rear oxygen sensor; Feedback the lean-rich condition of the air-fuel ratio control of the engine body through the measured value of the rear oxygen sensor; Use the average value of the continuously measured rear oxygen concentration for N times to query the ROL target compensation curve calibrated in the ECU, so as to obtain a ROL target compensation value to correct and calculate the ROL target value; and Then compare the corrected and calculated ROL target value with the actual ROL value, calculate the correction amount of the front oxygen concentration, and finally obtain the front oxygen concentration target value.

2. The control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to claim 1, Characterized in that, The control system further includes: An intercooler, which is arranged at the rear of the supercharger on the intake side of the engine body; and A throttle valve, which is arranged at the rear of the intercooler on the intake side of the engine body; Wherein air enters the engine body through the intake end of the supercharger, the intercooler, the throttle valve and the intake side, and the burned exhaust gas is discharged into the atmosphere through the exhaust side, the exhaust end of the supercharger, the front oxygen sensor, the three-way catalytic converter and the rear oxygen sensor, and part of the exhaust gas enters the engine body again for circulation through the EGR and the intake side from the exhaust side.

3. The control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to claim 1, Characterized in that, It further includes that the calculation of the average value of the rear oxygen concentration for N times includes the following formula: ； Where EGOlam is the real-time rear oxygen concentration value, EGOlam_avg is the average value of the rear oxygen concentration for n times, and n is a positive natural number.

4. The control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to claim 1, Characterized in that, It further includes that the calculation of the ROL target value includes the following formula: ； Where ROL_Tgt is the ROL target value, ROL_T_Def is the initial set value of the ROL target, and ROL_T_Offs is the ROL target compensation value.

5. The control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to claim 4, Characterized in that, It further includes that the calculation of the front oxygen concentration target value includes the following formula: ； Where Lam_Tgt is the target value of the front oxygen concentration, Lam is the real-time front oxygen concentration value, and Lam_T_Offs is the correction amount of the front oxygen concentration.

6. The control strategy for target compensation of the oxygen storage percentage of the air-fuel ratio of a natural gas engine according to claim 5, characterized in that it further includes that the calculation of the front oxygen concentration correction amount includes the following formula: ； Where ROL is the actual ROL value and k is the calculation correlation coefficient.

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