A natural gas engine EGR flow closed-loop control system and control method

Abstract

The present invention discloses a closed-loop EGR flow control system and control method for a natural gas engine. The control system includes: a controller for determining an EGR demand flow rate based on actual engine operating conditions; a controller for obtaining the pressure of an air and gas mixture detected by an intake pressure sensor; or, alternatively, for determining the pressure of an air and gas mixture based on the EGR demand flow rate, a threshold flow rate, the maximum opening of an EGR valve, the actual opening of the EGR valve, the gas flow rate, and the fresh air flow rate; a controller for determining an actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of gases in the cylinder, the pressure-to-flow conversion slope, the gas flow rate, and the fresh air flow rate; a controller for determining an EGR flow rate correction value based on the obtained actual EGR flow rate and the EGR demand flow rate; and a controller for adjusting the EGR valve opening based on the EGR flow rate correction value so that the actual EGR flow rate matches the EGR demand flow rate, thereby achieving closed-loop control of the EGR flow rate. The present invention can achieve precise control of the EGR flow rate in two ways.

Description

Technical Field

[0001] The present invention relates to the field of engine technology, and in particular to an EGR flow closed-loop control system and a control method for a natural gas engine. Background Art

[0002] Compared to diesel engines of the same displacement, natural gas engines offer similar power performance and significant environmental advantages, making them more compliant with increasingly stringent emissions regulations. Recognizing this trend, leading engine manufacturers both domestically and internationally have launched natural gas engine models. The electronic control system for natural gas engines primarily includes air path control, gas flow control, ignition control, and torque control.

[0003] In natural gas engines, the introduction of appropriate EGR flow can effectively disrupt the combustion environment within the engine, significantly reducing tail NOx concentrations and suppressing knock. Therefore, precise control of EGR flow is crucial. However, current EGR flow control is mostly based on an open-loop velocity-density method using an intake pressure sensor, and there is no fail-safe solution. Summary of the Invention

[0004] The present invention provides a natural gas engine EGR flow closed-loop control system and control method, which can achieve precise control of the EGR flow in two ways.

[0005] According to one aspect of the present invention, a natural gas engine EGR flow closed-loop control system is provided, comprising:

[0006] Intake air flow sensor, mixer, intake air pressure sensor, cylinder, EGR valve, EGR valve opening sensor and controller;

[0007] An intake air flow sensor is provided on the air pipeline, a first end of the mixer is connected to the air pipeline, and a second end of the mixer is connected to the gas pipeline; a third end of the mixer is connected to a first end of an intake air pressure sensor via a mixed gas pipeline, a second end of the intake air pressure sensor is connected to a first end of a cylinder, and a second end of the cylinder is connected to an exhaust gas pipeline; the third end of the mixer is also connected to a first end of an EGR valve via a mixed gas pipeline, a second end of the EGR valve is connected to a first end of an EGR valve opening sensor, and a second end of the EGR valve opening sensor is connected to an exhaust gas pipeline; the mixer is used to mix air and gas; the intake air flow sensor is used to detect a fresh air flow; the intake air pressure sensor is used to detect a pressure of a mixed gas of air and gas; and the EGR valve opening sensor is used to detect an actual opening of the EGR valve;

[0008] The controller is electrically connected to the intake air flow sensor, the intake air pressure sensor and the EGR valve respectively;

[0009] The controller is used to determine the EGR required flow rate according to the actual operating conditions of the engine;

[0010] The controller is used to obtain the pressure of the air and gas mixture detected by the intake pressure sensor; alternatively, the controller is used to determine the pressure of the air and gas mixture based on the EGR demand flow rate, the threshold flow rate, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow rate, and the fresh air flow rate; the controller is used to determine the actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the pressure-flow conversion slope, the gas flow rate, and the fresh air flow rate;

[0011] The controller is used to determine the EGR flow correction value based on the obtained EGR actual flow and EGR required flow; and adjust the opening of the EGR valve according to the EGR flow correction value so that the EGR actual flow reaches the EGR required flow, thereby realizing EGR flow closed-loop control.

[0012] Optionally, the actual EGR flow rate is:

[0013] EGR_Ms=(Map-Ofs_P_Cly)*Fac_P_Ms-Full_Ms-Air_Ms

[0014] Among them, EGR_Ms is the actual EGR flow rate, Map is the pressure of the air and gas mixture, Ofs_P_Cly is the partial pressure of the gas in the cylinder, Fac_P_Ms is the conversion slope of pressure and flow rate, Full_Ms is the gas flow rate, and Air_Ms is the fresh air flow rate.

[0015] Optionally, the natural gas engine EGR flow closed-loop control system also includes:

[0016] A throttle valve is provided on the air pipeline, a first end of the throttle valve is connected to the intake air flow sensor; a second end of the throttle valve is connected to the first end of the mixer through the air pipeline; and a controller is electrically connected to the throttle valve;

[0017] The controller is used to determine the fresh air demand according to the driver's required torque; the controller is used to control the throttle valve opening after obtaining the fresh air flow so that the fresh air flow reaches the fresh air demand;

[0018] The controller is used to calculate the gas flow rate based on the fresh air flow rate, equivalent air-fuel ratio and required excess air coefficient setting value.

[0019] Optionally, the controller is configured to determine an estimated EGR flow rate according to an actual opening of the EGR valve when the EGR demand flow rate is less than or equal to a threshold flow rate, and determine a pressure of the air and gas mixture according to the estimated EGR flow rate, the gas flow rate, and the fresh air flow rate;

[0020] The controller is used to determine the EGR estimated flow rate based on the actual opening of the EGR valve when the EGR demand flow rate is greater than the threshold flow rate, and determine the EGR additional flow rate value based on the EGR estimated flow rate, the threshold flow rate and the maximum opening of the EGR valve; and determine the pressure of the air and gas mixture based on the EGR additional flow rate value, the threshold flow rate, the gas flow rate and the fresh air flow rate.

[0021] Optionally, the controller is used to sum the EGR estimated flow, gas flow and fresh air flow when the EGR demand flow is less than or equal to the threshold flow, and then integrate and accumulate the pressure effect produced by the summed total flow through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

[0022] Optionally, the controller is used to determine the EGR estimated flow rate based on the actual opening of the EGR valve and the threshold opening based on the threshold flow rate when the EGR demand flow rate is greater than the threshold flow rate; determine the EGR maximum flow rate based on the maximum opening of the EGR valve; determine the EGR additional flow value based on the threshold flow rate, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve and the EGR maximum flow rate; after summing the EGR estimated flow rate, the EGR additional flow value, the gas flow rate and the fresh air flow rate, integrate and accumulate the pressure effect of the summed total flow rate through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

[0023] Optionally, the controller is used to determine the EGR additional flow value by interpolation calculation based on the threshold flow, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve and the EGR maximum flow.

[0024] Optionally, the natural gas engine EGR flow closed-loop control system also includes:

[0025] Boost pressure sensor and turbocharger, the boost pressure sensor is located in the air pipe on the side of the intake flow sensor away from the throttle valve, the turbocharger is located in the air pipe on the side of the boost pressure sensor away from the intake flow sensor, the boost pressure sensor is connected to the intake flow sensor; the turbocharger is connected to the boost pressure sensor; the turbocharger is used to increase the intake amount of fresh air; the boost pressure sensor is used to detect the boost pressure.

[0026] According to another aspect of the present invention, a natural gas engine EGR flow closed-loop control method is provided. The natural gas engine EGR flow closed-loop control system includes:

[0027] Intake air flow sensor, mixer, intake air pressure sensor, cylinder, EGR valve, EGR valve opening sensor and controller;

[0028] An intake air flow sensor is provided on the air pipeline, a first end of the mixer is connected to the air pipeline, and a second end of the mixer is connected to the gas pipeline; a third end of the mixer is connected to a first end of an intake air pressure sensor via a mixed gas pipeline, a second end of the intake air pressure sensor is connected to a first end of a cylinder, and a second end of the cylinder is connected to an exhaust gas pipeline; the third end of the mixer is also connected to a first end of an EGR valve via a mixed gas pipeline, a second end of the EGR valve is connected to a first end of an EGR valve opening sensor, and a second end of the EGR valve opening sensor is connected to an exhaust gas pipeline; the mixer is used to mix air and gas; the intake air flow sensor is used to detect a fresh air flow; the intake air pressure sensor is used to detect a pressure of a mixed gas of air and gas; and the EGR valve opening sensor is used to detect an actual opening of the EGR valve;

[0029] The controller is electrically connected to the intake air flow sensor, the intake air pressure sensor and the EGR valve respectively;

[0030] The closed-loop control method for EGR flow in a natural gas engine includes:

[0031] The controller determines the EGR required flow rate based on the actual engine operating conditions;

[0032] The controller obtains the pressure of the air and gas mixture detected by the intake pressure sensor; or the controller determines the pressure of the air and gas mixture based on the EGR demand flow, the threshold flow, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow, and the fresh air flow;

[0033] The controller determines the actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the conversion slope of pressure and flow, the gas flow rate and the fresh air flow rate;

[0034] The controller determines the EGR flow correction value based on the obtained EGR actual flow and EGR required flow; adjusts the opening of the EGR valve according to the EGR flow correction value so that the EGR actual flow reaches the EGR required flow, thereby realizing EGR flow closed-loop control.

[0035] The technical solution of the embodiment of the present invention provides a natural gas engine EGR flow closed-loop control system comprising: an intake air flow sensor, a mixer, an intake air pressure sensor, a cylinder, an EGR valve, an EGR valve opening sensor and a controller; the mixer is used to mix air and gas; the intake air flow sensor is used to detect the fresh air flow; the intake air pressure sensor is used to detect the pressure of the air and gas mixture; the controller is electrically connected to the intake air flow sensor, the intake air pressure sensor and the EGR valve respectively; the controller is used to determine the EGR required flow according to the actual working conditions of the engine; the controller is used to obtain the pressure of the air and gas mixture detected by the intake air pressure sensor; or The controller is used to determine the pressure of the air and gas mixture based on the EGR demand flow, threshold flow, maximum opening of the EGR valve, actual opening of the EGR valve, gas flow, and fresh air flow; the controller is used to determine the actual EGR flow based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the pressure-flow conversion slope, gas flow, and fresh air flow; the controller is used to determine the EGR flow correction value based on the obtained actual EGR flow and the EGR demand flow; the opening of the EGR valve is adjusted according to the EGR flow correction value so that the actual EGR flow reaches the EGR demand flow, thereby realizing closed-loop control of the EGR flow. In the embodiment of the present invention, when the intake pressure sensor fails, there is still an alternative solution to determine the pressure of the air and gas mixture. The pressure of the air and gas mixture is determined by two methods to achieve precise control of the EGR flow.

[0036] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 This is a schematic structural diagram of a natural gas engine EGR flow closed-loop control system provided by the first embodiment of the present invention;

[0039] Figure 2 This is a flow chart of a natural gas engine EGR flow closed-loop control method provided by the second embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] Example 1

[0043] The embodiment of the present invention provides a natural gas engine EGR flow closed-loop control system. Figure 1 This is a schematic diagram of a closed-loop control system for EGR flow in a natural gas engine provided by the first embodiment of the present invention. Figure 1 , including: an intake air flow sensor 10, a mixer 20, an intake air pressure sensor 30, a cylinder 40, an EGR valve 50, an EGR valve opening sensor 100 and a controller; the intake air flow sensor 10 is arranged on the air pipeline, the first end of the mixer 20 is connected to the air pipeline, and the second end of the mixer 20 is connected to the gas pipeline; the third end of the mixer 20 is connected to the first end of the intake air pressure sensor 30 through the mixed gas pipeline, the second end of the intake air pressure sensor is connected to the first end of the cylinder 40, and the second end of the cylinder 40 is connected to the exhaust gas pipeline ; The third end of the mixer 20 is also connected to the first end of the EGR valve 50 through the mixed gas pipeline, the second end of the EGR valve 50 is connected to the first end of the EGR valve opening sensor 100, and the second end of the EGR valve opening sensor 100 is connected to the exhaust gas pipeline; the mixer 20 is used to mix air and gas; the intake air flow sensor 10 is used to detect the fresh air flow; the intake air pressure sensor 30 is used to detect the pressure of the air and gas mixture; the controller is electrically connected to the intake air flow sensor 10, the intake air pressure sensor 30 and the EGR valve 50 respectively.

[0044] The controller is used to determine the EGR required flow rate according to the actual operating conditions of the engine; the controller is used to obtain the pressure of the air and gas mixture detected by the intake pressure sensor 30; or, the controller is used to determine the pressure of the air and gas mixture according to the EGR required flow rate, the threshold flow rate, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow rate and the fresh air flow rate; the EGR valve opening sensor 100 is used to detect the actual opening of the EGR valve 50;.

[0045] The controller is used to determine the actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the conversion slope of pressure and flow, the gas flow rate and the fresh air flow rate; the controller is used to determine the EGR flow rate correction value based on the obtained EGR actual flow rate and the EGR required flow rate; and adjust the opening of the EGR valve 50 based on the EGR flow rate correction value so that the actual EGR flow rate reaches the EGR required flow rate, thereby realizing EGR flow closed-loop control.

[0046] The controller is not in Figure 1 As shown in Figure 2 . In a natural gas engine, EGR valve 50 recirculates exhaust gas from the exhaust pipe, allowing it to re-enter cylinder 40 for combustion, thereby reducing exhaust nitrogen oxide (NOx) concentration and suppressing knock. The controller determines the required EGR flow rate based on the actual engine operating conditions. Experiments can be used to calibrate the required EGR flow rate under different operating conditions. If the engine is experiencing knock in cylinder 40 and requires engine cooling, or if combustion in cylinder 40 is sustained under high-temperature, oxygen-rich conditions, generating significant amounts of nitrogen oxides, the EGR flow rate can be determined based on the calibrated values ​​for these two operating conditions.

[0047] Specifically, in the current working cycle, the controller can directly determine the actual EGR flow rate based on the pressure of the air and gas mixture detected by the intake pressure sensor 10, the gas partial pressure in the cylinder, the pressure-flow conversion slope, the gas flow rate and the fresh air flow rate. The actual EGR flow rate is the actual exhaust gas flow passing through the EGR valve; the gas partial pressure in the cylinder and the pressure-flow conversion slope are calibration values ​​obtained by calibrating the relationship between the intake flow rate and the intake pressure through bench tests.

[0048] If the intake pressure sensor 30 fails, the controller determines the pressure of the air-gas mixture based on the EGR demand flow rate, the threshold flow rate, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow rate, and the fresh air flow rate. The controller then determines the actual EGR flow rate based on the determined pressure of the air-gas mixture, the partial pressure of the gas in the cylinder, the pressure-to-flow conversion slope, the gas flow rate, and the fresh air flow rate. The threshold flow rate can be the flow rate of the EGR valve 50 set by the user based on experiments. When the flow rate of the EGR valve 50 is less than or equal to the threshold flow rate, the opening of the EGR valve 50 can be adjusted based on the actual opening of the EGR valve 50 detected by the EGR valve opening sensor 100. If the flow rate of the EGR valve 50 is greater than the threshold flow rate, the actual opening of the EGR valve 50 is inaccurate, and the flow rate of the EGR valve 50 must be calculated using other methods. Exemplarily, when the EGR demand flow is less than or equal to the threshold flow, the controller determines the EGR estimated flow according to the actual opening of the EGR valve, sums the EGR estimated flow, the gas flow and the fresh air flow, integrates and accumulates the pressure effect generated by the summed total flow through the intake manifold dynamic model, and determines the pressure of the air and gas mixture; when the EGR demand flow is greater than the threshold flow, determines the threshold opening according to the threshold flow; determines the required opening of the EGR valve 50 according to the EGR demand flow; determines the maximum opening of the EGR valve 50 according to the maximum opening of the EGR valve 50 The EGR maximum flow is determined by the opening degree; the EGR estimated flow is determined according to the actual opening degree of the EGR valve, and the threshold opening degree is determined according to the threshold flow; the EGR maximum flow is determined according to the maximum opening degree of the EGR valve; the EGR additional flow value is determined according to the threshold flow, the threshold opening degree, the actual opening degree of the EGR valve, the maximum opening degree of the EGR valve and the EGR maximum flow; after summing the EGR estimated flow, the EGR additional flow value, the gas flow and the fresh air flow, the pressure effect generated by the summed total flow is integrated and accumulated through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

[0049] The controller determines an EGR flow correction value based on the actual EGR flow and the required EGR flow. If the actual EGR flow exceeds the required EGR flow, the EGR flow is excessive and the actual EGR flow needs to be reduced in the next operating cycle. The required reduction value is the EGR flow correction value. If the actual EGR flow equals the required EGR flow, the actual EGR flow is maintained in the next operating cycle, and the EGR flow correction value is zero. If the actual EGR flow is less than the required EGR flow, the EGR flow is too low and the actual EGR flow needs to be increased in the next operating cycle. The required increase value is the EGR flow correction value. The controller uses the EGR flow correction value to adjust the EGR valve opening to ensure that the actual EGR flow reaches the required EGR flow, achieving closed-loop control of the EGR flow. If the intake pressure sensor 30 fails, an alternative method is available to determine the pressure of the air and gas mixture. This allows for precise control of the EGR flow by determining the pressure of the air and gas mixture in two ways.

[0050] The EGR flow closed-loop control system of a natural gas engine provided by the technical solution of the embodiment of the present invention comprises: an intake air flow sensor 10, a mixer 20, an intake air pressure sensor 30, a cylinder 40, an EGR valve 50 and a controller; the mixer 20 is used to mix air and gas; the intake air flow sensor 10 is used to detect the fresh air flow; the intake air pressure sensor 30 is used to detect the pressure of the air and gas mixture; the controller is electrically connected to the intake air flow sensor 10, the intake air pressure sensor 30 and the EGR valve 50 respectively; the controller is used to determine the EGR required flow rate according to the actual working condition of the engine; the controller is used to obtain the pressure of the air and gas mixture detected by the intake air pressure sensor 30 force; or, the controller is used to determine the pressure of the air and gas mixture based on the EGR demand flow, threshold flow, maximum opening of the EGR valve 50, actual opening of the EGR valve 50, gas flow, and fresh air flow; the controller is used to determine the actual EGR flow based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the pressure-flow conversion slope, gas flow, and fresh air flow; the controller is used to determine the EGR flow correction value based on the obtained actual EGR flow and the EGR demand flow; the opening of the EGR valve is adjusted according to the EGR flow correction value so that the actual EGR flow reaches the EGR demand flow, thereby achieving EGR flow closed-loop control. In the embodiment of the present invention, when the intake pressure sensor 30 fails, there is still an alternative solution to determine the pressure of the air and gas mixture. The pressure of the air and gas mixture is determined by two methods to achieve precise control of the EGR flow.

[0051] Optionally, the actual EGR flow rate is:

[0052] EGR_Ms=(Map-Ofs_P_Cly)*Fac_P_Ms-Full_Ms-Air_Ms

[0053] Among them, EGR_Ms is the actual EGR flow rate, Map is the pressure of the air and gas mixture, Ofs_P_Cly is the partial pressure of the gas in the cylinder, Fac_P_Ms is the conversion slope of pressure and flow rate, Full_Ms is the gas flow rate, and Air_Ms is the fresh air flow rate.

[0054] Among them, the total flow is the sum of the actual EGR flow, gas flow and fresh air flow. The total flow can be calculated through the pressure of the air and gas mixture, the partial pressure of the gas in the cylinder and the conversion slope of pressure and flow. The fresh air flow is detected by the intake flow sensor. The gas flow can be calculated based on the fresh air flow, equivalent air-fuel ratio and the required excess air coefficient setting value.

[0055] Optional, reference Figure 1 The natural gas engine EGR flow closed-loop control system further includes: a throttle valve 60, which is disposed on an air pipeline, with a first end of the throttle valve 60 connected to an intake air flow sensor 10; a second end of the throttle valve 60 connected to a first end of a mixer 20 via an air pipeline; a controller electrically connected to the throttle valve 60; the controller is configured to determine a fresh air demand based on a driver's required torque; the controller is configured to control an opening of the throttle valve 60 after obtaining the fresh air flow so that the fresh air flow reaches the required fresh air flow; and the controller is configured to calculate a gas flow based on the fresh air flow, an equivalent air-fuel ratio, and a set value of a required excess air coefficient.

[0056] When the controller detects the degree of pedal opening depressed by the driver, it determines the driver's requested torque and, based on the driver's requested torque, the fresh air demand. The controller then controls the opening of throttle valve 30 based on the fresh air flow detected by intake air flow sensor 10. For example, if the detected fresh air flow is less than the fresh air demand, the controller increases the opening of throttle valve 60. If the detected fresh air flow is equal to the fresh air demand, the controller maintains the opening of throttle valve 60 unchanged to ensure that the fresh air flow reaches the fresh air demand. The intake air flow sensor 10 can detect the fresh air flow in real time. The controller uses the fresh air flow obtained by the controller to control and adjust the opening of throttle valve 60 to ensure that the fresh air flow reaches the fresh air demand, thus achieving closed-loop air flow control to meet the driver's driving needs.

[0057] Specifically, the controller can calculate the gas flow rate based on the fresh air flow rate, the equivalent air-fuel ratio, and the required excess air coefficient setting value. For example, the required excess air coefficient setting value can be 1. When the required excess air coefficient setting value is 1, stoichiometric combustion can be determined. Based on the equivalent air-fuel ratio, the fresh air flow rate and gas flow rate are required to achieve a 1:1 combustion ratio.

[0058] Optionally, the controller is used to determine the EGR estimated flow rate based on the actual opening of the EGR valve when the EGR demand flow rate is less than or equal to the threshold flow rate, and determine the pressure of the air and gas mixture based on the EGR estimated flow rate, the gas flow rate and the fresh air flow rate.

[0059] The controller is used to determine the EGR estimated flow rate based on the actual opening of the EGR valve when the EGR demand flow rate is greater than the threshold flow rate, and determine the EGR additional flow rate value based on the EGR estimated flow rate, the threshold flow rate and the maximum opening of the EGR valve; and determine the pressure of the air and gas mixture based on the EGR additional flow rate value, the threshold flow rate, the gas flow rate and the fresh air flow rate.

[0060] The controller is configured to, when the EGR demand flow rate is less than or equal to a threshold flow rate, determine an estimated EGR flow rate by referring to an inverse table of EGR flow characteristics based on the actual opening of the EGR valve detected by the EGR valve opening sensor; sum the estimated EGR flow rate, the gas flow rate, and the fresh air flow rate; and integrate and accumulate the pressure effect of the summed total flow rate using an intake manifold dynamic model to determine the pressure of the air-gas mixture. When the EGR demand flow rate is greater than a threshold flow rate, the controller is configured to determine an estimated EGR flow rate by referring to an inverse table of EGR flow characteristics based on the actual opening of the EGR valve; determine a threshold opening based on the threshold flow rate; determine a maximum EGR flow rate based on the maximum opening of the EGR valve; determine an additional EGR flow rate by interpolation based on the threshold flow rate, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve, and the maximum EGR flow rate; and sum the estimated EGR flow rate, the additional EGR flow rate, the gas flow rate, and the fresh air flow rate; and integrate and accumulate the pressure effect of the summed total flow rate using an intake manifold dynamic model to determine the pressure of the air-gas mixture.

[0061] Optionally, the controller is used to sum the EGR estimated flow, gas flow and fresh air flow when the EGR demand flow is less than or equal to the threshold flow, and then integrate and accumulate the pressure effect produced by the summed total flow through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

[0062] Among them, the total flow is obtained by summing the EGR demand flow, gas flow and fresh air flow. Through the intake manifold dynamic model, the pressure effect generated by the total flow is integrated and accumulated to obtain the pressure of the air and gas mixture.

[0063] Optionally, the controller is used to determine the EGR estimated flow rate based on the actual opening of the EGR valve and the threshold opening based on the threshold flow rate when the EGR demand flow rate is greater than the threshold flow rate; determine the EGR maximum flow rate based on the maximum opening of the EGR valve; determine the EGR additional flow value based on the threshold flow rate, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve and the EGR maximum flow rate; after summing the EGR estimated flow rate, the EGR additional flow value, the gas flow rate and the fresh air flow rate, integrate and accumulate the pressure effect of the summed total flow rate through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

[0064] When the EGR demand flow rate exceeds the threshold flow rate, a significant deviation in the estimated EGR flow rate is determined by consulting an inverse EGR flow characteristic table based on the actual EGR valve opening. The threshold opening corresponding to the threshold flow rate and the maximum EGR flow rate corresponding to the maximum EGR valve opening can be found by consulting the EGR flow characteristic table. The EGR excess flow rate can then be determined through interpolation. For example, the threshold flow rate is the flow rate at a threshold opening of 90%, and the maximum flow rate is the flow rate at a maximum opening of 100%. The EGR flow rate at an actual opening of 95% is calculated. The actual EGR flow rate between 90% and 95% can be determined through interpolation. The actual EGR flow rate between 90% and 95% is the EGR excess flow rate. The total flow rate is then summed by combining the EGR excess flow rate, the threshold flow rate, the gas flow rate, and the fresh air flow rate. The pressure effect of the total flow rate is integrated and accumulated using the intake manifold dynamic model to determine the pressure of the air-gas mixture.

[0065] Optionally, the controller is used to determine the EGR additional flow value by interpolation calculation based on the threshold flow, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve and the EGR maximum flow.

[0066] Among them, when the EGR demand flow is greater than the threshold flow, the controller is used to determine the EGR additional flow value through interpolation calculation based on the threshold flow, threshold opening, actual opening of the EGR valve, maximum opening of the EGR valve and EGR maximum flow, and then the actual flow value corresponding to the actual opening of the EGR valve can be determined by adding the EGR additional flow value and the threshold flow, so that the actual flow value will be more accurate.

[0067] Optional, reference Figure 1The natural gas engine EGR flow closed-loop control system also includes: a boost pressure sensor 70 and a turbocharger 80. The boost pressure sensor 70 is located in the air pipe on the side of the intake air flow sensor 10 away from the throttle valve 60, and the turbocharger 80 is located in the air pipe on the side of the boost pressure sensor 70 away from the intake air flow sensor 10. The boost pressure sensor 70 is connected to the intake air flow sensor 10; the turbocharger 80 is connected to the boost pressure sensor 70; the turbocharger 80 is used to increase the intake amount of fresh air; the boost pressure sensor 70 is used to detect the boost pressure.

[0068] The turbocharger 80 increases the intake volume of fresh air by compressing the fresh air. Figure 1 It also includes a turbine bypass valve 90, which is located on the exhaust pipe. When the boost pressure sensor 70 detects that the boost pressure is too high and exceeds a preset value, the controller can control the valve opening of the turbine bypass valve 90 to open, reduce the amount of exhaust gas, and reduce the boost pressure.

[0069] Example 2

[0070] An embodiment of the present invention, based on the above embodiment, provides a closed-loop EGR flow control method for a natural gas engine. The closed-loop EGR flow control system for a natural gas engine includes: an intake air flow sensor, a mixer, an intake air pressure sensor, a cylinder, an EGR valve, an EGR valve opening sensor, and a controller. The intake air flow sensor is disposed in an air line, a first end of the mixer is connected to the air line, and a second end of the mixer is connected to the gas line. A third end of the mixer is connected to a first end of the intake air pressure sensor via a mixed gas line, a second end of the intake air pressure sensor is connected to a first end of the cylinder, and a second end of the cylinder is connected to an exhaust gas line. The third end of the mixer is also connected to a first end of the EGR valve via a mixed gas line, a second end of the EGR valve is connected to a first end of the EGR valve opening sensor, and a second end of the EGR valve opening sensor is connected to the exhaust gas line. The mixer is configured to mix air and gas; the intake air flow sensor is configured to detect a fresh air flow rate; the intake air pressure sensor is configured to detect a pressure of a mixture of air and gas; and the EGR valve opening sensor is configured to detect an actual opening of the EGR valve. The controller is electrically connected to the intake air flow sensor, the intake air pressure sensor, and the EGR valve, respectively.

[0071] Figure 2 This is a flow chart of a natural gas engine EGR flow closed-loop control method provided by the second embodiment of the present invention, with reference to Figure 2 , the natural gas engine EGR flow closed-loop control method includes:

[0072] S110 : The controller determines the EGR required flow rate according to the actual operating condition of the engine.

[0073] S120. The controller obtains the pressure of the air and gas mixture detected by the intake pressure sensor; or, the controller determines the pressure of the air and gas mixture based on the EGR demand flow, threshold flow, maximum opening of the EGR valve, actual opening of the EGR valve, gas flow, and fresh air flow.

[0074] S130 , the controller determines the actual EGR flow rate based on the acquired pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the conversion slope of pressure to flow rate, the gas flow rate, and the fresh air flow rate.

[0075] S140. The controller determines an EGR flow correction value based on the obtained EGR actual flow and the EGR required flow; and adjusts the opening of the EGR valve based on the EGR flow correction value so that the EGR actual flow reaches the EGR required flow, thereby achieving EGR flow closed-loop control.

[0076] In the closed-loop control method for EGR flow of a natural gas engine provided by an embodiment of the present invention, when an intake pressure sensor fails, there is still an alternative solution to determine the pressure of the air and gas mixture. The pressure of the air and gas mixture is determined in two ways to achieve precise control of the EGR flow.

[0077] Optionally, the actual EGR flow rate is:

[0078] EGR_Ms=(Map-Ofs_P_Cly)*Fac_P_Ms-Full_Ms-Air_Ms

[0079] Among them, EGR_Ms is the actual EGR flow rate, Map is the pressure of the air and gas mixture, Ofs_P_Cly is the partial pressure of the gas in the cylinder, Fac_P_Ms is the conversion slope of pressure and flow rate, Full_Ms is the gas flow rate, and Air_Ms is the fresh air flow rate.

[0080] The natural gas engine EGR flow closed-loop control method provided by the technical solution of the embodiment of the present invention and the natural gas engine EGR flow closed-loop control system provided by the embodiment of the present invention belong to the same inventive concept and have the same beneficial effects. For technical details not detailed in this embodiment, please refer to the natural gas engine EGR flow closed-loop control system described in any embodiment of the present invention.

[0081] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0082] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A natural gas engine EGR flow closed-loop control system, characterized in that: include: Intake air flow sensor, mixer, intake air pressure sensor, cylinder, EGR valve, EGR valve opening sensor and controller; The intake air flow sensor is arranged on the air pipeline, the first end of the mixer is connected to the air pipeline, and the second end of the mixer is connected to the gas pipeline; the third end of the mixer is connected to the first end of the intake pressure sensor through the mixed gas pipeline, the second end of the intake pressure sensor is connected to the first end of the cylinder, and the second end of the cylinder is connected to the exhaust pipeline; the third end of the mixer is also connected to the first end of the EGR valve through the mixed gas pipeline, the second end of the EGR valve is connected to the first end of the EGR valve opening sensor, and the second end of the EGR valve opening sensor is connected to the exhaust pipeline; the mixer is used to mix air and gas; the intake air flow sensor is used to detect the fresh air flow; the intake pressure sensor is used to detect the pressure of the air and gas mixture; the EGR valve opening sensor is used to detect the actual opening of the EGR valve; The controller is electrically connected to the intake air flow sensor, the intake air pressure sensor and the EGR valve respectively; The controller is used to determine the EGR required flow rate according to the actual operating conditions of the engine; The controller is used to obtain the pressure of the air and gas mixture detected by the intake pressure sensor; or, the controller is used to determine the pressure of the air and gas mixture based on the EGR required flow rate, the threshold flow rate, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow rate, and the fresh air flow rate; The controller is used to determine the actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the conversion slope of pressure and flow rate, the gas flow rate and the fresh air flow rate; The controller is used to determine an EGR flow correction value according to the acquired EGR actual flow and the EGR required flow; adjusting the opening of the EGR valve according to the EGR flow correction value so that the actual EGR flow reaches the EGR required flow, thereby achieving EGR flow closed-loop control; If the intake pressure sensor fails, the controller determines the pressure of the air and gas mixture based on the EGR demand flow, threshold flow, maximum opening of the EGR valve, actual opening of the EGR valve, gas flow and fresh air flow, and determines the actual EGR flow based on the determined pressure of the air and gas mixture, partial pressure of the gas in the cylinder, conversion slope of pressure and flow, gas flow and fresh air flow.

2. The natural gas engine EGR flow closed-loop control system according to claim 1, characterized in that: The actual EGR flow rate is: ； in, is the actual EGR flow rate, is the pressure of the mixture of air and gas, is the partial pressure of gas in the cylinder, is the conversion slope of pressure and flow, is the gas flow rate, For fresh air flow.

3. The natural gas engine EGR flow closed-loop control system according to claim 2, characterized in that: Also includes: A throttle valve is provided on the air pipeline, a first end of the throttle valve is connected to the intake air flow sensor; a second end of the throttle valve is connected to the first end of the mixer through the air pipeline; and the controller is electrically connected to the throttle valve; The controller is used to determine the fresh air demand according to the driver's demand torque; The controller is used to control the valve opening of the throttle valve after obtaining the fresh air flow rate so that the fresh air flow rate reaches the fresh air demand; The controller is used to calculate the fuel gas flow rate according to the fresh air flow rate, the equivalent air-fuel ratio and the required excess air coefficient setting value.

4. The natural gas engine EGR flow closed-loop control system according to claim 1, characterized in that: The controller is configured to determine an estimated EGR flow rate according to an actual opening of the EGR valve when the required EGR flow rate is less than or equal to a threshold flow rate, and determine a pressure of an air-gas mixture according to the estimated EGR flow rate, the gas flow rate, and the fresh air flow rate; The controller is configured to determine an EGR estimated flow rate according to an actual opening of the EGR valve when the EGR demand flow rate is greater than a threshold flow rate, and determine an EGR additional flow rate value according to the EGR estimated flow rate, the threshold flow rate, and a maximum opening of the EGR valve; The pressure of the air and gas mixture is determined according to the EGR additional flow value, the threshold flow, the gas flow, and the fresh air flow.

5. The natural gas engine EGR flow closed-loop control system according to claim 4, characterized in that: The controller is used to sum the EGR estimated flow, gas flow and fresh air flow when the EGR demand flow is less than or equal to the threshold flow, and then integrate and accumulate the pressure effect generated by the summed total flow through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

6. The natural gas engine EGR flow closed-loop control system according to claim 4, characterized in that: The controller is configured to determine an EGR estimated flow rate according to an actual opening of the EGR valve and determine a threshold opening according to the threshold flow rate when the EGR demand flow rate is greater than a threshold flow rate; Determine the maximum EGR flow rate based on the maximum opening of the EGR valve; determining an EGR additional flow value according to the threshold flow rate, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve, and the EGR maximum flow rate; After summing the EGR estimated flow, the EGR additional flow value, the gas flow, and the fresh air flow, the pressure effect generated by the summed total flow is integrated and accumulated through the intake manifold dynamic model to determine the pressure of the air and gas mixture.

7. The natural gas engine EGR flow closed-loop control system according to claim 6, characterized in that: The controller is configured to determine an EGR additional flow value through interpolation calculation according to the threshold flow, the threshold opening, the actual opening of the EGR valve, the maximum opening of the EGR valve, and the EGR maximum flow.

8. The natural gas engine EGR flow closed-loop control system according to claim 3, characterized in that: Also includes: A boost pressure sensor and a turbocharger, wherein the boost pressure sensor is located in the air pipe on the side of the intake flow sensor away from the throttle valve, and the turbocharger is located in the air pipe on the side of the boost pressure sensor away from the intake flow sensor, the boost pressure sensor is connected to the intake flow sensor; the turbocharger is connected to the boost pressure sensor; the turbocharger is used to increase the intake amount of fresh air; and the boost pressure sensor is used to detect the boost pressure.

9. A natural gas engine EGR flow closed-loop control method, characterized in that: The natural gas engine EGR flow closed-loop control system includes: Intake air flow sensor, mixer, intake air pressure sensor, cylinder, EGR valve, EGR valve opening sensor and controller; The intake air flow sensor is arranged on the air pipeline, the first end of the mixer is connected to the air pipeline, and the second end of the mixer is connected to the gas pipeline; the third end of the mixer is connected to the first end of the intake pressure sensor through the mixed gas pipeline, the second end of the intake pressure sensor is connected to the first end of the cylinder, and the second end of the cylinder is connected to the exhaust pipeline; the third end of the mixer is also connected to the first end of the EGR valve through the mixed gas pipeline, the second end of the EGR valve is connected to the first end of the EGR valve opening sensor, and the second end of the EGR valve opening sensor is connected to the exhaust pipeline; the mixer is used to mix air and gas; the intake air flow sensor is used to detect the fresh air flow; the intake pressure sensor is used to detect the pressure of the air and gas mixture; the EGR valve opening sensor is used to detect the actual opening of the EGR valve; The controller is electrically connected to the intake air flow sensor, the intake air pressure sensor and the EGR valve respectively; The closed-loop control method for EGR flow in a natural gas engine includes: The controller determines the EGR required flow rate according to the actual operating conditions of the engine; The controller obtains the pressure of the air and gas mixture detected by the intake pressure sensor; or, the controller determines the pressure of the air and gas mixture based on the EGR required flow rate, the threshold flow rate, the maximum opening of the EGR valve, the actual opening of the EGR valve, the gas flow rate, and the fresh air flow rate; The controller determines the actual EGR flow rate based on the obtained pressure of the air and gas mixture, the partial pressure of the gas in the cylinder, the conversion slope of pressure and flow rate, the gas flow rate and the fresh air flow rate; The controller determines an EGR flow correction value based on the acquired EGR actual flow rate and the EGR required flow rate; and adjusts the opening of the EGR valve based on the EGR flow correction value so that the EGR actual flow rate reaches the EGR required flow rate, thereby achieving EGR flow closed-loop control; If the intake pressure sensor fails, the controller determines the pressure of the air and gas mixture based on the EGR demand flow, threshold flow, maximum opening of the EGR valve, actual opening of the EGR valve, gas flow and fresh air flow, and determines the actual EGR flow based on the determined pressure of the air and gas mixture, partial pressure of the gas in the cylinder, conversion slope of pressure and flow, gas flow and fresh air flow.

10. The natural gas engine EGR flow closed-loop control method according to claim 9, characterized in that: The actual EGR flow rate is: ； in, is the actual EGR flow rate, is the pressure of the mixture of air and gas, is the partial pressure of gas in the cylinder, is the conversion slope of pressure and flow, is the gas flow rate, For fresh air flow.

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