WO2022052854A1 - 一种具有低压egr系统的egr率控制方法、系统及汽车 - Google Patents

一种具有低压egr系统的egr率控制方法、系统及汽车 Download PDF

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WO2022052854A1
WO2022052854A1 PCT/CN2021/116174 CN2021116174W WO2022052854A1 WO 2022052854 A1 WO2022052854 A1 WO 2022052854A1 CN 2021116174 W CN2021116174 W CN 2021116174W WO 2022052854 A1 WO2022052854 A1 WO 2022052854A1
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exhaust gas
molar concentration
gas
egr
egr cooler
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PCT/CN2021/116174
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English (en)
French (fr)
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施信信
连学通
苏庆鹏
赵伟博
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广州汽车集团股份有限公司
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Publication of WO2022052854A1 publication Critical patent/WO2022052854A1/zh
Priority to US18/108,790 priority Critical patent/US20230193842A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0077—Control of the EGR valve or actuator, e.g. duty cycle, closed loop control of position
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
    • F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
    • F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F02D41/0007—Controlling intake air for control of turbo-charged or super-charged engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/005—Controlling exhaust gas recirculation [EGR] according to engine operating conditions
    • F02D41/0052—Feedback control of engine parameters, e.g. for control of air/fuel ratio or intake air amount
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F02D41/0072—Estimating, calculating or determining the EGR rate, amount or flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/144—Sensor in intake manifold
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/06—Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/45—Sensors specially adapted for EGR systems
    • F02M26/46—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition
    • F02M26/47—Sensors specially adapted for EGR systems for determining the characteristics of gases, e.g. composition the characteristics being temperatures, pressures or flow rates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
    • F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
    • F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
    • F02D2021/083—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine controlling exhaust gas recirculation electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F02D2041/0067—Determining the EGR temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D2041/1472—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being a humidity or water content of the exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/04—Engine intake system parameters
    • F02D2200/0406—Intake manifold pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/04—Engine intake system parameters
    • F02D2200/0414—Air temperature
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention relates to the technical field of engine control, in particular to an EGR rate control method, system and automobile with a low-pressure EGR system.
  • L-EGR Low Pressure-Exhaust Gas Recirculation
  • Triatomic molecules such as CO2 and water molecules with large specific heat capacity dilute the in-cylinder charge, reduce the combustion temperature in the cylinder at large loads, suppress knocking, increase the compression ratio, reduce exhaust temperature, protect and enrich; increase the throttle valve at medium and small loads opening, reducing pumping losses, thereby improving fuel economy and emissions performance of gasoline engines over the entire operating range.
  • the actuators include a mixing valve and an EGR valve, and the sensors include an intake air flow meter and a temperature and pressure sensor before and after the compressor.
  • the main function of LP-EGR is to ensure that the gasoline engine can accurately control the amount of exhaust gas and fresh air entering the cylinder in each cycle according to the requirements of the working conditions, and to ensure that the supercharging system and other
  • the reliability and life of related system components are not affected by the LP_EGR system. Under certain operating conditions, if the exhaust gas is condensed during the introduction into the intake system, it will cause damage to the compressor impeller of the supercharger and affect the reliability and life of engine components. Therefore, it is necessary to avoid this situation. .
  • the technical problem to be solved by the present invention is to provide an EGR rate control method, system and automobile with a low-pressure EGR system, which are used to solve the problem that condensation occurs when the exhaust gas is recycled in the existing gasoline engine, and the compressor impeller of the supercharger will be damaged. Cause damage and affect the reliability and life of engine components.
  • the present invention provides an EGR rate control method with a low pressure EGR system, the method comprising:
  • Step S11 Obtain the exhaust gas temperature after the EGR cooler and the exhaust gas pressure after the EGR cooler. According to the exhaust gas temperature after the EGR cooler, the exhaust gas pressure after the EGR cooler, and the preset maximum exhaust gas pressure after the EGR cooler The humidity limit calculates the molar concentration of water molecules at the maximum humidity limit value of the exhaust gas after the EGR cooler;
  • Step S12 obtaining the temperature of the mixed gas before the supercharger compressor and the pressure of the mixed gas before the supercharger compressor, according to the temperature of the mixed gas before the supercharger compressor, the pressure of the mixed gas before the supercharger Set the maximum humidity limit of the mixed gas before the supercharger compressor to calculate the molar concentration of water molecules under the maximum humidity limit of the mixed gas before the supercharger compressor;
  • Step S13 Obtain the excess air coefficient, and calculate the molar volume of the air according to the relative volume of nitrogen in the air relative to oxygen, the relative volume of carbon dioxide in the air relative to oxygen, the relative volume of water molecules in the air relative to oxygen, and the excess air coefficient. Compare;
  • Step S14 according to the molar concentration of water molecules and the molar volume ratio of the air at the maximum humidity limit value of the exhaust gas behind the EGR cooler, calculate the allowable EGR rate under the maximum humidity limit value of the exhaust gas behind the EGR cooler;
  • Step S15 take the smaller value between the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler and the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger compressor, and control the The smaller value is used as the maximum limit of EGR demand in actual operating conditions.
  • step S11 specifically includes:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • step S12 specifically includes:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • step S13 specifically includes:
  • the A is the molar volume ratio of the air
  • the nitrogen, oxygen, carbon dioxide in the air and the x are the relative volumes of nitrogen in the air relative to oxygen
  • the y is the relative volume of carbon dioxide in the air relative to oxygen
  • the z is the relative volume of water molecules relative to oxygen in the air
  • the M O2 , the M N2 , the M CO2 , the M H2O are the relative molecular masses of oxygen, nitrogen, carbon dioxide, water molecules, and gasoline.
  • step S14 according to the molar concentration of water molecules and the molar volume ratio of the air under the maximum humidity limit value of the exhaust gas behind the EGR cooler, the allowable EGR rate under the maximum limit humidity limit value of the exhaust gas after the EGR cooler is calculated. Specifically include:
  • the statistical chemical equation of gasoline engine gasoline combustion is obtained CH n +A[O 2 +xN 2 +yCO 2 +zH 2 O]+B[aCO 2 +cH 2 O+eO 2 + gCH n +hN 2 ](4), where n is the relative atomic ratio of hydrogen to carbon in gasoline, which is approximately equal to 1.87, A is the molar volume ratio of air, B is the molar volume ratio of the introduced exhaust gas, and x is the nitrogen relative to oxygen in the air y is the relative volume of carbon dioxide in the air relative to oxygen, z is the relative volume of water molecules in the air relative to oxygen, a is the molar concentration of carbon dioxide introduced into the exhaust gas, c is the molecular molar concentration of water introduced into the exhaust gas, and e is the introduced exhaust gas.
  • g is the molar concentration of hydrocarbons introduced into the exhaust gas
  • h is the molar concentration of nitrogen introduced into the exhaust gas
  • the introduced exhaust gas is the molar concentration g of hydrocarbons and the first introduced exhaust gas molar volume ratio B1, and the exhaust gas under the maximum humidity limit value behind the EGR cooler is the first introduced exhaust gas;
  • the air molar volume ratio A, the molar volume ratio B1 of the first introduced exhaust gas, the carbon dioxide molar concentration a1 in the first introduced exhaust gas, the water molecular molar concentration c1 of the first introduced exhaust gas, the oxygen molar concentration e1 in the first introduced exhaust gas and the first introduced In the exhaust gas is the molar concentration of hydrocarbons g 1, using the formula Calculate the allowable EGR rate under the limit value of the maximum humidity limit of the exhaust gas behind the EGR cooler, wherein Z egr 1 is the allowable EGR rate under the limit value of the maximum limit humidity limit value of the exhaust gas after the EGR cooler.
  • step S14 according to the molar concentration of water molecules and the molar volume ratio of the air under the maximum humidity limit value of the mixed gas before the supercharger compressor, calculate the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger compressor, Specifically include:
  • the statistical chemical equation of gasoline engine gasoline combustion is obtained CH n +A[O 2 +xN 2 +yCO 2 +zH 2 O]+B[aCO 2 +cH 2 O+eO 2 + gCH n +hN 2 ](4), where n is the relative atomic ratio of hydrogen to carbon in gasoline, which is approximately equal to 1.87, A is the molar volume ratio of air, B is the molar volume ratio of the introduced exhaust gas, and x is the nitrogen relative to oxygen in the air y is the relative volume of carbon dioxide in the air relative to oxygen, z is the relative volume of water molecules in the air relative to oxygen, a is the molar concentration of carbon dioxide introduced into the exhaust gas, c is the molecular molar concentration of water introduced into the exhaust gas, and e is the introduced exhaust gas.
  • g is the molar concentration of hydrocarbons introduced into the exhaust gas
  • h is the molar concentration of nitrogen introduced into the exhaust gas
  • the air molar volume ratio A, the molar volume ratio B2 of the second introduction waste gas, the carbon dioxide molar concentration a2 in the second introduction waste gas, the water molecular molar concentration c2 of the second introduction waste gas, the oxygen molar concentration e1 in the second introduction waste gas and the second introduction In the exhaust gas is the molar concentration of hydrocarbons g 1, using the formula
  • the present invention also provides an EGR rate control system with a low pressure EGR system, the system comprising:
  • a first calculation unit configured to obtain the exhaust gas temperature after the EGR cooler and the exhaust gas pressure after the EGR cooler, according to the exhaust gas temperature after the EGR cooler, the exhaust gas pressure after the EGR cooler and a preset EGR cooler Calculate the molar concentration of water molecules under the maximum humidity limit of exhaust gas after the EGR cooler after the maximum humidity limit of exhaust gas;
  • the second calculation unit is configured to obtain the temperature of the mixed gas before the supercharger and the compressor and the pressure of the mixed gas before the supercharger and the compressor, according to the temperature of the mixed gas before the supercharger and the compressor,
  • the gas pressure and the preset maximum humidity limit of the mixed gas before the supercharger and the compressor are used to calculate the molar concentration of water molecules under the maximum humidity limit of the mixed gas before the supercharger and compressor;
  • the third calculation unit is used to obtain the excess air coefficient, and calculate the relative volume of nitrogen in the air to oxygen, the relative volume of carbon dioxide in the air to oxygen, the relative volume of water molecules in the air to oxygen, and the excess air coefficient.
  • the fourth calculation unit is configured to calculate the allowable EGR under the maximum humidity limit value of the exhaust gas after the EGR cooler according to the molar concentration of water molecules and the molar volume ratio of the air under the maximum limit humidity limit value of the exhaust gas after the EGR cooler Rate;
  • the control unit is used to take the smaller value between the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler and the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger and compressor, and control the The smaller value is used as the maximum limit of EGR demand in actual operating conditions.
  • first computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the second computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the present invention also provides an automobile including the EGR rate control system with a low pressure EGR system.
  • first computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the second computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the allowable EGR rate under the maximum humidity limit value of the mixed gas before the supercharger compressor and the allowable EGR rate under the maximum limit humidity limit value of the exhaust gas after the EGR cooler are obtained through step-by-step calculation.
  • the allowable EGR rate under the maximum humidity limit value of the mixed gas and the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler shall take the smaller of the two. Condensation does not occur after and before the supercharger compressor, which solves the problem that under certain working conditions, if the exhaust gas is condensed during the process of introducing it into the intake system, it will cause damage to the compressor impeller of the supercharger. Issues affecting the reliability and life of engine components, while helping to reduce hardware costs.
  • FIG. 1 is a structural diagram of a low-pressure EGR system provided by the background art.
  • FIG. 2 is a flowchart of an EGR rate control method with a low pressure EGR system provided by an embodiment of the present invention.
  • FIG. 3 is a flowchart of an EGR rate control method with a low pressure EGR system provided by an embodiment of the present invention.
  • FIG. 4 is a structural diagram of an EGR rate control system with a low pressure EGR system provided by an embodiment of the present invention.
  • an embodiment of the present invention provides an EGR rate control method with a low-pressure EGR system, and the method includes:
  • Step S11 Obtain the exhaust gas temperature after the EGR cooler and the exhaust gas pressure after the EGR cooler. According to the exhaust gas temperature after the EGR cooler, the exhaust gas pressure after the EGR cooler, and the preset maximum exhaust gas pressure after the EGR cooler Humidity Limit Calculates the molar concentration of water molecules at the maximum humidity limit of the exhaust gas after the EGR cooler.
  • step S11 includes:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • Step S12 obtaining the temperature of the mixed gas before the supercharger compressor and the pressure of the mixed gas before the supercharger compressor, according to the temperature of the mixed gas before the supercharger compressor, the pressure of the mixed gas before the supercharger Set the maximum humidity limit of the mixed gas before the supercharger compressor to calculate the molar concentration of water molecules under the maximum humidity limit of the mixed gas before the supercharger compressor.
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • Step S13 Obtain the excess air coefficient, and calculate the molar volume of the air according to the relative volume of nitrogen in the air relative to oxygen, the relative volume of carbon dioxide in the air relative to oxygen, the relative volume of water molecules in the air relative to oxygen, and the excess air coefficient. Compare.
  • step S13 specifically includes:
  • the A is the molar volume ratio of the air
  • the nitrogen, oxygen, carbon dioxide in the air and the x are the relative volumes of nitrogen in the air relative to oxygen
  • the y is the relative volume of carbon dioxide in the air relative to oxygen
  • the z is the relative volume of water molecules relative to oxygen in the air
  • the M O2 , the M N2 , the M CO2 , the M H2O are the relative molecular masses of oxygen, nitrogen, carbon dioxide, water molecules, and gasoline.
  • x, y, and z are all known and preset fixed values here.
  • Step S14 according to the molar concentration of water molecules and the molar volume ratio of the air at the maximum humidity limit value of the exhaust gas behind the EGR cooler, calculate the allowable EGR rate under the maximum humidity limit value of the exhaust gas behind the EGR cooler;
  • the allowable EGR rate under the maximum humidity limit value of the mixed gas before the supercharger compressor is calculated.
  • step S14 according to the molar concentration of water molecules and the molar volume ratio of the air under the maximum humidity limit value of the exhaust gas behind the EGR cooler, the allowable EGR rate under the maximum limit humidity limit value of the exhaust gas after the EGR cooler is calculated. Specifically include:
  • the statistical chemical equation of gasoline engine gasoline combustion is obtained CH n +A[O 2 +xN 2 +yCO 2 +zH 2 O]+B[aCO 2 +cH 2 O+eO 2 + gCH n +hN 2 ](4), where n is the relative atomic ratio of hydrogen to carbon in gasoline, which is approximately equal to 1.87, A is the molar volume ratio of air, B is the molar volume ratio of the introduced exhaust gas, and x is the nitrogen relative to oxygen in the air y is the relative volume of carbon dioxide in the air relative to oxygen, z is the relative volume of water molecules in the air relative to oxygen, a is the molar concentration of carbon dioxide introduced into the exhaust gas, c is the molecular molar concentration of water introduced into the exhaust gas, and e is the introduced exhaust gas.
  • g is the molar concentration of hydrocarbons introduced into the exhaust gas
  • h is the molar concentration of nitrogen introduced into the exhaust gas
  • the introduced exhaust gas is the molar concentration g of hydrocarbons and the first introduced exhaust gas molar volume ratio B1, and the exhaust gas under the maximum humidity limit value behind the EGR cooler is the first introduced exhaust gas;
  • the air molar volume ratio A, the molar volume ratio B1 of the first introduced exhaust gas, the carbon dioxide molar concentration a1 in the first introduced exhaust gas, the water molecular molar concentration c1 of the first introduced exhaust gas, the oxygen molar concentration e1 in the first introduced exhaust gas and the first introduced In the exhaust gas is the molar concentration of hydrocarbons g 1, using the formula Calculate the allowable EGR rate under the limit value of the maximum humidity limit of the exhaust gas behind the EGR cooler, wherein Z egr 1 is the allowable EGR rate under the limit value of the maximum limit humidity limit value of the exhaust gas after the EGR cooler.
  • step S14 according to the molar concentration of water molecules and the molar volume ratio of the air under the maximum humidity limit value of the mixed gas before the supercharger compressor, the allowable EGR rate under the maximum humidity limit value of the mixed gas before the supercharger compressor is calculated. , including:
  • the statistical chemical equation of gasoline engine gasoline combustion is obtained CH n +A[O 2 +xN 2 +yCO 2 +zH 2 O]+B[aCO 2 +cH 2 O+eO 2 + gCH n +hN 2 ](4), where n is the relative atomic ratio of hydrogen to carbon in gasoline, which is approximately equal to 1.87, A is the molar volume ratio of air, B is the molar volume ratio of the introduced exhaust gas, and x is the nitrogen relative to oxygen in the air y is the relative volume of carbon dioxide in the air relative to oxygen, z is the relative volume of water molecules in the air relative to oxygen, a is the molar concentration of carbon dioxide introduced into the exhaust gas, c is the molecular molar concentration of water introduced into the exhaust gas, and e is the introduced exhaust gas.
  • g is the molar concentration of hydrocarbons introduced into the exhaust gas
  • h is the molar concentration of nitrogen introduced into the exhaust gas
  • Introduced in the exhaust gas is the molar concentration g2 of hydrocarbons and the molar volume ratio B2 of the second introduced exhaust gas, and the mixed gas under the maximum humidity limit value before the supercharger compressor is the second introduced exhaust gas;
  • the air molar volume ratio A, the molar volume ratio B2 of the second introduction waste gas, the carbon dioxide molar concentration a2 in the second introduction waste gas, the water molecular molar concentration c2 of the second introduction waste gas, the oxygen molar concentration e1 in the second introduction waste gas and the second introduction In the exhaust gas is the molar concentration of hydrocarbons g 1, using the formula
  • the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger compressor is calculated according to the water molecular molar concentration under the maximum humidity limit value of the mixed gas before the supercharger compressor.
  • the water molecular molar concentration at the maximum humidity limit value is converted into the water molecular molar concentration at the maximum humidity limit value of the exhaust gas after the EGR cooler.
  • the conversion in the strict mathematical sense needs to add an equation to solve, the solving process cannot be solved by linear algebra method, the solving process is more complicated, and it is more complicated to deploy the solution result to the controller for calculation.
  • a simple and reliable conversion method is the amplification method, which directly replaces the water molecular molar concentration at the maximum humidity limit value of the mixed gas before the supercharger compressor to replace the water molecular molar concentration at the maximum humidity limit value of the exhaust gas after the EGR cooler. This is to calculate Convenience and efficiency.
  • Step S15 take the smaller value between the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler and the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger compressor, and control the The smaller value is used as the maximum limit of EGR demand in actual operating conditions.
  • condensation there are two situations in which condensation may actually occur.
  • One is that condensation occurs after the EGR cooler, and the other is that LP_EGR introduces the exhaust gas into the rear intake system and mixes it with fresh air. The temperature and pressure state of the gas changes. , which in turn causes condensation before the supercharger compressor.
  • taking the calculated EGR rate allowed under the maximum humidity limit of the exhaust gas after the EGR cooler as the maximum limit of the actual operating condition EGR rate requirement can ensure that condensation does not occur after the EGR cooler.
  • taking the calculated allowable EGR rate under the maximum humidity limit of the mixture before the supercharger compressor as the maximum limit of the actual working condition EGR rate requirement can ensure that condensation does not occur before the supercharger compressor.
  • the allowable EGR rate under the maximum humidity limit of the mixture before the supercharger compressor and the allowable EGR rate under the maximum humidity limit of the exhaust gas after the EGR cooler are taken as the maximum limit of the actual working condition EGR demand, That is, the EGR rate that ensures that no condensed water enters the supercharger compressor is obtained.
  • an embodiment of the present invention provides an EGR rate control system with a low-pressure EGR system, and the system includes:
  • the first calculation unit 21 is used to obtain the exhaust gas temperature after the EGR cooler and the exhaust gas pressure after the EGR cooler, according to the exhaust gas temperature after the EGR cooler, the exhaust gas pressure after the EGR cooler and the preset EGR cooling
  • the maximum humidity limit of exhaust gas after the cooler is used to calculate the molar concentration of water molecules under the maximum humidity limit of exhaust gas after the EGR cooler;
  • the second calculation unit 22 is configured to obtain the temperature of the mixed gas before the supercharger and the compressor and the pressure of the mixed gas before the supercharger and the compressor, according to the temperature of the mixed gas before the supercharger and the compressor, The air pressure of the mixed gas and the preset maximum humidity limit of the mixed gas before the supercharger compressor are used to calculate the molar concentration of water molecules under the maximum humidity limit of the mixed gas before the supercharger and compressor;
  • the third calculation unit 23 is used to obtain the excess air coefficient, and calculates the excess air coefficient according to the relative volume of nitrogen in the air to oxygen, the relative volume of carbon dioxide in the air to oxygen, the relative volume of water molecules in the air to oxygen, and the excess air coefficient.
  • the fourth calculation unit 24 is configured to calculate the allowable limit value of the maximum humidity limit value of the exhaust gas after the EGR cooler according to the molar concentration of water molecules and the molar volume ratio of the air under the limit value of the maximum limit humidity limit value of the exhaust gas after the EGR cooler. EGR rate;
  • the control unit 25 is configured to take the smaller value between the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler and the allowable EGR under the maximum humidity limit value of the mixed gas before the supercharger compressor, The smaller value is controlled as the maximum limit of the actual operating condition EGR demand.
  • first computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the second computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • An embodiment of the present invention also provides an automobile, which includes the above-mentioned EGR rate control system with a low-pressure EGR system.
  • first computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the second computing unit is specifically used for:
  • the RH in is the gas humidity
  • the [H 2 O] in is the molar concentration of water molecules
  • the P in is the gas pressure
  • the P svpin is the gas saturated vapor pressure
  • the allowable EGR rate under the maximum humidity limit value of the mixed gas before the supercharger compressor and the allowable EGR rate under the maximum limit humidity limit value of the exhaust gas after the EGR cooler are obtained through step-by-step calculation.
  • the allowable EGR rate under the maximum humidity limit value of the mixed gas and the allowable EGR rate under the maximum humidity limit value of the exhaust gas after the EGR cooler shall take the smaller of the two. Condensation does not occur after and before the supercharger compressor, which solves the problem that under certain working conditions, if the exhaust gas is condensed during the process of introducing it into the intake system, it will cause damage to the compressor impeller of the supercharger. Issues affecting the reliability and life of engine components, while helping to reduce hardware costs.

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Abstract

提供一种具有低压EGR系统的EGR率控制方法、系统及汽车，包括计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；获取过量空气系数，根据过量空气系数计算空气的摩尔体积比；根据EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度、增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和空气的摩尔体积比，分别计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率和增压器压气机前混合气体最大湿度极限值下允许的EGR；在两者中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。本申请解决了现有汽油发动机废气引入发生冷凝的问题。

Description

一种具有低压EGR系统的EGR率控制方法、系统及汽车
相关申请
本申请要求于2020年9月14日提交中国国家知识产权局、申请号为CN202010959271.5、发明名称为“一种具有低压EGR系统的EGR率控制方法、系统及汽车”的中国专利申请的优先权，上述专利的全部内容通过引用结合在本申请中。
技术领域
本发明涉及发动机控制技术领域，尤其涉及一种具有低压EGR系统的EGR率控制方法、系统及汽车。
背景技术
低压废气再循环技术(Low Pressure-Exhaust Gas Recirculation，简称LP-EGR)是目前汽油发动机节能减排的热点技术，其原理是将汽油发动机燃烧产生的废气冷却后再次通入进气系统，能够利用比热容较大的CO2、水分子等三原子分子稀释缸内充量，在大负荷降低缸内的燃烧温度，抑制爆震，提高压缩比，减少排温保护加浓；在中小负荷增大节气门开度，降低泵气损失，从而在整个工况范围内改善汽油发动机的燃油经济性和排放性能。
为了将汽油发动机燃烧产生的废气冷却后再次通入进气系统，在原有空气系统的基础上，将前级催化器后的废气引入至涡轮增压器压气机前，同时为了实现对引入废气的量进行控制和估计，在相应的管路上增加了对应的执行器和传感器，具体参考图1，执行器包括混合阀、EGR阀，传感器包括进气空气流量计、压气机前后温度压力传感器。
对于整个汽油发动机控制系统来讲，LP-EGR主要功能是保证汽油发动机能够按照工况需求实现对每一循环进入气缸的废气量和新鲜空气量进行准确控制的同时，并且保证增压系统和其它相关系统零部件的可靠性和寿命不受LP_EGR系统的影响。在某些工况下，若废气在引入到进气系统的过程中发生冷凝，对增压器的压气机叶轮会造成损伤，影响发动机零部件的可靠性和寿命，因此需要避免这种情况产生。
发明内容
本发明所要解决的技术问题在于，提供一种具有低压EGR系统的EGR率控制方法、系统及汽车，用于解决现有汽油发动机将废气循环使用时发生冷凝，对增压器的压气机叶轮会造成损伤，影响发动机零部件的可靠性和寿命的问题。
为解决上述技术问题，本发明提供一种具有低压EGR系统的EGR率控制方法，所述方法包括：
步骤S11、获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
步骤S12、获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；
步骤S13、获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比；
步骤S14、根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR率；
步骤S15、在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
进一步地，所述步骤S11具体包括：
S21、将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000001
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
S22、将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000002
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述步骤S12具体包括：
S31、将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000003
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
S32、将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000004
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述步骤S13具体包括：
利用过氧传感器获得过量空气系数Z airFuel；
利用公式
Figure PCTCN2021116174-appb-000005
计算空气摩尔 体积比，
其中，所述A为所述空气摩尔体积比，所述空气中氮气、氧气、二氧化碳和所述x是空气中氮气相对氧气的相对体积，所述y是空气中二氧化碳相对氧气的相对体积，所述z是空气中水分子相对氧气的相对体积，所述M O2、所述M N2、所述M CO2、所述M H2O、所述
Figure PCTCN2021116174-appb-000006
分别是氧气、氮气、二氧化碳、水分子、汽油的相对分子质量。
进一步地，步骤S14中根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率具体包括：
根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
根据方程式(4)推导得到的方程组
Figure PCTCN2021116174-appb-000007
将空气摩尔体积比、第一引入废气水分子摩尔浓度分别代入方程组(5)中的A和c1，计算第一引入废气中二氧化碳摩尔浓度a1、第一引入废气中氧气摩尔浓度e1、第一引入废气中是碳氢的摩尔浓度g 1和第一引入废气的摩尔体积比B1，所述EGR冷却器后最大限湿度极限值下的废气为第一引入 废气；
根据空气摩尔体积比A、第一引入废气的摩尔体积比B1、第一引入废气中二氧化碳摩尔浓度a1、第一引入废气水分子摩尔浓度c1、第一引入废气中氧气摩尔浓度e1和第一引入废气中是碳氢的摩尔浓度g 1，利用公式
Figure PCTCN2021116174-appb-000008
计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率，其中Z egr1为所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率。
进一步地，步骤S14中根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR，具体包括:
根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
根据方程式(4)推导得到的方程组
Figure PCTCN2021116174-appb-000009
将空气摩尔体积比、第二引入废气水分子摩尔浓度分别代入方程组(5) 中的A和c2，计算第二引入废气中二氧化碳摩尔浓度a2、第二引入废气中氧气摩尔浓度e2、第二引入废气中是碳氢的摩尔浓度g2和第二引入废气的摩尔体积比B2，所述增压器压气机前最大限湿度极限值下的混合气体为第二引入废气；
根据空气摩尔体积比A、第二引入废气的摩尔体积比B2、第二引入废气中二氧化碳摩尔浓度a2、第二引入废气水分子摩尔浓度c2、第二引入废气中氧气摩尔浓度e1和第二引入废气中是碳氢的摩尔浓度g 1，利用公式
Figure PCTCN2021116174-appb-000010
计算增压器压气机前混合气体最大湿度极限值下允许的EGR，其中Z egr2为所述增压器压气机前混合气体最大湿度极限值下允许的EGR。
本发明还提供一种具有低压EGR系统的EGR率控制系统，所述系统包括：
第一计算单元，用于获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
第二计算单元，用于获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；
第三计算单元，用于获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比；
第四计算单元，用于根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所 述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR；
控制单元，用于在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
进一步地，所述第一计算单元具体用于：
将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000011
Figure PCTCN2021116174-appb-000012
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000013
Figure PCTCN2021116174-appb-000014
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述第二计算单元具体用于：
将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000015
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000016
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
本发明还提供一种汽车，所述汽车包括所述的具有低压EGR系统的EGR率控制系统。
进一步地，所述第一计算单元具体用于：
将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000017
Figure PCTCN2021116174-appb-000018
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000019
Figure PCTCN2021116174-appb-000020
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述第二计算单元具体用于：
将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000021
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000022
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为 气体气压，所述P svpin为气体饱和蒸气压。
实施本发明，具有如下有益效果：
通过本发明，通过逐步计算得到增压器压气机前混合气体最大湿度极限值下允许的EGR率和EGR冷却器后的废气最大限湿度极限值下允许的EGR率，根据增压器压气机前混合气体最大湿度极限值下允许的EGR率和EGR冷却器后的废气最大限湿度极限值下允许的EGR率取两者中较小者，在不增加湿度传感器的前提下，保证在EGR冷却器后不发生冷凝以及增压器压气机前不发生冷凝，解决了在某些工况下，若废气在引入到进气系统的过程中发生冷凝，对增压器的压气机叶轮会造成损伤，影响发动机零部件的可靠性和寿命的问题，同时有利于降低硬件成本。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是背景技术提供的低压EGR系统的结构图。
图2是本发明实施例提供的具有低压EGR系统的EGR率控制方法的流程图。
图3是本发明实施例提供的具有低压EGR系统的EGR率控制方法的流程图。
图4是本发明实施例提供的具有低压EGR系统的EGR率控制系统的结构图。
具体实施方式
本专利中，以下结合附图和实施例对该具体实施方式做进一步说明。
如图2所示，本发明实施例提供了具有低压EGR系统的EGR率控制方法，所述方法包括：
步骤S11、获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度 极限值下水分子摩尔浓度。
需要说明的是，获取EGR冷却器后的废气温度和EGR冷却器后的废气气压分别依靠温度传感器和压力传感器。进一步需要说明的是，在本方法实施例中结合图3的流程。
具体地，步骤S11包括：
S21、将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000023
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
S22、将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000024
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
步骤S12、获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度。
具体地，S31、将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000025
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
S32、将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000026
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
步骤S13、获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比。
具体地，所述步骤S13具体包括：
利用过氧传感器获得过量空气系数Z airFuel；
利用公式
Figure PCTCN2021116174-appb-000027
计算空气摩尔体积比，
其中，所述A为所述空气摩尔体积比，所述空气中氮气、氧气、二氧化碳和所述x是空气中氮气相对氧气的相对体积，所述y是空气中二氧化碳相对氧气的相对体积，所述z是空气中水分子相对氧气的相对体积，所述M O2、所述M N2、所述M CO2、所述M H2O、所述
Figure PCTCN2021116174-appb-000028
分别是氧气、氮气、二氧化碳、水分子、汽油的相对分子质量。
需要说明的是，这里x、y、z都是已知的且是预设固定值。
步骤S14、根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR率。
具体地，步骤S14中根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率具体包括：
根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
根据方程式(4)推导得到的方程组
Figure PCTCN2021116174-appb-000029
将空气摩尔体积比、第一引入废气水分子摩尔浓度分别代入方程组(5)中的A和c1，计算第一引入废气中二氧化碳摩尔浓度a1、第一引入废气中氧气摩尔浓度e1、第一引入废气中是碳氢的摩尔浓度g 1和第一引入废气的摩尔体积比B1，所述EGR冷却器后最大限湿度极限值下的废气为第一引入废气；
根据空气摩尔体积比A、第一引入废气的摩尔体积比B1、第一引入废气中二氧化碳摩尔浓度a1、第一引入废气水分子摩尔浓度c1、第一引入废气中氧气摩尔浓度e1和第一引入废气中是碳氢的摩尔浓度g 1，利用公式
Figure PCTCN2021116174-appb-000030
计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率，其中Z egr1为所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率。
具体地，步骤S14中根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR率，具体包括:
根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
根据方程式(4)推导得到的方程组
Figure PCTCN2021116174-appb-000031
将空气摩尔体积比、第二引入废气水分子摩尔浓度分别代入方程组(5)中的A和c2，计算第二引入废气中二氧化碳摩尔浓度a2、第二引入废气中氧气摩尔浓度e2、第二引入废气中是碳氢的摩尔浓度g2和第二引入废气的摩尔体积比B2，所述增压器压气机前最大限湿度极限值下的混合气体为第二引入废气；
根据空气摩尔体积比A、第二引入废气的摩尔体积比B2、第二引入废气中二氧化碳摩尔浓度a2、第二引入废气水分子摩尔浓度c2、第二引入废气中氧气摩尔浓度e1和第二引入废气中是碳氢的摩尔浓度g 1，利用公式
Figure PCTCN2021116174-appb-000032
计算增压器压气机前混合气体最大湿度极限值下允许的EGR，其中Z egr2为所述增压器压气机前混合气体最大湿度极限值下允许的EGR。
需要说明的是，根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度计算增压器压气机前混合气体最大湿度极限值下允许的EGR，需要将增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度转化为EGR冷却器后的废气最大湿度极限值下水分子摩尔浓度。严格数学意义上的转换需要增加一个方程求解，该求解过程不能通过线性代数方法求解，求解过程较为复杂，并且求解结果部署单到控制器上运算较为复杂。一种简单且可靠的转化方法是放大法，直接令增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度替代EGR冷却器后的废气最大湿度极限值下水分子摩尔浓度，这是为了计算方便和效率。
步骤S15、在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
需要说明的是，实际可能发生冷凝的情况有两种，一种是在EGR冷却器后发生冷凝，另一种是LP_EGR将废气引入后进气系统中与新鲜空气混合后气体温度压力状态发生变化，进而在增压器压气机前引起冷凝。针对第一种情况，将计算的EGR冷却器后废气最大湿度限值下允许的EGR率作为实际工况EGR率需求的最大限值可以保证在EGR冷却器后不发生冷凝，针对第二种情况，同理，将计算的增压器压气机前混合气最大湿度限值下允许的EGR率作为实际工况EGR率需求的最大限值可以保证在增压器压气机前不发生冷凝。故增压器压气机前混合气最大湿度限值下允许的EGR率和EGR冷却器后废气最大湿度限值下允许的EGR率两者取小后作为对实际工况EGR需求的最大限值，即得到保证无冷凝水进入增压器压气机的EGR率。
如图4所示，本发明实施例提供了具有低压EGR系统的EGR率控制系统，所述系统包括：
第一计算单元21，用于获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废 气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
第二计算单元22，用于获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；
第三计算单元23，用于获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比；
第四计算单元24，用于根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR；
控制单元25，用于在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
进一步地，所述第一计算单元具体用于：
将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000033
Figure PCTCN2021116174-appb-000034
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000035
Figure PCTCN2021116174-appb-000036
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述第二计算单元具体用于：
将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000037
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000038
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
本发明实施例还提供一种汽车，所述汽车包括上述具有低压EGR系统的EGR率控制系统。
进一步地，所述第一计算单元具体用于：
将所述EGR冷却器后的废气温度代入公式
Figure PCTCN2021116174-appb-000039
Figure PCTCN2021116174-appb-000040
计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
Figure PCTCN2021116174-appb-000041
Figure PCTCN2021116174-appb-000042
计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
进一步地，所述第二计算单元具体用于：
将所述增压器压气机前混合气体温度代入公式
Figure PCTCN2021116174-appb-000043
计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
Figure PCTCN2021116174-appb-000044
计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
实施本发明，具有如下有益效果：
通过本发明，通过逐步计算得到增压器压气机前混合气体最大湿度极限值下允许的EGR率和EGR冷却器后的废气最大限湿度极限值下允许的EGR率，根据增压器压气机前混合气体最大湿度极限值下允许的EGR率和EGR冷却器后的废气最大限湿度极限值下允许的EGR率取两者中较小者，在不增加湿度传感器的前提下，保证在EGR冷却器后不发生冷凝以及增压器压气机前不发生冷凝，解决了在某些工况下，若废气在引入到进气系统的过程中发生冷凝，对增压器的压气机叶轮会造成损伤，影响发动机零部件的可靠性和寿命的问题，同时有利于降低硬件成本。
以上内容是结合具体的优选实施方式对本发明所作的进一步详细说明，不能认定本发明的具体实施只局限于这些说明。对于本发明所属技术领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干简单推演或替换，都应当视为属于本发明的保护范围。

Claims (12)

  1. 一种具有低压EGR系统的EGR率控制方法，其特征在于，所述方法包括：
    步骤S11、获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
    步骤S12、获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；
    步骤S13、获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比；
    步骤S14、根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
    根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR率；
    步骤S15、在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
  2. 如权利要求1所述方法，其特征在于，所述步骤S11具体包括：
    S21、将所述EGR冷却器后的废气温度代入公式
    Figure PCTCN2021116174-appb-100001
    计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    S22、将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100002
    计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
  3. 如权利要求1所述方法，其特征在于，所述步骤S12具体包括：
    S31、将所述增压器压气机前混合气体温度代入公式
    Figure PCTCN2021116174-appb-100003
    计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    S32、将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100004
    计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
  4. 如权利要求1所述方法，其特征在于，所述步骤S13具体包括：
    利用过氧传感器获得过量空气系数Z airFuel；
    利用公式
    Figure PCTCN2021116174-appb-100005
    计算空气摩尔体积比，
    其中，所述A为所述空气摩尔体积比，所述空气中氮气、氧气、二氧化碳和所述x是空气中氮气相对氧气的相对体积，所述y是空气中二氧化碳相 对氧气的相对体积，所述z是空气中水分子相对氧气的相对体积，所述M O2、所述M N2、所述M CO2、所述M H2O、所述
    Figure PCTCN2021116174-appb-100006
    分别是氧气、氮气、二氧化碳、水分子、汽油的相对分子质量。
  5. 如权利要求1所述方法，其特征在于，步骤S14中根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率具体包括：
    根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
    根据方程式(4)推导得到的方程组
    Figure PCTCN2021116174-appb-100007
    将空气摩尔体积比、第一引入废气水分子摩尔浓度分别代入方程组(5)中的A和c1，计算第一引入废气中二氧化碳摩尔浓度a1、第一引入废气中氧气摩尔浓度e1、第一引入废气中是碳氢的摩尔浓度g1和第一引入废气的摩尔体积比B1，所述EGR冷却器后最大限湿度极限值下的废气为第一引入废气；
    根据空气摩尔体积比A、第一引入废气的摩尔体积比B1、第一引入废气中二氧化碳摩尔浓度a1、第一引入废气水分子摩尔浓度c1、第一引入废 气中氧气摩尔浓度e1和第一引入废气中是碳氢的摩尔浓度g1，利用公式
    Figure PCTCN2021116174-appb-100008
    计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率，其中Z egr1为所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率。
  6. 如权利要求5所述方法，其特征在于，步骤S14中根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR，具体包括:
    根据汽油发动机工作在当量模式或加浓模式，得到汽油机汽油燃烧统计化学方程式CH n+A[O 2+xN 2+yCO 2+zH 2O]+B[aCO 2+cH 2O+eO 2+gCH n+hN 2](4)，其中n是汽油氢碳相对原子比，该值约等于1.87，A是空气的摩尔体积比，B是引入废气的摩尔体积比，x是空气中氮气相对氧气的相对体积，y是空气中二氧化碳相对氧气的相对体积，z是空气中水分子相对氧气的相对体积，a是引入废气中二氧化碳摩尔浓度，c是引入废气中水分子摩尔浓度，e是引入废气中氧气摩尔浓度，g是引入废气中碳氢的摩尔浓度，h是引入废气中氮气的摩尔浓度；
    根据方程式(4)推导得到的方程组
    Figure PCTCN2021116174-appb-100009
    将空气摩尔体积比、第二引入废气水分子摩尔浓度分别代入方程组(5)中的A和c2，计算第二引入废气中二氧化碳摩尔浓度a2、第二引入废气中氧气摩尔浓度e2、第二引入废气中是碳氢的摩尔浓度g2和第二引入废气的摩尔体积比B2，所述增压器压气机前最大限湿度极限值下的混合气体为第二引入废气；
    根据空气摩尔体积比A、第二引入废气的摩尔体积比B2、第二引入废气中二氧化碳摩尔浓度a2、第二引入废气水分子摩尔浓度c2、第二引入废气中氧气摩尔浓度e1和第二引入废气中是碳氢的摩尔浓度g1，利用公式
    Figure PCTCN2021116174-appb-100010
    计算增压器压气机前混合气体最大湿度极限值下允许的EGR，其中Z egr2为所述增压器压气机前混合气体最大湿度极限值下允许的EGR。
  7. 一种具有低压EGR系统的EGR率控制系统，其特征在于，所述系统包括：
    第一计算单元，用于获取EGR冷却器后的废气温度和EGR冷却器后的废气气压，根据所述EGR冷却器后的废气温度、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值计算EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
    第二计算单元，用于获取增压器压气机前混合气体温度和增压器压气机前混合气体气压，根据所述增压器压气机前混合气体温度、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值计算增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度；
    第三计算单元，用于获取过量空气系数，根据空气中氮气相对氧气的相对体积、空气中二氧化碳相对氧气的相对体积、空气中水分子相对氧气的相对体积以及所述过量空气系数，计算所述空气的摩尔体积比；
    第四计算单元，用于根据所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算EGR冷却器后的废气最大限湿度极限值下允许的EGR率；
    根据增压器压气机前混合气体最大湿度极限值下水分子摩尔浓度和所述空气的摩尔体积比，计算增压器压气机前混合气体最大湿度极限值下允许的EGR；
    控制单元，用于在所述EGR冷却器后的废气最大限湿度极限值下允许的EGR率和所述增压器压气机前混合气体最大湿度极限值下允许的EGR中 取较小值，控制所述较小值作为实际工况EGR需求的最大限值。
  8. 如权利要求7所述系统，其特征在于，所述第一计算单元具体用于：
    将所述EGR冷却器后的废气温度代入公式
    Figure PCTCN2021116174-appb-100011
    (1)，计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100012
    (2)，计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
  9. 如权利要求7所述系统，其特征在于，所述第二计算单元具体用于：
    将所述增压器压气机前混合气体温度代入公式
    Figure PCTCN2021116174-appb-100013
    计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100014
    计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
  10. 一种汽车，其特征在于，所述汽车包括如权利要求7所述的具有低压EGR系统的EGR率控制系统。
  11. 如权利要求10所述汽车，其特征在于，所述第一计算单元具体用于：
    将所述EGR冷却器后的废气温度代入公式
    Figure PCTCN2021116174-appb-100015
    (1)，计算所述EGR冷却器后的废气饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    将所述EGR冷却器后的废气饱和蒸气压、所述EGR冷却器后的废气气压以及预设EGR冷却器后的废气最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100016
    (2)，计算所述EGR冷却器后的废气最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
  12. 如权利要求10所述汽车，其特征在于，所述第二计算单元具体用于：
    将所述增压器压气机前混合气体温度代入公式
    Figure PCTCN2021116174-appb-100017
    计算所述增压器压气机前混合气体温度饱和蒸气压，其中所述P svpin为气体饱和蒸气压，所述T in为气体温度；
    将所述增压器压气机前混合气体饱和蒸气压、所述增压器压气机前混合气体气压以及预设增压器压气机前混合气体最大湿度限值代入公式
    Figure PCTCN2021116174-appb-100018
    计算所述增压器压气机前混合气体最大限湿度极限值下水分子摩尔浓度；
    其中，所述RH in为气体湿度，所述[H 2O] in为水分子摩尔浓度，所述P in为气体气压，所述P svpin为气体饱和蒸气压。
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