阅读说明：本技术 一种发动机egr的闭环控制方法及系统 (Closed-loop control method and system for engine EGR ) 是由 耿元会 冯玮玮 解亮 朱凌龙 林园园 许可森 崔文军 陈召强 刘迎生 张娟 于 2021-08-12 设计创作，主要内容包括：本发明提供一种发动机EGR的闭环控制方法及系统,该方法包括：获取发动机的原排NO-(X) map图,并根据所述NO-(X) map图确定发动机各工况所对应的原排NO-(X)目标值；获取发动机各个工况达到所述原排NO-(X)目标值所对应的需求剩余氧量目标值；实时检测发动机排气的实际剩余氧气量,并将所述实际剩余氧气量与所述需求剩余氧气量目标值作为PID控制调节的输入参数,进行EGR阀的开度的PID控制。本发明能解决现有发动机EGR控制存在不精准的问题,能保证发动机全生命周期内EGR率的始终满足原排NOx目标值,提高发动机的汽油燃烧性能。(The invention provides a closed-loop control method and a closed-loop control system for engine EGR, wherein the method comprises the following steps: obtaining engine raw NO X map, and according to said NO X map for determining primary NO corresponding to each working condition of engine X A target value; obtaining the original NO of the engine under various working conditions X A required residual oxygen amount target value corresponding to the target value; and detecting the actual residual oxygen amount of the engine exhaust in real time, and performing PID control on the opening degree of the EGR valve by taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters for PID control regulation. The invention can solve the problem of inaccurate EGR control of the existing engine, can ensure that the EGR rate in the whole life cycle of the engine always meets the target value of the original NOx emission, and improves the gasoline combustion performance of the engine.)

1. A method of closed-loop control of engine EGR comprising:

obtaining engine raw NO_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value;

obtaining the original NO of the engine under various working conditions_XA required residual oxygen amount target value corresponding to the target value;

and detecting the actual residual oxygen amount of the engine exhaust in real time, and performing PID control on the opening degree of the EGR valve by taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters for PID control regulation.

2. The closed-loop control method for engine EGR according to claim 1, further comprising:

taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value;

and adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

3. Closed loop control method for engine EGR according to claim 2, characterized in that said obtaining engine operating conditions for said primary NO_XThe target value of the required residual oxygen amount corresponding to the target value comprises the following steps:

reaching the original NO according to various working conditions of the calibrated engine_XObtaining the corresponding residual oxygen amount by the target value, and forming a residual oxygen amount demand map;

and determining the required residual oxygen amount target value of each working condition of the engine according to the residual oxygen amount demand map.

4. Closed loop control method for engine EGR according to claim 3, characterized in that said calibration of engine individual operating conditions up to said in-line NO_XThe target value obtains the corresponding residual oxygen amount, including:

and manually adjusting the opening degree of the EGR valve for each working condition point on the engine bench, and recording the corresponding residual oxygen amount when each working condition point reaches the original NOx emission target value.

5. The closed-loop control method for engine EGR according to claim 4, further comprising:

acquiring a corresponding relation between the opening of an EGR valve and the residual oxygen amount of engine exhaust to form a corresponding table of the opening and the residual oxygen amount;

proportional coefficient K for PID control_PIntegral coefficient K_IAnd a differential coefficient K_DAnd calibrating and pre-controlling the opening of the EGR valve according to the corresponding table.

6. The closed-loop control method for engine EGR according to claim 5, further comprising:

acquiring an EGR valve opening and an EGR rate target value, and calculating according to the EGR valve opening to obtain an actual EGR rate;

and taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment, and carrying out PID control on the opening degree of the EGR valve.

7. A closed-loop control system for engine EGR comprising:

a first obtaining unit for obtaining the original NO of the engine_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value;

a second acquisition unit for acquiring the original NO of the engine under various working conditions_XA required residual oxygen amount target value corresponding to the target value;

an oxygen sensor for detecting an actual amount of residual oxygen of the engine exhaust in real time;

and the first PID controller is used for taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters of PID control adjustment and carrying out PID control on the opening degree of the EGR valve.

8. The closed-loop control system for engine EGR of claim 7, further comprising: an EGR valve opening degree adjusting unit;

the first PID controller is also used for taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value;

and the EGR valve opening degree adjusting unit is used for adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

9. The closed-loop control system for engine EGR of claim 8, further comprising:

a third acquisition unit, configured to acquire a correspondence between an opening degree of the EGR valve and a remaining oxygen amount of the engine exhaust gas to form a correspondence table of the opening degree and the remaining oxygen amount;

and the pre-control unit is used for calibrating a proportional coefficient KP, an integral coefficient KI and a differential coefficient KD controlled by the PID and pre-controlling the opening of the EGR valve according to the corresponding table.

10. The closed-loop control system for engine EGR of claim 9, further comprising:

the fourth acquisition unit is used for acquiring the EGR valve opening and the EGR rate target value and calculating the actual EGR rate according to the EGR valve opening;

and the second PID controller is used for performing PID control on the opening degree of the EGR valve by taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment.

Technical Field

The invention relates to the technical field of engine exhaust gas recycling, in particular to a closed-loop control method and a closed-loop control system for engine EGR.

Background

Exhaust Gas Recirculation (EGR) is a main means for reducing NOx emission of an engine, and as shown in fig. 1, a part of Exhaust Gas in an Exhaust pipe is introduced into an intake manifold, so that the oxygen concentration entering a cylinder of the engine is reduced by introducing Exhaust Gas with extremely low oxygen content, the combustion temperature is reduced, a low-temperature and low-oxygen combustion environment is achieved, and further, the generation of NOx is reduced. The EGR rate is generally defined as the ratio of EGR flow to total intake air amount (fresh air flow + EGR flow). Theoretically, higher EGR rates result in lower engine-out NOx, which is more beneficial for tail-out NOx control, but too high EGR rates are detrimental to engine combustion. Therefore, in the calibration process of the engine bench test, the opening degree of the EGR valve is adjusted, namely the EGR rate is adjusted, so that the actual primary NOx is slightly smaller than the NOx target emission value (generally controlled to be smaller than 10%), and the optimal EGR rate (calibration required value) of the operating point is found. Theoretically, although each operating point can reach the required EGR rate by presetting the EGR valve opening, actually, an EGR valve position sensor is not accurate, the EGR flow corresponding to the EGR valve opening under different air flow conditions cannot be in a linear relation, simultaneously, after the engine is used for a long time, a large amount of impurities are deposited on the hole wall of the EGR valve, the accumulation of the impurities inevitably leads to the reduction of the hole diameter, so that the actually-passing exhaust gas quantity of the engine on the whole vehicle is smaller than the exhaust gas throughput when in an ideal state, namely, the actual EGR rate is smaller than the ideal EGR rate, the gasoline combustion performance is reduced, and the performance of the whole vehicle is seriously influenced. Therefore, how to provide accurate control of EGR in the whole life cycle of the engine and enable the EGR rate to always meet the target value has important research significance.

Disclosure of Invention

The invention provides a closed-loop control method and a closed-loop control system for engine EGR, which solve the problem of inaccuracy in the existing engine EGR control, can ensure that the EGR rate in the full life cycle of an engine always meets the target value of original NOx emission, and improve the gasoline combustion performance of the engine.

In order to achieve the above purpose, the invention provides the following technical scheme:

a closed-loop control method of engine EGR, comprising:

obtaining engine raw NO_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value;

obtaining the original NO of the engine under various working conditions_XA required residual oxygen amount target value corresponding to the target value;

and detecting the actual residual oxygen amount of the engine exhaust in real time, and performing PID control on the opening degree of the EGR valve by taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters for PID control regulation.

Preferably, the method further comprises the following steps:

taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value;

and adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

Preferably, the acquisition of the engine operating conditions reaches the primary NO_XThe target value of the required residual oxygen amount corresponding to the target value comprises the following steps:

reaching the original NO according to various working conditions of the calibrated engine_XThe target value obtains the corresponding residual oxygen amount and formsMap of residual oxygen demand;

and determining the required residual oxygen amount target value of each working condition of the engine according to the residual oxygen amount demand map.

Preferably, the calibration of each working condition of the engine to reach the primary NO_XThe target value obtains the corresponding residual oxygen amount, including:

and manually adjusting the opening degree of the EGR valve for each working condition point on the engine bench, and recording the corresponding residual oxygen amount when each working condition point reaches the original NOx emission target value.

Preferably, the method further comprises the following steps:

acquiring a corresponding relation between the opening of an EGR valve and the residual oxygen amount of engine exhaust to form a corresponding table of the opening and the residual oxygen amount;

proportional coefficient K for PID control_PIntegral coefficient K_IAnd a differential coefficient K_DAnd calibrating and pre-controlling the opening of the EGR valve according to the corresponding table.

Preferably, the method further comprises the following steps:

acquiring an EGR valve opening and an EGR rate target value, and calculating according to the EGR valve opening to obtain an actual EGR rate;

and taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment, and carrying out PID control on the opening degree of the EGR valve.

The present invention also provides a closed loop control system for engine EGR, comprising:

a first obtaining unit for obtaining the original NO of the engine_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value;

a second acquisition unit for acquiring the original NO of the engine under various working conditions_XA required residual oxygen amount target value corresponding to the target value;

an oxygen sensor for detecting an actual amount of residual oxygen of the engine exhaust in real time;

and the first PID controller is used for taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters of PID control adjustment and carrying out PID control on the opening degree of the EGR valve.

Preferably, the method further comprises the following steps: an EGR valve opening degree adjusting unit;

the first PID controller is also used for taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value;

and the EGR valve opening degree adjusting unit is used for adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

Preferably, the method further comprises the following steps:

a third acquisition unit, configured to acquire a correspondence between an opening degree of the EGR valve and a remaining oxygen amount of the engine exhaust gas to form a correspondence table of the opening degree and the remaining oxygen amount;

a pre-control unit for controlling the proportional coefficient K of PID_PIntegral coefficient K_IAnd a differential coefficient K_DAnd calibrating and pre-controlling the opening of the EGR valve according to the corresponding table.

Preferably, the method further comprises the following steps:

the fourth acquisition unit is used for acquiring the EGR valve opening and the EGR rate target value and calculating the actual EGR rate according to the EGR valve opening;

and the second PID controller is used for performing PID control on the opening degree of the EGR valve by taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment.

The invention provides a closed-loop control method and a closed-loop control system for engine EGR (exhaust gas recirculation), which can solve the problem of inaccuracy in the existing engine EGR control by detecting the actual residual oxygen amount of engine exhaust in real time and taking the target value of the actual residual oxygen amount and the required residual oxygen amount as input parameters for PID control adjustment to perform PID control on the opening degree of an EGR valve, can ensure that the EGR rate in the whole life cycle of an engine always meets the target value of NOx emission, and can improve the gasoline combustion performance of the engine.

Drawings

In order to more clearly describe the specific embodiments of the present invention, the drawings to be used in the embodiments will be briefly described below.

FIG. 1 is a schematic diagram of engine EGR operation.

FIG. 2 is a schematic diagram of a closed-loop engine EGR control method provided by the present invention.

FIG. 3 is a schematic diagram of a closed loop control system for engine EGR provided by the present invention.

Detailed Description

In order to make the technical field of the invention better understand the scheme of the embodiment of the invention, the embodiment of the invention is further described in detail with reference to the drawings and the implementation mode.

Aiming at the problem of inaccurate control of the EGR of the engine at present, the invention provides a closed-loop control method and a closed-loop control system for the EGR of the engine, which are used for carrying out PID control on the opening degree of an EGR valve by detecting the actual residual oxygen amount of the exhaust gas of the engine in real time and taking the target value of the actual residual oxygen amount and the required residual oxygen amount as input parameters for PID control regulation, thereby solving the problem of inaccuracy of the existing EGR control of the engine, ensuring that the EGR rate of the engine in the whole life cycle always meets the target value of NOx emission, and improving the gasoline combustion performance of the engine.

As shown in FIG. 2, a closed-loop control method for engine EGR includes:

s1: obtaining engine raw NO_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value.

S2: obtaining the original NO of the engine under various working conditions_XThe target value corresponds to a target value of the required residual oxygen amount.

S3: and detecting the actual residual oxygen amount of the engine exhaust in real time, and performing PID control on the opening degree of the EGR valve by taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters for PID control regulation.

Specifically, according to the combustion principle of the engine, fuel enters a cylinder to be mixed with fresh air, and combustion is performed at high temperature and high pressureReaction to form H₂O、CO₂While also generating a portion of the exhaust pollutants, such as CO, NO, HC, etc.

For modes of oxygen-rich (oxygen excess, excess air factor generally above 1.2) combustion, O in fresh air₂There are 3 basic paths into the cylinder:

combustion reaction of diesel oil:

CxHy+l₀O₂→CO₂+H₂O；

the reaction is only related to the physicochemical property of the fuel, and the stoichiometric ratio l is determined by the fuel property₀Determined (e.g., for diesel fuel, the stoichiometric ratio is equal to about 3), the fraction O₂The consumption m' is l₀*m₂。

②N₂High-temperature oxygen-rich reaction occurs to generate NOx:

N₂+O₂→NOx；

n in the air under the oxygen-enriched high-temperature environment in the cylinder₂Will react with O₂A reaction occurs to form NOx. For diesel engines, the main component of NOx can be considered to be NO, i.e. the above formula can be simplified.

N₂+O₂→2NO；

This part O₂The relation between the consumption m 'and the exhaust gas NO is m' -2 m_NO。

③ O not participating in the reaction due to rich O2₂The rest is m_O2For example, the residual unreacted O2 in diesel exhaust accounts for about 15% of the total exhaust.

The basic principle of oxygen conservation shows that under a certain working condition, O participating in fuel combustion₂To determine known l₀*m₂And is with N₂This part of the reaction O₂As the temperature environment, EGR rate, etc. vary, and are uncertain. If an oxygen sensor is added to the exhaust to measure residual O₂Through the principle of conservation: and N₂Reacted O₂Amount-oxygen content in fresh intake air (generally considered to be about 21% oxygen content in air) -amount of oxygen consumed by fuel-amount of residual oxygen participating in the reactionGas quantity, i.e. m ═ m₁*21％-m'-m_O2。

The method comprises the steps of obtaining a map of the NOx of the original exhaust, determining a NOx target value of each working condition, adjusting the opening degree of an EGR valve to enable the actual measured value of the NOx of the original exhaust to reach the NOx target value, and recording the residual oxygen amount m of the exhaust at the moment_O2That is, the measured value of the exhaust oxygen sensor is obtained, and the residual oxygen amount m of the whole working condition is collected_O2To obtain the residual oxygen amount m_O2A map is required. During actual engine operation, PID regulation is adopted, so that the actual residual oxygen mO2 reaches the required value. For the closed-loop control of the EGR valve, namely the pre-control of the opening degree of the EGR valve and the amount m of the residual oxygen can be adopted_O2And carrying out closed-loop control in a PID regulation control combination mode. The EGR rate in the whole life cycle of the engine can be ensured to always meet the target value of the original NOx emission, and the gasoline combustion performance of the engine is improved.

The method further comprises the following steps:

s4: taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value;

s5: and adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

In practical application, for a certain operating point, for the (i + 1) th calculation, the EGR valve opening EGR_ACT(i+1)＝EGR_ACT(i)+u(i)。

The PID calculation output value u (i) in the above equation can be obtained according to the following calculation formula:

wherein e (i) is the difference between the residual oxygen demand value and the actual residual oxygen amount during the ith calculation; e (n) calculating the integral value of all the difference values for the previous n times; k_PFor the scaling factor, the actual engineering example may be constant, or may be a function of e (i), and the term P (K)_PE (i)) to approach a stable value; k_IFor integral coefficients, practical engineering examplesMay be constant or may be a function of e (I), term IEliminating dynamic error between the stable value and the target value; k_DFor the differential coefficient, the actual engineering example can be constant, or can be a function of e (i), and the D term (K)_D*[e(i)-e(i-1)]) The overshoot effect caused when the dynamic error is eliminated by introducing the integral term is eliminated to the maximum extent.

Through multiple iterative calculations, stable u (i) and EGR valve opening EGRACT are finally calculated, namely stable actual residual oxygen amount is obtained, and therefore the aim that the actual value reaches the required value is achieved.

Further, the obtained working conditions of the engine reach the original NO_XThe target value of the required residual oxygen amount corresponding to the target value comprises the following steps:

reaching the original NO according to various working conditions of the calibrated engine_XThe target value obtains the corresponding residual oxygen amount, and a residual oxygen amount demand map is formed.

And determining the required residual oxygen amount target value of each working condition of the engine according to the residual oxygen amount demand map.

Furthermore, the calibration of the engine to reach the original NO exhaust condition_XThe target value obtains the corresponding residual oxygen amount, including:

and manually adjusting the opening degree of the EGR valve for each working condition point on the engine bench, and recording the corresponding residual oxygen amount when each working condition point reaches the original NOx emission target value.

The method further comprises the following steps:

s6: acquiring a corresponding relation between the opening of an EGR valve and the residual oxygen amount of engine exhaust to form a corresponding table of the opening and the residual oxygen amount;

s7: proportional coefficient K for PID control_PIntegral coefficient K_IAnd a differential coefficient K_DAnd calibrating and pre-controlling the opening of the EGR valve according to the corresponding table.

The PID control coefficients (P term, I term and D term) are properly calibrated, so that the opening of the EGR valve can quickly and accurately reach a stable value by utilizing a PID controller in the actual engine running process, and the actual residual oxygen amount reaches a residual oxygen amount required value.

The method further comprises the following steps:

s8: acquiring an EGR valve opening and an EGR rate target value, and calculating according to the EGR valve opening to obtain an actual EGR rate;

s9: and taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment, and carrying out PID control on the opening degree of the EGR valve.

Therefore, the invention provides a closed-loop control method for engine EGR, which can solve the problem of inaccuracy of the existing engine EGR control by detecting the actual residual oxygen amount of the engine exhaust in real time and taking the target value of the actual residual oxygen amount and the required residual oxygen amount as the input parameters of PID control adjustment to perform PID control on the opening degree of an EGR valve, can ensure that the EGR rate in the whole life cycle of the engine always meets the target value of the original NOx emission, and improves the gasoline combustion performance of the engine.

Accordingly, as shown in FIG. 3, the present invention also provides a closed loop control system for engine EGR, comprising: a first obtaining unit for obtaining the original NO of the engine_Xmap, and according to said NO_Xmap for determining primary NO corresponding to each working condition of engine_XA target value. A second acquisition unit for acquiring the original NO of the engine under various working conditions_XThe target value corresponds to a target value of the required residual oxygen amount. And the oxygen sensor is used for detecting the actual residual oxygen amount of the engine exhaust in real time. And the first PID controller is used for taking the actual residual oxygen amount and the required residual oxygen amount target value as input parameters of PID control adjustment and carrying out PID control on the opening degree of the EGR valve.

The system further comprises: EGR valve opening degree adjusting unit. And the first PID controller is also used for taking the difference value between the actual residual oxygen amount and the required residual oxygen amount target value as a feedback value of PID control, and calculating to obtain the fluctuation amount output by the PID according to the feedback value. And the EGR valve opening degree adjusting unit is used for adjusting the opening degree of the EGR valve according to the fluctuation amount so as to gradually reduce the difference until the actual residual oxygen amount is equal to the required residual oxygen amount target value.

The system further comprises: and the third acquisition unit is used for acquiring the corresponding relation between the opening degree of the EGR valve and the residual oxygen amount of the engine exhaust so as to form a corresponding table of the opening degree and the residual oxygen amount. A pre-control unit for controlling the proportional coefficient K of PID_PIntegral coefficient K_IAnd a differential coefficient K_DAnd calibrating and pre-controlling the opening of the EGR valve according to the corresponding table.

The system further comprises: and the fourth acquisition unit is used for acquiring the EGR valve opening and the EGR rate target value and calculating the actual EGR rate according to the EGR valve opening. And the second PID controller is used for performing PID control on the opening degree of the EGR valve by taking the difference value between the actual EGR rate and the EGR rate target value as an input parameter for PID control adjustment.

Therefore, the invention provides a closed-loop control system for engine EGR, which can solve the problem of inaccuracy of the existing engine EGR control by detecting the actual residual oxygen amount of the engine exhaust in real time and taking the target value of the actual residual oxygen amount and the required residual oxygen amount as the input parameters of PID control adjustment to perform PID control on the opening degree of an EGR valve, can ensure that the EGR rate in the whole life cycle of the engine always meets the target value of the original NOx emission, and can improve the gasoline combustion performance of the engine.

The construction, features and functions of the present invention have been described in detail with reference to the embodiments shown in the drawings, but the present invention is not limited to the embodiments shown in the drawings, and all equivalent embodiments modified or modified by the spirit and scope of the present invention should be protected without departing from the spirit of the present invention.