CN110748425B - Natural gas engine transient air-fuel ratio control method - Google Patents
Natural gas engine transient air-fuel ratio control method Download PDFInfo
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- CN110748425B CN110748425B CN201910941224.5A CN201910941224A CN110748425B CN 110748425 B CN110748425 B CN 110748425B CN 201910941224 A CN201910941224 A CN 201910941224A CN 110748425 B CN110748425 B CN 110748425B
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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
- F02D41/02—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
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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
- F02D41/0002—Controlling intake air
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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
- F02D41/0027—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures the fuel being gaseous
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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
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
-
- 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
- F02D2041/001—Controlling intake air for engines with variable valve actuation
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
Abstract
The invention relates to a transient air-fuel ratio control method for a natural gas engine, which comprises the following steps: obtaining a basic intake air amount based on the engine speed and the intake pressure/intake flow rate; obtaining an air inflow corrected value based on the engine speed change rate, the throttle opening change rate and the basic air inflow; obtaining a basic fuel gas injection quantity based on the intake air amount correction value and the target air-fuel ratio; obtaining a gas injection quantity correction quantity based on the target air-fuel ratio and the air-fuel ratio detection value and based on the time delay of the feedback control system; obtaining the final gas injection quantity based on the gas injection quantity correction quantity and the basic gas injection quantity; and determining PWM output of the gas injection system based on the final gas injection quantity to realize the transient air-fuel ratio control of the engine. Compared with the prior art, the method corrects the intake air amount calculated value under the transient working condition, and takes the time delay characteristic of air-fuel ratio adjustment into consideration, so that the transient air-fuel ratio control of the engine is more accurate.
Description
Technical Field
The invention relates to the field of engine control, in particular to a transient air-fuel ratio control method for a natural gas engine.
Background
The use of natural gas as a fuel for engines has advantages of economy, low pollution discharge, and the replacement of increasingly scarce petroleum resources, and thus has been widely used. However, the advantages of natural gas start-up require reasonable combustion organization and control to be realized. The natural gas engine basically adopts the working mode of a gasoline engine, and can be controlled by adopting a classical electric control mode, namely, under the steady-state working condition, the excess air coefficient is controlled in a closed loop mode by utilizing the feedback of an oxygen sensor.
The Chinese patent of invention CN108119246A adjusts the PWM wave duty ratio of the EGR valve control motor according to the deviation between the measured air-fuel ratio and the theoretical air-fuel ratio to realize the adjustment of the air-fuel ratio, the method does not consider the time delay characteristic of the air-fuel ratio adjustment, the adjustment of the air-fuel ratio through the EGR valve has hysteresis, and the air injection quantity is not compensated through the throttle opening change rate and the rotating speed change rate.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a natural gas engine transient air-fuel ratio control method which considers the correction of the throttle opening change rate and the rotating speed change rate on the air intake quantity and the time delay characteristic of an air-fuel ratio control system.
The purpose of the invention can be realized by the following technical scheme:
a transient air-fuel ratio control method for a natural gas engine is characterized by comprising the following steps:
step S1: based on engine speed n and intake pressure pinIntake air flow rate QMObtaining the basic intake air quantity Mair；
Step S2: based on the engine speed change rate Deltan and the throttle opening change rate DeltathetathrottleAnd basic intake air quantity MairObtaining a corrected value M of the intake air quantityair'；
Step S3: based on the correction value M of the intake air quantityair' and the target air-fuel ratio AFR, the basic gas injection quantity M is obtainedfuel；
Step S4: obtaining the correction quantity delta M of the gas injection quantity based on the target air-fuel ratio AFR and the air-fuel ratio detection value and based on the time delay T of the feedback control systemfuel；
Step S5: correction quantity delta M based on gas injection quantityfuelAnd basic gas injection quantity MfuelTo obtain the final gas injection quantity Mfuel'；
Step S6: based on the final gas injection quantity MfuelDetermining the PWM output of the fuel gas injection system and realizing the transient air-fuel ratio control of the engine.
The basic intake air quantity M is obtainedairThe calculation formula of (2) is as follows:
Mair＝f(n，pin)/Mair＝f(n，QM)。
obtaining a corrected value M of the air inflowairThe formula for calculation of' is:
Mair'＝Mair·η(Δn,Δθthrottle)
wherein η is a correction coefficient, and is positively correlated with the rate of change of the engine speed and the rate of change of the throttle opening.
Obtaining the basic gas injection quantity MfuelThe calculation formula of (2) is as follows:
Mfuel＝Mair'/AFR。
the difference value delta AFR between the target air-fuel ratio AFR and the air-fuel ratio detection value is used as the input of the feedback controller, and is based on the difference value delta AFR and the time delay of the feedback control systemT, obtaining the correction quantity delta M of the gas injection quantityfuel。
The feedback controller is a PID feedback controller.
Time delay T based on feedback control system, parameter K to feedback controllerp、KiAnd KdMaking a correction to obtain a corrected feedback controller parameter Kp'、Ki' and Kd'：
Kp'＝Kp+ΔKp(T)
Ki'＝Ki+ΔKi(T)
Kd'＝Kd+ΔKd(T)
Wherein, Δ Kp(T)、ΔKi(T) and. DELTA.Kd(T) is a correction term, depending on the time delay T.
Gas injection quantity correction quantity delta MfuelThe calculation formula of (2) is as follows:
where t is time and Δ t is the time difference.
The final fuel gas injection quantity Mfuel' is represented as:
Mfuel'＝Mfuel+ΔMfuel。
compared with the prior art, the invention has the following advantages:
(1) and correcting the measured air inflow according to the throttle opening change rate and the rotating speed change rate to enable the air inflow to be closer to an actual value, and determining the fuel gas injection quantity based on the air inflow correction value, so that the accuracy and the response speed of air-fuel ratio control are improved.
(2) The time delay characteristic of the air-fuel ratio control system is considered, and the parameters of the PID controller are corrected according to the system time delay so as to reduce the steady-state error of the control system.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a feedback control system incorporating a delay element in accordance with the present invention;
FIG. 3 is a schematic diagram of a feedback control architecture of the present invention;
FIG. 4 is a logic block diagram of the present invention for determining a base gas injection quantity;
reference numerals:
1 is a throttle position sensor; 2 is an air inlet pressure sensor; 3 is an air inlet temperature sensor; 4 is a gas ejector; 5 is a spark plug; and 6 is an oxygen sensor.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
Examples
The embodiment provides a transient air-fuel ratio control method of a natural gas engine, which comprises the following steps as shown in FIG. 1:
step S1: based on engine speed n and intake pressure pinIntake air flow rate QMObtaining the basic intake air quantity Mair；
Step S2: based on the engine speed change rate Deltan and the throttle opening change rate DeltathetathrottleAnd basic intake air quantity MairObtaining a corrected value M of the intake air quantityair'；
Step S3: based on the correction value M of the intake air quantityair' and the target air-fuel ratio AFR, the basic gas injection quantity M is obtainedfuel；
Step S4: obtaining the correction quantity delta M of the gas injection quantity based on the target air-fuel ratio AFR and the air-fuel ratio detection value and based on the time delay T of the feedback control systemfuel；
Step S5: correction quantity delta M based on gas injection quantityfuelAnd basic gas injection quantity MfuelTo obtain the final gas injection quantity Mfuel'；
Step S6: based on the final gas injection quantity MfuelDetermining the PWM output of the fuel gas injection system and realizing the transient air-fuel ratio control of the engine.
FIG. 4 is a logic diagram for determining a base gas injection amount.
Under the steady state working condition, the air quantity entering the cylinder in each cycle can be determined according to the rotating speed of the engine and the air inlet pressure/air inlet flow, under the transient working condition, the air inlet state of the engine continuously changes along with time, such as the rapid acceleration working condition, the opening of a throttle valve is rapidly increased, the air inlet pressure and the air inlet flow are obviously improved, if the reaction of a flow meter is slow, a large error exists between the calculated value and the actual value of the air inlet quantity, so the air inlet quantity is corrected according to the rotating speed change rate of the engine and the opening change rate of the throttle valve, and the basic fuel gas injection quantity can be determined based on the.
In particular, the method of manufacturing a semiconductor device,
the basic intake air amount has a positive correlation with the engine speed and the intake pressure/intake air flow rate, and the relationship is expressed as:
Mair＝f(n，pin)/Mair＝f(n，QM)
based on the engine speed rate of change, the throttle opening rate of change and the basic intake air amount, the formula for obtaining the intake air amount correction value is as follows:
Mair'＝Mair·η(Δn,Δθthrottle)
wherein η is a correction coefficient, and is positively correlated with the rate of change of the engine speed and the rate of change of the throttle opening.
The formula for obtaining the basic gas injection quantity based on the intake air quantity correction value and the target air-fuel ratio is as follows:
Mfuel＝Mair'/AFR。
in order to eliminate or reduce errors and improve the response speed of the system, closed-loop control needs to be introduced. Fig. 3 is a schematic diagram of an air-fuel ratio feedback control structure, a throttle position sensor 1, an intake pressure sensor 2, an intake temperature sensor 3 and a gas injector 4 are installed on an intake side, a spark plug 5 is installed on a cylinder head, an oxygen sensor 6 is installed on an exhaust side, a throttle opening change rate can be obtained by the throttle position sensor 1, an intake pressure can be obtained by the intake pressure sensor 2, an intake density can be calculated by the intake temperature sensor 3, then an intake flow can be obtained, and an air-fuel ratio detection value can be obtained by the oxygen sensor 6. The feedback controller takes the difference value between the air-fuel ratio detection value and the air-fuel ratio target value as input, determines a gas injection quantity correction quantity according to the difference value, and the sum of the basic gas injection quantity and the gas injection quantity correction quantity is the final gas injection quantity.
From the combustible gas formed by injecting the fuel gas to the detection of the air-fuel ratio state by the oxygen sensor, obvious time delay exists, and in order to ensure that the design of the controller is more consistent with the practical application condition and improve the responsiveness and stability of the system, a time delay link needs to be introduced.
Fig. 2 shows a feedback control system with a delay unit, and the conventional feedback control method usually ignores the delay characteristic of the air-fuel ratio adjustment, so that the controller parameters obtained through simulation calculation are usually not optimal. The time delay is influenced by the rotating speed of the engine, the opening degree of a throttle valve and the installation positions of an ejector and an oxygen sensor, under the condition of a certain structure, the time delay is related to the operation condition of the engine, the selection of parameters of a feedback controller is influenced by the time delay, and the introduction of a time delay link has important significance for the parameter optimization of the controller.
Specifically, the difference between the target air-fuel ratio and the detected value of the air-fuel ratio is used as an input of the feedback controller, and the gas injection amount correction amount is obtained based on the difference and the time delay of the feedback control system.
Preferably, the feedback controller is a PID feedback controller.
Parameter K to feedback controller based on time delay of feedback control systemp、KiAnd KdMaking a correction to obtain a corrected feedback controller parameter Kp'、Ki' and Kd'：
Kp'＝Kp+ΔKp(T)
Ki'＝Ki+ΔKi(T)
Kd'＝Kd+ΔKd(T)
Wherein, Δ Kp(T)、ΔKi(T) and. DELTA.Kd(T) is a correction term, depending on the time delay T.
Gas injection quantity correction quantity delta MfuelThe calculation formula of (2) is as follows:
where t is time and Δ t is the time difference.
Final gas injection quantity Mfuel' is represented as:
Mfuel'＝Mfuel+ΔMfuel。
the embodiment has the following advantages:
correcting the measured and calculated air inflow according to the throttle opening change rate and the rotating speed change rate to enable the air inflow to be closer to an actual value, and determining the fuel gas injection quantity based on the air inflow correction value, so that the accuracy and the response speed of air-fuel ratio control are improved; the time delay characteristic of the air-fuel ratio control system is considered, and the parameters of the PID controller are corrected according to the system time delay so as to reduce the steady-state error of the control system.
Claims (5)
1. A transient air-fuel ratio control method for a natural gas engine is characterized by comprising the following steps:
step S1: based on engine speed n and intake pressure pinIntake air flow rate QMObtaining the basic intake air quantity Mair；
Step S2: based on the engine speed change rate Deltan and the throttle opening change rate DeltathetathrottleAnd basic intake air quantity MairObtaining a corrected value M of the intake air quantityair'；
Step S3: based on the correction value M of the intake air quantityair' and the target air-fuel ratio AFR, the basic gas injection quantity M is obtainedfuel；
Step S4: obtaining the correction quantity delta M of the gas injection quantity based on the target air-fuel ratio AFR and the air-fuel ratio detection value and based on the time delay T of the feedback control systemfuel；
Step S5: correction quantity delta M based on gas injection quantityfuelAnd basic gas injection quantity MfuelTo obtain the final gas injection quantity Mfuel'；
Step S6: based on the final gas injection quantity MfuelDetermining the PWM output of a fuel gas injection system to realize the transient air-fuel ratio control of the engine;
obtaining a corrected value M of the air inflowairThe formula for calculation of' is:
Mair'＝Mair·η(Δn,Δθthrottle)
wherein eta is a correction coefficient and is positively correlated with the change rate of the engine rotating speed and the change rate of the throttle opening;
the difference value delta AFR between the target air-fuel ratio AFR and the air-fuel ratio detection value is used as the input of a feedback controller, and the gas injection quantity correction quantity delta M is obtained based on the difference value delta AFR and the time delay T of a feedback control systemfuel；
Time delay T based on feedback control system, parameter K to feedback controllerp、KiAnd KdMaking a correction to obtain a corrected feedback controller parameter Kp'、Ki' and Kd'：
Kp'＝Kp+ΔKp(T)
Ki'＝Ki+ΔKi(T)
Kd'＝Kd+ΔKd(T)
Wherein, Δ Kp(T)、ΔKi(T) and. DELTA.Kd(T) is a correction term, dependent on the time delay T;
gas injection quantity correction quantity delta MfuelThe calculation formula of (2) is as follows:
where t is time and Δ t is the time difference.
2. The natural gas engine transient air-fuel ratio control method according to claim 1, characterized in that the basic intake air amount M is obtainedairIs calculated byComprises the following steps:
Mair＝f(n，pin)/Mair＝f(n，QM)。
3. the transient air-fuel ratio control method of a natural gas engine according to claim 1, characterized in that the basic gas injection quantity M is obtainedfuelThe calculation formula of (2) is as follows:
Mfuel＝Mair'/AFR。
4. the transient air-fuel ratio control method of the natural gas engine as claimed in claim 1, wherein the feedback controller is a PID feedback controller.
5. The transient air-fuel ratio control method for natural gas engine according to claim 1, characterized in that the final fuel gas injection quantity Mfuel' is represented as:
Mfuel'＝Mfuel+ΔMfuel。
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| CN111828191B (en) * | 2020-03-24 | 2021-10-08 | 同济大学 | Air-fuel ratio control system and method of hybrid power engine |
| CN112114090B (en) * | 2020-08-07 | 2023-02-24 | 宁波吉利罗佑发动机零部件有限公司 | Excess air coefficient control method, device, equipment and storage medium |
| CN112594073B (en) * | 2020-12-15 | 2022-09-23 | 潍柴动力股份有限公司 | Control method of air-fuel ratio of engine and engine |
| CN112761803A (en) * | 2021-01-04 | 2021-05-07 | 潍柴动力股份有限公司 | Gas injection transient compensation method and device, vehicle and storage medium |
| CN113343597B (en) * | 2021-06-01 | 2023-04-18 | 潍柴动力股份有限公司 | Method and device for calculating virtual pressure behind throttle valve |
| CN113202652B (en) * | 2021-06-18 | 2023-08-18 | 潍柴动力股份有限公司 | Gas engine gas injection correction method and gas engine |
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| JPH1030479A (en) * | 1996-07-18 | 1998-02-03 | Unisia Jecs Corp | Air-fuel ratio controller of internal combustion engine |
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| CN104734588B (en) * | 2015-03-09 | 2018-01-05 | 山东大学 | A kind of biogas internal combustion engine generator group method for controlling number of revolution |
| CN107387249B (en) * | 2017-06-20 | 2020-05-05 | 上海工程技术大学 | Method for controlling transient air-fuel ratio of high-power gas engine |
| CN109184932B (en) * | 2018-08-06 | 2020-10-02 | 天津内燃机研究所（天津摩托车技术中心） | Control method for transient working condition air-fuel ratio of high-speed gasoline engine |
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| JPH03237244A (en) * | 1990-02-13 | 1991-10-23 | Hitachi Ltd | Air-fuel ratio controller for each cylinder in idling in internal combustion engine |
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