CN115199422B - Control method of mixing valve of low-pressure EGR system - Google Patents

Control method of mixing valve of low-pressure EGR system Download PDF

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CN115199422B
CN115199422B CN202210755996.1A CN202210755996A CN115199422B CN 115199422 B CN115199422 B CN 115199422B CN 202210755996 A CN202210755996 A CN 202210755996A CN 115199422 B CN115199422 B CN 115199422B
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mixing valve
inlet
outlet
pressure difference
state
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CN115199422A (en
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鲁盼
秦龙
王冬
张凡武
赵宁
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Dongfeng Motor Corp
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Dongfeng Motor Corp
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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
    • 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
    • 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
    • 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
    • F02D2041/141—Introducing closed-loop corrections characterised by the control or regulation method using a feed-forward control element
    • 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
    • F02D2200/10—Parameters related to the engine output, e.g. engine torque or engine speed
    • F02D2200/101—Engine speed
    • 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
    • F02M2026/001—Arrangements; Control features; Details
    • F02M2026/003—EGR valve controlled by air measuring device
    • 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
    • F02M2026/001—Arrangements; Control features; Details
    • F02M2026/005—EGR valve controlled by an engine speed signal
    • 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

Abstract

The application discloses a control method of a mixing valve of a low-pressure EGR system. The minimum mixing valve opening is calculated by the pressure difference between the inlet and the outlet of the maximum mixing valve; the opening degree of the mixing valve is regulated according to the dynamic working condition, the pressure difference between the inlet and the outlet of the mixing valve is regulated according to the dynamic working condition, and the final actual pressure difference between the inlet and the outlet of the mixing valve is obtained by a feedforward part and an accumulation control part. The mixing valve control is performed to achieve the target EGR rate, namely, the maximum capacity increases the EGR rate, and meanwhile, the stability of an EGR control system is improved and the influence on torque precision is avoided.

Description

Control method of mixing valve of low-pressure EGR system
Technical Field
The application relates to a control method of a mixing valve, in particular to a control method of a mixing valve of a low-pressure EGR system, and belongs to the technical field of engine control.
Background
The low-pressure EGR can realize reduced oil consumption and HC emission, and is a good solution for achieving national 6B by adopting RDE real vehicle driving circulation. Compared with high-pressure EGR, low-pressure EGR is used for taking gas after a turbine, so that the turbine efficiency is not lost, and the low-pressure EGR can be used for almost all working conditions, so that the fuel efficiency is improved remarkably, but because the pressure difference is low, a large-caliber valve is needed to meet the flow requirement. And under partial working conditions, the pressure of the outlet of the EGR valve is regulated by the boost mixing valve, so that the pressure difference of two sides of the EGR valve is improved, and the EGR rate is improved.
Chinese patent publication No. CN112901361a, entitled EGR system mixing valve target opening determination method, discloses an EG system mixing valve target opening determination method, which determines a mixing valve target opening according to engine operating parameters after mixing valve opening control is activated. By controlling the opening of the mixing valve in the EGR system, the stability of the pressurizing capacity is ensured, and the response precision and accuracy of the EGR rate control are improved.
Disclosure of Invention
It is an object of this patent to provide a control method for a low pressure EGR system mixing valve that differs from the prior art control principle.
In order to make the description of the present application clear, the low-pressure EGR system to which the present application relates will be briefly described.
As shown in FIG. 1, the low pressure EGR system comprises an air filter, a booster compressor, a throttle valve, an engine, a booster turbine, a catalyst, a particulate trap, an EGR cooler, an EGR valve, an EGR temperature sensor, an EGR differential pressure sensor, a flow meter, a linear oxygen sensor, and a mixing valve.
The compressor of the booster, compress the fresh air and boost; the turbocharger turbine controls the working efficiency of the turbine by controlling the opening of a waste gate valve of the turbocharger, thereby realizing different supercharging capacities; wherein the low pressure EGR system has increased components relative to a non-low pressure EGR system: an EGR cooler, an EGR temperature sensor, an EGR valve, an EGR differential pressure sensor, a mixing valve, a flow meter and an oxygen sensor; wherein a flow meter is mounted between the air filter and the mixing valve for detecting the flow of fresh air into the engine; the mixing valve is used for adjusting the pressure of an outlet of the EGR valve, improving the pressure difference of two ends of the EGR valve and improving the EGR rate; an oxygen sensor installed between the compressor and the throttle valve, close to the throttle valve, for detecting the flow of the mixed gas into the cylinder; an EGR cooler for cooling the exhaust gas, facilitating an increase in the flow rate of the exhaust gas and a decrease in the temperature of the exhaust gas; an EGR valve, which controls the flow of exhaust gas into the cylinder; an EGR temperature sensor for detecting the temperature of exhaust gas entering the EGR valve; and an EGR differential pressure sensor for detecting a difference in exhaust gas pressure between both sides of the EGR.
The application provides a control method of a mixing valve of a low-pressure EGR system, which comprises the following steps:
firstly, determining the minimum mixing valve opening of a system, and then adjusting the opening of the mixing valve according to dynamic working conditions.
The further scheme is as follows:
the minimum mixing valve opening is calculated by the pressure difference between the inlet and the outlet of the maximum mixing valve.
The further scheme is as follows:
the calculation process of the maximum mixing valve inlet and outlet pressure difference is as follows:
setting the mixing valve inlet pressure p of the system InMixture Outlet pressure p OutMixture The pressure difference delta p between the inlet and the outlet of the mixing valve Mixture ＝p InMixture -p OutMixture The maximum value of the pressure difference between the inlet and the outlet of the mixing valve is deltap MixtureMax ；
Step one, according to the target fresh air charge density Rho of the engine AirDsrd With the actual engine speed n Eng Determining the pressure difference delta p between the inlet and the outlet of the maximum mixing valve of the rack MixtureMaxRaw 。
The method specifically comprises the following steps: under the conditions that the target fresh air intake density and the actual engine speed of each stage steady-state working condition are gradually reduced, on the premise that the EGR rate response accuracy and the torque accuracy are ensured to be met, the point with the maximum pressure difference between the inlet and the outlet of the mixing valve with the optimal oil consumption is selected as the maximum pressure difference delta p between the inlet and the outlet of the mixing valve of the stage MixtureMaxRaw 。
The further scheme is as follows:
on the premise of ensuring that the response accuracy of the EGR rate and the torque accuracy are met, namely that the difference between the actual EGR rate and the target EGR rate is in an index range, the difference between the actual EGR rate and the target EGR rate divided by the target EGR rate is not allowed to exceed 1%, and the torque accuracy error requires: the torque of the flywheel end of the engine is less than +/-5 Nm within 100Nm, and the torque of the flywheel end of the engine is less than +/-5% within more than 100 Nm.
And secondly, carrying out transition treatment on the pressure difference between the inlet and the outlet of the maximum mixing valve of the rack, so as to avoid that the power and the air inlet pressure output fluctuation exceed the preset fluctuation range.
The further scheme is as follows:
and setting the pressure difference increment change rate in the transitional process according to the power fluctuation allowable fluctuation range, wherein if the preset torque output fluctuation range exceeds +/-10 percent and the intake air pressure fluctuation is lower than +/-2 KPa, the torque control precision is not met.
The further scheme is as follows:
adjusting the final maximum mixing valve inlet and outlet pressure difference deltap according to different conditions MixtureMax Control setting state:
condition 1, the EGR valve front-rear pressure difference p when the EGR control state is changed from the unactivated state to the activated state (the EGR control state being in the activated state means that the EGR rate is greater than 0 and the EGR rate is in closed-loop control; the EGR control state being in the unactivated state means that the EGR rate is equal to 0 or the EGR rate is not in closed-loop control) InEGR -p OutEGR Less than the inlet and outlet pressure difference delta p of the maximum mixing valve of the rack MixtureMaxRaw When, i.e. max [ (Δp) MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]<Δp MixtureMaxRaw At the time, the final maximum mixing valve inlet and outlet pressure difference delta p MixtureMax The control state is in the Ramp Up state.
If the control state of the last sampling period deltat is in the Ramp Up state, the maximum mixing valve inlet and outlet pressure difference deltap of the last sampling period MixtureMaxOld Adding a variation dp MixtureDeltaInc X deltat is determined as the current maximum mixing valve inlet and outlet pressure differential deltap MixtureMax . Time of day monitoring Δp MixtureMaxOld +dp MixtureDeltaInc X Deltat and the pressure difference (p) between the front and rear of the EGR valve InEGR -p OutEGR ) Maximum max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]Less than the inlet and outlet pressure difference delta p of the maximum mixing valve of the rack MixtureMaxRaw At this time, the control state maintains the Ramp Up state. Ensuring front and rear pressure of EGR valveThe difference is maximized or the mixing valve differential pressure is maximized to ensure proper flow of EGR gas into the cylinder. The final requested maximum mixing valve inlet and outlet pressure differential Δp in the Ramp Up state MixtureMax Taking max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]。
Condition 2 once max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]Not less than the inlet and outlet pressure difference delta p of the maximum mixing valve of the rack MixtureMaxRaw And updating the control state into an Active state. Once the control state is Active, the control state does not enter the Ramp Up state from Active, but only enters the Ramp Down state according to condition 3. And finally the maximum mixing valve inlet and outlet pressure difference delta p MixtureMax Maintaining a maximum mixing valve inlet and outlet pressure differential Δp for a stand MixtureMaxRaw 。
And 3, when the EGR control state enters the inactive state, the control state enters the Ramp Down state from the Active state. Time of day monitoring Δp MixtureMaxOld +dp MixtureDeltaDec X Deltat and the pressure difference (p) between the front and rear of the EGR valve InEGR -p OutEGR ) The minimum value of (2), i.e., min [ (Δp) MixtureMaxOld +dp MixtureDeltaDec ×Δt),(p InEGR -p OutEGR )]When it is greater than 0, the control state is the Ramp Down state and the final requested maximum mixing valve inlet and outlet pressure differential Δp MixtureMax Equal to deltap MixtureMaxOld +dp MixtureDeltaDec X Δt, up to min [ (Δp) MixtureMaxOld +dp MixtureDeltaDec ×Δt),(p InEGR -p OutEGR )]When the pressure difference is not greater than 0, the control state is updated to be an Off state, and finally the maximum mixing valve inlet and outlet pressure difference delta p is requested MixtureMax Equal to 0. Once condition 1 is satisfied again, the state control of condition 1 is re-entered.
Up to this point, the final requested maximum mixing valve inlet and outlet pressure differential Δp MixtureMax And (5) determining.
The further scheme is as follows:
according to dynamic working conditionThe opening of the mixing valve is regulated according to the dynamic working condition Mixture R eq ，
Final actual mixing valve inlet and outlet pressure difference Δp MixtureReq Which is formed by a feedforward portion Deltap MixtureReqFF +accumulation control section Δp MixtureReqIPart Obtained.
The further scheme is as follows:
the feed forward portion is the engine target fresh air charge density Rho AirDsrd With the actual engine speed n Eng And (5) determining.
The further scheme is as follows:
accumulation control section Deltap MixtureReqIPart Is determined by the following method:
when the boost pressure increase control state is the Off state, the accumulation control portion Δp MixtureReqIPart Is 0;
when the boost pressure increase control state is not the Off state, the accumulation control portion Δp MixtureReqIPart The obtaining method comprises the following steps:
1) Rho based on engine target fresh air charge density AirDsrd With the actual engine speed n Eng Determining an optimal EGR control valve outlet and inlet exhaust gas target pressure ratio r EGRValvePresRatioDsrd Comparing it with actual pressureDifference is made to obtain r EGRValvePresRatioErr And find the rate of change dr of the difference EGRValvePresRatioErr . According to the pressure ratio difference r EGRValvePresRatioErr Sum pressure ratio difference change rate dr EGRValvePresRatioErr Determining an accumulation control section accumulation change rate Deltap MixtureReqIPartGain 。
Δp MixtureReqIPart (N+1)＝Δp MixtureReqIPart (N)+Δp MixtureReqIPartGain (N+1)×Δt×(r EGRValvePresRatioErr (N+1)-k MixtureWindUpGain ×Δp Satu (N+1))
In particular Δp MixtureReqIPart (0)＝0，k MixtureWindUpGain To inversely integrate the saturation coefficient Δp Satu (n+1) is the integral saturation differential pressure value in the (n+1) th sampling period, and the time interval of the sampling period is deltat.
The further scheme is as follows:
pressure difference delta p between inlet and outlet of mixing valve MixtureReq By a feed-forward part Δp MixtureReqFF +accumulation control section Δp MixtureReqIPart Obtained and limited to 0 and the maximum mixing valve inlet and outlet pressure difference deltap MixtureMax In, Δp Satu (N+1)＝Δp MixtureReq (N)-[Δp MixtureReqFF (N)+Δp MixtureReqIPart (N)]。
The further scheme is as follows:
according to the pressure difference delta p between the inlet and the outlet of the mixing valve MixtureReq And mixing valve inlet pressure p InMixture The mixing valve outlet pressure p can be determined OutMixture 。
Based on the compressible gas equationThe effective area of the mixing valve is obtained by back calculation, and then the target opening initial value pct of the mixing valve is obtained by back calculation MixtureDsrdRaw
The further scheme is as follows:
setting the target opening of the mixing valve into three modes, namely a non-throttling mode, a protection mode and a throttling mode, wherein:
1) Protection mode, i.e. initial value of target opening pct MixtureDsrdRaw The change rate exceeds a preset value, and the target opening initial value pct MixtureDsrdRaw Full opening (100%), and the actual opening of the current mixing valve is not full opening (not 100%), the absolute value S1 of the allowable opening change rate is limited, and according to experimental data and analysis conclusion, the condition that the fluctuation of the outlet pressure of the mixing valve is too large when the mixing valve enters the full opening (the fluctuation of the inlet pressure of a compressor of a supercharger is too large due to the excessive outlet pressure, and meanwhile, the fluctuation of the outlet pressure of an EGR valve is too large to cause poor combustion stability and unstable supercharging control is avoided)
2) Non-throttled mode: target opening degreeInitial value pct MixtureDsrdRaw Is fully opened, and the actual opening of the current mixing valve is also fully opened, the absolute value S2 of the allowable opening change rate is limited, and pressure fluctuation possibly occurs when the mixing valve is used as a throttle valve when the mixing valve enters the throttle state from the non-throttle state.
3) Throttle mode: the allowable opening degree change rate absolute value S3 is limited in the case other than the 1 st and 2 nd. That is, pressure fluctuation is avoided while the EGR rate response speed is ensured.
The priorities are lower and lower (i.e. the priority judgment of the 1 st condition is highest, the priority judgment of the 3 rd condition is lowest), and S1< S2< S3.
So far, the target opening of the mixing valve is completely determined, and the action of the motor of the valve plate of the mixing valve is controlled based on the target opening of the mixing valve and the actual opening of the mixing valve read by the sensor, so that the actual opening follows the target opening.
The application has the following beneficial effects:
the hybrid valve control is used to achieve a target EGR rate, i.e., maximum capacity increases the EGR rate while improving stability of the EGR control system and avoiding impact on torque accuracy.
Drawings
FIG. 1 is a schematic diagram of a low pressure EGR system architecture;
FIG. 2 is a flow chart of a method of controlling a mixing valve of a low pressure EGR system.
Detailed Description
The application will now be described in further detail with reference to the drawings and to specific examples.
Fig. 1 shows the basic constitution of a low-pressure EGR system, and this embodiment mainly describes the control method of a hybrid valve in the low-pressure EGR system. The mixing valve should be in an unthrottled/fully open state when not controlled, ensuring a sufficient amount of fresh air and throttling losses. However, under some conditions, the mixing valve needs to enter a throttled state to reduce the pressure at the EGR outlet, thereby increasing the pressure differential across the EGR valve and improving the EGR rate and its response rate, but a decrease in the opening of the mixing valve results in insufficient pressurization capability and a throttling loss (which increases pumping work). It is therefore desirable to select different mixing valve target opening under different conditions, i.e., to improve EGR system performance while reducing the impact on boost and throttle.
The opening of the mixing valve can determine the effective area A of the mixing valve according to the structural characteristics ValveEff Mixing valve flow from flowmeter sensorAnd mixing valve inlet temperature T Valve And pressure p InMixture Can be according to the compressible gas equationObtaining the outlet pressure p of the mixing valve OutMixture 。
Gas pressure p from outlet of mixing valve OutMixture Divided by mixing valve inlet pressure p InMixture Determining, determining specific calibration parameters according to flow prediction of the mixing valve and corresponding flow meter calibration results, wherein the results in the embodiment are as follows:
therefore, the effective area of the mixing valve and the outlet pressure of the mixing valve are in one-to-one correspondence on the premise that the flow rate, the inlet temperature and the pressure of the mixing valve are determined. According to the corresponding relation between the opening degree of the mixing valve and the effective area:
therefore, the opening degree of the mixing valve and the outlet pressure of the mixing valve are in one-to-one correspondence on the premise that the flow rate, the inlet temperature and the pressure of the mixing valve are determined. At this time, the larger the opening of the mixing valve is, the larger the outlet pressure is, and the smaller the pressure difference between the inlet and the outlet of the mixing valve is.
The embodiment simplifies the design, and under the dynamic working condition, the opening of the mixing valve is determined and calculated by the pressure difference between the inlet and the outlet of the mixing valve on the premise that the flow rate of the mixing valve and the inlet temperature and the inlet pressure change slowly.
As shown in figure 2, the method firstly determines the minimum mixing valve opening (the maximum pressure difference between the inlet and the outlet of the mixing valve) of the system, and then adjusts the opening of the mixing valve according to the dynamic working condition.
First, the pressure difference delta p between the inlet and outlet of the mixing valve of the system is determined Mixture ＝p InMixture -p OutMixture Is a maximum value deltap of (1) MixtureMax
First, according to the target fresh air charge density Rho of the engine AirDsrd With the actual engine speed n Eng Determining the pressure difference delta p between the inlet and the outlet of the maximum mixing valve of the rack MixtureMaxRaw . Under the conditions of each target fresh air intake density and the actual rotation speed of the engine under the steady-state working condition of the rack, the method selects a point with the maximum pressure difference between the inlet and the outlet of the mixing valve with the optimal oil consumption as the maximum pressure difference delta p between the inlet and the outlet of the mixing valve of the rack on the premise of ensuring the accurate response of the EGR rate and the satisfaction of the torque precision (namely, the difference between the actual EGR rate and the target EGR rate is within an index range, the difference between the actual EGR rate and the target EGR rate is not allowed to exceed 1% by the target EGR rate in the embodiment, the torque precision error requirement is that the torque of the flywheel end of the engine is less than +/-5 Nm within 100Nm, and the torque of the flywheel end of the engine is less than +/-5% within more than 100 Nm) MixtureMaxRaw . In this embodiment, the following is described
And secondly, carrying out transition treatment on the pressure difference between the inlet and the outlet of the maximum mixing valve of the rack, and avoiding that the power and the air inlet pressure output fluctuation exceed the preset fluctuation range. The rate of change of the differential pressure increase during the transition is set according to the allowable fluctuation range of the power fluctuation. The preset torque output fluctuation range of the embodiment exceeds +/-10%, and the intake air pressure fluctuation is lower than +/-2 KPa, which indicates that the torque control precision is not satisfied. This embodiment
1) The maximum pressure differential increase rate of change dp when the supercharger control closed loop is not activated MixtureDe l taInc The maximum pressure difference was reduced by the absolute value dp of the rate of change at 14kPa/s MixtureDe l taDec 25kPa/s.
2) The maximum pressure differential increases the rate of change dp upon activation of the supercharger control closed loop MixtureDe l taInc The maximum pressure difference was reduced by the absolute value dp of the change rate at 20kPa/s MixtureDe l taDec 40kPa/s.
Adjusting the final maximum mixing valve inlet and outlet pressure difference Δp MixtureMax Control sets 4 states:
1. when the EGR control state is changed from the inactive state to the active state (the EGR control state being in the active state means that the EGR rate is greater than 0 and the EGR rate is in closed-loop control; the EGR control state being in the inactive state means that the EGR rate is equal to 0 or the EGR rate is not in closed-loop control), the EGR valve front-rear pressure difference (p InEGR -p OutEGR ) (i.e., EGR valve inlet and EGR valve outlet gas pressure differential) is less than the bench maximum mixing valve inlet and outlet pressure differential Δp MixtureMaxRaw When, i.e. max [ (Δp) MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]<Δp MixtureMaxRaw At the time, the final maximum mixing valve inlet and outlet pressure difference delta p MixtureMax The control state is in the Ramp Up state.
If the control state of the last sampling period deltat (sampling time interval of 10ms in the present embodiment) is in the Ramp Up state, the maximum mixing valve inlet and outlet pressure difference deltap of the last sampling period MixtureMaxOld (i.e. Δp MixtureMax Last employed period value) plus a variation dp MixtureDeltaInc X deltat is determined as the current maximum mixing valve inlet and outlet pressure differential deltap MixtureMax . Time of day monitoring Δp MixtureMaxOld +dp MixtureDeltaInc X Deltat and the pressure difference (p) between the front and rear of the EGR valve InEGR -p OutEGR ) Maximum max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]Less than the inlet and outlet pressure difference delta p of the maximum mixing valve of the rack MixtureMaxRaw At this time, the control state maintains the Ramp Up state. The maximum pressure difference before and after the EGR valve or the maximum pressure difference of the mixing valve is ensured, so that the normal flow guiding of the EGR gas into the cylinder is ensured. The final requested maximum mixing valve inlet and outlet pressure differential Δp in the Ramp Up state MixtureMax Taking max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]。
2. Once max [ (Δp) MixtureMaxOld +dp MixtureDeltaInc ×Δt),(p InEGR -p OutEGR )]Not less than the inlet and outlet pressure difference delta p of the maximum mixing valve of the rack MixtureMaxRaw And updating the control state into an Active state. Once the control state is Active, the control state does not enter the Ramp Up state from Active, but only enters the Ramp Down state according to condition 3. And finally the maximum mixing valve inlet and outlet pressure difference delta p MixtureMax Maintaining a maximum mixing valve inlet and outlet pressure differential Δp for a stand MixtureMaxRaw 。
3. When the EGR control state is brought into the inactive state, the control state is brought from the Active state into the Ramp Down state. Time of day monitoring Δp MixtureMaxOld +dp MixtureDeltaDec X Deltat and the pressure difference (p) between the front and rear of the EGR valve InEGR -p OutEGR ) The minimum value of (2), i.e., min [ (Δp) MixtureMaxOld +dp MixtureDeltaDec ×Δt),(p InEGR -p OutEGR )]When it is greater than 0, the control state is the Ramp Down state and the final requested maximum mixing valve inlet and outlet pressure differential Δp MixtureMax Equal to deltap MixtureMaxOld +dp MixtureDeltaDec X Δt, up to min [ (Δp) MixtureMaxOld +dp MixtureDeltaDec ×Δt),(p InEGR -p OutEGR )]When the pressure difference is not greater than 0, the control state is updated to be an Off state, and finally the maximum mixing valve inlet and outlet pressure difference delta p is requested MixtureMax Equal to 0. Once condition 1 is satisfied again, the state control of condition 1 is re-entered.
To this end, the final requestMaximum mixing valve inlet and outlet pressure differential Δp MixtureMax And (5) determining.
Regulating the pressure difference delta p between the inlet and the outlet of the mixing valve according to the dynamic working condition MixtureReq
The next step will be to make the final actual mixing valve inlet and outlet pressure difference Δp MixtureReq Which is formed by a feedforward portion Deltap MixtureReqFF +accumulation control section Δp MixtureReqIPart Obtained. Wherein the feed forward portion is the engine target fresh air charge density Rho AirDsrd With the actual engine speed n Eng And (5) determining.
When the boost pressure increase control state is the Off state, the accumulation control portion Δp MixtureReqIPart Is 0; when the boost pressure increase control state is not the Off state, the accumulation control portion Δp MixtureReqIPart The obtaining method comprises the following steps:
1. rho based on engine target fresh air charge density AirDsrd With the actual engine speed n Eng Determining an optimal EGR control valve outlet and inlet exhaust gas target pressure ratio r EGRValvePresRatioDsr d (the determination of the target pressure ratio is based on the request for EGR rate under that condition), and comparing it to the actual pressure ratioDifference is made to obtain r EGRValvePresRatioErr And find the rate of change dr of the difference EGRValvePresRatioErr . According to the pressure ratio difference r EGRValvePresRatioErr Sum pressure ratio difference change rate dr EGRValvePresRatioErr Determining an accumulation control section accumulation change rate Deltap MixtureReqIPartGain 。
Δp MixtureReqIPart (N+1)＝Δp MixtureReqIPart (N)+Δp MixtureReqIPartGain (N+1)×Δt×(r EGRValvePresRatioErr (N+1)-k MixtureWindUpGain ×Δp Satu (n+1)), in particular Δp MixtureReqIPart (0)＝0，k MixtureWindUpGain For the inverse integral saturation coefficient, the present example takes 0.02/kPa, Δp Satu (n+1) is the integral saturation differential pressure value in the (n+1) th sampling period, and the time interval of the sampling period is deltat. Pressure difference delta p between inlet and outlet of mixing valve MixtureReq By a feed-forward part Δp MixtureReqFF +accumulation control section Δp MixtureReqIPart Obtained and limited to 0 and the maximum mixing valve inlet and outlet pressure difference deltap MixtureMax In, Δp Satu (N+1)＝Δp MixtureReq (N)-[Δp MixtureReqFF (N)+Δp MixtureReqIPart (N)]To this end, the final mixing valve inlet and outlet pressure differential Δp MixtureReq Control is completed.
According to the pressure difference delta p between the inlet and the outlet of the mixing valve MixtureReq And mixing valve inlet pressure p InMixture The mixing valve outlet pressure p can be determined OutMixture 。
Based on the compressible gas equationThe effective area of the mixing valve is obtained by back calculation, and then the target opening initial value pct of the mixing valve is obtained by back calculation MixtureDsrdRaw
Setting the target opening of the mixing valve into three modes, namely a non-throttling mode, a protection mode and a throttling mode, wherein:
1) Protection mode, i.e. initial value of target opening pct MixtureDsrdRaw The change rate exceeds a preset value (i.e. the request becomes larger, 50%/s is taken in this embodiment), and the target opening initial value pct MixtureDsrdRaw Full opening (100% at maximum opening) and the current actual opening of the mixing valve is not full opening (not 100% at maximum opening), limiting its allowanceXu Kaidu absolute value S1 (35%/S is taken in this embodiment), according to experimental data and analysis conclusion, to avoid the conditions of poor combustion stability and unstable control of boost pressure caused by excessive fluctuation of inlet pressure of a compressor of a supercharger due to excessive fluctuation of outlet pressure of an EGR valve when the mixing valve is fully opened
2) Non-throttled mode: target opening initial value pct MixtureDsrdRaw Is fully opened, and the actual opening of the current mixing valve is also fully opened, the absolute value S2 (the absolute value of the allowable opening change rate is-42%/S is limited, and the mixing valve is prevented from being used as a throttle valve to possibly generate pressure fluctuation once the target opening control mode of the mixing valve enters the throttle mode from the non-throttle mode.
3) Throttle mode: the allowable opening degree change rate absolute value S3 is limited in the case other than the 1 st and 2 nd. (80%/s is taken in this embodiment), that is, pressure fluctuation is avoided while the EGR rate response speed is ensured.
The priorities are lower and lower (i.e. the priority judgment of the 1 st condition is highest, the priority judgment of the 3 rd condition is lowest), and S1< S2< S3.
So far, the target opening of the mixing valve is completely determined, and the action of the motor of the valve plate of the mixing valve is controlled based on the target opening of the mixing valve and the actual opening of the mixing valve read by the sensor, so that the actual opening follows the target opening.
Although the application has been described herein with reference to the above-described illustrative embodiments thereof, the foregoing embodiments are merely preferred embodiments of the present application, and it should be understood that the embodiments of the present application are not limited to the above-described embodiments, and that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope and spirit of the principles of this disclosure.

Claims (1)

1. A control method of a low-pressure EGR system mixing valve, characterized by:
firstly, determining the minimum mixing valve opening of a system, and then adjusting the opening of the mixing valve according to dynamic working conditions; wherein the mixing valve is a throttle valve for regulating the EGR valve outlet pressure;
the minimum mixing valve opening is calculated by the pressure difference between the inlet and the outlet of the maximum mixing valve, and the pressure difference between the inlet and the outlet of the maximum mixing valve is calculated as follows:
setting the mixing valve inlet pressure of the systemOutlet pressure->The pressure difference between the inlet and the outlet of the mixing valveThe maximum value of the pressure difference between the inlet and the outlet of the mixing valve is +.>；
Step one, according to the target fresh air charge density of the engineIs +/from the actual engine speed>Determining the maximum pressure difference between the inlet and the outlet of the mixing valve of the rack +.>；
Step two, carrying out transition treatment on the pressure difference between the inlet and the outlet of the maximum mixing valve of the rack, so as to avoid that the output fluctuation of power and air inlet pressure exceeds a preset fluctuation range;
the first step specifically comprises: under the condition that the target fresh air intake density and the actual engine speed of each steady-state working condition of the rack are met, on the premise that the EGR rate response accuracy and the torque accuracy are ensured, the point with the maximum pressure difference between the inlet and the outlet of the mixing valve with the optimal oil consumption is selected as the maximum pressure difference between the inlet and the outlet of the mixing valve of the rackThe method comprises the steps of carrying out a first treatment on the surface of the The EGR rate response accuracy is ensured, namely the difference between the actual EGR rate and the target EGR rate is within an index range, and the difference between the actual EGR rate and the target EGR rate divided by the target EGR rate is not allowed to exceed 1%;
the second step specifically comprises: setting the increment change rate of the pressure difference in the transitional process according to the allowable fluctuation range of the power fluctuation, and adjusting the pressure difference between the inlet and the outlet of the final maximum mixing valve according to different conditionsControl setting state:
condition 1, pressure difference between front and rear of EGR valve when EGR control state is changed from inactive state to active state and />Is less than the maximum mixing valve inlet and outlet pressure difference of the rack>When, i.eAt the moment, the final maximum mixing valve inlet and outlet pressure difference +.>The control state is in a Ramp Up state;
if the last sampling periodIs in Ramp Up state, the maximum mixing valve inlet and outlet pressure difference of the last sampling period +.>Add variation->Determined as the current maximum mixing valve inlet and outlet pressure difference +.>The method comprises the steps of carrying out a first treatment on the surface of the Time of day monitoring->Pressure difference between front and rear of EGR valveMaximum value of>Less than the maximum mixing valve inlet and outlet pressure difference of the bench +.>When the control state is in a Ramp Up state; ensuring that the front-back pressure difference of the EGR valve reaches the maximum or the pressure difference of the mixing valve reaches the maximum so as to ensure that the EGR gas is normally guided into the cylinder; the maximum mixing valve inlet and outlet pressure difference finally requested in the Ramp Up state +.>Taking out；
Condition 2, onceNot less than the maximum mixing valve inlet and outlet pressure difference of the bench +.>When the control state is updated to be an Active state; once the control state is Active, the control state does not enter the Ramp Up state from Active, but only enters the Ramp Down state according to the condition 3; and finally the maximum pressure difference between the inlet and the outlet of the mixing valve/>Maintaining the maximum mixing valve inlet and outlet pressure difference of the stand +.>；
The condition 3, when the EGR control state enters the inactive state, the control state enters the Ramp Down state from the Active state; time of day monitoringPressure difference before and after the EGR valve>Minimum value of (2), i.eWhen it is greater than 0, the control state is the Ramp Down state and the final requested maximum mixing valve inlet and outlet pressure difference +.>Equal toUp to->When the pressure difference is not more than 0, the control state is updated to Off state, and the finally requested maximum mixing valve inlet and outlet pressure difference is +.>Equal to 0; once condition 1 is satisfied again, the state control of condition 1 is re-entered;
up to this point, the maximum mixing valve inlet and outlet pressure differential ultimately requestedDetermining;
according toThe opening degree of the mixing valve is regulated according to the dynamic working condition, and the pressure difference between the inlet and the outlet of the mixing valve is regulated according to the dynamic working condition，
Final actual mixing valve inlet and outlet pressure differentialWhich is made up of a feedforward part->+ accumulation control section->Obtaining;
the feed forward portion targets engine target fresh air charge densityIs +/from the actual engine speed>Determining;
accumulation control sectionIs determined by the following method:
when the boost pressure increase control state is an Off state, the accumulation control portionIs 0;
when the boost pressure increase control state is not the Off state, the accumulation control portionThe obtaining method comprises the following steps:
based on engine target fresh air charge densityIs +/from the actual engine speed>Determining the optimal EGR valve outlet and inlet exhaust gas target pressure ratio +.>Comparing it with the actual pressure +.>Difference is made to obtainAnd find the change rate of the difference +.>The method comprises the steps of carrying out a first treatment on the surface of the According to the differential pressure->And the rate of change of the pressure ratio difference +.>Determining the accumulation control section accumulation rate of change +.>；
，/>For the inverse integral saturation coefficient +.>Is the integral saturation pressure difference value in the (n+1) th sampling periodThe time interval of the sampling period is +.>；
Pressure difference between inlet and outlet of mixing valveIs added by the feedforward part>+accumulation control sectionObtained and limited to 0 and maximum mixing valve inlet and outlet pressure difference +.>In the inner part of the inner part,；
according to the pressure difference between the inlet and the outlet of the mixing valveAnd mixing valve inlet pressure->The mixing valve outlet pressure can be determined>；
Based on the compressible gas equationBack-calculating to obtain effective area of mixing valve, back-calculating to obtain target opening initial value +.>；
wherein ,representing the mixing valve flow rate from the flow meter sensor; />Indicating the mixing valve effective area; r represents a gas constant; t (T) Valve Indicating the mixing valve inlet temperature; />Indicating the calibration parameters, the gas pressure from the outlet of the mixing valve +.>Divided by mixing valve inlet pressure>Determining;
setting the target opening of the mixing valve into three modes, namely a non-throttling mode, a protection mode and a throttling mode, wherein:
1) Protection mode, i.e. initial value of target openingThe change rate exceeds a preset value and the target opening initial valueFully-opened, and the actual opening of the current mixing valve is not fully-opened, limiting the absolute value S1 of the allowable opening change rate of the current mixing valve, and according to experimental data and analysis conclusion, avoiding overlarge fluctuation of the outlet pressure of the mixing valve when the mixing valve enters fully-opened;
2) Non-throttled mode: initial value of target openingWhen the mixing valve is fully opened and the current actual opening of the mixing valve is fully opened, the allowable opening change rate absolute value S2 is limited, and the mixing valve is taken as a throttle valve to possibly generate pressure fluctuation when the mixing valve enters a throttle state from a non-throttle state;
3) Throttle mode: limiting the allowable opening degree change rate absolute value S3 in the case other than the 1 st and 2 nd; the EGR rate response speed is ensured, and meanwhile, pressure fluctuation is avoided;
priorities from 1) to 3) are lower and lower, and S1< S2< S3.
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