CN115559822A - Method for controlling target EGR rate - Google Patents
Method for controlling target EGR rate Download PDFInfo
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- CN115559822A CN115559822A CN202211185754.XA CN202211185754A CN115559822A CN 115559822 A CN115559822 A CN 115559822A CN 202211185754 A CN202211185754 A CN 202211185754A CN 115559822 A CN115559822 A CN 115559822A
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- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000002485 combustion reaction Methods 0.000 claims abstract description 38
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 38
- 238000010438 heat treatment Methods 0.000 claims abstract description 18
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- 238000009499 grossing Methods 0.000 claims description 3
- 230000008901 benefit Effects 0.000 abstract description 5
- 239000007789 gas Substances 0.000 description 17
- 230000002159 abnormal effect Effects 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 230000002542 deteriorative effect Effects 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 238000012544 monitoring process Methods 0.000 description 3
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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]
- F02D41/0065—Specific aspects of external EGR control
- F02D41/0072—Estimating, calculating or determining the EGR rate, amount or flow
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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
- F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
- F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
- F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
- F02D2021/083—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine controlling exhaust gas recirculation electronically
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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
- 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
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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
- F02D2200/00—Input parameters for engine control
- F02D2200/70—Input parameters for engine control said parameters being related to the vehicle exterior
- F02D2200/703—Atmospheric pressure
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- 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
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- Exhaust-Gas Circulating Devices (AREA)
- Output Control And Ontrol Of Special Type Engine (AREA)
Abstract
The invention discloses a control method of a target EGR rate, which comprises the following steps: determining a basic target EGR rate according to the engine speed and the load; determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion times, engine starting water temperature, outdoor temperature, engine working conditions, ignition efficiency, engine rotating speed and a heating request; and determining a standard target EGR rate according to the basic target EGR rate and the multiplication factor. Has the advantages that: the request conditions of different working conditions of the engine are considered, the possibility that the EGR rate is too large or too small is avoided, and the problem that the closed-loop control stability of the EGR rate is not high is solved.
Description
Technical Field
The invention relates to the technical field of engine control, in particular to a control method of a target EGR rate.
Background
Exhaust Gas Recirculation (EGR), which takes exhaust gas from the exhaust gas into the intake system. Research shows that the EGR system has certain advantages in improving emission, reducing oil consumption and improving anti-knock capability. However, the EGR system has a serious delay due to a long pipe distance from the control of EGR exhaust gas to the actual exhaust gas entering the cylinder, and the unstable control of the EGR system may deteriorate the combustion stability of the engine. In order to avoid the problems that the EGR rate is possibly too large or too small and the stability of the closed-loop control of the EGR rate is not high, a control method of the target EGR rate is provided on the basis of the problems.
Disclosure of Invention
In view of the above-identified deficiencies in the art or needs for improvement, it is an object of the present invention to provide a method for controlling a target EGR rate.
In order to achieve the purpose, the invention adopts the following technical scheme:
a control method of a target EGR rate, characterized by comprising the steps of:
determining a basic target EGR rate according to the engine speed and the load;
determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion times, engine starting water temperature, outdoor temperature, engine working conditions, ignition efficiency, engine rotating speed and a heating request;
and determining a standard target EGR rate according to the basic target EGR rate and the multiplication factor.
In a preferred embodiment, the step of determining the multiplication factor based on the atmospheric pressure, the current engine water temperature, the number of engine combustions, the engine starting water temperature, the outdoor temperature, the engine operating condition, the ignition efficiency, the engine speed, and the heating request comprises:
determining a first multiplication factor according to the atmospheric pressure and the current engine water temperature;
determining a second multiplication factor according to the engine combustion times and the outdoor temperature;
determining a third multiplication factor according to the current engine water temperature and the engine starting water temperature;
determining a fourth multiplication factor according to the current engine water temperature and the outdoor temperature;
determining a fifth multiplicative factor according to the ignition efficiency;
determining a sixth multiplicative factor as a function of the engine speed and the ignition efficiency in a catalyst diagnostic request;
determining a seventh multiplication factor according to the engine speed and the ignition efficiency in the GPF active regeneration control request;
the eighth multiplicative factor is determined based on a heating request in the engine other than a catalyst light-off heating request and a GPF active regeneration heating request.
In a preferred embodiment, the step of determining a standard target EGR rate based on the base target EGR rate and the multiplication factor includes:
the standard target EGR rate is determined by the base target EGR rate, a first multiplicative factor, a second multiplicative factor, a third multiplicative factor, a fourth multiplicative factor, a fifth multiplicative factor, a sixth multiplicative factor, a seventh multiplicative factor, and an eighth multiplicative factor.
In a preferred embodiment, the step of determining the standard target EGR rate further comprises:
and determining an ideal target EGR rate according to the actual EGR rate and the standard target EGR rate in a preset time period.
In a preferred embodiment, the step of determining an ideal target EGR rate based on the actual EGR rate and the standard target EGR rate for a preset period of time includes a first strategy of:
the absolute value of the deviation between the actual EGR rate and the standard target EGR rate is less than 1%, the second time duration and the time interval between the second time duration and the activation of the EGR rate closed-loop control zone bit reach the first time duration, and the ideal target EGR rate is determined to be the standard target EGR rate; or
And after the closed-loop control zone bit of the EGR rate is activated, if the ratio of the gas pressure behind the throttle valve to the gas pressure in front of the throttle valve is detected to be smaller than a preset value, determining the ideal target EGR rate as the standard target EGR rate.
In a preferred embodiment, the step of determining an ideal target EGR rate based on the actual EGR rate and the standard target EGR rate at the preset time period further comprises: if the first strategy is not satisfied, executing a second strategy, wherein the second strategy comprises:
and if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the previous preset time period is monitored to be smaller than or equal to a third threshold value or the engine request flame path torque exceeds a preset range of the maximum torque capacity, immediately restoring the ideal target EGR rate to be the standard target EGR rate.
In a preferred embodiment, the step of determining an ideal target EGR rate based on the actual EGR rate and the standard target EGR rate at the preset time period further comprises: if the first strategy and the second strategy are not satisfied, executing a third strategy, wherein the third strategy comprises:
if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the previous preset time period is monitored to be smaller than or equal to a first threshold, increasing a second threshold to the ideal target EGR rate to serve as a new ideal target EGR rate, wherein the first threshold, the second threshold and the third threshold are sequentially reduced;
and gradually restoring the standard target EGR rate as the ideal target EGR rate after maintaining the new ideal target EGR rate for a third time period.
In a preferred embodiment, the step of determining an ideal target EGR rate based on the actual EGR rate and the standard target EGR rate at the preset time period further comprises: if the first strategy, the second strategy and the third strategy are not satisfied, executing a fourth strategy, wherein the fourth strategy comprises:
if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the last preset time period is monitored to be between the first threshold and the third threshold, and the absolute value of the change rate of the difference between the actual EGR rate and the ideal target EGR rate exceeds a preset change rate, increasing the ideal target EGR rate by a fourth threshold to serve as a new ideal target EGR rate, wherein the fourth threshold is between the first threshold and the second threshold;
after maintaining the new desired target EGR rate for a fourth time period, gradually restoring the standard target EGR rate as the desired target EGR rate.
In a preferred embodiment, the step of determining an ideal target EGR rate based on the actual EGR rate and the standard target EGR rate at the preset time period further comprises: and if the first strategy, the second strategy, the third strategy and the fourth strategy are not satisfied, the standard target EGR rate is an ideal target EGR rate.
In a preferred embodiment, the step of determining the desired target EGR rate is followed by:
and performing smoothing treatment on the ideal target EGR rate to determine a final target EGR rate.
The invention has the beneficial effects that: the method comprises the steps of determining a basic target EGR rate according to the rotating speed and the load of an engine, determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion times, engine starting water temperature, outdoor temperature, engine working conditions, ignition efficiency, engine rotating speed and heating requests, considering the request conditions of different working conditions of the engine according to the basic target EGR rate and the multiplication factor, avoiding the possibility of overlarge or undersize of the EGR rate, and solving the problem of low stability of closed-loop control of the EGR rate.
Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.
Drawings
The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a low pressure EGR system in an automotive engine;
fig. 2 is a flowchart of a control method provided in the present application.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, removably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood by those within the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The invention provides a control method of a target EGR rate, which is applied to an automobile engine, and FIG. 1 is a schematic structural diagram of a low-pressure EGR system in the automobile engine. Referring to FIG. 1, the system includes an air filter, a supercharger compressor, a throttle, an engine, a supercharger turbine, a catalyst, a particulate trap, an EGR cooler, an EGR valve, an EGR temperature sensor, an EGR differential pressure sensor, a flow meter, and a linear oxygen sensor (or linear oxygen sensor instead of an integrated temperature and pressure sensor).
The supercharger compressor is used for compressing fresh air for supercharging, and the supercharger turbine is used for controlling the working efficiency of the turbine by controlling the opening degree of a waste gas bypass valve of the supercharger, so that different supercharging capacities are realized.
The low-pressure EGR system is added to the non-low-pressure EGR system by the following components: EGR cooler, EGR temperature sensor, EGR valve, EGR differential pressure sensor, mixing valve, flow meter and oxygen sensor.
A flow meter is mounted between the air filter and the mixing valve for sensing the flow of fresh air into the engine. The mixing valve is used for adjusting the pressure at the outlet of the EGR valve, improving the pressure difference at two ends of the EGR valve and improving the EGR rate. An oxygen sensor is mounted between the compressor and the throttle valve and adjacent to the throttle valve for sensing the flow of mixture into the cylinder. The EGR cooler is used to cool the exhaust gas, facilitating an increase in the exhaust gas flow and a decrease in the exhaust gas temperature. The EGR valve acts as a throttle for controlling the flow of exhaust gas into the cylinder. The EGR temperature sensor is used to detect the temperature of exhaust gas entering the EGR valve. The EGR differential pressure sensor is used to detect a difference in exhaust gas pressure between both sides of EGR.
The EGR system has a serious hysteresis due to a long line distance from the control of EGR exhaust gas to the actual intake of exhaust gas into the cylinder, and the unstable control of the EGR system may cause the combustion stability of the engine to deteriorate. In order to avoid the possibility of too large or too small EGR rate and the problem of low stability of closed-loop control of the EGR rate, a control method of the target EGR rate is provided on the basis of the problem.
Fig. 2 is a flowchart of a control method provided in the present application, and as shown in fig. 2, the method includes: and S10, determining a basic target EGR rate according to the engine speed and the load.
In the present embodiment, a MAP table of engine speed-load-basic target EGR rate is preset. In the MAP table, basic target EGR rates corresponding to different engine speeds and different loads can be determined.
And S20, determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion times, engine starting water temperature, outdoor temperature, engine working condition, ignition efficiency, engine rotating speed and a heating request.
Specifically, S20 includes:
s201, determining a first multiplication factor eta according to atmospheric pressure and the current engine water temperature 1 。
It can be understood that the lower the atmospheric pressure or the lower the temperature of the engine water, i.e. the leaner the air or the lower the temperature of the mixture/the poorer the atomization effect, the poorer the combustion stability of the engine is caused, and the EGR rate needs to be properly reduced to reduce the influence on the combustion stability of the engine and avoid the abnormal shaking of the engine.
S202, determining a second multiplication factor eta according to the combustion times of the engine and the outdoor temperature 2 。
The number of engine combustion times is the sum of the number of ignition times of each cylinder from the start of the engine. The smaller the combustion frequency of the engine is or the lower the outdoor temperature is, the engine is not in a warming-up working condition, the poorer the combustion stability of the engine is, the more the EGR rate needs to be properly reduced to reduce the influence on the combustion stability of the engine, and the abnormal shaking of the engine is avoided.
In this embodiment, the second multiplication factor eta is obtained when the outdoor temperature is higher than 20 DEG C 2 Set to 1, the lower the outdoor temperature is, the lower the temperature is, the second multiplication factor eta 2 The smaller.
S203, determining a third multiplication factor eta according to the current engine water temperature and the engine starting water temperature 3 。
The lower the engine water temperature or the lower the air-fuel water temperature, the worse the engine combustion stability if the engine is not warmed up, and it is necessary to appropriately reduce the EGR rate to reduce the influence on the engine combustion stability and avoid the occurrence of abnormal engine hunting.
In this embodiment, the third multiplication factor η is greater than 40 ℃ when the engine temperature is higher than 3 Set to 1, the lower the temperature is when the engine temperature is less than or equal to 40 ℃, the third multiplication factor eta 3 The smaller. When the water temperature of the engine is over 40 ℃, the third multiplication factor eta 3 Setting the water temperature to be 1, when the temperature of the engine starting water is less than or equal to 40 ℃, the lower the temperature is, and the third multiplication factor eta is 3 The smaller.
S204, determining a fourth multiplication factor eta according to the current water temperature and the outdoor temperature of the engine 4 。
The lower the current engine water Wen Yuede or the outdoor temperature is, namely the engine is not in a warm-up working condition, the worse the engine combustion stability is, the influence on the engine combustion stability needs to be reduced by properly reducing the EGR rate, and the abnormal shaking of the engine is avoided.
In this embodiment, when the current engine water temperature is greater than 40 ℃, the fourth multiplication factor η 4 Set to 1, the lower the temperature is when the current engine water temperature is less than or equal to 40 ℃, the fourth multiplication factor eta 4 The smaller. When the outdoor temperature exceeds 25 ℃, the fourth multiplication factor eta 4 Set to 1, when the temperature of the engine starting water is less than or equal to 40 ℃, the lower the temperature is, the fourth multiplication factor eta 4 The smaller.
The first multiplication factor, the second multiplication factor, the third multiplication factor and the fourth multiplication factor aim at identifying and improving the combustion stability in the EGR control process according to the current working condition of the engine; the first multiplication factor to the fourth multiplication factor are determined by adopting the prior technical scheme based on the conception when the working condition of the engine is poor (such as the temperature and pressure signals are too small, the combustion of the engine is poor, the EGR rate needs to be reduced to improve the combustion stability, and the combustion condition of the engine is better after the temperature is increased, so that the EGR rate is recovered to improve the EGR benefit).
S205, determining a fifth multiplication factor eta according to the ignition efficiency 5 。
It should be noted that the lower the ignition efficiency is, the lower the fifth multiplication factor η 5 The smaller the size, the less the combustion stability is to be prevented from deteriorating.
In the present embodiment, the ignition efficiency is greater than 0.65, and the fifth multiplication factor η 5 Taking 1, the lower the firing efficiency, the lower the fifth multiplication factor when the firing efficiency is less than or equal to 0.65.
S206, diagnosing the engine speed and the point in the request according to the catalystFire efficiency, determining a sixth multiplicative factor eta 6 . It should be noted that the sixth multiplication factor η 6 The smaller the size, the less the combustion stability is prevented from deteriorating. When the engine speed is lower than 1500rpm and the ignition efficiency is lower than 0.65, the lower the ignition efficiency is, the sixth multiplication factor eta 6 The smaller; the engine speed is not lower than 1500rpm and the ignition efficiency is more than 0.65, and a sixth multiplication factor eta 6 1 is taken.
S207, determining a seventh multiplication factor eta according to the engine speed and the ignition efficiency in the GPF active regeneration control request 7 。
It should be noted that the seventh multiplication factor η 7 The smaller the size, the less the combustion stability is prevented from deteriorating. When the engine speed is lower than 1500rpm and the ignition efficiency is lower than 0.65, the lower the ignition efficiency is, the seventh multiplication factor eta 7 The smaller; the engine speed is not lower than 1500rpm, the ignition efficiency is more than 0.65, and a seventh multiplication factor eta 7 1 is taken.
S208, determining an eighth multiplication factor eta according to heating requests except the catalyst light-off heating request and the GPF active regeneration heating request in the engine 8 。
The fourth multiplication factors are used for identifying the aim of improving the combustion stability in the EGR control process according to the current working condition of the engine; the above-described eighth multiplicative factors are determined based on the above-described concept that the engine ignition efficiency is low when the engine has some request for heating, and that the engine combustion stability is poor if the EGR rate is too high at that time.
All the above eight multiplication factors (all values are greater than or equal to 0 and less than 1) are determined by ensuring that the engine combustion stability evaluation index COV is within ± 3%.
After step S20, step S30 is performed to determine a standard target EGR rate from the basic target EGR rate and the eight multiplication factors.
Standard target EGR Rate r EGRSetpointNormal Determined according to the following formula:
r EGRSetpointNormal ＝r EGRSetpointBase ·(1-r 1 )·(1-r 2 )·(1-r 3 )·(1-r 4 )·(1-r 5 )·(1-r 6 )·(1-r 7 )·(1-r 8 )。
and step S30, performing step S40, and determining an ideal target EGR rate according to the actual EGR rate and the standard target EGR rate in a preset time period.
Specifically, step S40 includes a first policy.
The first strategy is as follows: and when the absolute value of the deviation between the actual EGR rate and the standard target EGR rate is less than 1% and lasts for 30ms, the time interval between the actual EGR rate and the activation of the closed-loop control zone bit of the EGR rate reaches a first time length (in the embodiment, the first time length is set to be 2 s), and the ideal target EGR rate is determined to be the standard target EGR rate.
The first strategy described above also includes another possibility of determining the ideal target EGR rate as the standard target EGR rate if it is detected that the ratio of the gas pressure once after the throttle valve to the gas pressure before the throttle valve is less than 0.72 after the closed-loop control flag for the EGR rate is activated.
It is to be understood that in the first strategy, the ideal target EGR rate is identified once, when either of the above occurs.
If the first policy is not satisfied, the second policy is performed, and it can be understood that the first policy has priority over the second policy, and the second policy is used as a candidate policy for the first policy.
The second strategy comprises: if the absolute value of the difference between the real-time monitored actual EGR rate and the ideal target EGR rate for the last time period does not exceed C3, or the engine requested spark torque exceeds 0.95 times its maximum torque capacity, then the ideal target EGR rate is immediately restored to the standard target EGR rate.
This example C3 is set to 0.08%.
When the difference between the actual EGR rate and the ideal target EGR rate is small, the EGR rate control precision is high, and the ideal target EGR rate can be adopted for control.
If the first policy and the second policy are not satisfied, a third policy is performed, and it can be understood that both the first policy and the second policy have priority over the third policy, and the third policy is used as an alternative policy of the second policy.
The third strategy comprises: if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate for the previous time period exceeds C1, the ideal target EGR rate for the previous time period is increased by a preset value C2 as the ideal target EGR rate. Wherein C1 is greater than C2, and C2 is greater than C3. It can be understood that when the error of the EGR rate is larger, the amplitude of the closed-loop regulation of the EGR rate is limited, and the phenomenon that the EGR lag system is out of order and the control precision is reduced is avoided. In this example, 2% of C1 and 0.8% of C2 were used.
After the maintenance for 50ms, the standard target EGR rate is gradually restored, and in the present embodiment, the change of the gradual restoration is 0.02%/10ms, that is, the standard target EGR rate before the restoration is used as the ideal target EGR rate.
It can be understood that, when the target EGR rate is greatly different from the actual EGR rate, if the target EGR rate is directly adjusted to be the standard target EGR rate, the closed-loop control of the EGR rate is overshot, which causes the problem of combustion stability, and even causes the problem of abnormal high emission.
When none of the first, second and third policies are satisfied, the fourth policy is executed, it being understood that the third policy takes precedence over the fourth policy.
The fourth strategy comprises; if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate for the previous time period is bounded between C1 and C3, and the absolute value of the difference between the actual EGR rate and the ideal target EGR rate exceeds 0.1%/10ms, the ideal target EGR rate for the previous time period is increased by a preset value C4 as a new ideal target EGR rate. This example C4 is between C1 and C2, specifically, C4 is set to 0.6%. It can be understood that when the error of the EGR rate is not too large but the variation trend is large, the amplitude of closed-loop adjustment of the EGR rate also needs to be limited in a stepped manner, so that overshoot of the EGR delay system is avoided, and the control accuracy is reduced.
After the new ideal target EGR rate is maintained for 30ms, the standard target EGR rate is gradually restored as the ideal target EGR rate. It can be understood that when the difference between the target EGR rate and the actual EGR rate is large, if the target EGR rate is directly adjusted to be the standard target EGR rate, the closed-loop control of the EGR rate is overshot, which causes the problem of combustion stability, even the problem of abnormal and high emission.
In other states where the first strategy, the second strategy, the third strategy, and the fourth strategy are not satisfied, the ideal target EGR rate is the standard target EGR rate determined in step S20.
The first strategy has the highest priority, and the second strategy, the third strategy, the fourth strategy and the fifth strategy are arranged in sequence, namely the fifth strategy has the lowest priority, and the ideal target EGR rate is determined according to the strategies. The method avoids overlarge PID parameter adjustment when the difference between the target EGR rate and the actual EGR rate is overlarge during closed-loop control of the EGR rate, improves the response rate of the closed-loop control, and the smaller the adjustment rate is, the lower the stability of the closed-loop control is possibly.
In order to further realize accurate control of the EGR rate, the control method further includes step S50 after step S40.
Step S50 includes: the ideal target EGR rate determined in step S40 is smoothed to determine the final target EGR rate. Step S50 further avoids the problem that combustion stability is caused by poor closed-loop control accuracy of the EGR rate due to too large control and adjustment of the EGR rate, and even the problem that abnormal emission is too high and the like occurs.
Step S50 includes: and monitoring the ideal target EGR rate in real time, limiting the change rate of the ideal target EGR rate, limiting the ascending change rate R2 not to exceed the preset value, and limiting the descending change rate absolute value R3 not to exceed the descending preset value, wherein the ascending preset value in the embodiment is 0.05%/10ms, and the descending preset value is 0.07%/10ms.
In the present embodiment, the rising preset value is not greater than the falling preset value, in order to avoid poor combustion stability caused by too low in-cylinder temperature due to rapid increase of the EGR rate. After limiting its rate of change, a target EGR rate is determined that limits the rate of change.
And determining the final target EGR rate according to the ideal target EGR rate monitored in real time and the target EGR rate with the limited change rate.
The real-time monitoring means monitoring at a fixed cycle.
If the ideal target EGR rate is not equal to the ideal target EGR rate in the last time period, the absolute value of the ideal target EGR rate is greater than or equal to the absolute value of the target EGR rate with the limited change rate in the current time period, and the change of the ideal target EGR rate in the current time period is too large, the final target EGR rate is equal to the target EGR rate with the limited change rate.
If the above condition is not satisfied, the smoothing processing method of the final target EGR rate is as follows:
judging an ideal target EGR rate r EGRSetpoint Ideal Whether or not it is less than the target EGR rate r in the previous period EGRSetpoint Ideal(z) 。
If yes, the final target EGR rate r EGRSetpoint in Final The calculation formula of (A) is as follows:
if not, the final target EGR rate r EGRSetpoint in Final The calculation formula of (A) is as follows:
wherein, T FilterUp And T FilterDn Are all filter time coefficients, T FilterUp Not less than T FilterDn Therefore, the EGR rate rising rate is not more than the EGR rate falling rate, and the combustion stability deterioration caused by too fast EGR rate rising is avoided.
In this example, T FilterUp Set as 50ms, T FilterDn Set to 35ms.
Note that the initial value of the final target EGR rate is determined by:
if the ideal target EGR rate is not equal to the ideal target EGR rate in the last time period, and the absolute value of the ideal target EGR rate is greater than or equal to the absolute value of the target EGR rate with the limited change rate in the current time period, the initial value is the target EGR rate with the limited change rate; otherwise, the initial value is the current ideal target EGR rate.
So far the final target EGR rate is determined.
According to the control method of the target EGR rate, the basic target EGR rate is determined according to the rotating speed and the load of the engine, the multiplication factor is determined according to the atmospheric pressure, the current water temperature of the engine, the combustion times of the engine, the starting water temperature of the engine, the outdoor temperature, the working condition of the engine, the ignition efficiency, the rotating speed of the engine and the heating request, the request conditions of different working condition conditions of the engine are considered according to the basic target EGR rate and the multiplication factor, the possibility that the EGR rate is too large or too small is avoided, and the problem that the stability of closed-loop control of the EGR rate is not high is solved.
It should be understood that, although the steps in the flowcharts of the figures are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and may be performed in other orders unless explicitly stated herein. Moreover, at least a portion of the steps in the flow chart of the figure may include multiple sub-steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of execution is not necessarily sequential, but may be performed alternately or alternately with other steps or at least a portion of the sub-steps or stages of other steps.
The foregoing is only a partial embodiment of the present application, and it should be noted that, for those skilled in the art, several modifications and decorations can be made without departing from the principle of the present application, and these modifications and decorations should also be regarded as the protection scope of the present application.
Claims (10)
1. A control method of a target EGR rate, characterized by comprising the steps of:
determining a basic target EGR rate according to the engine speed and the load;
determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion times, engine starting water temperature, outdoor temperature, engine working conditions, ignition efficiency, engine rotating speed and a heating request;
and determining a standard target EGR rate according to the basic target EGR rate and the multiplication factor.
2. The method of controlling a target EGR rate according to claim 1, wherein the step of determining a multiplication factor according to atmospheric pressure, current engine water temperature, engine combustion number, engine starting water temperature, outdoor temperature, engine operating condition, ignition efficiency, engine speed, and heating request includes:
determining a first multiplication factor according to the atmospheric pressure and the current engine water temperature;
determining a second multiplication factor according to the combustion times of the engine and the outdoor temperature;
determining a third multiplication factor according to the current engine water temperature and the engine starting water temperature;
determining a fourth multiplication factor according to the current engine water temperature and the outdoor temperature;
determining a fifth multiplicative factor according to the ignition efficiency;
determining a sixth multiplicative factor as a function of the engine speed and the ignition efficiency in a catalyst diagnostic request;
determining a seventh multiplication factor according to the engine speed and the ignition efficiency in the GPF active regeneration control request;
the eighth multiplier is determined based on heating requests in the engine other than catalyst light-off heating requests and GPF active regeneration heating requests.
3. The method of controlling a target EGR rate according to claim 2, wherein the step of determining a standard target EGR rate based on the base target EGR rate and the multiplication factor includes:
the standard target EGR rate is determined by the base target EGR rate, a first multiplicative factor, a second multiplicative factor, a third multiplicative factor, a fourth multiplicative factor, a fifth multiplicative factor, a sixth multiplicative factor, a seventh multiplicative factor, and an eighth multiplicative factor.
4. The method of controlling a target EGR rate according to claim 1, wherein the step of determining a standard target EGR rate is further followed by:
and determining an ideal target EGR rate according to the actual EGR rate and the standard target EGR rate in a preset time period.
5. The method of controlling a target EGR rate according to claim 4, wherein the step of determining an ideal target EGR rate from the actual EGR rate and the standard target EGR rate for a preset period of time includes a first strategy of:
the absolute value of the deviation between the actual EGR rate and the standard target EGR rate is less than 1%, the second time duration and the time interval between the second time duration and the activation of the EGR rate closed-loop control zone bit reach the first time duration, and the ideal target EGR rate is determined to be the standard target EGR rate; or
And after the closed-loop control zone bit of the EGR rate is activated, if the ratio of the gas pressure behind the throttle valve to the gas pressure in front of the throttle valve is detected to be smaller than a preset value, determining the ideal target EGR rate as the standard target EGR rate.
6. The method of controlling a target EGR rate according to claim 5, wherein the step of determining an ideal target EGR rate from the actual EGR rate and the standard target EGR rate for a preset period of time further comprises: if the first strategy is not satisfied, executing a second strategy, wherein the second strategy comprises:
and if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the previous preset time period is monitored to be smaller than or equal to a third threshold value or the engine request flame path torque exceeds a preset range of the maximum torque capacity, immediately restoring the ideal target EGR rate to be the standard target EGR rate.
7. The method of controlling a target EGR rate according to claim 6, wherein the step of determining an ideal target EGR rate from the actual EGR rate and the standard target EGR rate for a preset period of time further comprises: if the first strategy and the second strategy are not satisfied, executing a third strategy, wherein the third strategy comprises:
if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the previous preset time period is monitored to be smaller than or equal to a first threshold, increasing a second threshold to the ideal target EGR rate to serve as a new ideal target EGR rate, wherein the first threshold, the second threshold and the third threshold are sequentially reduced;
after maintaining the new ideal target EGR rate for a third period of time, gradually restoring the standard target EGR rate as the ideal target EGR rate.
8. The method of controlling a target EGR rate according to claim 7, wherein the step of determining an ideal target EGR rate from the actual EGR rate and the standard target EGR rate for a preset period of time further comprises: if the first strategy, the second strategy and the third strategy are not satisfied, executing a fourth strategy, wherein the fourth strategy comprises:
if the absolute value of the difference between the actual EGR rate and the ideal target EGR rate in the last preset time period is monitored to be between the first threshold and the third threshold, and the absolute value of the change rate of the difference between the actual EGR rate and the ideal target EGR rate exceeds a preset change rate, increasing the ideal target EGR rate by a fourth threshold to serve as a new ideal target EGR rate, wherein the fourth threshold is between the first threshold and the second threshold;
after maintaining the new desired target EGR rate for a fourth time period, gradually restoring the standard target EGR rate as the desired target EGR rate.
9. The method of controlling a target EGR rate according to claim 8, wherein the step of determining an ideal target EGR rate from the actual EGR rate and the standard target EGR rate for a preset period of time further comprises: and if the first strategy, the second strategy, the third strategy and the fourth strategy are not satisfied, the standard target EGR rate is an ideal target EGR rate.
10. The method of controlling a target EGR rate according to claim 4, wherein the step of determining a desired target EGR rate is further followed by:
and performing smoothing treatment on the ideal target EGR rate to determine a final target EGR rate.
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