CN114562372A - Compressed natural gas automobile gas rail pressure control method and system and automobile - Google Patents
Compressed natural gas automobile gas rail pressure control method and system and automobile Download PDFInfo
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- CN114562372A CN114562372A CN202210096574.8A CN202210096574A CN114562372A CN 114562372 A CN114562372 A CN 114562372A CN 202210096574 A CN202210096574 A CN 202210096574A CN 114562372 A CN114562372 A CN 114562372A
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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
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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
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2451—Methods of calibrating or learning characterised by what is learned or calibrated
- F02D41/2464—Characteristics of actuators
- F02D41/2467—Characteristics of actuators for injectors
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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
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2477—Methods of calibrating or learning characterised by the method used for learning
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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
- F02D2041/1409—Introducing closed-loop corrections characterised by the control or regulation method using at least a proportional, integral or derivative controller
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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
- Y02T10/30—Use of alternative fuels, e.g. biofuels
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- Combustion & Propulsion (AREA)
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- General Engineering & Computer Science (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
Abstract
The invention adopts the electric control pressure regulating valve to regulate the pressure of the gas rail, gives different expected pressures of the gas rail under different working conditions of the engine, introduces a feedforward control algorithm, and stabilizes the pressure of the gas rail in a small range of the expected pressure accessory of the gas rail by controlling the opening of the electric control pressure regulating valve. The method improves the problems that the pressure of the air rail is not adjustable, and the pressure of the air rail is insufficient or excessive due to hysteresis. And a self-learning algorithm is adopted, so that the instability of the air rail control caused by the flow difference caused by the production of the electric control pressure regulating valve is effectively avoided.
Description
Technical Field
The invention relates to the technical field of automobile control, in particular to a method and a system for controlling air rail pressure of an automobile based on canned natural gas as fuel.
Background
For Compressed Natural Gas (CNG) vehicles, the pressure regulating valve functions to reduce the pressure of the natural gas coming out of the gas cylinder to a pressure level required for normal operation while maintaining the pressure steady.
The pressure of an air rail is controlled by mostly adopting a mechanical pressure regulating valve in the prior art, when the pressure regulating valve is opened, if the required natural gas in a system is increased, the pressure in a low-pressure cavity of the pressure regulating valve is put on the shelf until an orifice is opened to reestablish the degree of the same natural gas pressure for the increased natural gas flow; when the pressure value of the natural gas in the low-pressure cavity exceeds the set value, the throttling hole is completely closed because no outflow natural gas enters the system.
The limitations of mechanical pressure regulating valves are: hysteresis occurs when increasing and decreasing flow; the rail pressure is determined by the valve body, which can lead to an under-pressure or an over-pressure due to hysteresis.
Disclosure of Invention
The invention adopts the electric control pressure regulating valve to regulate the pressure of the gas rail, gives different expected pressures of the gas rail under different working conditions of the engine, introduces a feedforward control algorithm, and stabilizes the pressure of the gas rail in a small range fluctuating near the expected pressure of the gas rail by controlling the opening of the electric control pressure regulating valve. The method improves the problems that the pressure of the air rail is not adjustable, and the pressure of the air rail is insufficient or excessive due to hysteresis. The self-learning algorithm is adopted, and instability of air rail control caused by flow difference caused by production of the electric control pressure regulating valve is effectively avoided. The specific technical scheme is as follows.
As a first aspect, the present invention provides a method for controlling a gas rail pressure of a compressed natural gas automobile, the method comprising:
s1, the ignition switch is powered on, and when the fuel mode is judged to be the gas mode and the rotating speed is not 0, the CNGON pressure regulating valve control mode is activated and the step S21 is executed; when the fuel mode is judged to be fuel oil or the rotating speed is 0 and the difference value of the expected rail pressure and the actual rail pressure meets a preset value, activating the CNGOFF pressure regulating valve control mode and executing the step S31;
S21, acquiring a preset expected rail pressure value according to the rotating speed and the air inlet pressure;
s22, selecting one of basic pulse width, volume flow and air inlet pressure of PWM signal according to engine working condition under CNGON pressure regulating valve control mode;
s23, obtaining a basic duty ratio under a CNGON pressure regulating valve control mode according to the selected parameters, guiding the basic duty ratio into PID for fine adjustment by adopting a PID adjusting mode when a non-zero difference value exists between an expected rail pressure value and an actual rail pressure value to obtain a PID closed-loop duty ratio, and executing the step S4;
s31, acquiring a preset expected rail pressure value according to the water temperature;
s32, acquiring a basic duty ratio of 0 under a CNGOFF pressure regulating valve control mode, introducing the basic duty ratio into PID for fine adjustment by adopting a PID setting mode when a non-zero difference value exists between an expected rail pressure value and an actual rail pressure value to obtain a PID closed-loop duty ratio, and executing a step S4;
and S4, correcting the sum of the basic duty ratio, the PID closed-loop duty ratio and the preset flow control quantity according to the battery voltage, and obtaining the final output duty ratio after the corrected duty ratio passes through the maximum and minimum duty ratio limit values.
With reference to the first aspect, a first case in any one of the cases that may occur is that the activation conditions of the mode activation in S1 are as follows:
Controlling unconditional activation under a CNGON mode;
control activation in CNGOFF mode: the expected rail pressure value-actual rail pressure value > -calibration threshold value 1;
control in CNGOFF mode is not active: the expected rail pressure value-actual rail pressure value < ═ calibration threshold value 2.
In combination with the first case described above, the second case, in any of its possible cases,
in step S21, the desired rail pressure value is corrected, and a final desired rail pressure value is obtained by performing low pass filtering and limiting on a preset maximum desired rail pressure value, wherein the method includes:
acquiring a preset basic expected rail pressure value according to the rotating speed and the air inlet pressure, and judging whether the pressure deviation of the electric control pressure regulating valve is enabled or not;
if the basic expected rail pressure value is enabled, the basic expected rail pressure value is added with the air inlet pressure value and then multiplied by an expected rail pressure correction coefficient for correction;
if not, multiplying the basic expected rail pressure value by the expected rail pressure correction coefficient for correction;
carrying out low-pass filtering on the corrected basic expected rail pressure value to obtain a basic expected rail pressure filtering value, and limiting the basic expected rail pressure filtering value through an expected rail pressure maximum limit value to obtain a final expected rail pressure value;
in step S31, the method for obtaining the desired rail pressure value includes: the method comprises the steps of obtaining a preset original expected rail pressure value according to water temperature, carrying out low-pass filtering on the original expected rail pressure value to obtain a basic expected rail pressure filtering value, and carrying out limiting on the basic expected rail pressure filtering value through an expected rail pressure maximum limit value to obtain a final expected rail pressure value.
In connection with the above second case, a third case in any one of the cases that may occur is that the basic duty cycle described in S23 is:
selecting a basic duty ratio according to the basic pulse width, the volume flow corresponding to the pulse width and the intake pressure, wherein:
basic pulse width: the basic duty ratio is a preset value set according to the rotating speed and the CNG quality of each cylinder,
volume flow corresponding to pulse width: the basic duty ratio is the preset value set according to the rotating speed and the volume of each cylinder after the mass of each cylinder is converted into the volume of each cylinder,
air inlet pressure: the basic duty ratio is a preset value set according to the rotating speed and the air inlet pressure;
acquiring a preset gas temperature correction according to the gas temperature;
acquiring a preset expected pressure correction according to the expected pressure;
the basic duty cycle limit value is in the range of [ basic duty cycle minimum limit coefficient, basic duty cycle maximum limit coefficient ];
and adding the gas temperature correction amount and the expected pressure correction amount to the basic duty ratio to obtain a corrected basic duty ratio.
With reference to the first aspect or any one of the first to third aspects, a fourth aspect in any one of the possible cases is that, after the flow rate control amount is learned by introducing the self-learning unit in S4, a self-learned flow rate control amount is obtained, and the method includes:
Judging whether the idle speed working condition is met or not, if the idle speed working condition is met, defining self-learning cells in the idle speed according to a rotating speed range, and calculating the ID of the cells; if the idle speed is not the idle speed, self-learning cells are defined according to the rotating speed and the air inlet pressure, and the ID of the cells is calculated;
judging whether self-learning entry conditions are met or not, wherein the conditions are as follows: the water temperature is greater than a certain threshold, the running time of the engine is greater than a certain threshold, the output duty ratio of the electric control pressure regulating valve is within a certain range, the expected rail pressure value is within a certain range, the actual rail pressure value is within a certain range, and no preset fault code is reported out of the electric control pressure regulating valve;
calculating self-learning quantity in a self-learning stage, and adjusting I item regulating quantity according to the current self-learning cells; accumulating the I items, taking an average value of 16 times, and adding the step value to the cell value if the average value is more than 2 times of the learning step length or the cell content is less than the average value; if the average value is less than-2 times of the learning step length or the cell content is greater than the average value, subtracting the step length value from the cell value, and finally storing the cell value of each cell ID into a nonvolatile area, namely the self-learning flow control quantity;
calculating self-learning quantity in a non-self-learning stage, and if the learning value of the current I item is greater than the self-learning unit grid value, subtracting the step length from the learning value to obtain self-learning flow control quantity; and if the learning value of the current I item is smaller than the self-learning unit cell value, adding the step length to the learning value to obtain the self-learning flow control quantity.
In combination with the above fourth case, a fifth case in any one of the cases that may occur is that, in the method, when the actual rail pressure value is greater than the sum of the preset limit value corresponding to the expected rail pressure value and the limit value of the preset limit value corresponding to the intake pressure, the duty ratio output is clear 0; and when the engine is started, the oil is cut off, and the actual rail pressure value is greater than the preset limit value of the expected rail pressure value, outputting a duty ratio output value of 0.
As a second aspect, the invention discloses a gas rail pressure control system of a compressed natural gas automobile, which comprises a pressure regulating valve, a computer readable storage medium and a processor, and is characterized in that,
the pressure regulating valve is used for controlling the rail pressure value of the gas rail according to the control instruction of the processor;
a computer readable storage medium storing one or more program instructions for implementing a method according to any one of claims 1 to 5;
and the processor is used for reading the program instructions in the computer readable storage medium for operation and issuing the control instructions according to the operation result.
With reference to the second aspect, in a sixth aspect in any one of the possible cases, the control system further includes a flow self-learning system, configured to perform learning cell definition according to an idle condition, calculate a cell ID, adjust an I adjustment amount according to a current self-learning cell, and obtain a self-learning flow control amount by the method in the fourth aspect, where the self-learning flow control amount is used for being called by a processor of the control system.
As a third aspect, the present invention provides a vehicle using compressed natural gas, the vehicle being equipped with the gas rail pressure control system of a compressed natural gas automobile.
The beneficial effects of the invention are:
the invention can control the air rail pressure to be about +/-50 KPa of the expected pressure under the steady-state working condition of the engine. And due to the introduction of a self-learning algorithm, the instability of control caused by the flow manufacturing deviation of the pressure regulating valve can be effectively avoided.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a logic flow diagram of a regulator valve control mode;
FIG. 3 is a logic flow diagram of system control activation;
FIG. 4 is a logic flow diagram of a desired rail pressure value;
FIG. 5 is a table look-up based on rotational speed and intake pressure;
FIG. 6 is a schematic diagram of a look-up table of expected rail pressure correction factors as a function of water temperature and engine run time;
FIG. 7 is a diagram illustrating a look-up table of an original expected rail pressure value according to water temperature;
FIG. 8 is a logic flow diagram of a base duty cycle;
FIG. 9 is a table lookup diagram of P entries during PID tuning;
FIG. 10 is a table lookup diagram of I terms during PID tuning;
FIG. 11 is a table lookup diagram of D terms during PID tuning;
FIG. 12 is a schematic diagram of the system of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings. It is obvious that the described embodiments are only some of the embodiments of the invention.
As shown in fig. 1, the present embodiment discloses a method for controlling a gas rail pressure of a compressed natural gas vehicle, which comprises the following steps:
step 1, determining pressure regulating valve control modes including CNGOn, CNGOff and CNGDsbl according to the fuel state and the operation condition of the engine.
CNGON mode: as shown in fig. 2, the ignition switch is powered on, and it is determined that the fuel mode is the gas mode and the rotation speed is not 0. The activation is controlled.
CNGOff mode: the ignition switch is powered on, and the fuel mode is fuel oil or the rotating speed is 0. When the expected rail pressure is larger than the actual rail pressure by a certain value, controlling activation; and when the expected rail pressure value is smaller than the actual rail pressure value by a certain value, the control is not activated.
As shown in fig. 3, the activation conditions for controlling activation are as follows:
and controlling unconditional activation in the CNGON mode.
Control activation in CNGOFF mode: the desired rail pressure value — actual rail pressure value > is the calibration threshold value 1.
Control not active in CNGOFF mode: and (3) setting the expected rail pressure value-actual rail pressure value <, which is the calibration threshold value 2.
I.e. whether the CNGOFF mode is active or not, a reference calibration threshold is required.
CNGDsbl mode: and the ignition switch is powered off, and the control is not activated.
And 2, determining expected air rail pressure (expected rail pressure value) according to the working condition and the requirement of the engine under different control modes, wherein the expected air rail pressure is a control target of the pressure regulating valve.
When the control mode of the pressure regulating valve is a CNGON mode, providing a calibration parameter, and when the calibration parameter is set, setting the basic expected rail pressure value as the sum of the rotating speed and the intake pressure; when the calibration parameter is reset, the basic expected rail pressure value is a table lookup value obtained according to the water temperature.
And when the control mode of the pressure regulating valve is the CNGOff mode, the basic expected rail pressure value is a table look-up value obtained according to the water temperature.
As shown in fig. 4, the basic expected rail pressure values of the above two modes are low-pass filtered and limited by the maximum expected rail pressure to obtain the final expected rail pressure value.
CNGON mode: as shown in FIG. 5, a table look-up is used to obtain a base desired rail pressure value based on the speed and intake pressure. And judging whether the pressure deviation of the electric control pressure regulating valve is enabled or not.
And if the basic expected rail pressure value is enabled, the basic expected rail pressure value is added with the air inlet pressure value and then multiplied by an expected rail pressure correction coefficient for correction.
If not, the base desired rail pressure value is multiplied by a desired rail pressure correction factor for correction.
As shown in FIG. 6, the desired rail pressure correction factor is obtained from a look-up table based on water temperature and engine run time.
And performing low-pass filtering on the corrected basic expected rail pressure value to obtain a basic expected rail pressure filtering value, and limiting the basic expected rail pressure filtering value through an expected rail pressure maximum limit value to obtain a final expected rail pressure value.
CNGOff mode: as shown in FIG. 7, the original desired rail pressure value is obtained from a look-up table of water temperatures. And performing low-pass filtering on the original expected rail pressure value to obtain a basic expected rail pressure filtering value, and limiting the basic expected rail pressure filtering value through the maximum expected rail pressure limit value to obtain a final expected rail pressure value.
And step 3: according to the working condition of the engine and the control mode of the pressure regulating valve, one of three parameters of basic pulse width of a PWM signal for determining control according to the working condition of the engine, volume flow corresponding to the pulse width and intake pressure is selected, corresponding basic duty ratio is obtained according to the selected parameter, closed-loop regulation is carried out on the basic duty ratio according to the difference value between an expected pressure value and an actual pressure value, PID terms are respectively calculated, and the closed-loop duty ratio of the PID is obtained. To improve the flexibility of the system, both the gain and the axis of the PID can be calibrated.
The duty ratio controlled by the pressure regulating valve is composed of three parts: basic duty ratio, PID closed-loop control and flow self-learning control quantity.
CNGON mode: as shown in fig. 8, when the expected rail pressure and the actual rail pressure have a difference, the basic duty cycle is fine-tuned by using a PID tuning method to obtain the PID closed-loop duty cycle.
The basic duty ratio is selected as one of the basic pulse width, the volume flow corresponding to the pulse width and the air inlet pressure, wherein:
basic pulse width: the basic duty ratio is a preset value set according to the rotating speed and the CNG quality of each cylinder;
volume flow rate corresponding to pulse width: the basic duty ratio is a preset value which is set according to the rotating speed and the volume of each cylinder after the mass of each cylinder is converted into the volume of each cylinder;
air inlet pressure: the basic duty ratio is a preset value set according to the rotation speed and the intake pressure.
And acquiring a preset gas temperature correction according to the gas temperature, and acquiring a preset expected pressure correction according to the expected pressure.
The basic duty cycle limit is within the range of [ basic duty cycle minimum limit coefficient 50, basic duty cycle maximum limit coefficient 90], and the basic duty cycle is added with the gas temperature correction amount and the desired pressure correction amount to obtain the corrected basic duty cycle.
non-CNGON mode, the base duty cycle is 0.
And importing the obtained final basic duty ratio into a PID closed loop for fine adjustment. As shown in FIG. 9/10/11, the terms P, I, and D during PID tuning are all obtained by looking up a table based on the intake air flow rate and the difference between the desired rail pressure value and the actual rail pressure value.
And 4, step 4: aiming at the flow difference caused by the manufacturing process of the electric control pressure reducing valve, a self-learning unit is introduced to participate in the output control of the electric control pressure regulating valve, and an internal model can be adopted in a closed-loop control method.
First, dividing the working condition cells
And (4) defining self-learning cells at the idling speed according to the rotating speed range at the idling speed, and calculating the ID of the self-learning cells. And when the automobile is not at idle speed, defining a learning cell during non-idle speed according to the rotating speed and the air inlet pressure, and calculating the ID of the self-learning cell.
The second step, entering self-learning condition calculation
When the water temperature is larger than a certain threshold value, the running time of the engine is larger than a certain threshold value, the output duty ratio of the electric control pressure reducing valve is in a certain range, the expected gas pressure is stable, the actual rail pressure is stable, and no related faults of the pressure reducing valve exist, the self-learning is carried out.
Thirdly, calculating self-learning quantity in the self-learning stage
And adjusting the adjustment quantity of the I item according to the current self-learning cell. Accumulating the I items, taking an average value of 16 times, and adding the step value to the cell value if the average value is more than 2 times of the learning step length or the cell content is less than the average value; if the average is less than-2 times the learning step size or the cell content is greater than the average, the step size value is subtracted from the cell value. And finally, storing the cell values into a nonvolatile area, namely the self-learning flow control quantity.
The fourth step, calculating the self-learning quantity in the non-self-learning stage
If the learning value of the current I item is larger than the cell value, the learning value minus the step length is the self-learning flow control quantity. And if the current learning value of the I item is smaller than the cell value, adding the step length to the learning value to obtain the self-learning flow control quantity.
And 5, considering the battery voltage correction of the duty ratio signal and making a limit value for the maximum duty ratio. And performing table look-up correction on the sum of the basic duty ratio, the PID closed-loop duty ratio and the self-learning flow control quantity, and obtaining the final output duty ratio after the corrected duty ratio passes through the maximum duty ratio limit value and the minimum duty ratio limit value. The pressure regulating valve is used for controlling the pressure of the air rail.
When the method monitors that the pressure is too high or the oil is cut off in the operation process, the following protection strategies are adopted:
and (4) over-pressure protection: when the actual rail pressure is greater than the sum of the desired rail pressure and the intake pressure lookup table limit, the duty cycle output is clear 0.
Oil-break protection: the engine is started, fuel is cut off, the actual rail pressure is greater than the expected rail pressure by a certain value, and the duty ratio is output to be clear 0.
Furthermore, in the test mode function, the duty cycle of the output can be modified by a single calibration.
As shown in fig. 12, the system control flow of the present invention is as follows: the pressure of the high-pressure gas in the steel cylinder on the vehicle is 20Mpa, and the pressure is controlled to be 1.8Mpa-2.0Mpa after passing through the first-stage stop valve. And then high-pressure gas is introduced into the gas rail through the secondary proportional valve, the introduced gas pressure is determined by the opening size of the proportional valve, and when the pressure at the gas outlet of the proportional valve is higher than 1.6Mpa, the pressure is released through the pressure release valve.
And (4) introducing the actual gas pressure and the expected rail pressure measured in the gas rail into the PID for regulation, and outputting the PID closed-loop duty ratio. And then outputting and controlling the opening of the secondary proportional valve according to the basic duty ratio, the closed-loop duty ratio and the self-learning flow control quantity after passing through the limit value. Thereby realizing the system control of the whole rail pressure.
The technical scheme can control the air rail pressure to be about +/-50 KPa of the expected pressure under the steady-state working condition of the engine. And due to the introduction of a self-learning algorithm, the instability of control caused by the flow manufacturing deviation of the pressure reducing valve can be effectively avoided.
It should be understood that the above-described embodiments are illustrative only and are not intended to limit the scope of the present invention. It should also be understood that various changes and modifications can be made by one skilled in the art after reading the disclosure of the present invention, and equivalents fall within the scope of the invention as defined by the appended claims.
Claims (9)
1. A method for controlling rail pressure of a compressed natural gas vehicle, the method comprising the steps of:
s1, the ignition switch is powered on, and when the fuel mode is judged to be the gas mode and the rotating speed is not 0, the CNGON pressure regulating valve control mode is activated and the step S21 is executed; when the fuel mode is judged to be fuel oil or the rotating speed is 0 and the difference value of the expected rail pressure value minus the actual rail pressure value meets a preset value, the CNGOFF pressure regulating valve control mode is activated and the step S31 is executed;
S21, acquiring a preset expected rail pressure value according to the rotating speed and the air inlet pressure;
s22, selecting one of basic pulse width, volume flow and air inlet pressure of PWM signal according to engine working condition under CNGON pressure regulating valve control mode;
s23, obtaining a basic duty ratio under a CNGON pressure regulating valve control mode according to the selected parameters, guiding the basic duty ratio into PID for fine adjustment by adopting a PID adjusting mode when a non-zero difference value exists between an expected rail pressure value and an actual rail pressure value to obtain a PID closed-loop duty ratio, and executing the step S4;
s31, acquiring a preset expected rail pressure value according to the water temperature;
s32, acquiring a basic duty ratio of 0 under a CNGOFF pressure regulating valve control mode, introducing the basic duty ratio into PID for fine adjustment by adopting a PID setting mode when a non-zero difference value exists between an expected rail pressure value and an actual rail pressure value to obtain a PID closed-loop duty ratio, and executing a step S4;
and S4, correcting the sum of the basic duty ratio, the PID closed-loop duty ratio and the preset flow control quantity according to the battery voltage, and obtaining the final output duty ratio after the corrected duty ratio passes through the maximum and minimum duty ratio limit values.
2. The method of claim 1, wherein the activation conditions for the mode activation in S1 are as follows:
Controlling unconditional activation under a CNGON mode;
control activation in CNGOFF mode: the expected rail pressure value-actual rail pressure value > -calibration threshold value 1;
control not active in CNGOFF mode: and (3) setting the expected rail pressure value-actual rail pressure value <, which is the calibration threshold value 2.
3. The method of claim 2, wherein the control of the rail pressure of the compressed natural gas vehicle,
in step S21, the desired rail pressure value is corrected, and a final desired rail pressure value is obtained by performing low pass filtering and limiting on a preset maximum desired rail pressure value, wherein the method includes:
acquiring a preset basic expected rail pressure value according to the rotating speed and the air inlet pressure, and judging whether the pressure deviation of the electric control pressure regulating valve is enabled or not;
if the basic expected rail pressure value is enabled, the basic expected rail pressure value is added with the intake pressure value and then multiplied by an expected rail pressure correction coefficient for correction;
if not, multiplying the basic expected rail pressure value by the expected rail pressure correction coefficient for correction;
the expected rail pressure correction coefficient is a preset value set according to the water temperature and the running time of the engine;
performing low-pass filtering on the corrected basic expected rail pressure value to obtain a basic expected rail pressure filtering value, and limiting the basic expected rail pressure filtering value through an expected rail pressure maximum limit value to obtain a final expected rail pressure value;
In step S31, the method for obtaining the expected rail pressure value includes: the method comprises the steps of obtaining a preset original expected rail pressure value according to water temperature, carrying out low-pass filtering on the original expected rail pressure value to obtain a basic expected rail pressure filtering value, and carrying out limiting on the basic expected rail pressure filtering value through an expected rail pressure maximum limit value to obtain a final expected rail pressure value.
4. The method as claimed in claim 3, wherein the basic duty ratio in S23 is:
selecting a basic duty ratio according to the basic pulse width, the volume flow corresponding to the pulse width and the intake pressure, wherein:
basic pulse width: the basic duty ratio is a preset value set according to the rotating speed and the CNG quality of each cylinder,
volume flow corresponding to pulse width: the basic duty ratio is the preset value set according to the rotating speed and the volume of each cylinder after the mass of each cylinder is converted into the volume of each cylinder,
air inlet pressure: the basic duty ratio is a preset value set according to the rotating speed and the air inlet pressure;
acquiring a preset gas temperature correction according to the gas temperature;
acquiring a preset expected pressure correction according to the expected pressure;
the basic duty cycle limit value is in the range of [ basic duty cycle minimum limit coefficient, basic duty cycle maximum limit coefficient ];
And adding the gas temperature correction amount and the expected pressure correction amount to the basic duty ratio to obtain a corrected basic duty ratio.
5. The method as claimed in any one of claims 1 to 4, wherein the flow control amount of S4 is learned by introducing a self-learning unit to obtain a self-learned flow control amount, and the method comprises:
judging whether the idle speed working condition is met, if the idle speed working condition is met, defining idle speed self-learning cells according to a rotating speed range, and calculating the ID of the cells; if the speed is not idle, defining self-learning cells during non-idle speed according to the rotating speed and the air inlet pressure, and calculating the ID of the cells;
judging whether the self-learning stage is available or not, wherein the judging conditions are as follows: the water temperature is greater than a certain threshold, the running time of the engine is greater than a certain threshold, the output duty ratio of the electric control pressure regulating valve is within a certain range, the expected rail pressure value is within a certain range, the actual rail pressure value is within a certain range, and no preset fault code is reported out of the electric control pressure regulating valve;
calculating self-learning quantity in a self-learning stage, and adjusting I regulation quantity according to the current self-learning cells; accumulating the I items, taking an average value of 16 times, and adding the step value to the cell value if the average value is more than 2 times of the learning step length or the cell content is less than the average value; if the average value is less than-2 times of the learning step length or the cell content is greater than the average value, subtracting the step length value from the cell value, and finally storing the cell value of each cell ID into a nonvolatile area, namely the self-learning flow control quantity;
Calculating self-learning quantity in a non-self-learning stage, and if the learning value of the current I item is greater than the self-learning unit grid value, subtracting the step length from the learning value to obtain self-learning flow control quantity; and if the current I item learning value is smaller than the self-learning unit cell value, adding the step length to the learning value to obtain the self-learning flow control quantity.
6. The method according to claim 5, wherein in the method, when the actual rail pressure value is greater than the sum of the preset limit value corresponding to the expected rail pressure value and the preset limit value corresponding to the intake pressure, a duty ratio output clear 0 is output; and when the engine is started, the fuel is cut off, and the actual rail pressure value is greater than the preset limit value of the expected rail pressure value, outputting a duty ratio output clear 0.
7. A gas rail pressure control system of a compressed natural gas automobile is characterized by comprising a pressure regulating valve, a computer readable storage medium and a processor,
the pressure regulating valve is used for controlling the rail pressure value of the air rail according to the control instruction of the processor;
a computer readable storage medium storing one or more program instructions for implementing a method according to any one of claims 1 to 6;
And the processor is used for reading the program instructions in the computer readable storage medium for operation and issuing the control instructions according to the operation result.
8. The system of claim 7, further comprising a flow self-learning system for defining learning cells according to idle conditions, calculating unit ID, adjusting I adjustment amount according to current self-learning cells, and obtaining self-learned flow control amount for the processor of the control system to call by the method of claim 5.
9. A vehicle using compressed natural gas, characterized in that the vehicle is equipped with a rail pressure control system of a compressed natural gas automobile according to claim 7 or 8.
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