A closed-loop control method based on mixing valve pressure ratio

Abstract

The present invention provides a closed-loop control method based on the mixing valve pressure ratio, comprising determining the target pressure ratio on both sides of the mixing valve under different conditions according to the EGR state; determining the effective area of ​​the mixing valve according to the target pressure ratio on both sides of the mixing valve; determining the target opening value of the mixing valve according to the effective area of ​​the mixing valve; controlling the mixing valve drive motor according to the target opening value so that the actual opening value follows the target opening value; repeating the above method at every sampling period to achieve dynamic closed-loop control of the target opening value of the mixing valve. Based on the mixing valve pressure ratio, the present invention adopts a dynamic closed-loop control method to control the target opening value of the mixing valve, achieving adaptive control of the target opening value of the mixing valve, thereby achieving precise control of the target opening value of the mixing valve and meeting the requirements of the EGR rate.

Description

Technical Field

[0001] The present invention relates to the field of engine control, and in particular to a closed-loop control method based on a mixing valve pressure ratio. Background Art

[0002] Exhaust Gas Recirculation (EGR) draws exhaust gas from the exhaust system into the intake system. Research has shown that EGR systems offer advantages in improving emissions, reducing fuel consumption, and improving anti-knock performance. Controlling the mixing valve in low-pressure EGR systems is particularly important for improving the EGR rate.

[0003] In the existing technology, patent application number CN202011247319.6 "A method and system for calculating the target EGR rate" calculates the initial target EGR rate from the throttle opening, manifold pressure difference and minimum ignition angle. It can accurately calculate the target EGR rate, and introduce EGR control activation conditions to perform secondary corrections on the final target EGR rate, but does not consider the control accuracy of the target opening value of the mixing valve; patent application number CN202110184826.8 "A method and system for controlling the target opening of an EGR mixing valve" corrects the target opening of the mixing valve according to various operating parameters, but does not consider the dynamic closed-loop control of the target opening value of the mixing valve. Summary of the Invention

[0004] The main purpose of the present invention is to provide a closed-loop control method based on the mixing valve pressure ratio to achieve dynamic closed-loop control of the mixing valve target opening value, improve the control accuracy of the mixing valve target opening value, and thus improve the response accuracy of the EGR rate.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] Determine the effective area of ​​the mixing valve based on the target pressure ratio on both sides of the mixing valve;

[0007] Determine the target opening value of the mixing valve based on the effective area of ​​the mixing valve;

[0008] According to the target opening value, the mixing valve drive motor is controlled to achieve the actual opening value following the target opening value;

[0009] The above method is repeated every sampling period to achieve dynamic closed-loop control of the target opening of the mixing valve.

[0010] According to the above scheme, the target pressure ratios on both sides of the mixing valve under different conditions are determined according to the EGR state by the following method:

[0011] If the EGR state is in the default state, the target pressure ratio on both sides of the mixing valve is set to 1; the default state is the closed state; the EGR state enters the default state when the vehicle is powered on;

[0012] If the EGR state is one of the ramp closed state, the ramp open state, and the ramp open state, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value;

[0013] If the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is less than the preset time, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value; if the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is not less than the preset time, the target pressure ratio on both sides of the mixing valve is set to 1;

[0014] Determine the operating conditions where the EGR state is the default state, and the EGR state enters the closed state from one of the ramp closed state, the open state, and the ramp open state, and the delay time is not less than the preset time as the mixing valve control inactive state;

[0015] The operating conditions in which the EGR state is one of the ramp closing state, the opening state and the ramp opening state, and the EGR state enters the closing state from one of the ramp closing state, the opening state and the ramp opening state, and the delay time is less than the preset time are determined as the mixing valve control activation state.

[0016] According to the above solution, the effective area of ​​the mixing valve is determined specifically by the following method:

[0017] Determine the actual pressure ratio on both sides of the mixing valve;

[0018] A mixing valve pressure ratio difference and a changing rate of the mixing valve pressure ratio difference are obtained based on the target pressure ratio on both sides of the mixing valve and the actual pressure ratio on both sides of the mixing valve, and a first-order low-pass filter is performed on the mixing valve pressure ratio difference and the changing rate of the mixing valve pressure ratio difference;

[0019] Determine the target intake air mass flow rate into the cylinder;

[0020] Determine the closed-loop dynamic flow of the mixing valve according to the mixing valve pressure ratio difference and the mixing valve pressure ratio difference change rate;

[0021] Determine the total target flow of the mixing valve based on the target intake mass flow entering the cylinder and the closed-loop dynamic flow of the mixing valve;

[0022] When the mixing valve is not in a control inactive state, the effective area of ​​the mixing valve is equal to the maximum effective area of ​​the mixing valve, and the maximum effective area of ​​the mixing valve is determined by the characteristics of the mixing valve body;

[0023] When the mixing valve is in the control activation state, the initial value of the mixing valve effective area is calculated based on the total target flow of the mixing valve, the gas temperature at the air filter outlet, and the target pressure ratio on both sides of the mixing valve. The initial value of the mixing valve effective area is limited to a range from a minimum value to a maximum value to obtain the effective area of ​​the mixing valve when the mixing valve enters the activation state.

[0024] According to the above solution, the target opening value of the mixing valve is determined specifically by the following method:

[0025] Determine the initial value of the target opening of the mixing valve;

[0026] Performing a first-order low-pass filter on the initial value of the mixing valve target opening, and outputting a filtered value of the mixing valve target opening;

[0027] The change rate of the mixing valve target opening value is limited based on the mixing valve target opening filter value to obtain a final mixing valve target opening value.

[0028] According to the above solution, the total target flow of the mixing valve is obtained by adding the closed-loop dynamic flow of the mixing valve and the target intake mass flow entering the cylinder, minus the actual exhaust flow of the EGR valve.

[0029] According to the above solution, the closed-loop dynamic flow of the mixing valve is obtained by adding the closed-loop dynamic flow P part of the mixing valve and the closed-loop dynamic flow I part of the mixing valve.

[0030] According to the above scheme, the closed-loop dynamic flow P item of the mixing valve is obtained by multiplying the initial value of the closed-loop dynamic flow P item of the mixing valve obtained based on the pressure ratio difference of the mixing valve and the time it takes for fresh air to flow from the mixing valve through the compressor to the throttle valve and then enter the cylinder, divided by the time constant of the PI dynamic control and its correction coefficient.

[0031] According to the above solution, the closed-loop dynamic flow I part of the mixing valve is obtained by continuously accumulating the accumulated value of the closed-loop dynamic flow I part of the mixing valve;

[0032] When the initial value of the effective area of ​​the mixing valve obtained in the previous sampling period is equal to the maximum value or the minimum value, the accumulated value part of the closed-loop dynamic flow item I based on the mixing valve is 0; when the initial value of the effective area of ​​the mixing valve obtained in the previous sampling period is not equal to the maximum value or the minimum value, the accumulated value part of the closed-loop dynamic flow item I based on the mixing valve is equal to the initial value part of the accumulated value of the closed-loop dynamic flow item I of the mixing valve.

[0033] According to the above scheme, the time for the fresh air to flow from the mixing valve through the compressor to the throttle valve and then enter the cylinder is obtained by the average value of multiple sampling data under different engine speeds and different actual intake air densities entering the cylinder, and each sampling data is obtained by bench calibration.

[0034] According to the above scheme, the initial value part of the accumulated value of the closed-loop dynamic flow I item of the mixing valve is obtained by dividing the initial value part of the closed-loop dynamic flow I item of the mixing valve obtained based on the pressure ratio difference of the mixing valve by the time constant of the PI dynamic control and its correction coefficient.

[0035] According to the above scheme, the first-order low-pass filtering is performed on the initial value of the target opening of the mixing valve, specifically, the difference between the initial value of the target opening of the mixing valve and the filtered value of the target opening of the mixing valve in the previous sampling period, multiplied by the ratio of the sampling period to the filtering time coefficient, and the resultant is added to the filtered value of the target opening of the mixing valve in the previous sampling period.

[0036] According to the above solution, the filtering time coefficient is obtained by adding the filtering time coefficient determined based on the mixing valve pressure ratio difference and the deviation;

[0037] When the actual pressure ratio across the mixing valve is greater than a first preset value, the deviation is equal to a time coefficient determined based on the target pressure ratio across the mixing valve;

[0038] When the actual pressure ratio on both sides of the mixing valve is less than the second preset value, the deviation is equal to the filter time coefficient deviation;

[0039] In other cases, the deviation is equal to the filter time coefficient deviation;

[0040] The first preset value is greater than the second preset value.

[0041] According to the above scheme, the rate of change of the target opening value of the mixing valve is limited, specifically, when the target opening value of the mixing valve increases, the maximum allowable rate of change of the target opening value of the mixing valve is limited; when the target opening value of the mixing valve decreases, the absolute value of the maximum allowable rate of change of the target opening value of the mixing valve is limited.

[0042] The beneficial effects of the present invention are as follows: based on the mixing valve pressure ratio, a dynamic closed-loop control method is adopted to control the target opening value of the mixing valve, thereby realizing adaptive control of the target opening value of the mixing valve, thereby realizing precise control of the target opening value of the mixing valve and meeting the EGR rate requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the architecture of the low-pressure EGR system;

[0044] Figure 2 Flow chart of the method of the present invention.

[0045] In the figure: 1-air filter, 2-flow meter, 3-mixing valve, 4-supercharger compressor, 5-oxygen sensor, 6-throttle, 7-engine, 8-supercharger turbine, 9-catalyst, 10-particulate matter trap, 11-EGR valve, 12-differential pressure sensor, 13-temperature sensor, 14-EGR cooler. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] like Figure 1 As shown, the low-pressure EGR system includes an air filter, a mixing valve, a supercharger compressor, a throttle body, an engine, a supercharger turbine, a catalyst, a particulate matter trap, an EGR cooler, an EGR valve, an EGR temperature sensor, an EGR differential pressure sensor, a flow meter, and a linear oxygen sensor.

[0048] Among them, the supercharger compressor is used to compress fresh air for supercharging; the supercharger turbine controls the working efficiency of the turbine by controlling the opening of the supercharger's wastegate valve, thereby achieving different supercharging capabilities;

[0049] At the same time, compared to a non-low-pressure EGR system, the low-pressure EGR system has the following additional components: an EGR cooler, an EGR temperature sensor, an EGR valve, an EGR differential pressure sensor, a mixing valve, a flowmeter, and an oxygen sensor. The flowmeter is installed between the air filter and the mixing valve to detect the flow of fresh air entering the engine. Some engines may not have a flowmeter installed. Estimating the flow of fresh air entering the engine by estimation is not within the scope of this invention. The mixing valve is used to adjust the pressure at the EGR valve outlet, increasing the pressure differential across the EGR valve and thus increasing the EGR rate. The oxygen sensor is installed between the compressor and the throttle, close to the throttle, to detect the flow of mixed air entering the cylinder. The EGR cooler cools the exhaust gas, facilitating increased exhaust gas flow and reduced exhaust gas temperature. The EGR valve has a throttling function, controlling the flow of exhaust gas entering the cylinder. The EGR temperature sensor detects the temperature of the exhaust gas entering the EGR valve. The EGR differential pressure sensor detects the pressure at the EGR inlet and outlet.

[0050] The present invention provides a closed-loop control method based on the mixing valve pressure ratio, which is used for the above low-pressure EGR system. If there is a dynamic correction of power demand, the control method of patent application number CN202211337426.7 "Calculation method, device, terminal device and storage medium of mixing valve target opening" is adopted. The present invention is mainly a control method for the mixing valve target opening when non-power demand has dynamic correction, so as to improve the control accuracy of EGR rate, such as Figure 2 As shown, the method includes the following steps:

[0051] S1. Determine the target pressure ratio on both sides of the mixing valve under different conditions according to the EGR state.

[0052] Patent application number CN202011247319.6 "A method and system for calculating a target EGR rate" shows that there are four EGR states, namely, the off state (Off state), the ramp off state (Ramp Off state), the on state (On state) and the ramp on state (Ramp In state). The target pressure ratio on both sides of the mixing valve in different states is:

[0053] If the EGR state is in the default state, the target pressure ratio on both sides of the mixing valve is set to 1; the default state is the closed state; the EGR state enters the default state when the vehicle is powered on;

[0054] If the EGR state is one of the ramp closed state, the ramp open state, and the ramp open state, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value;

[0055] If the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is less than the preset time, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value; if the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is not less than the preset time, the target pressure ratio on both sides of the mixing valve is set to 1;

[0056] Determine the operating conditions where the EGR state is the default state, and the EGR state enters the closed state from one of the ramp closed state, the open state, and the ramp open state, and the delay time is not less than the preset time as the mixing valve control inactive state;

[0057] The operating conditions in which the EGR state is one of the ramp closing state, the opening state and the ramp opening state, and the EGR state enters the closing state from one of the ramp closing state, the opening state and the ramp opening state, and the delay time is less than the preset time are determined as the mixing valve control activation state.

[0058] When the mixing valve is in the control activation state, the initial value of the target pressure ratio on both sides of the mixing valve is calculated. The calculation method is:

[0059]

[0060] in, is the real-time air filter outlet pressure, The maximum pressure allowed for activation of the EGR system (101 kPa in this example). The minimum pressure allowed for activation of the EGR system (55kPa in this example). is the target pressure ratio on both sides of the mixing valve when the atmospheric pressure is p1, It is the target pressure ratio on both sides of the mixing valve when the atmospheric pressure is p2. and The calibration method is to set the minimum pressure ratio on both sides of the mixing valve (the smaller the pressure ratio on both sides of the mixing valve, the greater the EGR rate achieved) under the premise of meeting the pressure control accuracy of the boost system and the stability of the charging efficiency at the corresponding atmospheric pressures p1 and p2, so as to achieve the EGR rate.

[0061] The boost system's pressure control accuracy is evaluated by the deviation between the actual and target boost pressures. The smaller the deviation, the higher the pressure control accuracy. This deviation can be determined based on individual projects. This project, assuming the target boost pressure remains constant, ultimately ensures the difference between the actual and target boost pressures is less than ±2kPa. The charging efficiency stability evaluation metric is that the fresh air intake density entering the cylinder is stable relative to the engine's requested fresh air intake density, with fluctuations within ±2%.

[0062] In this example, the maximum value of the initial target pressure ratio on both sides of the mixing valve is set to 1, and the minimum value is set to 0.93 to prevent the supercharger oil from entering the compressor and damaging the compressor.

[0063] S2. Determine the effective area of ​​the mixing valve based on the target pressure ratio on both sides of the mixing valve under different conditions, specifically including:

[0064] S21. Determine the actual pressure ratio on both sides of the mixing valve.

[0065] Actual pressure ratio on both sides of the mixing valve : ,in The outlet pressure of the mixing valve can be replaced by the outlet pressure of the EGR valve. Instead, it is detected by the EGR valve differential pressure sensor.

[0066] S22. Obtain a mixing valve pressure ratio difference and a changing rate of the mixing valve pressure ratio difference based on the target pressure ratio on both sides of the mixing valve and the actual pressure ratio on both sides of the mixing valve, and perform first-order low-pass filtering on the mixing valve pressure ratio difference and the changing rate of the mixing valve pressure ratio difference.

[0067] The mixing valve pressure ratio difference is obtained by subtracting the actual pressure ratio on both sides of the mixing valve from the target pressure ratio on both sides of the mixing valve. The purpose of filtering is to avoid poor control robustness due to excessive pressure ratio fluctuations.

[0068] Among them, the first-order low-pass filtering algorithm for the mixing valve pressure ratio difference and the rate of change of the mixing valve pressure ratio difference is as follows:

[0069]

[0070] in, is the signal before filtering, is the signal before filtering in the Nth sampling period, is the filtered signal after filtering, is the filtered signal of the Nth sampling period, is the filtered signal of the N-1th sampling period, N=1,2,3…, The signal before filtering is equal to the 0th sampling period (the 0th sampling period refers to the moment when the vehicle is powered on); in this example, the sampling period interval 10ms; The coefficient is , and the mixing valve pressure ratio difference and the rate of change of the mixing valve pressure ratio difference in this example are taken as 0.13 and 0.1 respectively (the pressure ratio difference change rate fluctuates more violently, and its filter coefficient is updated to reduce the fluctuation range of the pressure ratio difference change rate).

[0071] S23. Determine a target intake air mass flow rate entering the cylinder.

[0072] Patent application number CN202210332492.9 "Target intake density control method, device, equipment and readable storage medium" can obtain the real-time target intake density entering the cylinder , and converted into the target intake mass flow rate entering the cylinder :

[0073]

[0074] in, is the current engine speed, is the number of engine cylinders, is the engine displacement.

[0075] S24. Determine the closed-loop dynamic flow rate of the mixing valve according to the mixing valve pressure ratio difference and the rate of change of the mixing valve pressure ratio difference.

[0076] Closed loop dynamic flow of mixing valves Based on the mixing valve pressure ratio difference It is determined that the main purpose is to adjust the dynamic flow of the mixing valve to control the mixing valve pressure ratio difference to become smaller and smaller, so as to achieve the mixing valve pressure ratio.

[0077] Closed loop dynamic flow of mixing valves , that is, the closed-loop dynamic flow of the mixing valve is obtained by adding the closed-loop dynamic flow P item of the mixing valve and the closed-loop dynamic flow I item of the mixing valve.

[0078] Among them, the closed-loop dynamic flow P part of the mixing valve :

[0079] ,

[0080] Based on the mixing valve pressure ratio difference The initial value of the closed-loop dynamic flow P of the mixing valve is obtained by calibration. It is the time for fresh air to flow from the mixing valve through the compressor to the throttle valve and then into the cylinder. This part is obtained through bench calibration. This part can be adjusted for different engine speeds. and different actual intake air densities entering the cylinder The average value of multiple sampling data under . is the time constant of PI dynamic control, The larger it is, the smaller P and I are, and the slower the dynamic closed-loop adjustment is. The smaller it is, the larger P and I are, and the faster the dynamic closed-loop adjustment is. Based on the mixing valve pressure ratio difference and the mixing valve pressure ratio difference change rate Time constant The correction factor of the mixing valve pressure ratio difference Or the mixing valve pressure ratio change rate The smaller the absolute value, the larger the value, to avoid the mixing valve in the small pressure ratio difference (or rate of change) fluctuations caused by the boost control pressure also fluctuates, from the priority of the boost pressure closed loop control adjustment and then adjust the mixing valve pressure ratio difference, to avoid the boost and mixing valve adjustment conflict, to improve the boost pressure adjustment and mixing valve pressure ratio adjustment process of the pressure and mixing valve opening vibration problem. Pressure difference in mixing valve Not more than ±0.4 or the mixing valve pressure ratio difference change rate Not more than ±2 (s -1 ) is greater than 1, and other times Equal to 1. Pressure difference in mixing valve Greater than ±0.4 or the mixing valve pressure ratio difference change rate Greater than ±2 (s -1 ) is based on the fact that, under the premise that the target boost pressure remains unchanged, the difference between the actual boost pressure and the target boost pressure can ultimately be guaranteed to be less than ±2kPa.

[0081] Closed loop dynamic flow I part of the mixing valve , is based on the cumulative value of the closed-loop dynamic flow I item of the mixing valve Continuously accumulating:

[0082] ,

[0083] in, The closed-loop dynamic flow I part of the mixing valve in the previous sampling period is 0 when the vehicle is powered on. In particular, when the mixing valve enters the inactive state, the closed-loop dynamic flow I part of the mixing valve is Reset to 0.

[0084] Among them, if the previous sampling period (sampling period interval ) to obtain the initial value of the effective area of ​​the mixing valve Equal to its maximum allowed value (The maximum effective area of ​​the mixing valve is determined by the mixing valve hardware and provided by the supplier), or the effective area of ​​the mixing valve obtained in the previous sampling period If the minimum value of the effective area of ​​the mixing valve is equal to the minimum value allowed (the minimum value of the effective area of ​​the mixing valve is determined by the mixing valve hardware and provided by the supplier), the accumulated value of the closed-loop dynamic flow I of the mixing valve is =0.

[0085] In other cases, .

[0086] It is the initial value of the accumulated value of the closed-loop dynamic flow I of the mixing valve, and its calculation method is:

[0087]

[0088] in, Based on the mixing valve pressure ratio difference The initial value of the closed-loop dynamic flow I of the mixing valve is also obtained by calibration.

[0089] S25. Determine a total target flow rate of the mixing valve according to the target intake air mass flow rate entering the cylinder and the closed-loop dynamic flow rate of the mixing valve.

[0090] The final total target flow of the mixing valve The calculation method is:

[0091]

[0092] That is, the total target flow of the mixing valve is obtained by adding the closed-loop dynamic flow of the mixing valve and the target intake mass flow entering the cylinder, minus the actual exhaust flow of the EGR valve. It can also be considered as the total target flow rate of the mixed gas after the EGR exhaust gas and fresh air are mixed, and the exhaust gas flow rate of the EGR valve is subtracted from it to obtain the total target flow rate of the mixing valve. .

[0093] in, The actual exhaust gas flow rate of the EGR valve can be obtained by referring to the calculation method in patent application number CN202110633093.1 "A Cylinder Exhaust Gas Flow Estimation Method and System":

[0094] ,Will Replaced with the gas pressure at the EGR valve outlet 、 Replaced with the actual exhaust gas flow of the EGR valve 、 Replaced with the effective area of ​​the mixing valve That's it.

[0095] In this calculation method, It is the learning value of the effective area of ​​the EGR control valve, which is saved after the vehicle is powered off. is the gas temperature of the EGR valve, Detected by the EGR valve differential pressure sensor, is the gas constant of the exhaust gas, which is 290 J / (kg·K) in this example. Determined by calibration.

[0096] Finally, when the mixing valve is in the control inactive state, the effective area of ​​the mixing valve is equal to the maximum effective area of ​​the mixing valve, that is, ,in The maximum effective area of ​​the mixing valve is determined by the characteristics of the mixing valve body. In this example, it is 2550m 2 ;

[0097] When the mixing valve is in the control activation state, first determine the initial value of the mixing valve effective area according to the formula :

[0098]

[0099] in, are other constants for fresh air, in this example, 287 J / (kg·K), is the gas temperature at the air filter outlet, which is replaced by the mixing valve inlet temperature in the present invention. The target pressure ratio on both sides of the mixing valve The specific calibration parameters are determined based on the flow estimation of the mixing valve and the corresponding flow meter calibration results. In this example, the results are as follows:

[0100]

[0101] Finally, the initial value of the effective area of ​​the mixing valve Limit to minimum value (In this example, 2.2m 2 ) to the maximum value The effective area of ​​the mixing valve when the mixing valve is activated is obtained. .

[0102] S3. Determine the target opening value of the mixing valve based on the effective area of ​​the mixing valve, specifically including:

[0103] S31. Determine an initial value of the target opening of the mixing valve.

[0104] Initial value of target opening of mixing valve Effective area of ​​mixing valve The corresponding relationship is determined by the characteristics of the mixing valve body. In this example, the corresponding relationship between the initial value of the mixing valve target opening and the effective area of ​​the mixing valve is as follows:

[0105]

[0106] Based on the above, the initial value of the target opening of the mixing valve is determined .

[0107] S32. Perform a first-order low-pass filter on the initial value of the target opening of the mixing valve, and output a filtered value of the target opening of the mixing valve.

[0108] The purpose of performing a first-order low-pass filter on the initial value of the target opening of the mixing valve is to avoid excessive changes in the opening of the mixing valve. The calculation method is:

[0109]

[0110] in, is the target opening filter value of the mixing valve in the previous sampling period (its initial value is 0), is the sampling period, is the filter time coefficient, The calibration basis is to avoid the mixing valve outlet pressure fluctuation exceeding ±2kPa / 10ms, and to avoid the mixing valve opening fluctuation exceeding ±1.2% / 10ms.

[0111] in, Based on The determined filtering time coefficient is larger when the pressure ratio difference is small, to avoid excessively aggressive control and mixing valve vibration;

[0112] deviation When the actual pressure ratio of the mixing valve is close to 1, the opening of the mixing valve is controlled to change slowly to avoid pressure fluctuations at the mixing valve outlet. The status rules are:

[0113] If the actual pressure ratio on both sides of the mixing valve When it is greater than 0.97, the deviation The state is state 1;

[0114] If the actual pressure ratio on both sides of the mixing valve When it is less than 0.95, the deviation The state is state 2;

[0115] Deviations in other cases The state of remains the previous state, in particular, the default state is state 2;

[0116] In state one, ; In state 2, .

[0117] in, Based on the target pressure ratio on both sides of the mixing valve The corresponding relationship of the determined deviation time coefficient is:

[0118]

[0119] in, is the filter time coefficient deviation. In this example, Take 15ms.

[0120] S33: Limiting the change rate of the mixing valve target opening value based on the mixing valve target opening filter value to obtain a final mixing valve target opening value.

[0121] The purpose of this step is to prevent the mixing valve from changing too quickly when the mixing valve is close to its maximum position (100%) and minimum position (0%), which may damage the mixing valve drive motor. Based on this, the change rate of the mixing valve target opening value is limited. The calibration of this example is as follows:

[0122] When the target opening value of the mixing valve increases, the maximum allowable rate of change is as follows:

[0123]

[0124] When the target opening value of the mixing valve decreases, the absolute value of the maximum allowable rate of change is as follows:

[0125]

[0126] S4. According to the target opening value, the mixing valve drive motor is controlled to achieve that the actual opening value follows the target opening value.

[0127] S5. Repeat steps S1 to S4 every time a sampling cycle is passed to achieve dynamic closed-loop control of the target opening of the mixing valve.

[0128] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0129] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0130] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A closed-loop control method based on mixing valve pressure ratio, characterized in that: The method includes: Determine the target pressure ratio on both sides of the mixing valve under different conditions according to the EGR state; Determine the effective area of ​​the mixing valve based on the target pressure ratio on both sides of the mixing valve; Determine the target opening value of the mixing valve based on the effective area of ​​the mixing valve; According to the target opening value, the mixing valve drive motor is controlled to achieve the actual opening value following the target opening value; The above method is repeated every time a sampling cycle is passed to realize dynamic closed-loop control of the target opening value of the mixing valve; The target pressure ratios on both sides of the mixing valve under different conditions are determined according to the EGR state by: If the EGR state is in the default state, the target pressure ratio on both sides of the mixing valve is set to 1; the default state is the closed state; the EGR state enters the default state when the vehicle is powered on; If the EGR state is one of the ramp closed state, the ramp open state, and the ramp open state, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value; If the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is less than the preset time, the target pressure ratio on both sides of the mixing valve is obtained by limiting the initial value of the target pressure ratio on both sides of the mixing valve to a range from the maximum value to the minimum value; if the EGR state enters the closed state from one of the three states of ramp closed state, open state and ramp open state, and the delay time is not less than the preset time, the target pressure ratio on both sides of the mixing valve is set to 1; Determine the operating conditions where the EGR state is the default state, and the EGR state enters the closed state from one of the ramp closed state, the open state, and the ramp open state, and the delay time is not less than the preset time as the mixing valve control inactive state; The operating conditions in which the EGR state is one of the ramp closing state, the opening state and the ramp opening state, and the EGR state enters the closing state from one of the ramp closing state, the opening state and the ramp opening state, and the delay time is less than the preset time are determined as the mixing valve control activation state.

2. A closed-loop control method based on mixing valve pressure ratio according to claim 1, characterized in that: The effective area of ​​the mixing valve is determined specifically by the following method: Determine the actual pressure ratio on both sides of the mixing valve; A mixing valve pressure ratio difference and a changing rate of the mixing valve pressure ratio difference are obtained based on the target pressure ratio on both sides of the mixing valve and the actual pressure ratio on both sides of the mixing valve, and a first-order low-pass filter is performed on the mixing valve pressure ratio difference and the changing rate of the mixing valve pressure ratio difference; Determine the target intake air mass flow rate into the cylinder; Determine the closed-loop dynamic flow of the mixing valve according to the mixing valve pressure ratio difference and the mixing valve pressure ratio difference change rate; Determine the total target flow of the mixing valve based on the target intake mass flow entering the cylinder and the closed-loop dynamic flow of the mixing valve; When the mixing valve is in a control-inactivated state, the effective area of ​​the mixing valve is equal to the maximum effective area of ​​the mixing valve, and the maximum effective area of ​​the mixing valve is determined by the characteristics of the mixing valve body; When the mixing valve is in the control activation state, the initial value of the mixing valve effective area is calculated based on the total target flow of the mixing valve, the gas temperature at the air filter outlet, and the target pressure ratio on both sides of the mixing valve. The initial value of the mixing valve effective area is limited to a range from a minimum value to a maximum value to obtain the effective area of ​​the mixing valve when the mixing valve enters the activation state.

3. The closed-loop control method based on mixing valve pressure ratio according to claim 1, characterized in that: The target opening value of the mixing valve is determined specifically by the following method: Determine the initial value of the target opening of the mixing valve; Performing a first-order low-pass filter on the initial value of the mixing valve target opening, and outputting a filtered value of the mixing valve target opening; The change rate of the mixing valve target opening value is limited based on the mixing valve target opening filter value to obtain a final mixing valve target opening value.

4. The closed-loop control method based on mixing valve pressure ratio according to claim 2, characterized in that: The total target flow of the mixing valve is obtained by adding the closed-loop dynamic flow of the mixing valve and the target intake mass flow entering the cylinder, and then subtracting the actual exhaust gas flow of the EGR valve.

5. The closed-loop control method based on mixing valve pressure ratio according to claim 2, characterized in that: The closed-loop dynamic flow of the mixing valve is obtained by adding the closed-loop dynamic flow P part of the mixing valve and the closed-loop dynamic flow I part of the mixing valve.

6. The closed-loop control method based on mixing valve pressure ratio according to claim 5, characterized in that: The closed-loop dynamic flow P term of the mixing valve is obtained by multiplying the initial value of the closed-loop dynamic flow P term of the mixing valve obtained based on the pressure ratio difference of the mixing valve by the time it takes for fresh air to flow from the mixing valve through the compressor to the throttle valve and then enter the cylinder, divided by the time constant of the PI dynamic control and its correction coefficient.

7. The closed-loop control method based on mixing valve pressure ratio according to claim 5, characterized in that: The closed-loop dynamic flow I part of the mixing valve is obtained by continuously accumulating the accumulated value of the closed-loop dynamic flow I part of the mixing valve; When the initial value of the effective area of ​​the mixing valve obtained in the previous sampling period is equal to the maximum value or the minimum value, the accumulated value part of the closed-loop dynamic flow item I based on the mixing valve is 0; when the initial value of the effective area of ​​the mixing valve obtained in the previous sampling period is not equal to the maximum value or the minimum value, the accumulated value part of the closed-loop dynamic flow item I based on the mixing valve is equal to the initial value part of the accumulated value of the closed-loop dynamic flow item I of the mixing valve.

8. The closed-loop control method based on mixing valve pressure ratio according to claim 6, characterized in that: The time it takes for the fresh air to flow from the mixing valve through the compressor to the throttle valve and then enter the cylinder is obtained by averaging multiple sampling data at different engine speeds and different actual intake air densities entering the cylinder. Each sampling data is obtained by bench calibration.

9. The closed-loop control method based on mixing valve pressure ratio according to claim 7, characterized in that: The initial value portion of the accumulated value of the closed-loop dynamic flow I of the mixing valve is obtained by dividing the initial value portion of the closed-loop dynamic flow I of the mixing valve obtained based on the pressure ratio difference of the mixing valve by the time constant of the PI dynamic control and its correction coefficient.

10. The closed-loop control method based on mixing valve pressure ratio according to claim 3, characterized in that: The first-order low-pass filtering of the initial value of the target opening of the mixing valve is specifically obtained by multiplying the difference between the initial value of the target opening of the mixing valve and the filtered value of the target opening of the mixing valve in the previous sampling period by the ratio of the sampling period to the filtering time coefficient, and adding the filtered value of the target opening of the mixing valve in the previous sampling period.

11. The closed-loop control method based on mixing valve pressure ratio according to claim 10, characterized in that: The filtering time coefficient is obtained by adding the filtering time coefficient determined based on the mixing valve pressure ratio difference and the deviation; When the actual pressure ratio across the mixing valve is greater than a first preset value, the deviation is equal to a time coefficient determined based on the target pressure ratio across the mixing valve; When the actual pressure ratio on both sides of the mixing valve is less than the second preset value, the deviation is equal to the filter time coefficient deviation; In other cases, the deviation is equal to the filter time coefficient deviation; The first preset value is greater than the second preset value.

12. The closed-loop control method based on mixing valve pressure ratio according to claim 3, characterized in that: The aforementioned limiting of the rate of change of the target opening value of the mixing valve is specifically to limit the maximum allowable rate of change of the target opening value of the mixing valve when the target opening value of the mixing valve increases; and to limit the absolute value of the maximum allowable rate of change of the target opening value of the mixing valve when the target opening value of the mixing valve decreases.

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