Smoking limit calibration method for diesel engine

Abstract

The invention discloses a diesel engine smoking limit calibration method, and relates to the technical field of automobile engine testing. The method comprises the following steps: setting basic parameters of smoking limitation by determining the calibration opportunity of the smoking limitation, and carrying out MAP horizontal and vertical coordinate design based on the calibration thought of the smoking limitation; and calibrating the smoking limitation of the engine pedestal and the whole vehicle, and performing evaluation based on a calibration result of the smoking limitation. The method has the beneficial effects that the smoke intensity and PM emission of the diesel engine under the transient working condition are reduced, the load response time of the engine is shortened, meanwhile, the test progress can be promoted, the test period is shortened, the development cost of the engine is reduced, and the development efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of automotive engine technology, and in particular to a method for calibrating the smoke limit of a diesel engine. Background Technology

[0002] In daily life, diesel engines frequently experience sudden, rapid increases in throttle, such as when a diesel vehicle accelerates up a steep slope, a truck crane experiences a sudden increase in load, or a bulldozer comes into contact with soil. During operation, when more power is needed, the fuel injection volume increases rapidly. The turbocharger's response lags, and as engine speed increases, the fuel injection volume cannot simply match the throttle demand. This results in excessive fuel injection and insufficient air intake. Simultaneously, the short mixing time between fuel and air in the cylinder can create localized overly rich zones, leading to incomplete combustion and causing the engine to emit black smoke during acceleration.

[0003] To address the issue of smoke during diesel engine acceleration, a smoke limit calibration control strategy is introduced. This strategy adds a smoke limit (Smoke_limit) to the control strategy and controls the actual fuel injection quantity based on the intake air volume during acceleration. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for calibrating the smoke limit of a diesel engine.

[0005] The objective of this invention is achieved through the following technical solution: a method for calibrating the smoke limit of a diesel engine, comprising the following steps: S101: The calibration timing for defining smoke limits is defined as the first calibration development of a diesel engine, changes in intake system leading to changes in charging efficiency, changes in fuel system leading to changes in equivalence ratio, and changes in air system control strategy. S102: Setting of basic parameters for smoke limitation; setting the minimum intake air volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake air flow algorithm source, smoke limitation EGR correction path selection, and maximum and minimum limit coefficients for smoke limitation according to the engine model. S103: Based on the calibration approach of smoke limitation, the MAP horizontal and vertical axes are designed; based on the MAP of normal, heating and regeneration modes, the horizontal axis starts from idle speed -200r / min, and increases to 1600r / min every 100r / min from the start of idle speed as the torque point; the vertical axis starts from idle speed intake volume -300mg / str, and within 60% of the maximum intake volume, the difference between the second and first gear cycle intake volume corresponding to 900r / min is used to adjust the cycle intake volume axis at intervals; 60% of the maximum intake volume and the maximum intake volume are evenly distributed according to the coordinate dimensions. S104: Engine bench and vehicle smoke emission limit calibration; S105: Evaluate the calibration results of smoke limits.

[0006] In step S101, defining the calibration timing of the smoke limit includes calculating the smoke limit flow rate, preparing for the calibration of the smoke limit, defining the calibration conditions for the smoke limit, and defining the calibration requirements for the smoke limit.

[0007] The formula for calculating the smoke limit flow rate is: qsmk=m / (λ*14.5), where qsmk is the smoke limit fuel quantity under the current operating conditions, in mg / hub, m is the intake air flow rate per cylinder of the engine, in mg / str, λ is the calibrated smoke limit coefficient, and 14.5 is the theoretical air-fuel ratio. During acceleration, when the accelerator is fully depressed, the current fuel injection quantity is injected according to the smoke limit fuel quantity, and the smoke limit is activated. At this time, the fuel injection quantity is less than the current external characteristic fuel quantity.

[0008] The calibration preparation for smoke limit is as follows: the engine is in a stable state, and external characteristic tests or repeat point confirmations confirm normal engine performance. The calibration conditions for smoke limit are: precise calibration of the intake airflow meter with an error of less than 1%; stable fuel temperature control at 38±2℃; precise calibration of the 439 opacity meter with an error of less than 1%; precise calibration of the 483 opacity meter with an error of less than 1%. The calibration requirements for smoke limit are: connect the electronic throttle pedal; throttle settings: response time from 0 to 100% should be ≤0.2s; at 100%, the torque should reach at least 95% of the external characteristic torque; 100% throttle dwell time ≥30s; zero torque dwell time ≥60s before proceeding to the second test. After the engine is warmed up, control the calibration point boundaries and stabilize for 5 minutes; the temperature change of the coolant and engine oil should not exceed 2℃.

[0009] Step 102, the setting of the basic parameters for smoke limitation specifically includes: The smoke limit is based on the intake pressure at the intake manifold measured by the intake pressure sensor. The velocity density method is used based on the intake pressure value, and the current intake temperature is taken into account for correction. The air flow rate is consistent with the actual intake air flow rate. The theoretically calculated intake air flow rate is multiplied by the current intake system charging efficiency to obtain the actual circulating intake air flow rate entering each cylinder of the engine. When initially calibrating the intake smoke limit, the relevant parameters of the intake system need to be calibrated. The variables for smoke limitation are set according to the engine model, including minimum intake air volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake air flow algorithm source, smoke limitation EGR correction path selection, and maximum and minimum smoke limitation coefficients.

[0010] In step S104, the engine bench smoke limit calibration includes zero-load point setting, external characteristic point setting, free acceleration calibration, constant speed loading calibration, constant torque transient verification, and WHTC transient emission verification; among which, When the 0-load point is set, the engine runs at 0 load at the corresponding speed axis point. The excess air coefficient (engine cylinder intake flow rate / (circulation oil quantity + 30) / 14.5) at each operating point is recorded as the limit of the maximum excess air coefficient, and this is used as the basic calibration value of the pulse spectrum. During the free acceleration calibration, the engine bench was used for free acceleration tests, and the opacity of the smoke was controlled to be within 0.4 / m-1. After calibration, the free acceleration process was collected, and the response time from engine idle speed +100r / min to the calibration speed was recorded. During constant speed loading calibration, the engine bench is subjected to constant speed loading at speeds below the torque range. The maximum opacity value is controlled according to the index. After calibration, the constant speed loading process is collected, and the response time of the engine from 1 second to torque percentage and the engine load from 10% to 90% are recorded at each speed. During constant torque transient verification, the engine runs from idle speed to maximum torque at 100 Nm intervals from 0 load to maximum torque. The peak value of the maximum opacity during the transient process is recorded. If the target is not met, fine-tuning is required again. During WHTC transient emission verification, WHTC transient emission verification is carried out. During the test, the opacity of the smoke is recorded. If the PM value is within the original emission index range, if it exceeds the index, targeted optimization is carried out on the areas with excessive opacity of the smoke and some areas of WHTC. Finally, the complete WHTC is used for verification and confirmation.

[0011] In step S104, the vehicle smoke emission limit specification includes: free acceleration verification, acceleration verification at each gear, and acceleration verification during gear shifting, wherein, During free acceleration verification, when verifying the smoke emission of the whole vehicle during free acceleration, there should be no visible smoke during free acceleration without DPF. If there is smoke, targeted optimization is required. Pay attention to the difference between the MAP path traversed by the whole vehicle during free acceleration and the MAP path traversed by the bench during free acceleration. After confirmation, collect the whole vehicle free acceleration data and record the response time from engine idle speed +100r / min to the calibrated speed. During acceleration verification at each gear, the vehicle was tested under both unloaded and fully loaded conditions. Smoke emission during acceleration at each gear was verified. Without a DPF, there should be no visible smoke. If smoke occurred during acceleration at any gear, the vertical axis of the smoke limit pulse spectrum was refined using the difference in circulating air volume between first and second gear at 800 rpm as a benchmark. The circulating air volume axis was adjusted from idle air volume to within 60% of the maximum air volume, with the difference in circulating air volume between second and first gear corresponding to an engine speed of 800 rpm as the interval. The maximum air volume of 60% and the engine's maximum air volume were evenly distributed according to the axis dimensions. Smoke limit values ​​were specifically calibrated for different gear conditions, with a focus on second-gear acceleration (evaluating vehicle starting performance) and fourth-gear acceleration (evaluating hill-climbing performance). After confirmation, acceleration data for each gear was collected, and the response time from idle speed +100 rpm to the calibrated speed was recorded for each gear. During the shift acceleration verification, the entire vehicle is tested for smoke emission during shift acceleration. Without a DPF, there should be no visible smoke.

[0012] In step S104, after the smoke limit of the whole vehicle is completed, the data is returned to the engine bench for free acceleration, constant speed loading below the torque range, and WHTC verification and confirmation. The final smoke limit MPA is bench verified by conducting free acceleration, constant speed loading, WHTC and other tests to confirm whether the results meet the requirements. If not, the non-compliant areas need to be fine-tuned.

[0013] Step S105 includes the evaluation of smoke limit indicators in normal mode, heating mode, and regeneration mode. In normal mode, to balance carbon accumulation and regeneration mileage, the opaque smoke level at constant speed loading (1100 r / min and below) is set at 0.4 m. -1 ~0.6m -1 For speeds above 1100 r / min, use 0.2 m. -1 ~0.4m -1 Limit control is required. Heating mode is a common operating mode for the engine. The smoke density in rapid heating mode is also a factor determining the regeneration mileage. Therefore, the constant-speed loading opaque smoke density in rapid heating mode at low speeds (1100 r / min and below) is set at 0.6 m. -1 ~0.8m -1 For speeds above 1100 r / min, use 0.4 m-1 ~0.6m -1 Limit control is required; the regeneration mode aims to ensure oxygen content and improve regeneration efficiency during the regeneration process, and therefore also needs to constrain the smoke opacity of the regeneration model. Thus, the constant-rate loading opacity of the regeneration mode at low speeds of 1100 r / min and below is set at 0.8 m. -1 ~1m -1 For speeds above 1100 r / min, use 0.6 m -1 ~0.8m -1 Limit control.

[0014] The present invention has the following advantages: the diesel engine smoke limit calibration method of the present invention helps to reduce the smoke opacity and PM emissions of diesel engines under transient operating conditions, and shortens the engine load response time. At the same time, it can accelerate the testing process, shorten the testing cycle, reduce engine development costs, and improve development efficiency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the workflow of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0017] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0019] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0021] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] like Figure 1 As shown, a method for calibrating the smoke limit of a diesel engine includes the following steps: S101: The calibration timing for defining smoke limits is defined as the first calibration development of a diesel engine, changes in intake system leading to changes in charging efficiency, changes in fuel system leading to changes in equivalence ratio, and changes in air system control strategy. S102: Setting of basic parameters for smoke limitation; setting the minimum intake air volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake air flow algorithm source, smoke limitation EGR correction path selection, and maximum and minimum limit coefficients for smoke limitation according to the engine model. S103: Based on the calibration approach of smoke limitation, the MAP horizontal and vertical axes are designed; based on the MAP of normal, heating and regeneration modes, the horizontal axis starts from idle speed -200r / min, and increases to 1600r / min every 100r / min from the start of idle speed as the torque point; the vertical axis starts from idle speed intake volume -300mg / str, and within 60% of the maximum intake volume, the difference between the second and first gear cycle intake volume corresponding to 900r / min is used to adjust the cycle intake volume axis at intervals; 60% of the maximum intake volume and the maximum intake volume are evenly distributed according to the coordinate dimensions. S104: Engine Bench and Vehicle Smoke Limit Calibration; Engine bench and vehicle smoke limit calibration requires verification of visible smoke and response time under transient conditions. For engine bench smoke limit calibration, zero-load and external characteristic point settings, free acceleration and constant speed loading calibration, constant torque transient and WHTC transient emission verification are performed. For engine bench constant speed loading smoke limit calibration, taking 1100 r / min as an example, under zero load operation, the engine's per-cylinder intake air flow rate is 900 mg / str, and the circulating fuel quantity is 8.1 mg / hub. The maximum excess air system limit is... max =900 / (8.1+30) / 14.5=1.63; At maximum load operation, the engine's intake air flow rate per cylinder is 2900 mg / str, and the circulating oil volume is 150 mg / hub. Therefore, the minimum excess air coefficient limit is £. min =2900 / (150+30) / 14.5=1.1, according to the excess air coefficient shown in Table 1, the preset MAP; 1000 1100 1200 600 1.650 1.650 1.650 900 1.630 1.630 1.630 1050 1.583 1.583 1.583 1150 1.551 1.551 1.551 1220 1.529 1.529 1.529 1270 1.513 1.513 1.513 1320 1.498 1.498 1.498 1370 1.482 1.482 1.482 1420 1.466 1.466 1.466 1470 1.450 1.450 1.450 1570 1.419 1.419 1.419 1800 1.347 1.347 1.347 2200 1.221 1.221 1.221 2600 1.175 1.175 1.175 2900 1.100 1.100 1.100 3300 1.000 1.000 1.000 Turn off the anti-shake function, mark the smoke limit, turn off EGR, and mark the smoke limit with the throttle fully open. Based on the smoke index, optimize and adjust the £ in this area until the transient smoke peak and response time meet the index requirements. Write £ into the smoke limit MAP to obtain the initial smoke limit. Perform the initial smoke limit verification with EGR open and throttle fully open. It is required that EGR can be fully closed and the throttle can be fully open during transient acceleration. If this is not achieved, the transient EGR and throttle control need to be optimized. At the same time, the transient smoke and responsiveness should be consistent with those with EGR closed and throttle open. For the whole vehicle smoke limit calibration, perform free acceleration, acceleration in each gear, and acceleration during gear shifts for verification. After the whole vehicle smoke limit calibration verification is completed, the data is returned to the engine bench for free acceleration, constant speed loading below the torque range, and WHTC verification confirmation.

[0023] S105: Evaluate the calibration results of the smoke limit, based on the engine's normal mode constant speed loading opaque smoke at low speeds of 1100 r / min and below, using 0.4 m. -1 ~0.6m -1 For speeds above 1100 r / min, use 0.2 m. -1 ~0.4m -1 Limit control; under heating mode, constant-speed loading, opaque smoke at low speeds of 1100 r / min and below, with a limit of 0.6 m. -1 ~0.8m -1 For speeds above 1100 r / min, use 0.4 m -1 ~0.6m -1 Limit control; under regeneration mode, constant-speed loading of opaque smoke at low speeds of 1100 r / min and below, with a limit of 0.8 m. -1 ~1m-1 For speeds above 1100 r / min, use 0.6 m -1 ~0.8m -1 Limit control.

[0024] In this embodiment, step S101 clarifies the timing of the smoke limit calibration, including calculating the smoke limit flow rate, preparing for the smoke limit calibration, defining the smoke limit calibration conditions, and specifying the smoke limit calibration requirements. The formula for calculating the smoke limit flow rate is: qsmk=m / (λ*14.5), where qsmk is the smoke limit fuel quantity under the current operating conditions, in mg / hub, m is the intake air flow rate per cylinder of the engine, in mg / str, λ is the calibrated smoke limit coefficient, and 14.5 is the theoretical air-fuel ratio. During acceleration, when the accelerator is fully depressed, the current fuel injection quantity is based on the smoke limit fuel quantity, and the smoke limit is activated. At this time, the fuel injection quantity is less than the current external characteristic fuel quantity.

[0025] In this embodiment, the calibration preparation for the smoke limit is as follows: the engine is in a stable state, and the engine performance is confirmed to be normal by external characteristic tests or repeat points. The calibration conditions for the smoke limit are: precise calibration of the intake air flow meter with an error of less than 1%, stable fuel temperature control at 38±2℃, precise calibration of the 439 opacity meter with an error of less than 1%, and precise calibration of the 483 opacity meter with an error of less than 1%. The calibration requirements for the smoke limit are: connect the electronic throttle pedal, and set the throttle to: a response time of ≤0.2s from 0 to 100%, a torque of at least 95% of the external characteristic torque at 100%, a 100% throttle dwell time of ≥30s, and a zero torque dwell time of ≥60s before a second test can be conducted. After the engine is warmed up, control the calibration point boundaries and stabilize for 5 minutes, with the water temperature and engine oil temperature changes not exceeding 2℃.

[0026] In this embodiment, step 102, setting the basic parameters for smoke limitation specifically includes: the basic intake volume for smoke limitation is based on the intake pressure measured at the intake manifold by the intake pressure sensor, the velocity density method is used based on the intake pressure value, and correction is made with reference to the current intake temperature; the air flow rate is consistent with the actual intake flow rate value, the theoretically calculated intake flow rate is multiplied by the current intake system charging efficiency to obtain the actual circulating intake flow rate entering each cylinder of the engine, and the relevant parameters of the intake system need to be calibrated during the initial calibration of the intake smoke limitation; the variable setting for smoke limitation includes setting the minimum circulating intake volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake flow rate algorithm source, smoke limitation EGR correction path selection, and maximum and minimum limitation coefficients for smoke limitation according to the engine model.

[0027] In step S104, the engine bench smoke limit calibration includes 0-load point setting, external characteristic point setting, free acceleration calibration, constant speed loading calibration, constant torque transient verification, and WHTC transient emission verification. Specifically, during 0-load point setting, the engine operates at 0 load at the corresponding speed axis point, and the excess air coefficient (engine cylinder per cycle intake air flow / (cycle oil volume + 30) / 14.5) is recorded at each operating point as the maximum excess air coefficient limit, which is used as the basic calibration value for the pulse spectrum. During free acceleration calibration, the engine bench undergoes a free acceleration test, controlling the opacity to be within 0.4 / m⁻¹. After calibration, the free acceleration process is collected, and the response time from engine idle speed + 100 r / min to the calibrated speed is recorded. During constant speed loading calibration, the engine bench undergoes a torque test... For constant-speed loading below the torque range, the maximum opacity value is controlled according to the index. After calibration, the constant-speed loading process is collected, and the response time of the engine from 1 second to torque percentage and from 10% to 90% of engine load at each speed is recorded. During constant-torque transient verification, the engine runs from idle speed to maximum torque at 100 Nm intervals from 0 load to maximum torque, and the peak value of the maximum opacity during the transient process is recorded. If the index is not met, fine-tuning is required. During WHTC transient emission verification, WHTC transient emission verification is performed, and the opacity is recorded during the test. If the PM value is within the original emission index range, if it exceeds the index, targeted optimization is performed on areas with excessive opacity and WHTC areas. Finally, the complete WHTC is used for verification and confirmation.

[0028] In this embodiment, step S104 specifies the following for limiting vehicle smoke emissions: free acceleration verification, acceleration verification at each gear, and acceleration verification during gear shifting. During free acceleration verification, the vehicle's free acceleration smoke emission is verified. Without a DPF, there should be no visible smoke during free acceleration. If visible smoke is present, targeted optimization is required. It is important to compare the MAP path traversed by the vehicle during free acceleration with the MAP path traversed by the bench test. After confirmation, vehicle free acceleration data is collected, and the response time from engine idle speed +100 r / min to the calibrated speed is recorded. During acceleration verification at each gear, the vehicle is tested under both no-load and full-load conditions. Without a DPF, there should be no visible smoke. If smoke occurs during acceleration at any gear, the engine speed is adjusted to 800 r / min in first and second gear. Using the difference in air intake volume as a benchmark, the vertical axis of the air intake volume in the smoke limit pulse spectrum is refined. From the idle air intake volume to within 60% of the maximum air intake volume, the air intake volume axis is adjusted at intervals based on the difference in air intake volume between second and first gear corresponding to an engine speed of 800 r / min. The maximum air intake volume of 60% and the maximum air intake volume of the engine are evenly distributed according to the axis dimension. For smoke conditions in different gears, smoke limit values ​​for each gear are specifically calibrated, with a focus on second-gear acceleration (evaluating the vehicle's starting performance) and fourth-gear acceleration (evaluating climbing performance). After confirmation, acceleration data for each gear is collected, and the response time from idle speed +100 r / min to the calibrated speed is recorded for each gear. During gear shift acceleration verification, the smoke condition during gear shift acceleration is verified for the whole vehicle. Without DPF, there should be no visible smoke.

[0029] In this embodiment, in step S104, after the vehicle smoke limit is completed, the data is returned to the engine bench for free acceleration, constant speed loading below the torque range, and WHTC verification. The final smoke limit MPA is then bench-verified by conducting free acceleration, constant speed loading, and WHTC tests to confirm whether the results meet the requirements. If not, the non-compliant areas need to be fine-tuned.

[0030] In this embodiment, step S105 includes evaluating smoke limit indicators in normal mode, heating mode, and regeneration mode. The normal mode is used to balance carbon regeneration mileage and power efficiency; therefore, a constant-speed loading, opaque smoke level of 0.4m is set at low speeds of 1100 r / min and below. -1 ~0.6m -1 For speeds above 1100 r / min, use 0.2 m. -1 ~0.4m -1 Limit control is required. Heating mode is a common operating mode for the engine. The smoke density in rapid heating mode is also a factor determining the regeneration mileage. Therefore, the constant-speed loading opaque smoke density in rapid heating mode at low speeds (1100 r / min and below) is set at 0.6 m. -1~0.8m -1 For speeds above 1100 r / min, use 0.4 m -1 ~0.6m -1 Limit control is required; the regeneration mode aims to ensure oxygen content and improve regeneration efficiency during the regeneration process, and therefore also needs to constrain the smoke opacity of the regeneration model. Thus, the constant-rate loading opacity of the regeneration mode at low speeds of 1100 r / min and below is set at 0.8 m. -1 ~1m -1 For speeds above 1100 r / min, use 0.6 m -1 ~0.8m -1 Limit control.

[0031] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calibrating the smoke limit of a diesel engine, characterized in that: Includes the following steps: S101: The calibration timing for defining smoke limits is defined as the first calibration development of a diesel engine, changes in intake system leading to changes in charging efficiency, changes in fuel system leading to changes in equivalence ratio, and changes in air system control strategy. S102: Setting of basic parameters for smoke limitation; setting the minimum intake air volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake air flow algorithm source, smoke limitation EGR correction path selection, and maximum and minimum limit coefficients for smoke limitation according to the engine model. S103: Based on the calibration approach of smoke limitation, the MAP horizontal and vertical axes are designed; based on the MAP of normal, heating and regeneration modes, the horizontal axis starts from idle speed -200r / min, and increases to 1600r / min every 100r / min from the start of idle speed as the torque point; the vertical axis starts from idle speed intake volume -300mg / str, and within 60% of the maximum intake volume, the difference between the second and first gear cycle intake volume corresponding to 900r / min is used to adjust the cycle intake volume axis at intervals; 60% of the maximum intake volume and the maximum intake volume are evenly distributed according to the coordinate dimensions. S104: Engine bench and vehicle smoke emission limit calibration; S105: Evaluate the calibration results of smoke limits.

2. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: In step S101, defining the calibration timing of the smoke limit includes calculating the smoke limit flow rate, preparing for the calibration of the smoke limit, defining the calibration conditions for the smoke limit, and defining the calibration requirements for the smoke limit.

3. The method for calibrating the smoke limit of a diesel engine according to claim 2, characterized in that: The formula for calculating the smoke limit flow rate is: qsmk=m / (λ*14.5), where qsmk is the smoke limit fuel quantity under the current operating conditions, in mg / hub, m is the intake air flow rate per cylinder of the engine, in mg / str, λ is the calibrated smoke limit coefficient, and 14.5 is the theoretical air-fuel ratio. During acceleration, when the accelerator is fully depressed, the current fuel injection quantity is injected according to the smoke limit fuel quantity, and the smoke limit is activated. At this time, the fuel injection quantity is less than the current external characteristic fuel quantity.

4. The method for calibrating the smoke limit of a diesel engine according to claim 2, characterized in that: The calibration preparation for smoke limit is as follows: the engine is in a stable state, and external characteristic tests or repeat point confirmations confirm normal engine performance. The calibration conditions for smoke limit are: precise calibration of the intake airflow meter with an error of less than 1%; stable fuel temperature control at 38±2℃; precise calibration of the 439 opacity meter with an error of less than 1%; precise calibration of the 483 opacity meter with an error of less than 1%. The calibration requirements for smoke limit are: connect the electronic throttle pedal; throttle settings: response time from 0 to 100% should be ≤0.2s; at 100%, the torque should reach at least 95% of the external characteristic torque; 100% throttle dwell time ≥30s; zero torque dwell time ≥60s before proceeding to the second test. After the engine is warmed up, control the calibration point boundaries and stabilize for 5 minutes; the temperature change of the coolant and engine oil should not exceed 2℃.

5. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: Step 102, the setting of the basic parameters for smoke limitation specifically includes: The smoke limit is based on the intake pressure at the intake manifold measured by the intake pressure sensor. The velocity density method is used based on the intake pressure value, and the current intake temperature is taken into account for correction. The air flow rate is consistent with the actual intake air flow rate. The theoretically calculated intake air flow rate is multiplied by the current intake system charging efficiency to obtain the actual circulating intake air flow rate entering each cylinder of the engine. When initially calibrating the intake smoke limit, the relevant parameters of the intake system need to be calibrated. The variables for smoke limitation are set according to the engine model, including minimum intake air volume per cylinder, engine displacement, number of engine cylinders, smoke limitation fault path activation selection switch, engine intake air flow algorithm source, smoke limitation EGR correction path selection, and maximum and minimum smoke limitation coefficients.

6. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: In step S104, the engine bench smoke limit calibration includes zero-load point setting, external characteristic point setting, free acceleration calibration, constant speed loading calibration, constant torque transient verification, and WHTC transient emission verification; among which, When the 0-load point is set, the engine runs at 0 load at the corresponding speed axis point. The excess air coefficient (engine cylinder intake flow rate / (circulation oil quantity + 30) / 14.5) at each operating point is recorded as the limit of the maximum excess air coefficient, and this is used as the basic calibration value of the pulse spectrum. During free acceleration calibration, the engine bench underwent free acceleration testing, with the opacity of the smoke controlled at 0.4 / m. -1 Within this range, after calibration, the free acceleration process is collected, and the response time from engine idle speed +100r / min to the calibrated speed is recorded. During constant speed loading calibration, the engine bench is subjected to constant speed loading at speeds below the torque range. The maximum opacity value is controlled according to the index. After calibration, the constant speed loading process is collected, and the response time of the engine from 1 second to torque percentage and the engine load from 10% to 90% are recorded at each speed. During constant torque transient verification, the engine runs from idle speed to maximum torque at 100 Nm intervals from 0 load to maximum torque. The peak value of the maximum opacity during the transient process is recorded. If the target is not met, fine-tuning is required again. During WHTC transient emission verification, WHTC transient emission verification is carried out. During the test, the opacity of the smoke is recorded. If the PM value is within the original emission index range, if it exceeds the index, targeted optimization is carried out on the areas with excessive opacity of the smoke and some areas of WHTC. Finally, the complete WHTC is used for verification and confirmation.

7. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: In step S104, the vehicle smoke emission limit specification includes: free acceleration verification, acceleration verification at each gear, and acceleration verification during gear shifting, wherein, During free acceleration verification, when verifying the smoke emission of the whole vehicle during free acceleration, there should be no visible smoke during free acceleration without DPF. If there is smoke, targeted optimization is required. Pay attention to the difference between the MAP path traversed by the whole vehicle during free acceleration and the MAP path traversed by the bench during free acceleration. After confirmation, collect the whole vehicle free acceleration data and record the response time from engine idle speed +100r / min to the calibrated speed. During acceleration verification at each gear, the vehicle was tested under both unloaded and fully loaded conditions. Smoke emission during acceleration at each gear was verified. Without a DPF, there should be no visible smoke. If smoke occurred during acceleration at any gear, the vertical axis of the smoke limit pulse spectrum was refined using the difference in circulating air volume between first and second gear at 800 rpm as a benchmark. The circulating air volume axis was adjusted from idle air volume to within 60% of the maximum air volume, with the difference in circulating air volume between second and first gear corresponding to an engine speed of 800 rpm as the interval. The maximum air volume of 60% and the engine's maximum air volume were evenly distributed according to the axis dimensions. Smoke limit values ​​were specifically calibrated for different gear conditions, with a focus on second-gear acceleration (evaluating vehicle starting performance) and fourth-gear acceleration (evaluating hill-climbing performance). After confirmation, acceleration data for each gear was collected, and the response time from idle speed +100 rpm to the calibrated speed was recorded for each gear. During the shift acceleration verification, the whole vehicle is tested for smoke during shift acceleration. Without DPF, there should be no visible smoke.

8. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: In step S104, after the smoke limit of the whole vehicle is completed, the data is returned to the engine bench for free acceleration, constant speed loading below the torque range, and WHTC verification and confirmation. The final smoke limit MPA is bench verified by conducting free acceleration, constant speed loading, WHTC and other tests to confirm whether the results meet the requirements. If not, the non-compliant areas need to be fine-tuned.

9. The method for calibrating the smoke limit of a diesel engine according to claim 1, characterized in that: Step S105 includes the evaluation of smoke limit indicators in normal mode, heating mode, and regeneration mode. In normal mode, to balance carbon accumulation and regeneration mileage, the opaque smoke level at constant speed loading (1100 r / min and below) is set at 0.4 m. -1 ~0.6m -1 For speeds above 1100 r / min, use 0.2 m. -1 ~0.4m -1 Limit control is required. Heating mode is a common operating mode for the engine. The smoke density in rapid heating mode is also a factor determining the regeneration mileage. Therefore, the constant-speed loading opaque smoke density in rapid heating mode at low speeds (1100 r / min and below) is set at 0.6 m. -1 ~0.8m -1 For speeds above 1100 r / min, use 0.4 m -1 ~0.6m -1 Limit control is required; the regeneration mode aims to ensure oxygen content and improve regeneration efficiency during the regeneration process, and therefore also needs to constrain the smoke opacity of the regeneration model. Thus, the constant-rate loading opacity of the regeneration mode at low speeds of 1100 r / min and below is set at 0.8 m. -1 ~1m -1 For speeds above 1100 r / min, use 0.6 m -1 ~0.8m -1 Limit control.

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