Real-time prediction method of blow-by gas amount based on crankcase pressure and cylinder pressure difference model

Abstract

The application discloses a real-time prediction method for blow-by gas amount based on a crankcase pressure and cylinder pressure difference model, comprising: a cylinder pressure reconstruction output module for providing in-cylinder pressure, in-cylinder temperature and in-cylinder volume in real time; a crankcase pressure sensor installed near a crankcase ventilation pipeline or a main oil passage for measuring the gas pressure in the crankcase in real time; an engine working condition sensor for acquiring engine speed, coolant temperature and intake pressure signals; a blow-by gas amount calculation module based on a Weller gas flow model, using input in-cylinder parameters, an online identification submodule using equivalent flow area and flow coefficient to make the model automatically adapt to engine wear and working condition changes; a flow state judgment submodule automatically judging the gas flow state according to the pressure ratio of the cylinder and the crankcase; and an output and application module for outputting the blow-by gas mass flow value in real time and taking the value as a direct quantitative index of piston-cylinder liner wear, and triggering a maintenance warning when the blow-by gas flow and the blow-by gas flow area exceed preset threshold values.

Description

Technical Field

[0001] This invention relates to the field of engine design and manufacturing technology, and in particular to a method for real-time prediction of blow-by volume based on a crankcase pressure and cylinder pressure differential model. Background Technology

[0002] Crankcase blow-by is a key parameter for evaluating engine health, piston-cylinder wear, and combustion seal performance, directly affecting engine emissions, oil degradation rate, and overall engine reliability. Traditional blow-by methods primarily rely on installing flow sensors on the crankcase ventilation lines or using tracer gas analysis. While these methods offer high accuracy, they suffer from the following drawbacks:

[0003] High cost: Dedicated flow sensors are expensive, making large-scale deployment in mass-produced engines difficult;

[0004] Complex installation: It requires modifications to the engine structure, which affects production and maintenance efficiency;

[0005] Poor real-time performance: Some methods cannot meet the needs of online monitoring and real-time control;

[0006] Poor environmental adaptability: The sensor has low reliability in harsh environments such as high temperature, oil, and vibration.

[0007] In recent years, some indirect prediction methods based on speed fluctuations, vibration signals, or intake pressure changes have emerged. However, these methods usually rely on a large amount of experimental data for black-box modeling, lack physical interpretability, have poor generalization ability when operating conditions change, and the prediction results are unstable.

[0008] Therefore, there is an urgent need for a gas leakage prediction scheme that is both supported by physical mechanisms and can achieve online, low-cost monitoring.

[0009] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0010] The purpose of this invention is to provide a real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference models. This method offers high accuracy, low cost, and real-time prediction of engine crankcase blow-by volume, addressing the problems of high cost, complex installation, and difficulty in online monitoring associated with traditional blow-by volume measurement technologies.

[0011] To achieve the above objectives, the present invention provides a real-time prediction method for blow-by volume based on a crankcase pressure and cylinder pressure difference model, which is used in a real-time prediction system for blow-by volume based on a crankcase pressure and cylinder pressure difference model. The real-time prediction system for blow-by volume includes a signal input module and a core prediction and identification module.

[0012] The signal input module includes a cylinder pressure reconstruction output module, a crankcase pressure sensor, and an engine condition sensor. The cylinder pressure reconstruction output module provides real-time cylinder pressure, cylinder temperature, and cylinder volume. The crankcase pressure sensor is installed near the crankcase ventilation pipe or main oil passage to measure the gas pressure inside the crankcase in real time. The engine condition sensor acquires engine speed, coolant temperature, and intake pressure signals. The core prediction and identification module includes a blow-by volume calculation module, an online parameter identification submodule, a flow state judgment submodule, and an output and application module. The blow-by volume calculation module is based on the Weller gas flow model and utilizes the input cylinder pressure and temperature... The system calculates the instantaneous blow-by mass flow rate based on volume, crankcase pressure, and blow-by flow area; the online parameter identification submodule uses the equivalent flow area and flow coefficient to enable the model to automatically adapt to engine wear and operating condition changes; the flow state judgment submodule automatically judges the gas flow state based on the pressure ratio between the cylinder and the crankcase and calls the corresponding flow function ψ; the output and application module outputs the instantaneous value and cumulative value of the blow-by mass flow rate in real time, and performs self-calibration of the blow-by flow area based on the crankcase pressure change under the same operating conditions, serving as a direct quantitative indicator of piston-cylinder wear. When the blow-by flow rate and blow-by flow area exceed the preset threshold, different levels of maintenance warnings are triggered.

[0013] In a preferred embodiment, the model calculation formula of the gas leakage calculation module includes:

[0014] The pressure ratio is calculated and the flow state is determined using the following formula:

[0015] (1)

[0016] (2)

[0017] In the formula It is the crankcase pressure (Pa) obtained by a pressure sensor. This is a cylinder pressure reconstruction model, which is based on intake pressure, temperature, cylinder volume, speed, fuel characteristics, combustion system control parameters, and coolant temperature; G is the pressure ratio, Gcr is the critical pressure ratio, and γ is the specific heat ratio of the in-cylinder mixture.

[0018] If G≤Gcr, it is critical (blocked) flow, where the gas velocity through the gap reaches the local speed of sound, and changes in crankcase pressure do not affect the flow rate; if G>Gcr, it is subcritical flow; the flow state is judged based on the pressure ratio calculated in real time by the cylinder pressure reconstruction model.

[0019] In a preferred embodiment, the model calculation formula of the gas leakage calculation module further includes:

[0020] Calculate the flow function based on the flow state:

[0021] (3)

[0022] Calculate the instantaneous mass flow rate of gas leakage:

[0023] (4)

[0024] Where R is the gas constant, Cd is the flow coefficient, and A gap The flow area of ​​the gas leakage (m²) 2 P and T need to be calculated based on the cylinder pressure reconstruction model.

[0025] In a preferred embodiment, the model calculation formula of the gas leakage calculation module further includes:

[0026] Gas flow area A gap Determine and automatically calibrate:

[0027] (5)

[0028] In the formula, D is the cylinder diameter (m). This is the minimum radial clearance (m) between the piston rings and the cylinder wall, obtained through measurement. However, this value can vary significantly due to thermal deformation and wear. Therefore, it needs to be automatically calibrated within a certain timeframe. Under the same operating conditions, the blow-by area is calibrated proportionally based on the crankcase pressure changes. The specific formula is as follows:

[0029] (6)

[0030] Determination of flow coefficient:

[0031] (7)

[0032] In the formula, Re represents the Reynolds number.

[0033] In a preferred embodiment, the cylinder pressure reconstruction output module incorporates a physical guidance prediction model based on the first law of thermodynamics. This model takes real-time sensor data as input and, through a series of injection rate prediction sub-models, in-cylinder working fluid heat transfer prediction sub-models, and cumulative heat release rate prediction sub-models, ultimately solves for the predicted in-cylinder pressure-crankshaft angle curve of the target cylinder in one or more working cycles. The model calculation formula includes:

[0034] The fuel injection rate prediction module uses injector structural parameters, injection pressure, and injection pulse width data as input, and performs polynomial fitting with the experimentally measured fuel injection rate curve. The fitting formula is as follows:

[0035] (8)

[0036] (9)

[0037] (10)

[0038] (11)

[0039] (12)

[0040] (13)

[0041] In the above polynomial, the time unit is ms, and the injection rate unit is mg / ms; , , , , and These represent the quick-opening stage of the needle valve. Needle valve slow opening stage Needle valve full opening stage Needle valve fluctuation stage Needle valve slow closing stage and needle valve quick-closing stage Corresponding fuel injection rate; parameters j and k are calibrated parameters that can be calibrated based on experimental data. They are obtained by fitting the second stage (needle valve slow-opening stage) with different injection pressures. and The values ​​are -0.53 and 1.6. The value of varies with the injection pressure and can be solved by combining it with the following formula (14);

[0042] Similarly and The value can then be determined. and The value also needs and Perform a joint solution; The parameters need to be determined first according to the following formula (17). The value of is then solved. = and Two equations determine and ;

[0043] The value of Z is related to the peak injection rate.

[0044] In a preferred embodiment, the fitting formula of the fuel injection rate prediction module further includes:

[0045] (14)

[0046] (15)

[0047] (16)

[0048] (17)

[0049] Where, n represents the number of injection holes of the injector, Cd, ρ f A0 and These represent the injector's flow coefficient, fuel density, injector orifice cross-sectional area, and calibration parameters, respectively; u th Representing the theoretical injection speed, the calculation formula is as shown in equation (15), P rail Represents the injection pressure; Cd is calculated as shown in equation (16), where Re represents the Reynolds number.

[0050] In a preferred embodiment, the model calculation formula for the cylinder pressure reconstruction output module further includes: a cumulative heat release prediction model, which is calculated using a method based on the concept of cumulative fuel mass in the cylinder. The input of this model is the injection rate curve, and the calculation formula includes:

[0051] (18)

[0052] (19)

[0053] (20)

[0054] , , , , , , and These are the cumulative fuel mass in the cylinder (mg), the amount of fuel injected into the cylinder (mg), the fuel consumption rate in the cylinder, the heat release, the combustion efficiency, the crankshaft angle (deg), the ignition delay (deg), and the lower heating value of diesel fuel, respectively. The principle is to calculate the amount of fuel that can be completely burned at the current crankshaft angle based on equation (17). The first term is the amount of fuel injected into the cylinder that can be completely burned at the current crankshaft angle, and the second term is the amount of fuel remaining in the cylinder at the previous crankshaft angle. The second term is 0 before the injection starts. The sum of the two is the amount of fuel that can be completely burned in the cylinder at the current crankshaft angle. Then, according to equation (18), the heat release at the current crankshaft angle is calculated and added to the heat release at the previous crankshaft angle to obtain the cumulative heat release at the current crankshaft angle. .

[0055] In a preferred embodiment, the formula for calculating the cylinder pressure model according to the first law of thermodynamics includes:

[0056] (twenty one)

[0057] (twenty two)

[0058] (twenty three)

[0059] The calculation of heat transfer loss Qw is given by equation (22); where h represents the heat transfer coefficient (W / m). 2 ·K); As represents the area where heat loss occurs; T represents the in-cylinder temperature (determined according to the ideal gas equation); Tref = 363.15K; the heat transfer coefficient of the engine is calculated using Hohenberg's heat transfer coefficient relation (23); V, P and T are the in-cylinder volumes (m³) respectively. 3 ), pressure (Pa) and temperature (K); vm represents the speed of piston movement (m / s).

[0060] In a preferred embodiment, the calculation of the in-cylinder temperature T includes two cases:

[0061] The first method involves calculating the cylinder temperature under known cylinder pressure by assuming the cylinder is a closed system and using the ideal gas law. This method is primarily used in analyzing the impact of each term in the first law of thermodynamics on the calculation of the heat release rate; and

[0062] The second method is cylinder pressure reconstruction under unknown cylinder pressure conditions. In this paper, it is assumed that the compression stroke before injection is a reversible adiabatic process. The cylinder temperature is calculated using equation (24), and the pressure is calculated using equation (25). During the expansion stroke, the combustion of fuel releases heat, which in turn heats the working fluid in the cylinder. The cylinder temperature calculation needs to be combined with equation (26) based on equation (24). Since the change in volume between adjacent crankshaft angles is very small, it can be ignored. Therefore, the constant volume specific heat capacity cv is used for calculation. The calculation of ΔQ in equation (26) will be introduced below. At the same time, K1 is an empirical parameter. The calculation formula includes:

[0063] (twenty four)

[0064] (25)

[0065] (26)

[0066] Among them, compared with no cross-flow loss ( ), and the latent heat of vaporization of fuel oil ( The heat release rate calculated by the first law of thermodynamics model when two terms are ignored. or The calculated heat release rate is almost identical to that obtained using the full formula.

[0067] 10. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 8, characterized in that the principle formula of the cylinder pressure reconstruction model is:

[0068] (27)

[0069] Wherein, γ is the specific heat ratio of the in-cylinder air-fuel mixture.

[0070] Compared with existing technologies, the real-time blow-by volume prediction method based on crankcase pressure and cylinder pressure differential models of this invention has the following advantages: This invention directly calculates the blow-by mass flow rate by judging the gas flow state (critical or subcritical) using a piecewise flow function. This method utilizes classical gas flow theory to achieve physical modeling of the blow-by phenomenon, replacing the traditional method that relies on expensive flow meters or purely data-driven black-box models. Online self-calibration mechanism for blow-by flow area: An innovative method is proposed to dynamically calibrate the blow-by flow area under the same engine operating conditions based on the temporal variation ratio of crankcase pressure. This mechanism requires no additional sensors and can automatically track changes in flow characteristics caused by engine thermal deformation and wear, significantly improving the prediction accuracy of the model throughout its entire lifecycle. Collaborative fusion architecture with cylinder pressure reconstruction model: The independent "in-cylinder pressure reconstruction model" is deeply coupled with the "blow-by volume prediction model," reusing the cylinder pressure reconstruction results as the core input for blow-by volume prediction. This architecture fully utilizes existing engine sensor signals, avoids the installation of dedicated cylinder pressure sensors, and achieves low-cost, high-precision real-time monitoring of blow-by volume. Direct Engine Health Assessment Function: Based on predicted blow-by volume and flow area change trends, the system directly quantifies and assesses the wear degree of the piston-cylinder. When the blow-by flow rate or flow area exceeds a preset threshold or its growth rate changes abruptly, the system can automatically trigger maintenance warnings at different levels, extending functionality from condition monitoring to health management. Adaptive Modeling of Flow Coefficient Under Changing Conditions: Establishing a correlation between the flow coefficient and Reynolds number, the model can automatically adjust the flow coefficient according to operating parameters such as engine speed, load, and temperature, improving the model's predictive accuracy and adaptability under varying operating conditions. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of the system architecture of a real-time prediction system for cross-flow volume according to an embodiment of the present invention.

[0072] Figure 2 This is a schematic diagram of the temperature prediction result of the real-time prediction method for cross-flow volume according to an embodiment of the present invention.

[0073] Figure 3 This is a schematic diagram of the pressure prediction result of the real-time prediction method for gas leakage volume according to an embodiment of the present invention.

[0074] Figure 4 This is a schematic diagram of the volume prediction result of the real-time prediction method for cross-flow volume according to an embodiment of the present invention. Detailed Implementation

[0075] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0076] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0077] 1. Purpose of the invention

[0078] This invention aims to provide a high-precision, low-cost, and real-time method for predicting engine crankcase blow-by volume, solving the problems of high cost, complex installation, and difficulty in online monitoring associated with traditional blow-by volume measurement technologies. The core idea of ​​this invention is:

[0079] By reusing the existing in-cylinder pressure reconstruction model and combining it with a low-cost crankcase pressure sensor, a blow-by volume prediction model is constructed based on classical gas flow theory. An online parameter identification mechanism is introduced to achieve real-time, adaptive, and high-precision prediction of blow-by volume, while directly reflecting the wear state of the engine piston and cylinder.

[0080] 2. System Architecture

[0081] like Figure 1 As shown, according to a preferred embodiment of the present invention, a real-time prediction method for blow-by volume based on a crankcase pressure and cylinder pressure differential model is applied to a real-time prediction system for blow-by volume, wherein the system architecture includes the following modules integrated into the engine electronic control unit (ECU):

[0082] The signal input module includes:

[0083] The cylinder pressure reconstruction module outputs real-time cylinder pressure, cylinder temperature, and cylinder volume. This forms the basis of the present invention and reuses existing innovative achievements.

[0084] Crankcase pressure sensor: Installed near the crankcase ventilation pipes or main oil passage, it measures the gas pressure inside the crankcase in real time. This is a newly added, low-cost core sensing unit.

[0085] Engine operating condition sensors: Reuse existing sensors to acquire signals such as engine speed, coolant temperature and intake pressure for model building.

[0086] The core prediction and identification module (software algorithm) includes:

[0087] Blow-by volume calculation module: Based on the Weller gas flow model, it calculates the instantaneous blow-by mass flow rate using the input in-cylinder pressure, temperature, volume, crankcase pressure, and blow-by flow area.

[0088] Online parameter identification submodule: — Equivalent flow area and flow coefficient, enabling the model to automatically adapt to engine wear and changes in operating conditions.

[0089] The flow state determination submodule automatically determines the gas flow state (critical or subcritical) based on the pressure ratio between the cylinder and crankcase, and calls the corresponding flow function φ.

[0090] Output and Application Modules:

[0091] Real-time output: Mass flow rate of cross-flow gas (instantaneous value and cumulative value of circulation).

[0092] Health status indicators: The blow-by area is self-calibrated based on the crankcase pressure change under the same working conditions, serving as a direct quantitative indicator of piston-cylinder wear.

[0093] Warning signals: When the gas flow rate and gas flow area exceed the preset threshold, different levels of maintenance warnings are triggered.

[0094] 3. Technical Solution Overview

[0095] 3.1 The specific calculation formula for the gas leakage flow prediction model is as follows:

[0096] Step 1: Calculate the pressure ratio and determine the flow state

[0097] (1)

[0098] (2)

[0099] In the formula It is the crankcase pressure (Pa) obtained by a pressure sensor. This is the cylinder pressure reconstruction model, which is based on intake pressure, temperature, cylinder volume, engine speed, fuel characteristics, combustion system control parameters, and coolant temperature. It will be discussed later. G represents the pressure ratio, Gcr is the critical pressure ratio, and γ is the specific heat ratio of the in-cylinder mixture (taken as 1.34). If G ≤ Gcr, it is critical (blocked) flow, where the gas velocity through the gap reaches the local speed of sound, and changes in crankcase pressure do not affect the flow rate. If G > Gcr, it is subcritical flow. The flow state is determined based on the pressure ratio calculated in real-time by the cylinder pressure reconstruction model.

[0100] Step 2: Calculate the flow function based on the flow state:

[0101] (3)

[0102] Step 3: Calculate the instantaneous mass flow rate of gas leakage.

[0103] (4)

[0104] R is the gas constant (taken as 287 J / (kg·K)), Cd is the flow coefficient, and A gap The flow area of ​​the gas leakage (m²) 2 P and T need to be calculated based on the cylinder pressure reconstruction model; the specific calculation principle is included in the technical documentation that helps in understanding this application. The predicted results for temperature, pressure, and volume are as follows: Figure 2 As shown.

[0105] Step 4: Gas flow area A gap Determine and automatically calibrate

[0106] (5)

[0107] In the formula, D is the cylinder diameter (m). This is the minimum radial clearance (m) between the piston rings and the cylinder wall, obtained through measurement. However, this value can vary significantly due to thermal deformation and wear. Therefore, it needs to be automatically calibrated within a certain timeframe. Under the same operating conditions, the blow-by area is calibrated proportionally based on the crankcase pressure changes. The specific formula is as follows:

[0108] (6)

[0109] Step 5: Determining the Flow Coefficient

[0110] (7)

[0111] In the formula, Re represents the Reynolds number.

[0112] 3.2 Specific Calculation Formulas for Cylinder Pressure Reconstruction Model

[0113] This module incorporates a physical guidance prediction model based on the first law of thermodynamics. Taking real-time sensor data as input, this model uses a series of sub-models—one for fuel injection rate prediction, one for in-cylinder working fluid heat transfer prediction, and one for cumulative heat release rate prediction—to ultimately obtain the predicted in-cylinder pressure-crankshaft angle curves for the target cylinder over one or more operating cycles. The principle is as follows:

[0114] (1) Injection rate prediction module: The injector structural parameters, injection pressure, injection pulse width and other data are used as inputs, and polynomial fitting is performed with the experimentally measured injection rate curve. The fitting formula is as follows:

[0115] (8)

[0116] (9)

[0117] (10)

[0118] (11)

[0119] (12)

[0120] (13)

[0121] The time unit in the above polynomial is ms, and the injection rate unit is mg / ms. , , , , and These represent the quick-opening stage of the needle valve. Needle valve slow opening stage Needle valve full opening stage Needle valve fluctuation stage Needle valve slow closing stage and needle valve quick-closing stage The corresponding fuel injection rate. Parameter j and k are calibrated parameters that can be calibrated based on experimental data. They are obtained by fitting the second stage (the needle valve slow-opening stage) with different injection pressures. and The values ​​are -0.53 and 1.6. The value of varies with the injection pressure and can be solved by combining it with formula (14). Similarly... and The value can be determined. and The value also needs and Perform a joint solution. The parameters need to be determined first according to equation (17). The value of is then solved. = and Two equations determine and The value of Z is related to the peak injection rate.

[0122] (14)

[0123] (15)

[0124] (16)

[0125] (17)

[0126] In the formula, n represents the number of injection holes of the injector, Cd, ρ fA0 and These represent the injector's flow coefficient, fuel density, injector orifice cross-sectional area, and calibration parameters, respectively. th Representing the theoretical injection speed, the calculation formula is as shown in equation (15), P rail Represents the injection pressure. Cd is calculated as shown in equation (16), where Re represents the Reynolds number.

[0127] (2) Heat transfer prediction model: The Hohenberg model was used for calculation;

[0128] (3) Cumulative heat release prediction model: The model is calculated using a method based on the concept of cumulative fuel mass in the cylinder. The input to this model is the injection rate curve, and the formula is:

[0129] (18)

[0130] (19)

[0131] (20)

[0132] , , , , , , and These are the cumulative fuel mass in the cylinder (mg), the amount of fuel injected into the cylinder (mg), the in-cylinder fuel consumption rate, heat release, combustion efficiency, crankshaft angle (deg), ignition delay (deg), and the lower heating value of diesel fuel, respectively. The principle is based on formula (17) to calculate the amount of fuel that can be completely burned at the current crankshaft angle. The first term is the amount of fuel injected into the cylinder that can be completely burned at the current crankshaft angle, and the second term is the amount of fuel remaining in the cylinder at the previous crankshaft angle. This second term is 0 before injection begins. The sum of the two terms is the amount of fuel that can be completely burned in the cylinder at the current crankshaft angle. Then, according to equation (18), the heat release at the current crankshaft angle is calculated and added to the heat release at the previous crankshaft angle to obtain the cumulative heat release at the current crankshaft angle. .

[0133] (4) The cylinder pressure model is calculated using the first law of thermodynamics, and the formula is:

[0134] (twenty one)

[0135] The heat transfer loss Qw is calculated as shown in equation (22). In the equation, h represents the heat transfer coefficient (W / m³). 2·K). As represents the area where heat loss occurs. T represents the in-cylinder temperature (determined according to the ideal gas equation). Tref = 363.15K. The heat transfer coefficient of the engine is calculated using Hohenberg's heat transfer coefficient relation (Equation (23)). V, P and T are the in-cylinder volumes (m³, K) respectively. 3 ), pressure (Pa) and temperature (K). vm represents the speed of piston movement (m / s).

[0136] (twenty two)

[0137] (twenty three)

[0138] like Figures 2 to 4 As shown, there are two cases for calculating the in-cylinder temperature T. The first case is under the condition of known in-cylinder pressure. The in-cylinder temperature is calculated by assuming that the cylinder is a closed system and using the ideal gas law. This case is mainly used in the analysis of the influence of each term in the first law of thermodynamics on the calculation of the heat release rate. The second case is under the condition of unknown in-cylinder pressure, i.e., cylinder pressure reconstruction. In this paper, it is assumed that the compression stroke before fuel injection is a reversible adiabatic process. Equation 24 is used to calculate the in-cylinder temperature, and Equation 25 is used to calculate the pressure. During the expansion stroke, since the fuel combustion releases heat and heats the working fluid in the cylinder, the calculation of the in-cylinder temperature needs to be combined with Equation 26 based on Equation 24. Since the change in volume between adjacent crankshaft angles is very small and can be ignored, the constant volume specific heat capacity cv is used for calculation. The calculation of ΔQ in Equation 6 will be introduced below. At the same time, K1 is an empirical parameter, which is equal to 1.2.

[0139] (twenty four)

[0140] (25)

[0141] (26)

[0142] To further reduce the model's calibration and accelerate its computation, the impact of each term in Equation 21 on the final heat release rate was analyzed, and comparisons were made between the results without cross-flow loss ( ), and the latent heat of vaporization of fuel oil ( The heat release rate calculated by the first law of thermodynamics model is calculated when two terms are ignored. It can be observed that when these terms are not considered... or The calculated heat release rate is almost identical to that obtained using the complete formula; in other words, the calculation process is virtually the same. and The impact on the calculated heat release rate is negligible. Therefore, these two terms can be ignored when calculating heat release using the first law of thermodynamics. Thus, the principle formula for the in-cylinder pressure reconstruction model is shown in Equation 27. γ is the specific heat ratio of the in-cylinder mixture, which can be taken as 1.32-1.35.

[0143] (27)

[0144] Then, the cylinder temperature T and volume variation curves with crankshaft angle can be calculated using the ideal gas equation, which can be achieved through simple kinetic equations.

[0145] In summary, the real-time blow-by prediction method based on crankcase pressure and cylinder pressure differential models of this invention has the following advantages: This invention directly calculates the blow-by mass flow rate by judging the gas flow state (critical or subcritical) using a piecewise flow function. This method utilizes classical gas flow theory to achieve physical modeling of the blow-by phenomenon, replacing the traditional approach that relies on expensive flow meters or purely data-driven black-box models. Online self-calibration mechanism for blow-by flow area: An innovative method is proposed to dynamically calibrate the blow-by flow area under the same engine operating conditions based on the temporal variation ratio of crankcase pressure. This mechanism requires no additional sensors and can automatically track changes in flow characteristics caused by engine thermal deformation and wear, significantly improving the prediction accuracy of the model throughout its entire lifecycle. Collaborative fusion architecture with cylinder pressure reconstruction model: The independent "in-cylinder pressure reconstruction model" is deeply coupled with the "blow-by volume prediction model," reusing the cylinder pressure reconstruction results as the core input for blow-by volume prediction. This architecture fully utilizes existing engine sensor signals, avoids the installation of dedicated cylinder pressure sensors, and achieves low-cost, high-precision real-time monitoring of blow-by volume. Direct Engine Health Assessment Function: Based on predicted blow-by volume and flow area change trends, the system directly quantifies and assesses the wear degree of the piston-cylinder. When the blow-by flow rate or flow area exceeds a preset threshold or its growth rate changes abruptly, the system can automatically trigger maintenance warnings at different levels, extending functionality from condition monitoring to health management. Adaptive Modeling of Flow Coefficient Under Changing Conditions: Establishing a correlation between the flow coefficient and Reynolds number, the model can automatically adjust the flow coefficient according to operating parameters such as engine speed, load, and temperature, improving the model's predictive accuracy and adaptability under varying operating conditions.

[0146] References cited in this invention

[0147] Venkata Harish Babu Manne et al. "3D CFD Analysis of Predicting Engine Blowby Considering Ring Dynamics." SAE Technical Paper Series (2025). This method proposes a CFD simulation approach for predicting engine blow-by losses, which improves engine thermal efficiency by reducing blow-by volume. However, this model has high computational efficiency and computational power requirements, making it unsuitable for engineering applications.

[0148] A. Oliva et al. "Numerical simulation of the multiphase flow phenomenon in the crankcase of an internal combustion engine." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 231 (2017): 1718 - 1731. This method provides an in-cylinder multiphase flow analysis method for diesel engines, but it also requires high computational resources and is not suitable for engineering applications.

[0149] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for real-time prediction of blow-by volume based on a crankcase pressure and cylinder pressure difference model, used in a real-time prediction system for blow-by volume based on a crankcase pressure and cylinder pressure difference model, characterized in that, The real-time prediction system for cross-flow gas volume includes: The signal input module includes: The cylinder pressure reconfiguration output module is used to provide real-time cylinder pressure, cylinder temperature, and cylinder volume. A crankcase pressure sensor, installed near the crankcase ventilation pipe or main oil passage, is used to measure the gas pressure inside the crankcase in real time; and Engine operating condition sensor is used to acquire engine speed, coolant temperature and intake air pressure signals; The core prediction and identification module includes: The blow-by gas calculation module is based on the Weller gas flow model and uses the input in-cylinder pressure, temperature, volume, crankcase pressure and blow-by gas flow area to calculate the instantaneous blow-by gas mass flow rate. The online parameter identification submodule utilizes the equivalent flow area and flow coefficient to enable the model to automatically adapt to engine wear and changes in operating conditions. The flow state determination submodule automatically determines the gas flow state based on the pressure ratio between the cylinder and the crankcase, and calls the corresponding flow function ψ. The output and application module outputs the instantaneous value and cumulative value of blow-by mass flow rate in real time, and performs self-calibration of the blow-by flow area based on the crankcase pressure change under the same working conditions, serving as a direct quantitative indicator of piston-cylinder wear. When the blow-by flow rate and blow-by flow area exceed the preset threshold, different levels of maintenance warnings are triggered.

2. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 1, characterized in that, The model calculation formula of the gas leakage calculation module includes: The pressure ratio is calculated and the flow state is determined using the following formula: (1) (2) In the formula It is the crankcase pressure (Pa) obtained by a pressure sensor. This is a cylinder pressure reconstruction model, which is based on intake pressure, temperature, cylinder volume, speed, fuel characteristics, combustion system control parameters, and coolant temperature; G is the pressure ratio, Gcr is the critical pressure ratio, and γ is the specific heat ratio of the in-cylinder mixture. If G≤Gcr, it is critical flow, where the gas velocity through the gap reaches the local speed of sound, and changes in crankcase pressure do not affect the flow rate; if G>Gcr, it is subcritical flow; the flow state is judged based on the pressure ratio calculated in real time by the cylinder pressure reconstruction model.

3. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 1, characterized in that, The model calculation formula of the gas leakage calculation module also includes: Calculate the flow function based on the flow state: (3) Calculate the instantaneous mass flow rate of gas leakage: (4) Where R is the gas constant, Cd is the flow coefficient, and A gap The flow area of ​​the gas leakage (m²) 2 P and T need to be calculated based on the cylinder pressure reconstruction model.

4. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 3, characterized in that, The model calculation formula of the gas leakage calculation module also includes: Gas flow area A gap Determine and automatically calibrate: (5) Where D is the cylinder diameter (m). This is obtained by measuring the minimum radial clearance (m) between the piston rings and the cylinder wall; however, this value can vary significantly due to thermal deformation and wear. Therefore, it is necessary to perform automatic calibration within a certain time period. Under the same operating conditions, the blow-by area should be calibrated proportionally based on the pressure changes in the crankcase. The specific formula is as follows: (6) Determination of flow coefficient: (7) In the formula, Re represents the Reynolds number.

5. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 1, characterized in that, The cylinder pressure reconstruction output module incorporates a physical guidance prediction model based on the first law of thermodynamics. This model takes real-time sensor data as input and, through a series of sub-models—injection rate prediction, in-cylinder working fluid heat transfer prediction, and cumulative heat release rate prediction—finally calculates the predicted in-cylinder pressure-crankshaft angle curve for the target cylinder within one or more working cycles. The model's calculation formulas include: The fuel injection rate prediction module uses injector structural parameters, injection pressure, and injection pulse width data as input, and performs polynomial fitting with the experimentally measured fuel injection rate curve. The fitting formula is as follows: (8) (9) (10) (11) (12) (13) In the above polynomial, the time unit is ms, and the injection rate unit is mg / ms; , , , , and These represent the quick-opening stage of the needle valve. Needle valve slow opening stage Needle valve full opening stage Needle valve fluctuation stage Needle valve slow closing stage and needle valve quick-closing stage Corresponding fuel injection rate; parameters j and k are calibrated parameters that can be calibrated based on experimental data. They are obtained by fitting the second stage (needle valve slow-opening stage) with different injection pressures. and The values ​​are -0.53 and 1.

6. The value of varies with the injection pressure and can be solved by combining it with the following formula (14); Similarly and The value can then be determined. and The value also needs and Perform a joint solution; The parameters need to be determined first according to the following formula (17). The value of is then solved. = and Two equations determine and ; The value of Z is related to the peak injection rate.

6. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 5, characterized in that, The fitting formula for the fuel injection rate prediction module also includes: (14) (15) (16) (17) Where, n represents the number of injection holes of the injector, Cd, ρ f A0 and These represent the injector's flow coefficient, fuel density, injector orifice cross-sectional area, and calibration parameters, respectively; u th Representing the theoretical injection speed, the calculation formula is as shown in equation (15), P rail Represents the injection pressure; Cd is calculated as shown in equation (16), where Re represents the Reynolds number.

7. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 6, characterized in that, The model calculation formula of the cylinder pressure reconstruction output module also includes: a cumulative heat release prediction model, which is calculated using a method based on the concept of cumulative fuel mass in the cylinder. The input of this model is the injection rate curve, and the calculation formula includes: (18) (19) (20) , , , , , , and These are the cumulative fuel mass in the cylinder (mg), the amount of fuel injected into the cylinder (mg), the fuel consumption rate in the cylinder, the heat release, the combustion efficiency, the crankshaft angle (deg), the ignition delay (deg), and the lower heating value of diesel fuel, respectively. The principle is to calculate the amount of fuel that can be completely burned at the current crankshaft angle based on equation (17). The first term is the amount of fuel injected into the cylinder that can be completely burned at the current crankshaft angle, and the second term is the amount of fuel remaining in the cylinder at the previous crankshaft angle. The second term is 0 before the injection starts. The sum of the two is the amount of fuel that can be completely burned in the cylinder at the current crankshaft angle. Then, according to equation (18), the heat release at the current crankshaft angle is calculated and added to the heat release at the previous crankshaft angle to obtain the cumulative heat release at the current crankshaft angle. .

8. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 1, characterized in that, The formulas for calculating cylinder pressure models based on the first law of thermodynamics include: (21) (22) (23) The calculation of heat transfer loss Qw is given by equation (22); where h represents the heat transfer coefficient (W / m). 2 ·K); As represents the area where heat loss occurs; T represents the cylinder temperature; Tref = 363.15K; the engine heat transfer coefficient is calculated using Hohenberg's heat transfer coefficient formula (23); V, P and T are the cylinder volumes (m³) respectively. 3 ), pressure (Pa) and temperature (K); vm represents the speed of piston movement (m / s).

9. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 8, characterized in that, The calculation of the cylinder temperature T includes two cases: The first method involves calculating the cylinder temperature under known cylinder pressure by assuming the cylinder is a closed system and using the ideal gas law. This method is mainly used in the analysis of the influence of each term in the first law of thermodynamics on the calculation of the heat release rate. as well as The second method is cylinder pressure reconstruction under unknown cylinder pressure conditions. In this paper, it is assumed that the compression stroke before injection is a reversible adiabatic process. The cylinder temperature is calculated using equation (24), and the pressure is calculated using equation (25). During the expansion stroke, the combustion of fuel releases heat, which in turn heats the working fluid in the cylinder. The cylinder temperature calculation needs to be combined with equation (26) based on equation (24). Since the change in volume between adjacent crankshaft angles is very small, it can be ignored. Therefore, the constant volume specific heat capacity cv is used for calculation. The calculation of ΔQ in equation (26) will be introduced below. At the same time, K1 is an empirical parameter. The calculation formula includes: (24) (25) (26) Among them, compared with no cross-flow loss ( ), and the latent heat of vaporization of fuel oil ( The heat release rate calculated by the first law of thermodynamics model when two terms are ignored. or The calculated heat release rate is almost identical to that obtained using the full formula.

10. The real-time prediction method for blow-by volume based on crankcase pressure and cylinder pressure difference model as described in claim 8, characterized in that, The principle formula of the cylinder pressure reconstruction model is as follows: (27) Wherein, γ is the specific heat ratio of the in-cylinder air-fuel mixture.

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