Method for optimizing knock noise of engine piston and engine

Abstract

The application relates to the technical field of engine NVH analysis, in particular to a knocking noise optimization method of an engine piston and an engine. The knocking noise optimization method comprises the following steps: determining a knocking sound energy threshold of the piston and a vibration acceleration threshold of a cylinder body according to a pre-stored knocking sound energy database of each engine type; performing bench testing on a test engine to obtain the knocking sound energy of a piston knocking characteristic frequency band and the vibration acceleration of the cylinder body; establishing a one-dimensional multi-body dynamics model of the test engine; inputting a working condition in which the piston knocks into the one-dimensional multi-body dynamics model as a boundary condition; selecting multiple optimization design parameters, performing single-factor sensitivity analysis on each optimization design parameter, and obtaining a plurality of key influence factors affecting the piston knocking noise; performing full-factor test design analysis on the plurality of key influence factors, and selecting a parameter combination with the smallest knocking power and the vibration acceleration smaller than the vibration acceleration threshold as an optimization scheme.

Description

Technical Field

[0001] This application relates to the field of engine NVH analysis technology, specifically to a method for optimizing the knocking noise of engine pistons and an engine. Background Technology

[0002] With the continuous upgrading of the vehicle market and the increasing maturity of consumer concepts, users are paying more and more attention to vehicle vibration and noise. The piston is one of the main moving parts of a vehicle engine. Its main function is to withstand the pressure of combustion gases and transmit this force to the connecting rod through the piston pin to drive the crankshaft to rotate. The piston skirt plays a guiding role, withstands lateral thrust, and transfers heat within the cylinder. During engine operation, the frequent reversal of the piston within the cylinder causes collisions between components, resulting in vibration and noise. Piston knocking noise is easily recognized and perceived by users, seriously affecting user experience, leading to numerous complaints, impacting after-sales costs, and damaging brand image. Especially with the trend towards lower friction and lower fuel consumption in engines, and the increasing prevalence of large-clearance, low-viscosity lubricating oils, knocking noise is even more pronounced, causing piston knocking to repeatedly occur during bench and vehicle testing.

[0003] Because piston slap occurs inside the cylinder, conventional noise, vibration, and harshness (NVH) tests cannot detect internal excitations; they can only test external responses. Currently, piston slap identification mainly relies on bench vibration and noise testing and subjective evaluation. Signals suspected of piston slap noise are analyzed using wavelet and phase analysis to indirectly pinpoint the issue as piston slap. Then, adjustments and rectifications are made through experimentation, a process that takes two months to a year. This approach fails to quickly identify the problem and propose solutions, severely impacting product development efficiency and hindering improvements in in-vehicle sound quality. Summary of the Invention

[0004] The purpose of this application is to provide a method for optimizing piston knocking noise and an engine, which can quickly and accurately identify and optimize piston knocking phenomena, reduce piston knocking noise levels, and improve in-vehicle sound quality.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0006] A method for optimizing piston knocking noise in an engine includes: determining the piston knocking sound energy threshold and the cylinder vibration acceleration threshold based on a pre-stored knocking sound energy database for various engine models; conducting bench tests on a test prototype to obtain the knocking sound energy and cylinder vibration acceleration in the characteristic frequency band of piston knocking; if the knocking sound energy is greater than the knocking sound energy threshold, it is determined that the piston is knocking; establishing a one-dimensional multibody dynamics model of piston knocking noise, including the cooperating piston rings, piston pin, piston, cylinder liner, and connecting rod, wherein the piston is a flexible body, characterized by the radial stiffness matrix of the elastic piston, and the other components are rigid bodies; inputting the working condition of piston knocking as a boundary condition into the one-dimensional multibody dynamics model; selecting multiple optimization design parameters, performing single-factor sensitivity analysis on each optimization design parameter to obtain several key influencing factors affecting piston knocking noise; conducting full-factor experimental design analysis on several key influencing factors, and selecting a set of parameter combinations with the minimum knocking power and vibration acceleration less than the vibration acceleration threshold as the optimization scheme.

[0007] Furthermore, the calculation method for the radial stiffness matrix of the elastic piston includes: establishing a finite element analysis model of the piston; applying a temperature field and force load to the finite element analysis model, wherein the temperature field is determined by the working condition of the piston undergoing a knocking phenomenon; and calculating the thermal deformation of the piston using symmetrical boundary conditions to obtain the radial stiffness matrix of the elastic piston.

[0008] Furthermore, the multiple optimized design parameters include at least: piston design profile, piston pin offset, cylinder clearance, cylinder liner design profile, piston weight, piston inertia, piston center of mass position, piston pin weight, connecting rod weight, crank offset, and cylinder pressure.

[0009] Furthermore, a single-factor sensitivity analysis was performed on each optimized design parameter to obtain the key influencing factors affecting piston impact noise. These factors included: calculating the impact power corresponding to each optimized design parameter using a one-dimensional multibody dynamics model; ranking the sensitivity of each optimized design parameter according to the magnitude of the impact power to obtain several key influencing factors with higher sensitivity; setting multiple levels for each key influencing factor and calculating the impact power corresponding to each level of the key influencing factor using a one-dimensional multibody dynamics model; connecting the calculation results into a curve and selecting the interval with a larger curve slope and feasibility as the engineering economic interval of the optimized design parameters.

[0010] Furthermore, in conducting full factorial experimental design analysis on key influencing factors, the number of full factorial experimental design simulation analyses should be at least e. K The number of key impact factors is K, and e is the number of levels for each key impact factor, where K = 3 to 5 and e ≥ 3.

[0011] Furthermore, bench testing was conducted on the test prototype to obtain the knocking sound energy and cylinder vibration acceleration of the piston knocking characteristic frequency band. This included: placing the test prototype in a semi-anechoic chamber, suspending the test prototype on the wheel system side and setting the dynamometer drive shaft on the flywheel side; wrapping the intake high-pressure and intake low-pressure pipelines with sound-absorbing cotton and exposing the intake and exhaust noise; placing microphones at preset distances from the center points of the outer envelope surfaces of the engine on the front, left, top, and right sides of the test prototype; placing an acceleration sensor outside the cylinder corresponding to the piston knocking; raising the engine's water and oil temperatures to the normal operating temperature of the engine; stabilizing the engine under the piston knocking condition and collecting noise and vibration acceleration data; performing spectral analysis on the collected noise and vibration acceleration data, and obtaining the knocking sound energy and cylinder vibration acceleration of the piston knocking characteristic frequency band through the energy integration method.

[0012] Furthermore, after stabilizing the engine under the condition where piston knocking occurs, the process also includes: measuring cylinder pressure, piston and cylinder liner operating temperatures, surface roughness between piston and cylinder liner, cylinder liner design profile and cylinder clearance, as boundary conditions for the one-dimensional multibody dynamics model.

[0013] Furthermore, the knocking noise optimization method also includes: establishing a three-dimensional solid dynamics model of the test prototype, inputting the optimization scheme into the three-dimensional solid dynamics model for calibration, and verifying the improvement of the optimization scheme on the piston knocking phenomenon.

[0014] Furthermore, establishing a three-dimensional solid dynamics model of the test prototype includes: establishing finite element models of each component of the test prototype, and performing submodal reduction on the finite element models to obtain the mass matrix and stiffness matrix characterizing the inherent features of the structure; using the mass matrix and stiffness matrix as input files for the three-dimensional solid dynamics model.

[0015] Furthermore, the knocking noise optimization method also includes optimizing the oil injection pressure of the piston cooling nozzle and analyzing the influence of the surface roughness of the piston and cylinder liner and the viscosity of the lubricating oil on the knocking noise.

[0016] Furthermore, the optimization design of the oil injection pressure of the piston cooling nozzle includes: obtaining the critical value of the oil film when the contact surface between the piston and cylinder liner of the test prototype is well lubricated; calculating the initial oil film thickness between the piston and cylinder liner using a three-dimensional solid dynamics model; if the initial oil film thickness is greater than the critical value of the oil film, then deriving the oil injection pressure of the piston cooling nozzle in reverse based on the critical value of the oil film.

[0017] Furthermore, the knocking noise optimization method also includes: making a test prototype again based on the optimized parameters and conducting bench tests to verify whether the piston knocking phenomenon has been improved.

[0018] An engine, wherein the components of the engine are designed according to the optimization scheme in the engine piston knocking noise optimization method described above.

[0019] This application offers the following advantages: During the engine design and development phase, it establishes a correspondence between piston knocking phenomena and test data, determines the acoustic energy threshold and vibration acceleration threshold within the characteristic frequency band of piston knocking sound, quantifies the piston knocking phenomenon, and quickly and accurately identifies the piston knocking problem; it establishes a one-dimensional multibody dynamics model of piston knocking noise, considering the influence of operating temperature on piston motion and force state, and fully calibrates the simulation model using test data to ensure simulation accuracy; it performs sensitivity analysis on various optimization design parameters, and conducts multi-parameter, multi-factor experimental design analysis through the simulation model to screen the optimal combination of solutions, ensuring that the interaction of various sensitive factors is incorporated into the design system; thus, through simulation analysis, the piston knocking process can be reproduced, guiding the optimization design of piston parameters, thereby quickly and accurately identifying and optimizing the piston knocking phenomenon, reducing the piston knocking sound level, and improving the in-vehicle sound quality. Attached Figure Description

[0020] Figure 1 A flowchart illustrating the method for optimizing engine piston knocking noise provided in an embodiment of this application is shown.

[0021] Figure 2 Show Figure 1 A front view of the test prototype undergoing bench testing;

[0022] Figure 3 Show Figure 1 A top view of the test prototype undergoing bench testing;

[0023] Figure 4 Show Figure 1 A schematic diagram of the structure of the one-dimensional multibody dynamics model described above;

[0024] Figure 5 The graph showing the effect of operating temperature on piston material properties is shown.

[0025] Figure 6 Show Figure 1 The key factor mentioned is the trend diagram of the effect of cylinder clearance on knocking power.

[0026] Wherein, 1-engine; 2-engine outer envelope; 3a-front microphone; 3b-right microphone;

[0027] 3c - Top microphone; 3d - Left microphone; 4 - Accelerometer sensor; 5 - Dynamometer drive shaft;

[0028] 11-Piston ring; 12-Piston pin; 13-Piston; 14-Cylinder liner; 15-Connecting rod. Detailed Implementation

[0029] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0030] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0031] like Figure 1 As shown in the figure, this application provides a method for optimizing the knocking noise of an engine piston, including the following steps S1 to S6. The following is a detailed description in conjunction with the attached figure. Figures 2-4 The method for optimizing the impact noise is explained.

[0032] Step S1: Determine the piston's impact sound energy threshold and the cylinder's vibration acceleration threshold based on the pre-stored impact sound energy database for each model.

[0033] Specifically, test prototypes of various engine models are prepared in advance, and noise databases for each model are established through bench tests. Sound energy analysis of the characteristic frequency bands of piston knocking is performed on multiple noise data points in the noise database where piston knocking did not occur, thereby setting the piston knocking sound energy threshold. Based on theoretical acoustics, the relationship between sound energy and vibration acceleration is established to obtain the vibration acceleration threshold.

[0034] Step S2: Perform bench testing on the test prototype to obtain the impact sound energy of the piston impact characteristic frequency band and the vibration acceleration of the cylinder. If the impact sound energy is greater than the impact sound energy threshold, it is determined that the piston is impacting.

[0035] like Figure 2 and Figure 3 As shown, the bench test of the test prototype includes the following steps:

[0036] Step S21: Place the test prototype in a semi-anechoic chamber. The test prototype is suspended on the wheel system side and the dynamometer drive shaft is installed on the flywheel side. The intake high-pressure pipeline and intake low-pressure pipeline are wrapped with sound-absorbing cotton, and the intake noise and exhaust noise are drawn out. The test prototype includes a generator and a compressor, but does not include a transmission.

[0037] Step S22: Microphones 3a to 3d are set at preset distances from the center points of the outer envelope surfaces of the engine front, left, top and right sides of the test prototype; where the outer envelope surface refers to the smallest rectangular hexahedron that imagines the main noise radiation parts of the engine when the engine is in the installed posture (excluding the air filter and exhaust pipe). The protruding parts of individual parts with small radiated noise can be ignored.

[0038] In addition, in this embodiment, the preset distance between the center points of the outer envelope surfaces of the engine front end, left side, top and right side is 1 meter.

[0039] Step S23: Place an acceleration sensor outside the cylinder corresponding to the piston impact;

[0040] Step S24: Raise the engine coolant and oil temperatures to the normal operating temperatures of the engine;

[0041] Step S25: After stabilizing the engine under the condition where piston knocking occurs, collect noise data and vibration acceleration data;

[0042] Step S26: Perform spectrum analysis on the collected noise data and vibration acceleration data, and obtain the impact sound energy and cylinder vibration acceleration of the piston impact characteristic frequency band by using the energy integration method.

[0043] During testing, multiple sets of data are collected for each operating condition where piston knocking occurs, for example, three sets of data, with each set lasting at least 16 seconds. Then, spectral analysis is performed on the collected noise and vibration acceleration data to obtain the sound energy and vibration acceleration within the characteristic frequency band of the piston knocking sound. This allows for the quantification of the piston knocking phenomenon, quickly and accurately pinpointing whether engine piston knocking is occurring.

[0044] Step S3: Establish a one-dimensional multibody dynamics model of piston knocking noise, including the cooperating piston rings, piston pin, piston, cylinder liner and connecting rod. The piston is a flexible body, which is characterized by the radial stiffness matrix of the elastic piston, and the other components are rigid bodies.

[0045] like Figure 4As shown, the one-dimensional multibody dynamics model is a simplified model, which includes mating piston rings 11 (including two compression rings and one oil ring), piston pin 12, piston 13, cylinder liner 14, and connecting rod 15. Piston rings 11, piston pin 12, cylinder liner 14, and connecting rod 15 are all considered rigid bodies, while piston 13 is considered a flexible body, characterized by an elastic piston radial stiffness matrix. The input parameters are the engine stroke and bore, as well as the geometric dimensions, mass, inertia, precisely measured cylinder clearance, and surface roughness of each component, including cylinder liner 14, piston 13, piston pin 12, connecting rod 15, and piston rings 11. The cylinder combustion pressure curve determined during the engine design and development phase is used as the excitation for dynamic analysis. Simulation control parameters are set, model debugging and simulation calculations are performed, and the deformation of piston 13 under motion and stress is analyzed.

[0046] Step S4: Input the piston knocking condition as a boundary condition into the one-dimensional multibody dynamics model. Step S25, after stabilizing the engine under the piston knocking condition, also includes: measuring cylinder pressure, piston and cylinder liner operating temperatures, surface roughness between piston and cylinder liner, cylinder liner design profile, and cylinder clearance, as boundary conditions for the one-dimensional multibody dynamics model, thus ensuring the accuracy of the simulation calculation.

[0047] Step S5: Select multiple optimization design parameters and perform single-factor sensitivity analysis on each optimization design parameter to obtain several key influencing factors affecting piston knocking noise.

[0048] Optionally, based on the generation mechanism of piston knocking noise, select several relevant optimized design parameters, which include at least: piston design profile, piston pin offset, cylinder clearance, cylinder liner design profile, piston weight, piston moment of inertia, piston center of mass position, piston pin weight, connecting rod weight, crank offset, and cylinder pressure.

[0049] Piston profile design is a key technology for pistons. An excellent piston profile design can meet piston reliability and NVH requirements while reducing piston friction losses. During engine operation, the piston transfers heat from the combustion gases and undergoes thermal expansion and deformation. To design and optimize a top-performing piston profile, it is necessary to consider the piston's deformation under operating conditions and, conversely, design the piston's cold-state profile.

[0050] In this embodiment, the simulation of the piston profile takes into account the effects of radial deviation of the cold profile and thermal expansion. The radial deviation of the cold profile is the piston's design profile, which is obtained from the drawings. The thermal expansion is calculated based on the piston's operating temperature and its coefficient of thermal expansion. The piston's operating temperature is obtained through bench testing.

[0051] The cylinder liner profile simulation takes into account both installation deformation and thermal expansion deformation. The installation deformation of the cylinder liner is obtained through testing, while the thermal expansion deformation is calculated based on the operating temperature and coefficient of thermal expansion of the cylinder liner. The operating temperature of the cylinder liner is obtained through bench testing.

[0052] Since there are many optimization design parameters, and each optimization parameter has a different impact on improving piston knocking noise, in order to improve computational efficiency and quickly and accurately locate the optimization design parameters with a greater impact, a single-factor sensitivity analysis can be performed on each optimization design parameter. Then, the sensitivity of each single factor can be ranked to obtain several key influencing factors with higher sensitivity. Then, optimization analysis can be performed on several key influencing factors to reduce the workload of computation.

[0053] Step S6: Conduct full factorial experimental design analysis on several key influencing factors, and select a set of parameter combinations with the minimum impact power and vibration acceleration less than the vibration acceleration threshold as the optimization scheme.

[0054] Key influencing factors are generally optimization design parameters that are easy to implement and have the lowest design change cost. For example, in this embodiment, key influencing factors may be cylinder clearance, piston design profile, piston pin offset, etc.

[0055] Design of Experiment (DOE) analysis involves performing the same number of simulations on different combinations of levels for each key influencing factor. By conducting DOE analysis on multiple parameters and factors, optimization is ensured to pass on the first attempt, reducing the number of physical iterations for verification, shortening the development cycle, lowering development and verification costs, and effectively improving product development efficiency. This embodiment aims to minimize impact power. DOE analysis is performed on key influencing factors such as cylinder clearance, piston design profile, and piston pin offset to obtain a set of parameter combinations as an optimization scheme. Minimizing impact power corresponds to minimizing vibration acceleration, but the vibration acceleration must be below a vibration acceleration threshold to be considered the final optimization scheme.

[0056] According to the piston knocking noise optimization method provided in this application embodiment, a correspondence between piston knocking phenomena and test data is established during the engine design and development stage. The sound energy threshold and vibration acceleration threshold within the characteristic frequency band of piston knocking sound are determined, quantifying the piston knocking phenomenon and quickly and accurately identifying the piston knocking problem. A one-dimensional multibody dynamics model of piston knocking noise is established, considering the influence of operating temperature on the piston's motion and force state. The simulation model is fully calibrated using test data to ensure simulation accuracy. Sensitivity analysis is performed on various optimization design parameters. Multi-parameter and multi-factor experimental design analysis is conducted through the simulation model to screen the optimal combination of solutions, ensuring that the interaction of each sensitive factor is incorporated into the design system. Therefore, the piston knocking process can be reproduced through simulation analysis, guiding the optimization design of piston parameters, thereby quickly and accurately identifying and optimizing the piston knocking phenomenon, reducing the piston knocking sound level, and improving the in-vehicle sound quality.

[0057] In some embodiments, in step S3, establishing a one-dimensional multibody dynamics model of piston knocking noise, the piston is a flexible body, characterized by an elastic piston radial stiffness matrix. The calculation method for the elastic piston radial stiffness matrix includes:

[0058] Step S31: Establish the finite element analysis model of the piston;

[0059] Step S32: Apply a temperature field and force load to the finite element analysis model. The temperature field is determined by the working condition of the piston knocking.

[0060] Step S33: Calculate the thermal deformation of the piston using symmetrical boundary conditions to obtain the radial stiffness matrix of the elastic piston.

[0061] like Figure 4 As shown, the piston 13 is typically made of aluminum alloy, which has a large coefficient of linear expansion, making its thermal deformation highly susceptible to temperature variations. The radial stiffness of the piston 13's skirt is controlled by the skirt wall thickness and internal cavity shape, significantly impacting the contact between the piston 13 and the cylinder liner 14. For example... Figure 5 As shown, the nonlinear effect of operating temperature on the elastic modulus and coefficient of thermal expansion of piston 13 is illustrated. It can be seen that the elastic modulus gradually decreases with increasing operating temperature, and the decrease in elastic modulus becomes more significant after the operating temperature exceeds 200℃. The coefficient of thermal expansion changes slowly before the operating temperature reaches 150℃, but increases sharply and shows a significant change after the operating temperature exceeds 150℃. Therefore, to fully consider the influence of temperature on the radial stiffness of piston 13, a temperature field and force load are simultaneously applied in the finite element model. Using symmetrical boundary conditions, the thermal deformation of the piston is solved, thereby obtaining the elastic piston stiffness matrix at the operating temperature.

[0062] In some embodiments, step S5 involves performing a single-factor sensitivity analysis on each optimized design parameter to obtain several key influencing factors affecting piston knocking noise, including:

[0063] Step S51: Calculate the impact power corresponding to each optimized design parameter using a one-dimensional multibody dynamics model;

[0064] Step S52: Sort the sensitivity of each optimized design parameter according to the magnitude of the striking power to obtain several key influencing factors with high sensitivity;

[0065] Step S53: Set multiple levels for each key influencing factor and use a one-dimensional multibody dynamics model to calculate the knocking power corresponding to each level of the key influencing factor;

[0066] Step S54: Connect the calculation results into a curve, and select the interval with a larger curve slope and feasibility as the engineering economic interval for optimizing the design parameters.

[0067] In this embodiment, the impact power corresponding to each optimized design parameter is first calculated using a one-dimensional multibody dynamics model. The sensitivity of each optimized design parameter is then ranked according to the magnitude of the impact power, resulting in several key influencing factors with high sensitivity. Next, multiple levels (including the original design scheme) are set for each key influencing factor within the design range. The impact of each level on the impact noise is calculated using the one-dimensional multibody dynamics model. Finally, the optimal combination of schemes is selected to ensure that the interaction of each influencing factor is incorporated into the design system.

[0068] As shown in Table 1, several key influencing factors are listed in order of sensitivity from highest to lowest: cylinder clearance, piston pin offset, crank offset, piston design profile, etc. Each key influencing factor has at least 6 levels. The data in the dashed box is the data of the original design scheme. Then, the influence of each level on the knocking noise is calculated using a one-dimensional multibody dynamics model.

[0069] Table 1

[0070]

[0071] The following analysis uses cylinder clearance as a key influencing factor to examine the impact of its various levels on knocking noise. First, a one-dimensional multibody dynamics model is used to calculate the knocking power corresponding to each level of cylinder clearance. Then, the calculation results are plotted as a curve, and the slope is used to determine the sensitivity of each level to knocking noise. A steeper curve indicates a greater impact of changing this key factor on the results; optimization of this factor is necessary for significant improvement, and higher sensitivity is indicated.

[0072] from Figure 6It can be seen that the sensitivity is highest when the cylinder clearance is between 22μm and 34μm. Dividing the curve into three intervals, interval 1 has the steepest slope and the smallest impact power amplitude, theoretically indicating that optimizing the cylinder clearance within interval 1 would yield better results. However, excessively small cylinder clearance drastically increases friction, thus affecting engine thermal efficiency. Therefore, interval 3 is selected as the engineering economic interval for further optimization. In the next optimization, the original cylinder clearance of 36μm can be adjusted to a range of 30μm to 34μm.

[0073] Furthermore, in step S6, the number of full factorial design simulation analyses performed on the key influencing factors is at least e. K The number of key impact factors is K, and e is the number of levels for each key impact factor, where K = 3 to 5 and e ≥ 3.

[0074] To comprehensively analyze the impact of key influencing factors on impact noise and accurately determine its engineering economic range, three key influencing factors with the easiest implementation and lowest design change costs can be selected for DOE full factorial simulation design. As shown in Table 2, with three levels for each key influencing factor, a total of 27 scheme combinations are generated. The impact power is obtained by analyzing and calculating these 27 schemes using a one-dimensional multibody dynamics model. From the results of the 27 impact power sets, the parameter combination with the lowest impact power and vibration acceleration less than the vibration acceleration threshold is selected as the optimal scheme.

[0075] Given sufficient computation time and resources, full factorial DOE analysis can be performed on more selected key influencing factors. The number of levels can also be designed to be greater, such as 5 key influencing factors, 6 levels for each key influencing factor, and a total of 7776 analyses. The more levels, the more accurate the optimization scheme design and the better the optimization effect.

[0076] Table 2

[0077]

[0078] In some embodiments, the knocking noise optimization method further includes:

[0079] Step S7: Establish a three-dimensional solid dynamics model of the test prototype, input the optimized scheme into the three-dimensional solid dynamics model for calibration, and verify the improvement of the optimized scheme on the piston knocking phenomenon. This can reduce the number of physical verifications, reduce verification costs, and improve verification efficiency.

[0080] Furthermore, in step S7, establishing the three-dimensional solid dynamic model of the test prototype includes:

[0081] Step S71: Establish finite element models of each component of the test prototype, and perform submodal reduction on the finite element models to obtain the mass matrix and stiffness matrix that characterize the inherent features of the structure.

[0082] Step S72: Use the mass matrix and stiffness matrix as input files for the three-dimensional solid dynamics model.

[0083] The 3D solid dynamics model is kept as consistent as possible with the test prototype. It includes the geometric and structural parameters of the cylinder block, cylinder liners, pistons, piston pins, connecting rods, and crankshaft. Parameters such as engine stroke, cylinder bore, precisely measured cylinder clearance, and surface roughness are calibrated against the 3D solid dynamics model. To realistically simulate the test prototype, finite element models of the cylinder block, cylinder liners, pistons, piston pins, connecting rods, and crankshaft are established. Submodal reduction is performed on the finite element models to obtain the mass and stiffness matrices characterizing the inherent structural features. These are used as input files for the 3D solid dynamics model, where the thermal profiles of the cylinder liners and pistons need to be represented in the model.

[0084] Using the cylinder combustion pressure curve determined during the engine design and development phase as the excitation for dynamic analysis, simulation control parameters are set, model debugging and simulation calculations are performed to obtain vibration acceleration data, which is then compared with vibration acceleration data from bench tests to verify whether the simulation accuracy meets the requirements. The acceleration extraction position in the simulation model must be consistent with the position in the bench test. If the simulation accuracy is lower than 90%, the three-dimensional solid dynamic model needs further calibration, such as fine-tuning material parameters, to ensure that the experimental error of the simulation analysis is less than 10%. If the calculated cylinder vibration acceleration is less than the vibration acceleration threshold, the optimization is successful; otherwise, further screening of better solutions using a one-dimensional multibody dynamic model is required.

[0085] In some embodiments, the knocking noise optimization method further includes:

[0086] Step S8: Optimize the injection pressure of the piston cooling nozzle and analyze the impact of piston and cylinder liner surface roughness and lubricating oil viscosity on knocking noise. Since the contact surface between the piston and cylinder liner is non-forced lubricated, there is an initial oil film thickness. When the initial oil film thickness is less than a critical value, lubrication deteriorates sharply, leading to severe piston knocking noise and reliability issues, failing to meet design requirements. Therefore, this application optimizes the injection pressure of the piston cooling nozzle (PCJ) to provide more reliable design parameters for the engine and further improve the piston knocking noise problem.

[0087] Specifically, in step S8, optimizing the oil injection pressure of the piston cooling nozzle includes:

[0088] Step S81: Obtain the critical oil film value corresponding to good lubrication of the contact surface between the piston and cylinder liner of the test prototype;

[0089] Step S82: Calculate the initial oil film thickness between the piston and cylinder liner using a three-dimensional solid dynamics model;

[0090] Step S83: If the initial oil film thickness is greater than the critical oil film value, the injection pressure of the piston cooling nozzle is deduced in reverse based on the critical oil film value.

[0091] In this embodiment, the initial oil film thickness is calculated using a three-dimensional solid dynamics model. Based on the critical oil film value corresponding to good lubrication of the test prototype, the injection pressure requirement of the PCJ is deduced, and the injection strategy of the PCJ is optimized. This can reproduce the piston knocking process, guide the optimization of piston design parameters, ensure that the optimization is qualified on the first attempt, reduce test costs, and shorten the development cycle.

[0092] Furthermore, the methods for optimizing knocking noise also include:

[0093] Step S9: Based on the optimized parameters, fabricate a test prototype again and conduct bench tests to verify whether the piston knocking phenomenon has been improved.

[0094] Because a precise simulation model is established to optimize design parameters, the piston knocking noise optimization in this application can be achieved with fewer attempts. This allows for the assessment and optimization of engine piston knocking noise levels during the design phase, improving in-vehicle sound quality and better guiding product design. Compared to related technologies where piston knocking noise testing requires repeated adjustments and takes two months to a year, this application not only comprehensively optimizes design parameters but also saves manpower, resources, and time for problem rectification. The entire simulation optimization process, from prototype manufacturing to solution verification, takes only about one month, improving verification efficiency by at least two times.

[0095] In addition, this application embodiment also provides an engine, the components of which are designed according to the optimization scheme in the engine piston knocking noise optimization method described above.

[0096] During the engine design and development phase, a correspondence between piston knocking phenomena and test data was established. The acoustic energy threshold and vibration acceleration threshold within the characteristic frequency band of piston knocking sound were determined, quantifying the piston knocking phenomenon and quickly and accurately identifying the piston knocking problem. A one-dimensional multibody dynamics model of piston knocking noise was established, considering the influence of operating temperature on piston motion and stress state. The simulation model was fully calibrated using test data to ensure simulation accuracy. Sensitivity analysis was performed on various optimization design parameters, and multi-parameter, multi-factor experimental design analysis was conducted through the simulation model to screen the optimal combination of solutions, ensuring that the interaction of various sensitive factors was incorporated into the design system. Therefore, through simulation analysis, the piston knocking process can be reproduced, guiding the optimization design of piston parameters, thereby quickly and accurately identifying and optimizing the piston knocking phenomenon, reducing piston knocking noise levels, and improving in-vehicle sound quality.

[0097] It should be noted that the terms "one embodiment," "embodiment," "exemplary embodiment," "some embodiments," etc., mentioned in the specification indicate that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0098] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for optimizing the knocking noise of an engine piston, characterized in that, include: The impact sound energy threshold of the piston and the vibration acceleration threshold of the cylinder are determined based on the pre-stored impact sound energy database of each model. A bench test is performed on the test prototype to obtain the impact sound energy of the piston impact characteristic frequency band and the vibration acceleration of the cylinder. If the impact sound energy is greater than the impact sound energy threshold, it is determined that the piston is impacting. A one-dimensional multibody dynamics model of piston knocking noise is established, including the cooperating piston rings, piston pin, piston, cylinder liner and connecting rod, wherein the piston is a flexible body, which is characterized by the radial stiffness matrix of the elastic piston, and the other components are rigid bodies; The condition of piston knocking is input as a boundary condition into the one-dimensional multibody dynamics model; Multiple optimization design parameters were selected, and a single-factor sensitivity analysis was performed on each optimization design parameter to obtain several key influencing factors affecting piston knocking noise. A full factorial experimental design analysis was conducted on the aforementioned key influencing factors, and a set of parameter combinations with the minimum impact power and vibration acceleration less than the vibration acceleration threshold was selected as the optimization scheme.

2. The method for optimizing impact noise according to claim 1, characterized in that, The method for calculating the radial stiffness matrix of the elastic piston includes: Establish a finite element analysis model of the piston; A temperature field and a force load are applied to the finite element analysis model. The temperature field is determined by the working condition in which the piston experiences a knocking phenomenon. The thermal deformation of the piston is calculated using symmetrical boundary conditions to obtain the radial stiffness matrix of the elastic piston.

3. The method for optimizing impact noise according to claim 1, characterized in that, The multiple optimized design parameters include at least: piston design profile, piston pin offset, cylinder clearance, cylinder liner design profile, piston weight, piston inertia, piston center of mass position, piston pin weight, connecting rod weight, crank offset, and cylinder pressure.

4. The method for optimizing impact noise according to claim 1, characterized in that, The key influencing factors affecting piston knocking noise obtained by performing single-factor sensitivity analysis on each optimized design parameter include: The impact power corresponding to each optimized design parameter is calculated using the one-dimensional multibody dynamics model. The sensitivity of each optimized design parameter is ranked according to the magnitude of the impact power to obtain several key influencing factors with high sensitivity. Multiple levels are set for each key influencing factor, and the knocking power corresponding to each level of the key influencing factor is calculated using the one-dimensional multibody dynamics model. Connect the calculation results into a curve, and select the interval with a larger curve slope and feasibility as the engineering economic interval for optimizing the design parameters.

5. The method for optimizing impact noise according to claim 4, characterized in that, In the full factorial experimental design analysis of the key influencing factors, the number of full factorial experimental design simulation analyses is at least e. K The number of key influencing factors is K, and e is the number of levels for each key influencing factor, where K = 3 to 5 and e ≥ 3.

6. The method for optimizing impact noise according to claim 1, characterized in that, The bench test of the test prototype to obtain the impact sound energy and cylinder vibration acceleration in the characteristic frequency band of piston impact includes: The test prototype was placed in a semi-anechoic chamber. The test prototype was suspended on the wheel system side and the dynamometer drive shaft was set on the flywheel side. The high-pressure intake pipe and the low-pressure intake pipe were wrapped with sound-absorbing cotton, and the intake noise and exhaust noise were brought out. Microphones are placed at predetermined distances from the center points of the outer envelope surfaces of the engine at the front, left, top, and right sides of the test prototype. An acceleration sensor is placed outside the cylinder corresponding to the piston strike. The engine's water and oil temperatures are raised to the normal operating temperatures of the engine. After stabilizing the engine under the condition of piston knocking, noise data and vibration acceleration data were collected. Spectral analysis was performed on the collected noise and vibration acceleration data, and the impact sound energy and cylinder vibration acceleration of the piston impact characteristic frequency band were obtained by energy integration method.

7. The method for optimizing impact noise according to claim 6, characterized in that, After stabilizing the engine under the condition where piston knock occurs, the method further includes: The cylinder pressure, piston and cylinder liner operating temperatures, piston and cylinder liner surface roughness, cylinder liner design profile and cylinder clearance are measured as boundary conditions for the one-dimensional multibody dynamics model.

8. The method for optimizing impact noise according to claim 1, characterized in that, Also includes: A three-dimensional solid dynamics model of the test prototype was established, and the optimization scheme was input into the three-dimensional solid dynamics model for calibration to verify the improvement of the piston knocking phenomenon by the optimization scheme.

9. The method for optimizing impact noise according to claim 8, characterized in that, The establishment of the three-dimensional solid dynamic model of the test prototype includes: Finite element models of each component of the test prototype were established, and submodal reduction was performed on the finite element models to obtain the mass matrix and stiffness matrix that characterize the inherent features of the structure. The mass matrix and the stiffness matrix are used as input files for the three-dimensional solid dynamics model.

10. The method for optimizing impact noise according to claim 8, characterized in that, Also includes: The oil injection pressure of the piston cooling nozzle was optimized, and the effects of piston and cylinder liner surface roughness and lubricating oil viscosity on knocking noise were analyzed.

11. The method for optimizing impact noise according to claim 10, characterized in that, The optimization design of the oil injection pressure of the piston cooling nozzle includes: Obtain the critical oil film value corresponding to good lubrication of the contact surface between the piston and cylinder liner of the test prototype; The initial oil film thickness between the piston and the cylinder liner is calculated using the three-dimensional solid dynamics model. If the initial oil film thickness is greater than the critical oil film value, the injection pressure of the piston cooling nozzle is deduced in reverse based on the critical oil film value.

12. The method for optimizing impact noise according to claim 10, characterized in that, Also includes: Based on the optimized parameters, a test prototype was fabricated again for bench testing to verify whether the piston knocking phenomenon had been improved.

13. An engine, characterized in that, Each component of the engine is designed according to the optimization scheme in the engine piston knocking noise optimization method as described in any one of claims 1 to 12.

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