A method for predicting the attenuation of combustion noise by automobile engine structure

Abstract

The present invention proposes a method for predicting the attenuation of combustion noise by engine structure. In the engine design stage, the structural attenuation is quickly predicted through a virtual prototype, and the engine structure design is improved and optimized according to the prediction results. In the design stage, the radiation noise level of the engine can be evaluated and optimized, the requirements for engine radiation noise can be reduced, the number of physical iteration verifications can be reduced, the development cycle can be shortened, and the development verification cost can be reduced. It can be well applied to guide product design.

Description

Technical Field

[0001] The invention relates to the technical field of computer-aided engineering (CAE), and in particular to a method for predicting the attenuation of combustion noise by an automobile engine structure. Background Art

[0002] The noise of automobile engines can be divided into combustion noise, mechanical noise and aerodynamic noise. The periodic ignition and combustion of the engine and the periodic movement of its motion mechanism are the main sources of engine vibration and noise. When the cylinder burns, pressure fluctuations are generated in the cylinder. It is widely believed that the dynamic load and high-frequency vibration caused by the change in gas pressure generated during the combustion process are transmitted to the outside through the cylinder head, cylinder body and piston-connecting rod-crankshaft-cylinder body, causing engine vibration and noise problems. The engine combustion noise is related to factors such as the combustion form and combustion speed in the cylinder, and is also affected by the engine structure. The greater the rigidity of the engine structure and the greater the attenuation, the smaller the combustion noise transmitted to the outer surface.

[0003] Generally, the attenuation of combustion noise by engine structure can be obtained through testing. Usually, the noise is separated into combustion noise by radiating noise during actual operation of the engine, and the attenuation of combustion noise by engine structure is further estimated by combining with the in-cylinder gas pressure. This test procedure is cumbersome, the in-cylinder pressure test of the engine is difficult to operate, requires a lot of equipment, and can only be carried out after a physical prototype is available. It is impossible to evaluate the attenuation of the structure in the early stage of engine structure design, and it is difficult to guide the optimization and iteration of the design scheme.

[0004] Patent document CN111241734 discloses a numerical simulation method for vibration noise of a piston engine. The method requires multi-body dynamics analysis of the engine to obtain the load, and the final calculated amount is the engine surface radiation noise.

[0005] Patent document CN104834763B discloses a method for obtaining engine radiation noise and an engine design optimization method. The method requires performing engine multi-body dynamics analysis to obtain loads, and the final calculated amount is the engine surface radiation noise.

[0006] The above analysis methods all obtain engine excitation by performing multi-body dynamics calculations, which are computationally intensive and time-consuming. They cannot evaluate the attenuation of the structure in the early stages of engine structure design and are difficult to guide the optimization and iteration of the design solution. Summary of the invention

[0007] The purpose of the present invention is to provide a method for predicting the attenuation of combustion noise based on engine structure, so as to achieve the requirements of evaluating and optimizing the radiated noise level of the engine and reducing the radiated noise of the engine in the design stage.

[0008] The technical solution of the present invention is as follows:

[0009] The method for predicting the attenuation of combustion noise by an engine structure of the present invention comprises the following steps:

[0010] S1. Perform three-dimensional finite element modeling on the non-moving parts structure of the engine, solve the structural mode, and obtain the modal vibration shape, modal frequency and coordinate file of the grid node of the engine structure;

[0011] S2. Take a constant pressure of X Pa as the load, and act on the top surface of the piston of a cylinder. Through the force decomposition of the crank-connecting rod mechanism, the force magnitude of the two adjacent main bearings of the cylinder is obtained. Here, X can be any value.

[0012] S3. The main bearing load calculated in S2 is loaded in the form of white noise at the main bearing seat grid node position corresponding to the result file obtained in step S1, and the surface vibration response of the engine structure is calculated based on the modal superposition method.

[0013] S4. Make an engine structure surface envelope mesh to solve the acoustic response of the engine structure, and construct an acoustic boundary element or acoustic finite element model. Construct a free sound field, and define a virtual microphone field point at the center of the hexahedral envelope surface 1 meter away from the outer surface of the engine to obtain the sound pressure at the 1m far field point. Load the surface vibration response obtained in S3 above onto the acoustic envelope mesh through mapping. Further, the acoustic physical quantity radiated by the engine assembly is solved by surface radiated sound power = characteristic impedance of air * vibration surface area * spatial average value of the mean square value of vibration velocity * surface sound radiation efficiency.

[0014] S5. The constant pressure X Pa is taken as input, and the average sound pressure at the 1-meter far-field point position is taken as output, recorded as output. The input / output is the attenuation of the engine combustion noise by the engine structure.

[0015] The engine structure mentioned in the present invention may be a simple engine structure or a powertrain structure including a transmission.

[0016] The technical effects of the present invention are as follows:

[0017] The method for predicting the attenuation of combustion noise by the engine structure described in the present invention can quickly predict the structural attenuation through a virtual prototype during the engine design stage. The loaded excitation does not need to be obtained through a complex dynamic model. The loading method is simple and easy to operate. The prediction can be carried out with only an engine design plan. The calculated result data after processing is the ratio relationship between the input excitation and the structural response, which can fully characterize the attenuation characteristics of the structure, and improve and optimize the engine structure design based on the prediction results. Using a virtual prototype for prediction reduces the number of physical iteration verifications, shortens the development cycle, and reduces the development verification cost.

[0018] The present invention can evaluate and optimize the radiated noise level of the engine and reduce the requirements for the radiated noise of the engine during the design stage, and can be well applied to guide product design. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : is a flow chart of a method for predicting combustion noise attenuation by engine structure according to an example of the present invention;

[0020] Figure 2 : Comparison diagram of the predicted value of structural attenuation and the test structure. DETAILED DESCRIPTION

[0021] In order to make the simulation prediction method of the present invention clearer, the present invention is clearly and detailedly explained below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] like Figure 1 As shown, a method for predicting the attenuation of combustion noise by an automobile engine structure is provided in an embodiment of the present invention, which includes the following steps.

[0023] Step 1: Perform three-dimensional meshing, assembly, and material attribute assignment on the non-moving parts structure of the engine, and solve the structural modes to obtain the modal vibration shape, modal frequency, and coordinate file of the mesh nodes of the engine structure.

[0024] Step 2: Take a constant pressure of X Pa as the load and apply it to the top surface of a cylinder piston. Decompose the force of the crank-connecting rod mechanism to obtain the force magnitude of the two adjacent main bearings of the cylinder. X has no range and any value is acceptable, for example, the excitation is 1 Pa.

[0025] In one embodiment of the present application, a constant pressure of 1 Pa is used as a load to act on the top surface of the piston of the second cylinder of the engine, which approximately simulates the gas pressure acting on the top surface of the piston during combustion in the engine cylinder, and is transmitted to the main bearing seat through the crank-connecting rod structure, and generates vibration and radiates noise through the excitation structure. When the second cylinder is burning, the main loads are the second and third main bearing seats. The structural attenuation when the piston is at the top dead center position is simulated, and the forces at the two main bearing seats are obtained by decomposing the force of the crank-connecting rod mechanism as F and F respectively. 2 and F 3 . F 2 +F 3 =X*piston area. The distances between the center of the second and third main bearings and the center line of the cylinder are L 2 and L 3 According to F 2 *L 2 =F 3 *L 3 It can be decomposed into F 2 and F3 .

[0026] Step 3: Load the force calculated above in the form of white noise (the amplitude of the force is the same in the entire frequency domain) to the grid node positions of the second and third main bearing seats corresponding to the result file obtained in step 1, and calculate the surface vibration response of the engine structure based on the modal superposition method, including displacement, velocity, and acceleration.

[0027] The modal superposition method is a theoretical method and is widely used in the mechanical industry. In this application, the calculation process is implemented using commercial software.

[0028] Step 4, make an engine structure surface envelope mesh for solving the acoustic response of the engine structure, and construct an acoustic boundary element or acoustic finite element model. Construct a free sound field, and in accordance with the requirements of the nine-point sound power method of the national standard GB / T1859.1, define a virtual microphone field point at the center of the hexahedral envelope surface 1 meter away from the outer surface of the engine to obtain the sound pressure at the 1m far field point position. Load the surface vibration response obtained in S3 above onto the acoustic envelope mesh through mapping. Further, the acoustic physical quantity radiated by the engine assembly is solved by surface radiated sound power = characteristic impedance of air * vibration surface area * spatial average value of the mean square value of vibration velocity * surface sound radiation efficiency.

[0029] Step 5: Take the constant pressure X Pa as input and the average sound pressure at 1 m from the field point in step 4 as output, denoted as output. Then the input / output is the attenuation of the combustion noise by the structure. The sound pressure level or weighted sound pressure level is usually used to characterize the attenuation of the combustion noise by the structure, that is, 20log(X / output).

[0030] like Figure 2 As shown, the attenuation of combustion noise by the engine structure predicted by the method of the present invention is consistent with the trend of the test value, indicating that the present invention has guiding significance for engineering practice.

[0031] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0032] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations. In addition, the various different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the ideas of the present disclosure, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for predicting the attenuation of combustion noise by engine structure, characterized in that: The steps include: S1. Perform three-dimensional finite element modeling on the non-moving parts structure of the engine, solve the structural mode, and obtain the modal vibration shape, modal frequency and coordinate file of the grid node of the engine structure; S2. Take a constant pressure of X Pa as the load and act on the top surface of the piston of a cylinder. Decompose the force of the crank-connecting rod mechanism to obtain the force magnitude of the two adjacent main bearings of the cylinder. S3, loading the main bearing load calculated in S2 in the form of white noise at the main bearing seat grid node position corresponding to the result file obtained in step S1, and calculating the surface vibration response of the engine structure based on the modal superposition method; S4. Prepare an engine structure surface envelope mesh for solving the acoustic response of the engine structure, and construct an acoustic boundary element or acoustic finite element model; construct a free sound field, and define a virtual microphone field point at the center of a hexahedral envelope surface 1 meter away from the outer surface of the engine to obtain the sound pressure at the 1m far field point; load the surface vibration response obtained in S3 above onto the acoustic envelope mesh through mapping; solve the acoustic physical quantity radiated by the engine assembly by surface radiated sound power = characteristic impedance of air * vibration surface area * spatial average value of the mean square value of vibration velocity * surface sound radiation efficiency; S5. The constant pressure X Pa is taken as input, and the average sound pressure at the 1-meter far-field point position is taken as output, recorded as output. The input / output is the attenuation of the engine combustion noise by the engine structure.

2. The method for predicting the attenuation of combustion noise by engine structure according to claim 1, characterized in that: The engine structure surface vibration response in step S3 includes displacement, velocity, and acceleration.

3. The method for predicting the attenuation of combustion noise by engine structure according to claim 1, characterized in that: The magnitude of the structural attenuation is characterized by the sound pressure level, ie, 20log(X / output).

4. The method for predicting the attenuation of combustion noise by engine structure according to claim 1, characterized in that: The engine structure is a simple engine structure, or a powertrain structure including a transmission.

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