METHOD TO REDUCE A VEHICLE PASS-BY NOISE

Abstract

A simulation method of a vehicle Pass-By Noise (PBN), which method comprises the following steps: (i) providing a tyre model, a vehicle model and one or more sound absorbent material models as inputs to a calculation module; (ii) simulating, by means of the calculation model, a Pass-By noise (PBN) generation profile of one or more rolling tyres based upon the tyre model; (iii) identifying, by means of the calculation module, one or more noise paths at the vehicle body; and (iv) selecting a position and an absorbent material property of an absorbent material to be positioned at vehicle body in order to minimize Pass-By Noise.

Claims

1-5. (canceled)

6. A computer-implemented simulation method of a vehicle Pass-By Noise (PBN), the method comprising: (i) providing a tyre acoustic model including modelled pattern features comprising: one or more of lateral slots, sipes, and chamfers; a vehicle body part model; and one or more sound absorbent material models as inputs to a calculation module; (ii) identifying, using the calculation module, one or more noise paths at the vehicle body part for each frequency of a predetermined frequency range; and (iii) selecting a position and a material property of a sound absorbent material to be positioned at the vehicle body part in order to minimize Pass-By Noise, wherein step (iii) comprises minimizing Pass-By Noise at one or more frequencies in a range of about 500-2000 Hz, and wherein in step (iii) the selected position of the sound absorbent material is one or more specific locations within a vehicle wheel-arch and/or a vehicle underbody.

7. The method of claim 6, wherein the one or more sound absorbent material models include a model of a foam material, of polyurethane (PU), or of an Ethylene-Propylene Diene Monomer (EPDM).

8. The method of claim 6, wherein step (iii) comprises selecting a combination of different sound absorbing materials.

9. A vehicle designing method, which comprises the computer-implemented simulation method of claim 6.

10. The vehicle designing method of claim 9, wherein the one or more sound absorbent material models include a model of a foam material, of polyurethane (PU), or of an Ethylene-Propylene Diene Monomer (EPDM).

11. The vehicle designing method of claim 9, wherein the step (iii) comprises selecting a combination of different sound absorbing materials.

12. A vehicle manufacturing method, which comprises the computer-implemented simulation method of claim 6.

13. The vehicle manufacturing method of claim 12, wherein the one or more sound absorbent material models include a model of a foam material, of polyurethane (PU), or of an Ethylene-Propylene Diene Monomer (EPDM).

14. The vehicle manufacturing method of claim 12, wherein the step (iii) comprises selecting a combination of different sound absorbing materials.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Reference will be made to the figures of the annexed drawings, wherein:

[0028] FIG. 1 shows a schematic block representation of a simulation method according to a preferred embodiment of the invention;

[0029] FIG. 2 shows a schematic block representation of an exemplary simulation set-up according to a preferred embodiment of the invention;

[0030] FIG. 3 shows representations from a simulation step of critical noise path identification and subsequent sound absorbing material application;

[0031] FIG. 4 shows structural and simplified acoustic mesh that are used during a mapping process of a simulation method step according to a preferred embodiment of the invention;

[0032] FIG. 5 shows a schematic representation of a specific simulation sub-step according to a preferred embodiment of the invention;

[0033] FIGS. 6A and 6B show each a graph representing vibration maps of a tire (in particular the ODS, Operational Deflection Shape) obtained by a preferred embodiment of the invention, at a respective frequency;

[0034] FIG. 7A represents a noise spectrum obtained from an experimental test while FIG. 7B represents a noise spectrum obtained from an embodiment of the method according to the invention; an objective is to have similar spectral shape so that same noise generation phenomena are represented;

[0035] FIG. 8 shows an exemplary subdivision of structural and acoustic tire meshes in lateral section to speed up interpolation during the mapping process of FIG. 1;

[0036] FIGS. 9 and 10 are exemplary representations relating to a specific applicative example of the method of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0037] With reference to FIG. 1, a simulation method according to a preferred embodiment of the invention receives as inputs: [0038] a vehicle body model, e.g. obtained by existing processes of body scan and meshing; [0039] a tire model, e.g. a FEM model; [0040] a sound-absorbing material model, in particular a foam material, obtained, e.g., by known art material characterization and modelling as expressed also in charts, for example as based upon sound absorption index mapped vs frequency; a plurality of material models may also be inputted, in order to allow the method to select the most appropriate one, possibly also depending upon the application regions.

[0041] According to a preferred embodiment, the tire model can be obtained as follows.

[0042] Exterior noise of atire, in particular Pass-By Noise (PBN), is due to vibrations induced by tire/road interaction that convert into noise (vibro-acoustic approach).

[0043] According to the invention, acoustic simulation of a rolling tire is performed. In preferred embodiments, the simulation is based upon the following steps.

[0044] In a first step, structural simulation of a rolling tire is performed and tirevibration on the exterior tire surface—i.e. at the tire contour—is calculated.

[0045] This step can be performed by using Finite Element Methods (FEMs) and Analysis (FEA) tools currently available in the art.

[0046] Preferably, this step entails developing or providing a complete tire model, including construction and pattern element geometries. The tire pattern features—e.g. slots, sipes and so on—may make the model non-axialsymmetric and generate (further) vibrations during rolling.

[0047] Preferably, the vibration is expressed as velocity, acceleration or displacement of nodes of a mesh.

[0048] The result of this step is a vibration model, or map, of the tire, for each sampled instant of time, as explained in detail below.

[0049] In the simulation environment, the inflated tire is modelled and loaded on, i.e. associated with, a reference surface, wherein the tire is rotated at a certain speed for a certain time period.

[0050] During the simulation time period, the vibration of exteriortire, i.e. the position, speed or acceleration of each node, is stored for each sampled time instant or frame (i.e. time increment of the simulation), wherein the time sampling pitch can be chosen depending upon the frequency range of interest. In this way, a vibration map for each sampled instant of time is obtained.

[0051] As said above, the output of this step is a structural model, mesh or vibration map, of a rollingtire, wherein the instant position of each node is defined by the tire structural deformation as deriving from vibration and pressure and load application.

[0052] This step may be performed, e.g., by using the Abaqus Explicit® software tool commercially available or by equivalent means. Explicit FEM solver is particularly suited to simulate transient dynamic events such as the periodic tread block impact on ground during tire rolling. Differently from implicit solvers, explicit software solves the equation of motions through time including all the inertial effects and offer many computational advantages with complex non linear problems.

[0053] As exemplified in FIG. 4, in a second step the method provides mapping the results from the structural rolling mesh obtained by the above structural simulation step into a (stationary, non rolling) acoustic mesh. Preferably, this step converts the vibration map, i.e. the rolling structural mesh obtained in the first step, from the Lagrangian domain into an Eulerian domain, the latter being subsequently used for noise simulation.

[0054] According to preferred embodiments, the mapping is obtained as follows.

[0055] A vibration variable of the target acoustic mesh is selected, which variable is preferably chosen among velocity, acceleration and displacement. Velocity and acceleration may be preferred over displacement.

[0056] As exemplified in FIG. 5, for each sampled time instant the vibration variable is calculated as follows. [0057] For each target node of the output acoustic mesh, a number of closest nodes of the input structural mesh is selected. [0058] An interpolation between nodes of the structural and acoustic mesh is performed to transfer the vibrational results to the latter mesh. In particular, a weighted average of the vibration variable for the target node is calculated, starting from the values of said variable of the selected closest input nodes. [0059] The number of closest input nodes are in the preferred range of 1 to 8 and an inverse distance weighted interpolation is used:

[00001]$v_j=A\underset{i=1}{\overset{n}{.Math.}}\frac{v_i}{d_{i,j}}$

[0060] wherein:

[0061] A=normalization factor

[0062] v.sub.j=vibration at node j of acoustic mesh

[0063] v.sub.i=vibration at node i of the structural mesh

[0064] d.sub.i,j=distance between node i of the structural mesh and node j of acoustic mesh.

[0065] The numerical method is intended to be applied to a FE model of a real tire having all pattern features (including small pattern features like sipes) leading to a very heavy mesh (with number of nodes/elements >1M)

[0066] Interpolation between two meshes (Lagrangian and Eulerian) of such magnitude, to be repeated for all the time step of simulation (depending of sampling frequency but typically >1000-2000 time increment) would became computationally very demanding.

[0067] In order to reduce computational time both the Lagrangian (input) and Eulerian (target) meshes might be divided into sections in lateral direction (in the range of 2-20 sections) as shown in FIG. 8.

[0068] The interpolation is done separately within each corresponding tire section that have a lower number of nodes, drastically reducing the overall computational time.

[0069] After repeating the above interpolation process for all time frames, a time history is available for all nodes of the target mesh in conjunction with the respective values of the vibration variable.

[0070] For each node, a FFT (Fast Fourier Transform), or equivalent tool, is therefore calculated to have the vibration variable in frequency domain. The result of this step is the tire vibration map (ODS—Operational Deflection Shape) at any specific frequency, as exemplified in the graphs of FIGS. 6A and 6B were the displacement of each node of stationary mesh is represented (in logarithmic scale) for a given frequency band (low frequency band 100-300 Hz in FIG. 6A and high frequency band 400-600 Hz in FIG. 6B).

[0071] Preferably, in said step operation in a range of about 20-2000 Hz, preferably 500-2000 Hz, is provided.

[0072] In specific embodiments, the acoustic mesh can be a simplified one with respect to mesh size (coarser mesh) and/or pattern elements to be included (e.g. only longitudinal grooves may be modelled). The use of a simplified mesh will reduce computational time with potentially minimum impact on results. In fact, when using lower spatial resolution of acoustic mesh (i.e. less number of nodes and elements) the interpolation and acoustic simulation steps will be faster (while no change of simulation time for structural simulation).

[0073] This step can be implemented by Matlab® or any equivalent calculation code or tool.

[0074] In a third step, the stationary mesh obtained in the second step is converted into noise, in particular as propagating in a free-field condition, by an acoustic simulation tool. The vibration data as mapped in the second step are used as boundary condition for this acoustic simulation.

[0075] The method calculates the acoustic response (Sound Pressure field) in any position of space for each sampled instant of time, thus replicating experimental tests, like those measuring PbN.

[0076] This step can be performed by using commercially available acoustic solvers. A preferred tool for this step is based upon acoustic FEM, e.g. using commercially available software such as Siemens VIRTUALLAB®, FFT ACTRAN® or Dassault Systemes WAVE6®. A technique known as PML (Perfectly Matching Layer) may be used for simulating free-field propagation Main advantage of PML use is that only a thin layer of acoustic FEM domain has to be modelled. Alternatively, BEM (Boundary Element Method) tools can be used.

[0077] FIGS. 7A and 7B show a graph representing the method performance vs experimental tests. The graph shows a comparison of the Sound Pressure Level (SPL) spectra at 7.5 m from the tire measured with microphones (FIG. 7A—dot line) and simulated with an embodiment of the simulation method according to the invention (FIG. 7B—solid line).

[0078] The “Process” box in FIG. 1 indicates the complex of software procedures run upon a computer and implementing calculation algorithms configured for: [0079] providing noise paths as developing at the vehicle body, e.g. by virtue of transmission, amplification and reflection of the tire acoustic radiation, with particular reference to regions interested by noise levels above a threshold, also as mapped in frequency; [0080] simulating application of sound absorbing materials with different mechanical and/or physical properties, in particular in terms of frequency-specific absorbance; [0081] selecting the optimal material position, dimensions and/or properties, based upon a criterion of high absorption at a selected frequency or frequency range and, e.g., low added weight.

[0082] As outputs, the simulation method according to the embodiment represented provides absorption material features, in particular: [0083] absorption material positioning and mechanical/physical properties, particularly in terms of absorbance at a given frequency or frequency range and preferably including material parts thickness gauges.

[0084] The user thus receives a preferred scenario defining the positioning of one or more absorption materials at respective vehicle body parts.

[0085] FIG. 2 shows schematically an exemplary simulation deck associated with the simulation method of FIG. 1. The set up is mainly composed of the following virtual elements: [0086] vehicle model, as said above based upon a mesh and including a decomposition in WA and UB components for a sensitivity analysis; [0087] absorption material model, as defined above; [0088] tire model for fourtires, each as defined above; [0089] acoustic simulation profile over the vehicle, preferably with a resolution of 8 Hz; [0090] measurement points, e.g. simulating microphones, preferably positioned according to bi-dimensional or three-dimensional arrangement.

[0091] Test data show that by applying sound absorbing foams on wheel-arch and underbody parts based upon the results of the simulation method allows reducing PBN up to 0.7-1.4 dB, most frequently 1.2-1.4 dB.

[0092] In specific simulated cases, by using PU the added weight is about 5-10 kg, while with EPDM the added weight is about 15-25 kg.

[0093] With reference to FIG. 3, an exemplary result of the simulation is provided in graph form, for three different exemplary noise frequencies. As already in FIG. 1, the absorbent material model is exemplified by a diagram mapping sound absorbance vs sound frequency.

[0094] The most critical noise paths are identified, which are represented in FIG. 3 by rectangles at which different absorbent materials are applied. The method simulates the application of various kinds of sound absorbing material different for dimensions, mechanical/physical properties and acoustic absorbance at different frequencies and then selects the best performance according to the criteria expressed above.

Specific Example

[0095] To show exemplary results of application of the method according to the invention, we can refer to FIG. 9, wherein results of method application as simulation outputs are reported. Specifically, in the plot we have: [0096] a. On the X axis the PBN Reduction of passenger vehicle; [0097] b. On the Y axis the additional weight of an Underbody and Wheel-arch sound package, featuring parts made of noise absorption materials.

[0098] In the plot there are displayed the following items. [0099] a. A Vehicle where no Underbody sound pack is applied, hence there are no PBN savings and no vehicle weight increase (left bottom point at 0,0). [0100] b. A vehicle with an Underbody and Wheel-arch sound pack covering the full available space in the vehicle and wheel-arch underbody region. This configuration mimic the existing commercial solutions and simulating it allows to reduce 2.2 dB vs no underbody sound pack and its weight (additional weight for the vehicle) is referenced as 100% (depending on material type it is around 5 to 10 kg). [0101] c. Finally, it is reported the result of applying the process behind the invention where, as it is possible to see from displayed vehicle underbody, the noise absorption materials are placed only in some specific positions and with specific dimensions and shapes and noise absorption features. It is clear that an optimal positioning allows obtaining similar PBN reduction (2 dB vs 2.2 dB) of full underbody sound pack, but with much less material, in this case only 30% of material vs full underbody sound pack is enough. The positioning and dimensioning of the noise absorption material parts is obtained applying the method as described in conjunction with FIGS. 1 and 3.

[0102] The reliability of the method according to the embodiments of the invention disclosed above, as based on the above simulation deck, is confirmed experimentally, as exemplified in FIG. 10. Here again it is reported: [0103] a. X axis: Measurements of PBN reduction, [0104] b. Y axis: Values of the additional weight coming from the underbody and wheel-arch sound pack.

[0105] As represented in FIG. 10, measurements involved the following. [0106] a. A vehicle as it is, without featuring noise absorption materials, so this case is represented by 0 PBN reduction and 0 as additional weight 0 the vehicle. [0107] b. A vehicle fully covered by noise absorption materials, placed in all the space allowed by underbody and wheel-arch package. And this case is reproducing the existing commercial solutions. Measurements says that this configuration allows to reduce up to 1.5 dB and is reference 100% for the additional weight, again ranging from 5 to 10 kg of additional weight based on the type of noise absorption material. [0108] c. An underbody and wheel-arch sound pack designed through the method disclosed above, placing the right material, in the right amount and with proper shapes and dimensions. This optimized solution allows reducing up to 1.2 dB, so very close to the 1.5 dB of reference solution by using just half of the materials. So with half weight and possibly having lower costs. [0109] d. Finally, in FIG. 10 another configuration is reported, where still using 50% of noise absorption material vs full coverage, a PBN reduction of only 0.75 dB is obtained. This is the proof that if design of underbody and wheel-arch sound pack is not optimized, PBN reduction keeps remaining just proportional to noise absorption material amount.

[0110] The present invention has been described so far with reference to preferred embodiments. It is intended that there may be other embodiments which refer to the same inventive concept as defined by the scope of the following claims.