汽车前沿技术 | NVH前沿工程技术
“乘员不应该听到脚下的电池组和电驱动系统运行的声音，而车外的噪音仍然需要感知到。”Saha断言：“在某些时候，这些噪音将成为一项质量问题。”
无论是方兴未艾的电动车，还是燃油发动机车型，客户对产品精致程度的期望从未降低。在内燃机汽车中，大约50%的NVH问题与动力系统有关。另一半主要由路噪和风噪产生。在电动汽车中，噪声来源更加平衡；电力驱动装置（EDU）的噪声是主要贡献源，但中低速行使时的路噪和高速路上的风噪“往往占主导地位”，FEV的动力系统、电动出行和整车产品高级副总裁Kiran Govindswamy解释道。
他说：“看待这个问题的一种角度是，牵引电机或齿轮传动系统发出的噪音如果被客户在车内听到了，那就是问题。路噪和风噪可以在一定程度上掩盖来自EDU(传动系统)的噪声。能被掩盖自然是好的，但你能寄希望于非常糟糕的[路噪和风噪]来掩盖系统噪声，毕竟路噪或风噪太大，也容易让客户觉得这根本不是一辆精致的汽车。”
不断发展的仿真试验
Govindswamy指出，更精致的高端电动车通常在减少进入座舱内的路噪和风噪方面“做得非常好”，但有时也是以暴露高转速电机和齿轮系统的高频噪音为代价的。动力逆变器也会表现出10,000赫兹范围内的高频噪声。
EDU噪声有三个主要来源：包括来自电机本身的电磁噪声，它从设备的外壳上辐射出来；齿轮传动系统噪声；以及来自轴承、流场和旋转系统运行时的整体机械噪声。对NVH工程师来说，定义噪声源、传输路径以及确定可接受的水平，几乎是一个临床诊断过程。例如，FEV公司采用了基于仿真的流程来开发EDU，从而满足客户的声学目标。
“我们使用所谓的‘多体系统仿真’（对相互关联的多个运动部件如何相互作用的动态系统级分析）和有限元分析的组合，考虑了电磁力以及齿轮传动系统的作用力，从而可预测出噪声水平。FEV正在不断改进其预测结果的置信度和准确性，以确保能满足客户的目标。”Govindswamy说：“当我们导入第一个原型进入测试单元时，我们发现离我们需要达到的目标并不遥远。”
专家断言，仿真试验正在不断改进，但在关联性方面仍有许多工作要做。“我们却非常依赖仿真分析，但我认为许多新公司（汽车初创公司）有些过于信赖仿真结果。”Saha认为：“他们在开发到较晚阶段时才验证仿真结果，或者他们的仿真预测可能不完全正确。我们已经看到了根据测量结果来反调预测的例子。我无法理解他们是如何达到目标的。”
他指出，虽然那些正在进入电动车领域的传统主机厂也在使用预测性仿真模拟，但“他们有更强大的测量经验背景”，并在开发过程中能更早地验证他们的预测。
轻量化设计和仿真
电动卡车、大型公共设施和高性能电动车中的锂离子电池组有着惊人的载荷，这就需要车身工程师用轻量化材料方案来抵消这些重量，在某些情况下，这也导致了座舱层面的NVH问题。
“为了实现轻量化设计，我们看到钢材和其他金属被聚合物材料所取代，屏障解耦器被耗散系统所取代。”Saha指出：“更轻的车身面板带来了振动声学相关问题。乘客希望有一个更安静的座舱，而工程团队则专注于质量(重量)效率。这就把新型和不同类型的轻质阻尼材料和其他技术带入了研发阶段。”
尽可能减少额外的NVH处理装置和声学包的质量是一个重点。“这又回到了从源头上减少噪声的重要性。”Govindswamy说：“大量的仿真工作正在进行中，这是一个挑战。但这也教会了工程师们能更有效地使用更轻的声学材料。”
与汽车开发的所有领域一样，仿真试验越来越成为缓解NVH噪声的组成部分。“我把它看作是一个金字塔，顶端是目标定义签字，下面是大量的具体工作，以实现定义目标。”VI-grade公司产品管理高级主管Dave Bogema说。该公司是NVH和车辆动力学工作的仿真工具制造商。NVH分析从桌面开始，工程师们使用最新的、功能越来越强的分析软件快速处理各种想法并剔除那些不可行的想法。下一步是主观评价，如果想让决策具有很高的置信度，就必须真正体验一下NVH状态。
“你可以从电脑界面上得到一定程度的答案。”Bogema说：“但电脑仿真并不能提供在物理模拟器上体验虚拟原型所带来的沉浸感和现实感的全部好处。”
由于物理领域的多样性和这些领域之间复杂的相互作用，预测由电机产生的声学噪音和振动是具有挑战性的。电磁学、热力学和振动声学分析需要以耦合的方式对电机产生的声学噪声进行精确预测。根据Ansys解决方案，准确预测声学噪声有四个基本要素：需要一个高保真仿真解决方案来说明所有涉及的物理学科；一个耦合所有不同的物理学元素的平台；为每个涉及的物理学参数设置和优化的设计能力，以及加速模拟的高性能算力。
还有车辆动力学，在许多方面与NVH密不可分，包括如何影响虚拟样车的评估过程和乘员对车辆精良性的感知等。物理仿真工具也在扩大，以满足电动车改进的各个方面。
“当你驾驶一辆车时，你能体会到周遭的一切。”VI-grade的Bogema说：“如果你在做乘坐舒适性评价，这是一种多感官的运动、振动和声音体验，把NVH和车辆动力学结合在一起，可以提供很好的重复性和管控力，这对提高整体置信度来说至关重要。”他的公司最近在2023年SAE噪声和振动会议上推出了新的紧凑型全频谱模拟器（FSS）。紧凑型FSS能够进行0.5Hz到20kHz的模拟，同时提供主要和次要驱动运动、振动和异响。虽然不是传统的六足式模拟器设计，但FSS的四条腿使它能够准确地再现，在坑洞、鹅卵石或任何其他表面行驶时发生的道路状态。它的振动器通过方向盘和座椅产生高频振动，此外还模拟有来自路面的运动。
VI-grade还提供了一个专用的紧凑型NVH驾驶模拟器，使工程师能够准确地调出汽车在NVH方面的感觉。它的座椅结构允许尝试一系列的虚拟座椅设计，而FSS需要改变座椅的物理形式。专用的NVH模拟器“可以立即改变座椅参数，感受座椅之间的差异”，Bogema指出。“他们是为不同的使用场景而设计的。”他说。FSS在很大程度上是针对乘坐舒适性课题的；而NVH版本则是为了精调设计的。
工程师们也意识到，他们可以在桌面软件上进行声音设计，相应地，模拟出不同的汽车声效。振动也是如此。“你真的需要在声音设计中考虑到车辆的整体运动吗？也许不是所有的时候。”Bogema说。
定制版NVH组件
提高车辆精良性的门槛并不是电动汽车的专利。专家们说，电动车和混合动力车正在推动新的设计和降低NVH的方法，包括那些仍然由内燃发动机汽车主导的产品领域。然而，他们也注意到，成本压力会使复杂的设计变得难以销售，除非其NVH性能十分出众。
全球领先的汽车NVH解决方案供应商Vibracoustic最近推出的用于空气悬架供气装置（ASU）的新型可调支架就是一个注重NVH的例子。简单而复杂的新ASU，如附图所示，具有一个塑料底座（以前是钢），以改善阻尼性能，以及波纹管式橡胶衬套和防撞块。衬套的特殊材料特性恰好满足了所需的刚度水平，同时也对压缩机产生的径向和轴向振动提供避震。
据Vibracoustic称，新的安装支架比传统支架更轻、更坚固，并能在各个方向上就NVH性能进行调整，这是通常用于此类应用的螺旋弹簧所无法做到的。此外，波纹管式衬套设计允许在低应变水平上实现高位移，重现了弹簧的性能。该公司工程师称，橡胶材料还有助于将共振峰值保持在合理的范围内，因为橡胶化合物表现出的动态刚度峰值比螺旋弹簧低60%。
据FEV的Govindswamy介绍，未来电动车NVH技术和工程的关键是取得一种平衡：在不降低车辆续航能力的情况下满足客户的精细化期望。“如果你能保证电动马达的效率并接受稍高的噪音，使其对客户的影响最小化，这就是我们正在努力的挑战，而这要归结为系统优化。”
NVH软件模拟解决方案
在几十家提供NVH仿真软件工具的供应商中，有很多受SAE读者欢迎的产品：
Actran
作为Hexagon AB的一部分，Actron是一种基于FE(有限元)的工具，用于对机械系统和部件的声学行为进行建模。其被广泛用于解决中频（400-1500Hz）范围内的NVH问题，这对电动汽车设计至关重要。作为一个"开放"的工具，它利用现有的FE和CFD仿真模型，用于研究电动汽车的传动和辅助系统（泵、压缩机）噪声源。例如，通用汽车工程师使用Actran来优化凯迪拉克Lyric电动车的噪音减震处理。
Altair
HyperWorks仿真套件包含广泛的NVH建模、装配、诊断、分析和优化的解决方案。该套件的可定制NVH Director功能通过整合网格划分、装配、载荷设置和后处理的整个过程，使NVH分析的任务自动化，以减少整车NVH仿真时间。
Ansys
在概念设计阶段的快速NVH工作流程中可比较不同电动马达设计/拓扑结构的噪声水平，以预测全速扫描的噪声。它可以在早期确定电机噪声的起因，并帮助在与其他电机性能目标的权衡中做出相关的设计改变，使NVH、热和电磁表现同时得到研究。NVH工作流程集成到了Ansys Motor-CAD中，为设计者提供各种力、位移和声功率的表示方法。然后可以在Ansys Maxwell中生成2D和3D模型，并在Ansys Mechanical中进行振动声学分析。
AVL
X-FEM NVH是一个4通道采集模块，适用于所有常见的声学传感器输出类型，如电压、电荷和ICP/IEPE。每个通道可以单独配置，原始信号以高分辨率和时间同步的格式存储于压缩文件中。AVL IndiCom或AVL Concerto的可选NVH工具箱包括最常用的NVH分析工具和在线NVH宏。
Brüel & Kjær
Desktop NVH、SimSound、Source Path Contribution和VSound使工程师能够为任何配置的车辆设计和评估车内和车外声音。Insight+实现了NVH数据的全面体验，直接从CAE模型中创建声音，NVH工程师可以聆听体验。CAE模型数据可以与测试数据结合起来，创造一个身临其境的真实环境。
Dassault
广泛使用的标志性的SIMULIA套件为NVH工作提供了全面的仿真工具集。
Dewesoft
在以NVH为重点的工具中，声音质量测量工具很好地解决了以往按经验评估不同种类机器产生的声音如何被人耳感知的工作。该工具可帮助工程师确定声音是如何被感知的，并调校声音，并使其更容易被客户接受或更具吸引力。
Hexagon
该公司的Romax Spectrum能够进行机电动力总成NVH仿真，并提供完整的、参数化的动力总成全系统建模，包括齿轮和轴承接触面。Romax套件提供与第三方CAE工具的接口，包括用于声学的Actran; 用于多体仿真的Adams；用于电磁模拟的JMAG和Maxwell; 用于FE建模的Nastran；用于整车NVH和声音质量的VI-grade。
Siemens Digital Industries西门子的Simcenter套件会继续增加NVH分析工具，这些工具受益于数字孪生法，可准确预测车辆内部和外部NVH性能。
Electrification brings new benchmarks, tools, and challenges to the ongoing battle with noise, vibration and harshness. NVH testing at FEV’s Auburn Hills, Michigan, tech center using HEAD Acoustics digital artificial head instruments. With two parallel analog-to-digital converters the HEAD units cover the entire audible dynamic range.
The complex science of analyzing and abating noise, vibration, and harshness has entered a “new frontier” as the industry transitions to electrified vehicles, experts in the NVH field tell SAE Media. New design and engineering challenges at the component, system, and full-vehicle levels continue to emerge as EV offerings expand beyond the initial wave of predominantly premium-spec products. Engineers note that benchmarking activity and the introduction of new analysis and testing tools related to NVH mitigation are at “crazy” levels.
“Our interest in acoustically improved vehicles always is going to accelerate and the NVH technology must always meet customer expectations,” observed Pranab Saha, whose company Kolana & Saha Engineers specializes in acoustics, noise and vibration analysis and testing. He noted that some of the latest EV designs show progress in attacking both NVH sources and their propagation paths. There is less reliance on “patch” materials —urethane foams deployed in body cavities and mastics baked into underbody areas that add mass, cost and complexity. But Saha and other experts do not believe those so-called “Band-Aid”sound dampers will be eliminated entirely.
“Occupants should not hear anything going on underneath them in the battery pack and electric drive system, while outside the vehicle noise remains,” Saha asserted. “At some point, those noises are going to become a quality issue.”
Customer expectations of refinement in EVs versus the incumbent IC-engine vehicles are still evolving. In ICE vehicles, about 50% of NVH issues are related to the powertrain. The other half are generated mainly by road and wind noise. In EVs, the noise sources are more balanced; the electric drive unit (EDU) noise is important but road noise at low- to mid- speeds and wind noise at high speeds “tend to dominate,” explained Kiran Govindswamy, senior VP - Drivetrain, e-Mobility and Vehicle, at FEV.
“One way to look at this is, noise coming from the traction motor or geartrain is only important if the customer hears it in the vehicle,” he said. “Sufficient road and wind noise can, to an extent, mask the noise coming from the EDU. This might be beneficial, but you don’t want it [road and wind noise] to be so bad that the customer feels it’s not a refined vehicle at all.”
Evolving simulation
Govindswamy noted that higher-end EVs that are more refined typically “do a very good job” at reducing the road and wind noise entering the cabin—but sometimes at the expense of exposing the higher-frequency whine of the high-rpm electric machine and geartrain. Power inverters also exhibit high-frequency noise in the range of 10,000 Hz.
Three main sources of EDU noise include electromagnetic noise from the motor itself that radiates off the unit’s housing; geartrain noise, and overall mechanical noise from bearings, fluids and rotating systems. Defining the noise sources, their transmission paths, and establishing acceptable levels, is almost a clinical process for NVH engineers. FEV, for example, employs simulation-based processes that develop EDUs to meet customer acoustic targets.
“We use a combination of what we call ‘multibody systems simulation’ [a dynamic system-level analysis of how interconnected multiple moving parts interact with each other] and finite-element analysis, which consider the electromagnetic forces as well as the geartrain forces, then predicts what the noise levels are.” FEV is continuously improving the fidelity and accuracy of its predictions to ensure it can meet customer targets. “When we come into the test cell with the first prototype, we’re not too far off from where we need to be,” Govindswamy said.
Simulation is evolving and continues to improve, but it’s still a work in progress in terms of correlation, experts assert. “We rely a lot on simulation, but I think many new companies [automotive start-ups] rely on it too much,” Saha opined. “They’re not verifying the simulated results until very late in development, or their simulation predictions may not be totally correct. We’ve seen examples of predictions being adjusted based on what the measurements were telling. I can’t understand how they get to their target.”
He noted that while the established OEMs who are moving into EVs also are using predictive sim, “they have a much stronger measurement background” and verify their predictions much sooner in the development process.
Lightweighting and Simulation
The alarming mass of lithium-ion battery packs in electric trucks, large utilities and high-performance EVs has led body engineers to offset that weight with lightweighting material solutions that, in some cases, have caused NVH issues at the cabin level.
“In the interest of lightweighting we’re seeing steel and other metals being replaced by polymeric materials, and barrier decouplers being replaced by dissipative systems,” noted Saha. “There are vibracoustic issues associated with lighter weight body panels. Passengers want a quieter cabin, while the engineering team is focused on mass efficiency. This is bringing new and different types of lightweight damping materials and other technologies into the picture.”
Reducing the mass of all the additional NVH treatments and acoustic packages is a related focus. “This comes back to the importance of reducing noise at the source,” said Govindswamy. “A lot of simulation work is going into that, and it’s a challenge. But it’s also teaching engineers to use lighter weight acoustical materials more efficiently.”
As with all areas of vehicle development, simulation is increasingly integral to NVH mitigation. “I see it as a pyramid with the sign-off at the top tip and an immense amount of work that goes on underneath it to get to the sign-off point,” observed Dave Bogema, senior director of product management at VI-grade, maker of simulation tools for NVH and vehicle dynamics work. NVH analysis begins at the desktop where engineers using the latest, increasingly capable analysis software rapidly work through various ideas and wee d out those that are unfeasible (see sidebar). The next step is subjective evaluation, where NVH really must be experienced if decisions are to be made with confidence.
“You can get a certain level of answers from the desktop,”Bogema said. “But desktop simulation doesn’t have the full benefit of immersion and reality that experiencing virtual prototypes on physical simulators delivers.”
Predicting acoustic noise and vibration generated by electric machines is challenging due to the variety of physical domains and complex interactions among these domains. Electromagnetics, thermodynamics, and vibro-acoustic analyses are required in a coupled fashion for a precise prediction of acoustic noise generated by electric machines. According to Ansys Solutions, there are four essential elements for accurately predicting acoustic noise: need for a high-fidelity simulation solution to account for all the physics involved; a platform to couple all the different physics elements; ability to parameterize and optimize machine design parameters for each of the physics involved, and high-performance computing capability to accelerate the simulation.
There’s also vehicle dynamics, in many ways inseparable from NVH including how they influence the virtual-prototype evaluation process and the occupant’s perception of vehicle refinement. Physical simulation tools are expanding to meet the many facets of EV refinement.
“When you drive a vehicle, you feel everything at the same time,” VI-grade’s Bogema said. “If you’re doing ride comfort, which is a multi-sensory motion, vibration, and sound experience, putting NVH and vehicle dynamics together delivers the repeatability and control that are vital to overall fidelity.” His company recently launched its new Compact Full-Spectrum Simulator (FSS) at the 2023 SAE Noise and Vibration Conference. Capable of simulations from 0.5Hz to 20kHz, the Compact FSS delivers both primary and secondary driving motion, vibration, and sound, simultaneously. While not a traditional hexapod-type simulator design, the FSS’s four legs enable it to accurately replicate the motion of the road as generated when driving over potholes, cobblestones, or any other surface. Its vibration shakers produce high-frequency vibration through the steering wheel and the seat, in addition to the motion from the road.
VI-grade also offers a dedicated Compact NVH driving simulator that allows engineers to dial in exactly what the car is going to feel like for NVH. Its seat structure allows an array of virtual seat designs to be tried, where the FSS requires a physical seat change. The dedicated NVH simulator “can instantly change the seat parameters and feel the difference between seats,”Bogema noted. “They’re designed for different use cases,” he said—the FSS is very much aimed at ride comfort; the NVH version is for dialing in refinement.”
Engineers also are realizing they can do sound design at the desktop, interactively, and come up with different soundscapes for the car. Vibration plays into that. “Do you really need the whole motion of the car in the sound design? Maybe not all the time,” Bogema said.
Bespoke NVH Components
Raising the thresholds of vehicle refinement is not exclusive to EVs. Experts say EVs and hybrids are driving new designs and NVH-reduction approaches across product segments including those still dominated by IC-engine vehicles. They note, however, that cost pressures can make sophisticated designs a tough sell unless their NVH performance is exceptional.
An example of a new NVH-focused component is a new tunable bracket for air suspension air-supply units (ASU) recently launched by Vibracoustic, a leading global automotive NVH solutions supplier. The simple yet sophisticated new ASU, shown in the accompanying image, features a plastic base (previously steel) for improved damping, and bellow-style rubber bushings and bump stops. The bushings’ special material properties give the required stiffness levels while also damping both radial and axial excitations generated by the compressor.
The new mounting bracket is lighter and more robust than traditional brackets, according to Vibracoustic, and enables NVH tuning in all directions—something not possible with coil springs typically used in such applications, the company claims. Additionally, the bellow-type bushing design allows for high displacement at low strain levels, replicating the performance of springs. The rubber material also helps maintain resonance peaks within a reasonable range, because the rubber compound demonstrates a dynamic stiffness peak that is up to 60% lower than of a coil spring, company engineers claim.
The key to NVH science and engineering in EVs going forward, according to Govindswamy at FEV, is striking a balance: meeting customer refinement expectations without degrading vehicle range. “If you can secure the electric motor’s efficiency and accept a slightly higher noise but improve the traditional vehicle to minimize the effect to the customer—that’s the challenge we’re working on. And it comes down to systems optimization.”
NVH software simulation solutions
Among dozens of suppliers offering NVH simulation software tools are these popular products used by SAE readers:
Actran
Part of Hexagon AB (see below), Actron is an FE-based tool for modeling acoustic behavior of mechanical systems and components. It is widely used to solve NVH problems in the mid-frequency (400-1500Hz) range that are critical for EV design. An ‘open’tool, it leverages existing FE and CFD sim models and is used to study EV transmission and ancillary (pumps, compressors) noise sources. GM engineers used Actran to optimize noise-damping treatments in the Cadillac Lyric EV.
Altair
The HyperWorks simulation suite contains a broad range of solutions for NVH model build, assembly, diagnostics, analysis and optimization. The suite’s customizable NVH Director automates the tasks involved in NVH analysis by integrating the entire process of meshing, assembly, loadcase setup, and post-processing, to reduce full-vehicle NVH simulation time.
Ansys
Rapid NVH workflow for the concept design stage compares noise levels for different e-motor designs/topologies to predict the noise over a full speed sweep. It can identify the cause of motor noise early on and help make relevant design changes in trade-off with other motor performance targets, allowing the NVH, thermal, and electromagnetic behavior to be investigated at the same time. The NVH workflow is integrated into Ansys Motor-CAD to provide designers with various representations of force, displacement, and acoustic power. 2D and 3D models can then be generated in Ansys Maxwell and vibroacoustic analysis performed in Ansys Mechanical.
AVL
The X-FEM NVH is a 4-channel acquisition module suitable for use with all common acoustic sensor output types such as voltage, charge and ICP/IEPE. Each channel can be individually configured and raw signals are stored in a compressed file at high resolution and in time-synchronized formats. An optional NVH TOOLBOX for AVL IndiCom or AVL Concerto includes the most common NVH analysis tools and online NVH macros.
Brüel & Kjær
Desktop NVH, SimSound, Source Path Contribution, and VSound allow engineers to design and evaluate interior and exterior vehicle sounds for vehicles of any configuration. Insight+ enables the total experience of NVH data – creating sounds directly from CAE models that NVH engineers can listen to and experience. The CAE model data can be combined with test data to create an immersive, realistic environment.
Dassault
The widely used, iconic SIMULIA suite offers a comprehensive simulation toolset for NVH work.
Dewesoft
Among the NVH-focused tools is Sound Quality Measurement, which addresses the need to empirically evaluate how sound produced by different kinds of machines is perceived by the human ear. The tool helps engineers determine how the sound is perceived, tune the sound, and make it appealing to the customer.
Hexagon
The company’s Romax Spectrum enables electro-mechanical powertrain NVH simulation and offers complete, parametric whole-system modelling of the powertrain including gear and bearing contact surfaces. The Romax suite offers interfaces to third-party CAE tools, including Actran for acoustics: Adams for multibody sim; JMAG and Maxwell for electromagnetic simulation Nastran for FE modeling, and VI-grade for vehicle NVH and sound quality.
Siemens Digital Industries
Siemens’ Simcenter suite continues to add NVH analysis tools that benefit from the digital twin approach to accurately predicting vehicle interior and exterior NVH performance.
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