研究汽车盘式制动器热和力学性能的优化设计.doc

中国石油大学（华东）毕业设计外文翻译研究汽车盘式制动器热和力学性能的优化设计制动系统是汽车最重要的系统。如果制动失败，结果是很可怕的。制动系统实际上是能量转换装置，将汽车的动能转换为热能。典型的制动系统包括盘式制动器和鼓式制动器。汽车上使用的是两个完整的独立的制动系统。他们是行车制动和驻车制动。行车制动在减速，停车，或正常行驶时驻车起作用。他们通过司机踩踏和放松制动踏板来实现。制动器的主要目的是在无人看管是保持车辆平稳停止。驻车制动是在拉起手刹或制动脚踏板时由机械操纵的。盘式制动器因为产生的热和停车时的机械载荷很容易引起噪声和震动问题。这种噪音，震动和NVH现象不仅不舒服，而且很危险。此外，由于热摩擦产生的温度变化，导致制动盘和转子之间摩擦转变和垫衬材料机械压力系数变化。压力变化是一种非线性现象，正如摩擦现象是一般非线性耦合问题。特别是在汽车盘式制动系统中热抖动噪声振动是非线性耦合问题。这些现象也共享核心设计等因素，如转子和衬里之间的压力分布，转子的形状和刚度，空气排气口组成，散热的性能和摩擦的变化。因此，应在考虑和分析抖动和噪声的同时优化盘式制动器的设计。当出现严重的摩擦加热超过一定的转子和垫之间的滑动速度（临界速度）时，会发生热弹性形变。一些关键的因素，如临界速度，外部温度，运动时阀板厚度变化可能会导致制动盘的热变形。此外，频繁制动也能诱导制动器的高热。这些情况导致较高的热变形和热点，这是热颤动的原因之一。一个相对高强度，低频率的震动，应该是从盘式制动系统通过枢纽，悬浮驱动，方向盘，刹车踏板和地板。此外，频繁和高温热点结合，很容易导致物质损失，其中包括制动盘表面裂纹的产生。该热点现象，也称为摩擦性热弹性不稳定，被Barber首次发现并应用到摩擦系统。Lee和Barber解决了假设随着时间推移，在温度和应力场的扰动成倍增加的TEI问题。他们表明，不稳定的发病总是由一个反对称的对应圆周屈曲变形模式导致热点在制动盘两侧交替。此外，使用汽车盘式模型，他们发现，由两个半空间模型计算的临街转速高出实验。Yeo和Barber衍生出的有限元摄动方法，即线性方程组是利用时间获取与指数变化扰动分隔的变量的解决方案制定。他们利用有限元分析解决了盘式制动器和离合器的TEI问题。他们解释说，主波长和临界速度并非主要受三维效果的影响，被很好的预测一个二维（平面）的分析，但不包括弯曲模式。他们通过有限元分析与实验验证制动盘的TEI问题。对TEI的理论，可以在受热抖动制动系统的标准设计准则上进行设计。尽管努力减少或消除噪声的发生，噪声呈现出另一种整个汽车行业的主要制动器的NVH问题。这是一种当司机减速或低速是产生的高频率的噪声。因为他是耦合的制动系统，噪声不容易解决。因此，噪声问题应该仔细评估。有两种利用有限元分析的方法来模拟和分析盘式制动器的噪声问题：一是非线性瞬态模拟或动态瞬态分析，另一种是线性或非线性稳定分析。这两种方法各有优缺点，要准确的分析和预测噪声，都需要在转子和其他制动元件固有特性研究方面有良好的相关性。目前有很多以通过实验方法和仿真的研究。Dessouki等把噪声分为卡钳托架诱导（2-6.5千赫），垫诱导（4-11千赫）和转子诱导（7-16千赫）几类。通过FEA，Junior等研究了某些操作参数如摩擦系数，材料性能，磨损以及绝缘体对盘式制动系统的影响。Fieldhouse根据一些具体的噪声频率研究了垫的形状，并解释说动态的不稳定行能被预测。Kung等使用复杂的特征值问题的方法研究了低频噪声，并报告说，这是种有效的分析方法。Dihau和Jiang利用有限元分析研究耦合模式解决了复杂的特征值问题。Triches等采用模态分析技术，选择适当的制动闸以减少刹车噪声。Kung等在ABAQUS标准使用新的复杂的特征值分析了前盘式制动器的噪声问题。他们指出，考虑接触条件和其他非线性的堆载预压效果，制订复杂的本征解的基本状态。Giannini和Sestieri使用了复杂的特征值分析和实验研究了模型的稳定性。他们讨论了制动盘和垫的关键作用。在这项研究中，通过三个转子标本对TEI和机械稳定性进行了研究。制动测功机和高速红外摄像机被用于TEI分析。圆锥角是根据制动盘的形状确定，角度的改变能改变制动盘和垫之间的接触压力分布，是改变压力分布的主要因素。压力分布影响着热稳定性和机械稳定性。首先，热变形和圆锥角的在恒定温度下的变化是计算所考虑的几何转子。焊盘的压力分布按照卡尺增压类型计算，并将结果和TEI进行分析和比较。临界转速的分析结果通过商业软件HOTSPOTTER获得。将从实验和分析方法得到的结果进行比较和分析。要进行复杂的特征值分析，自然频率和模式是由制动盘和垫片的模态试验和有限元分析得出的。通过有限元分析，按照制动盘厚度，衬砌弧长度和增压类型来决定不稳定耦合模式并估计不稳定的机械力学性能差异来解决复杂的特征值问题。最后，利用这些成果为优化热性能和力学性能进行评估和分析。盘式制动器转子部分由顶部，颈部，气孔和内外侧板组成。摩擦热被认为是转子的主要热源，其产生是由于内外侧板和刹车片之间的接触摩擦。如热传导，热对流过程，和辐射产生的转子温度梯度，并导致热变形。此外，内外侧的密度层不仅在接触表面的局部热集中，由于密度方向传到速度的差异，还影响转子刚度（特别是在外平面）。这三个几何模型是基本模型，2t-0t模型和2t-2t模型。所有这3个转子直径均为254毫米。在2t-0t转子模型中，外侧的钢板厚度减少了2毫米。类似的，在2t-2t转子模型中，内侧和外侧的钢板厚度均减少了2毫米。转子的热变形是由于摩擦生热产生的制动盘和焊盘之间的非均匀压力分布。转子之间的接触压力和高垫影响TEI和机械不稳定性。摩擦热源是法向力，摩擦系数和相对速度的一个表现。制动盘和垫之间眼里分布产生的偏心是由于锥角偏转，DTV和加压性卡钳及可能导致的快速非均匀发热。在这些因素中，可以对转子的形状设计适当降低圆锥角。对此进行热变形和压力分布的有限元分析。圆锥角没有固定值由于在行驶时转子的温度分布变化。通常，通过实验和有限元分析调节制动工况来实现圆锥角，热应力和热容量。然而，在这项研究中，为了通过转子厚度有限元分析来寻找相应的圆锥角假定了一个均匀100C的温度。通过仿真结果，对热性能进行评价并按照内外侧的厚度差别进行分析。根据TEI和按照垫形状和增压条件的机械不稳定性对压力分布进行非线性有限元分析。为了产生一个垫上对应一点到两点加压卡钳的压力分布，应用一个反映卡钳活塞形状的压力条件。静态和动态条件下都适用。在静态条件下，旋转速度为零，静压力为1.5MPa。在动态条件下，转子转速为10转/分，压力大小为1.5MPa，摩擦系数为0.4。在TEI分析，该垫的压力分布可用于预测有效压力和有效内衬弧长，它反映了热点数目和临界速度。热点数目和临界速度与内衬弧长密切相关。因此，利用有效压力和有效内衬弧长的概念可以使TEI模型更加准确。使用有限元分析套件ABAQUS 6.6对热变形和结构分析来计算出圆锥角和压力分布。圆锥角是根据制动盘厚度并通过对热结构有限元分析来计算的。模拟结果显示了再100C时圆锥角和内测板的偏转。圆锥角的相对比率是转子标准锥角和基准的比。结果表明，圆锥角有一个相对较低的绝对值。然而，由于恒定温度边界条件需要根据转子形状实现一个相对热变形差，所以相对圆锥角差值比绝对圆锥角更重要。根据转子的基本标准，2t-0t模型显示了最小的圆锥角比例。这一结果表明，颈部的截面差异很大的作用于导致变形差的几何约束。因此，内外侧厚度差异不仅显著的影响结构特征，而且引起热变形。在实际的汽车上，在严重的热负荷和机械负荷下，转子边缘的挠度与由于DTV和跳动产生的非均匀压力下相比相对值较高。因此，它不能够被忽视。虽然DTV和跳动还增加了制动盘和焊盘之间的局部压力，他们不依赖与转子横截面的形状。因此，为了制动盘的优化设计，考虑热变形和转子锥角以及热容量是必要的。在优化设计中，转子和衬里之间的压力分布均匀是最重要的因素之一。一个均匀的压力分布意味着更大的接触面积，更广泛的接触热的产生和可能会导致更多的热点和刹车噪声的硬衬。一个均匀的压力分布也可能导致刹车的NVH问题。然而，为了获得高效稳定的制动力，均匀分布的压力比非均匀分布的压力更加稳定。此外，由于与非均匀压力分布相比较小的压力大小，它有相对较好的热和机械性能和磨损性能。加压式卡钳和衬里弧长的变量可以改变刹车的压力分布，接触面积和衬砌刚度。因此，制动盘和垫之间的压力分布应该分析增压类型和垫长度进行优化设计，特别是关于热点现象。模拟条件如下：在停止状态，转子旋转速度和压力大小分别为零和1.5兆帕；在旋转状态，转子的转速，压力大小和摩擦系数分别为10转/分，1.5兆帕和0.4。表2显示了压力分布和复杂的特征值分析模拟的实验条件。垂直轴是压力比P/Pmax，水平轴是衬弧长比L/Lmax。黑色曲线，虚线曲线和虚线是在停止状态垫压比，在旋转状态（=10转/分）的垫压比和有效垫压比，于其对应的黑色曲线的整合价值。结果表明，由于衬里弧长的降低，有效垫压比增加。对于一点加压型，该衬砌在较短的有效衬里弧长结果死区。死区表明相对较低的压力分布的位置。这一结果与TEI分析密切相关，因为临界速度与衬砌弧长密切相关。在旋转状态时，应力分布是沿着旋转方向的。此外，由于发生在圆周方向的相对速度差，内外环之间的压力分布差异。图显示了双点式卡钳的衬砌压力分布。有效垫压和有效衬砌弧长比一点型在中心路径上要高。根据TEI，较高的有效垫压和有效衬砌弧长意味着更低的临界速度。一点型的压力分布相对比较均匀。然而，上层路径应力分布相对不均匀，这可能导致死区。上层路径比较低的路径有一个更高的相对速度，这可能会导致转子速度差和接触面积压力差。在旋转状态，压力分布与一点型有相同的趋势。特别是，压力主要集中在径向方向，内外圆周压力分布在由相对速度方向的圆周上。为减少由于圆周方向之间的相对速度差导致的热插入和内部两点式卡钳以外的解决方案之一是减少在径向方向的增压活塞的大小。当在刹车时是采用相同压力时，对比一点型可以增加内衬硬度。在耦合失稳下的这样的结果会导致噪声现象。分布均匀的压力分布也影响到制动稳定性。因此，对垫的优化设计不仅要考虑到相对速度在径向和圆周方向的差异，还要考虑到卡钳的增压类型。临界速度是TEI业绩评价的根本标准。速度大于临界速度可能导致热点。制动盘表面的热点，不仅会引起震动，而且导致热抖动磨损，物质损失和热裂解。因此，对于优化TEI绩效的评价是至关重要的。临界速度是按照转子厚度，加压类型和主缸压力确定的。实验中用到了三种不同的制动盘和两种垫片。制动功率用于实施制动。主缸压力分别为1.5bar和2.0bar。使用高速红外摄影机观测热点。根据2t-0t和2t-2t样本进行评估。进行了不同转子厚度的十八个实验和垫标本的十二个实验，即每个压力设置三个实验。压力是手动应用的。对所有实验，初始温度为15C，跳动被设置为小雨10毫米。为了探讨在TEI条款的盘式制动器性能，分别用各种制动盘厚度，垫标本和主缸压力测量临界速度。实验总数是30，其中被分成四个组。图显示了用高速红外摄影机获取的各种转子厚度，主缸压力，温度分布和衬砌弧长。除涉及2.0bar主缸压力和80%两锅增压钳电弧长度，在所有情况下观察到的六个热点。图分别显示各种厚度的制动盘，垫的标本和主油缸的压力的临界转速的方针与实验结果的图形。结果显示较小的转子厚度与较高的临界速度相关联。此外，临界速度不只取决于主缸压力也与衬砌弧长有关。临界转速下降时，衬砌弧长和压力增加。接触压力分布结果显示，有效衬砌弧长取决于压力边界条件。因此，对于更精确的模拟，有效衬砌弧长适应于模拟真实的制动系统中。图中模拟结果表示高估临界转速为2t-2t转子除外。标本衬砌两锅卡钳的弧长的80%，由于热点的数目达到两个临界速度。热点的数量取决于衬砌弧长。有TEI理论得知，当热点由于失稳的热模式增加时，临界速度很高。发生的热不稳定性会导致产生更多的热点，瞬间高热能被需要。根据TEI理论它不可能有比垫弧长盘圆周长比率更少的热点。因此，80%的面积上的各种主缸压力在衬砌的临界速度模拟结果显示不同的值，以及从这些实验结果的不同趋势。这些结果表明临界转速是高度依赖的压力分布和制动盘和垫之间的规模。此外，由于对压力依赖的临界压力也还存在。不过，要考虑制动盘与片之间的压力变化，应用TEI理论计算垫不同压力程度的刚度。在这个模拟中，临界速度不能被计算因为有不同程度但free-free的条件。有效的衬砌弧长和压力的一锅加压类型低于两锅类型的情况下。在衬砌弧的情况下生成39.2，2.0bar，旋转速度1000转/分，和两罐增压类型，八个热点主缸压力的长度。表中显示了有效影响衬砌弧长的热点问题和各种加压的临界转速的数字结果。通过接触压力有限元分析和压力分布的相对差估计有效衬砌弧长的长度结果。通过使用有效的仿真结果，衬砌弧长可以比试验结果更准确。此外，它是可以确定卡钳的加压类型。因此，更准确的计算临界速度，应考虑通过实验和模拟结果TEI和压力分布和其规模与制动盘垫之间的相关性。热力耦合和热抖动过程造成制动盘表面产生热点，不稳定的摩擦生热，热弹性形变和弹性接触。总所周知，首先，司机会感到如方向盘，踏板的抖动（在较高频率内伴随着震动声音）；然后，制动抖动主要影响舒适性，或有可能当一个没有经验的司机第一次面对时导致了错误的反应会影响行车安全；最后，热抖动会造成制动盘永久性的扭曲或开裂。高温也可能导致刹车过度磨损，尤其是在出现热点的位置。实验技术在热力耦合调查中发挥主要作用。在捷克克大学最新技术研究中心，Pilsen对在实验室和实际情况下的热力耦合进行实验研究。其目的是弄清各种物理参数的影响，包括起源，发展和热力耦合在宏观和微观的后果。其结果将被应用到设计人员的结构建议中，并转化为对制动系统和技术用户的技术建议。A study of thermal and mechanical behaviour for the optimal design of automotive disc brakesThe braking system is the most important system in cars. If the brakes fail, the result can be disastrous. Brakes are actually energy conversion devices, which convert the kinetic energy (momentum) of the vehicle into thermal energy (heat). The typical brake system consists of disk brakes in front and either disk or drum brakes.Two complete independent braking systems are used on the car. They are the service brake and the parking brake. The service brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The primary purpose of the brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by when a separate parking brake foot pedal or hand lever is set.Disc brake systems are prone to noise and vibration problems arising because of the severe thermal and mechanical loads applied to stop the vehicle. This noise, vibration, and harshness (NVH) phenomenon is not only uncomfortable but also dangerous. In addition thermal variations, which occur by frictional heat, generate mechanical pressure variation between the disc and lining owing to a change in the friction coefficient between the rotor and pad lining materials. The pressure variation is a non-linear phenomenon, as friction phenomena are generally non-linear coupled problems. In particular, hot judder vibration and squeal noise are non-linear coupled phenomena in automotive disc brake systems. These phenomena also share core design factors such as the pressure distribution between rotor and lining, the shape of the rotor and pad(stiffness), the number of air vents, cooling performance, and friction variation. Hence, judder and squeal should be considered and analysed at the same time for optimization of disc brake design.When severe friction heating occurs over a certain sliding speed (critical speed) between the rotor and pad, thermoelastic distortion occurs. Some critical factors such as the critical speed, external temperature, run-out, and disc thickness variation (DTV) can cause thermal distortion of the brake disc. In addition, frequent braking also induces highthermal deformation in the brake disc. These conditions cause relatively high thermal distortion and hot spots, which are one of the origins of hot judder vibration. Hot judder vibration, a relatively high-magnitude but low-frequency vibration (1030 Hz), is transmitted from the disc brake system to the driver through the hub, suspension, steering wheel, brake pedal, and floor. Moreover, combined with frequent and high-temperature hot spots,it can easily lead to material damage, including the formation of thermal cracks on the disc surface. The hot-spots phenomenon, also known as frictionally excited thermoelastic instability (TEI), was first observed and explained by Barber for sliding systems involving frictional heating. Lee and Barber solved the TEI problem by assuming that perturbation in the temperature and stress field increases exponentially with time. They showed that the onset of instability is always characterized by an antisymmetric perturbation corresponding to a circumferentially buckled deformation mode that leads to hot spots at alternating locations on the two sides of the disc. Furthermore, using the automotive disc model, they showed that critical speeds calculated by two half-space models overestimate the experiment. Yeo and Barber derived a finite element (FE) formulation of the perturbation method in which the linearity of the governing equations is exploited to obtain separated-variable solutions for the perturbation with exponential variation in time. Yi et al. solved the TEI problem for the geometry of disc brakes and clutches by using a finite element analysis (FEA). They explained that the dominant wavelength (hot-spot spacing) and critical speed are not substantially affected by the three-dimensional (3D) effects, being well predicted by a two-dimensional (2D) analysis, excluding the bending mode. Yi et al. verified the TEI problem of a brake disc through an FEA and experiments. On the basis of TEI theory, a standard design criterion for brake systems subjected to hot judder can be constructed.Despite efforts to reduce or eliminate its occurrence, squeal noise presents another major brake NVH problem throughout the automotive industry .It is a high-frequency noise produced when the driver decelerates and/or stops the vehicle at a low speed. Because it is coupled to the brake system, squeal cannot be solved easily. Therefore, the squeal problem should be evaluated carefully. There are two main approaches to simulate and analyse disc brake squeal using FEA methods: one is non-linear transient simulation or dynamic transient analysis, and the other is linear or non-linear stability analysis using complex mode evaluation. Both methods have their advantages and limitations; to analyse and predict squeal accurately, both need to have good correlation between simulation and test in terms of modal characteristics of rotor and other brake components. There have been many research studies through simulation and experimental approaches. Dessouki et al. characterized squeal into caliper-bracket-induced (26.5 kHz), pad-induced (411 kHz), and rotor-induced (716 kHz) classes. Using FEA, Junior et al. studied the effects of some operating parameters such as friction coefficients, material properties, wear, and insulators on the stability characteristics of adisc brake system. Fieldhouse studied some specific noise frequencies in accordance with the shapes of the pad, and explained that dynamic instability can be predicted and developed by a method where the caliper operates as a one-pot or two-pot type. Kung et al. studied a low-frequency squeal problem using a complex eigenvalue method, reporting that this approach is effective for squeal analysis. Dihau and Jiang studied mode couplings to solve a complex eigenvalue problem using the FE method. Triches et al.used modal analysistechniques to select appropriate brake dampers to reduce brake squeal. Kung et al. analysed the squeal problem on a front disc brake using the new complex eigenvalue capability in ABAQUS/Standard. They showed that contact conditions and other non-linear effects from the preloading are taken into account to formulate the base state for the complex eigensolution. Giannini and Sestieri studied the stability of the model using complex eigenvalue analysis and experiments. They discussed the key role of the disc and the pad dynamics.In this study, TEI and mechanical instability are investigated in accordance with three rotor specimens: lining arc lengths of one-pot pressurization and two-caliper pressurization types (one-pot and two-pot types). A brake dynamometer and a high-speed infrared camera are used for the TEI analysis. The coning angle is formed in accordance with brake disc shapes such as hat and neck, and this angle alters the contact pressure distribution between the disc and the pad, and is one of the main factors that change the pressure distribution of the lining. The pressure distribution strongly affects thermal and mechanical instability as well as thermal performance. First, thermal deformations and coning angles under the constant temperature change are calculated by consideration of the geometry of rotors using an FE commercial code, ABAQUS 6.6. The pressure distributions of the pad in accordance with caliper pressurization types were calculated, and the results were analysed and compared with the TEI experimental results. The analytical results for the critical speed are obtained using TEI-based commercial software, HOTSPOTTER TM. The results obtained from experimental and analytical methods are compared and analysed. To conduct a complex eigenvalue analysis, natural frequencies and modes are determined by modal tests and FEA of discs and pads. Using FEA, the complex eigenvalue problem is solved in accordance with the disc thicknesses, lining arc lengths, and pressurization type to determine unstable coupled modes and difference of mechanical instability for estimating mechanical performance. Finally, the thermal and mechanical behaviours for the optimal design are evaluated and analysed using these results. Figure 1 shows the optimal design factors for the disc brake system. The design factors in the dotted box were considered for optimal disc brake design in this study.The disc brake rotor consists of a hat section, neck section, air vent, and outboard and inboard plates. Frictional heat, which occurs because of contact between the inboard and outboard plates and the brake pad, is assumed to be the main heat source of the rotor. Thermal processes such as heat conduction, convection, and radiation generate temperature gradients on the rotor and cause thermal deformation. In addition, the inboard and outboard thicknesses govern not only the local heat concentration on the contact surface due to conduction velocity difference of the thickness direction, but also the rotor stiffness (especially out of plane). The three employed geometric models are a base model, 2t0t model, and 2t2t model. All three rotors have a diameter of 254 mm. In the 2t0t rotor model, the outboard plate thickness is reduced by 2 mm. Similarly, in the 2t2t rotor model, both the inboard and the outboard blade thicknesses are reduced by 2 mm.The thermal deformation of the rotor due to frictional heating produces a non-uniform pressure distribution between the disc and pad. The contact pressure between the rotor and pad highly affects the TEI and the mechanical instability. The frictional heat source is a function of the normal force, friction coefficient, and relative velocity. This eccentric pressure distribution between the disc and pad arises because of the coning angle, run-out, DTV, and pressurization type of caliper and can lead to rapid non-uniform heat generation. Among these factors, the coning angle can be reduced by appropriate rotor shape design. For this, thermal deformation and pressure distribution FEA are performed.The coning angle has no fixed value because the temperature distribution of the rotor varies during driving. Generally, experiment and FEA through regulated braking condition are performed to achieve coning angles, thermal stress, and thermal capacity 25,28,29. However, in this study, a uniform temperature distribution of 100 C is assumed in the thermal FEA for finding the relative coning angle according to the rotor thicknesses. Through the simulation results, thermal behaviours were evaluated and analysed in accordance with the inboard and outboard thickness differences. Non-linear pressure distribution FEA was performed for analysing the TEI and mechanical instability in accordance with the pressurization condition and pad shape. In order to produce a pressure distribution on the pad corresponding to one-pot and two-pot pressurization calipers, pressure conditions reflecting the caliper piston shape are applied. Both static and dynamic conditions are applied. In the static condition, the rotation speed is zero and a static pressure of 1.5 MPa is applied. In the dynamic condition, the rotation speed of the rotor, the pressure magnitude, and the friction coefficient are 10 r/min, 1.5 MPa, and 0.4 respectively. In the TEI analysis, the pressure distribution of the pad can be used to predict the effective pressure and the effective lining arc length, which governs the number of hot spots and critical speed 30. The number of hot spots and critical speed are closely related to the lining arc length 5.Therefore, utilizing the concept of effective pressure and effective lining arc length can make the TEI simulation more accurate. A thermal deformation and structural analysis is performed to calculate the coning angle and pressure distribution using ABAQUS 6.6, a commercial FEA package.The coning angles in accordance with the thicknesses of the brake