汽车麦弗逊悬架结构设计及有限元分析说明书论文
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毕 业 设 计（论 文）外 文 参 考 资 料 及 译 文译文题目：The principle Of Car Suspensions 汽车悬架的原理 学生姓名： 祝望晋 学 号： 1204104038 专 业： 车辆工程 所在学院： 机电工程学院 指导教师： 智淑亚 职 称： 副教授 2016 年 1 月 15 日The principle Of Car Suspensions When people think of automobile performance, they normally think of horsepower, torque and zero-to-60 acceleration. But all of the power generated by a piston engine is useless if the driver cant control the car. Thats why automobile engineers turned their attention to the suspension system almost as soon as they had mastered the four-stroke internal combustion engine. The job of a car suspension is to maximize the friction between the tires and the road surface, to provide steering stability with good handling and to ensure the comfort of the passengers. In this article, well explore how car suspensions work, how theyve evolved over the years and where the design of suspensions is headed in the future. 1.Vehicle Dynamics If a road were perfectly flat, with no irregularities, suspensions wouldnt be necessary. But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels of a car. Its these imperfections that apply forces to the wheels. According to Newtons laws of motion, all forceshave both magnitude and direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The magnitude, of course, depends on whether the wheel is striking a giant bump or a tiny speck. Either way, the car wheel experiences a vertical acceleration as it passes over an imperfection. Without an intervening structure, all of wheels vertical energy is transferred to the frame, which moves in the same direction. In such a situation, the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface. What you need is a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road. The study of the forces at work on a moving car is called vehicle dynamics, and you need to understand some of these concepts in order to appreciate why a suspension is necessary in the first place. Most automobile engineers consider the dynamics of a moving car from two perspectives: 1)Ride - a cars ability to smooth out a bumpy road 2)Handling - a cars ability to safely accelerate, brake and corner These two characteristics can be further described in three important principles- road isolation, road holding and cornering. The table below describes these principles and how engineers attempt to solve the challenges unique to each. A cars suspension, with its various components, provides all of the solutions described.The Chassis SystemThe suspension of a car is actually part of the chassis, which comprises all of the important systems located beneath the cars body. These systems include: 1)The frame - structural, load-carrying component that supports the cars engine and body, which are in turn supported by the suspension 2)The suspension system - setup that supports weight, absorbs and dampens shock and helps maintain tire contact 3)The steering system - mechanism that enables the driver to guide and direct the vehicle 4)The tires and wheels - components that make vehicle motion possible by way of grip and/or friction with the road So the suspension is just one of the major systems in any vehicle. With this big-picture overview in mind, its time to look at the three fundamental components of any suspension: springs, dampers and anti-sway bars.3.SpringsCoil springs - This is the most common type of spring and is, in essence, a heavy-duty torsion bar coiled around an axis. Coil springs compress and expand to a the Leaf springs - This type of spring consists of several layers of metal (called “ leaves“) bound together to act as a single unit. Leaf springs were first used on horse-drawn carriages and were found on most American automobiles until 1985. They are still used today on most trucks and heavy-duty vehicles.Torsion bars - Torsion bars use the twisting properties of a steel bar to provide coil-spring-like performance. This is how they work: One end of a bar is anchored to the vehicle frame. The other end is attached to a wishbone, which acts like a lever that moves perpendicular to the torsion bar. When the wheel hits a bump, vertical motion is transferred to the wishbone and then, through the levering action, to the torsion bar. The torsion bar then twists along its axis to provide the spring force. European carmakers used this system extensively, as did Packard and Chrysler in the United States, through the 1950s and 1960s. Air springs - Air springs, which consist of a cylindrical chamber of air positioned between the wheel and the cars body, use the compressive qualities of air to absorb wheel vibrations. The concept is actually more than a century old and could be found on horse-drawn buggies. Air springs from this era were made from air-filled, leather diaphragms, much like a bellows; they were replaced with molded-rubber air springs in the 1930s.Based on where springs are located on a car - i.e., between the wheels and the frame -engineers often find it convenient to talk about the sprung mass and the unsprung mass.The sprung mass is the mass of the vehicle supported on the springs, while the unsprung mass is loosely defined as the mass between the road and the suspension springs. The stiffness of the springs affects how the sprung mass responds while the car is being driven. Loosely sprung cars, such as luxury cars (think Lincoln Town Car),can swallow bumps and provide a super-smooth ride; however, such a car is prone to dive and squat during braking and acceleration and tends to experience body sway or roll during cornering. Tightly sprung cars, such as sports cars (think Mazda Miata), are less forgiving on bumpy roads, but they minimize body motion well, which meansthey can be driven aggressively, even around corners.So, while springs by themselves seem like simple devices, designing and implementing them on a car to balance passenger comfort with handling is a complex task. And to make matters more complex, springs alone cant provide a perfectly smooth ride. Why? Because springs are great at absorbing energy, but not so good at dissipating it. Other structures, known as dampers, are required to do this.3.Damper：Shock AbsorbersUnless a dampening structure is present, a car spring will extend and release the energy it absorbs from a bump at an uncontrolled rate. The spring will continue to bounce at its natural frequency until all of the energy originally put into it is used up. A suspension built on springs alone would make for an extremely bouncy ride and, depending on the terrain, an uncontrollable car.Enter the shock absorber, or snubber, a device that controls unwanted spring motion through a process known as dampening. Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid. To understand how this works, its best to look inside a shock absorber to see its structure and function. A shock absorber is basically an oil pump placed between the frame of the car and the wheels. The upper mount of the shock connects to the frame (i.e., the sprung weight), while the lower mount connects to the axle, near the wheel (i.e., the unsprungweight). In a twin-tube design, one of the most common types of shock absorbers, the upper mount is connected to a piston rod, which in turn is connected to a piston, which in turn sits in a tube filled with hydraulic fluid. The inner tube is known as the pressure tube, and the outer tube is known as the reserve tube. The reserve tube stores excess hydraulic fluid.When the car wheel encounters a bump in the road and causes the spring to coil and uncoil, the energy of the spring is transferred to the shock absorber through the upper mount, down through the piston rod and into the piston. Orifices perforate the piston and allow fluid to leak through as the piston moves up and down in the pressure tube. Because the orifices are relatively tiny, only a small amount of fluid, under greatpressure, passes through. This slows down the piston, which in turn slows down the spring.Shock absorbers work in two cycles - the compression cycle and the extension cycle. The compression cycle occurs as the piston moves downward, compressing the hydraulic fluid in the chamber below the piston. The extension cycle occurs as the piston moves toward the top of the pressure tube, compressing the fluid in the chamber above the piston. A typical car or light truck will have more resistance during its extension cycle than its compression cycle. With that in mind, the compression cycle controls the motion of the vehicles unsprung weight, while extension controls the heavier, sprung weight. All modern shock absorbers are velocity-sensitive - the faster the suspension moves, the more resistance the shock absorber provides. This enables shocks to adjustto road conditions and to control all of the unwanted motions that can occur in a moving vehicle, including bounce, sway, brake dive and acceleration squat. Another common dampening structure is the strut - basically a shock absorber mounted inside a coil spring. Struts perform two jobs: That means struts deliver a bit more than shock absorbers, which dont support vehicle weight - they only control the speed at which weight is transferred in a car, not the weight itself.Because shocks and struts have so much to do with the handling of a car, they can be considered critical safety features. Worn shocks and struts can allow excessive vehicle-weight transfer from side to side and front to back. This reduces the tires ability to grip the road, as well as handling and braking performance.Anti-sway bars (also known as anti-roll bars) are used along with shock absorbers or struts to give a moving automobile additional stability. rod that spans the entire axle and effectively joins each side of the suspension together. When the suspension at one wheel moves up and down, the anti-sway bar transfers movement to the other wheel. This creates a more level ride and reduces vehicle sway. In particular, it combats the roll of a car on its suspension as it corners. For this reason, almost all cars today are fitted with anti-sway bars as standard equipment, although if theyre not, kits make it easy to install the bars at any time.4.The Future of Car Suspensions While there have been enhancements and improvements to both springs and shock absorbers, the basic design of car suspensions has not undergone a significant evolution over the years. But all of thats about to change with the introduction of a brand-new suspension design conceived by Bose -the same Bose known for its innovations in acoustic technologies. Some experts are going so far as to say that the Bose suspension is the biggest advance in automobile suspensions since the introduction of an all-independent design. How does it work? The Bose system uses a linear electromagnetic motor (LEM) at each wheel in lieu of a conventional shock-and-spring setup. Amplifiers provide electricity to the motors in such a way that their power is regenerated with each compression of the system. The main benefit of the motors is that they are not limited by the inertia inherent in conventional fluid-based dampers. Virtually eliminating all vibrations in the passenger cabin. The wheels motion can be so finely controlled that the body of the car remains level regardless of whats happening at the wheel. The LEM can also counteract the body motion of the car while accelerating, braking and cornering, giving the driver a greater sense of control. Unfortunately, this paradigm-shifting suspension wont be available until 2009, when it will be offered on one or more high-end luxury cars. Until then, drivers will have to rely on the tried-and-true suspension methods that have smoothed out bumpy rides for centuries.汽车悬架的原理 当人们考虑汽车性能的时候，他们通常会想到汽车的功率，扭矩和0到60的加速时间。但是，如果司机无法控制汽车，由一个活塞发动机产生的功率都是无用的。这就是为什么汽车的工程师在掌握四冲程内燃机开始将注意力转向悬挂系统。 汽车悬架的工作是尽量在轮胎和路面之间提供良好的操纵稳定性，并确保乘客的舒适度。在这篇文章中，我们将探讨汽车悬架如何的工作，在这些年中是如何演变的以及未来悬架设计的发展方向在哪里。 1.车辆动力性 如果道路是完全平坦，那么悬架就没有存在的必要了。但道路是绝对不会平坦的，即使是刚铺好的公路上也有细微的缺陷，与汽车的车轮会与地面相互作用。正是这些路面不平将力传给了车轮。根据牛顿运动定律，所有的力都大小和方向。路面的冲击导致车轮向上和向下垂直移动。力大小，取决于所撞到的障碍物的大小。无论哪种方式，车轮经过路面不平的地方时，就产生一个垂直的加速度。 如果没有介于车轮和车架的中间结构，所有车轮的垂直能量将全部转移到车架，而且车轮和车架在同一方向运动。在这种情况下，车轮与路面可能完全失去接触。接着，在向下的重力作用下，车轮会陷到地面以下。这样就需要一种系统，将吸收的车轮垂直加速度的能量，使车轮在遇到不平路面时，车架和车身不受干扰的运行。 用来研究行驶中的汽车受力的学科
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