车辆工程外文翻译---汽车悬架如何工作

附录A外文翻译-原文部分How Car Suspensions WorkTable of Contents:› Introduction to How Car Suspensions Work› Vehicle Dynamics› The Chassis› Springs› Springs: Sprung and Unsprung Mass› Dampers: Shock Absorbers› Dampers: Struts and Anti-sway Bars› Suspension Types: Front› Suspension Types: Rear› Specialized Suspensions: T› Specialized Suspensions: Formula One Racers› Spec ialized Suspensions: Hot Rods› The Future of Car Suspensions› Lots More Information› Compare Prices for Car SuspensionsWhen 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 can't control the car. That's why automobile engineers turned their attention to the suspension system almost as soon as they had mastered the four-stroke internal combustion engine.Photo courtesy Honda Motor Co., Ltd.Double-wishbone suspension on Honda Accord 2005CoupeThe 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, we'll explore how car suspensions work, how they've evolved over the years and where the design of suspensions is headed in the future.Vehicle DynamicsIf a road were perfectly flat, with no irregularities,suspensions wouldn't be necessary. But roads are far fromflat. Even freshly paved highways have subtle imperfectionsthat can interact with the wheels of a car. It's theseimperfections that apply forces to the wheels. According toNewton's laws of motion, all forces have both magnitude anddirection. A bump in the road causes the wheel to move upand down perpendicular to the road surface. The magnitude,of course, depends on whether the wheel is striking a giantbump or a tiny speck. Either way, the car wheel experiences avertical acceleration as it passes over an imperfection.Without an intervening structure, all of wheel's 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:∙Ride - a car's ability to smooth out a bumpy road∙Handling - a car's ability to safely accelerate, brake and cornerThese 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 car's suspension, with its various components, provides all of the solutions described.Let's look at the parts of a typical suspension, working from the bigger picture of the chassis down to the individual components that make up the suspension proper.The ChassisThe suspension of a car is actually part of the chassis, which comprises all of the important systems located beneath the car's body.ChassisThese systems include:∙The frame - structural, load-carrying component that supports the car's engine and body, which are in turn supported by the suspension∙The suspension system - setup that supports weight, absorbs and dampens shock and helps maintain tire contact∙The steering system - mechanism that enables the driver to guide and direct the vehicle∙The tires and wheels - components that make vehicle motion possible by way of grip and/or friction with the roadSo the suspension is just one of the major systems in any vehicle.With this big-picture overview in mind, it's time to look at the three fundamental components of any suspension: springs, dampers and anti-sway bars.SpringsToday's springing systems are based on one of four basic designs:Coil springs - This is the most common type of spring and is, in essence, aheavy-duty torsion bar coiled around an axis. Coil springs compress and expand to absorb the motion of the wheels.∙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 twistsalong its axis to provide the spring force. European carmakers used thissystem extensively, as did Packard and Chrysler in the United States, through the 1950s and 1960s.Photo courtesy HowStuffWorks ShopperTorsion bar∙Air springs - Air springs, which consist of a cylindrical chamber of air positioned between the wheel and the car's 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 werereplaced with molded-rubber air springs in the 1930s.Photo courtesy HSW ShopperAir springsBased 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.Springs: Sprung and Unsprung MassThe 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 means they 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 can't 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.Dampers: 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, it's 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 unsprung weight). 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 great pressure, 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, thecompression cycle controls the motion of the vehicle's 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 adjust to 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.Dampers: Struts and Anti-sway BarsAnother common dampening structure is the strut -- basically a shock absorber mounted inside a coil spring. Struts perform two jobs: They provide a dampening function like shock absorbers, and they provide structural support for the vehicle suspension. That means struts deliver a bit more than shock absorbers, which don't 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 tire's ability to grip the road, as well as handling and braking performance.Anti-sway BarsAnti-sway bars (also known as anti-roll bars) are used along with shock absorbers or struts to give a moving automobile additional stability. An anti-sway bar is a metal 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 thisreason, almost all cars today are fitted with anti-sway bars as standard equipment, although if they're not, kits make it easy to install the bars at any time.Suspension Types: FrontSo far, our discussions have focused on how springs and dampers function on any given wheel. But the four wheels of a car work together in two independent systems -- the two wheels connected by the front axle and the two wheels connected by the rear axle. That means that a car can and usually does have a different type of suspension on the front and back. Much is determined by whether a rigid axle binds the wheels or if the wheels are permitted to move independently. The former arrangement is known as a dependent system, while the latter arrangement is known as an independent system. In the following sections, we'll look at some of the common types of front and back suspensions typically used on mainstream cars.Front Suspension - Dependent SystemsDependent front suspensions have a rigid front axle that connects the front wheels. Basically, this looks like a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. Common on trucks, dependent front suspensions haven't been used in mainstream cars for years.Front Suspension - Independent SystemsIn this setup, the front wheels are allowed to move independently. The MacPherson strut, developed by Earle S. MacPherson of General Motors in 1947, is the most widely used front suspension system, especially in cars of European origin.The MacPherson strut combines a shock absorber and a coil spring into a single unit. This provides a more compact and lighter suspension system that can be used for front-wheel drive vehicles.The double-wishbone suspension, also known as an A-arm suspension, is another common type of front independent suspension.Double-wishbone suspension on Honda Accord 2005CoupeWhile there are several different possible configurations, this design typically uses two wishbone-shaped arms to locate the wheel. Each wishbone, which has two mounting positions to the frame and one at the wheel, bears a shock absorber and a coil spring to absorb vibrations. Double-wishbone suspensions allow for more control over the camber angle of the wheel, which describes the degree to which the wheels tilt in and out. They also help minimize roll or sway and provide for a more consistent steering feel. Because of these characteristics, the double-wishbone suspension is common on the front wheels of larger cars.Now let's look at some common rear suspensions.Suspension Types: RearRear Suspension - Dependent SystemsIf a solid axle connects the rear wheels of a car, thenthe suspension is usually quite simple -- based eitheron a leaf spring or a coil spring. In the former design,the leaf springs clamp directly to the drive axle. Theends of the leaf springs attach directly to the frame,and the shock absorber is attached at the clamp thatholds the spring to the axle. For many years,American car manufacturers preferred this designbecause of its simplicity. The same basic design can be achieved with coil springs replacing the leaves. In this case, the spring and shock absorber can be mounted as a single unit or as separate components. When they're separate, the springs can be much smaller, which reduces the amount of space the suspension takes up.Rear Suspension - Independent SuspensionsIf both the front and back suspensions are independent, then all of the wheels are mounted and sprung individually, resulting in what car advertisements tout as"four-wheel independent suspension." Any suspension that can be used on the front of the car can be used on the rear, and versions of the front independent systemsdescribed in the previous section can be found on the rear axles. Of course, in the rear of the car, the steering rack -- the assembly that includes the pinion gear wheel and Photo courtesyHowStuffWorks Shopper Leaf springenables the wheels to turn from side to side -- is absent. This means that rear independent suspensions can be simplified versions of front ones, although the basic principles remain the same.Specialized Suspensions: The Baja BugFor the most part, this article has focused on the suspensions of mainstream front- and rear-wheel-drive cars -- cars that drive on normal roads in normal driving conditions. But what about the suspensions of specialty cars, such as hot rods, racers or extreme off-road vehicles? Although the suspensions of specialty autos obey the same basic principles, they do provide additional benefits unique to the driving conditions they must navigate. What follows is a brief overview of how suspensions are designed for three types of specialty cars -- Baja Bugs, Formula One racers and American-style hot rods.Baja BugsThe Volkswagen Beetle or Bug was destined to become a favorite among off-road enthusiasts. With a low center of gravity and engine placement over the rear axle, the two-wheel-drive Bug handles off-road conditions as well as some four-wheel-drive vehicles. Of course, the VW Bug isn't ready for off-road conditions with its factory equipment. Most Bugs require some modifications, or conversions, to get them ready for racing in harsh conditions like the deserts of Baja California.One of the most important modifications takes place in the suspension. Thetorsion-bar suspension, standard equipment on the front and back of most Bugs between 1936 and 1977, can be raised to make room for heavy-duty, off-road wheels and tires. Longer shock absorbers replace the standard shocks to lift the body higher and to provide for maximum wheel travel. In some cases, Baja Bug converters remove the torsion bars entirely and replace them with multiple coil-over systems, an aftermarket item that combines both the spring and shock absorber in one adjustable unit. The result of these modifications is a vehicle that allows the wheels to travelvertically 20 inches (50 cm) or more at each end. Such a car can easily navigate rough terrain and often appears to "skip" over desert washboard like a stone over water.Specialized Suspensions: Formula One RacersThe Formula One racing car represents the pinnacle of automobile innovation and evolution. Lightweight, composite bodies, powerful V10 engines and advanced aerodynamics have led to faster, safer and more reliable cars.To elevate driver skill as the key differentiating factor in a race, stringent rules and requirements govern Formula One racecar design. For example, the rules regulating suspension design say that all Formula One racers must be conventionally sprung, but they don't allow computer-controlled, active suspensions. To accommodate this, the cars feature multi-link suspensions, which use a multi-rod mechanism equivalent to a double-wishbone system.Recall that a double-wishbone design uses two wishbone-shaped control arms to guide each wheel's up-and-down motion. Each arm has three mounting positions -- two at the frame and one at the wheel hub -- and each joint is hinged to guide the wheel's motion. In all cars, the primary benefit of a double-wishbone suspension is control. The geometry of the arms and the elasticity of the joints give engineers ultimate control over the angle of the wheel and other vehicle dynamics, such as lift, squat and dive. Unlike road cars, however, the shock absorbers and coil springs of a Formula One racecar don't mount directly to the control arms. Instead, they are oriented along the length of the car and are controlled remotely through a series of pushrods and bell cranks. In such an arrangement, the pushrods and bell cranks translate the up-and-down motions of the wheel to the back-and-forth movement of the spring-and-damper apparatus.Specialized Suspensions: Hot RodsThe classic American hot rod era lasted from 1945 to about 1965. Like Baja Bugs, classic hot rods required significant modification by their owners. Unlike Bugs, however, which are built on Volkswagen chassis, hot rods were built on a variety of old, often historical, car models: Cars manufactured before 1945 were considered ideal fodder for hot rod transformations because their bodies and frames were often in good shape, while their engines and transmissions needed to be replaced completely. For hot rod enthusiasts, this was exactly what they wanted, for it allowed them to install more reliable and powerful engines, such as the flathead Ford V8 or the Chevrolet V8.The Future of Car SuspensionsWhile there have been enhancements and improvements to both springs and shockabsorbers, the basic design of car suspensions has not undergone a significant evolution over the years. But all of that's 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. As a result, an LEM can extend and compress at a much greater speed, virtually eliminating all vibrations in the passenger cabin. The wheel's motion can be so finely controlled that the body of the car remains level regardless of what's 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 won't 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.For more information on car suspensions and related topics, check out the links on the next page.附录B 外文翻译-译文部分汽车悬架如何工作目录列表：对汽车悬架如何工作的介绍车辆动力学底盘弹簧弹簧：簧载质量和非簧载质量减震器：震动吸收装置减震器：减震器支柱和横向稳定杆悬架形式：前悬架悬架形式：后悬架特种悬架：T型悬架特种悬架：一级方程式赛车悬架特种悬架：改装车悬架未来汽车悬架更多信息汽车悬架的价格比较当人们提到汽车的性能时，人们通常会想到功率、扭矩和0到60的加速时间。