汽车制动系统外文翻译

河南理工大学万方科技学院河南理工大学万方科技学院 毕毕 业业 设设 计 论计 论 文 附文 附 录录 I 中中 英英 文文 文文 献献 翻翻 译译 姓姓 名 名 王 奎 所在院系 所在院系 机械与动力工程系 专业班级 专业班级 机械设计 08 3 班 学学 号 号 0828070005 指导教师 指导教师 赵 武 原文标题 原文标题 Automobile Brake System 20122012 年年 5 5 月月 2525 日日 精品文档 1欢迎下载 Automobile Brake System The 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 When stepping on the brakes the driver commands a stopping force ten times as powerful as the force that puts the car in motion The braking system can exert thousands of pounds of pressure on each of the four 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 The brake system is composed of the following basic components the master cylinder which is located under the hood and is directly connected to the brake pedal converts driver foot s mechanical pressure into hydraulic pressure Steel brake lines and flexible brake hoses connect the master cylinder to the slave cylinders located at each wheel Brake fluid specially designed to work in extreme conditions fills the system Shoes and pads are 精品文档 2欢迎下载 pushed by the slave cylinders to contact the drums and rotors thus causing drag which hopefully slows the car The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder Basically all car brakes are friction brakes When the driver applies the brake the control device forces brake shoes or pads against the rotating brake drum or disks at wheel Friction between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is braked In most modern brake systems there is a fluid filled cylinder called master cylinder which contains two separate sections there is a piston in each section and both pistons are connected to a brake pedal in the driver s compartment When the brake is pushed down brake fluid is sent from the master cylinder to the wheels At the wheels the fluid pushes shoes or pads against revolving drums or disks The friction between the stationary shoes or pads and the revolving drums or disks slows and stops them This slows or stops the revolving wheels which in turn slow or stop the car The brake fluid reservoir is on top of the master cylinder Most cars today have a transparent r reservoir so that you can see the level without opening the cover The brake fluid level will drop slightly as the brake pads wear This is a normal condition and no cause for concern If the level drops noticeably over ashort period of time or goes down to about two thirds full have your brakes checked as soon as possible Keep the reservoir covered except for 精品文档 3欢迎下载 the amount of time you need to fill it and never leave a cam of brake fluid uncovered Brake fluid must maintain a very high boiling point Exposure to air will cause the fluid to absorb moisture which will lower that boiling point The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses Rubber hoses are only used in places that require flexibility such as at the front wheels which move up and down as well as steer The rest of the system uses non corrosive seamless steel tubing with special fittings at all attachment points If a steel line requires a repair the best procedure is to replace the compete line If this is not practical a line can be repaired using special splice fittings that are made for brake system repair You must never use copper tubing to repair a brake system They are dangerous and illegal Drum brakes it consists of the brake drum an expander pull back springs a stationary back plate two shoes with friction linings and anchor pins The stationary back plate is secured to the flange of the axle housing or to the steering knuckle The brake drum is mounted on the wheel hub There is a clearance between the inner surface of the drum and the shoe lining To apply brakes the driver pushes pedal the expander expands the shoes and presses them to the drum Friction between the brake drum and the friction linings brakes the wheels and the vehicle stops To release brakes the driver release the pedal the pull back spring retracts the shoes thus permitting free rotation of the wheels Disk brakes it has a metal disk instead of a drum A flat shoe or disk brake pad is located on each side of the disk The shoes squeeze the rotatin g disk to stop the car Fluid from the master 精品文档 4欢迎下载 cylinder forces the pistons to move in toward the disk This action pushes the friction pads tightly against the disk The friction between the shoes and disk slows and stops it This provides the braking action Pistons are made of either plastic or metal There are three general types of disk brakes They are the floating caliper type the fixed caliper type and the sliding caliper type Floating caliper and sliding caliper disk brakes use a single piston Fixed caliper disk brakes have either two or four pistons Brakes what do they do Brakes are designed to slow down your vehicle but probably not by the means that you think The common misconception is that brakes squeeze against a drum or disc and the pressure of the squeezing action is what slows you down This in fact is only part of the equation Brakes are essentially a mechanism to change energy types When you re travelling at speed your vehicle has kinetic energy When you apply the brakes the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction The cooling of the brakes dissipates the heat and the vehicle slows down It s the First Law of Thermodynamics sometimes known as the law of conservation of energy This states that energy cannot be created nor destroyed it can only be converted from one form to another In the case of brakes it is converted from kinetic energy to thermal energy Angular force Because of the configuration of the brake pads and rotor in a disc brake the location of the point of contact where the friction is generated also provides a mechanical moment to resist the turning motion of the rotor Thermodynamics brake fade and drilled rotors 精品文档 5欢迎下载 If you ride a motorbike or drive a race car you re probably familiar with the term brake fade used to describe what happens to brakes when they get too hot A good example is coming down a mountain pass using your brakes rather than your engine to slow you down As you start to come down the pass the brakes on your vehicle heat up slowing you down But if you keep using them the rotors or drums stay hot and get no chance to cool off At some point they can t absorb any more heat so the brake pads heat up instead In every brake pad there is the friction material that is held together with some sort of resin and once this starts to get too hot the resin starts to vapourise forming a gas Because the gas can t stay between the pad and the rotor it forms a thin layer between the two whilst trying to escape The pads lose contact with the rotor reducing the amount of friction and voila Complete brake fade The typical remedy for this would be to get the vehicle to a stop and wait for a few minutes As the brake components cool down their ability to absorb heat returns and the next time you use the brakes they seem to work just fine This type of brake fade was more common in older vehicles Newer vehicles tend to have less outgassing from the brake pad compounds but they still suffer brake fade So why It s still to do with the pads getting too hot With newer brake pad compounds the pads transfer heat into the calipers once the rotors 精品文档 6欢迎下载 are too hot and the brake fluid starts to boil forming bubbles in it Because air is compressible brake fluid isn t when you step on the brakes the air bubbles compress instead of the fluid transferring the motion to the brake calipers Voila Modern brake fade So how do the engineers design brakes to reduce or eliminate brake fade For older vehicles you give that vapourised gas somewhere to go For newer vehicles you find some way to cool the rotors off more effectively Either way you end up with cross drilled or grooved brake rotors While grooving the surface may reduce the specific heat capacity of the rotor its effect is negligible in the grand scheme of things However under heavy braking once everything is hot and the resin is vapourising the grooves give the gas somewhere to go so the pad can continue to contact the rotor allowing you to stop The whole understanding of the conversion of energy is critical in understanding how and why brakes do what they do and why they are designed the way they are If you ve ever watched Formula 1 racing you ll see the front wheels have huge scoops inside the wheel pointing to the front see the picture above This is to duct air to the brake components to help them cool off because in F1 racing the brakes are used viciously every few seconds and spend a lot of their time trying to stay hot Without some form of cooling assistance the brakes would be fine for the first few corners but then would fade and become near useless by half way around the track Rotor technology If a brake rotor was a single cast chunk of steel it would have terrible heat dissipation properties and leave nowhere for the vapourised gas to go Because of this brake rotors are typically modified with all manner of extra design features to help them cool 精品文档 7欢迎下载 down as quickly as possible as well as dissapate any gas from between the pads and rotors The diagram here shows some examples of rotor types with the various modification that can be done to them to help them create more friction disperse more heat more quickly and ventilate gas From left to right 1 Basic brake rotor 2 Grooved rotor the grooves give more bite and thus more friction as they pass between the brake pads They also allow gas to vent from between the pads and the rotor 3 Grooved drilled rotor the drilled holes again give more bite but also allow air currents eddies to blow through the brake disc to assist cooling and ventilating gas 4 Dual ventilated rotors same as before but now with two rotors instead of one and with vanes in between them to generate a vortex which will cool the rotors even further whilst trying to actually suck any gas away from the pads An important note about drilled rotors Drilled rotors are typically only found and to be used on race cars The drilling weakens the rotors and typically results in microfractures to the rotor On race cars this isn t a problem the brakes are changed after each race or weekend But on a road car this can eventually lead to brake rotor failure not what you want I only mention this because of a lot of performance suppliers will supply you with drilled rotors for street cars without mentioning this little fact Big rotors 精品文档 8欢迎下载 How does all this apply to bigger brake rotors a common sports car upgrade Sports cars and race bikes typically have much bigger discs or rotors than your average family car A bigger rotor has more material in it so it can absorb more heat More material also means a larger surface area for the pads to generate friction with and better heat dissipation Larger rotors also put the point of contact with the pads further away from the axle of rotation This provides a larger mechanical advantage to resist the turning of the rotor itself To best illustrate how this works imagine a spinning steel disc on an axle in front of you If you clamped your thumbs either side of the disc close to the middle your thumbs would heat up very quickly and you d need to push pretty hard to generate the friction required to slow the disc down Now imagine doing the same thing but clamping your thumbs together close to the outer rim of the disc The disc will stop spinning much more quickly and your thumbs won t get as hot That in a nutshell explains the whole principle behind why bigger rotors better stopping power The different types of brake All brakes work by friction Friction causes heat which is part of the kinetic energy conversion process How they create friction is down to the various designs Bicycle wheel brakes 精品文档 9欢迎下载 I thought I d cover these because they re about the most basic type of functioning brake that you can see watch working and understand The construction is very simple and out in the open A pair of rubber blocks are attached to a pair of calipers which are pivoted on the frame When you pull the brake cable the pads are pressed against the side or inner edge of the bicycle wheel rim The rubber creates friction which creates heat which is the transfer of kinetic energy that slows you down There s only really two types of bicycle brake those on which each brake shoe shares the same pivot point and those with two pivot points If you can look at a bicycle brake and not understand what s going on the rest of this page is going to cause you a bit of a headache Drum brakes single leading edge The next more complicated type of brake is a drum brake The concept here is simple Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel When you apply the brakes the shoes are expanded outwards to press against the inside of the drum This creates friction which creates heat which transfers kinetic energy which slows you down The example below shows a simple model The actuator in this case is the blue elliptical object As that is twisted it forces against the brake 精品文档 10欢迎下载 shoes and in turn forces them to expand outwards The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are released See the later section for more information on actuator types The single leading edge refers to the number of parts of the brake shoe which actually contact the spinning drum Because the brake shoe pivots at one end simple geometry means that the entire brake pad cannot contact the brake drum The leading edge is the term given to the part of the brake pad which does contact the drum and in the case of a single leading edge system it s the part of the pad closest to the actuator This diagram right shows what happens as the brakes are applied The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge The action of the drum spinning actually helps to draw the brake pad outwards because of friction which causes the brakes to bite The trailing edge of the brake shoe makes virtually no contact with the drum at all This simple geometry explains why it s really difficult to stop a vehicle rolling backwards if it s equipped only with single leading edge drum brakes As the drum spins backwards the leading edge of the shoe becomes the trailing edge and thus doesn t bite Drum brakes double leading edge 精品文档 11欢迎下载 The drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator Now when the brakes are applied the shoes are pressed outwards at two points So each brake pad now has one leading and one trailing edge Because there are two brake shoes there are two brake pads which means there are two leading edges Hence the name double leading edge Disc brakes Some background Disc brakes were invented in 1902 and patented by Birmingham car maker Frederick William Lanchester His original design had two discs which pressed against each other to generate friction and slow his car down It wasn t until 1949 that disc brakes appeared on a production car though The obscure American car builder Crosley made a vehicle called the Hotshot which used the more familiar brake rotor and calipers that we all know and love today His original design was a bit crap though the brakes lasted less than a year each Finally in 1954 Citro n launched the way ahead of its time DS which had the first modern incarnation of disc brakes along with other nifty stuff like self levelling suspension semi automatic gearbox active headlights and composite body panels all things which were re introduced as new by car makers in the 90 s 精品文档 12欢迎下载 Disc brakes are an order of magnitude better at stopping vehicles than drum brakes which is why you ll find disc brakes on the front of almost every car and motorbike built today Sportier vehicles with higher speeds need better brakes to slow them down so you ll likely see disc brakes on the rear of those too The brake system assemblies are actuated by mechanical hydraulic or pneumatic devices The mechanical leverage is used in the parking brakes fitted in all automobile When the brake pedal is depressed the rod pushes the piston of brake master cylinder which presses the fluid The fluid flows through the pipelines to the power brake unit and then to the wheel cylinder The fluid pressure expands the cylinder pistons thus pressing the shoes to the drum or disk If the pedal is released the piston returns to the initialposition the pull back springs retract the shoes the fluid is forced back to the master cylinder and braking ceases The primary purpose of the parking brake is to hold the vehicle stationary while it is unattended The parking brake is mechanically operated by the driver when a separate parking braking hand lever is set The hand brake is normally used when the car has already stopped A lever is pulled and the rear brakes are approached and locked in the on position The car may now b