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1、河南理工大学万方科技学院毕 业 设 计（论 文）附 录I中 英 文 文 献 翻 译姓 名： 王 奎 所在院系： 机械与动力工程系 专业班级： 机械设计08-3班 学 号： 0828070005 指导教师： 赵 武 原文标题： Automobile Brake System2012 年 5 月 25 日Automobile Brake SystemThe braking system is the most important system in cars. If the brakes fail, the result can be disastrous. Brakes are actually
2、 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 pres
3、sure 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 peda
4、l. 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 loc
5、ated under the hood, and is directly connected to the brake pedal, converts driver foots 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
6、extreme conditions, fills the system. “Shoes” and “pads” are 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
7、 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 th
8、e 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 drivers comp
9、artment. 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 o
10、r 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
11、 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 the amount of time you need to fill it and never leave a cam of brake f
12、luid 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 ar
13、e 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 th
14、e 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,
15、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
16、 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 permitt
17、ing 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 cylinder forces the pistons to move in, toward the disk. This action pu
18、shes 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 th
19、e 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 tha
20、t 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 youre travelling at speed, your vehicle has kinetic energy. When you apply the brakes,
21、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. Its the First Law of Thermodynamics, sometimes known as the law of conservation of energy. This states that ene
22、rgy 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 th
23、e friction is generated also provides a mechanical moment to resist the turning motion of the rotor. Thermodynamics, brake fade and drilled rotors.If you ride a motorbike or drive a race car, youre probably familiar with the term brake fade, used to describe what happens to brakes when they get too
24、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 poi
25、nt they cant 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 cant stay between the pad and the ro
26、tor, 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, t
27、heir 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? Its still to do with th
28、e pads getting too hot. With newer brake pad compounds, the pads transfer heat into the calipers once the rotors are too hot, and the brake fluid starts to boil forming bubbles in it. Because air is compressible (brake fluid isnt) when you step on the brakes, the air bubbles compress instead of the
29、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. Eit
30、her 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
31、 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 youve ever watched Formula 1 racing, youll see
32、 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 fo
33、rm 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 vapo
34、urised gas to go. Because of this, brake rotors are typically modified with all manner of extra design features to help them cool 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 modificati
35、on 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 betwe
36、en 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
37、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
38、 in microfractures to the rotor. On race cars this isnt 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 ro
39、tors for street cars without mentioning this little fact. Big rotors.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 abso
40、rb 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
41、 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 youd need to push pretty hard to generate the friction required to slow the d
42、isc 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 wont get as hot. That, in a nutshell explains the whole principle behind why bigger rotors = better stopping power.The differ
43、ent 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 brakesI thought Id cover these because theyre about the most basic type of functioning brake that you ca
44、n 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 rubbe
45、r creates friction, which creates heat, which is the transfer of kinetic energy that slows you down. Theres 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
46、s going on, the rest of this page is going to cause you a bit of a headache. Drum brakes - single leading edgeThe 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 t
47、he 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
48、 forces against the brake 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
49、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, its the part of the pad closest to the actuator. This diagram (right) shows w
