制动器外文翻译 制动器 精品.docx

1、制动器外文翻译 制动器 精品本科生毕业设计（论文）外文翻译毕业设计（论文）题目：几种典型的制动器的对比分析与设计外文题目：THE BRAKE BIBLE译文题目：制动器学 生 姓 名： 专 业： 车辆工程 指导教师姓名： 评 阅 日 期： THE BRAKE BIBLEBrakes - what do they do?The simple answer: they slow you down.The complex answer: brakes are designed to slow down your vehicle but probably not by the means that y

2、ou 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 youre travelling at speed, your vehicle has ki

3、netic 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. Its the First Law of Thermodynamics, sometimes known as the law of con

4、servation 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 l

5、ocation 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.If you ride a motorbike or drive a race car, youre probably familiar with the term brake fade, used to describe w

6、hat 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 an

7、d get no chance to cool off. At some point 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

8、gas cant 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 minute

9、s. 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 brak

10、e fade. So why? Its still to do with the 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, t

11、he 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 coo

12、l 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 resi

13、n 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 youve eve

14、r watched Formula 1 racing, youll 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 tim

15、e 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 prop

16、erties 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 down as quickly as possible as well as dissapate any gas from between the pads and rotors. The diagram here shows some examples of ro

17、tor 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 T

18、hey 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 r

19、otors 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 weak

20、ens the rotors and typically results 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 suppl

21、iers will supply you with drilled rotors 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 ha

22、s 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 ad

23、vantage 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 youd need to push pretty hard to generate

24、 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 wont get as hot. That, in a nutshell explains the whole principle behind why bigger rotor

25、s = 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 brakesI thought Id cover these because theyre about the most basic t

26、ype 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

27、 of the bicycle wheel rim. The rubber 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 b

28、icycle brake and not understand whats 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 att

29、ached 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 ellip

30、tical object. As that is twisted, it 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 singl

31、e 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

32、 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 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 its really difficult to stop a vehicle r