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附 錄A
Hydraulic Brake Systems
When you step on the brake pedal,you expect the vehicle to stop.The brake pedal operates a hydraulic that is used for two reasons.First,fluid under pressure can be carried to all parts of the vehicle by small hoses or metal lines without taking up a lot of room of causing routing problems.Second,the hydraulic fluid offers a great mechanical advantage-little foot pressure is required on the pedal,
but a great deal of pressure is generated at the wheels.The brake pedal is linked to a piston in the brake master cylinder containing a small piston and a fluid reservoir.
Modern master cylinders are actually two separate cylinders.Such a system is called a dual circuit,because the front cylinder is connected to the front brakes and the rear cylinder to the rear brakes.(Some vehicles are connected diagonally).
The two cylinders are actually separated,allowing for emergency stopping power should one part of the system fail.
The entire hydraulic system from the master cylinder to the wheels is full of hydraulic brake fluid.When the brake pedal is depressed,the piston in the master cylinder are forced to move,exerting tremendous force on the fluid in the lines.The fluid has nowhere to go,and forces the wheel cylinder pistons(drum brakes) or
caliper pistons(disc brakes) to exert pressure on the brake shoes or pads.The friction between the brake shoe and wheel drum or the brake pad and rotor (disc) slows the vehiche and eventually stops it.
Also attached to the brake pedal si a switch that lights the brake lights as the pedal is depressed.The lights stay on until the brake pedal is released and returns to its normal position.
Each wheel cylinder in a drum brake system contains two pistons,one at either end,which push outward in opposite directions.In disc brake systems,the wheel cylinders are part of the caliper (there can be as many as four or as few as one ).Whether disc or drum type,all pistons use some type of rubber seal to prevent leakage around the piston,and a rubber dust boot seals the outer of the wheel cylinders against dirt and moisture.
When the brake pedal is released,a spring pushes the master cylinder pistons back to their normal positions.Check valves in the master cylinder piston allow fluid to flow toward the wheel cylinders or calipers as the piston returns.Then as the brake shoe return springs pull the brake shoes back to the released position,excess fluid returns to the master cylinder through compensating ports,which have been uncovered as the pistons move back.Any fluid that has leaked from the system will also be replaced through the compensating ports.
All dual circuit brake systems use a switch to activate a light,warning of brake failure.The switch si located in a valve mounted near the master cylinder.A piston in the valve reveives pressure on each end from the front and rear brake circuits.When the pressures are balanced,the piston remains stationary,but when one circuit has a leak,greater pressure during the application of the brakes will force the piston to one side or the other,closing the switch and activating the warning light.The light can also be activated by the ignition switch during engine starting or by the parking brake.
Front disc,rear drum brake systems also have a metering valve to prevent the front disc brakes from engaging before the rear brakes have contacted the drums.This ensures that the front brakes will not normally be used alone to stop the vehicle.A proportioning valve is also used to limit pressure to the rear brakes to prevent rear wheel lock-up during hard braking.
Brake shoes and pads are constructed in a similar.The pad or shoe is composed of a metal backing plate and a priction lining.The lining is either bonded(glued) to the metal,or riveted.Generally,riveted linings provide superior performance,but good quality bonded linings are perfectly adequate.
Friction materials will vary between manufacturers and type of pad and the material compound may be referred to as asbestos,organic,semi-metallic,metallic.The difference between these compounds lies in the types and percentages of friction materials used,material binders and performance modifiers.
Generally speaking,organic and non-metallic asbestos compound brakes are quiet,easy on rotors and provide good feel.But this comes at the expense of high temperature operation,so they may not be your best choice for heavy duty use or mountian driving.In most cases,these linings will wear somewhat faster than metallic compound pads,so you will usually replace them more often.But,when using these pads,rotors tend to last longer.
Semi-metallic or metallic compound brake linings will vary in performance based on the metallic contents of the compound.Again,generally speaking,the higher the metallic content,the better the friction material will resist heat.This makes them more appropriate for heavy duty applications,but at the expense of braking performance before the pad reaches operating temperature.The first few applications on a cold morning may not give strong braking.Also,metallics and semi-metallics are more likely to squeal,In most cases,metallic compounds last longer than non-metallic pads,but they tend to cause more wear on the rotors.If you use metallic pads,expect to replace the rotors more often.
When deciding what type of brake lining is right for you,keep in mind that today’s modern cars have brake materials which are matched to the expected vehicle’s performance capabilities.Changing the material from OEM specification could adversely addect brake feel or responsiveness.Before changing the brake materials,talk to your deaker or parts supplier to help decide what is most appropriate for your application.
Remenber that use applications such as towing,stop and go driving,driving down mountain roads,and racing may require a change to a higher performance material.
Some more exotic materials are also used in brake linings,among which are Kevlar and carbon compounds.These materials have the capability of extremely good performance for towing,mountain driving or racing.Wear characteristics can be similar to either applications tend to wear like metallic linings,while many of the streetapplications are more like the non-metallics.
附 錄B
液壓制動(dòng)系統(tǒng)
?????當(dāng)踩下制動(dòng)踏板，您希望該車輛停下。液壓制動(dòng)踏板控制兩個(gè)部分。首先，在液壓作用下，由于采用細(xì)小的軟管或金屬線因此不必占用很大的空間。其次，液壓機(jī)構(gòu)提供了一個(gè)很大的優(yōu)勢(shì)，由一個(gè)很小的力踩在制動(dòng)踏板上，會(huì)產(chǎn)生很大的力作用于車輪上。制動(dòng)踏板連接在充滿制動(dòng)液的制動(dòng)液壓缸的活塞上，液壓缸由活塞和油箱組成。
現(xiàn)代主缸其實(shí)是兩個(gè)獨(dú)立的腔體。這種結(jié)構(gòu)稱之為雙回路系統(tǒng)，因?yàn)榍扒贿B接到前制動(dòng)器與后腔連接到后制動(dòng)器。（有些車輛是對(duì)角連接）。兩個(gè)腔實(shí)際是分離的，允許緊急制動(dòng)時(shí)一個(gè)系統(tǒng)失效另一個(gè)系統(tǒng)起作用。
整個(gè)液壓系統(tǒng)是從主缸到車輪都充滿制動(dòng)液。當(dāng)制動(dòng)踏板放松時(shí)，活塞在總泵中移動(dòng)，在整個(gè)液壓回路中產(chǎn)生壓力?；芈分谐錆M液壓力，強(qiáng)制輪（鼓式制動(dòng)器）或（盤(pán)式制動(dòng)器）壓迫制動(dòng)蹄或制動(dòng)盤(pán)。壓力壓迫制動(dòng)蹄或制動(dòng)片作用于制動(dòng)鼓或制動(dòng)盤(pán)最終是車輛停止。
此外，制動(dòng)踏板控制一個(gè)燈的開(kāi)關(guān)，剎車燈的踏板放松時(shí)，開(kāi)關(guān)回到正常位置而燈滅。
每一個(gè)鼓式制動(dòng)器包含兩個(gè)活塞，二個(gè)并排放置，向相反方向推動(dòng)施加制動(dòng)力。盤(pán)式制動(dòng)器中，輪缸都是制動(dòng)鉗（有的可能有多達(dá)4個(gè)或是1個(gè) ）的一部分。所有活塞都使用某種類型的橡膠密封，防止液壓液泄漏出活塞，以及用橡膠密封防塵或污垢和水分進(jìn)入輪缸。
當(dāng)制動(dòng)踏板被釋放，彈簧推動(dòng)總泵活塞移動(dòng)到總泵活塞在正常位置?；亓鏖y允許液體流向輪缸或流回制動(dòng)總缸。當(dāng)制動(dòng)液流向制動(dòng)輪缸，多余的液體回流，補(bǔ)償已被活塞移動(dòng)距離的液壓油。液壓油若泄露也由回油閥回流。
所有雙回路制動(dòng)系統(tǒng)使用一個(gè)開(kāi)關(guān)來(lái)激活，并監(jiān)控液壓油的壓力。開(kāi)關(guān)閥門(mén)位于警告位置安裝在主缸主閥門(mén)附近。活塞每次從前回路和后回路之間循環(huán)。當(dāng)結(jié)束制動(dòng)是壓力是平衡的，活塞位置是穩(wěn)定的，但是當(dāng)一個(gè)回路有泄漏，在更大的制動(dòng)系統(tǒng)壓力下將迫使偏向活塞一方或另一方，關(guān)閉開(kāi)關(guān)，就啟動(dòng)警示燈. 點(diǎn)火開(kāi)關(guān)起動(dòng)發(fā)動(dòng)機(jī)時(shí)或駐車制動(dòng)時(shí)報(bào)警燈也是被激活的。
前盤(pán)，后鼓制動(dòng)系統(tǒng)也有一個(gè)計(jì)量閥，以防止前，后制動(dòng)器有制動(dòng)間隙。用以確保前盤(pán)式制動(dòng)器一般不會(huì)單獨(dú)使用，停止汽車。壓力控制閥也可以用來(lái)限制壓力，以防止在后輪制動(dòng)中鎖定。
制動(dòng)蹄和制動(dòng)片使用相似材料。制動(dòng)蹄或制動(dòng)塊由金屬信號(hào)板和摩擦襯片組成。襯片是由粘結(jié)劑(被膠合)粘結(jié)或鉚接的。通常，鉚接的襯片效果比較好，但是粘結(jié)的襯片是更能充分表現(xiàn)摩擦材料的性能。
摩擦材料在不同的制造商中生產(chǎn)是不同的，并且大致的類型可被分為：石棉類，有機(jī)類，半金屬類，金屬類。在不同的類型中成分和成分的百分比是不同的。
一般來(lái)說(shuō)，有機(jī)和非金屬石棉化合物是常用的，容易在電子設(shè)備中有好的表現(xiàn)。但是對(duì)于高溫操作來(lái)，他們可能不是您的耐用或山地駕駛的最佳的選擇。在許多情況下，這些襯片將比有些金屬化合物片更快速磨損，因此您經(jīng)常得將替換他們。但是，當(dāng)使用這些制動(dòng)襯片時(shí)，電子設(shè)備將有更長(zhǎng)的壽命。
半金屬剎車片或金屬化合物的表現(xiàn)因成分的不同而有所不同。一般來(lái)說(shuō)，金屬含量越高，性能越好，摩擦材料的散熱性將越好。所以使它們更適合重型汽車使用，但是，金屬和半金屬為更容易發(fā)生嘯叫，在大多數(shù)情況下，金屬化合物比非金屬片更容易發(fā)生嘯叫。因此需要更經(jīng)常更換襯片。
當(dāng)你想確定什么類型的剎車片是適合你，請(qǐng)記住，在今天現(xiàn)代汽車制動(dòng)系統(tǒng)是汽車的預(yù)期相匹配的表現(xiàn)性能之一。原始設(shè)備制造商從規(guī)格材質(zhì)到剎車材料感覺(jué)并不能給你提供幫助。所以在你改變剎車材料前，先談?wù)勀愕牧慵?yīng)商，以幫助決定什么是最適合您的剎車片。
記住若你經(jīng)常使用例如拖曳，停止并且頻繁駕駛，行駛在山路和賽跑也許都對(duì)性能材料有更高的要求因此需要你經(jīng)常更換剎車片。
一些特殊的材料也用在剎車片中，其中有芳綸，碳材料。這些材料具有極其良好的剎車性能，山區(qū)駕駛或在賽場(chǎng)上駕駛都表現(xiàn)很好。耐磨性可能更勝于金屬材料，而許多的其他性能更像非金屬。
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