【正文】 efficiency. If air is suspected, then the system must be bled to remove the air. There are “bleeder screws” at each wheel cylinder and caliper for this purpose.On a disk brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, inturn, squeezes two brake pads against the disk (rotor) which is attached to the wheel, forcing it to slow down or stop. This process is similar to a bicycle brake where two rubber pads rub against the wheel rim creating friction.With drum brakes, fluid is forced into the wheel cylinder which pushes the brake shoes out so that the friction linings are pressed against the drum which is attached to the wheel, causing the wheel to stop.In either case, the friction surfaces of the pads on a disk brake system or the shoes on a drum brake convert the forward motion of the vehicle into heat. Heat is what causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require replacement.Brake fluid is special oil that has specific properties. It is designed to withstand cold temperatures without thickening as well as very high temperatures without boiling. (If the brake fluid should boil, it will cause you to have a spongy pedal and the car will be hard to stop). Figure shows a brake hydraulic system.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 a short 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 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 noncorrosive seamless steel tubing with special fittings at all attachment points. If a steel line requires a repair, the best procedure is to replace the pete 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.Other Components in the Hydraulic System:1. Proportioning Valve or Equalizer ValveThese valves are mounted between the master cylinder and the rear wheels. They are designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping. The shorter you stop, the more of the vehicle’s weight is transferred to the front wheels, in some cases, causing the rear to lift and the front to dive. These valves are designed to direct more pressure to the front and less pressure to the rear the harder you stop. This minimizes the chance of premature lockup at the rear wheels.2. Pressure Differential ValveThis valve is usually mounted just below the master cylinder and is responsible for turning the brake warning light on when it detects a malfunction. It measures the pressure from the two sections of the master cylinder and pares them. Since it is mounted ahead of the proportioning or equalizer valve, the two pressures it detects should be equal. If it detects a difference, it means that there is probably a brake fluid leak somewhere in the system. 3. Combination ValveThe Combination valve (Figure) is simply a proportioning valve and a pressure differential valve that is bined into one unit.The parking brake (a．k．a(chǎn)．emergency brake ) system controls the rear brakes through a series of steel cables that are connected to either a hand lever or a foot pedal. The idea is t。這不僅是我個人的努力外，更多的是老師和同學們給我的幫助。他們在我最需要幫助的時候，向我伸出了援助之手，讓我知道團結(jié)才是力量，使我信心倍增。XXX老師的這種敬業(yè)精神是我學習的榜樣。王老師平日里工作很忙，但在做畢業(yè)設(shè)計的每個階段，從外出實習到查閱資料，設(shè)計草案的確定和修改，中期檢查，后期詳細設(shè)計，裝配草圖等整個過程中都給予了我細心的指導(dǎo)。參考文獻[1] 李春明, 趙宇生主編. 汽車設(shè)計. 北京:機械工業(yè)出版社, 2001[2] 余志生主編. 汽車理論. 北京:機械工業(yè)出版社, 2000[3] :人民交通出版社,2000[4] :國防工業(yè)出版社,2003[5] : 清華大學出版社,2001[6] :[7] :[8] 龐劍，諶剛，:[9] 米奇克M主編. . 北京:[10] 唐嘉平主編. :清華大學出版社．2006[11] 黃韶炯，欒志強主編. :[12] :[13] 胡亞莊主編. :人民交通出版社. 1993[14] 汪立亮，（ABS）:[15] Rudolf Limpert. Brake Design and Safety (Second Edition). Warrendale, PA, USA: SAE, Inc.,1999致 謝轉(zhuǎn)眼間，畢業(yè)設(shè)計就要結(jié)束了，畢業(yè)設(shè)計是我大學生活中的最后一項任務(wù)，也是將理論學習和實踐設(shè)計相結(jié)合起來的一個教學環(huán)節(jié)。采用的駐車制動滿足國家對汽車駐車坡度的要求。又由計算可知人力無法滿足制動力的要求，加裝了真空助力伺服制動系統(tǒng)。為了提高汽車的安全性和舒適性，設(shè)計此轎車時采用了前、后盤式制動器；采用HH型雙管路制動系統(tǒng)和間隙可調(diào)的制動器的設(shè)計方式。 故符合要求。則 ，故符合要求。能量負荷愈大，則摩擦襯片（襯塊）的磨損亦愈嚴重。此時由于在短時間內(nèi)制動摩擦產(chǎn)生的熱量來不及逸散到大氣中，致使制動器溫度升高。汽車的制動過程，是將其機械能（動能、勢能）的一部分轉(zhuǎn)變?yōu)闊崃慷纳⒌倪^程。 摩擦襯片（襯塊）的磨損特性計算摩擦襯片的磨損與摩擦副的材質(zhì)，表面加工情況、溫度、壓力以及相對滑磨速度等多種因素有關(guān)，因此在理論上要精確計算磨損性能是困難的。當I線在β線下方時，前輪先抱死。充分說明了實際制動力分配的合理性與可行性。 實際的前、后制動器制動力分配曲線綜合上述，通過合理選擇同步附著系數(shù)，計算制動器制動力實際分配曲線，（如圖所示）把理想曲線和實際曲線進行比較、分析、論證。此時的前、后輪制動器制動力和的曲線關(guān)系，常稱為理想的前、后輪制動器制動力分配曲線。 地面對前、后車輪的法向反作用力在分析前、后制動器制動力分配比例以前，必須先了解在制動時地面作用于前、后車輪的法向反作用力。3）前、后輪同時抱死拖滑。 前、后制動器制動力分配對于一般汽車而言，根據(jù)其前、后軸制動器制動力的分配、載荷情況及路面附著系數(shù)和坡度等因素，當制動器制動力足夠時，制動過程可能出現(xiàn)如下三種情況：1）前輪先抱死拖滑，然后后輪抱死拖滑。最大停駐坡高度應(yīng)不小于16%～20%，故符合要求。因此，從保證汽車方向穩(wěn)定性的角度考慮，最理想的情況就是防止任何車輪抱死，前后車輪都處于滾動狀態(tài)。一般情況下，若后軸車輪比前軸車輪先抱死拖滑，就可能發(fā)生后軸側(cè)滑。側(cè)滑是指車輪連帶車軸的側(cè)向滑移，這常常是由于緊急制動車輪被抱死后，側(cè)向附著系數(shù)趨于零，使胎面喪失了抵抗側(cè)滑的能力造成的。因此，國標GB72582004對制動力平衡做了具體要求:在制動力增長全過程中同時測得的左右輪制動力差的最大值，與全過程中測得的該軸左右輪最大制動力中大者之比，對前軸不應(yīng)大于20%，對后軸(及其它軸)在軸制動力不小于該軸軸荷的60%時不應(yīng)大于24%。因此，常用制動時汽車按給定路徑行駛的能力來評價汽車制動時的方向穩(wěn)定性，對制動距離和制動減速度兩指標測試時都要求了其試驗通道的寬度。影響方向穩(wěn)定性的包括制動跑偏、后軸側(cè)滑或前輪失去轉(zhuǎn)向能力三種情況。則汽車將偏離原來的路徑。 制動時汽車的方向穩(wěn)定性制動時汽車的方向穩(wěn)定性，常用制動時汽車給定路徑行駛的能力來評價。因為制動過程實際上是把汽車行駛的動能通過制動器吸收轉(zhuǎn)換為熱能，所以制動器溫度升高后能否保持在冷態(tài)時的制動效能，已成為設(shè)計制動器時要考慮的一個重要問