寧波大紅鷹學院畢業(yè)設計（論文）外文翻譯所在學院： 宋體四號加粗 班 級： 姓 名： 學 號： 指導教師： 合作導師： 2013 年 11 月 15 日原文：題目 Brake systems （PDF 原件）We all know that pushing down on the brake pedal slows a car to a stop. But how does this happen? How does your car transmit the force from your leg to its wheels? How does it multiply the force so that it is enough to stop something as big as a car?When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot. It does this in two ways: ? Mechanical advantage (leverage) ? Hydraulic force multiplication The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using friction also. Before we begin our discussion on the components of the brake system, we'll cover these three principles: ? Leverage ? Hydraulics ? Friction Leverage and HydraulicsIn the figure below, a force F is being applied to the left end of the lever. The left end of the lever is twice as long (2X) as the right end (X). Therefore, on the right end of the lever a force of 2F is available, but it acts through half of the distance (Y) that the left end moves (2Y). Changing the relative lengths of the left and right ends of the lever changes the multipliers. The basic idea behind any hydraulic system is very simple: Force applied at one point is transmitted to another point using an incompressible fluid, almost always an oil of some sort. Most brake systems also multiply the force in the process. Here you can see the simplest possible hydraulic system: Your browser does not support JavaScript or it is disabled. Simple hydraulic system In the figure above, two pistons (shown in red) are fit into two glass cylinders filled with oil (shown in light blue) and connected to one another with an oil-filled pipe. If you apply a downward force to one piston (the left one, in this drawing), then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good -- almost all of the applied force appears at the second piston. The great thing about hydraulic systems is that the pipe connecting the two cylinders can be any length and shape, allowing it to snake through all sorts of things separating the two pistons. The pipe can also fork, so that one master cylinder can drive more than one slave cylinder if desired, as shown in here: Your browser does not support JavaScript or it is disabled. Master cylinder with two slaves The other neat thing about a hydraulic system is that it makes force multiplication (or division) fairly easy. If you have read How a Block and Tackle Works or How Gear Ratios Work, then you know that trading force for distance is very common in mechanical systems. In a hydraulic system, all you have to do is change the size of one piston and cylinder relative to the other, as shown here: Your browser does not support JavaScript or it is disabled. Hydraulic multiplication To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r2. The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).A Simple Brake SystemBefore we get into all the parts of an actual car brake system, let's look at a simplified system:Your browser does not support JavaScript or it is disabled. A simple brake system You can see that the distance from the pedal to the pivot is four times the distance from the cylinder to the pivot, so the force at the pedal will be increased by a factor of four before it is transmitted to the cylinder. You can also see that the diameter of the brake cylinder is three times the diameter of the pedal cylinder. This further multiplies the force by nine. All together, this system increases the force of your foot by a factor of 36. If you put 10 pounds of force on the pedal, 360 pounds (162 kg) will be generated at the wheel squeezing the brake pads. There are a couple of problems with this simple system. What if we have a leak? If it is a slow leak, eventually there will not be enough fluid left to fill the brake cylinder, and the brakes will not function. If it is a major leak, then the first time you apply the brakes all of the fluid will squirt out the leak and you will have complete brake failure. Drum brakes work on the same principle as disc brakes: Shoes press against a spinning surface. In this system, that surface is called a drum.Figure 1. Location of drum brakes. See more drum brake pictures.Many cars have drum brakes on the rear wheels and disc brakes on the front. Drum brakes have more parts than disc brakes and are harder to service, but they are less expensive to manufacture, and they easily incorporate an emergency brake mechanism. In this edition of HowStuffWorks, we will learn exactly how a drum brake system works, examine the emergency brake setup and find out what kind of servicing drum brakes need. Figure 2. Drum brake with drum in placeFigure 3. Drum brake without drum in placeLet's start with the basics. The Drum BrakeThe drum brake may look complicated, and it can be pretty intimidating when you open one up. Let's break it down and explain what each piece does. Figure 4. Parts of a drum brakeLike the disc brake, the drum brake has two brake shoes and a piston. But the drum brake also has an adjuster mechanism, an emergency brake mechanism and lots of springs. First, the basics: Figure 5 shows only the parts that provide stopping power. Your browser does not support JavaScript or it is disabled. Figure 5. Drum brake in operation When you hit the brake pedal, the piston pushes the brake shoes against the drum. That's pretty straightforward, but why do we need all of those springs? This is where it gets a little more complicated. Many drum brakes are self-actuating. Figure 5 shows that as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force. The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But, because of the wedging action, the shoes must be pulled away from the drum when the brakes are released. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates. Brake AdjusterFor the drum brakes to function correctly, the brake shoes must remain close to the drum without touching it. If they get too far away from the drum (as the shoes wear down, for instance), the piston will require more fluid to travel that distance, and your brake pedal will sink closer to the floor when you apply the brakes. This is why most drum brakes have an automatic adjuster. Figure 6. Adjuster mechanismNow let's add in the parts of the adjuster mechanism. The adjuster uses the self-actuation principle we discussed above. Your browser does not support JavaScript or it is disabled. Figure 7. Drum brake adjuster in operation In Figure 7, you can see that as the pad wears down, more space will form between the shoe and the drum. Each time the car stops while in reverse, the shoe is pulled tight against the drum. When the gap gets big enough, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes close to the drum. Some cars have an adjuster that is actuated when the emergency brake is applied. This type of adjuster can come out of adjustment if the emergency brake is not used for long periods of time. So if you have this type of adjuster, you should apply your emergency brake at least once a week. ServicingThe most common service required for drum brakes is changing the brake shoes. Some drum brakes provide an inspection hole on the back side, where you can see how much material is left on the shoe. Brake shoes should be replaced when the friction material has worn down to within 1/32 inch (0.8 mm) of the rivets. If the friction material is bonded to the backing plate (no rivets), then the shoes should be replaced when they have only 1/16 inch (1.6 mm) of material left. Photo courtesy of a local AutoZone storeFigure 9. Brake shoeJust as in disc brakes, deep scores sometimes get worn into brake drums. If a worn-out brake shoe is used for too long, the rivets that hold the friction material to the backing can wear grooves into the drum. A badly scored drum can sometimes be repaired by refinishing. Where disc brakes have a minimum allowable thickness, drum brakes have a maximum allowable diameter. Since the contact surface is the inside of the drum, as you remove material from the drum brake the diameter gets bigger. The current Bosch component Anti-lock Braking System (ABSⅡ), is a second generation design wildly used by European automakers such as BWM, Mercedes-Benz and Porsche. ABSⅡ system consists of : four wheel speed sensor, electronic control unit and modulator assembly. A speed sensor is fitted at each wheel sends signals about wheel rotation to control unit. Each speed sensor consists of a sensor unit and a gear wheel. The front sensor mounts to the steering knuckle and its gear wheel is pressed onto the stub axle that rotates with the wheel. The rear sensor mounts the rear suspension member and its gear wheel is pressed onto the axle. The sensor itself is a winding with a magnetic core. The core creates a magnetic field around the winding, and as the teeth of the gear wheel move through this field, an alternating current is induced in the winding. The control unit monitors the rate o change in this frequency to determine impending brake lockup. The control unit’s function can be divided into three parts: signal processing, logic and safety circuitry. The signal processing section is the converter that receives the alternating current signals form the speed sensors and converts them into digital form for the logic section. The logic section then analyzes the digitized signals to calculate any brake pressure changes needed. If impending lockup is sensed, the logic section sends commands to the modulator assembly. The hydraulic modulator assembly regulates pressure to the wheel brakes when it receives commands from the control utuit. The modulator assembly can maintain or reduce pressure over the level it receives from the master cylinder, it also can never apply the brakes by itself. The modulator assembly consists of three high-speed electric solenoid valves, two fluid reservoirs and a turn delivery pump equipped with inlet and outlet check valves. The modulator electrical connector and controlling relays are concealed under a plastic cover of the assembly. Each front wheel is served by electric solenoid valve modulated independently by the control unit. The rear brakes are served by a single solenoid valve and modulated together using the select-low principle. During anti-braking system operation, the control unit cycles the solenoid valves to either hold or release pressure the brake lines. When pressure is released from the brake lines during anti-braking operation, it is routed to a fluid reservoir. There is one reservoir for the front brake circuit. The reservoirs are low-pressure accumulators that store fluid under slight spring pressure until the return delivery pump can return the fluid through the brake lines to the master cylinder. 譯文：題目 制動系統(tǒng) 眾所周知，踩下制動踏板可以使汽車減速至停止。但這是如何產生的呢？汽車是如何將力從你的腿傳遞到車輪的呢？汽車是如何將力放大到足夠大以致可以將像汽車一樣大的東西制動的呢？ 制動系統(tǒng)組件當你踩下制動踏板的時候，汽車通過液體把力從腳傳遞到制動器。因為制動器需要的真正力量比你的腿能提供的要大的多，所以汽車必須放大腳產生的力 有兩種方式：機械杠桿作用液力放大制動器通過摩擦把力傳遞給輪胎，并且輪胎也是通過摩擦把力傳遞給路面的。 在我們討論制動系統(tǒng)的組成之前，先來介紹以下三條原則：杠桿液力摩擦力杠桿和液力在下面的圖中，一個力 F 加在杠桿的左端。左端的杠桿長度（2X）是右端（X ）的兩倍。因此杠桿右端可施加的力為 2F ，但是右端移動的距離 (Y)是左端距離(2Y)的一半。改變杠桿的左端和右端的長度可以改變放大系數(shù)。 任何液壓系統(tǒng)背后的基本原理都是非常簡單的：作用在某一點力通過通常是油一類的不可壓縮的液體傳遞到另一點。大多數(shù)的制動系統(tǒng)也在這個過程中放大力。下面的是最簡單的液壓系統(tǒng)：簡單液壓系統(tǒng)在上圖中，兩個活塞放在兩個充滿油的玻璃液壓缸中并且由充滿油的管道相連。如果在一個活塞上施加一個向下的力，那么力將通過管道中的油傳遞到第二個活塞。因為油液是不可壓縮的，所以傳遞效率很好，大部分的作用力都傳遞到了另一個活塞。液壓系統(tǒng)的好處連接兩液壓缸的管道可以是任何長度和形狀，這樣就可以使管道彎曲的通過兩活塞之間的各種部件。管道也可以是分叉的，如果有需要的話，這樣一個主缸可以驅動數(shù)個副缸。如下圖所示：帶有兩個副缸的主缸液壓系統(tǒng)的另一個好處是產生放大（或者縮?。?力相當?shù)厝菀?。如果你一讀過滑車設備工作原理或者齒輪齒數(shù)比原理，那么你就會知道在機械系統(tǒng)中把力轉化為距離處理是很常見的。在液壓系統(tǒng)中，我們所要做的就是相對地改變一組活塞和液壓缸的尺寸。如下圖所示： 液壓增力原理為了確定上圖中的放大因子，先由觀察活塞的尺寸開始。假設左邊活塞的直徑為2 英尺（5.08cm 而右邊的直徑為 6 英尺（15.24cm ）。兩個活塞的面積是 Pi * r2 。因此左面活塞的面積是 3.14，而右面的面積是 28.26。右面活塞的面積是左邊的九倍大。這就意味著無論在左面的活塞上施加多大的力，在右面的活塞上就會輸出九倍于左面的力。所以，如果在左邊活塞上施加 100 磅向下的力，那么在右面活塞上將產生900 磅向上的力。唯一的補償是左面的活塞要移動 9 英尺（ 22.86cm）來使右面提升1 英尺（2.54cm ）一個簡單的制動系統(tǒng)在我們深入了解一個真實的制動系統(tǒng)的各部分之前，讓我們先來看一個簡化的系統(tǒng)： 我們可以看到踏板到樞軸的距離是液壓缸到樞軸距離的 4 倍，所以施加在踏板上的力在傳遞到液壓缸之前將被增加 4 倍。我們還可以看到制動缸的直徑是踏板缸直徑的 3倍。這就將力進一步放大了九倍。最終這個系統(tǒng)將腿上的力增加了 36 倍。所以，如果在踏板上施加 10 磅的力，將在擠壓制動帶的輪上產生 369 磅（162kg）的力。下面是這種簡單系統(tǒng)所存在的問題。要是系統(tǒng)有泄漏該怎么辦呢？如果是輕微泄漏，最終將會沒有足夠的油使制動缸充滿，并且制動器將停止工作。如果是嚴重泄漏，那么在你制動的第一時間，所有的油液將從泄露處噴射而出，并且制動系統(tǒng)將徹底地不起作用。鼓式制動器的工作原理和盤式制動器是一樣的：制動面接觸一個磨砂的表面。在這個系統(tǒng)中，那個表面稱作制動鼓圖 1.制動鼓的位置許多汽車的后輪安裝鼓式制動器，而盤式制動器安裝在前面。鼓式制動器比盤式制動器有更多的零件并且更難檢修。 但是制造成本相對便宜，還有鼓式制動器容易組裝一個緊急使用的制動裝置。在本版本的 How StuffWorks 中，我們將詳盡了解鼓式制動系統(tǒng)是如何工作的?？疾炀o急制動系統(tǒng)的組成，并且找到鼓式制動器需要何種檢修工作。圖 2. 有鼓的鼓式制動器 圖 3.未安裝鼓的鼓式制動器讓我們基礎開始：鼓式制動器鼓式制動器可能看起來比較復雜，它可以是很復雜的，當你打開一個的時候。讓我們拆開它，并解釋每一塊的作用。圖 4. 鼓式制動器的組成如盤式制動器，鼓式制動器有兩個制動蹄和一個活塞。 但是鼓式制動器也有一個調節(jié)機制，緊急剎車機制和大量的彈簧 。首先，基礎知識： 圖 5 顯示只有部分提供的制動力。圖 5.工作狀態(tài)下的鼓式制動器當你踩下剎車踏板時，活塞推動緊靠著鼓的制動蹄。 這是很簡單的，但為什么我們需要所有這些彈簧呢？這使它變的有點復雜許多鼓式制動器是自增力式的。圖 5 表明，當制動蹄與鼓相接觸的時候，兩者間有一個楔入運動，這起到了產生更多的力量將制動蹄向鼓擠壓。由楔入運動提供的額外制動力使得鼓式制動器可以使用比盤式制動器更小的活塞。但是由于這種楔入運動，在制動釋放的時候制動蹄必須從鼓拉離開。這是使用其中部分彈簧的原因。其它彈簧的作用是將制動蹄固定并且驅動調節(jié)臂返回。制動調節(jié)器為了使鼓式制動器正確的工作，制動蹄必須緊貼著鼓但是不碰到它。如果離鼓太遠的話，活塞將需要更多的油液以通過那段距離，并且當你制動時，制動踏板將下行而離地板更近。這就是為什么大多數(shù)的鼓式制動器有一個自動調節(jié)裝置的原因。圖 6.調節(jié)機構現(xiàn)在讓我們在把調節(jié)機構也加進來，這個調節(jié)器使用的是上面討論過的自增力原理。圖 7.工作狀態(tài)下的鼓式制動調節(jié)器在圖 7 中，我們可以看到由于摩擦片的磨損，這使得制動蹄和鼓之間形成更大的空間。每次車停下的時候，相反的是制動蹄被拉的和鼓更緊。當間隙變的足夠大時，調節(jié)杠桿足夠擺動推進調節(jié)齒輪先前轉動一個齒。調節(jié)裝置有一個行程，就像一個螺栓，以便當它轉動時旋開一點點，延長以填補間隙。當制動蹄進一步磨損，調節(jié)器又可以再向前。所以它總是保持制動蹄緊靠著鼓。有些汽車緊急剎車時有一個被驅動的調節(jié)器。如果緊急制動很長一段時間沒有使用，這種類型的調節(jié)器可以產生調節(jié)作用。所以如果你有這種類型的調節(jié)器，你應該每周至少使用一次緊急制動裝置。檢修鼓式制動器最常見的檢修是更換制動蹄。一些鼓式制動器在背面設置了一個檢查孔，通過這個孔，你可以看到制動蹄上還剩余多少摩擦材料。當摩擦材料磨損到鉚釘內 1/32 英寸（0.8mm）時，必須更換制動蹄。如果摩擦材料和墊板直接連接（無鉚釘），那么當摩擦材料只剩下 1/16 英寸（1.6mm）時，就該換制動蹄了。圖 9.制動蹄正如在盤式制動器中，深的刻痕可能會磨穿到制動鼓。如果一個磨損的制動蹄使過長的時間，把摩擦片固定到墊板上鉚釘可以將制動鼓摸出一條凹槽。一個嚴重磨損的制動鼓有時可以被修補修復。盤式制動器有最小允許厚度，鼓式制動器有一個最大允許直徑。因為接觸表面是鼓的內側。當你將材料從制動器中取出時，制動鼓的直徑變大了。 防抱死制動系統(tǒng)除了上面基本操作，還有兩個特點。首先，當制動系統(tǒng)的壓力上升到使輪胎抱死或即將抱死的時候，防抱死制動系統(tǒng)才會啟動；當制動系統(tǒng)在正常情況下，防抱死制動系統(tǒng)停止運作。其次，如果防抱死制動系統(tǒng)有問題時，制動器會獨立地繼續(xù)運行。但控制板上的指示燈亮起提醒司機系統(tǒng)出現(xiàn)問題。目前歐洲汽車生產商，如：寶馬、奔馳、寶時捷等廣泛使用的是波許（Bosch）防抱死制動系統(tǒng)。這種系統(tǒng)基本組成包括車輪轉速傳感器，電子控制裝置和調節(jié)裝置。每個有一個向電子控制裝置發(fā)出車輪轉動情況的信號的傳感器，它一般由磁感應傳感頭和齒圈組成。前面的傳感器安在輪轂上，齒圈安在輪網(wǎng)上。后面的傳感器安在后部的監(jiān)測系統(tǒng)上，齒圈安在輪軸上。傳感器本身是纏繞電磁核的電線圈，電磁核才線圈的周圍產生磁場。當齒圈的齒移動到磁場時，就會改變線圈的電流。電子控制裝置會監(jiān)測這種變化，然后判斷車輪是否即將抱死。電子控制裝置有三個作用，即：信號的處理，編輯和安全防護。信號的處理起到轉換器的作用，它是將接受的脈沖電信號處理轉換成數(shù)值，為編輯做準備。編輯就是分析這些數(shù)值，計算出需要制動壓力。如果檢測出車輪即將抱死，電控裝置就會計算出數(shù)值向調節(jié)裝置發(fā)出指令。當接受到電子控制裝置的指令后，液壓執(zhí)行裝置會調節(jié)制動輪缸的液壓的大小。調節(jié)裝置能保持或減小來自制動主缸的液壓，而裝置本身是不能啟用制動器的。這種裝置有三個高速率的電磁閥，兩個油液存儲器和一個帶有內外檢測閥的傳動泵。調節(jié)裝置中的電子連接器隱藏在塑料蓋下。每個電磁閥都是其獨立控制的，并作用于前輪。后部的制動輪缸受到一個電磁閥控制，并依照------的原理進行調節(jié)。當防抱死制動系統(tǒng)運行時，電子控制裝置會使電磁閥循環(huán)運作，這樣既能收回又能釋放制動器的壓力。當壓力釋放時，它會釋放到液壓單元。前部的制動器電路有一個單元。存儲器低壓存儲器，它在低壓下存儲油液，直到回流泵打開，油液流經(jīng)制動輪缸進入制動主缸。