600_輕型貨車設計（離合器及操縱機構與傳動軸設計）

600_輕型貨車設計（離合器及操縱機構與傳動軸設計）,輕型,貨車,設計,離合器,操縱,機構,傳動軸 CLUTCH The engine produces the power to drive the vehicle. The drive line or drive train transfers the power of the engine to the wheels. The drive train consists of the parts from the back of the flywheel to the wheels. These parts include the clutch, the transmission, the drive shaft, and the final drive assembly (Figure 8-1). The clutch which includes the flywheel, clutch disc, pressure plate, springs, pressure plate cover and the linkage necessary to operate the clutch is a rotating mechanism between the engine and the transmission (Figure 8-2). It operates through friction which comes from contact between the parts. That is the reason why the clutch is called a friction mechanism. After engagement, the clutch must continue to transmit all the engine torque to the transmission depending on the friction without slippage. The clutch is also used to disengage the engine from the drive train whenever the gears in the transmission are being shifted from one gear ratio to another. To start the engine or shift the gears, the driver has to depress the clutch pedal with the purpose of disengagement the transmission from the engine. At that time, the driven members connected to the transmission input shaft are either stationary or rotating at a speed that is slower or faster than the driving members connected to the engine crankshaft. There is no spring pressure on the clutch assembly parts. So there is no friction between the driving members and driven members. As the driver lets loose the clutch pedal, spring pressure increases on the clutch parts. Friction between the parts also increases. The pressure exerted by the springs on the driven members is controlled by the driver through the clutch pedal and linkage. The positive engagement of the driving and driven members is made possible by the friction between the surfaces of the members. When full spring pressure is applied, the speed of the driving and driven members should be the same. At the moment, the clutch must act as a solid coupling device and transmit all engine power to the transmission, without slipping. However, the transmission should be engaged to the engine gradually in order to operate the car smoothly and minimize torsional shock on the drive train because an engine at idle just develops little power. Otherwise, the driving members are connected with the driven members too quickly and the engine would be stalled. The flywheel is a major part of the clutch. The flywheel mounts to the engine’s crankshaft and transmits engine torque to the clutch assembly. The flywheel, when coupled with the clutch disc and pressure plate makes and breaks the flow of power from the engine to the transmission. The flywheel provides a mounting location for the clutch assembly as well. When the clutch is applied, the flywheel transfers engine torque to the clutch disc. Because of its weight, the flywheel helps to smooth engine operation. The flywheel also has a large ring gear at its outer edge, which engages with a pinion gear on the starter motor during engine cranking. The clutch disc fits between the flywheel and the pressure plate. The clutch disc has a splined hub that fits over splines on the transmission input shaft. A splined hub has grooves that match splines on the shaft. These splines fit in the grooves. Thus, the two parts are held together. However, back-and-forth movement of the disc on the shaft is possible. Attached to the input shaft, At disc turns at the speed of the shaft. The clutch pressure plate is generally made of cast iron. It is round and about the same diameter as the clutch disc. One side of the pressure plate is machined smooth. This side will press the clutch disc facing are against the flywheel. The outer side has various shapes to facilitate attachment of spring and release mechanisms. The two primary types of pressure plate assemblies are coil spring assembly and diaphragm spring (Figure 8-3). In a coil spring clutch the pressure plate is backed by a number of coil springs and housed with them in a pressed-steel cover bolted to the flywheel. The springs push against the cover. Neither the driven plate nor the pressure plate is connected rigidly to the flywheel and both can move either towards it or away. When the clutch pedal is depressed a thrust pad riding on a carbon or ball thrust bearing is forced towards the flywheel. Levers pivoted so that they engage with the thrust pad at one end and the pressure plate at the other end pull the pressure plate back against its springs. This releases pressure on the driven plate disconnecting the gearbox from the engine (Figure 8-4). Diaphragm spring pressure plate assemblies are widely used in most modern cars. The diaphragm spring is a single thin sheet of metal which yields when pressure is applied to it. When pressure is removed the metal springs back to its original shape. The centre portion of the diaphragm spring is slit into numerous fingers that act as release levers. When the clutch assembly rotates with the engine these weights are flung outwards by centrifugal forces and cause the levers to press against the pressure plate. During disengagement of the clutch the fingers are moved forward by the release bearing. The spring pivots over the fulcrum ring and its outer rim moves away from the flywheel. The retracting spring pulls the pressure plate away from the clutch plate thus disengaging the clutch (Figure 8-5). When engaged the release bearing and the fingers of the diaphragm spring move towards the transmission. As the diaphragm pivots over the pivot ring its outer rim forces the pressure plate against the clutch disc so that the clutch plate is engaged to the flywheel. The advantages of a diaphragm type pressure plate assembly are its compactness, lower weight, fewer moving parts, less effort to engage, reduces rotational imbalance by providing a balanced force around the pressure plate and less chances of clutch slippage. The clutch pedal is connected to the disengagement mechanism either by a cable or, more commonly, by a hydraulic system. Either way, pushing the pedal down operates the disengagement mechanism which puts pressure on the fingers of the clutch diaphragm via a release bearing and causes the diaphragm to release the clutch plate. With a hydraulic mechanism, the clutch pedal arm operates a piston in the clutch master cylinder. This forces hydraulic fluid through a pipe to the clutch release cylinder where another piston operates the clutch disengagement mechanism. The alternative is to link the clutch pedal to the disengagement mechanism by a cable. The other parts including the clutch fork, release bearing, bell-housing, bell housing cover, and pilot bushing are needed to couple and uncouple the transmission. The clutch fork, which connects to the linkage, actually operates the clutch. The release bearing fits between the clutch fork and the pressure plate assembly. The bell housing covers the clutch assembly. The bell housing cover fastens to the bottom of the bell housing. This removable cover allows a mechanic to inspect the clutch without removing the transmission and bell housing. A pilot bushing fits into the back of the crankshaft and holds the transmission input shaft. Torque Converter The Basics Just like manual transmission cars, cars with automatic transmissions need a way to let the engine turn while the wheels and gears in the transmission come to a stop. Manual transmission cars use a clutch, which completely disconnects the engine from the transmission. Automatic transmission cars use a torque converter. A torque converter is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. If the engine is turning slowly, such as when the car is idling at a stoplight, the amount of torque passed through the torque converter is very small, so keeping the car still requires only a light pressure on the brake pedal. If you were to step on the gas pedal while the car is stopped, you would have to press harder on the brake to keep the car from moving. This is because when you step on the gas, the engine speeds up and pumps more fluid into the torque converter, causing more torque to be transmitted to the wheels. Inside a Torque Converter There are four components inside the very strong housing of the torque converter: 1. Pump; 2. Turbine; 3. Stator; 4. Transmission fluid. The housing of the torque converter is bolted to the flywheel of the engine, so it turns at whatever speed the engine is running at. The fins that make up the pump of the torque converter are attached to the housing, so they also turn at the same speed as the engine. The cutaway below shows how everything is connected inside the torque converter (Figure 8-6). The pump inside a torque converter is a type of centrifugal pump. As it spins, fluid is flung to the outside, much as the spin cycle of a washing machine flings water and clothes to the outside of the wash tub. As fluid is flung to the outside, a vacuum is created that draws more fluid in at the center. The fluid then enters the blades of the turbine, which is connected to the transmission. The turbine causes the transmission to spin, which basically moves the car. The blades of the turbine are curved. This means that the fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin. The fluid exits the turbine at the center, moving in a different direction than when it entered. The fluid exits the turbine moving opposite the direction that the pump (and engine) is turning. If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator. The stator resides in the very center of the torque converter. Its job is to redirect the fluid returning from the turbine before it hits the pump again. This dramatically increases the efficiency of the torque converter. The stator has a very aggressive blade design that almost completely reverses the direction of the fluid. A one-way clutch (inside the stator) connects the stator to a fixed shaft in the transmission. Because of this arrangement, the stator cannot spin with the fluid - it can spin only in the opposite direction, forcing the fluid to change direction as it hits the stator blades. Something a little bit tricky happens when the car gets moving. There is a point, around 40 mph (64 kph), at which both the pump and the turbine are spinning at almost the same speed (the pump always spins slightly faster). At this point, the fluid returns from the turbine, entering the pump already moving in the same direction as the pump, so the stator is not needed. Even though the turbine changes the direction of the fluid and flings it out the back, the fluid still ends up moving in the direction that the turbine is spinning because the turbine is spinning faster in one direction than the fluid is being pumped in the other direction. If you were standing in the back of a pickup moving at 60 mph, and you threw a ball out the back of that pickup at 40 mph, the ball would still be going forward at 20 mph. This is similar to what happens in the turbine: The fluid is being flung out the back in one direction, but not as fast as it was going to start with in the other direction. At these speeds, the fluid actually strikes the back sides of the stator blades, causing the stator to freewheel on its one-way clutch so it doesn’t hinder the fluid moving through it. Benefits and Weak Points In addition to the very important job of allowing a car come to a complete stop without stalling the engine; the torque converter actually gives the car more torque when you accelerate out of a Stop. Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission. At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions. To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency. 外文資料譯文 離合器 發(fā)動機產生動力用以驅動車輛。動力傳動系將發(fā)動機動力傳到車輪。傳動系由飛輪后端到車輪之間的零件組成。這些零件包括離合器、變速器、傳動軸和減速器總成。 離合器是位于發(fā)動機和變速器之間的一個旋轉裝置，它包括飛輪、離合器（從動盤）磨擦片、壓盤、壓緊彈簧、離合器蓋及操作離合器所需的連接桿件等。它通過零件間的接觸磨擦工作。這是離合器為什么會稱為磨擦機構的原因。離合器接合后，給變速器傳遞所有的發(fā)動機轉矩磨擦沒有打滑。離合器也被用于在變速器傳動比變換時從傳動系中分離發(fā)動機。 為了起動發(fā)動機或換檔，駕駛員必須踩下離合器踏板以便實現(xiàn)變速器和發(fā)動機的分離。在那時，與變速器輸入軸相聯(lián)的離合器從動件可能處于靜止狀態(tài)，也可能以一定的速度旋轉，這一速度可能高于或低于與發(fā)動機相聯(lián)的離合器主動件的旋轉速度。沒有彈簧壓力作用于離合器總成器件上。因此在主動件和從動件之間沒有磨擦。當駕駛員松開離合器踏板時，彈簧對離合件器件壓力增加。各個器件之間的磨擦也會增加。彈簧對從動件所施加的壓力由駕駛員通過離合器踏板和連桿機構來控制。主從動件的有效接合是通過其表面的摩擦來實現(xiàn)的。當彈簧壓力全部應用時，主從動件的轉速是相同的。此時，離合器充當一個剛性連接裝置，沒有滑轉，將發(fā)動機全部功率傳遞給變速器。 但是，為了使汽車操作平穩(wěn)，變速器應該逐漸與發(fā)動機接合，并減小傳動系的扭轉沖擊，因為發(fā)動機空轉時的功率輸出很小。否則，主動件與從動件連接過快，發(fā)動機會停轉。 飛輪是離合器的一個主要部件。飛輪安裝在發(fā)動機的曲軸上，給離合器總成傳遞發(fā)動機轉矩。飛輪與離合器摩擦片和壓盤結合在一起來傳遞或中斷發(fā)動機給變速器的功率流。 飛輪也為離合器總成提供裝配位置。當離合器作用時，飛輪將發(fā)動機轉矩傳遞給離合器從動盤。飛輪重，所以有助于發(fā)動機的運轉平穩(wěn)。飛輪外緣還有一個大齒圈，在起動發(fā)動機時，它與起動機的小齒輪嚙合。 離合器從動盤安裝在飛輪和壓盤之間，有一個花鍵轂套在變速器輸入軸上的花鍵上?；ㄦI轂上的槽與輸入軸上的花鍵配合。花鍵裝配在槽內，因此，兩個零件結合在一起。但是，從動盤可以在軸上前后移動。從動盤連接在輸入軸上，與軸的轉速相同。 離合器壓盤一般由鑄鐵制成。它是圓形，與（離合器）從動盤的直徑相同。壓盤一側被加工平滑。這側會把離合器摩擦襯面壓到飛輪上。外側有各種形狀，以有利于彈簧與分離機構的連接。有兩種主要的壓盤總成分別是螺旋彈簧總成和膜片彈簧總成。 螺旋彈簧離合器中，壓盤背部有許多螺旋彈簧支撐（壓緊），并和它們一起安裝在一個通過螺栓連接到飛輪上的壓制鋼（離合器）蓋中。彈簧推壓離合器蓋。從動盤和壓盤都不是嚴格連接到飛輪上，兩個都可以相對飛輪前后移動。當離合器踏板被踩下時，安放在碳質或滾珠推力軸承上的止推墊被壓向飛輪。分離杠桿（在樞軸上）轉動，使它們能夠與一側的止推墊和另一側的壓盤接合，然后將壓盤拉向彈簧。這會釋放施加在從動盤上的壓力，變速器和發(fā)動機脫離。 現(xiàn)代轎車普遍采用膜片彈簧壓盤總成。膜片彈簧是一個薄金屬片，在壓力作用下會彎曲。當壓力釋放時，這個金屬彈簧會回到原來的形狀。膜片彈簧的中心部分有許多切開的分離指作為分離杠桿。當離合器總成隨著發(fā)動機旋轉時，由于離心力的作用，它們的重量會被甩到膜片彈簧的外緣，從而使分離杠桿對壓盤釋壓。在離合器分離時，分離指在分離軸承作用下向前移動。支撐環(huán)（圈）上的彈簧樞軸和它的外緣從飛輪分離。彈簧收縮將壓盤拉離離合器片，從而將離合器分離。 當離合器結合時，分離軸承和膜片彈簧的分離指向變速器方向移動。當膜片樞軸越過支承環(huán)時，它的外緣將壓盤壓在離合器片上，使離合器片和飛輪接合。 膜片式壓盤總成的優(yōu)點在于它的結構緊湊，重量輕，運動部件少，接合費力?。ㄝp便），通過對壓盤周圍施加的平衡力來減小轉動時的不平衡現(xiàn)象，離合器滑轉率小。 離合器踏板可通過繩索或常見的液壓系統(tǒng)連接到分離機構。無論采用哪種方式，踩下踏板，操縱分離機構，通過分離軸承對離合器膜片彈簧指施加壓力，均可解除膜片彈簧對離合器盤的壓緊。如果帶有液壓機構，由離合器踏板臂來操縱離合器主缸中的活塞，將液壓油通過管道壓入到離合器工作（分離）缸，此后由工作缸中的活塞操縱離合器分離機構。另外一種是由繩索將離合器踏板連接到分離機構的。 其它零部件包括離合器（分離）叉、分離軸承、離合器殼、離合器蓋和導軸襯（套），用來接合和分離變速器。分離叉連接到杠桿機構，實際用來操縱離合器。分離軸承安裝在離合器分離叉和壓盤總成之間。離合器殼用來封閉離合器總成。而離合器蓋固定在離合器殼的底部。這個活動蓋可使技工（維修工）在檢查離合器時不必拆卸變速器和離合器殼。導軸襯安裝在曲軸的后端，用來固定變速器輸入軸。 扭矩變矩器 基礎 就像裝有手動變速器的汽車（有離合器）一樣，裝有自動變速器的汽車需要有一個裝置，使發(fā)動機在車輪和變速器齒輪停止轉動時能繼續(xù)運轉。手動變速器汽車是通過離合器，使變速器完全與發(fā)動機脫離。而自動變速器汽車采用的是液力變矩器（轉矩變換器）。 液力變矩器是一種液力偶合器，它使發(fā)動機的旋轉與變速器基本上不相關。如果發(fā)動機轉動很慢，例如在制動燈亮時汽車怠速行駛，通過液力變矩器傳遞的轉矩很小，所以要使汽車停下來，只需要用很小的力踩制動踏板。 液力偶合器 如果在汽車停止時，踩下加速踏板。就必須用很大的力來踩制動器，使汽車制動。這是因為當你加速時，發(fā)動機轉速增加，泵入液力變矩器的液體量增多，從而使更大的轉矩被傳遞給車輪。 變矩器內部結構 有液力變矩器的堅固外殼內有4個部件：泵輪、渦輪、導輪和傳動液。 液力變矩器的外殼用螺栓固定在發(fā)動機的飛輪上，因此它與發(fā)動機的轉速相同。液力變矩器泵輪葉片連接在外殼上，因此它的轉速與發(fā)動機相同。下面的剖視圖說明了液力變矩器部件在其內部是如何連接的。 液力變矩器內的泵輪是一種離心泵。當它旋轉時，傳動液會被甩到外側，非常像洗衣機的旋轉周期，將水和衣服甩到洗衣桶外側。當傳動液甩向外側時，會在中心產生真空，從而吸入更多的液體。 然后傳動液進入到渦輪葉片中間，葉片與變速器相連。渦輪帶動變速器旋轉，其本質是用來驅動汽車。渦輪的葉片是彎曲的。這說明從外側進入到渦輪中的傳動液在離開渦輪中心之前會改變方向。正是這種方向的改變使渦輪旋轉。 傳動液從渦輪中心流出，流出時的方向與它進入時的方向不同。流出渦輪的液體流動方向與泵輪旋轉方向相反。如果允許傳動液沖擊泵輪，它會使發(fā)動機減速，損耗功率。這就是為什么液力變矩器要有一個導輪的原因。 導輪位于液力變矩器的正中心。它的工作是讓從渦輪返回的液體在它再次沖擊泵輪之前，使其改變方向。這會戲劇性地增加液力變矩器的效率。 導輪葉片具有很強的（侵襲性）主動性，它的方向與傳動液流動方向完全相反。導輪通過單向離合器連接在變速器的固定軸上。因為采用這種布置方式，導輪不會隨著傳動液旋轉，它只能按照與其相反的方向旋轉，從而在傳動液沖擊導輪葉片時強迫其改變方向。 當汽車開始運動時，會有一些棘手的事情發(fā)生。當行駛速度在40英里/時左右時，泵輪和渦輪轉速基本上相同（泵輪總是旋轉的稍快）。此時，從渦輪返回的傳動液流入泵輪時的方向已經與泵輪相同，因此不需要導輪。 盡管渦輪改變傳動液的流動方向，并將它甩到后面，傳動液仍以渦輪旋轉方向始終流動，因為渦輪在一個方向上的旋轉速度大于傳動液從另一方向泵入的速度。如果你站在駛速在60英里/時的皮卡車后面，將一個小球從皮卡后方以40英里/時的速度扔出，這個小球仍會以20英里/時速度前進。這與渦輪相似，傳動液從一個方向甩出時的速度與它在另一個方向上的初始速度不一致。 在這些速度上，傳動液實際上是在沖擊導輪葉片的背面，從而使導輪在單向離合器上空轉，因此不妨礙傳動液從它中間穿過。 優(yōu)缺點 除了在發(fā)動機轉動時，使汽車達到完全停止之外，液力變矩器實際上在加速起動時能給汽車提供更大的轉矩。現(xiàn)代液力變矩器能夠使發(fā)動機的轉矩增大2－3倍。這種效果只在發(fā)動機旋轉速度明顯快于變速器時出現(xiàn)。 在高速運轉時，變速器隨發(fā)動機轉動，最終轉速幾乎相同。雖然在理想情況下，變速器旋轉速度可以與發(fā)動機相同，但由于速度消耗功率，因此實際是不同的。這是為什么裝有自動變速器的汽車比裝有手動變速器的汽車燃油經濟性差的原因之一。 為了使這種結果相反，一些汽車上的液力變矩器帶有鎖止離合器。當液力變矩器的兩半部分達到合適速度時，鎖止離合器將它們鎖在一起來消除滑轉和提高效率。 5