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How Clutches Work
If you drive a manual transmission car, you may be surprised to find out that it has more than one clutch. And it turns out that folks with automatic transmission cars have clutches, too. In fact, there are clutches in many things you probably see or use every day: Many cordless drills have a clutch, chain saws have a centrifugal clutch and even some yo-yos have a clutch.
Clutch Image Gallery
Diagram of car showing clutch location. See more clutch images
In this article, you'll learn why you need a clutch, how the clutch in your car works and find out some interesting, and perhaps surprising, places where clutches can be found.
Clutches are useful in devices that have two rotating shafts. In these devices, one of the shafts is typically driven by a motor or pulley, and the other shaft drives another device. In a drill, for instance, one shaft is driven by a motor and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed, or be decoupled and spin at different speeds.
In a car, you need a clutch because the engine spins all the time, but the car's wheels do not. In order for a car to stop without killing the engine, the wheels need to be disconnected from the engine somehow. The clutch allows us to smoothly engage a spinning engine to a non-spinning transmission by controlling the slippage between them.
To understand how a clutch works, it helps to know a little bit about friction, which is a measure of how hard it is to slide one object over another. Friction is caused by the peaks and valleys that are part of every surface -- even very smooth surfaces still have microscopic peaks and valleys. The larger these peaks and valleys are, the harder it is to slide the object. You can learn more about friction in How Brakes Work.
A clutch works because of friction between a clutch plate and a flywheel. We'll look at how these parts work together in the next section.
Fly Wheels, Clutch Plates and Friction
In a car’s clutch, a flywheel connects to the engine, and a clutch plate connects to the transmission. You can see what this looks like in the figure below.
When your foot is off the pedal, the springs push the pressure plate against the clutch disc, which in turn presses against the flywheel. This locks the engine to the transmission input shaft, causing them to spin at the same speed.
Pressure plate
The amount of force the clutch can hold depends on the friction between the clutch plate and the flywheel, and how much force the spring puts on the pressure plate. The friction force in the clutch works just like the blocks described in the friction section of How Brakes Work, except that the spring presses on the clutch plate instead of weight pressing the block into the ground.
When the clutch pedal is pressed, a cable or hydraulic piston pushes on the release fork, which presses the throw-out bearing against the middle of the diaphragm spring. As the middle of the diaphragm spring is pushed in, a series of pins near the outside of the spring causes the spring to pull the pressure plate away from the clutch disc (see below). This releases the clutch from the spinning engine.
Common Problems
From the 1950s to the 1970s, you could count on getting between 50,000 and 70,000 miles from your car's clutch. Clutches can now last for more than 80,000 miles if you use them gently and maintain them well. If not cared for, clutches can start to break down at 35,000 miles. Trucks that are consistently overloaded or that frequently tow heavy loads can also have problems with relatively new clutches.
Photo courtesy Carolina Mustang
Clutch plate
The clutch only wears while the clutch disc and the flywheel are spinning at different speeds. When they are locked together, the friction material is held tightly against the flywheel, and they spin in sync. It's only when the clutch disc is slipping against the flywheel that wearing occurs. So, if you are the type of driver who slips the clutch a lot, you'll wear out your clutch a lot faster.
Sometimes the problem is not with slipping, but with sticking. If your clutch won't release properly, it will continue to turn the input shaft. This can cause grinding, or completely prevent your car from going into gear. Some common reasons a clutch may stick are:
Broken or stretched clutch cable - The cable needs the right amount of tension to push and pull effectively.
Leaky or defective slave and/or master clutch cylinders - Leaks keep the cylinders from building the necessary amount of pressure.
Air in the hydraulic line - Air affects the hydraulics by taking up space the fluid needs to build pressure.
Misadjusted linkage - When your foot hits the pedal, the linkage transmits the wrong amount of force.
Mismatched clutch components - Not all aftermarket parts work with your clutch.
A "hard" clutch is also a common problem. All clutches require some amount of force to depress fully. If you have to press hard on the pedal, there may be something wrong. Sticking or binding in the pedal linkage, cable, cross shaft, or pivot ball are common causes. Sometimes a blockage or worn seals in the hydraulic system can also cause a hard clutch.
Another problem associated with clutches is a worn throw-out bearing, sometimes called a clutch release bearing. This bearing applies force to the fingers of the spinning pressure plate to release the clutch. If you hear a rumbling sound when the clutch engages, you might have a problem with the throw-out.
Types of Clutches
There are many other types of clutches in your car and in your garage.
An automatic transmission contains several clutches. These clutches engage and disengage various sets of planetary gears. Each clutch is put into motion using pressurized hydraulic fluid. When the pressure drops, springs cause the clutch to release. Evenly spaced ridges, called splines, line the inside and outside of the clutch to lock into the gears and the clutch housing. You can read more about these clutches in How Automatic Transmissions Work.
An air conditioning, compressor in a car has an electromagnetic clutch. This allows the compressor to shut off even while the engine is running. When current flows through a magnetic coil in the clutch, the clutch engages. As soon as the current stops, such as when you turn off your air conditioning, the clutch disengages.
Most cars that have an engine-driven cooling fan have a thermostatically controlled viscous clutch -- the temperature of the fluid actually drives the clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This type of clutch is a lot like the viscous coupling sometimes found in all-wheel drive cars. The fluid in the clutch gets thicker as it heats up, causing the fan to spin faster to catch up with the engine rotation. When the car is cold, the fluid in the clutch remains cold and the fan spins slowly, allowing the engine to quickly warm up to its proper operating temperature.
Many cars have limited slip differentials or viscous couplings, both of which use clutches to help increase traction. When your car turns, one wheel spins faster than the other, which makes the car hard to handle. The slip differential makes up for that with the help of its clutch. When one wheel spins faster than the others, the clutch engages to slow it down and match the other three. Driving over puddles of water or patches of ice can also spin your wheels. You can learn more about differentials and viscous couplings in How Differentials Work.
Gas-powered chain saws and weed eaters have centrifugal clutches, so that the chains or strings can stop spinning without you having to turn off the engine. These clutches work automatically through the use of centrifugal force. The input is connected to the engine crankshaft. The output can drive a chain, belt or shaft. As the rotations per minute increase, weighted arms swing out and force the clutch to engage. Centrifugal clutches are also often found in lawn mowers, go-karts, mopeds and mini-bikes. Even some yo-yos are manufactured with centrifugal clutches.
Clutches are valuable and necessary to a number of applications. For more information on clutches and related topics, check out the links on the following page.
離合器工作原理
如果您駕駛手動變速箱的汽車,您可能會驚訝地發(fā)現(xiàn),它有一個以上的離合器。事實證明,與自動變速器汽車離合器相比,有許多種類離合器在你可能看到或每天使用:許多無繩演習(xí)有離合器,鏈鋸有離心離合器,甚至一些部件也有一個離合器。
Diagram of car showing clutch location. See more clutch images.
在本文中,您會了解為什么你需要一個離合器,在您的汽車離合器工程和一些有趣的發(fā)現(xiàn),也許不足為奇。
離合器是有用的設(shè)備,有兩個旋轉(zhuǎn)軸。在這些設(shè)備中,其中一個軸通常是驅(qū)動馬達(dá)或滑輪,其他軸驅(qū)動其他設(shè)備。例如,一軸驅(qū)動電機(jī)和其他驅(qū)動鉆夾頭。離合器連接從動盤和壓盤,以便它們可以被貼在一起,旋轉(zhuǎn)同樣的速度,或脫鉤,并以不同的速度旋轉(zhuǎn)。
在汽車中,您需要一個離合器,因為發(fā)動機(jī)的轉(zhuǎn)速所有的時間中,但并不是所有的時間都傳遞動力。為了讓汽車停止傳遞動力不造成發(fā)動機(jī)過載,車輪需要斷開發(fā)動機(jī)傳遞動力。離合器使我們能夠順利地進(jìn)行旋轉(zhuǎn)發(fā)動機(jī)的非線性傳遞,通過控制離合器壓盤與摩擦片之間的滑動。
了解離合器的特點,它有助于了解一點摩擦片,這是衡量離合器的標(biāo)準(zhǔn)。摩擦所造成的傳力高峰和低谷的每一部分,每一個平面-甚至是非常平滑的表面仍然有微小的高峰和低谷。這些較大的高峰和低谷,就是摩擦片研究的對象。您可以了解更多關(guān)于離合器如何摩擦工作。
離合器的工作,產(chǎn)生于摩擦離合器壓盤和飛輪。我們將探討如何共同工作,這些零件將在下面介紹。
飛輪,離合器片和摩擦在汽車的離合器,一個飛輪連接到發(fā)動機(jī),離合器踏板連接傳輸。
當(dāng)你的腳離開踏板,彈簧推動壓力板對離合器盤,而這反過來壓力又回位。這種轉(zhuǎn)速控制包括發(fā)動機(jī),變速器輸入軸,使他們自旋同樣的速度。
壓盤
離合器傳遞的動力取決于摩擦離合器盤和飛輪,有多少轉(zhuǎn)矩通過飛輪壓盤傳遞給膜片彈簧。摩擦離合器作用就像描述的摩擦制動器的工作一樣,但彈簧壓力離合器壓盤不是像制動器那樣依靠抱緊制動盤。
當(dāng)離合器踏板被踏下時,機(jī)械或液壓活塞推動撥叉,這些壓力通過分離軸承對中間的膜片彈簧起作用。把膜片彈簧是推離了壓盤的附近達(dá)到讓離合器分離的效果。
請注意彈簧離合器從動盤。這些彈簧有助于緩解傳輸?shù)倪^大動力沖擊離合器盤轂。這種設(shè)計通常非常有效,但它確實有一些缺點。讓我們分別看看離合器問題和其他用途的離合器在以下的內(nèi)容中講解。
從動盤
常見問題:
從20世紀(jì)50年代到20世紀(jì)70年代,你可以指望得到5萬至七萬里程汽車的離合器。離合器現(xiàn)在可以超過去年八點零零零萬英里如果您使用它們輕輕地和維持好。如果不是照顧,離合器就可以開始打破在35000英里??ㄜ囈回灣d或經(jīng)常拖重物,也可以有問題相對較新的離合器。
最常見的問題是,離合器摩擦材料的磨損。摩擦材料在離合器盤非常相似的摩擦材料的墊片的盤式制動器的鼓式制動器-過了一段時間,它磨穿了。當(dāng)大部分或全部的摩擦材料已經(jīng)一去磨損了了,離合器效率將開始下滑,并最終將不會傳送任何轉(zhuǎn)矩從發(fā)動機(jī)到車輪。
離合器只能傳送離合器盤和飛輪的旋轉(zhuǎn)速度不同。當(dāng)他們被鎖在一起,摩擦材料是緊密舉行接合與飛輪,他們自旋同步。只有當(dāng)離合器盤下滑對飛輪的穿著發(fā)生。因此,如果您是一個司機(jī),踩離合器的次數(shù)多,您的離合器磨損快得多。
有時,問題不在于傳遞的摩擦力下滑,但問題是。如果您的離合器裝配不正確,它將繼續(xù)聯(lián)入輸入軸。這可能會導(dǎo)致磨,或完全防止您的車進(jìn)入齒輪。一些常見的原因可能導(dǎo)致離合器出問題:
? 損壞或拉伸離合器拉線-拉線需要適量的張緊力。
? 液壓泵有缺陷/或主離合器液壓瓶-泄漏保持液壓瓶必須建立必要的壓力。
? 空氣中的氣壓線-空氣影響液壓,空氣流體需要建立適當(dāng)壓力。
? 不匹配的離合器組件-并非所有的售后配件與您的離合器能匹配。
“硬”離合器也是一種常見的問題。所有離合器需要一些相應(yīng)的轉(zhuǎn)矩范圍。如果您必須緊逼踏板上,可能會有一些錯誤的。堅持或有約束力的踏板聯(lián)系,電纜,交叉軸或旋轉(zhuǎn)球的常見原因。有時堵塞或磨損在液壓系統(tǒng)也可能導(dǎo)致硬離合器。
另一個問題與離合器是一個破舊投擲出軸承,有時稱為離合器釋放軸承。以手指旋轉(zhuǎn)壓力板松開離合器。如果你聽到隆隆聲時,離合器繼續(xù)接合,您可能有一個問題,間隙沒有調(diào)整好。
離合器診斷試驗
如果您發(fā)現(xiàn)您的離合器已經(jīng)失效,這是一個在家的診斷測試,任何人都可以執(zhí)行:
啟動你的車,設(shè)置停車休息,并把汽車停在原位。
讓您的汽車空轉(zhuǎn),聽取了咆哮的噪音的前提下,如果你聽到離合器有這種聲音,這是最有可能傳輸裝置有問題。如果您沒有聽到噪音,請繼續(xù)執(zhí)行步驟 。
讓汽車仍處于原地,開始推動離合器和聆聽噪音。如果你能聽到一些唧唧噪音,這是最有可能的離合器分離軸承的故障。如果您沒有聽到噪音,請繼續(xù)執(zhí)行步驟 用盡全力推動離合器。如果你聽到尖叫聲的噪音,可能故障出自軸承或套管。
如果你聽不到任何噪音在這四個步驟,那么你的問題可能不是出自離合器。如果你能聽到的噪音,并在停止時消失時,離合器可能的一個問題是離合器的操縱機(jī)構(gòu)出了問題。
在以下的內(nèi)容中,我們會研究一些不同類型的離合器以及他們?nèi)绾问褂谩?
各類離合器:
還有許多其他類型的離合器在并不在您的知識庫。自動變速器包含幾個離合器。這些離合器接觸和脫離接觸的各種成套行星齒輪。每個離合器付諸實施使用加液壓油。當(dāng)壓力下降,彈簧導(dǎo)致離合器分離。間隔均勻的離合器鎖環(huán),稱為樣條線的內(nèi)部和外部的離合器鎖定齒輪和離合器。你可以看到更多關(guān)于這些離合器在自動變速器如何工作。
空調(diào)壓縮機(jī)的汽車有一個電磁離合器。這使得壓縮機(jī)即使在引擎關(guān)閉也能正常運行。當(dāng)電流流經(jīng)磁場線圈的離合器,如當(dāng)您關(guān)閉您的空調(diào),離合器分離。
大多數(shù)汽車的發(fā)動機(jī)驅(qū)動的冷卻風(fēng)扇的溫控粘性離合器-溫度流體實際驅(qū)動離合器。這離合器是處于樞紐的地位,氣流通過散熱器。這種類型的離合器是一種很像粘性聯(lián)軸器,在全輪驅(qū)動汽車經(jīng)常出現(xiàn)。液體離合器較多,因為它熱量大,導(dǎo)致風(fēng)扇旋轉(zhuǎn)的速度要快趕上發(fā)動機(jī)旋轉(zhuǎn)。當(dāng)汽車是冷車時,流體在離合器仍然寒冷,風(fēng)扇轉(zhuǎn)速慢,使發(fā)動機(jī)迅速升溫,以適當(dāng)?shù)牟僮鳒囟取?
許多汽車有限滑差或粘性聯(lián)軸器,兩者都使用離合器,以提高牽引力。當(dāng)您的汽車變成一個車輪轉(zhuǎn)動速度超過了其它車輪時,這使汽車難以應(yīng)付。在防滑差速器以及離合器的幫助下,當(dāng)一個車輪轉(zhuǎn)動速度超過了其它車輪,這樣會使離合器緩慢下來,并符合其它三個車輪的轉(zhuǎn)速。車下有水坑的水或浮動的冰塊也可以讓車輪空轉(zhuǎn)。您可以了解更多關(guān)于差速粘性聯(lián)軸器在如何工作。
天然氣動力鏈鋸離心式離合器,從而使鏈反轉(zhuǎn)可以停止旋轉(zhuǎn),而您不需要關(guān)掉引擎。這些工作自動離合器通過利用離心力。輸入連接到發(fā)動機(jī)曲軸。輸出可以驅(qū)動鏈條,皮帶或骨干。由于輪調(diào),每分鐘增加,逼迫滾珠移出,并迫使離合器進(jìn)行。離心離合器也常常發(fā)現(xiàn)于割草機(jī),卡丁車,輕便摩托車和小型摩托車。甚至一些纜車離心離合器。