发布时间 : 星期四 文章01M自动变速器电液控制系统原理设计 - 图文更新完毕开始阅读
天津工程师范学院2009届本科生毕业设计
英文资料及翻译：
Automatic transmission
The modern automatic transmission is by far，the most complicated mechanical component in today’s automobile．Automatic transmissions contain mechanical systems，hydraulic systems，electrical systems and computer controls，all working together in perfect harmony which goes virtually unnoticed until there is a problem．This article will help you understand the concepts behind what goes on inside these technological marvels and what goes into repairing them when they fail．
1 What is a transmission
The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels．An automobile engine runs at its best at a certain RPM(Revolutions Per Minute)range and it is the transmission’s job to make sure that the power is delivered to the wheels while keeping the engine within that range．It does this through various gear combinations．In first gear，the engine turns much faster in relation to the drive wheels，while in high gear the engine is loafing even though the car may be going in excess of 70 MPH．In addition to the various forward gears，a transmission also has a neutral position which disconnects the engine from the drive wheels，and reverse，which causes the drive wheels to turn in the opposite direction allowing you to back up．Finally，there is the Park position．In this position，a latch mechanism(like a deadbolt lock on a door)is inserted into a slot in the output shaft to lock the drive wheels and keep them from turning，thereby preventing the vehicle from rolling．
The modern automatic transmission consists of many components and systems that are designed to work together in a symphony of clever mechanical，hydraulic and electrical technology that has evolved over the years into what many mechanically inclined individuals consider to be an art form．We try to use simple，generic explanations where possible to describe these systems，but due to the complexity of some of these components，you may have to use some mental gymnastics to visualize their operation．
2 The main components that make up an automatic transmission include
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天津工程师范学院2009届本科生毕业设计
2．1 Planetary Gear Sets
Automatic transmissions contain many gears in various combinations．In a manual transmission，gears slide along shafts as you move the shift lever from one position to another，engaging various sized gears as required in order to provide the correct gear ratio．In an automatic transmission，however，the gears are never physically moved and are always engaged to the same gears．This is accomplished through the use of planetary gear sets．
The basic planetary gear set consists of a sun gear，a ring gear and two or more planet gears，all remaining in constant mesh．The planet gears are connected to each other through a common carrier which allows the gears to spin on shafts called “pinions’’ which are attached to the carrier．
One example of the way that this system can be used is by connecting the ring gear to the input shaft coming from the engine，connecting the planet carrier to the output shaft，and locking the sun gear so that it can’t move．In this scenario，when we turn the ring gear．the planets will “walk” along the sun gear(which is held stationary) causing the planet carrier to turn the output shaft in the same direction as the input shaft but at a slower speed causing gear reduction(similar to a car in first gear)．
If we unlock the sun gear and lock any two elements together，this will cause all three elements to turn at the same speed so that the output shaft will turn at the same rate of speed as the input shaft．This is like a car that is in third or high gear．Another way that we can use a Planetary gear set is by locking the planet carrier from moving，then applying power to the ring gear which will cause the sun gear to turn in the opposite direction giving us reverse gear．
Many more combinations are possible using two or more planetary sets connected in various ways to provide the different forward speeds and reverse that are found in modern automatic transmissions．
Some of the clever gear arrangements found in now ，four and five-speed automatics are complex enough to make a technically astute lay person’s head spin trying to understand the flow of power through the transmission as it shifts from first gear through top gear as the vehicle accelerates to highway speed．On newer vehicles，the vehicle’s computer monitors and controls these shifts so that they are almost imperceptible． 2．2 Clutch Packs
A clutch pack consists of alternating disks that fit inside a clutch drum．Half of the
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天津工程师范学院2009届本科生毕业设计
disks are steel and have splines that fit into groves on the inside of the drum．The other half have a friction material bonded to their surface and have splines on the inside edge that fit groves on the outer surface of the adjoining hub．There is a piston inside the drum that is activated by oil pressure at the appropriate time to squeeze the clutch pack together so that the two components become locked and turn as one． 2．3 One-Way Clutch
A one-way clutch(also known as a “sprang” clutch) is a device that will allow a component such as ring gear to turn freely in one direction but not in the other．This effect is just like that of a bicycle，where the pedals will turn the wheel when pedaling forward．but will spin free when pedaling backward．
A common place where a one-way clutch is used is in first gear when the shifter is in the drive position．When you begin to accelerate from a stop，the transmission starts out in first gear．But have you ever noticed what happens if you release the gas while it is still in first gear? The vehicle continues to coast as if you were in neutral．Now．shift into Low gear instead of Drive．When you let the gas in this case go of，you will feel the engine slow you down just like a standard shift car．The reason for this is that in Drive，a one-way clutch is used ，whereas in Low，a clutch pack or a band is used． 2．4 Bands
A band is a steel strap with friction material bonded to the inside surface．One end is anchored against the transmission case while the other end is connected to the appropriate time． Hydraulic oil is sent to the servo under pressure to tighten the band around the drum to stop it from turning． 2．5 Torque Converter
On automatic transmissions，the torque converter takes the place of the clutch found on standard shift vehicles．It is that to allow the engine to continue running when the vehicle comes to a stop．The principle of a torque converter is like taking a fan that is plugged into the wall and blowing air into another fan which is unplugged．If you grab the blade on the unplugged fan，you are able to hold it from turning but as soon as you let go，it will begin to speed up until it comes close to the speed of the powered fan．The difference with a torque converter is that instead of using air，it uses oil or transmission fluid， to be more precise．
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天津工程师范学院2009届本科生毕业设计
A torque converter is a large doughnut shaped device(“10 to 15” in diameter)that is mounted between the engine and the transmission．It consists of three internal elements that work together to transmit power to the transmission．The three elements of the torque converter are the Pump，the Turbine，and the Stator．The pump is mounted directly to the converter housing which in turn is bolted directly to the engine’s crankshaft and turns at engine speed．The turbine is inside the housing and is connected directly to the input shaft of the transmission providing power to move the vehicle．The stator is mounted to a one-way clutch so that it can spin freely in one direction but not in the other．Each of the three elements have fins mounted in them to precisely direct the flow of oil through the converter．
With the engine running，transmission fluid is pulled into the pump section and is pushed outward by centrifugal force until it reaches the turbine section which starts it turning．The fluid continues in a circular motion back towards the center of the turbine where it enters the stator．If the turbine is moving considerably slower than the pump，the fluid will make contact with the front of the stator fins which push the stator into the one way clutch and prevent it from turning．With the stator stopped，the fluid is directed by the stator fins to re-enter the pump at a “helping” angle providing a torque increase．As the speed of the turbine catches up with the pump，the fluid starts hitting the stator blades on the backside causing the stator to turn in the same direction as the pump and turbine．As the speed increases，all three elements begin to turn at approximately the same speed．
Since the 80’s，in order to improve fuel economy，torque converters have been equipped with a lockup clutch，which locks the turbine to the pump as the vehicle speed reaches approximately 45-50 MPH．This lockup is controlled by computer and usually won’t engage unless the transmission is in 3 rd or 4th gear． 2．6 Hydraulic System
The hydraulic system is a complex maze of passages and tubes that sends transmission fluid under pressure to all parts of the transmission and torque converter．Transmission fluid serves a number of purposes including：shift control，general lubrication and transmission cooling．Unlike the engine，which uses oil primarily for lubrication，every aspect of a transmission’s functions are dependant on a constant supply of fluid under pressure．This is not unlike the human circulatory system (the fluid is red blood) where even a few minutes of operation when there is a lack of pressure can be harmful or even fatal to the life of the transmission．In order to keep the transmission at normal operating
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