发布时间 : 星期二 文章A340E自动变速器实验台说明书更新完毕开始阅读
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How Automatic Transmissions Work
If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and a manual transmission:
1.There is no clutch pedal in an automatic transmission car.
2.There is no gear shift in an automatic transmission car. Once you put the transmission into drive, everything else is automatic.
Both the automatic transmission (plus its Torque converter) and a manual transmission (with its clutch) accomplish exactly the same thing, but they do it in totally different ways. It turns out that the way an automatic transmission does it is absolutely amazing!
In this article, we'll work our way through an automatic transmission. We'll start with the key to the whole system: planetary gearsets. Then we'll see how the transmission is put together, learn how the controls work and discuss some of the intricacies involved in controlling a transmission.
Just like that of a manual transmission, the automatic transmission's primary job is to allow the engine to operate in its narrow range of speeds while providing a wide range of output speeds.
Without a transmission, cars would be limited to one gear ratio, and that ratio would have to be selected to allow the car to travel at the desired top speed. If you wanted a top speed of 80 mph, then the gear ratio would be similar to third gear in most manual transmission cars.
You've probably never tried driving a manual transmission car using only third gear. If you did, you'd quickly find out that you had almost no acceleration when starting out, and at high speeds, the engine would be screaming along near the red-line[15]. A car like this would wear out very quickly and would be nearly undriveable.
The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission, the same set of gears produces all of the different gear ratios. The planetary gearset is the device that makes this possible in an automatic transmission.
Let's take a look at how the planetary gearset works.
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When you take apart and look inside an automatic transmission, you find a huge assortment of parts in a fairly small space. Among other things, you see:
1.An ingenious planetary gearset 2.A set of bands to lock parts of a gearset
3.A set of three wet-plate clutches to lock other parts of the gearset 4.An incredibly odd hydraulic system that controls the clutches and bands 5.A large gear pump to move transmission fluid around
The center of attention is the planetary gearset. About the size of a cantaloupe, this one part creates all of the different gear ratios that the transmission can produce. Everything else in the transmission is there to help the planetary gearset do its thing. This amazing piece of gearing has appeared on HowStuffWorks before. You may recognize it from the electric screwdriver article. An automatic transmission contains two complete planetary gearsets folded together into one component. See How Gear Ratios Work for an introduction to planetary gearsets.
Any planetary gearset has three main components: 1.The sun gear
2.The planet gears and the planet gears' carrier 3.The ring gear
Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset.
So this one set of gears can produce all of these different gear ratios without having to engage or disengage any other gears[16]. With two of these gearsets in a row, we can get the four forward gears and one reverse gear our transmission needs. We'll put the two sets of gears together in the next section.
Automatic transmission is through a variety of hydraulic multi-plate clutch and brake to limit or group of planetary gear connected to some of the different gears of the transmission ratio. So good shift quality with the clutch and brake are directly related. Block times based on different vehicle, for cost considerations, economic Model of the automatic transmission control agencies are usually very simple design.
Braking through brake restrictions brought about by the movement of planetary gear. Braking with the lever quickly, driven by tight package was braking gear or shaft, thereby creating a powerful braking force of the planetary gear restrictions to meet the purpose of movement. Lever is driven directly by the mandrel, the mandrel and from the hydraulic power. Planetary gear so completely by the hydraulic braking to decide. With this brake design, structure is very simple, low cost, commonly used in the Economic Model of the automatic transmission which. However, due to a very abrupt braking with brake, braking
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force to a very fierce, so a relatively large shift shock. Car in the high block rarely use this design. High block with a lot of cars is a multi-plate clutch-brake design.
Servo-type brake lever with automatic transmission system is the most commonly used brake institutions. Restrictions brought about by planetary gear brake movement. Braking with the lever quickly, driven by tight package was braking gear or shaft, thereby creating a powerful braking force of the planetary gear restrictions to meet the purpose of movement. Lever is driven directly by the mandrel, the mandrel and from the hydraulic power. Planetary gear so completely by the hydraulic braking to decide. With this brake design, structure is very simple, low cost, commonly used in the Economic Model of the automatic transmission which. However, due to a very abrupt braking with brake, braking force to a very fierce, so a relatively large shift shock. Car in the high block rarely use this design, high block with the larger vehicles is a multi-plate clutch-brake design.
If you have read about manual trasmission,you know that an engine is connected to a transmission by way of a clutch. Without this connection, a car would not be able to come to a complete stop without killing the engine. But cars with an automatic transmission have no clutch that disconnects the transmission from the engine. Instead, they use an amazing device called a torque converter. It may not look like much, but there are some very interesting things going on inside.
In this article, we'll learn why automatic transmission cars need a torque converter, how a torque converter works and what some of its benefits and shortcomings are.
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
As shown in the figure below, there are four components inside the very strong housing of the torque converter: Pump，Turbine ，Stator and 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
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converter are attached to the housing, so they also turn at the same speed as the engine.
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.
In addition to motor vehicle can not turn off the engine stopped, the torque converter in the car started to speed up a matter of fact, when greater torque output. Modern torque converter to the engine torque two to three times to enlarge. When the engine speed faster than the gearbox to the torque converter when the engine can be larger than the output torque to the.
High-speed, the transmission speed of the engine gradually catch up with the speed. The ultimate speed of the two very close. Of course the best is the same speed because they are so different, there is energy loss. That is why the autopilot to manual cars fuel consumption than one of the reasons why.
To solve this problem, some car has a torque converter clutch locking. Torque converter when the speed is similar to the two halves, the locking clutch just linking them, so there is no sliding between them to improve the transmission efficiency.
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