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1、外文资料外文资料1TransmissionsTransmissions have to compromise on either ride comfort or efficiency, but a new approach to the dog engagement gearbox could improve both.With tightening emissions regulations, carmakers are not just confining their efforts to improving combustion and after-treatment. Many are
2、 finding that modern engines are so advanced that the benefits of some engine technologies are small compared to the huge development costs involved.Its important to look at the whole vehicle in order to improve emissions. As the second most expensive piece of kit in the car, the transmission is the
3、 logical next place to look.Of all transmission technologies, the manual gearbox is the most efficient; around 96percent of the energy that is put in comes out of the other end. But not everyone can drive one or wants to. Because you have to dip the clutch pedal, its less comfortable to drive in hea
4、vy traffic. It makes the driver tired and the torque interruptions head-nod effect on passengers can be wearing.The drivers clutch control and corresponding torque interruptions are also the manuals weak point. When accelerating up through the gearbox, each up-shift requires the driver to cut the to
5、rque momentarily by lifting the gas pedal and dipping the clutch. It may just take a second to complete the operation, but during this time the vehicle is losing speed and acceleration.At the opposite and of the spectrum is the traditional automatic. Its shift quality is good thanks to its torque co
6、nverter, but efficiency is relatively poor despite recent advances. Because of this ,a lot of the current research is trying to find an efficient alternative to the conventional automatic.The main technologies are continuously variable transmissions (CVTs); dual clutch transmissions(DCTs) and automa
7、ted manual transmissions(AMTs).They all offer different benefits over the conventional planetary automatic.The CVT uses a belt chain or toroidal shaped dish drive to vary an infinite number of gear ratios. It has improved efficiency and cost when compared to conventional automatics.Its advantage com
8、es from its simplicitu. It consists of very few components; usually a rubber or metal-link belt; a hydraulically operated driving pulley, a mechanical torque-sensing driving pulley, microprocessors and some sensors.The transmissions works by varying the distance between the faces of the two main pul
9、leys.The pulleys have V-shaped grooves in which the connecting belt rides. One side of the pulley is fixed axially; the other side moves, actuated by hydraulics.When actuatec, the cylinder can increase or reduce the amount of space between the two sides of the pulley. This allows the belt to ride lo
10、wer or higher along the walls of the pulley, depending on driving conditions. This changes the gear ratio. A torodial-type design works in a similar way but runs on discs and power-rollers.The “stepless“ nature of its design is CVTs biggest draw for automotive engineers. Because of this, a CVT can w
11、ork to keep the engine in its optimum power range, thereby increasing efficiency and mileage. A CVT can convert every point on the 外文资料外文资料2engines operating curve to a corresponding point on its own operating curve.The transmission is most popular with Japanese carmakers and Japanese supplier JATCO
12、 is a major producer. But in the US and Europe driving styles are different. Uptake has been slow despite Audi and other manufacturers having offered CVT otions on their ranges.The DCT is, in effect, two manual gearboxes coupled together. Gear shifts are made by switching from one clutch on one gear
13、box to another clutch on the other. The shift quality is equal to a conventional automatic, but slip, fluid drag and lydraulic losses in the system result in only slightly improved efficiency and acceleration over the conventional planetary automatic. Developing the control strategy is costly too.“R
14、ecent advances in conventional automatic technology have weakened the argument to develop and set up production for CVT or DCT.“ says Bill Martin, managing director of transmission firm zeroshift. “Some carmakers have cancelled DCT projects because of the cost.“ The cheapest way to build an automati
15、c is with an AMT. AMTs use actuators to replace the clutch pedal and gear stick of a conventional manual. They keep the high efficiency and acceleration of a manual gearbox, but the shift quality on some models is lacking. Torque interruptions and the head-nod effect are the most common complaint.so
16、 what is the alternative? There are always new ideas in transmissions, but Zeroshift says that its technology has efficiency benefits over a manual, delivering fuel economy improvements to city driving. Shift quality can also be equal to that of a refined automatic.Zeroshifts approach is an upgrade to the AMT. The synchromesh is replaced with an advanced dog enqaqement system. Dog engagement has been used for many years in motor sport t
