1、 附录 B 翻译资料 Automatic Transmissions The modern automatic transmission is by far, the most complicated mechanical component in todays automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony whi
2、ch goes virtually unnoticed until there is a problem. This article will help you understand the concepts behind what goes on inside these technological marvels This article is broken down into two sections: What is a transmissionbreaks down in the simplest terms what the purpose of a transmission is
3、. Transmission Componentsdescribes the general principals behind each system in simple terms to help you understand how an automatic transmission works. 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 w
4、heels. An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmissions 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 tu
5、rns 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
6、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 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. Th
7、ere are two basic types of automatic transmissions based on whether the vehicle is rear wheel drive or front wheel drive. On a rear wheel drive car, the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal pos
8、ition. A drive shaft connects the rear of the transmission to the final drive which is located in the rear axle and is used to send power to the rear wheels. Power flow on this system is simple and straight forward going from the engine, through the torque converter, then through the transmission an
9、d drive shaft until it reaches the final drive where it is split and sent to the two rear wheels. On a front wheel drive car, the transmission is usually combined with the final drive to form what is called a transaxle. The engine on a front wheel drive car is usually mounted sideways in the car wit
10、h the transaxle tucked under it on the side of the engine facing the rear of the car. Front axles are connected directly to the transaxle and provide power to the front wheels. In this example, power flows from the engine, through the torque converter to a large chain that sends the power through a
11、180 degree turn to the transmission that is along side the engine. From there, the power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles. There are a number of other arrangements including front drive vehicles where the
12、 engine is mounted front to back instead of sideways and there are other systems that drive all four wheels but the two systems described here are by far the most popular. A much less popular rear drive arrangement has the transmission mounted directly to the final drive at the rear and is connected
13、 by a drive shaft to the torque converter which is still mounted on the engine. This system is found on the new Corvette and is used in order to balance the weight evenly between the front and rear wheels for improved performance and handling. Another rear drive system mounts everything, the engine,
14、 transmission and final drive in the rear. This rear engine arrangement is popular on the Porsche. Transmission Components 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 technol
15、ogy 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 v
16、isualize their operation. The main components that make up an automatic transmission include: Planetary Gear Setswhich are the mechanical systems that provide the various forward gear ratios as well as reverse. The Hydraulic Systemwhich uses a special transmission fluid sent under pressure by an Oil
17、 Pumpthrough the Valve Bodyto control the Clutchesand the Bandsin order to control the planetary gear sets. Seals and Gasketsare used to keep the oil where it is supposed to be and prevent it from leaking out. The Torque Converterwhich acts like a clutch to allow the vehicle to come to a stop in gea
18、r while the engine is still running. The Governorand the Modulatoror Throttle Cable that monitor speed and throttle position in order to determine when to shift. On newer vehicles, shift points are controlled by Computer which directs electrical solenoids to shift oil flow to the appropriate component at the right instant. Planetary Gear Sets
