doingaytaingo 14 Tháng bảy 2007 - #1 LESSON 1 (Lượt xem: 877) Lesson 01: <span style="font-size:14pt;line-height:100%">The Automobile </span> The earliest automobiles consisted of carriages to which a primitive engine and drivetrain and steering controls were added. Typically, such cars had a strong steel frame that supported the body of the car. The wheels were attached to this frame by a set of springs and shock absorber that permitted the car to travel over the uneven road surfaces. This same general configuration persisted in most passenger cars until some time after World War II, although there was an evolution in car size, shape, and features as technology permitted. This early configuration is depicted in Figure 1, in which many of the important automotive systems are illustrated. These system include the following: 1. Engine 2. Drivetrain (transmission, differential, axle) 3. Suspension 4. Steering 5. Brakes 6. Instrumentation 7. Electrical/Electronic equipment 8. Motion control 9. Comfort/ convenience 10. Entertainment/communication/navigation In Figure 1 the frame or chassis on which the body is mounted is supported by the suspension system. The wheels’ brakes are connected to the opposite end of the suspension components. The steering and the other major mechanical systems are mounted on one of these components and attached as necessary through mechanical components to other subsystems. This basic vehicle configuration was used from the earliest car through the late 1960s or 1970s, with some notable exceptions. The increasing importance of fuel efficiency and government mandated safety regulations led to major changes in vehicle design. The body and frame evolved into an integrated structure to which the power train, suspension, wheels, etc., were attached. Once again with a few notable exceptions, most cars had an engine in front configuration with the drive axle at the rear. While it is an advantage for several reasons (crash protection, efficient engine cooling) to have the engine in front, this location has a disadvantage from a traction standpoint. Because the engine is a relatively heavy component, its location influences weight distribution. Ideally, the engine should be located near the driver wheels for optimal drive traction. It is this fact that has led car makes to configure the font wheels as drive wheels. This change has led to the engine being mounted transversely (i.e., with the rotation axis orthogonal to the vehicle axis as opposed to along the vehicle axis). The transmission is mounted adjacent to the engine and oriented with its axis parallel to the engine axis. The differential and drive axle configuration is normally mounted in the transmission; the combined unit is thus called the transaxle. For stability purposes the steering is still via the front wheels. The combination of steering and drive mechanisms results in a somewhat more complicated front – wheel system configuration than the traditional orientation.