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1、UNIT 11 SUSPENSION AND STEERING SYSTEMS TEXT A Basic Parts and Types of the Suspension and Steering Systems,PROFESSIONAL ENGLISH,TEXT A Basic Parts and Types of the Suspension and Steering Systems Basic Suspension System Components Types Steering System Steering Gear Power Steering,本次课学习内容,本次课学习目标,掌
2、握转向与悬架系统的英文专业词汇 掌握转向与悬架系统主要类型 训练快速阅读能力，提高阅读速度,NEW WORDS,PHRASES AND EXPRESSIONS,Basic Parts and Types of the Suspension and Steering Systems Suspension System If a vehicles axles were bolted directly to its frame or body, every rough spot in the road would transmit a jarring force throughout the veh
3、icle. Riding would be uncomfortable, and handling at freeway speeds would be impossible. The fact that the modern vehicle rides and handles well is a direct result of a suspension system. Even though the tires and wheels must follow the road contour, the body should be influenced as little as possib
4、le 1. The purpose of any suspension system is to allow the body of the vehicle to travel forward with a minimum amount of up-and-down movement. The suspension should also permit the vehicle to make turns without excessive body roll or tire skidding.,Suspension System Components Vehicle Frame A vehic
5、les frame or body must form a rigid structural foundation and provide solid anchorage points for the suspension system. There are two types of vehicle construction in common use today: body-over-frame construction, which uses a separate steel frame to which the body is bolted at various points and u
6、nibody construction, in which the body sections serve as structural members. Unibody construction is the most common, but body-over-frame construction is still used on pickup trucks and large cars. Springs The springs are the most obvious part of the suspension system. Every vehicle has a spring of
7、some kind between the frame or body and the axles. There are three types of springs in general use today: leaf spring, coil spring, and torsion bar. Two different types of springs can be used on one vehicle. Air springs were once used in place of the other types of springs, but are now obsolete. Man
8、y modern vehicles have air-operated suspensions, but they are used to supplement the springs.,Shock Absorbers When the vehicle is traveling forward on a level surface and the wheels strike a bump, the spring is rapidly compressed (coil springs) or twisted (leaf springs and torsion bars). The spring
9、will attempt to return to its normal loaded length. In so doing, it will rebound, causing the body of the vehicle to be lifted. Since the spring has stored energy, it will rebound past its normal length. The upward movement of the vehicle also assists in rebounding past the springs normal length. Th
10、e weight of the vehicle then pushes the spring down after the spring rebounds. The weight of the vehicle will push the spring down, but since the vehicle is traveling downward, the energy built up by the descending body will push the spring below its normal loaded height. This causes the spring to r
11、ebound again. This process, called spring oscillation, gradually diminishes until the vehicle is finally still. Spring oscillation can affect handling and ride quality and must be controlled.,Air Shock Absorbers Some suspension systems incorporate two adjustable air shock absorbers that are attached
12、 to the rear suspension and connected to an air valve with flexible tubing. Air operated shock absorbers have hydraulic dampening systems which operate in the same manner as those on conventional shocks. In addition, they contain a sealed air chamber, which is acted on by pressure from a height cont
13、rol sensor. Varying the pressure to the air chamber causes the air shock to increase or decrease its length or operating range. Air pressure is delivered to the air shocks through plastic tubing. The tubing connects the shocks to an air valve. Air pressure for raising the shocks is generally obtaine
14、d from an outside source, such as a service station compressor, and is admitted through the air valve. To deplete the shocks of unwanted air (lower vehicle curb height), the air valve core is depressed, allowing air to escape.,Control Arms All vehicles have either control arms or struts to keep the
15、wheel assembly in the proper position. The control arms and struts allow the wheel to move up and down while preventing it from moving in any other direction. The wheel will tend to move in undesirable directions whenever the vehicle is accelerated, braked, or turned. Vehicle suspensions may have co
16、ntrol arms only or a combination of control arms and struts. Types of the Suspension Front Suspension Systems Almost all modern front suspension systems are independent. With an independent suspension, each front wheel is free to move up and down with a minimum effect on the other wheel. In an independent suspension system, there is also far less twisting motion imposed on the frame than in a system with a solid axle. Nevertheless, a few off-road, four wheel drive ve
