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1、UNIT 11 SUSPENSION AND STEERING SYSTEMS TEXT C Wheel Alignment,PROFESSIONAL ENGLISH,TEXT A Wheel Alignment Alignment Measurement Values Front Wheel Alignment Adjustments Rear Wheel Alignment Adjustments Alignment Equipment,本次课学习内容,本次课学习目标,掌握车轮定位的英文专业词汇 训练快速阅读能力，提高阅读速度,NEW WORDS,PHRASES AND EXPRESSIO
2、NS,Wheel Alignment 4 Wheel alignment is the process of measuring and correcting the various angles formed by the front and rear wheels, spindles, and steering arms. Correct alignment is vital. Improper alignment can cause hard steering, pulling to one side, wandering, noise, and rapid tire wear. Typ
3、es of Wheel Alignment 11 Rear-wheel drive vehicles require a two-wheel alignment or front-wheel alignment only. The rear wheels are attached to a solid rear axle assembly which cannot be adjusted, and generally stays in alignment throughout the life of the vehicle. 12 Today, most front-wheel drive v
4、ehicles have provisions for adjusting the rear wheels. In addition, many rear-wheel drive vehicles are equipped with independent rear suspensions, which also must be adjusted. Also, modern solid rear axles and suspension systems are lightweight and can become misaligned. Therefore, the four-wheel al
5、ignment, in which the front and rear wheel alignment angles are checked and adjusted, is commonly performed.,159 Adjustable front wheel settings on most modern vehicles are caster, camber, and toe. Nonadjustable settings are steering axis inclination and toe-out on turns. Rear wheel settings that ca
6、n be made on many modern vehicles are camber and toe. Modern practice is to check both front and rear wheel alignment. Note that the various alignment angles are all related. A change in one can alter the others. Alignment Measurement Values 14 All alignment values, except for toe, are measured in d
7、egrees. Toe is measured in fractions of an inch or millimeters. Caster 15 Positive caster tends to force the wheels to travel in a straight ahead position. It also assists in recovery (wheels turning back to straight ahead position) after making a turn. On late model cars, there is often little or n
8、o positive caster. Positive caster makes it more difficult to turn the wheels from the straight ahead position than when no caster angle is present 1.,17 Another aspect of positive caster is a mild tipping effect when cornering. When making a right turn, the right wheel will cause the steering knuck
9、le to raise slightly, while the left wheel will allow the knuckle to lower, creating the tipping effect. If the left side of the vehicle was allowed to rise during a right turn, it would have an adverse effect on the vehicles cornering ability. 18 To ease turning, many cars employ a negative caster
10、angle, which angles the top of the steering knuckle to front of car. This will ease steering while also causing the mild tipping effect needed when cornering. Camber 19 Camber is the tilting of the wheel centerline, viewed from the front of the vehicle, away from a true vertical line. Camber angles
11、are usually small, usually no more than 1 positive or negative from zero. An incorrect camber setting will cause pulling and tire wear.,Steering Axis Inclination 42 The steering knuckle ball joints are closer together at the top than the bottom. The steering axis (view from the front of the car) pla
12、ces the centerline of the steering ball joints closer to the centerline of the wheel. This angle is known as steering axis inclination, or SAI. 43 When the wheel centerline is to the outside of the center line of the steering axis (where they intersect the road), the wheels tend to toe-out. This is
13、caused by the road-tire resistance pushing back on the spindle, causing it to swivel backward on the ball joints or toe-out. When the centerline of the wheel intersects the road at a point inside of the steering axis centerline intersection, the wheels tend to toe-in (tires are closer together in th
14、e front than in the back).,Toe 45 Toe is the relative positions of the front and rear of a tire in relation to the other tire on the axle. Note that distance at the back of the tires is greater than distance in the front. Rear-wheel drive vehicles are toed in to compensate for the natural tendency o
15、f the road-to-tire friction to force the wheels apart. 46 On some front-wheel drive vehicles, the front tires are toed out. This is done to offset the force created by the drive axles, which tend to pull the tires inward during operation. The toe setting compensates for this and allows the front tir
16、es to run parallel to one another while rolling straight down the road. 47 Toe compensates for the wheel movement tendencies plus any wear or play in the steering linkage. Proper toe will allow the tires to move forward without a scrubbing, scraping action between the tire and road. Excessive toe conditions will cause a rapid tire wear condition called feathering. Toe can also be adjusted on most vehicles to set the steering wheel in the centered position when driving stra
