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1、车辆动力学基础(1)1.外倾角(Camber Angle)从车头望向车轮,车轮与铅垂线的夹角称为外倾角，若轮胎上端向外倾斜即左右 轮呈V形，称为正外倾角，向内倾斜为负外倾角。基本上，正外顷角的设定有较 佳的灵活度，而负外顷角具较稳定的直进性。Center Line of CarVerticalPDsitiveC-ambrrd eg al ive Camber2.Pointed the Right Waystory by john hagermanCamber, Caster and Toe: What Do They Mean?The three major alignment paramet
2、ers （定位参数）on a car are toe （前束角，从上 往下看），camber （外倾角，从前往后看），and caster （后倾角，主销）.Most enthusiasts （爱好者）have a good understanding of what these settings are and what they involve, but many may not know why a particular setting is called for, or how it affects performance. Lets take a quick look at this
3、 basic aspect of suspension tuning（悬架校准）.UNDERSTANDING TOEWhen a pair of wheels is set so that their leading edges （前边缘）are pointed slightly towards each other （略微相向放置），the wheel pair is said to have toe-in （前轮内 倾）.If the leading edges point away from each other （背向放置），the pair is said to have toe-o
4、ut （前轮外倾）.The amount of toe can be expressed in degrees as the angle to which the wheels are out of parallel （两轮不平行的角度），or more commonly, as the difference between the track widths （轮距）as measured at the leading and trailing edges of the tires or wheels. Toe settings affect three major areas of perf
5、ormance: tire wear （轮胎磨损），straight-line stability （直线行驶稳定性）and corner entry handling characteristics （转弯操纵特性）.For minimum tire wear and power loss （功率损耗），the wheels on a given axle of a car should point directly ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the
6、 tires to scrub （摩擦），since they are always turned relative to the direction of travel. Too much toe-in causes accelerated wear at the outboard （夕卜 侧） edges of the tires, while too much toe-out causes wear at the inboard （内侧） edges.Toe-inToe-outSo if minimum tire wear and power loss are achieved with
7、 zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms （作用原理）involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Un
8、der this condition, the wheels are at odds with each other, and no turn results.When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If its a minor disturbance （小幅
9、度的外界扰动），the disturbed wheel will steer only a small amount, perhaps so that its rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still dont describe a turn. The wheels have absorbed the irregularity （凹凸路 面的干扰）without s
10、ignificantly changing the direction of the vehicle （显著地改变 车辆行驶方向）.In this way, toe-in enhances straight-line stability （前轮前束增强 车辆直线行驶稳定性）.If the car is set up with toe-out, however, the front wheels are aligned （对齐的）so that slight disturbances cause the wheel pair to assume （保证）rolling directions th
11、at do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius （转弯半径）than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So its clear that t
12、oe-out encourages the initiation of a turn, while toe-in discourages it （前轮后束会造成转向过大，而前轮前束会造成转向不 足）.With toe-in （left） a deflection of the suspension does not cause the wheels to initiate a turn as with toe-out （right）.The toe setting on a particular car becomes a tradeoff （折中）between the straight-l
13、ine stability afforded by toe-in （前束保证直线行驶稳定性）and the quick steering response promoted by toe-out （后束保证转向灵敏性）.Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stabi
14、lity on the straightaway for a sharper turn-in to the corners. So street cars （公共汽车）are generally set up with toe-in, while race cars （赛车） are often set up with toe-out.With four-wheel independent suspension （四驱独立悬架），the toe must also be set at the rear of the car. Toe settings at the rear have esse
15、ntially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are oft
16、en set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This i
