1、翻译原文 624 Race Car Vehicle Dynamics Besides providing linear motion the restraint device must provide lateral force reactionsbetween the sprung and unsprung masses. In so doing it is most desirable that the forcesare transmitted only in a purely lateral sense, with no vertical component. For example,
2、if a Panhard bar (track bar) is utilized, the slope of the bar in the rear view dictates the force coupling. If it is horizontal the coupling is zero. If it is sloped the coupling willeither lift the sprung mass or pull it down depending on the direction of cornering and theslope of the bar. Some co
3、nsiderations in the design of a track bar include whether it isnormally in tension or compression. For circle track racing, always turning left means that the bar should be attached to the body on the right side and to the axle on the left assuring that it is always in tension when cornering. The pa
4、ir of arms, the A-arm, and the sliding pin tend to have very low vertical-lateralcoupling. The Panhard bar and theWatts linkage will always have some, but with attentionto detail it can be minimized. This coupling effect must be controlled as much aspossble because it tends to vary with the ride hei
5、ght and roll angle positions ofthe suspenson. By keeping the angle small, the changes will be small and the effect minimized. 17.5 Front Suspensions lntroduction Many types offront suspensions have been used over the years. They include variousbeam type axles with steering via kingpins at each end o
6、f the axle, the parallel trailingarm type such as the VW, the Morgan sliding pillar type, and the Chevrolet Dubonnet.In recent history, passenger car designs have come down to basically two types: the MacPherson Strut and the SLA (Short-Long-Arm). This chapter will deal only with the last two mentio
7、ned as these make up the majority offront suspensions that will be encountered. The other types suffer from either high bendingloads, poor geometry, high friction， or a combination ofthese problems. The bestway to discuss each type is to go through the design process step by step. For each step a de
8、cision has to be made that is often a compromise. By discussing these decisions, hopefullya feeling for the limitations of the design will develop. FrontSuspension Design lssues-General The frist task in designing a front suspension of any type is to establish the packaging parameters that are fixed
9、， or absolutely cannot be changed for whatever reason (see Figure17.17). These should be listed so that they are not overlooked. The next task is to package the wheel, tire, brakes, and bearings. This is done in car position, so the track widthhas to be known. If it is not yet established, it should
10、 be made as wide as practical. Thissounds evasive, but there are trade-offs in everything, even things as simple as choosingthe track width. For example, what do the rules allow? What is the predominant race track type on which the car will run? Is top speed, thus low frontal area important? Areslow
11、-speed tight street circuits of concern? All these issues can affect the decision on thebasic track width! Tire size and rim diameter and width must be settled. The specific wheel manufacturerneeds to be known and a cross section ofthe wheel is desirable for optimizing the use ofthat wheel. Tire siz
12、es are usually limited by the sanctioning body rules. In general, useallthe tire they will Iet you get away with. Another point is to always design for the latest sizes being developed by the suppliers； this guarantees that the latest compounds andconstructions will fit your car. Remember, the tire
13、is the single most important chassiscomponent on the car. The wheel offset is worked out in conjunction with fitting the brake caliper to clear theinside surface of the wheel. Once the caliper is located, this automatically locates thebrake rotor. With the rotor location comes the absolute farthest
14、outboard location for thelower balljoint. Wheel bearings need to be looked at soon, as ideally they should belocated such that the tire center is between the two rows ofballs or rollers (to minimizeloads on the bearings). Now that the lower ball joint cross car boundary (lateral position) has been s
15、et, the heightofthe lower balljoint comes next. In production cars it must be above a 5-in. wash rackclearance requirement, but on race cars it should be made as low as possible for structuralreasons. Usually there is no rule but some practical considerations such as deflatedtire ground clearance mi
16、ght be in order. If it is totally inside the wheel all it has to do isclear the wheel and the brake rotor under all travel and load conditions. The decision about the kingpin angle in the front view is the next order ofbusiness. Theissues here become scrub radius, spindle length, and kingpin angle.
17、They are interrelatedand a compromise is needed. If you want a certain scrub radius you now have two pointsestablished, i.e., the lower balljoint and the ground contact point ofthe kingpin (set bythe scrub radius)-一 the kingpin angle becomes fixed automatically. Ifyou want a certainkingpin angle the
18、n the scrub radius will not necessarily be what you want. Basically, onrear-wheel-drive cars push the lower ball joint out as far as possible and run a fairly lowkingpin angle, less than 80 , and accept the scrub radius that results. Ifyou are dealingwith afront-wheel-drive car you must minimize the
19、 spindle length and have a negativescrub radius. This may result in a kingpin angle as high as 160 , but you will have to acceptit or find another clever way around it. Kingpin ang1e affects the performance of the car when the wheels are steered. One conceptthat should be understood is that the more
20、 the kingpin angle the more the car is liftedwhen it is steered. This is one source of steering returnability, the weight of the car returnsthe steering to center. The amount the car is lifted is also a function of the spindlelength where a longer spindle means more lift. The camber of the wheels wh
21、en steered is a function of the kingpin angle and the casterangle. With no kingpin angle (and no caster angle) there is no camber change with steerlock. As kingpin is added (but stillno caster) the wheel willlose camber with steerlock, or in other words it will change in a direction giving positive
22、camber on the outside wheel.60 As caster is added this modifies the effect ofkingpin. With positive caster andno kingpin angle, the whee1 gains negative camber on the outside wheel and positivecamber on the inside wheel. Thus caster can add favorable camber angle to the effects ofkingpin angle. In o
23、ther words, the reason that low kingpin angles are desirable is thatkingpin angle subtracts from the negative camber gain due to caster on the outside wheel. The decision on a rack location depends on several packaging factors such as engine location and orientation， front-wheel drive vs. rear-wheel
24、 drive, whether it is to be high- orlow-mounted, etc. In addition there are performance reasons for choosing the rack location. First we must assume that every structure is a spring and should be treated as such.As an example the rack mounting stiffness versus the upper or lower control arm mounting
25、stiffness to the chassis will not necessarily be the same. Therefore, when a corneringforce is applied, any difference in the lateral displacement of the ball joints in relation to the tie rod outer pivot willcause a steer angle. To assure stability it is better to have lateralforce deflection toe-o
26、ut (lateral force understeer) rather than toe-in. We can assurethat this happens by the proper location of the rack. If a high-mounted rack is required itmust be behind wheel center and if it is low-mounted then it must be ahead of wheel center as shown by the shaded areas in Figure 17.17. Structura
27、l requirements for the suspension design must always be considered when packagingeach element ofthe total system. Control arms that have one leg straight acrossfromthe ball joint are superior in system stiffness to arms that are splayed. Establishinglinkage ratios for the spring, shock, and stabilizer bar as close to 1: 1 as possible will providemore direct load paths thus improving system stiffness
