有D甘嘅事嗎？
lhy92725 發表於 2016-7-3 09:36 AM  
Recovery is Very Difficult, even for a Professional Driver Once a rolling action has begun, everything gets a lot worse, very fast.This drawing shows the situation once a vehicle has tilted only10 degrees sideways. With some soft vehicle suspensions, and under-inflatedtires, this much of a (body roll)tilt is nearly possible while all the wheels are still on the pavement.Let's look at how the forces we have been discussing change.
To start with, this doesn't look all that different.
 But compare thisdrawing with the similar ones above.You can see that the center-of-gravity has gotten a little higher.At a 10° tilt, it is actually raised up by 5.2".And if the tire's low pressure allows it to deform horizontally,then it is less far horizontally from the tire footprint. We willestimate 2". These two effects combine in making that importantθ angle bigger. We would now have (vertical) 30 + 5.2 or 35.2"and (horizontally) 30 - 2 or 28". The tangent is now 35.2/28,or 1.257. Our 3400 pound horizontal centripetal force then wouldhave the effect of 3400 * 1.257 or 4274 pounds of vertical lift!
The (initial) 3400 pound lifting/rolling effect has already gotten FARgreater, above 4200 pounds already. Even worse, there is now no realisticchance of recovery. Where the problem began with a lifting force just alittle more than the vehicle weight, as soon as the vehicle starts tilting,the geometry gets catastrophically worse. An experienced driver would tendto immediately try to straighten the wheels out. In many vehicles, and ifthe driver reacted fast enough, this can resolve the rollover situationsafely. However, the driver had had to steer the vehicle towarda direction that might not be safe or acceptable! He might even thenhave to again make a fast steering change to cause a second startof a rollover. But in tall vehicles such as SUVs, there is a commontendency for a driver to rock the vehicle back the other way (inertia,momentum, etc) (again depending on what obstacles are nearby) and theaction of trying to recover tends to cause even faster steeringactions and therefore can cause theSUV to roll over to the opposite side. So, even experienced drivershave great difficulty in recovering from incipient rolloversin tall vehicles. Imagine a less experienced soccer mom!
FYI: This is why test vehicles always have those "training wheels"arms on them, because once a rollover begins, it gets so much worseso fast that even professional drivers have great difficulty inrecovering.
(Once a rollover has begun, the geometry actually gets even morecomplicated, but always WORSE, involvingthe dynamic rotational inertia of the vehicle and the fact that theeffective weight of the vehicle becomes less (even zero as it crossesabove the tire tread), but this last calculationessentially shows how the problem gets far worse as the rolloverproceeds. These complicating effects all act to make the rollovereffect even worse. All of the earlier "level vehicle"calculations were exactly correct. They represent the mostgenerous analysis regarding stability.) |
發表於 2016-7-2 02:42 PM
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你真以為我可以打中國字?
只是警告你爸下次不要買suv
已經解釋... 
高重心