Differential car serves only one purpose - to redistribute torque during cornering. At this its useful function, in general, and exhausted. It is clear that the twists in the life of any car is a lot, and throw out a similar mechanism of transmission is not possible. Moreover, to fully replace the rather primitive construction not get nothing, despite the scientific and technological progress, "intelligent all wheel drive", so beloved by advertisers automobile, and a set of electronic "bloat" in the transfer of torque to the wheels. It is known that all genius is simple. And differential genius in its simplicity. Requires no maintenance, and nothing at all, except for lubricants. This site, as a rule, the resource is much greater than your vehicle, ie car, and gets to the landfill is absolutely perfect condition. Consider, of course, the average data. There are people who can "ruin" any mechanism for half an hour, but do not talk about them now. The machine is known, four-wheel drive. Here is where the problems begin. When you rotate each of them is in their radius. If a drive axle, the differential is needed too one - cross-axle, between the driving wheels. If not, the time on the right and left wheel will be the same if needed to pass different distances. Further, the following will occur: either the wheels will slip or break drives that quite likely, given the weight of modern cars. So a set of gears called the differential, promptly throws the excess torque between the wheels, helping to avoid breakdowns and dramatically improved manageability. In the case of permanent four-wheel drive situation is very complicated. To have traction at all wheels, differentials should be three - two interwheel and an inter-axle. Incidentally, the permanent four-wheel drive and just all-wheel drive - two big differences, "as they say in Odessa. The vast majority of cars, proudly calling themselves the all-wheel drive, in fact, these are very big stretch. In normal situations, the drive is carried out on one axis, the second connects automatically when the slips are either manually by the driver. Permanent 4WD is different from the plug in only one - the presence in the construction of a center differential. If not, there is no permanent 4WD, despite what the salesman in the showroom. Of course, he can "kerf" four-wheel drive on the Nissan Patrol, for example, and take a ride around the dealership because of its technical ignorance or hoping that such a short distance does not happen. But to repeat such a car with a hard-plug bridge not advise it. If a second axis involves electronics (Volkswagen Tiguan, for example), then in the AWD mode, the drive is still only one bridge, the transfer time is carried out only when slippage of driving wheels. There is also a full-fledged four-wheel drive cars, but not so much - "Americans" with "razdatkoy» Selec Trac, Mitsubishi Pajero, the new Pajero Sport with Super Select, Toyota Land Cruiser, our "Niva", etc. It is impossible not to recall the brand of Subaru. True, and they began to cheat by setting to be combined with automatic transmission system with active torque distribution. Well before the Tribeca has not yet arrived, but the Impreza and Forester center differential is eliminated. Pluses differentials understood and cons? There are downsides, and the lot. First of all, the differential is much worse patency. If one wheel on ice, it will rotate, as is the case with a 2WD and c 4WD with three free differentials. Imagine the scene: four-wheel drive car sits on the ground, one wheel on ice, and can not budge. Unsurprisingly, all three differentials working, throwing time at the least loaded direction. However, there is such a thing as a lock, which helps in situations like this: lock inter-axle - is transmitted to both axles, but if the stall three differentials, "row" will have all four wheels, regardless of any off-road or on ice. Even at the professional off-road, as a rule, all three locks are not available, then put them in the aftermarket shops engaged in the preparation for serious off-road SUVs. Permanent 4WD is necessary in one case - for powerful sports cars. Vehicle is moving due to friction forces. If the friction on two wheels a little, why not use the other two? Controllability of the car with all-wheel drive also improves significantly. What would make for a more intense crackdown, cross-country, especially without straining the driver switch modes? There are similar developments, and they are called limited slip differential. The principle is simple. If the ordinary differential spur gear, the self-locking or helical or spiral. For what? When the difference between the moments at the wheels in the helical / helical gearing arises axial force presses the ends of the gears to the housing, forcing the latter to rotate. Blocking is not complete, but the effect is noticeable. There is still such a thing as blocking factor - the greater the slope of the teeth, the higher the axial component and, accordingly, the final effect. Design features would be nice to commensurate with the final destination of the vehicle, you must understand, "best is the enemy of the good, the differential high-gain control of the machine will lock some unusual and often unpredictable. I note that such decisions are not purely tuning designs, they are often offered as standard equipment or factory option on the off-known manufacturers (on the same Land Cruiser). There is another partial blocking scheme implemented by viscous coupling. Then uses the physical properties of silicone substance - the viscosity increases of temperature, loss of efficiency differential with a big difference in angular velocities. Here are just a similar design are very fond of the company's engineers Subaru. But this, of course, not all. Much has been done clever inventors, to at least partially neutralize the disadvantages when operating conventional differential. Another design - LSD (Limited Slip Differential) with friction clutches. Traction Control is struggling with the shortcomings in his own way - stalled wheel brakes, throwing the moment so the opposite. They say the future of electronics. Maybe it is certainly true, but to get rid of the planetary gear in the transmission, called a differential, yet still can not.
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