主题：【原创】试驾森林人 -- 虎头

LSD是differential的一种,放到中间就是central diff了。central diff可以是LSD, 也可以是open diff。LSD也分好多，有机械式的（clutch pack,torsen:audi quattro）,粘性式的，现在还有电子控制的。 现在的广为流行的电控半时四驱（类似haldex系统），基于电控clutch pack没有central diff， 机械上称为耦合器coupler。 这个haldex的链接你看一下，前几页能看懂的话就全明白了 http://www.billswebspace.com/HALDEX.pdf

看不明白的话（可以理解，明白的话你也不会和我争了），建议您找本齿轮设计的书瞧一瞧，就明白很多东西，至少不容易犯基本错误了...还有我给你的连接，你看这一段，我给你摘出来了，讲的再清楚不过了：

AT: No center diff. Front axle is directly driven by engine, as in a

FWD car. The automated clutch pack allows the rear axle to be driven in

addition, when appropriate. Torque is diverted to the back in certain

circumstances, e.g., under acceleration, but the system lacks the array

of sensors that more advanced AWD technologies offer. It is somewhat

proactive in the sense that the rear may be (partially) locked to the

front before any slippage occurs. However, the clutchpack operates

almost in an on-off mode, with 90:10(*) being the default (almost FWD).

As a result, the AT has a bit more understeer in corners. Also, on

very slippery roads you may feel the rear kick in every-so-often, rather

than being active all the time, which some drivers have described as

unsettling.

MT: Has a real center diff. The viscous coupling connects the two

output shafts of the differential. Normally, torque distribution is

50:50 like with a traditional open diff. Thus, this car has more

neutral handling during cornering. When slippage occurs, the viscous

fluid thickens and the diff becomes almost locked. This system is

reactive in the sense that some slippage must occur before the diff

locks. On the other hand, the system starts out with 50:50, so you are

less likely to get into trouble in the first place. Also, the slippage

required for the viscous coupling to activate is minimal - it does not

require wheel spin per se, just a difference in the rate of rotation

between the axles. Moreover, on very slippery roads the viscous

coupling will be almost continuously active, so it feels almost like a

4WD vehicle, then.

All in all, I think both systems are pretty good. Many drivers will not

be able to tell much of a difference between the two AWD systems.

Handling may be more affected by your tire pressure and pressure ratio

between front and back, or the diameter of your anti-sway bars, if you

change them. I think most people decide between the two based on other

reasons, whether they do a lot of stop-and-go commute or towing (AT) or

like a little extra performance/ power (MT).