4WD/AWD some basic idea

HRU · 发表于 2008-11-25 13:17

I saw some discussions about the drive-train of a SUV or a Truck or evan a cross over.

I hereby cite some idea that comes from Land Rover manufacture about the 4WD and AWD

A. 4WD system

4WD (4-Wheel-Drive) is a traditional way to manage complicated road conditons. In 4WD system, there are 2 sub-type 4WD.

1. Part Time 4WD The drive mode is decided by drive by a transfercase selector (Butoons or lever). Driver will decide 2WD or 4WD. This is very traditional way on trucks and SUVs. The problem of this system is that 4WD is not good for dry road, otherwise you might damage the driving train. However, switch the 2WD and 4WD is always doubtful for some drivers because they do not know the exact chance to switch. For this reason, some trucks add a hybrid way with AUTO model, detecting the slips for the wheel and then engage into 4WD system to solve this uncertainty.

2. Full time 4WD The 4WD is always engaged no matter what road condition is. BMW/Mercedes/Audi/SAAB actually are all this group to maximaze the driving safty and plesure. Some of them are very sophiscated that can make a vehicle 1+1+1+1 driving mode to maximaze the traction in difficult and assure the corner manner.

AWD system is a automatic switching system, it is actually a 4WD system as well but the computer decides when shift the power to the other axis. (Subaru is a special one claim itself a AWD actually it is a full time 4WD system with or without LSD)

HIGH_LOW lock tranfer case

Some SUVs equipt with HIGH-LOW case selector to handle the extra off road capacity. Low range can increase the torque at low speed locking the wheel. (two wheels spin at the same speed which is not good for normal driving when cornering)

It does not matter for most drivers if a car or SUV is a 4WD or AWD. (you won't feel it) unless it is a parttime 4WD without AUTO mode. This means drive such car (SUV) nees driver's judgement to switch.

For the industries common sense, the MB/BMW/Audi driving system (full time 4WD) are the best becuase they are smart 1+1+1+1 mode (not traditional 2+2). A good all weather car or SUV not neccessary gets a differential locking in system.

chevyli · 发表于 2013-5-23 21:08

kingkang · 发表于 2013-7-3 22:12

ttcv4 · 发表于 2014-3-27 09:11

MingJ · 发表于 2014-3-28 21:28

"The problem of this system is that 4WD is not good for dry road, otherwise you might damage the driving train."
这根本就不是个问题，我开PT 4WD都块10年了。在一般路面根本就不需要四驱，何来问题？偶尔就算不小心挂在4-Hi，短时间行驶不会对drive train有什么损坏，及时切回2wd，找个地倒车开几十米，齿轮箱里的应力就释放了。现在用PT 4WD加auto mode各种路况适用性就更好了。

HRU · 发表于 2014-3-29 19:29

Part Time 4WD surely has some risk when you are driving in a mountain territory where the weather and road conditions change unexpectedly.

I was driving to Vancouver in January with 2WD on a good road passing Jasper. But suddenly, the truck lost traction and swirled to the opposite lane. I was lucky calmly regained the control. After that, I always engage into 4WD high when drive in an unfamiliar area with cautions especially in rocky mountain.

Driving a full time 4WD is always the best choice.

红绿灯 · 发表于 2014-5-11 09:28

littlefish2011 · 发表于 2014-5-13 14:50

Xuxualin · 发表于 2014-6-5 15:29

missile · 发表于 2014-6-21 10:39

AWD省心，适合初级平时开city，有打滑时全靠电脑来调节。
4WD放心，适合老手有时开off road，看路况和天气提前做好准备开四驱，不受电脑控制。
两种类型各有市场，不过好像没有pickup是AWD的，为什么，不解释。

卫子夫 · 发表于 2014-11-17 21:16

xvxvalin · 发表于 2014-12-24 20:16

heibais · 发表于 2015-1-29 11:37

小鸟依人 · 发表于 2015-3-27 18:13

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小鸟依人 · 发表于 2015-3-27 18:15

小鸟依人 · 发表于 2015-3-27 18:15

小鸟依人 · 发表于 2015-3-27 18:15

小鸟依人 · 发表于 2015-3-27 18:15

cdt · 发表于 2015-3-27 22:07

nmz · 发表于 2015-3-27 22:12

nmz · 发表于 2015-3-27 22:12

newelec · 发表于 2015-3-28 07:35

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