The 4 wheel drive technology
The 4-wheel drive in the vehicles become more and more popular. The Offroad or SUV segment is at present the one with increasing sales figures. That is reason of enough for me to explain and to compare the products and to clarify the many terms. SUV, the term stands for sport utility vehicle and is mentioned as much as "vehicle for sport purposes". The craziest thing I ever seen is the AWD (All Wheel Drive) System for bikes and Motorcycles of christini.com. Important to all readers of this content: All names and terms used here may is a trademark of the respective manufacturers or owners. I use it for the better description. If the respective name owner should not agree with it, please contact me and ask for clarifying.
The following text is applicable naturally also to 6x6 and 8x8 vehicles. But those ones are usually heavy duty trucks with dual tire and - in the case of the 8x8 - with two steering axles in front. This would blow up the framework here. I remain with the passenger cars only.
Differences
There are at least two technologies today available: The permanently or full-time-4WD and the insertable 4WD.
Insertable 4WD
Vehicles with insertable 4WD operates with power to one axle. The second axle can be connected with a clutch rigidly to the transmission outlet of the transfer case (e.g. OPEL Frontera, Isuzu Trooper, Suzuki SJ410, Fiat Panda 4x4 Sisley, Mercedes G (only series 460/461), Nissan Patrol GR, Toyota Landcruiser HDJ 73 and 80 and - the classic 4WD car of a new european member: Lada Niva). In connected 4WD-mode there is no reconciliation between both axles. Exception Mercedes G460 with limited revs reconciliation. Now each ABS system is out of operation . The major reason is that the rear wheels and rear axle turns in a curve not often as the front wheels axle and front axle.
The advantage of this system is the handling during the predominant driving condition, because the driver a normal powered car, front axle powered or rear axle powered. This 4WD system is designed for really offroad use only.
Full Time 4WD
Vehicles with full time 4WD have a differential in the transfer case for number of revolutions reconciliation between front axle and rear axle. Mostly it is designed in a identical fashion with the differential in the rear axle and in the front axle or it is designed as a planetary gear. Now a ABS system will work properly (e.g. Mercedes G (only series 463), Range Rover, VOLKSWAGEN 4Motion, BMW X5/ix, Mercedes 4Matic (2.Generation). and M-class, Subaru (all models), AUDI Quattro, Volvo XC90, VOLKSWAGEN Touareg, Porsche Cayenne). Unfortunately this number of revolutions reconciliation between the axles takes place also whenever you need it or not. Indeed on snow-smooth, frozen roadway when a wheel lost ground contact. A differential works in principle always. The advantage of the full time 4WD system is, that the "normal" drive will be simulated. All non-offroader and normal-bleached will be happa to get the feeling of a normal powered car. If ou want to use cars with such a 4WD system, you will need a traction assistance. Otherwise the full motor power will be lost on a wheel wich stays on slippery ground or do not touch the ground anymore..
Traction Controls
There are a lot of possibilities to inactivate the function of the diff. The easyiest way is to slow down the opposite wheel using the brake system. The advantage is, that you do not need any additional material, so it is cheap. According to experience this technology will help help to get traction enough to drive on. If this system starts working, the driver will be informed in his display. Another method is to use for example a Torsen diff.
This diff is designed to put the most torque to that wheel, which has the most grip. This is of cause a great idea, but the activity of this diff is not displayed, so the driver do not know how critical the situation really is. As additional traction control system there are diff - locks. Please look downwards for more informations.
Physical unchangeable params
1. Anyway - Whatever you prefer. The major thing is to do something to put your wheels to where the grip is: To the ground! The second reason to have a look to that major thing is the vehicle weight. If the whole weight rests up at least 3 wheels, the weight per wheel raises up to 33% . This is more worse, if the ground is very soft after for example long period of rain..
2. Try not to stop the car. A very good help for not stopping is a automatic transmission. The gearbox switches between the gears without interrupting the torque, and more, the torque is tuned up to 4 times higher.
Tips for all those, who seems that this is not enough traction offroad
The very best construction for driving off road is using fix axles with coil springs. With this combination all your wheels will permanently touch the ground. The great manufacturer Jeep (Wrangler, Rubicon ) proves it day for day.
Diff Locks
Last but not least take a look at diff-locks. Diff-locks connect both wheels on one axle. The left and the right wheels turn same speed. The result is, that the car only is able to drive straight on, but all wheels are powered by the full motor power.
Lots of cars for the european market are manufactured in Austria . They are pioneers in 4 wheel technology. Ok, now I told you the differences about the available technologys. What kind of 4WD you have or need please refer to your manual.
Content, translation and Copyright: Bernd Marscheider, Bremen