Most of the development went into traditional 4x4 systems until
the field was blown wide open with the racing dominance of rally
racing by Audi, did you notice a flurry of development by everyone.
About that time, if not earlier, we started to have different types
of 4x4 categories
Part time 4x4
full time 4x4
All wheel drive
Real time 4x4
Let us look at the basics
A basic 4x4 system has 2 axles connected by driveshafts to a transfercase.
This transfer case, when applied splits the torque of the engine equally
between the front and rear axles. the axles use a diffrential to split the torque
betwwen the 2 wheels in a ratio as needed by terrain. The Transfer Case can
have differnt speeds or ranges in it used to multiply the torque delivered to it
Different kinds of 4x4 systems are made for on road or off road reasons
Lets look at the differences
Real time 4x4 is a system that works like all wheel drive, but it uses
the computer to tell it when to switch. it uses a transfer case with no
low range to transfer between axles and is normally a 2 wheel dive style
vehicle with the ability to transfer the torque to any wheel the computer
says needs traction. It works quite well but is basically a on road system
All Wheel drive, while working much the same as a real time 4x4 system is normally
controlled mechanically. The results are impressive, Audi's Quattro's are
outlawed in Rally racing. This system is usually biased in the transfer case
as in a 40/60% split front to rear and has great highway capabilities
Snow, no problem, Rain is a breeze, but there is no lowrange.
Full Time 4x4 takes a system such as All Wheel drive and adds a low range
to it in the transfer case, these systems are getting better all the time and
many of the traditional harder core vehicles are coming with a version of
this as an option. It in many ways gives you the best of both worlds
Both a all wheel drive, then a locked center diff in 4 high, and then a
low range for true torque multiplication in the dirt.
Part Time 4x4 is the off road enthusiast long time friend.
No center differential, but a transfer case that splits the torque
evenly. And then a low range in the transfer case. It usually has,
but not always, a stronger components than a full time system,
and Has been the main stay of off roading for many a decade.
I hope this explains a lot of the differences
I did not want to go deep into the details but to clear up a lot of the
Questions. After all technology is charging on all the time.
and what is the norm now, will get fogged up real soon