Not sure where the 100% FWD information came from, but it's wrong. I thought the AWD system was fully activated when the front tires slip, not so....
http://forum.mazda6tech.com/about4221.html
It is controlled by the AWD CM (control module)
Some snipets from the docs:
- Based on a signal from the AWD CM, it operates the electromagnetic clutch and transmits drive torque to the rear wheels.
- When the AWD solenoid control current is OFF, no torque is generated in the pilot clutch because there is no current folowing to the AWD solenoid.
- When starting off or accelerating during straight-ahead driving, torque transmitted to the rear wheels is optimally controlled to ensure sufficient acceleration performance.
- If a parking brake signal input to the AWD CM indicates, the module controls the torque transmitted to the rear wheels.
- When the AWD CM determines, based on the four-wheel signal and steering wheel angle signal, that the vehicle is in tight cornering, it reduces the torque transmitted to the rear wheels to avoid tigh corner braking characteristics.
So, I must conclude that the AWD is 50/50 under most conditions, since it
reduces torque to rear wheels when tight cornering.
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This is a rather far fetched conclusion from the given information. If the torque distro was 50/50 most of the time you would not be able to steer the car. The only way you can have 50/50 distribution all the time while still retaining independent wheel rotation is with a center diff. An electromagnetic coupling is unable to produce this torque distribution under normal driving conditions without drivetrain binding.
This is the reason why it must reduce torque to the rear wheels, in order to steer.
http://forum.mazda6club.com/index.php?showtopic=53530#7
previous explaination here...
It would take me forever to explain but it has been discussed before. I am well aware and have researched the basics of how a haldex system works and its shortcomings. If you have time to read the entire thread...
You will find that what I have stated is 100 percent true in order for a haldex system to work.
The basic shortcoming of haldex comes from the reason why cars need differentials in the first place...
http://forum.mazda6club.com/index.php?show...=50136&st=0
If all the tyres are the same diameter, how can the rear's possibly be moving (assume you mean rotating) slower than the front's?
When a car is turning the outside wheels have farther to travel and rotate faster than the inside wheels. Thats the only time wheels of the same diameter on the same car rotate at different rates, with the exception of power spin/brake slip.
And where do you get "the sharper the turn the less AWD"? Do you own a speed6, have you even driven one through all configurations? Or do you just read too much?
Lets get something straight, front wheel spin is not a prerequisite for transfering torque to the rear wheels. The system is active, not reactive. Given the type of driving I do my rear wheels are alive almost all of the time.
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Powering out of a turn if the haldex ever attempts to go full lock you will loop the car because it tries to sync the front and rear wheels together. Without diffrerentials the wheels cannot spin independently while still delivering power. Any amount of haldex lock will impart a syncing effect on the front and rear set of wheels which are spinning at diffrent rates.
All this more agressive haldex software is great... but the last place I want the haldex to lock up is when agressively powering out of an increasing radius turn causing me to completely loose it when my rear wheels which are spinning slower than the front wheels mid turn decide to match each other in speed at the limits of adhesion.
The more it locks the more it tries to sync the drivetrain together and force wheels spinning at diffrent rates to spin at the same rate. To prevent this it has to decouple partially if the computer detects a change in steering input. In performance situations, ie corner exit, hairpins, sweepers, it takes away AWD when you need it the most.
By definitition it can never be rear biased its just a clutchpack that takes power from the front and attempts to couple the front and rear wheels together.
Haldex can be defined as an automaticly acting part-time AWD system since it lacks a center diffrential.
To answer your question....
Visual aids...
Only when going straight all four wheels are turning at the same speed rate.
As soon as a turn is initiated all four wheels will rotate at different rates since each of them follows a different imaginary circle.
This is what happens during a turn:
The inside wheels will rotate with less rpm than the outside wheels.
The differential on the rear axle guarantees that the rpm delivered via drive shaft from the transfer case are distributed to the left and right wheel as needed. Meaning equal rpm when traveling straight - less rpm to the inside wheel and more rpm to the outside wheel when in a turn.
The differential of the front axle does exactly the same thing.
The axle differentials take care of the need for different wheel rpm.
Interestingly enough during a turn the front axle needs more rpm than the rear axle. Here is why:
The front inside wheel will need more rpm than the rear inside wheel.
The front outside wheel will need more rpm than the rear outside wheel.
This means that the front wheels need more rpm than the rear wheels in a turn
When you add the rpm of front wheels (A+B) you will find that the number is higher than the combined rpm of the rear wheels (C+D).
Unlike full time AWD with a differential - Part time "active" AWD is not able to accomodate the need for different axle speeds because it uses a Coupling or a PTU. To allow rotation the PTU must DECOUPLE reducing the amount of power delivered to the rear wheels.
Full time systems allow all 4 tires to push or pull at maximum rate. In part time active AWD this is not the case.