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Acura's SH AWD is excellent in the snow/ice. Torque vectoring can help in many situations. It handles very well even for a fwd based system.
funny you bring this up, i too remember seeing this clip back when the MDX really was (in my view) king of the midsize luxury 3 row suv market, which is why i was quite surprised when i got my mom's 2016 MDX stuck in some mild snow the other night
i eventually got it out but in the process just about every single warning light came on (transmission problem, adaptive cruise control problem, SH-AWD problem, braking system problem, FCW problem)
the car actually wouldn't let me put it into P, have really any power at all... i had to turn it off and back on again before it would even let me select a gear! and i was literally just defending the capable AWD system of the MDX to my friend who had just scoffed at it...
I think this video was what I was referring to as part of the issue with AWD systems. Its basically a system that experiments in low friction environments.Loss of traction takes a bit of time to register to the system. Whereas an full time 4wd system, forward momentum is always available
Originally Posted by Stroock639
funny you bring this up, i too remember seeing this clip back when the MDX really was (in my view) king of the midsize luxury 3 row suv market, which is why i was quite surprised when i got my mom's 2016 MDX stuck in some mild snow the other night
i eventually got it out but in the process just about every single warning light came on (transmission problem, adaptive cruise control problem, SH-AWD problem, braking system problem, FCW problem)
the car actually wouldn't let me put it into P, have really any power at all... i had to turn it off and back on again before it would even let me select a gear! and i was literally just defending the capable AWD system of the MDX to my friend who had just scoffed at it...
There must have been something wrong with that mdx or it needed a software update, I have driven them in worse conditions then that and it worked fine.
I think this video was what I was referring to as part of the issue with AWD systems. Its basically a system that experiments in low friction environments.Loss of traction takes a bit of time to register to the system. Whereas an full time 4wd system, forward momentum is always available
Of course but I heard Quattro engineer saying their system response time is in Nano-second range. I thought it was typo for milli-second range but Nono is correct.
I think this video was what I was referring to as part of the issue with AWD systems. Its basically a system that experiments in low friction environments.Loss of traction takes a bit of time to register to the system. Whereas an full time 4wd system, forward momentum is always available
Full time 4wd is usually referred to as AWD, and 4wd is usually part time.
Of course but I heard Quattro engineer saying their system response time is in Nano-second range. I thought it was typo for milli-second range but Nono is correct.
Nothing mechanical (at least not at the scale of a driveline) happens in nanoseconds.
It can, with electro-magnetic clutches. And electric cars with individual electric motors at each wheel also can do it.
Nope. The clutch can energize and create a magnetic field almost instantaneously, but the mechanical work it needs to do takes time.
Elements of EM
Both EM clutches and brakes share basic structural components: a coil in a shell, also referred to as a field; a hub; and an armature. A clutch also has a rotor, which connects to the moving part of the machine, such as a driveshaft.
The coil shell is usually carbon steel, which combines strength with magnetic properties. Copper wire forms the coil, although sometimes aluminum is used. A bobbin or epoxy adhesive holds the coil in the shell.
Activating the unit’s electric circuit energizes the coil. The current running through the coil generates a magnetic field. When magnetic flux overcomes the air gap between the armature and field, magnetic attraction pulls the armature — which connects to the hub — into contact with the rotor.
Magnetic and friction forces accelerate the armature and hub to match rotor speed. The rotor and armature slip past each other for the first 0.02 to 1.0 sec until the input and output speeds are the same. The matching of speeds is sometimes called 100% lockup.
Now the acceleration/deceleration process can be sped up somewhat by greatly increasing the voltage, a process called overexitation:
To speed responses, some EM clutches and brakes use overexcitation. The unit’s power supply gives the coil a burst of voltage significantly higher than its nominal rating for a few milliseconds. Higher voltage lets the coil generate a more-powerful magnetic field more quickly, starting the process of attracting the armature and accelerating or decelerating the load.
Three times the rated voltage typically gives around one-third faster response. Overexcitation of 15 times the normal coil voltage produces responses three times faster. For instance, a clutch coil rated for 6 V should be overexcited to 90 V to cut response time to one-third of the original.
Once overexcitation is no longer needed, the power supply returns to its normal operating voltage. Overexcitation can be repeated as needed, but the high-voltage bursts must be short enough that they do not overheat the coil.
The bottom line is, anything that involves changing the speed or torque delivery of something with significant inertia does not happen in nanoseconds. Force can certainly be applied that quickly, as in the case of EM clutches. But overcoming inertia still takes at least milliseconds.
Yes and no. It depends on how the center-differential and torque-management is set up....and whether power flows to all four wheels, all of the time, or whether it goes to the two primary drive-wheels, and shifts to the other wheels only when the primary wheels spin.
Yes and no. It depends on how the center-differential and torque-management is set up....and whether power flows to all four wheels, all of the time, or whether it goes to the two primary drive-wheels, and shifts to the other wheels only when the primary wheels spin.
mmarshall, it does not depend, they are not the same. Do not spread false information. A full time 4WD and part time 4WD have a transfer case that can lock in addition to a LO gear. These Subaru's do not. And for the record, full time 4WD is determined because it has a LO range gear and a center lock diff. None of these AWD set ups have it. The Escalade once had AWD with no LO gear, it was always referred to as AWD, typically GM cost cutting. No center lock either.
Last edited by Toys4RJill; Jan 13, 2018 at 08:49 AM.
mmarshall, it does not depend, they are not the same. A full time 4WD and part time 4WD have a transfer case that can lock. These Subaru's do not. And for the record, full time 4WD is determined because it has a LO range gear and a center lock diff. None of these AWD set ups have it. The Escalade once had AWD with no LO gear, it was always referred to as AWD, typically GM cost cutting.
Thank you, Jill, but I'm aware of how Subaru AWD is set up. I owned one for six years. You're arguing semantics....AWD is a particular type of full-time 4WD, but you're correct that it lacks the transfer case and low-range (which is primarily used for off-roading). And, no, Subaru AWD systems usually don't have a differential lock...but other car-based systems sometimes do. The car-based AWD Mazda Protege sedan, for example (now out of production) has a locking differential. So do most small car-based SUVs like my brother's Kia Sportage....even though it lacks a low-range.
i'll leave this here, he does a pretty good job of explaining the difference. didn't think there was still this much of a debate between the two systems
