4WD systems are usually either part-time or full-time, and include a transfer case (i.e. 2H/4H/4L) comprised of normal running gear and specialized low-range running gear... Usually the low range is on a ratio of 2:1.
Think of it this way: You max out 1st gear at a speed of 40KM/h... In 1st gear low-range, you max out 1st gear at 20KM/h. This allows for more torque at a lower speed, needed when going offroad.
4WD systems are mechanical.

AWD systems are basically just a way of giving all wheels power, be it for more performance, better handling etc.
They do not have a transfer case and are more often than not, full-time systems. The user cannot control them. (In the case of the Kia's, they can however. To some degree.)
AWD systems are usually electronic.

Think of it this way:
Land Rover Defender = Full-time 4WD with transfer case, diff lock, and other offroad things.
Nissan Patrol = Part-time 4WD with all the rest.
Audi TT = AWD
Mitsubishi Lancer = AWD

There are more examples but those are just a few.

 

The line between AWD and 4WD can get murky, and some systems combine both. The general delineator is the low range gearset. AWD does not have a low range, 4WD does. This then leads to the other more generalized differences. 4WD drivetrains are usually much more stoutly built than AWD; AWD drivetrains are usually much lighter. I'll go into the internals of a few of the cases that I'm most familiar with to show the differences.
The GM autotrack transfer case, as found in my Yukon. It is a hybrid of AWD/4WD. It is an electronically actuated transfer case, which has 2WD, 4WD high, 4WD Low, and auto modes. I was going to write up a power transfer chart, but I found this on performancetrucks.net which does a great job:
In the 4HI mode, the power flow to the rear propshaft (10) is the same as it is in the 2HI mode. To deliver power flow to the front propshaft (13) during the 4HI position, the transfer control module commands the encoder motor (15) to apply the clutch to a calibrated torque. The encoder motor (15) turns the control actuator lever shaft (14). A brake in the encoder motor (15) holds the control actuator lever shaft (14) in the full clutch position. The control actuator lever shaft (14) is cam designed and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the clutch lever pivot studs and moves toward the clutch apply plate, to engage the clutch. As more pressure is applied to the clutch apply plate, the clutch discs are compressed. Using inner clutch discs, which are engaged with the clutch hub (5), and the outer clutch discs, which are engaged with the clutch housing (6), the power flow is delivered to the clutch housing (6). The clutch hub (5) is splined to the rear output shaft (9), and the clutch housing (6) rotates on a needle bearing on the rear output shaft (9). The chain drive sprocket (7) is splined to the clutch housing (6). The power flows from the drive sprocket (7), through the chain (11), to the chain driven sprocket. The driven sprocket is splined to the front output shaft (12). The power flow is delivered to the front propshaft (13) through the front output shaft (12).

During the Auto 4WD mode, the power flow is the same as it is in the 4HI mode. Except, during the Auto 4WD mode, the encoder motor (15) rotates the control actuator shaft lever (14) to the correct torque level positions. Rotating the control actuator (14) to the various positions changes the clutch torque level. When a difference of front propshaft (13) to rear propshaft (10) speed is recognized, the transfer case control modules command for more, or less clutch torque.

exploded view of np246 ? - PerformanceTrucks.net Forums

All props to the original poster.

 

Next up is the NV/NVG/NP 249 quadratrack from early jeep grand cherokees. This had 4WD high and 4WD low. This was a true fulltime all wheel drive system. It's greatness was also it's greatest failing, the power transfer through it's viscous coupling.

The Viscous coupling, or VC, is used in many different AWD systems so it deserves a little explanation. the VC is a sealed device with an input and output, either splined or geared. It is closely related to a clutch, in that it is filled with interleaved discs, one set splined to the input and one to the output. The magic is that it's filled with a Non-Newtonian fluid - Wikipedia, the free encyclopedia non-newtonian fluid. Think silly putty. Now imagine that this is sitting between two wheels. If the wheels are spinning the same speed, there is no speed difference between the two halves. If there is a slight speed difference, there is still a small amount of resistance. If one starts to spin relative to the other however, the fluid begins to thicken just like silly putty and it starts to lock the two together, transferring torque between the two. As soon as the speed difference is gone, the fluid goes back to a more fluid state.

Ok, the early 249 had the power go from the transmission to the input of the tcase, then through the chain to the reduction gearset and then the VC. The VC then output to the front and rear driveshafts. The genius in this was that it was all wheel drive, all the time. You could drive around on the street in 4WD low, which is exciting. The failure was that the VC was a wear item, and when it failed would fail either open or closed. If it failed open, then you could spin both front tires or both rear tires, and not transfer any torque to the other axle. This was annoying but preferable to failing closed. When it failed closed, it locked the front and rear axles together, allowing no slippage. This is bad because when you go around a corner, the front wheels travel a further distance than the rear. If you don't allow for that speed difference, it binds the drivetrain and leads to premature tire wear, all manner of strange noises, and can lead to breakage in the drivetrain.

Next up is the 242. This had 2WD, 4WD high, 4WD fulltime, 4WD low. In all modes other than 4WD fulltime it operated as a normal transfer case. In 4wd Fulltime however, instead of locking the front and rear outputs solid, it ran them through an open differential. This acted exactly like the previously mentioned 249 with a VC that has failed open.

Finally is the quadradrive system. This has 4WD and 4WD Low. This is an engineers wet dream, as it is a fully mechanical torque sensing automatic torque transferring drivetrain which can put power wherever it's actually needed and usable. Note that in the other ones I didn't really talk about anything other than the transfer case, as the rest of those systems were just regular axles and differentials. The qdrive however is a complete system. In general, you can think of it as a fulltime system with open differentials, and this is how it acts. However the clever bit is a series of oil pumps and clutch packs. Any pump operates by a speed difference between two items. The qdrive has a pump in each diff (front, center, and rear) which is connected to opposite shafts. Front and rear diffs use the axles, center uses the front and rear driveshafts. The output from each pump is fed to a clutch pack, which also couples each pair of shafts. In operation it acts like this: Imagine the vehicle with three wheels on ice, one on pavement. You apply power, and immediately one rear wheel spins. The spinning causes a speed difference between the two axleshafts, causing the pump to pump fluid. The fluid then locks the clutch pack causing power to be transferred to the other wheel on that axle. It's also on ice, so they both spin. This spinning causes a speed difference between the front and rear driveshaft, activating the pump/clutch pack combo in the transfer case. This sends power to the front axle, where the other tire on ice starts to spin. Once again, the speed difference activates the pump and clutch, now sending all available power (variable based on wheelspeed, viscosity, etc; never 100% but a goodly portion thereof) to the wheel on asphalt, pulling the vehicle off the ice. As soon as the other wheels hit pavement, they stop spinning and the lack of wheelspin releases the clutches and it's a regular open diff again. Pure genius.

One final note, is that 4WD systems almost always include a Neutral position, and AWD doesn't. This neutral is somewhat like the neutral in a transmission, in that it totally de-couples the driveshafts from the engine/transmission.

 

Thanks Whodat and Mysticality, I think I managed to grasp atleast the fundamentals of the systems. However these mechanics are way too complicated to my somewhat rudimentary mechanical knowledge!!!!

I am waiting to take delivery of my Sorento which is equipped with AWD. Will see if it behaves any different to my Sportage!

Cheers!

 

No worries.

I often use our AWD Diesel offroad and the only thing that lets me down is the tyres. (Still got stock on it. -facepalm-)
On the road its a dream... Never loses traction, even when I try!

 

I am a little confused my sorento has 4wd badges and was a xm version made august of 2010 for the uk market

But Jan 2011+ the badging changed from 4wd to awd

Was that just a badge change or a different type drive fitted?

Puddy
ps all UK sorento are made in Korea

 

My Sorento also has 4WD badges (Aussie, thus Korean made)
Manf. date: 01/10
Its the same system, still AWD... I'm not sure why they kept the 4WD badges. Perhaps to continue the bloodline from the previous ('real' 4WD) Sorento?

-Matt

EDIT: I see you have the 6spd manual... How is it?
Personally, I would have loved one but the end decision of purchase was not mine and thus we were stuck with an auto.

 

I much prefer the 4wd on my old blazer that i sold, than the awd on my 2012 sorento (i love the new truck, just wish i could have full-time 4wd on it at all speeds, for driving in slippery conditions). just my two cents.

 

I tromp on the gas at this stop sign with a right turn incline road a few blocks from my house when the weather is wet or snowy and my XS with AWD jumps around this turn with no problem. That's AWD. Any FWD car just spins. My Saturn with AWD (very different setup) would spin the front a bit then the back would kick in, but you usually had to be heavy on the gas to get that back to lock-up.
So far no problems with the SX AWD. Very little slip before you get going.
With 26mpg on the highways... an AWD I can like.

 

I have a couple of questions about this. When you write:

The disadvantages of this system are that you take a gas mileage hit; there is a fair amount of parasitic drag.

Where is the parasitic drag coming from? It seems to me that the only extra moving parts in FWD mode are the added transfer case to direct torque rearward, and the rear driveshaft. These can't weigh more than a few pounds apiece so it would seem to me that they would not add too much resistance to the drivetrain. Is there something I am missing here or are these small parts enough to induce a significant drop in the fuel economy?

Since it's connected by a clutch pack, it cannot transfer 100% of the engine's torque;

Simply put why not? A clutch pack "should" be able to transfer 100% of an engine's torque if it is designed that way. If I were to push the AWD lock button and the front wheels were elevated what would happen? Would the clutch pack lock completely together to allow all engine power to flow from the motor, to the transmission, to the transfer case, through the driveshaft, and into the rear differential where it is split to the two rear wheels, or will the computer sense that "too much" torque is coming through the clutch pack, torque beyond the ability of the friction materials on the clutch plates to grip, and will begin pulsing the clutches to prevent them from pulling too hard on each other?

The important bit-the coupler. Note, I haven't yet put a multimeter on the actuator to find out whether it's a variable coupling (as would be evidenced by variable voltage between 0-14.4v) or a simple on/off (as would be evidenced by either 0 or 14.4v)

Did you ever test this? It would seem most logical for it to be able to "pulse" off an on, meaning a 0 or a 14.4v reading. Its hard to imagine it using some intermediate voltage as that would be a lot of slip which one would think would rapidly degrade the friction material on the clutch plates.


Finally is the system employed in the Sorento the Borg Warner iTM3e system used in the Hyundai Santa Fe? I have looked around for confirmation of this but have not seen anything definite. Thanks.

 

Simply put why not? A clutch pack "should" be able to transfer 100% of an engine's torque if it is designed that way. If I were to push the AWD lock button and the front wheels were elevated what would happen? Would the clutch pack lock completely together to allow all engine power to flow from the motor, to the transmission, to the transfer case, through the driveshaft, and into the rear differential where it is split to the two rear wheels, or will the computer sense that "too much" torque is coming through the clutch pack, torque beyond the ability of the friction materials on the clutch plates to grip, and will begin pulsing the clutches to prevent them from pulling too hard on each other?

50% to front, 50% to rear.
The front is always engaged so 100% of power cannot be sent to rear, ever.
Not unless you break both front drive shafts.

 

Truth be told, I'm not 100% sure, having never had both front wheels off the ground.
In my times offroad, I have had one wheel each, front and rear (alternate sides), off the ground and without traction control they just spun.
I know that the TC brakes the spinning wheels, causing torque to be applied to the wheels with grip.
That being said, I have been in situations where, when the engine is pushed from a standing start on a gravel road, when the turbo kicks in the wheels would have an immense push and lose all grip, then the rear would activate and the vehicle would literally take off. The looks you get when the passengers get whiplash still makes me smile.


EDIT: I do remember one situation where the front of the vech. was hung up over a ditch I couldn't quite cross. Put the AWD lock on, put it in reverse, floored it and it popped right out, easier than I expected.
Didn't have time to brake and nearly smashed the wing mirror on a tree, but better than being stuck!

 

Late post, but is the awd in the 2013 sorento the same as the 2011?

Also curious is traction control should be turned off when going up a steep
snowy, icy grade? I turn off traction control on my 2005 crv in those conditions up our 1/2 mile mountain driveway and it seems to work. If I leave it on, you can feel the engine being dragged down by the braking.

 

Most stability control systems cut the throttle in addition to pulsing the brakes. Your bogging down is probably due to the lost throttle, not to the braking.

 

klrman, the biggest problem with snowy roads is the poor grip from the OEM tires. Don't expect much from these Kumho KL21s. I've upgraded my winter rubber to Hankook i*cept evo.

Try your climb with the traction control both on and off, and please give us the results. It is likely different from your '05 Honda. By the way, stability control and traction control are different. Traction control cuts power to a spinning wheel, either by a bit of brake and/or a bit less power (engine power cut). Stability control tries to straighten us out in a side skid by braking and/or cutting power to the tires on one side to try to pull us straight. Both are generally a good idea and neither is perfect.

I'm still trying to get a feel for the AWD system in our Sorentos. The magic box is the electrically actuated clutch assembly just forward of the rear differential. I find it hard to believe that the dry clutches are made to slip on demand, and I'm not at all sure about pulsing on and off. I haven't had enough time on steep slippery roads to be able to feel exactly what's happening. You do know that the 4wd button on the dash is speed-related?...it only activates below 15 mph, deactivates at 19, reactivates at 15, or at speeds something like that. Above those speeds we are dependent on the computer to know when to switch into 4WD. (I call AWD a system with a center differential or viscous coupling that allows a speed differential between the front and rear drive shafts. Our cars do not have that. I call cars where the front & rear driveshafts locked together 4WD. This is what our cars do (note that the book explains a possible shudder on dry roads when cornering slowly and 4WD is turned on, a locked 4WD characteristic), unless the clutch assembly modulates somehow, all a mystery. Car makers call AWD or 4WD whatever the company marketing department wants to call it.)

How does your KLR do on that icy hill? Have you got studs for it? It can be helpful for Kia answers if you put a bit more info into your profile...year & model car, and at least the country you're in.

 

Hi there KLS. I updated my profile and noticed we're neighbours and both have Vstroms lol. I have studded Hankooks on my CRV and they always do the job year after year in Winter around here.

I just purchased the Sorento in Vegas last week and drove it back to BC. Passed BC inspection yesterday, drove it home up my hill and will store it in my warm garage for the Winter. Too shiny and good looking to abuse it for the first Winter Not much snow on our hill yet, but very icy and with the stock tires it ran up the mountain with ease and TS was not turned off so that was a bonus.

While it's parked for the season, I want to get to the bottom of the transmission "clunk" that happened twice on the way back to canada. Both times were when it was shifting from 1st to second moving slowly. I did noticed that an ecm upgrade was suggested when we got the warranty printout but I want to do more research if that upgrade is actually worth doing or not as otherwise it just runs way to good to mess with it. Also read that it is common on the sorento's but I don't buy that yet. Need to do some more research this Winter.

Yes, I read that in the manual that at 19 mph the awd lock will disengage so will always try and remember that. Not sure myself how it all works on the Sorento. You're right, TS and SC are different and sometimes I forget that. Pretty sure my CRV has SC as it kicks in on the flats if I go a little too fast on the ice in a corner. Doesn't work up our hill though so we always need to turn it off before climbing.

My KLR runs fine up the hill. I just screw sheet metal screws in my D606's and that does the trick on the hard ice. Got to love those KLR's.

 

Thank you for all the helpful explanations. Just wish we could stud our tires here in Ontario. Of all the dumb laws.

 

What winter rubber do you run? I've found modern studless winter tires to be quite good. Studs are better on glare ice, but otherwise, I'm happy with studless. I just put a set of Hankook i*cept evo studless tires on the Sorento (haven't been on snow yet), and I have had great results with Bridgestone Blizzak DM-V1 studless tires on my truck.

Here's some customer results from Tirerack
http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=W&VT=LT
http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=W&VT=C

Not included in the lists above are the brands they don't sell...Nokian, some Hankook, Cooper (& Mastercraft and Dean), some others.

 

I think it would be more clear if we just said that the system will control how the engine "drives" the front wheels or drives all four wheels. Or something simple and clear like that. If the front wheels slip under power, the system will tell the engine to drive the fronts and rears at the same time. This also happens under 19 mph when the 4wd button is pushed. Is this good enough for most folks?

 

there is a mix of power cut and selective wheel brakes. Does the power is completely cut when ESC kicks in? I do not know. I guess it depends on situation, but from MY personal experience with Rondo, power is always 100% off and only brakes are activated.
And yes, it does its job.

How it does? Simply by torque and momentum. If you slide out of tight right turn (you slide to the left) braking left wheels will shift momentum to the right straightening the car trajectory. If you oversteer to the other side - opposite will happen. And then depending on the angle of the steering wheel and your speed and current direction of movement - some wheel will slow down more some not at all.

Drive with one side on snow, one on pavement. Hit the brakes (non-ABS) you will feel how car wants to go.



It really looks funny when you look on it from a side (still standing) and a driver in oncoming car fights with ESC. You literally see each wheel being activated in side slide...

 

@PLP thanks for the info, Appreciated.

 

Hi guy I'm own a 2011 Kia sorento EX 2.2 diesel, week ago I have an issue with the AWD, I don't have rear traction and is a problem when I go off road because the front wheels drift I didn't have this problem before. I hope you can help me. Thank you!!

 

if you dont have any dash lights that come on or errors im sure your issue is the same as mine. seems to be a common issue. the splines strip on the transfer case or on the gearbox coupling that transfers the power to the transfer box ive seen a video how they create new sleeves for them and they stronger

 

Hi all how good and reliable is the 11 kia sorento 4WD i need to start doing alot more off road and don't want to get stuck, Ive had my 11 sorento 2.2 Diesel around 5 to 7 years now and it seems to be a nice car but ive noticed the 4wd doesn't work as ive gotten stuck in some clay/ sand and even with diff lock on the rear doesn't work. ive now taken it to my mechanic to replace the 4 shocks and check the 4wd as i thought the transfer case splines was stripped but it seems that its the female coupling splines on the gearbox and not the transfer box this seems quite pricey where i live so im looking at options to repair it or just leave it as is and rather fix my 2005 honda crv driveshaft for the 4wd to work when i need it,

my kia is the mk2 4wd and not AWD branded think its the same but not sure if their is a big difference
i like the kia as its 7 seater auto

i was also looking to put the 235/60/18 falcon wild peak all terrain on to help

thanks