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2011 Sorento AWD explained

73K views 59 replies 20 participants last post by  Jstorresn 
#1 · (Edited)
I'm going to start with a link to a website that explains all the different AWD systems. Then I'm going to post pictures from the parts manual and Kiatechinfo, which will show the transfer of power.
All Wheel Drive Explained | awd, 4x4, 4wd, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works
The 2011 Sorento uses the automatic all wheel drive version.
First, the components: There is a front output. It is a ring and pinion similar to those in a differential, without the spider gears to allow for differential speeds of the output shafts. It's purpose is purely to change the direction of the power from the transverse of the engine to longitudinal; from sideways to front and back. Important to note is that the output is directly coupled to the transmission, if it's spinning the output of this is spinning.
Next is the driveshaft, or as Kia calls it, a Propeller Shaft. Standard simple driveshaft that goes from front output to rear coupler. This is a two-piece shaft with a ujoint between the front output and the front shaft, then a middle carrier, and the rear shaft is directly bolted to the coupler assembly.
Next is the coupler assembly, which is the mechanical key to the system. It is a clutch system which, when power is applied, pushes against the clutch pack with a dual-ramp system to connect the input and output. Of note is that unless voltage is applied to the actuator, the clutch pack is open and no power is transmitted.
Finally is the rear differential assembly. This is a standard differential, one input, two outputs at 90* to the input. There is no limited slip, just an open carrier with two spider gears on one cross-shaft.

Ok, theory of operation. In normal operation, the vehicle is front wheel drive, 100%. The driveshaft/propeller shaft spins whenever the vehicle is in motion, as parasitic loss. The rear wheels are turned by the road, which spin the rear differential. It's this way because the system cannot take torque away from the front, it can only send 'waste' torque to the rear. Waste torque is identified by the AWD/TCS/VSCS (All Wheel Drive/Traction Control System/Vehicle Stability Control System) noting a condition such as front wheel speed higher than the rear, or a lateral slip of the vehicle caused by wheel slippage.
Once the need for all wheel drive is identified, the computer sends voltage into the actuator which squeezes the clutch pack, completing the transfer of power from the engine to the rear wheels. Once the wheelspeed is what the computer decides is correct, or the vehicle instability condition is passed, it removes voltage and the vehicle goes back to front wheel drive. Of note is that there is no center diff. The vehicle is not designed to be full time AWD. This is why if you press the 4wd button, which applies voltage to the actuator, the vehicle will hop and jump around corners. There must be some differentiation of wheelspeed between the front and rear wheels when you go around a corner. If there is no differential to even out the speeds, the difference must be taken up in wheel slip.
The disadvantages of this system are that you take a gas mileage hit; there is a fair amount of parasitic drag. Also, it is not a fulltime AWD system, so is not theoretically as responsive. Unlike some vehicles with a true transfer case, you cannot in an emergency pull one or the other driveshaft and operate as a 2wd vehicle (in some 4x4s if you lose a rear driveshaft, you can put it in 4wd part-time and drive in front wheel drive, etc.)
The advantages are lighter weight than a fulltime all wheel drive system, since there is no center differential. The system is simpler mechanically, but more complex electrically. It is much easier to graft onto a front wheel drive vehicle than a fulltime system. Since it's connected by a clutch pack, it cannot transfer 100% of the engine's torque; I tried and failed to back mine up onto a pair of ramps in 4wd mode because the clutch pack kept slipping. Finally, it's failsafe; if the system fails, you still have a front wheel drive vehicle.

The system is similar to one used in my son's Volvo S40, although he pointed out that the Kia system reacts much more quickly than his; he can get some wheelspin in the front before it engages the rear. On mine, as soon as slip is noticeable (flooring it from a dead stop in my gravel drive) it engages the rear and the vehicle accelerates.

If requested, later posts will compare and contrast this system to others, as this is somewhat of a hobby of mine.

Edit: Of interest to other tech-heads, Kiatechinfo now has the info up for the 2012 models, including the GDI engine.
 
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#3 · (Edited)
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) The AWD actuator computer is in the passenger footwell, I may tap into the actuator output wires and hook a meter or LED so I have a visual indicator in the cab of 4WD activation. Offhand I believe it's simply on/off. As you can see from the second pic, which shows the actuator, it uses a pair of opposing ramps to apply clutch force. This is very similar to a detroit locker, where the more torque applied, the more torque it applies to the clutch (or in the detroit, to the engagement dogs)

Even more wild conjecture on my part: The system cannot mechanically transfer any significant power to the rear unless the front wheels are slipping. Using the dog clutch as shown below, it requires torque to be applied from the front against resistance in the rear to separate those plates (think of it this way; how much torque can you apply to a freely spinning wheel? Only as much as it takes to spin it. The wheel must resist your force for greater torque to be applied. Don't take this last paragraph as absolute yet, I'm still working this part out in my head, and have to do some experiments to verify.
 

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#5 ·
Proof of concepts:
Vehicle in park, parking brake off, vehicle on. Jack up one rear wheel. If you can spin it, the rear is completely independent of the front. (that wheel spinning, the carrier spinning at half that speed, and the differential pinion spinning inside the coupler) Now hit the 4wd button and try again. The wheel should not spin, or should spin with great resistance. This is the actuator connecting the front and rear.
 
#7 ·
Thanks. Contrary to how it must look, this thread is not meant 'at' someone. It's simply because I love to teach, and believe this info may be useful in a wiki kind of way to the forum at large. I'm sure it's too technical for some, and not enough for others. I'd be happy to clarify or expound on anything someone asks, and (believe it or not) I'd love to learn something new if someone has something to offer, or better yet to show me where I'm wrong in my conclusions. It took me plenty of years to get to where I like being proven wrong, but now I look at it as learning something I didn't or unlearning something incorrect that I did.
Edit: The quote is actually from the book 'Starship Troopers', which is a million times better than the movie. One of my favorites. Everything said by the H&MP teachers is genius.
 
#9 ·
Very nice Whodat , I like the way you teach .

Frankly I cant add anything on the topic except my choice
to not go for the 4wd even I live in snowy Quebec , the sori
is so well balanced that 2wd is plenty enough , the 4wd is practical
but a luxury for me ...with a lot a millage and the horrendous price of gas.

I had a 1990 legacy subi ...and with my intrepid caracter I get caught
in too many start@stop fights in slippery conditions ....the problem with
awd : gain speed faster but the braking is not at par.
 
#10 ·
You hit on a very important point that many first-time AWD/4WD owners fail to understand. You may now have 4wd/AWD, but everyone has all wheel brakes. The ability to accelerate faster in no way equates to the ability to stop faster. A good set of winter tires will do more for snow/ice driving than any fancy drivetrain. The winter tires will allow you to slow down faster as well as accelerate faster. There are a great set of videos on tirerack.com showing the differences between summer, all season, and winter tires on ice and snow.
 
#11 ·
I'm waiting for my new service manual to get here, but I figured I'd also touch on the stability control. There are a few ways to handle stability control, and unfortunately the way the Sorento handles it is my least favorite. In the Sorento, if the vehicle decides that you're doing something that would upset the vehicle's stability, it's first reaction seems to be to cut engine to reduce available power to meet available traction. This seems to be their system across the board, as my Rondo and a rented Optima did the same thing. From a vehicle sliding out of control standpoint it works fine, from a reality standpoint I hate it. Imagine (or try this, for fun) you're trying to pull out into traffic, and there is a large dip or bump in the road directly in front of you. You hit the gas, turn the wheel and hit the bump all at the same time. Vehicle decides that you're about to spin, so it starts retarding the ignition and cutting the fuel, leaving you fully in control of a stable vehicle at a near dead stop in the face of oncoming traffic. Not great. Other systems I feel handle this better by using the ABS to transfer torque around; if it notes a spinning wheel, it applies the brakes on that wheel to slow it to the same wheelspeed as the other wheels. If it notices you over-rotating to the left, it applies the right rear brake to slow the yaw rate. The disadvantage of this system is that it requires a fairly strong computer to be able to parse the data. Also, and this is the bigger one, it can overheat your brakes very quickly in any kind of prolonged low-traction situation. Deep mud, slippery ice, long snowy road, etc. That kind of system is really meant for momentary losses of traction, and is often paired with a different style of AWD.
 
#12 ·
Is it worth getting the AWD Sorento

Whodat - Thanks for your time and effort in explaining the nuances of the AWD system in the Sorento. I have a very basic question. When driving in adverse conditions snow/sleet/rain is it safer to be driving the AWD or FWD sorento? I am going to be moving to a snowy climate and have never purchased an AWD before.
 
#16 ·
Whodat - Thanks for your time and effort in explaining the nuances of the AWD system in the Sorento. I have a very basic question. When driving in adverse conditions snow/sleet/rain is it safer to be driving the AWD or FWD sorento? I am going to be moving to a snowy climate and have never purchased an AWD before.
I think the answer lies in 2 folds :

the more safety the 4wd gives could be nulled by your behavior :
if you are driving faster because you feel more secure ....

if money is not a factor : go for 4wd + top tires , next time you
will be able to judge the value of each system.

In both case , you need top tires $$$ and drive with longer safety distance :eek:
 
#13 ·
That's not an easy queation at all!! It's far too general of a question so I'm afraid no one will be answer it for you, I'd recommend reading the previous posts in this thread which provides information on how the AWD vs. FWD system will perform in various specific situations. I understand you want life to be simplified and have a solid answer that "yes" or "no" it's safer but that isn't going to happen.

In certain specific situations the AWD will be more covenient for you, such as in deep snow, it will allow you to keep traction and plow through the snow with lower risk of getting stuck, but that's not normally considered a safety issue.

On icy winter roads the #1 safety factor is your tires, plain and simple. If you have all-seasons you'll be less safe than with snow/winter tires, and you'll be less safe running old all-seasons with little tread depth vs. newer quality all-seasons with lots of tread. AWD does NOTHING to help you stop or maintain traction if you're on icy roads in an emergency situation. If you're in an emergency steering situation where you need to avoid obostacles the AWD may help.

Bottom line tires are what keep you safe in winter, and brakes come next. The anti-lock brakes on your Sorento will do MUCH MORE to keep you safe than the AWD system, as will the stability/traction control that comes standard on all Sorentos.

My personal opinion: unless you're going offroad or driving through lots of deep snow the AWD system won't offer much benefit, but it will significantly reduce your fuel efficiency, and it will cost you more in maintenance costs and potential components to break down later in the vehicles life.

The AWD misconception started with trucks. All trucks are rear-wheel-drive, so adding the front wheels in a 4x4 or AWD makes a lot of sense, it is much safer to drive in icy, snowy, gravel, mudding conditions with the front wheels powered than with just the rear wheels. Therefore the universal truth was born: AWD or 4x4 is more safe than 2WD. For RWD trucks this is true, and for rear wheel drive SUV's this was true too. But guess what, very few cars are rear-wheel drive SUV's anymore, almost none. So if you start with a base vehicle that is Front wheel drive such as with the Sorento and all of it's competitors, the AWD advantage is a completely different concept. You've already got front wheel drive so adding the rears offers very limited advantages (I didn't say there aren't advantages, but they are far less significant than if you added AWD to a rear wheel drive base vehicle).

Now if you drive through deep snow and mud, go offroad, and if you tow then AWD may be the way to go for you, but for the vast majority of people AWD is completely unnessary, and actually is less safe because it gives you a false sense of security. Rather than staying home in a severe snow storm for example, you say to yourself, "I've got AWD, I'm going to go out and brave this storm, I'll be fine". Most of the time the AWD vehicle has all-season tires not suitable for winter driving and this results in very dangerous driving.

Bottom line, AWD is a money grab for the dealer and manufacturer for most potential buyers, and probably for you too, but only you can decide exactly what features you need in your vehicle.
 
#14 · (Edited)
I respectfully disagree. In general, AWD will be much more forgiving and safe in inclement conditions than FWD or RWD. How much more, and how much it matters to you, is a variable I can't pinpoint. Best case scenario is AWD and winter tires.
 
#15 · (Edited)
just my 2 cents.
If you want to change car only because FWD is "too weak" for winter, it would be better to try winter tires first.

4x4 or AWD will be nothing if there is no grip... right?



EDIT:

whodat90, to answer you. Yes, in any case 4 driving wheels will be better than 2. My only comment is to FIRST try winter tires to see if this solves problems as opposed to buying a new car.

YES, 100% yes AWD with winter tires is better than FWD.

As for all-season tires. Hard to say to me, as comparing Rondo to Intrepid (both 2.7 V6), but different all-season tires (although both 225) - Intrepid handled much better in winter. So tires themselves make huge difference. OEM Michelin on Rondo is terrible in snow...
 
#17 ·
I understand that driving habits dictate safety, specially in bad weather. I am a conservative driver anyway (and even more so when it snows) so I wont have a false sense of security if I were to be in an AWD.

You guys make a good point about the importance of good tires and that is a point well taken.

I know there are different types of AWD systems out there that respond in different ways as to how they transfer power and deal with a spinning wheel. Some are obviously better than others. Some articles I have read say it can be more dangerous to have an AWD in slick conditions than a FWD. I known that depends on the nuances of the particular AWD though. I don't plan on going off-roading or plowing thru 18" of snow, just general type driving on Chicago roads. I have a newborn baby and safety is more important to me now than it has been in the past, hence my initial question.

PLP - I am going to be buying a new Sorento anyway, its just a question of whether or not I am going to go with the AWD or FWD. Its time for a new vehicle. Either way I will make sure I have a good set of tires.
 
#18 ·
AWD, FWD, RWD, 4x4... and whatever other systems exist. Each requires THE driver to learn how to drive it. And no matter what kind of electronics control the system, no matter how good tires you have - you will not trick physics law.
How safe the car is depends on... the driver only. Everything else may or may not help you. 50 years ago we did not dream about ESC, and we (OK, not me...) still could drive cars in any condition.

My point is LEARN how to drive your car.
Whether it is RWD or 4x4 or anything else. Especially in winter time, take it to an empty parking lot covered with snow and try your car. Specifically AWD - let it engage to see how it works.

whodat90 did GREAT job explaining how it works. Since you know theory, get behind the wheel and try it. Be safe, of course. But let the car show how it acts so that you are not SURPRISED in extreme situation.

From my experience with drivers I taught/worked with, most of the time a cause of any problems was lack of knowledge how systems work and how they act when they engage or in extreme situations.
 
#19 ·
PLP makes an excellent point. In general, I've found the Sorento's AWD to be nearly transparent, simply being there when needed. However, in a previous career I had we had a saying; Currency is not Proficiency. Meaning, knowing the minimum doesn't mean you know how to effectively field that knowledge. I make a point of playing with the system, in different (controlled) environments so I know how it'll react. Icy parking lot, dead stop, floor it to see what happens. Then turn off VSS and see what it does, then turn on diff lock and see what it does. Pitch it sideways at 10mph, etc. I've made the system activate under every conceivable circumstance I could come up with, just to see how it felt.
As has been stated, tires make a huge difference, although much less of a difference nowadays than in the past, and less of a difference on modern AWD vehicles. Tirerack.com has some great videos on youtube showing the differences between summer tires, winter tires, and all season tires. Winter tires are of course the best in the winter, but the all season tires with the snowflake logo do surprisingly well, especially when all 4 are contributing. The stock Kumhos on mine do pretty well in snow and ice, and have the M+S rating without the snowflake. One caveat to the stock tires are that they are high silicate models designed among other things for low rolling resistance and high mileage. Tradeoffs; better traction means less mileage. Snow tires give less mileage and wear much faster on dry pavement; it's always a crapshoot when I swap between the summer tires and winter tires. Leave the winter tires on too long, they wear out. Swap them out too fast, there'll be an ice storm.
 
#23 ·
@Whodat- If you want any specific data etc, I could always take a look next time I take the Sorento off-road... (Its a regular occurrence :D)
Have found that the only thing that holds it back is the tyres. (Am running OEM "Roadian"s; can't afford the A/T's or M/T's I dream about.)
 
#24 ·
I've been an off-roader for a long time, I just finally changed what I do it in. The Kia for me is specifically a family runabout, and the paint is too pretty/fragile to play offroad. My GMC just weighs too much, if it gets stuck at all it's 7000lbs stuck so that doesn't get to play either. I bought a dirtbike (xr400) and a four wheeler (300EX) for my dirt fix, figuring that if I total either one of those I'd be out less than if I dented the Sorento. :0
 
#25 ·
Heheh, nice.
Sorento is a quite capable vehicle... So long as you don't get two wheels stuck in the air. -.-
The traction control system seems quite, well... Bad.
And the ABS seems to be a system-wide affair... Not individual wheels. If I slam the brakes on and one rear wheel looses grip, all four wheels are lessened on the brakes, not just one... This probably leads to the dodgy TC when the alternate wheels are 'flying high'.
 
#26 ·
Heheh, nice.
Sorento is a quite capable vehicle... So long as you don't get two wheels stuck in the air. -.-
The traction control system seems quite, well... Bad.

Since when you drive off road with ESC activated?? Turn it OFF. It helps.

And the ABS seems to be a system-wide affair... Not individual wheels. If I slam the brakes on and one rear wheel looses grip, all four wheels are lessened on the brakes, not just one...
ABS on one wheel only?

Just think of it - one wheel looses its grip. How is it possible? Unless very deep turn when one of the wheels lifts of the ground.
Otherwise it is impossible due to one thing. Rear wheels follow front wheels.
So, if one side looses grip, how can you expect the system (ABS) to keep high pressure on the other side? This would end up with spinning car.
Besides, ABS is designed to keep braking force even on all axles.

Yes, ABS is 4 channel, but only for ESC. ESC is allowed to brake one or more wheels at a time only. ABS itself does not do that. It will detect slippage of one wheel, but will adjust braking force to all wheels to maintain straight course.

And all ABS's work like that.
 
#29 ·
see page 6/22 in the owners manual

On 4WD vehicles, your vehicle must be towed with a wheel lift and dollies or flatbed equipment with all the wheels off the ground.

CAUTION
The 4WD vehicle should never be towed with the wheels on the ground. This can cause serious damage to the transaxle or the 4WD system.

On 2WD vehicles, it is acceptable to tow the vehicle with the rear wheels on the ground (without dollies) and the front wheels off the ground.
 
#30 · (Edited)
Thanks Whodat, great job explaining. But I am a little confused about the AWD. Could you lead this child to knowledge by explaining the difference between an AWD system and a 4WD system?
My understanding was that in a 4WD system the front 2 wheels and the rear 2 wheels act as separate independent units and get engine power to them in an ratio according to the need, wheras in an AWD system all 4 wheels act as individual units which receive power as needed. In which case, how is it possible to have an AWD without a limited slip differential?
(apologies in advance if my question is stupid! :) )
 
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