2011 Sorento AWD explained - Kia Forum
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#1 (permalink) Old 05-20-2011, 10:05 PM
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Default 2011 Sorento AWD explained

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.

"One can lead a child to knowledge, but one cannot make him think." -Robert Heinlein, Starship Troopers

Last edited by whodat90; 05-23-2011 at 05:50 AM.
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#2 (permalink) Old 05-20-2011, 10:06 PM
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Front power transmission take-off
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#3 (permalink) Old 05-20-2011, 10:11 PM
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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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Last edited by whodat90; 05-20-2011 at 10:24 PM.
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#4 (permalink) Old 05-20-2011, 10:13 PM
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Rear Differential
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#5 (permalink) Old 05-20-2011, 10:28 PM
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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.

"One can lead a child to knowledge, but one cannot make him think." -Robert Heinlein, Starship Troopers
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#6 (permalink) Old 05-20-2011, 10:32 PM
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Great explanation.....but as you state..."you can't make them think"....
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#7 (permalink) Old 05-20-2011, 10:40 PM
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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.

"One can lead a child to knowledge, but one cannot make him think." -Robert Heinlein, Starship Troopers
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#8 (permalink) Old 05-21-2011, 02:59 PM
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+1 on the explanation.

btw loved that book when i was in highschool and totally different then the movie, which kind of disappointed me at how different they did it, in a way i wish they did the book the real way would be a good movie.
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#9 (permalink) Old 05-22-2011, 08:46 PM
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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.
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#10 (permalink) Old 05-23-2011, 05:54 AM
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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.

"One can lead a child to knowledge, but one cannot make him think." -Robert Heinlein, Starship Troopers
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