[whodat90]

Front power transmission take-off

 

[whodat90]

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.

 

[whodat90]

Rear Differential

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

Crew Chief.

 

[whodat90]

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

 

[whodat90]

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.

 

[whodat90]

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.

 

[whodat90]

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




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?

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?

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.

Ok, the parasitic drag comes from a couple of places. The thing to remember is that the driveshaft is always spinning, and the rear axles are always spinning, and the rear diff is always spinning (when the car is moving) The magic of the system is that they aren't always connected to each other. Then there's the additional weight of the system, according to kia the weight difference between the fwd and awd is ~175lbs.

Next, the clutch pack/power transfer. This gets a bit tricky. A clutch can transmit 100% of available power, as does the clutch in any car or motorcycle (btw I'm a Vstrom owner too!) The thing is, the clutch in this system is a ramped dog style clutch. The electrical system just activates it a little bit, then a set of rollers slide up ramps and compress the clutch pack as they go. It's a great system in that the amount of torque it transmits is directly related to how much resistance it encounters. I haven't had a chance to get under and throw the multimeter on it, but with a ramped dog clutch I don't believe that varying the amount of voltage/current/PWM to the clutch would make any effective change; as soon as it starts to engage, the rest is mechanical. Kind of like that G80 that was mentioned, it's flywheel activated. As soon as the wheelspin reaches some threshold, BANG! its engaged totally.

And I'm not sure exactly what 'system' they call the one in the kia, sometimes they sell the same thing with different software packages and give it a new name, sometimes they have totally different systems with the same concept and call it the same. Sorry.

 

[whodat90]

I do not have a diagram of the Sorento AWD system, but I do have one in front of me from the Hyundai Santa Fe (from hmaservice.com) which I am assuming is identical in design and operation to the Sorento.

It looks to me like power flows from the engine, to the transmission, and from there to what looks to be a unified front differential and transfer case (they label it as "transfer"). From there the power can flow into the rear prop shaft which goes to the awd coupling device and to the rear differential, finally reaching the rear wheels.

It looks to me that if there were no traction for the front tires, because they were on wet ice, or were elevated, or some extreme situation, that the engine torque would flow into that hybrid transfer case/front diff, the front diff would take zero torque since the front wheels have zero traction, and all remaining torque would be directed through the driveshaft through the coupling device and into the rear differential.

Am I misunderstanding the diagram I am looking at? I would post the image but I am not sure how to here. In what amounts to the artificial situation I am presenting here - front wheels elevated - would it be possible to direct all torque rearward? Or am I still misunderstanding something simple?

Here is where the term 'engine power' and 'torque' become unclear. Power will always flow to the wheel with the least resistance. Regular 2wd car with one wheel on ice, that wheel will spin and take all the 'power.' Add a limited slip diff in the mix however, and the wheel speed difference will cause some of the power to flow to the higher resistance of the wheel with traction, and will hopefully be enough to move the car. Throw a locker in there and it gets complex. It's either receiving 50% of the power (since both wheels now receive equal power) or 100% of the power (because no power is being put to the ground through the wheel on ice) The Sorento is a FWD vehicle that transitions to a part-time 4WD vehicle on demand, which averages out to AWD. If you jacked the front wheels off the ground and tried to drive, the gee whiz electronics package would see the front wheels spinning and activate the clutch, and you'd immediately have a bad day as the vehicle drove off the jacks. (BTW, jeep actually has a procedure for that to check the 4WD system in their WJ series Grand Cherokees. There are lots of warnings in that book) Instead of looking at 'power' or 'torque', it's easier to consider it as potential torque. The key to moving is to apply torque to the ground. If you have no resistance, you can't have torque. If you're spinning a tire, there's no resistance so almost none of your power and torque are being delivered to the ground. Activate the traction control systems (lockers, AWD, etc. ) and it tries to find a wheel with resistance it can send power to.

As for the actual stability control, it's the one thing I don't like about kias. High end systems operate under the concept of 'we're going to control your traction to maintain control' and do neat things like differential braking, differential torque splitting, etc. The kias operates under the concept of 'we're going to lower your power to meet available traction' and simply starts cutting the engine power till the wheelspin stops. Effective but terrifying. A while back I rented an optima, and there was a bump in the drive between my hotel and the busy street I was trying to pull out into. Every single time I tried to pull out it'd see the bump/turn as a threat and kill my engine for a few seconds. Ended up just having to turn it off. Now for going up a snowy hill, the reason you'd turn the TCS off is because as I said, the system is designed to match your power to the traction you have right now. If instead you turn it off, you can go looking for traction of your own by spinning the tires and trying to dig down to more traction. This past Friday I went out and played a bit on some snowy roads, and was able to easily get all four wheels spinning, then the traction control would start killing the power until I could accelerate slowly away. However, on the way home from that I managed to do something that caused the vehicle to slip unintentionally, and the kia immediately killed the power, activated the abs and awd, and recovered control within 10 feet. I was impressed.