Please Help to understand 4x4
03-13-14, 06:40 AM
#16
Pole Position
Glad to help.
One more system I meant to include is Honda's VTM-4, used on the Pilot and the Ridgeline. It has a front and rear differential -- the front is open (since they're primarily FWD vehicles), the rear has a set of clutches driven by electromagnets. When the computer senses wheel slip, it engages the clutch and directs power to the wheel. You can "lock" them.. sortof.. by a dash switch, under certain conditions (1st or 2nd gear, low speeds). The system does something clever in ordinary driving - it applies a partial "lock" when you take off from a stop, so you don't get front wheel slip and torque steer.
It's not a true 4x4 system, more of a traction aid. But it does remarkably well in snow. Especially if you have snow tires (the most important part of the system, IMO). Just don't expect to go rock crawling with it..
Chip H.
One more system I meant to include is Honda's VTM-4, used on the Pilot and the Ridgeline. It has a front and rear differential -- the front is open (since they're primarily FWD vehicles), the rear has a set of clutches driven by electromagnets. When the computer senses wheel slip, it engages the clutch and directs power to the wheel. You can "lock" them.. sortof.. by a dash switch, under certain conditions (1st or 2nd gear, low speeds). The system does something clever in ordinary driving - it applies a partial "lock" when you take off from a stop, so you don't get front wheel slip and torque steer.
It's not a true 4x4 system, more of a traction aid. But it does remarkably well in snow. Especially if you have snow tires (the most important part of the system, IMO). Just don't expect to go rock crawling with it..
Chip H.
03-13-14, 10:38 AM
#17
Pole Position
Glad to help.
One more system I meant to include is Honda's VTM-4, used on the Pilot and the Ridgeline. It has a front and rear differential -- the front is open (since they're primarily FWD vehicles), the rear has a set of clutches driven by electromagnets. When the computer senses wheel slip, it engages the clutch and directs power to the wheel. You can "lock" them.. sortof.. by a dash switch, under certain conditions (1st or 2nd gear, low speeds). The system does something clever in ordinary driving - it applies a partial "lock" when you take off from a stop, so you don't get front wheel slip and torque steer.
It's not a true 4x4 system, more of a traction aid. But it does remarkably well in snow. Especially if you have snow tires (the most important part of the system, IMO). Just don't expect to go rock crawling with it..
Chip H.
One more system I meant to include is Honda's VTM-4, used on the Pilot and the Ridgeline. It has a front and rear differential -- the front is open (since they're primarily FWD vehicles), the rear has a set of clutches driven by electromagnets. When the computer senses wheel slip, it engages the clutch and directs power to the wheel. You can "lock" them.. sortof.. by a dash switch, under certain conditions (1st or 2nd gear, low speeds). The system does something clever in ordinary driving - it applies a partial "lock" when you take off from a stop, so you don't get front wheel slip and torque steer.
It's not a true 4x4 system, more of a traction aid. But it does remarkably well in snow. Especially if you have snow tires (the most important part of the system, IMO). Just don't expect to go rock crawling with it..
Chip H.
03-13-14, 09:25 PM
#18
The GX has three differentials - one front, one rear, one center. Normally, they are all "open" meaning they'll spin as you go around corners as you drive.
One thing about all-open diffs is if one wheel loses traction (is lifted in the air, or is on ice) all the engine power will go to it. To reduce this effect, Toyota includes a system called A-TRAC, which is enabled all the time on the GX. What it does it look for wheel spin (via the ABS sensors), and applies the brake to only that wheel. This permits power to return to the other wheels and hopefully get you going again.
If you lock the center differential, that fixes the power ratio between the front & rear axles (sorry, don't know what it is on the GX - let's say it's 40:60 for now). If you lift a front wheel, that means that you lose 40% of your traction (since the front diff is open, it's going to let all that power go to the spinning wheel), up until A-TRAC kicks in and you'll get some of that power back. You'll still have 60% power going to the rear axle.
What if you have two wheels lift? One front, one rear? You'll lose 100% of your traction ... until A-TRAC kicks in. This is because the front & rear diffs are still seeing the percentages that the center diff is sending their way, but sending all that power to the spinning wheel on their axle. Once A-TRAC applies the brakes, you'll get some of your power back.
Mercedes M-Class runs with all open differentials and relies entirely on brake-applied traction aids (their 4-MATIC system) and for most situations is quite good.
Stock Jeeps are like the GX, but the owners will sometimes add locking systems to the front & rear differentials, so that not only is there a 40:60 rear split, but then at the axle, there's a further 50:50 left/right split (the front left wheel gets 50% of 40%, or 20% engine power, for example)
You should never lock a differential when you are on pavement or other high-traction surface. As you go around corners, the differential accounts for the different distances along the curve that the left & right wheels have to travel. If it is locked, that difference gets applied to the axles and other expensive drive-line components, up to something breaking, or the tires losing traction.
Hope this helps.
Chip H.
One thing about all-open diffs is if one wheel loses traction (is lifted in the air, or is on ice) all the engine power will go to it. To reduce this effect, Toyota includes a system called A-TRAC, which is enabled all the time on the GX. What it does it look for wheel spin (via the ABS sensors), and applies the brake to only that wheel. This permits power to return to the other wheels and hopefully get you going again.
If you lock the center differential, that fixes the power ratio between the front & rear axles (sorry, don't know what it is on the GX - let's say it's 40:60 for now). If you lift a front wheel, that means that you lose 40% of your traction (since the front diff is open, it's going to let all that power go to the spinning wheel), up until A-TRAC kicks in and you'll get some of that power back. You'll still have 60% power going to the rear axle.
What if you have two wheels lift? One front, one rear? You'll lose 100% of your traction ... until A-TRAC kicks in. This is because the front & rear diffs are still seeing the percentages that the center diff is sending their way, but sending all that power to the spinning wheel on their axle. Once A-TRAC applies the brakes, you'll get some of your power back.
Mercedes M-Class runs with all open differentials and relies entirely on brake-applied traction aids (their 4-MATIC system) and for most situations is quite good.
Stock Jeeps are like the GX, but the owners will sometimes add locking systems to the front & rear differentials, so that not only is there a 40:60 rear split, but then at the axle, there's a further 50:50 left/right split (the front left wheel gets 50% of 40%, or 20% engine power, for example)
You should never lock a differential when you are on pavement or other high-traction surface. As you go around corners, the differential accounts for the different distances along the curve that the left & right wheels have to travel. If it is locked, that difference gets applied to the axles and other expensive drive-line components, up to something breaking, or the tires losing traction.
Hope this helps.
Chip H.
Our center diff is a torsen. IIRC it's a "type 2 torsen" but not sure. This is a torque biasing differential. Ours happens to have a default torque split of 40:60 F:R that can be shifted (IIRC) up to 90 or perhaps 100% to either axle. This differential is incredibly effective at managing torque transfer and maintaining traction.
FWIW, the center torsen diff has been the key to Audi quattros since the mid 90s (with the exception of the FWD "haldex" quattros. We've had a bunch of quattros over the years and I'm a fan of the torsen.
I believe, as you noted, our front & rear diffs are "open" and brake controlled. As you note, if one spins on a given axle, the brake engages to "push" torque to the other wheel on that axle. This is a super common and relatively cheap way to approximate a limited slip diff. Unfortunately it "subtracts" power being applied. Not awesome for performance cars, but great if you're just optimizing for traction.
I believe locking our center diff just fixes the torque split of the Torsen so it no longer varies torque application between the front & rear. It fixes it at 40:60.
Mostly a dupe, but wanted to bring the torsen info into the thread.
03-14-14, 04:51 AM
#19
FWIW I think the GX uses the T3 http://www.torsen.com/products/T-3.htm
03-14-14, 06:04 AM
#20
Pole Position
I had a coworker that had an Audi Coupe GT when I was stationed in Germany in the early 1980's. Drove down to Innsbruck in it at a very high rate of speed.
Truly impressive, and Quattro has only gotten better since then.Chip H.
03-14-14, 12:46 PM
#21
Sure hope I never have to figure this out I have had no issues with snow . .and getting stuck , thanks for the information I may need to study
I always thought the GX 4WD was being in 4wheel drive all time ?
I have had no issues with snow . .and getting stuck , thanks for the information I may need to study I always thought the GX 4WD was being in 4wheel drive all time ?
03-14-14, 01:26 PM
#22
Pole Position
12-14-14, 04:33 PM
#23
Driver School Candidate
Join Date: Aug 2012
Location: CA
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Slight addition or tweak:
Our center diff is a torsen. IIRC it's a "type 2 torsen" but not sure. This is a torque biasing differential. Ours happens to have a default torque split of 40:60 F:R that can be shifted (IIRC) up to 90 or perhaps 100% to either axle. This differential is incredibly effective at managing torque transfer and maintaining traction.
FWIW, the center torsen diff has been the key to Audi quattros since the mid 90s (with the exception of the FWD "haldex" quattros. We've had a bunch of quattros over the years and I'm a fan of the torsen.
I believe, as you noted, our front & rear diffs are "open" and brake controlled. As you note, if one spins on a given axle, the brake engages to "push" torque to the other wheel on that axle. This is a super common and relatively cheap way to approximate a limited slip diff. Unfortunately it "subtracts" power being applied. Not awesome for performance cars, but great if you're just optimizing for traction.
I believe locking our center diff just fixes the torque split of the Torsen so it no longer varies torque application between the front & rear. It fixes it at 40:60.
Mostly a dupe, but wanted to bring the torsen info into the thread.
Our center diff is a torsen. IIRC it's a "type 2 torsen" but not sure. This is a torque biasing differential. Ours happens to have a default torque split of 40:60 F:R that can be shifted (IIRC) up to 90 or perhaps 100% to either axle. This differential is incredibly effective at managing torque transfer and maintaining traction.
FWIW, the center torsen diff has been the key to Audi quattros since the mid 90s (with the exception of the FWD "haldex" quattros. We've had a bunch of quattros over the years and I'm a fan of the torsen.
I believe, as you noted, our front & rear diffs are "open" and brake controlled. As you note, if one spins on a given axle, the brake engages to "push" torque to the other wheel on that axle. This is a super common and relatively cheap way to approximate a limited slip diff. Unfortunately it "subtracts" power being applied. Not awesome for performance cars, but great if you're just optimizing for traction.
I believe locking our center diff just fixes the torque split of the Torsen so it no longer varies torque application between the front & rear. It fixes it at 40:60.
Mostly a dupe, but wanted to bring the torsen info into the thread.
07-28-21, 09:44 AM
#24
Driver School Candidate
Join Date: Jul 2021
Location: Georgia
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
Gx 470 is a full time 4wd
No , the Gx 470 is not AWD it is full time "4 wheel Drive " regardless of having the transfer case in low or high it is always in 4 wd. Also all Gx470's have " A Trac " computerized system that sends power to whatever wheel needs it. So if drivers front tire starts spinning power will be transferred to the passenger front tire. It works very well . That's why so many owners say " all you need is a rear locker really ."
correct me if I am w rong, but the truck is an AWD in standard mode, ie it transfers power, as subare says, from the wheel that slips to a wheel that grips....lock the center diff and it is now a four wheel drive vehicle...locking the front diff, ie, both wheels spin at the same rate so driving on pavement causes the tires to scuff in a turn....moving the transfer case lever from high to low just gives you lower gearing, ie, more torque at very low speeds.
07-28-21, 11:31 AM
#25
Pole Position
No , the Gx 470 is not AWD it is full time "4 wheel Drive " regardless of having the transfer case in low or high it is always in 4 wd. Also all Gx470's have " A Trac " computerized system that sends power to whatever wheel needs it. So if drivers front tire starts spinning power will be transferred to the passenger front tire. It works very well . That's why so many owners say " all you need is a rear locker really ."
4x4 is engaged when the center diff lock is pressed, providing 50/50 front/rear power distribution.
"4WD" or "4 wheel drive" is just Toyota/Lexus marketing talk, what does it really mean? "Full Time 4WD" is often thrown around, but we know these trucks are not in 4x4 until the CDL is locked...so that can't mean 4x4...it's got to mean AWD.
07-28-21, 11:41 AM
#26
I don't believe there's any power to front diff until you "lock 4x4" using the 4x4 button in the cab. There is no locking diff on these GX's, the x-case is where the locking happens to drive the front.
07-28-21, 11:44 AM
#27
Pole Position
I live where it snows, how things work becomes very obvious when tires start spinning on a regular basis, lol. There is definitely power to the front axle when the CDL is not engaged, it functions as AWD under normal conditions.
07-28-21, 02:32 PM
#28
this is how Toyota describes the system in their product brochure…you all can debate what it means.
Full- time four-wheel drive with TORseN® limited-slip Center Differential (lsCD)3 • Manual- locking center differential • Downhill Assist Control (DAC)1 • Hill-start Assist Cont
Full- time four-wheel drive with TORseN® limited-slip Center Differential (lsCD)3 • Manual- locking center differential • Downhill Assist Control (DAC)1 • Hill-start Assist Cont
07-28-21, 03:10 PM
#29
I see a lot of online info that seems odd. Many posts suggest that the center diff is like a LSD and when a wheel slips it sends power to the other wheels. This is not possible in context of redirecting power, there's only two driveshafts that come out of the that center diff/x-fer case which drive std differentials, thus that center component cannot redirect power to other wheels, and, I see no way for the center diff to know when any one wheel is slipping, it's not a quattro setup.
07-28-21, 05:15 PM
#30
Pole Position
I see a lot of online info that seems odd. Many posts suggest that the center diff is like a LSD and when a wheel slips it sends power to the other wheels. This is not possible in context of redirecting power, there's only two driveshafts that come out of the that center diff/x-fer case which drive std differentials, thus that center component cannot redirect power to other wheels, and, I see no way for the center diff to know when any one wheel is slipping, it's not a quattro setup.
When the CDL is locked, power is sent 50/50 to both the front and rear axles, this is what people call "4x4" mode. Both front and rear diffs remain open, and A-TRAC does its thing as needed.
