How Do AWD and 4WD Work?
#1
Junior Member
Thread Starter
How Do AWD and 4WD Work?
How do AWD and 4WD work?
Had a 1992 F150 Custom w/4WD w/topper. Go rid of it cuz it was my ******** wagon and the new wife wanted to get rid of my memories. More reasons to get rid of it included, 160k, she had a tendency to push thru turns in 4WD in winter conditions and rust. I hear Fords’ current 4WD system has not changed much. Still forces 50/50 front/rear. So, in a turn you go into an automatic skid as the fronts are pushed thru the turn.
So, now have a 2008 Honda Ridgeline with 60k and want another ******** wagon. So, what am I getting into?
My RL is great in snow, which is important to me. In winter, New Hampshire, it seems half of the vehicles in the ditch are trucks. The RL is front WD oriented, adds rear when needed. It also had vehicle stability which is proactive. Go into an icy turn too hot, hit the gas and the computer brakes the wheels as needed to keep you on the road in the proper attitude.
So, I know Ford Trucks are different. Rear wheel drive and all. Also, AWD is only available on Lariats and up. For that reason a Lariat would be my preference. So what is Fords Big secret? No matter where I look (haven’t crawled under a truck on the lot) cannot find which Borg Warner differential is in the new Fords (2008 info is available). My questions are about the differential. Asking a sales person these questions is like talking to a rock.
In the Lariat
Is the transfer case a Borg Warner? If so which one. Where can I find more info about it?
Under what conditions is power sent to the front?
What sensors activate the power transfer?
Limited slip is available for the rear, is it on the front?
Is available torque sent where needed via ABS controlling the spinning tire? (front)
What kind of clutch controls the transfer? (front/rear) Magnetic or mechanical
What mechanism allows different wheel speeds (front to back) and left front to right front.
These are things I’d like to know.
Had a 1992 F150 Custom w/4WD w/topper. Go rid of it cuz it was my ******** wagon and the new wife wanted to get rid of my memories. More reasons to get rid of it included, 160k, she had a tendency to push thru turns in 4WD in winter conditions and rust. I hear Fords’ current 4WD system has not changed much. Still forces 50/50 front/rear. So, in a turn you go into an automatic skid as the fronts are pushed thru the turn.
So, now have a 2008 Honda Ridgeline with 60k and want another ******** wagon. So, what am I getting into?
My RL is great in snow, which is important to me. In winter, New Hampshire, it seems half of the vehicles in the ditch are trucks. The RL is front WD oriented, adds rear when needed. It also had vehicle stability which is proactive. Go into an icy turn too hot, hit the gas and the computer brakes the wheels as needed to keep you on the road in the proper attitude.
So, I know Ford Trucks are different. Rear wheel drive and all. Also, AWD is only available on Lariats and up. For that reason a Lariat would be my preference. So what is Fords Big secret? No matter where I look (haven’t crawled under a truck on the lot) cannot find which Borg Warner differential is in the new Fords (2008 info is available). My questions are about the differential. Asking a sales person these questions is like talking to a rock.
In the Lariat
Is the transfer case a Borg Warner? If so which one. Where can I find more info about it?
Under what conditions is power sent to the front?
What sensors activate the power transfer?
Limited slip is available for the rear, is it on the front?
Is available torque sent where needed via ABS controlling the spinning tire? (front)
What kind of clutch controls the transfer? (front/rear) Magnetic or mechanical
What mechanism allows different wheel speeds (front to back) and left front to right front.
These are things I’d like to know.
#2
Senior Member
A four wheel drive [4x4] powers all four wheels through a selective transfer case and the front and rear axles are locked together when it is engaged and most have 2 speed transfer case [4x4 low range] but should not be operated in four wheel drive except on slick, loose, steep, or other low traction conditions.
An all wheel drive [AWD] has a differential between the front and rear drive and may be operated on dry paved roads some AWD systems are selectable some are not also some have a low range [2 speed] transfer case.
Your lariat uses a differential which can be locked between the front and rear drive. [4x4 lock] also standerd is brake bias to control wheel spin but I believe it can be equipped with rear limited slip or a rear electronic locking axle.
An all wheel drive [AWD] has a differential between the front and rear drive and may be operated on dry paved roads some AWD systems are selectable some are not also some have a low range [2 speed] transfer case.
Your lariat uses a differential which can be locked between the front and rear drive. [4x4 lock] also standerd is brake bias to control wheel spin but I believe it can be equipped with rear limited slip or a rear electronic locking axle.
Last edited by bubbabud; 04-25-2016 at 04:45 PM.
#3
Senior Member
Weird, I dont think I would have ever described driving any of the 4wd vehicles I've had as 'pushing' through turns. I guess maybe that sensation comes from the fact that in a turn the front an rear wheels travel a different distance while being forced to rotate at the same speed? Never been a problem for me...
My wife's crosstour has a similar setup (probably exactly the same) as your Ridgeline but if we go anywhere in a snowstorm, we take the truck because it is better in snow. Honda's AWD system works pretty well though.
The reason you see mostly trucks off the road has nothing to do with the drivetrain (unless they left it in 2wd when they should have been in 4wd) and more to do with people not realizing that just because they can 'go' does not mean they can 'stop' so they think the roads are better than they are and overdrive them, then they slip, overcorrect and land in the ditch.
My wife's crosstour has a similar setup (probably exactly the same) as your Ridgeline but if we go anywhere in a snowstorm, we take the truck because it is better in snow. Honda's AWD system works pretty well though.
The reason you see mostly trucks off the road has nothing to do with the drivetrain (unless they left it in 2wd when they should have been in 4wd) and more to do with people not realizing that just because they can 'go' does not mean they can 'stop' so they think the roads are better than they are and overdrive them, then they slip, overcorrect and land in the ditch.
Last edited by 11screw50; 04-25-2016 at 04:47 PM.
#4
2018 XLT FX4
AWD -
4WD -
4WD -
Last edited by Scott2373; 04-25-2016 at 05:28 PM.
#5
Junior Member
Thread Starter
I am probably over thinking the concept. But, given the current weather, a test drive to test capabilities is out of the question. I "get" The basics...
It is the specifics that interest me... A Ford or Borg Warner link, with technical info, would be helpful.
edit... just found this link Some performance info but mostly marketing hype. I want more info!!
It is the specifics that interest me... A Ford or Borg Warner link, with technical info, would be helpful.
edit... just found this link Some performance info but mostly marketing hype. I want more info!!
Last edited by WickedBeast; 04-25-2016 at 06:48 PM.
#7
Junior Member
I too am from NH. I bought my truck in Feb so I've had a couple small storms to play around a bit. I love the 4A in my Lariat! In the rain it's great ...no more spinning taking off quickly. It does seem to disengage as soon as you let off the gas or there is no rear slippage. The rear end will come around more so in 4A than 4hi. If you are coasting or moderate throttle thru a corner in 4A there is no snow plowing as its not engaged. If it is engaged there is a fair amount of plow but not like 4hi. I did have a time when i was gently try and back into my space up to a wall in 4A and it was ...slip, grab, slip, grab til I brake torqued it into my spot. Way better than my ram was with only 4hi. Hope this helps. I'm no authority, Just my experience
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WickedBeast (04-25-2016)
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#8
It's my first day
Hi there internet,
Your gonna want to grab a coffee before you read this. It's long and thorough but it belongs here rather than make a new thread for now. If I've made a mistake, correct me with proof and I will make an edit. I'm trying to make a comprehensive outline of how 4A works specifically in the 2015 and up F150's so other owners don't need to read through the entire internet like I did.
I just want to say that I understood how 4x4 works in most vehicles and how conventional AWD works in most late 2000's cars and crossovers before I looked into this. Thinking about 4A in the new F150 hurt my brain. I understand it now though and in short: it's not an AWD system like you'd be used to in a car, where ABS will selectively apply brake to a slipping wheel to redistribute torque to the others.
Instead, the way 4A works in the F150 is: there are unicorns on hamster wheels inside the transfer case. If you don't like to read, assume this is fact and stop here, lol.
Actually as I found out, the transfer case control module receives input parameters from the PCM and runs those numbers in an algorithm. If the front drive line needs to receive a variable percentage of torque; as 4A works its magic, then the TCCM will activate a solenoid to increase hydraulic fluid pressure and through centrifugal force, that fluid will smoothly flow into cavities to compress a wet clutch pack in the T case where greater compression = greater torque percentile distribution to the front drive line. Again this is only for 4A, not 4H, 4L or 2H.
So this is what I came up with from paraphrasing some Motocraft guides:
The 2-speed TOD (torque on demand) system allows the driver to choose between 2H and three different 4WD modes: 4A, 4H and 4L.
When 4H is selected the TCCM (Transfer Case Control Module) sends a command to the transfer case electronic magnetic coil, which then activates the clutch within the transfer case and transfers torque equally to the front and rear drive line (again, 4H). When 2H mode is selected, the TCCM duty cycle command is turned OFF and the IWEs (hubs) located at each front wheel become disengaged to reduce drag on the front drive line.
Engagement and disengagement of the front wheels is done by the IWEs. The IWEs are normally engaged (no vacuum). Vacuum is supplied to the IWEs by actuation of the IWE solenoid commanded by the TCCM. When actuated, the IWE solenoid allows vacuum to pass through to each IWE. The IWEs disengage and allow the front wheel hubs to be turned freely from the front axel.
Note: when shifting to 2H mode in order for the IWEs to completely disengage, the vehicle steering wheel must be less that 90 deg and 5 seconds must have elapsed since the shift to 2H has been initiated.
The electric shift motor is mounted externally to the transfer case. It drives a rotary cam which moves the range fork within the transfer case between the HIGH range (2H, 4A, 4H) and the LOW range (4L). The electric shift motor only moves during a shift to and from 4L and neutral.
The TCCM directly controls the electric shift motor and can reverse polarity to reverse rotary of the cam and shift fork direction. The shift motor sense plate, an integral part of the shift motor assembly informs the TCCM of the transfer case position.
This transfer case is equipped with an electronically controlled clutch which is located inside the case. This clutch is used to synchronize the speed of the front driveline with the rear driveline as well as transfer torque in either of the three different 4WD modes. When the MSS is switched between 2H and 4A or 4H modes, the TCCM first energizes the clutch. Once the transfer case front and rear output shafts are synchronized, the front axel IWEs are engaged (no vacuum).
When the front and rear drive line are synchronized, the TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on a combination of pre-emptive and wheel slip response algorithm. Pre-emptive response is based on: steering wheel angle, vehicle speed, throttle positions and available power train torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.
The TCCM has an alternative cold strategy which is used to warm up the front axel in cold temperatures to improve driveline synchronization. When ambient temperature is below 0 degrees Celsius (32 F), IWEs engage after initial key cycle and a drive gear is selected. The hubs remain engaged regardless of 4WD mode change for 3KM (2 miles). Once distance traveled has been achieved, IWEs disengage (supplied vacuum) if the vehicle is in 2H. Distance traveled resets only if the temperature is below the calibrated threshold and another key cycle has occurred OR if the customer has shifted to park and back to a drive gear within the same key cycle.
In 4A, the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. When 4WD is no longer needed (during cruising or steady state driving) the system defaults back to RWD mode by setting the duty cycle output to 0. In situations where it’s necessary to negotiate a tight turn, the clutch duty cycle output is reduced which allows for a slight difference between the front and rear drive shafts; however, the system remains on an alert mode and when it’s necessary torque will be transferred automatically.
How is torque transferred you ask? Just watch this. Keep in mind this T case isn't in the F150. Although it is the same TOD operating principal from the same manufacturer:
Below I attached a media release PDF from Borg Warner Co. Ford uses a lot of their components including their TOD Transfer Case.
Now with this in mind I ask myself: how is Ford's history with wet clutch packs in the F150? and then I think about Ford's never ending issues with Limited Slip Diffs and realize that as great as 4A might be in the short term, it's gonna be nothing more than a 'Service at dealer mode' for guys who never change their T case fluid.
Lesson from all this: Do your proper maintenance checks!
I'm nearly certain that my 2016 F150's uses a Borg Warner 4417 TOD TC
Your gonna want to grab a coffee before you read this. It's long and thorough but it belongs here rather than make a new thread for now. If I've made a mistake, correct me with proof and I will make an edit. I'm trying to make a comprehensive outline of how 4A works specifically in the 2015 and up F150's so other owners don't need to read through the entire internet like I did.
I just want to say that I understood how 4x4 works in most vehicles and how conventional AWD works in most late 2000's cars and crossovers before I looked into this. Thinking about 4A in the new F150 hurt my brain. I understand it now though and in short: it's not an AWD system like you'd be used to in a car, where ABS will selectively apply brake to a slipping wheel to redistribute torque to the others.
Instead, the way 4A works in the F150 is: there are unicorns on hamster wheels inside the transfer case. If you don't like to read, assume this is fact and stop here, lol.
Actually as I found out, the transfer case control module receives input parameters from the PCM and runs those numbers in an algorithm. If the front drive line needs to receive a variable percentage of torque; as 4A works its magic, then the TCCM will activate a solenoid to increase hydraulic fluid pressure and through centrifugal force, that fluid will smoothly flow into cavities to compress a wet clutch pack in the T case where greater compression = greater torque percentile distribution to the front drive line. Again this is only for 4A, not 4H, 4L or 2H.
So this is what I came up with from paraphrasing some Motocraft guides:
The 2-speed TOD (torque on demand) system allows the driver to choose between 2H and three different 4WD modes: 4A, 4H and 4L.
When 4H is selected the TCCM (Transfer Case Control Module) sends a command to the transfer case electronic magnetic coil, which then activates the clutch within the transfer case and transfers torque equally to the front and rear drive line (again, 4H). When 2H mode is selected, the TCCM duty cycle command is turned OFF and the IWEs (hubs) located at each front wheel become disengaged to reduce drag on the front drive line.
Engagement and disengagement of the front wheels is done by the IWEs. The IWEs are normally engaged (no vacuum). Vacuum is supplied to the IWEs by actuation of the IWE solenoid commanded by the TCCM. When actuated, the IWE solenoid allows vacuum to pass through to each IWE. The IWEs disengage and allow the front wheel hubs to be turned freely from the front axel.
Note: when shifting to 2H mode in order for the IWEs to completely disengage, the vehicle steering wheel must be less that 90 deg and 5 seconds must have elapsed since the shift to 2H has been initiated.
The electric shift motor is mounted externally to the transfer case. It drives a rotary cam which moves the range fork within the transfer case between the HIGH range (2H, 4A, 4H) and the LOW range (4L). The electric shift motor only moves during a shift to and from 4L and neutral.
The TCCM directly controls the electric shift motor and can reverse polarity to reverse rotary of the cam and shift fork direction. The shift motor sense plate, an integral part of the shift motor assembly informs the TCCM of the transfer case position.
This transfer case is equipped with an electronically controlled clutch which is located inside the case. This clutch is used to synchronize the speed of the front driveline with the rear driveline as well as transfer torque in either of the three different 4WD modes. When the MSS is switched between 2H and 4A or 4H modes, the TCCM first energizes the clutch. Once the transfer case front and rear output shafts are synchronized, the front axel IWEs are engaged (no vacuum).
When the front and rear drive line are synchronized, the TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on a combination of pre-emptive and wheel slip response algorithm. Pre-emptive response is based on: steering wheel angle, vehicle speed, throttle positions and available power train torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.
The TCCM has an alternative cold strategy which is used to warm up the front axel in cold temperatures to improve driveline synchronization. When ambient temperature is below 0 degrees Celsius (32 F), IWEs engage after initial key cycle and a drive gear is selected. The hubs remain engaged regardless of 4WD mode change for 3KM (2 miles). Once distance traveled has been achieved, IWEs disengage (supplied vacuum) if the vehicle is in 2H. Distance traveled resets only if the temperature is below the calibrated threshold and another key cycle has occurred OR if the customer has shifted to park and back to a drive gear within the same key cycle.
In 4A, the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. When 4WD is no longer needed (during cruising or steady state driving) the system defaults back to RWD mode by setting the duty cycle output to 0. In situations where it’s necessary to negotiate a tight turn, the clutch duty cycle output is reduced which allows for a slight difference between the front and rear drive shafts; however, the system remains on an alert mode and when it’s necessary torque will be transferred automatically.
How is torque transferred you ask? Just watch this. Keep in mind this T case isn't in the F150. Although it is the same TOD operating principal from the same manufacturer:
Below I attached a media release PDF from Borg Warner Co. Ford uses a lot of their components including their TOD Transfer Case.
Now with this in mind I ask myself: how is Ford's history with wet clutch packs in the F150? and then I think about Ford's never ending issues with Limited Slip Diffs and realize that as great as 4A might be in the short term, it's gonna be nothing more than a 'Service at dealer mode' for guys who never change their T case fluid.
Lesson from all this: Do your proper maintenance checks!
I'm nearly certain that my 2016 F150's uses a Borg Warner 4417 TOD TC
Last edited by Airborne_Ape; 12-08-2016 at 07:25 PM.
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