AWD vs. automatic-4WD (4A)
12-08-2016, 07:19 PM
#52
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 // Part Number GL34-7A195-BD
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 // Part Number GL34-7A195-BD
Last edited by Airborne_Ape; 12-08-2016 at 07:31 PM.
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02-05-2023, 04:19 PM
#54
Senior Member
I haven't tried it in 4A.
The probem with 4H is it will help you hook up like a **** out of the hole, but it will hurt your top end speed. You can shift back to 2H, but it won't come out of 4H until you let off the throttle.
The probem with 4H is it will help you hook up like a **** out of the hole, but it will hurt your top end speed. You can shift back to 2H, but it won't come out of 4H until you let off the throttle.