Control Trac Technical Discussion

[gijoecam]

Dogfriend sparked a discussion in another thread that got me thinkin, and I wanted to do some more research and get some discussion going here.

So as not to hijack the other thread, this is where it started:

http://www.explorerforum.com/forums/showthread.php?p=1422405#post1422405


I understand the PWM as that makes perfect sense... by varying the pulse width, you vary the voltage, BUT, mechanically, how can 2.1V (roughly 13% of 14V) in 4high cause the wheels to hop and buck when making a tight turn in a parking lot? Mechanically, the transfer case has to be locked-up, regardless of what that voltage is, no?

Granted, all I can measure is the voltage, so I'm not seeing the duty cycle called for by the GEM, but as you mentioned, the voltage I measured is a function of the duty cycle, with a roughly linear relationship between 0 and 100%, right? That means that 0V at the brown wire is 0% duty cycle and 14V is 100% duty cycle, right? Everything in between is roughly a linear relationship, no? (i.e. 50% duty cycle should result in roughly 7V)


Here's what I just found out on the drive.
In 4 auto
Idle---0.740V
Rolling---- variable with throttle position and speed, everywhere from .74v to 14V when rear wheels are slipping.
Anytime the rear wheels were spinning, the voltage was 14V.
I did a brake torque just for the heck of it, and found that the max voltage at WOT with the rear wheels stationary was 5.8V.

4High
Idle and stopped---- 2.1V
Rolling less than 12 mph---- 2.1V
Rolling more than 12 mph, any throttle position---14.0V

4Low
Idle---2.1V
Moving at all, or any throttle--- 14V

So, what's that mean? I dunno.... This is why I wanted to open a new thread for some discussion. Basically, it appears that the GEM varies the pulse width, which, of course, varies the voltage at the clutch (which we already knew from numerous other discussions, and is evidence by the varying brightness of the LED for those of us that used a lighted switch for the BWM).

But, mechanically, is the transfer case locked, unlocked, or allowing some amount of slippage? Based on my limited knowledge of the inner workings of the case, I don't see how varying the voltage (and of course, the amperage) to the TCCC will vary the amount of torque sent to the front wheels. That would require something less than a 50/50 power split, which would also mean the clutches in the t-case were slipping as well.

Beyond that, in 4auto, as soon as any wheel slippage is detected, the voltage spikes to 100% (14V), which tells me that the TOD relay is telling the transfer case to lock completely (at least momentarily), right?

I really wish there was someone over at Borg-Warner that could answer these questions, or someone in the PDC I could talk to that designed this PITA system!!

-Joe

 

[dogfriend]

My understanding is that the duty cycle is measuring the current not the voltage.

I will dig out the scanner over the next couple of days and take some readings. It has been about 2 years since I last did it. The readings were rolling on dry pavement. I didn't leave it in 4wd high for very long because it was dry pavement.

 

[IZwack]

I don't see how varying the voltage (and of course, the amperage) to the TCCC will vary the amount of torque sent to the front wheels. That would require something less than a 50/50 power split, which would also mean the clutches in the t-case were slipping as well.

Many interesting questions brought up and I think this is a great topic.

But to add my 2-cents to the question above, yeah the clutches do slip somewhere below 100% lock (50/50 split). And as the friction plates wear away over time, it is harder and harder for the transfer case to achieve 100% lock.

But one point that must be made is that most of the time when the vehicle switches to 4HI, there isnt that much of a difference in speed between the front and rear wheels so the clutches arent being burnt away like it is when moving a manually-shifted vehicle from a stand-still using third gear. Simply put it, the computer detects a speed difference and reacts to it before that speed difference becomes too large. This is in agreement to your "idle" test - at idle, both the front and rear wheels should all be moving at the same speed (zero mph most of the time) so there is no speed difference.

I think the reason why the engagement gear cracks in some vehicles is related to this. In my opinion, the reason why the engagement "ramp" gear cracks is, when we "floor" it in 4wd when were stuck in a ditch, the speed difference between the front and rear wheels grows too rapidly per unit of time and there is a great amount of speed and kinetic energy difference between the front (which is usually not moving at all because 2.1v is still letting the case to slip) and rear (which by now is moving rapidly) output components that this gear is just shattered when it is squeezed by the "ramping" balls/electromagnet.

Well I dont know if what ive said aided in the discussion at all cauz to me, it sounds like im just yapping!

 

[gijoecam]

Well I dont know if what ive said aided in the discussion at all cauz to me, it sounds like im just yapping!

Naah.... as far as I'm concerned, you're the expert on the mechanicals of the 44-05. That's why we missed you so much when you were out sick there.

The duty cycle is going to result in a net current and a net voltage, with the difference being the current will peak at about 4.6A at 14V. (I ran the DMM that way too just out of curiosity)

I know that, when creeping in 4high, I get the typical driveline bind-up and hopping as thought the case is locked-up solid. Maybe as the clutches wear over time, that'll start to happen, but I'm not entirely sure that would be considered *normal*....

Just thinking out loud, in theory, the only time there should be any significant difference in driveline speeds would be at low speeds when cornering or parking. Anytime you're rolling in a straight line, if you nail it, there will be very minimal slippage before it locks. I suspect you're right about the sudden application causing that cracked ball-ramp. If the system didn't react fast enough, then, yes, the longer it waits to engage, the more jarring the application would be.

Buuuut.... If the clutches were wearing, wouldn't that reduce the severity of that impact? Like popping the clutch on a worn-out transmission....??

Again, just rambling out loud here.....

Getting back to the engagement issue... It would be neat if we could rig one up on a bench attached to a variable voltage generator, and measure an input torque and a front and rear output torque..... or just lock the input and measure the torque between the two output shafts.... this could be fun!!

I still think that the case is either locked or unlocked.... It just doesn't seem to act otherwise, and I would think that the Ford marketing department would have advertised it as a variable torque splitting system if that's what it did.... That was in a time when those systems were getting hyped on a few other vehicles. It was also advertised as 'Automatic 4 Wheel Drive', not 'All Wheel Drive.'

-Joe

 

[Wrench]

Explorer Control Trac

The drive shaft speed sensors are taking a measurement 50 times per second for an almost seamless adjustment of the electromechanical clutch that controls the transfer case output in the 4x4 systems "automatic" setting.

In 4x4 "high" the system effectively locks the front and rear driveshafts together.

In 4x4 low the system locks the front and rear driveshafts together but adds a 2.48:1 gear reduction

 

[Wrench]

Control Trac

I could be a bit confused here but did not the 4404 t-case come with a Viscous Coupling to control the torque split and this is what Ford called Control Trac. Was the 4405 t-case (part-time) also called control trac?

 

[dogfriend]

In the Factory Repair Manual, Ford calls the 4404 AWD (All Wheel Drive) and they call the 4405 A4WD (Auto 4 Wheel Drive). The 4405 is also known as Control Trac. The 4404 Viscous Coupled system was used with the V8 Engine only. The 4405 was used with the 4.0L V6 engines (both OHV and SOHC).

 

[dogfriend]

more

 

[gijoecam]

They were both called Control Trac systems. Control Trac is a copyrighted brand name from Borg-Warner. Both systems were Control Trac units, but if you look closely to the door emblems, one says Control Trac and the V-8s say Control Trac All Wheel Drive.

 

[dogfriend]

Ok, I did some runs with my scan tool connected on a muddy road so I could test out all three modes. I made a movie of it here , but it is probably a little hard to read.

I output four parameters (the max allowed at one time), 4wd Switch Position, PWM duty cycle #1 (there is only one, so I don't know why they called it that), Transfer Case Front Output Shaft Speed, Transfer Case Rear Output Shaft Speed.

In 4wd Auto, the PWM duty cycle starts at 0.78% and stays there unless the rear wheels start to slip. In the movie, I get the signal up to 12%, but on a steeper uphill, I saw 26% at one point. At highway speeds, the signal stays at 0.78%.

In 4wd High, the PWM signal is 13.33% both stopped and rolling. It stayed at 13.33% no matter what I did, even when I punched the throttle on uphill sections.

4wd Low is very interesting: the signal is 3.92% when stopped, but increases to 38.44% immediately after the truck starts rolling. It stays at 38.44% no matter what , except it goes back to 3.92% when stopped.

 

[Alfonzman00]

Sorry to jump in with something a bit off topic, but... I was wondering what changed in the Control Trac system when Ford changed the 4WD mode selection from 2WD, 4WD AUTO, 4WD LOW as in my 96 EB, to the newer setup in the 97 models, which doesn't include a 2WD mode, and has a 4WD HIGH mode. I am assuming that they took the default setting, 2WD which delivers power to the rear wheels only, and made it 4WD AUTO, which is continuously monitoring the wheels for slip. Did they change the programming in the GEM? If so, is there any difference in the transfercase hardware, or is it just a programming setup. I am of course assuming the transfer case was not hugely modified from 96 to 97. I am curious because if it is just a software change, could one, theoretically replace a 96 GEM and dash switch, with a 97's setup, and instantly get a 4WD system upgrade.

Just wondering, Thanks!

 

[gijoecam]

Hmmmm... Interesting.... so it would appear that in 4 auto or 4 low, the veriation in the duty cycle is enough to produce 14V at the coil when the circuit is open (i.e. BWM switch off). So, maybe now what we could look at is what the current through the transfer case does when it's engaging.... I'd still be curious to bench-test a transfer case. Anyone got a spare working t-case laying around?

Alfonz,

the differences between 96 and 97 were many. The lack of 2wd is just one of them. They also got rid of the center axle disconnect on the front axle, and changed the front output shaft on the transfer case from a yoke to a flange IIRC. They got rid of the 2wd mode, and completely reprogrammed the GEM. Swapping out the GEM would be difficult as there were numerous other changes. I'm not saying it's impossible, but it's not going to get you where you want to go. If you're looking for a true 4wd mode, look for the 'anti-brown wire mod' information for the 95s and 96s in the 'Comprehensive Brown Wire Mod' thread.

-Joe