How AWD works (Includes Ford's 4A system)

[Glcmranger]

@Glcmranger: Not only was that covered in the opening section of the article, but one of the contributors to the article (and is credited at the bottom of the article if you cared to look up his profession/industry), @Rocketeer Rick, commented on exactly your question yesterday.

Feel free to ask questions which weren't immediately covered in the article. It's quite detailed and informative!

Thank you for the response. The question posed was truncated for the sake of brevity. The question still stands, does the Bronco have a dual range transfer case or not? If the Bronco does not have a dual range transfer case, then by definition, it is All Wheel Drive (AWD) system in the traditional sense. it is acknowledged that both the 4WD and AWD systems function to manage torque to specific axles and or wheels. Calling both systems synonymous by unifying the two constructs of both systems under the rubric of "AWD" is possible but ignores the matter of low range gearing capability. The distinguishing and unique difference between the two is the existence of a dual range transfer case. Once an AWD system adds a dual range transfer case, the system has traditionally be called 4WD. If the existence of a dual range transfer case is irrelevant to the distinctions of the two, then yes, all systems may be classified as AWD. The point is that there is a difference and that difference is in the existence of a transfer case which allows the use of a lower range gearing. The contention is that this difference turns any AWD system into a 4WD system by definition. If for the sake of unifying the two into one construct, there is no useful advantage other than the application of preference for all systems to be the same but with technical distinctions based on which wheel gets how much torque, when and under what traction/friction conditions. Making the distinction between having a dual range transfer case and not having a dual range transfer case is significant in off road capability and utility. Bottom line, it is proposed that a significant and material difference exists between a 4WD system and an AWD system based on the presence/lack of a dual range transfer case and that being one of dual range capability. If an AWD system can achieve the same capabilities associated with a system that has a low range capability, then yes, there is no difference at where the rubber meets the road. If there is a material difference, then the ability to distinguish between the systems (one with transfer case and the other without) becomes meaningful and useful.

With great respect,

Glcmranger

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[Rick Astley]

yeah, but will it make coffee? That's the big question

The article makes no mention of cupholders. I think a strongly worded email to Ford is required to understand the full cupholder potential here.

The article is longer than War & Peace, perhaps a few crib notes and answers would not hurt.

Hope it didn't come across that I wrote this article. I'm not experienced enough in these new technologies to have written this at all. Give me some nice 50's/60's tech and I can fumble my way through most of it with a shop manual

It's an article that is more technical than most people will want to go in understanding their vehicle. There is a nice comment section at the bottom of the article that has more questions from us plebes, that's sort of like crib notes. Otherwise, like many things in life, you're going to have to take the 10-15 minutes and actually read an entire article (not trying to be rude or curt here, i'm impartial. Read the article if you want, or not.)

This type of situation is also why you see people driving AWD/4wd vehicles who have no idea how to properly drive a vehicle based on the inherent advantages/weaknesses of their drivetrain. Spending the 4-5 hours of self-study or going out to your local performance driving school for a half day introduction to fundamentals class is astronomically beyond what 99% of car owners are willing to invest in their own driving skill.

It took me multiple reads to understand some of the basics in that article, especially as the technology evolved to where we are today. There were also videos embedded in the article that helped me visually understand the topic a lot. I'm not a mechanical engineer, so it's not common knowledge to me at all. I had to read, re-read, contemplate, and do further reading to understand parts of it.

Once I grasped it then it was pretty cool and it's going to be helpful for off road driving to know WHAT the vehicle is doing mechanically and why, and thus work with the system as designed.

 

[Carolina Jim]

Give me some nice 50's/60's tech

If I recall, the height of technology then was the hand-held TI calculator

 

[Rick Astley]

If I recall, the height of technology then was the hand-held TI calculator

Before my time to know exactly, but I thought it was the underwire bra that was the height of tech at the time?

 

[Boston182]

 

[Burndog]

Gonna have to wait till tomorrow on that, but much appreciated Rick

 

[NotApplicable]

So Jalop has a tendency to continuously crash my mobile Safari tab for long articles and I can only scroll so far in this one without it crashing and reloading.

Can someone explain the difference between the 4A mode in the Bronco’s advanced transfer case and something like (insert brand here)’s AWD system?

I know that there are threads on the 4A system, but the information being spread in those threads is not consistent. Some claim the Bronco’s 4A setting automatically switches between 2H and 4H based on conditions, but I assumed it was capable of some variable ratio of F:R torque split; something more than 2H but less than locking the axles?

Most importantly: are there any speed limitations to 4A mode, is it bad to run on dry surfaces, etc? If no to both, why run 2H instead of 4A even on-road during your region’s bad season?

 

[mdepll]

So Jalop has a tendency to continuously crash my mobile Safari tab for long articles and I can only scroll so far in this one without it crashing and reloading.

Can someone explain the difference between the 4A mode in the Bronco’s advanced transfer case and something like (insert brand here)’s AWD system?

I know that there are threads on the 4A system, but the information being spread in those threads is not consistent. Some claim the Bronco’s 4A setting automatically switches between 2H and 4H based on conditions, but I assumed it was capable of some variable ratio of F:R torque split.

Most importantly: are there any speed limitations to 4A mode, is it bad to run on dry surfaces, etc? If no to both, why run 2H instead of 4A even on-road during your region’s bad season?

Completely confused. Can anyone explain in layman’s terms. Bronco is 4WD but ha advanced 4 auto. So, is it still 4WD or not when optioned with advanced 4 auto.

 

[NotApplicable]

Completely confused. Can anyone explain in layman’s terms. Bronco is 4WD but ha advanced 4 auto. So, is it still 4WD or not when optioned with advanced 4 auto.

Both the normal and advanced transfer case have the “traditional 4WD” 2-speed settings of 2H, 4H, and 4Lo.

 

[grimmjeeper]

Cheat notes anyone ?

Yep.

Read the article.

 

[mdepll]

Yep.

Read the article.

Well, for this novice that’s not a helpful response. Hopefully someone else is able to help. Thanks anyway.

 

[OmahaKevin]

Before my time to know exactly, but I thought it was the underwire bra that was the height of tech at the time?

1972 for the first consumer handheld calculator by TI

 

[Rocketeer Rick]

Sigh. I'll type it again. OK, its like this - by the SAE (Society of Automotive Engineers) definition, AWD means that all wheels on a vehicle can be driven. On a motorcycle, that would be 2WD. On an Oshkosh fire truck, it would be 8WD. So in the case of a normal 4-wheeled vehicle, 4WD is AWD, or at least it is the specific subset that applies to the situation. Now, of course, you'll get strong pushback by folks that have bought into the old saw that 4WD has to mean a 2-speed transfer case, etc. etc. But by the actual industry definition, no, those beliefs mean little. So the article talks about that.

It also dives into the different categories of AWD/4WD system types and what their distinguishing features are, and what you can do with them. This is often where hype and media and marketing really mush up the issue. In the case of a typical crossover vehicle or AWD sedan, the base vehicle is FWD. The rear wheels are driven in a number of different ways in an on-demand fashion. Bronco Sport falls into this category and has two distinct systems for achieving sending torque to the rear wheels, depending on version.

The article also talks about AWD systems that use a a center differential and how they tend to distribute torque. It delves into the specific sub-case of the Subaru STI, and the way it gives the driver control over its operation.

It talks about different variations of transfer case drive systems, which are distinct from the typical CUV in that the platform is inherently RWD, and has one of several means to drive the front. Typical truck or 4x4 applications fall into this category. But there are a lot of on-road systems that are transfer case based as well. The Cadillac CTS sedan, for example, has a very compact t-case that contains an on-demand clutch to drive the front and is very tightly packed against the transmission and oil pan. The new Explorer is back to being RWD, but it is still built on a version of the CD6 platform that underpins the Fusion. But it still has a north-south engine, trans and a transfer case. Its laid out sort of similar to the CTS. Its an "SUV" and is relatively boxy, but still only available as an on-demand AWD with no low range.

The Bronco is much more of the traditional truck lay out. There is a 2-speed transfer case in all versions. This is pretty well described in Ford's documentation, actually. All models have a low range, and the low range in the 4A version of the case is actually lower than the base case, and will yield a shorter crawl ratio. The 4A is different in that it adds an automatic mode to the 4WD that exists in addition to the normal modes of 2HI, 4HI & 4LO. That "4A" mode uses a clutch that allows it send torque to the front axle on demand. There will be several facets to control logic; different control maps to look and wheel slippage, throttle position, even vehicle stability, etc to predict when it'll be needed. So, in that operation, you could argue that its working like an AWD system by the old off-roaders' definition. But it still falls back on being 4WD when you manually engage 4HI or 4LO. That will engage a rigid coupling to lock the front and rear axles together. I believed I touched on that in the Bronco Sport overheating thread when it was asked over there.

So, consider the 4A to be a hybrid function system; traditional 4WD with an AWD element overlaid on it to allow street / all weather use.

 

[mds5917]

my head did hurt...

...but your 'cliff note summary' of the 'cliff note article' of the technical docs made me feel better already....

 

[Rocketeer Rick]

my head hurts

You get used to it after a few years...

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