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mds5917

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Rocketeer Rick

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I want to throw in a silly anecdote that I've told before. 30 years ago (yow, that long? Now my head hurts), my family had a red over red 1991 2-door Explorer Sport. 4.0L, 5-speed, the first push-button 4WD vehicle my parents had owned. Dad was/is a big advocate of hubs that have to be locked in. Anyway, one winter, my mom wiped it out driving to work in the snow, hit a tree with the right side. Dad asked "where you in 4WD?" "No". "why not?" "I didn't want to use it all up".

Teasing Mom about it aside, it underscores the point someone else made in that most people have no idea how these things work. So it became very important to develop AWD systems that just work on their own without driver input. That's probably not in question, but it is exactly why the 4A option exists. The '91 was replaced with a black '98 Explorer Sport, this one with an automatic trans because that was paired with Ford's then cutting-edge "Control-Trac" system. The first 4A t-case used in midsized Ford SUVs. So, there's nothing truly novel or scary about 4A, it is just an ever-refined version of what's been around for decades.
 

TheObiJuan

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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.
This sums up the (intelligent) i4WD system that Ford developed for my 2020 Explorer ST. I really enjoy the on-screen 4 wheel-display showing how the vehicle is primarily RWD, unless torque demand or throttle position dictate otherwise. In ECO mode I notice it stays in RWD until I use heavy throttle or leave from a light too quickly.

I’m really glad Ford included the 4A mode in the Bronco.
 

Rocketeer Rick

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This sums up the (intelligent) i4WD system that Ford developed for my 2020 Explorer ST. I really enjoy the on-screen 4 wheel-display showing how the vehicle is primarily RWD, unless torque demand or throttle position dictate otherwise. In ECO mode I notice it stays in RWD until I use heavy throttle or leave from a light too quickly.

I’m really glad Ford included the 4A mode in the Bronco.
It really sums up the AWD system in almost every 4WD CUV and sedan on the market in the US, except for some Audis and Toyotas that still use a true full-time, differential-based AWD system. But the intelligent on-demand systems are by far the norm; they get there in different ways, but ultimately all allow the designers to minimize drag losses when not in use. And these days they are chasing every advantage in the MPG war.
 

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Yeah, I've now guessed your age at around 75. That's not meant as an insult, it's meant as someone that has a very solid mechanical/engineering mind that you typically don't see these days. And also someone that tends to use 10x the amount of words as the next generation. I'd like to introduce you to my dad(mechanical engineer), you all would have a field day:)
 

Mattwings

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I thought this article was excellent and I picked up knowledge that I didn't have before, so thanks Rick. I have posted this before, but the article details the Raptor case and design. From my understanding and research, the Bronco uses the same case and definitely the same transmission This might help add some real world application to the technical explanations in the article.

https://www.truckcamperadventure.com/ford-raptor-features-new-cutting-edge-transfer-case/
 

drive21bronco

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Do we know for sure that the Bronco's axles on the base model will have welded on ring gears? Or are we still just assuming this because that is how they are on the Ranger?
 

Natai

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Yes, you will have to do a bit of reading. You'll most likely also have to do a bit of noodling in your noodle basket to understand some of this, but it's not rocket science so have at it and read the whole article.
Thanks for posting the article, and for this comment.

The level of TLDR these days is just depressing. If it's much more than a tweet in length, most people won't even try.
 

NotApplicable

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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.
Thanks for all your info. Can you answer: is there a compelling reason for someone to _not_ leave the vehicle in 4A rather than 2H for _all_ normal use, given you’ve likened this mode to many other vehicles’ AWD systems that are always “on” (waiting for slippage)?

I’d assumed that there was indeed some such reason (other than just “you know you don’t need to drive the front axle on dry roads, so why not turn off AWD altogether” etc.), and that this reason was likely due to some significant difference between Bronco’s 4A and “AWD” of most modern cars.
 

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SamSepiol

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Hey everyone,

This is my first post here and I've been wondering if the 4A system in the bronco is the same as the Raptor. It sounds like a few of you have answered the question and that it is. If this is the case then this video could help explain how it works.

The New Ford Raptor Has Both 4WD & AWD!
 
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Rick Astley

Rick Astley

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Yeah, I've now guessed your age at around 75. That's not meant as an insult, it's meant as someone that has a very solid mechanical/engineering mind that you typically don't see these days. And also someone that tends to use 10x the amount of words as the next generation. I'd like to introduce you to my dad(mechanical engineer), you all would have a field day:)
Yea, those engineers, wily old guys!

Thanks for posting the article, and for this comment.

The level of TLDR these days is just depressing. If it's much more than a tweet in length, most people won't even try.
Had to look up what TLDR meant..... Guess I'm that old and out of touch, or have to use critical reading skills on a daily basis for work. Thankfully I'm not 75 quite yet.
 

harpo

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I want to throw in a silly anecdote that I've told before. 30 years ago (yow, that long? Now my head hurts), my family had a red over red 1991 2-door Explorer Sport. 4.0L, 5-speed, the first push-button 4WD vehicle my parents had owned. Dad was/is a big advocate of hubs that have to be locked in. Anyway, one winter, my mom wiped it out driving to work in the snow, hit a tree with the right side. Dad asked "where you in 4WD?" "No". "why not?" "I didn't want to use it all up".

Teasing Mom about it aside, it underscores the point someone else made in that most people have no idea how these things work. So it became very important to develop AWD systems that just work on their own without driver input. That's probably not in question, but it is exactly why the 4A option exists. The '91 was replaced with a black '98 Explorer Sport, this one with an automatic trans because that was paired with Ford's then cutting-edge "Control-Trac" system. The first 4A t-case used in midsized Ford SUVs. So, there's nothing truly novel or scary about 4A, it is just an ever-refined version of what's been around for decades.
the Problem isn't that it was 30years ago, the Problem is that 30 years ago is 1991! In my head 30 years ago is the early 70's.....
 

frinesi2

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I haven't read the article because I already know everything (lol jk I just haven't had time) but I can vouch for the authors and quality of the content.
 

wjfawb0 [hacked account]

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It's irritating to me how the regulatory environment has driven driver nannies, fuel economy, and cold start emissions to control so many aspects of new cars today. I'm sure well over 99% of car buyers have no clue, and that's why things are the way they are. I'm definitely an outlier. The lack of electronic nannies and fuel economy aids convinced me to buy the STI even with the old engine tech. The drivetrain is awesome, though.
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