Most interesting - More 4WD ramblings

"HammerheadFistpunch" (hammerheadfistpunch) 11/26/2018 at 17:53 • Filed to: hhfp, 4wd

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So I’ve got a thing about 4WD... !!!error: Indecipherable SUB-paragraph formatting!!! ? Anyway, I was looking for the history of the systems and terms (because fun) and I found something interesting - The SAE actually has a paper on this topic. !!!error: Indecipherable SUB-paragraph formatting!!! .

It’s a recommendation for classification of All-Wheel Drive systems through class III (1 ton trucks). Anyway in my mind there is no difference between AWD and 4WD and that there are only 3 overarching systems for 4 wheel drive systems that are as follows:

Part time

Full time

On demand

I had no idea until just now. I can’t actually read the paper without parting with $80 or so of my real monies but wikipedia has a summary:

Part-Time AWD systems require driver intervention to couple and decouple the secondary axle from the primarily driven axle and these systems do not have a center differential (or similar device). The definition notes that part-time systems may have a low range.

Full-Time AWD systems drive both front and rear axles at all times via a center (inter-axle) differential. The torque split of that differential may be fixed or variable depending on the type of center differential. This system can be used on any surface at any speed. The definition does not address inclusion or exclusion of a low range gear.

On-Demand AWD systems drive the secondary axle via an active or passive coupling device or “by an independently powered drive system”. The standard notes that in some cases the secondary drive system may also provide the primary vehicle propulsion. An example is a hybrid AWD vehicle where the primary axle is driven by an internal combustion engine and secondary axle is driven by an electric motor. When the internal combustion engine is shut off the secondary, electrically driven axle is the only driven axle. On-demand systems function primarily with only one powered axle until torque is required by the second axle. At that point either a passive or active coupling sends torque to the secondary axle.

In addition to the above primary classifications the J1952 standard notes secondary classifications resulting in a total of eight system designations:

Part-Time Non Synchro System

Part-Time Synchro System

Full-Time Fixed Torque System

Full-Time Variable Torque Passive System

Full-Time Variable Torque Active System

On-Demand Synchro Variable Torque Passive System

On-Demand Synchro Variable Torque Active System

On-Demand Independently Powered Variable Torque Active System

!!!error: Indecipherable SUB-paragraph formatting!!! . Whats funny is I came to this conclusion seperatly.

Of course the difference is I say there is no AWD and they say there is no 4WD. Tomato/potatoh. The moral of the story is that they refuse to play the “4WD vs AWD” game.

Good Job SAE.

p.s. if any of you engineering types have access to the SAE site and want to slip me a copy of that report I would LOVE to read it. You can reach me at hhfp.kinja@yahoo.com

Future next gen S2000 owner > HammerheadFistpunch 11/26/2018 at 17:56

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Today I found a boat that was listed as FWD. Not that this is relevant but I thought I’d share.

HammerheadFistpunch > Future next gen S2000 owner 11/26/2018 at 17:56

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pffft, no enthusiast buys a FWD boat!

For Sweden > HammerheadFistpunch 11/26/2018 at 17:57

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Driven wheels? pfft

Future next gen S2000 owner > HammerheadFistpunch 11/26/2018 at 17:59

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But it’s the best handling FWD boat ever. Better packaging, more fuel efficient, and other FWD arguments.

For the life of me, I can’t wrap my head around what that are creating the acronym from.

HammerheadFistpunch > Future next gen S2000 owner 11/26/2018 at 18:02

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Forward?

Urambo Tauro > Future next gen S2000 owner 11/26/2018 at 18:03

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That’s funny. I’ve never driven a motorb oat, but I’ve always imagined that it would be like driving a FWD car in reverse in an icy  parking lot.

Future next gen S2000 owner > HammerheadFistpunch 11/26/2018 at 18:05

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Wrong Wheel Drive (41%) > HammerheadFistpunch 11/26/2018 at 19:10

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Interesting take on this, I always have had people ask what the difference was between 4WD and AWD. The way I have always explained it is that Part-Time was 4WD and that Full-Time/On-Demand were AWD in a nutshell. Since that is at least generally how they are marketed.

On the topic of 4WD/AWD though I have always wanted to play with the DCCD in my Subaru but have seen as gimmicky to some degree. Maybe it would be better to set it to full rear, it might understeer less. But I have always just left it set to Auto since I dont really push it to the limit anyways. Still would be nice to know how much of an effect it really has.

SilentButNotReallyDeadly...killed by G/O Media > HammerheadFistpunch 11/26/2018 at 20:45

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I’ ve always thought that, while it is possible to have four driven wheels, it almost never comes to pass unless the drivetrain is completely locked across all four wheels . O therwise the engine power just takes the path of least resistance (or is mechanically redirected from that path to another so forward momentum is not lost). And besides all that, a fully locked 4x4 drivetrain is not all that practical nor functional in most real world situations.

So both 4x4 and AWD are actually just misleading  marketing terms...

HammerheadFistpunch > SilentButNotReallyDeadly...killed by G/O Media 11/26/2018 at 21:10

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in terms of triple locked or is not 4 wheel drive I’ve always taken the stance that it can drive any and all 4 wheels at a given time... but it doesn’t have to at all times to be 4 wheel drive. i mean a 300 hp engine doesn’t make 300 hp most of the time 

functionoverfashion > Future next gen S2000 owner 11/26/2018 at 22:01

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Forward-facing drive where the prop leads the gearcase. I don’t think it’s an acronym except in a marketing boardroom maybe I think it’s literally just called a forward drive. When I left the marina world they weren’t much of a thing, still a new idea. That was only 5 years ago.. 

functionoverfashion > HammerheadFistpunch 11/26/2018 at 22:03

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Funny, but I think it’s mostly true. The true boating enthusiasts I know mostly have either direct drive, v-drive, or outboards. The sterndrive is the FWD-only Toyota Highlander of boats. Pretty good at everything, great at nothing. 

nermal > HammerheadFistpunch 11/26/2018 at 22:18

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It would be interesting to see the minimum number of wheels that need traction in order for the vehicle to move.

Put 1 /2 / 3 wheels on rollers to simulate zero traction to test. Both flat and on an incline.

Kinda like that failed Honda CRV test that was posted a few yrs ago, but more involved. 

Tim > HammerheadFistpunch 11/26/2018 at 22:58

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For me, 4WD means it’s selectable and has a 2-speed transfer case. Full-time 4WD is a bit of a gray area because some (Quadradrive II) run in 2-Hi until the system senses the need to engage the front axle, but shifting to 4-Lo locks it in. AWD is single speed, full-time, including torque on demand. Basically, 4WD is what I drive, and AWD is what I pull out of the sand and snow.

HammerheadFistpunch > functionoverfashion 11/26/2018 at 23:04

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surfing is making them popular since there is now a real benefit to not have a meat mincer on the back

HammerheadFistpunch > nermal 11/26/2018 at 23:34

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1 is the correct answer.  if i locked all 3 diffs in my truck 100% or engine torque could go to that one wheel (to the limits of traction).  even with brake based systems you could do it assuming the engine and gearing produce enough torque.

HammerheadFistpunch > Wrong Wheel Drive (41%) 11/26/2018 at 23:41

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I think thats the way a lot of people think of it, but it gets you into a lot of trouble when it comes to exceptions. I think the SAE method covers the exceptions.

as for the dccd, you and are in the same boat that if you want full rear it means locking the center and disconnecting the front axle.  all the DCCD does for bias is increases the locking effect from (I would guess about 2.5:1 bias ratio) to fully locked (100:0) but that means the fronts and the rear are forced to go the same speed, no matter how you set the DCCD you wont get any more rear bias, just more potential torque transfer (100% either way vs say 75% either way)

SilentButNotReallyDeadly...killed by G/O Media > HammerheadFistpunch 11/27/2018 at 04:18

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Exactly. Work with what’s possible not what’s actually happening...

In which case, distinctions are dust.

Future next gen S2000 owner > functionoverfashion 11/27/2018 at 10:11

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I know what the drive is. I’ve read about them quite a bit. It is the FWD that is throwing me off. Forward? Forward Drive Drive - like a PIN number.

functionoverfashion > Future next gen S2000 owner 11/27/2018 at 12:23

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oh, I gotcha. I guess it’s just short for forward? Yeah, doesn’t make a lot of sense. I also don’t really feel that leading with your prop is a great idea, at least not in any body of water with rocks (mine has many). 

Future next gen S2000 owner > functionoverfashion 11/27/2018 at 13:25

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Trade-offs. Sure you mess up your prop but you eliminate the possibility of a wake surfer getting there face chewed up. I wonder if it would be better to strike the prop over a lower unit though.

functionoverfashion > Future next gen S2000 owner 11/27/2018 at 20:45

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The surfing thing is for sure a driver of that. I think if you whack a rock hard enough, it’s going to be the same either way. But on that note, it may not be any worse having it forward vs. “normal”