Teach me -- Electro-magnetic coupler

Potcher · Sep 18, 2015

Anyone have good knowledge of the electro-magnetic coupler in the rear that applies power to the rear wheels? I generally understand how these types of couplers work, just not certain how Toyota has implemented it.

Setting aside how the ECU decides to apply power, I'm curious how it the coupler actually works. Doesn't seem that there is a lot of info specific on the HL, but I have found a little info on Rav4 sites and assume they are the same units. Some of my questions:

Does the prop shaft (driveshaft, whatever you want to call it) to the rear constantly spin regardless of whether the coupler is engaged?

Is it really just the clamping force of the coupler that "picks" up 50% of the power? I.e., is thereotically possible for greater than 50% of the power to go to the rear if the the clamping force was greater? Without a lockable center differential, it's not clear to me how that "50%" gets to the rear.

Is the coupler fluid filled? Is this a future maintenance issue?

Will the coupler slip/give if the rear wheels were hung up (ignore how you might do this, just trying to add to my understanding)?

I have other questions, but this is a start.

MN-10kLakes · Sep 18, 2015

Master Sweeney has given a great summary that addresses many of your questions.

http://www.toyotanation.com/forum/333-3rd-generation-2014/772266-awd-system-specifications.html

Potcher · Sep 18, 2015

MN-10kLakes said:
Master Sweeney has given a great summary that addresses many of your questions.

http://www.toyotanation.com/forum/333-3rd-generation-2014/772266-awd-system-specifications.html

Thanks, I think my use of a hyphen between electro and magnetic precluded it from my search...

Potcher · Sep 18, 2015

Read through Sweeney post referenced above... thanks, Sweeney.

Still have a question. With open diffs everywhere, what's going to happen if the front wheels have no traction? Won't it rob all the power to the rear even if coupler is engaged at 50% and the rear has traction?

WishinItWas · Sep 18, 2015

I could be wrong but wouldn't the brakes be selectively or intermittently applied to those front wheels to allow the rear to work?

sweeneyp · Sep 18, 2015

Ideally both front brakes should pulse to pulse power to the rear via the center diff. The job is not to overbrake and stop the vehicle. However from what I've seen of AWD systems on crossovers, they all pretty much suck at this except for a few exceptions. This is where a true locking center differential comes into play and is so dang helpful. Unfortunately you can only get that on 4x4's. This was one reason I prefer the 2nd gen's setup over the 3rd gen's slip-n-grip. It uses a viscous coupling in the t-case to "automatically" (in actuality it always has power) divert power to the rear if the front axle spins faster than the rear axle. No brakes needed (though it still used torque vectoring via brakes like the 3rd gen). That's what made it a full time 50:50 AWD setup.

As for that ramp, all I can say is good luck. I've nearly gotten mine stuck like that (I have FWD though).

Potcher · Sep 18, 2015

Agreed. I would take the mpg hit to have a viscous, at least you know half the power will be there. Other vehicle is a '12 Touareg with a Torsen center, 40/60 split, open diffs though relying on ABS, it's still superior to the HL, so it may get duty that day.

Teach me -- Electro-magnetic coupler

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