Thommo Thompson

Im trying to work out what system the new 2018 X253 GLC class models use for transmitting power to all wheels.
Not looking for marketting terms, im tyring to work out what exactly is the coupling mechanism; electro hydraulic, electromagnetic, electro-mechanical (worm-gear & cam) and what exactly is the typical at rest torque split.

I read on this website that V6 diesel models (like that in the 350d) have permanent type system which is 40:60 front to rear wiht an electromagnetic locking clutch as well.
https://media.daimler.com/marsMediaS...l?oid=29978631

Now, mercedes dont put any of this kind of information in specs sheets or brochures, so theres nothing enticing the consumer to perhaps look at the benefits of the more expensive model during their research. Fools.
Also, when i look up any 4matic information on the net, all I can find is generic marketting garbage which i dont think applies to the GLC class' 4matic system. (talks about 50 50 splits, and 45/55 splits.)
Where is the coupling, (trasnfer case or diferential), this makes a big difference. if its at the rear diff, then max torque to the rear can only possibly be 50%, and all my resarch suggests thats where its located. so what is going on.

Its jsut all about as clear as mud.

PLease dont send me a link to the 4matic marketting garbage on mercedes benz website.
Id like to hear form anyone who knows whta the actual technical implimentations are on the current 2018-19 model GLC class.

mtberman

The US-spec GLC300 4matic has a permanent AWD system. It is roughly comparable to earlier Audi Quattro setups, and is similar to Subaru's systems in VDC, XT, WRX, and 6-cylinder models prior to their switch to CVTs. The system features a planetary gear transfer case that distributes power 45 front and 55 rear as the default. The transfer case is mounted to the transmission in modular fashion, as opposed to previous versions where it was integrated into the transmission case. Power is then fed to a center differential. It is a mechanical multi-disc clutch that operates as a limited slip differential would. I don't know if it's wet or dry. It senses F/R slip and manages F/R power distribution as needed, allowing significant power to be sent to the rear wheels if necessary. Once power is downstream, the system uses the ABS and VSC sensors to manage left/right power distribution at both the front and rear.

Thommo Thompson

ok.
The system features a planetary gear transfer case that distributes power 45 front and 55 rear as the default.
Power is then fed to a center differential.
Isnt THAT a differential?
A multiplate clutch isnt a differential so this is where everything confuse me.
m a logical thinker, everything has to be described in perfect terminology or else it doesnt make sense and just muddies up the picture.

So let me just double check i have it right in my head.
Power is fed into the 45/55 differential, but then some kind of electronicaly controlled muticlutch pack can competely disconnect... what? Is it locking the diff housing to effectively lock the cenre diff (like an active rear dif)? or is it disconnecting a set of wheels and if so which wheels is it disconnecting? front or rear?

Now torque (engine torque, not availabel torque) can only possibly be sent maximum 55 to the rear, and a maximum 50 to the front, or anywhere in between using the electro-hydraulic operated locking disc clutch which i think locks the centre diff in varying strengths.
So the electronic clutch in this system is doing something completley different for a different purpose than most AWD soft roaders, whos electro clutches are used to disconnect or connect an axle.

Thommo Thompson

See i refer to a multiplate clutch as mechanical, if it is mechanically controlled and not electronicaly controlled.
Here my list of differnet mechanisms and how i am describing them.
in order of my opinion worst to best:

electromagnetic - field coil pulls a pilot clutch plate with steel ***** together which uses rotating force to clamp the input and output together, crappy for torque distribution as they really can only lock or release. no real measurable active torque distribution possible, regardless of what the manufacturer sais. Even though they are multiple plate clutches, the system realy only makes use of the multiple clutches by gently locking the axles rather than an abrupt lock.

Electro-Hydraulic - electric Pump and electric controlled valves control hydraulic pressure to apply clamping force on a series of clutch plates, which can much better adjust minor amounts of torque between front and rear. This is why this type of system is used in lots of rear axle differentials with active torque distribution between left and right.

Electro-Mechanical - A clutch pack whos clamping force is goverened by a rotating cam disc which is roteated by either a worm gear (superior to all other systems in its speed and clamping strength), or a geared motor and lever, (like BMWs Xdrive uses)

Torsen - Purely mechanical centre differnetial with no electronics involved. good for sand but no good on rock climbing as a 100% slipping wheel cannot be limited

Dog clutch - Common in part time 4WD vehicles, and bulletproof and simple.



So of all these i think this GLC uses the electro hydraulic one, but uses it to clamp the diff to the output axle variably locking the diff.