4Matic in CLA explained (german comment) - Page 2 - Mercedes CLA Forum
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post #11 of 14 Old 08-06-2013, 05:28 AM Thread Starter
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Hello, as i understand, the clutch acts like a locking device between the front and rear axle.
If the clutch is fully locked, the actual torque distribution depends on weight distribution between the front and rear, tire parameters, and of course friction coefficient, and others.
If the front wheels are on a low µ surface, and the rear wheels are on high µ-surface, the front wheels can take no significant torque, and all the driving force is generated by the rear wheels (clutch in locked state). In this case, almost 100% of the torque is transferred to the rear wheels.
The valve can limit the transferred torque, and the clutch will start to slip in that case.

I think it has its similarities to a haldex system, but in its details, its different, as far as i can see. (they also state that its a new development)

Last edited by petera; 08-06-2013 at 05:35 AM.
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post #12 of 14 Old 08-06-2013, 07:28 AM
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Everything I've read about the CLA's 4MATIC system says the max torque to the rear is 50% giving it a 50/50 split. Since the CLA without 4MATIC is a front wheel drive with a transversly mounted engine, is it possible to eliminate all torque from the front wheels? Similiar question can be asked of other MB models which are RWD. Can the 4MATIC version of the same car divert all the torque to the front wheels if the conditions dictate?
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post #13 of 14 Old 08-06-2013, 12:33 PM Thread Starter
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In the video they state, that it can transfer almost 100% of torque depending in the driving situation. In the video, the vehicle is on snow with the front wheels, and on (wet) tarmac with the rear wheels.
Since the clutch is locate between the front and rear wheels, it is able to lock them, i think. If the front wheels are on a slippery surface, they would spin, and not transfer a lot of torque. But the rear wheels have much more grip, and will transfer more torque than the front wheels.

The torque distribution for other 4matic systems depends on the setup of the system. Sometimes open center differentials are used, that have a fixed torque split ratio. They can be combined with a mechanism to fully lock them (manually). This forces the same speed upon the front and rear axle. If one axle starts to slip, the torque is tranferred to the other axle. (similar to CLA clutch).
Center differentials can also be equipped with a partially locking device (such as torsen differentials), or with electronically actuated locking mechanisms.

MB models use different techniques in the various models.

Here is a link to a more detailed article that gives an overview of 4matic system and goes into detail for the cla:
http://www.greencarcongress.com/2012...-20121218.html

The image in this article is also available in a slightly higher resolution at
http://blog.mercedes-benz-passion.co...cla-tech-1.jpg

Last edited by petera; 08-06-2013 at 01:45 PM.
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post #14 of 14 Old 08-07-2013, 12:41 PM
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I'll be interested to try for myself on slippery ice.
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