Originally Posted by evo200
The drive is taken into the epicyclic through the planet carrier.
The planet gears have 13 teeth
The rear output anulus has 58 teeth
The front output sun has 32 teeth
So you have a rear output ratio of 13/58, and a front output ratio of 13/32, or 4.46:1 versus 2.46:1
Wont bore you with the maths, but you end up with 0.64reccurring to the rear, and 0.35reccurring to the front.
The viscous coupling connects between the sun and the annulus to PROMOTE equal drive between the two.
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So does that mean that the annulus driving the rear prop, and the sun gear driving the front prop, are rotating at different speeds and the VC tightens up to stop the slip between them to give an equal rpm beween the two outputs providing there is an equal amount of grip at all four tyres when driving in a straight line?????????!!!
Hope that makes sense!!!!!!!!!!!!!!!!
no - when all wheels have equal grip and rotate together, the sun and annulus rotate at the same SPEED, and in this condition the VC does nothing, as both sides of it are rotating at the same speed too.
The gear ratios between the sun/planets and planets/anulus create the TORQUE split, not a SPEED split - however the epicyclic gear assembly does allow differential speed to occur between sun and anulus (ie front and rear prop, when there is loss of grip at one end), this is when the VC starts working as it now has both halves moving with respect to each other which effectively causes 'drag' if you like, between the front and rear outputs, which is the bit Bernie refers to as 'promoting' equal drive.
Remember, the centre diff action (the epicyclic gear assembly) is TORQUE sensitive, whereas the VC is SPEED sensitive. Apart from the viscous 'drag' effect when the front and rear shafts turn at different speeds during front/rear slippage conditions, the VC plays no part in the torque split front-to-rear.