It had already almost been forgotten, the spur-wheel gear for the offset between the driven wheels or even axles. In the picture below, you can see how it was normally drawn. Now, Schaeffler has brought it back into the discussion, indeed, with a previously unknown compactness. You can compare the pictures 1 to 3 yourselves, with the customary bevel-wheel differential (see picture 4).
The new Spur-wheel differential gear, can have either diagonally- or straight cut teeth, the difference in price depends on the size and the amount of torque to be transferred. However, the narrow width that the Schaeffler engineers have created for the front-wheel drive, does seem to be unbeatable. Of course, 70% less width also means less weight, in this case 6 kg compared with 9 kg. This is a considerable amount, even if the longer drive shaft somewhat reduces the difference.
In the front-wheel drive, it almost fits into the spur-wheel, which partly meshes directly with the gear on the gearbox output shaft. When driving in a straight line, all the gearwheels inside the spur-wheel rotate as a block. None of the small ones rotates on its shaft. What we would like to do, is radically simplify the cornering or any other event that would cause an inequality, by stopping the left wheel, thus allowing the right wheel to turn twice as fast.
The right hand driven wheel would be linked with front, large spur-wheel and the left hand wheel, with the rear, large spur-wheel. When it's standing still, it is circled by the meshed in small spur-wheels which now rotate on their axles. The axles of the remaining small, spur-wheels run at the same speed, exactly half the speed of the front, large spur-wheel. Thus the interaction of the small spur-wheels, offsets the differing speeds.
With the space gained by the compact construction method, one could: 1. Realise an engageable rear-axle despite the two, as in the past, unequally long drive shafts, 2. integrate an electric motor for the completion of a hybrid-drive, 3. realise a differential lock in the shape of a multiple disc clutch.
What it boils down to is, that this construction form saves weight everywhere, where in the past the bevel-wheel differential was used. 05/15