The 2014 Active Line and Performance Line drives have significant changes to the Gen 1 or Classic Line drive (see some comparisons below).
The shape of the motor is completely different (Oval shape and more discrete), one of the advantages of the new shape is a substantially increased ground clearance. The front sprocket is also significantly smaller (relatively tiny) compared to the older Classic Line, which contributes to the higher ground clearance.
The reason the new Bosch motors are able to use such a small front sprocket is that the drive is geared from the inside to the outside, that is every revolution of the pedals turns a gear inside the motor at a ratio of 1:2.5. The small sprocket also means that it’s much harder for the chain to come off at any point.
The new system allows sensors within the new motor to measure gear changes much more precisely, as you change gear the motor can detect this and actually reduces the torque applied, at exactly the right time ensuring a smooth gear change and significantly reduced pressure on both the motor and chain, leading to a more durable system. The batteries (300Wh & 400Wh) have also been slimed down into a neater package.
In summary, the new Gen II Bosch motors are smaller, lighter, neater and slightly more powerful (the Performance Line can now assist up to 275% up from 250%, with 60Nm of torque through a derailleur system and 50Nm through a hub gear).
Click here to view a video about the Gen II Bosch crank drive system.