The extra internal gear

[Rune]

Can anyone help me understand the rationale behind the extra gear of most Bosch engines?

My guess is that each rpm I make, allows the engine to spin 2.5 times faster than it otherwise could. And somehow this is preferable when it comes to small Electric motors. But if there is some truth in that, can someone explain in depth or give me a link to somewhere that does?

I can't get myself to belive that the only reason is that this allows a smaler drive sprocket and more ground clearance.

 

[Finlandier]

There is two nested axles, inner for cranks and outer for sprocket. Power from pedal to sprocket is attached via other same way axle which is mounted to engine frame with torque meter unit. So, when you push pedal, second axle get power also and torque meter unit measures how much power is given to electric motor. Ofcourse this construction makes extra load to power line from your pedals to fronts sprocket.
I think that Bosch developed construction is not used anymore in their future models. But I think that this construction is reason that Bosch can sniff so good when cyclists are changin gear and cut down motor power for a while.