Automotive Why automotive alternators are mostly driven by belt drives

(1) It is simple and cheap .

(2) It allows the alternator to be configured as a quick swap change unit .

 

What everyone else said. A major reason for low cost and accessibility is that belts don't require oiling, and therefore don't need to be in an enclosed compartment.

 

I posted some stuff on physics forum on belt drive versus chain vs gear drive for the camshaft a while back. It dealt in depth with parasitic horse power. Do a search and look it up. From an OEM point of view, belts have evolved to the point that they are pretty much bullet proof. The cost of a belt , pulleys and a belt tensioner are super cheap compared to cost of manufacture a gear drive. Having run gear drives on the cam shaft the noise is always there from day one. Not a problem for a 600 hp drag car but on a family grocery getter, big problem. You also pick up induced harmonics that can impact on longevity of the engine over time. Belts are naturally sound deadening so its one huge factor on the final decision. So look at it from cost to manufacture, over all assembly time, long term maintenance, drive quality (noise)...

 

Belts impart less radial load onto the alternator's input shaft.
Belts do not require lubrication like a gear train would in that application.
Less parasitic losses
Lower moment of inertia on acceleration

 

When designing the engine bay of a motor vehicle, the last few decisions made are where to place the cooling water circulation pump, then the ancillary components such as the alternator and AC pump. The use of a belt drive gives greater freedom in choice of position.

The use of a belt also frees the choice of ancillary component manufacturer since pulley diameter and profile can be selected to suit different manufacturers standard products. That also reduces price and availability dependencies. A belt quietens drive noise and reduces vibration.