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Automotive Why automotive alternators are mostly driven by belt drives

  1. Oct 18, 2016 #1
    I am trying to list down all possible reasons because of which gear train drive is not preferred for driving alternators in automobiles, can you suggest some?
    Last edited by a moderator: Oct 18, 2016
  2. jcsd
  3. Oct 18, 2016 #2


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    Welcome to the PF.

    Is this question for schoolwork? What are some of the reasons you can list yourself?
  4. Oct 18, 2016 #3

    No it isn't a schoolwork. Some of the reasons which I think are:
    1) It would increase overall weight of the engine, which would reduce power to weight ratio of the engine.
    2) Nowadays, n number of auxiliary devices are mounted on engine which are usually driven by serpentine belt, which would be difficult to drive with gear train due to packaging constraint.
    3) Gear train will affect NVH performance of the engine.

    Besides these reasons, is there any specific technical reason behind it?
  5. Oct 18, 2016 #4


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    (1) It is simple and cheap .

    (2) It allows the alternator to be configured as a quick swap change unit .
  6. Oct 18, 2016 #5

    Randy Beikmann

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    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.
  7. Oct 19, 2016 #6

    Ranger Mike

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    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)...
  8. Feb 7, 2017 #7
    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
  9. Feb 7, 2017 #8


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    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.
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