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Auto-stop systems

Discussion in 'Gen 3 Prius Fuel Economy' started by bwilson4web, Apr 28, 2010.

  1. bwilson4web

    bwilson4web BMW i3 and Model 3

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    The best way to start a new subject is with a fresh thread. Let me help:
    From gasser thread.

    Auto-stop systems, both manual and automatic, have a long history:

    • Forced Auto Stop (FAS) - modifications to ordinary cars to kill the engine, popular with manual transmission cars that can be 'bump started.'
    • Belt Assisted S(??) (BAS) - popular in GM 'mild' hybrids, it was a heavy duty alternator modified to work as both an alternator and ~5 hp motor. There was still a standard 12 V. system with starter for cold starts. This typically 48 V system handled engine stop and start automatically.
    • Euro drivers - there were wide spread reports that during the past, high fuel periods, Europeans often stopped their engines at lights and restarted them when the light turned.
    The problem is idling fuel burn is pretty modest compared to 'inertial losses.' Inertial losses are the amount of energy needed to accelerate the car to any reasonable speed. At idle, the fuel burn is what it takes to overcome engine friction and the duration compared to the trip is all but insignificant. Sure there are extreme cases where it might help, mostly it is "green wash."

    BTW, neither the Honda IMA nor Toyota/Ford systems are just auto-stop systems. The Honda IMA substantially improves the low-end torque of their engine while the Toyota/Ford systems provide substantial, vehicle motive power. The auto-stop is trivial but not the primary reason for their excellent mileage. This is why auto-stop systems are "green wash" and IMHO, terribly misleading to the just this side of a fraud.

    Bob Wilson
     
    #1 bwilson4web, Apr 28, 2010
  2. austingreen

    austingreen Senior Member

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    When done properly, they have value. Time at idle often produces extra pollution as most engines do not cleanly burn the extra lean fuel mixtures. Small displacement engines often idle roughly as they age so removing idle noise is a premium feature.

    But to do things properly the cars need bigger alternators or motor/generators to smoothly start the engine. For those of us in warmer climates it also requires electric ac so we can remain cool when stopped, and a larger battery to power it. Electric ac has other efficiency benefits. While your at it, why not make that motor/generator large enough to add some start up torque.

    The only things required to jump from this well designed auto start/stop is electronic assist power steering and regenerative braking. So I would expect most cars with auto stop/start to be mild hybrids in the future.
     
    #2 austingreen, Apr 28, 2010
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    You brought up another good point, start-up pollution. Unless part of the design, most vehicles are horrible emitters when first started. Their goal is to get the engine running and then they enable any variable, emissions systems. Imagine a street full of gassers and diesels not designed to auto-stop. When the light turns green, the drivers start the cars and a belch of sooty start-up smoke rich in hydrocarbons would be the likely result . . . not a happy thought.

    Bob Wilson
     
    #3 bwilson4web, Apr 28, 2010
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