5 ms·

You'd need to drive the automaic in semi automatic mode for it to be as efficient, right?

• Zak 2y ago
  Very unlikely. The default gear selection algorithm is optimized for efficiency in most cars.
  • rightbyte 2y ago
    Automatics usually don't plan ahead. And my experience is that responsiveness is prioritized over fuel efficiency. There should be more coasting with no gear engaged and low gear low rpm for low loads, than what automatics chose in practice. But I don't have any data at hand for practical fuel efficiency and modern automatics versus manual.
    • Zak 2y ago
      Coasting with no gear engaged consumes some fuel to keep the engine idling; coasting in gear consumes no fuel at all.
      • rightbyte 2y ago
        Yes but if you don't want to retard higher rpm in the motor gives higher losses. I think it is accurate enough to think of each revolution as a fixed cost for 'low' or idle power. At idle power the motor should probably only be engaged when also braking.
        • serf 2y ago
          >At idle power the motor should probably only be engaged when also braking. a cars' stability is aided by engine braking; if that isn't there it must be accommodated by knowledge of such a fact by the ABS/TCS/VCS systems, or a skilled driver that is expecting it. A regular car that expects engine braking, thrown into neutral and coasting down the highway is a more fragile handling and car-dynamics situation without these precautions. The Mercedes Glide Mode accommodates this by using the ABS/TCS systems to keep the weight where it needs to be regardless of applied engine torque one way or another; the driver does not experience a differently handling car.
          • rightbyte 2y ago
            That seems strange. I guess the "apply motor torque to speed up wheel" dynamic stability control would be slower to apply torque when in neutral, when control has been lost? Or is there some effect in the rubber from engine braking that make the front wheel more "prepared"?
      • lttlrck 2y ago
        Yes but "no gear" disconnects the transmission and engine load from the wheels so you can coast farther. In other words you remove engine braking from the equation. Mercedes Glide Mode for example does this automatically to increase MPG (allegedly).
    • dingaling 2y ago
      > Automatics usually don't plan ahead. The latest ones do, being integrated with GPS and a terrain database to anticipate changes.
      • nielsbot 2y ago
        what, seriously?
        • serf 2y ago
          yes. for at least 20+ years now BMW/Porsche/VW also use the onboard IMUs and gyros and wheelspeed sensors to determine whether or not a shift should happen , say, in the middle of a long high speed banking turn.
      • fragmede 2y ago
        That still won't tell it if I want to accelerate to pass the person ahead or slow to keep my distance from them, or slow to let someone behind me pass, or speed up to not let them.
• serf 2y ago
  No. The method of action is different. An automatic transmission using a torque converter loses more energy in the form of heat than a traditional manual gearbox. The only gearboxes that have the same efficiency regardless of whether or not they're manually shifted are true automated manual gearboxes like BMW DCT or other such auto-magic boxes that use clutches rather than viscous (liquid) coupling to facilitate gear changes.
  • Zak 2y ago
    Modern torque converter automatics have lockup clutches. https://en.wikipedia.org/wiki/Torque_converter#Lock-up_torque_converters https://en.wikipedia.org/wiki/Torque_converter#Lock-up_torqu...