h a l f b a k e r yA dish best served not.
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Oddly reminiscent of "The Endochronic Properties of Resublimated Thiotimoline" story. |
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Hmm, how does an author check the spelling of made-up items? |
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what mode were you specifically thinking of that when switched on, would save fuel? Is it the "turning off the fuel when you are paradoxically accelerating while about to stomp on the brakes", or the fuel shutoff that already engages when you lift your foot off the throttle, in all cars already in production. |
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Wouldn't you put it in the gas pedal? The only reason
you
would take your foot off of it is if you're about to
brake. Or
if you have cruise control turned on, but that's only
the
case relatively infrequently. |
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Start/stop tech: the gas and brake pedals are both "clickable" like computer mice; covers that ride 1/8 - 1/4" above the pedals, with a mechanical clicker. The idea is to have the system know when you're on the pedal but not pushing it. |
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Long story short: removing the foot from the brake or putting it onto the gas starts the engine, whereas removing the foot from the gas or putting it onto the brake stops the engine. |
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tis better to let the engine slow the vehicle is it not? might even be good to also let the accessories slow the car too, no? So why stop the engine? I feel like there is a major principal misunderstanding about the relationship between the engine and the inertia of the car.
One simple way to improve fuel economy would be to have a system that allowed the car to coast, and for the engine to die unless you pressed the brake, gas or clutch, at which point the engine would be spun up again by stealing some inertia. |
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So, to clarify: when you take your foot off the accelerator your car 100% stops using fuel until the engine is at an idle speed, no matter what you do with the brakes. |
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//might even be good to also let the accessories slow the car too, |
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A large-ish pop-out wind turbine? |
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I'm not referring to the engine but to some advanced control jiggery that happens inside the transmission of a hybrid vehicle. Mechanical components take time to engage / disengage. If you can disengage them when they are not needed in a quick time period smoothly, then the effort of keeping them spinning is not required and spin losses are reduced. |
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Sadly, because of my current assignment, I cannot get into more specifics. |
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ok so in a hybrid car you likely have the equivalent of an overrun clutch which means that when the engine isn't proving toque to the wheels, it isn't connected to them. In this situation there is no engine braking when you let your foot off the gas, the engine is either idle, spinning a generator or dead. In the hybrid scenario the electric motors are not slowing the car at all until you actually touch the brake at which point they provide dynamic braking in conjunction with a conventional braking system. While the pedal might provide a conventional linear feel the relationship between regenerative and friction braking is managed by a computer. In my mind the best scenario is one of greater reliance on the regenerative component before the conventional brakes do any work, but the automotive engineers take a more pragmatic approach. |
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When you want to stop, spin losses (compression work) is a pretty efficient way to do so. So long as you are slowing down only regeneration of some sort will do anything to increase fuel efficiency. |
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I'm not talking about engine braking. |
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I am an HEV transmission hardware engineer. |
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//In the hybrid scenario the electric motors are not slowing the car at all until you actually touch the brake at which point they provide dynamic braking in conjunction with a conventional braking system.// |
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This statement is false when it gets to the details. There are always drag losses associated with spinning the motor. They are somewhat minor, but this is a game of incremental improvements. Slogging oil around the geartrain connected to the motor, bearing losses, etc. |
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Some hybrid transmissions, when the vehicles run at certain freeway speeds, forcibly idle the electric motor because of the arrangement of the planetary system with two inputs and one output. Mechanically stalling the motor in this state is more efficient than electrically stalling it, although the latter is frequently done. But mechanical mechanisms take time to operate and can be an NVH disaster under the right conditions. |
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