If the powertrain could get a bit of advanced notice when you're going to brake, some fuel efficiency savings could be realized by flipping this mode on and that mode off before it actually occurs. A proximity sensor of somesuch installed in the pedal could detect if the driver were covering the brake at x distance.-- RayfordSteele, Aug 20 2013 Oddly reminiscent of "The Endochronic Properties of Resublimated Thiotimoline" story.
Hmm, how does an author check the spelling of made-up items?-- not_morrison_rm, Aug 20 2013 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.-- WcW, Aug 20 2013 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.-- ytk, Aug 20 2013 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.
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.-- FlyingToaster, Aug 21 2013 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.
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.-- WcW, Aug 21 2013 //might even be good to also let the accessories slow the car too,
A large-ish pop-out wind turbine?-- not_morrison_rm, Aug 21 2013 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.
Sadly, because of my current assignment, I cannot get into more specifics.-- RayfordSteele, Aug 21 2013 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.
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.-- WcW, Aug 21 2013 I'm not talking about engine braking.
I am an HEV transmission hardware engineer.
//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.//
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.
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.-- RayfordSteele, Aug 22 2013 random, halfbakery