Quote:
Originally Posted by redpoint5
You misunderstand. I didn't say the engine comes on and then engine brakes. It just comes on and has no effect on the speed. Vehicles in general don't automatically engine break, you have to initiate that.
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Technically, as long as the car is not in neutral, or the engine is not disconnected from the transmission in some other way, a car will always engine brake whenever you're not on the throttle. Top gear will have the weakest braking force, increasing as you go down. The light regen while off the throttle in many hybrids is basically simulating engine braking in conventional cars.
Example, let's imagine you're on top of a mountain pass and you are rolling down with gentle pressure on the brake pedal to control the speed. Since you don't need that much braking force, the ECU only uses regen braking to convert kinetic energy into the electricity stored in the battery.
However, after 5 minutes the battery is full and it cannot use regen braking anymore.
Option 1, it replaces regen braking with brake pads. This can work for a short period of time, but you still have another hour of downhill to go, using the brake pads for that long will leave the brake fluid boiling and unusable.
Option 2, the motors waste electrical energy spinning the engine like an air pump in order to get the battery drained enough to continue regen braking, and for the purpose of this thought experiment can do this practically forever.
As long as your requested brake level is constant, the engine spinning up won't result in a noticeable increase in braking force, and you don't burn up the brake pads doing so. Being effectively a CVT the engine can spin at any rate and deliver whatever braking force (wasting 5 kW of battery power to absorb 5 kW from the wheels, etc) is required within reason.