Quote:
Originally Posted by NiHaoMike
You don't. Just let the vehicle speed change. Except at hills, where the elevation of the vehicle is used as energy storage for no extra cost, reducing the speed variations.
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Absolutely.
In a perfect world you could have the hills at the perfect grade so you could maintain speed uphill at the perfect BSFC for your car. Then you could coast, with the engine off on the down slope.
Under those perfect circumstances you could P&G and maintain a constant speed.
My solution allows for P&G benefits without perfect grades, or even dedicated driving techniques for absolute mileage.
In a 60-0 panic stop, you have less than 25 revolutions of the wheels to recover all of the energy stored in the mass of your car as inertia.
Hybrids have proven than engine off techniques with literally thousands of restarts are practical. 10 seconds engine on and 30 seconds engine off, would be practical at speeds up to 50-55 MPH, at higher speeds the percentage of engine on time would be higher. In heavy stop and go traffic the engine on time could go to less than 10%, in some cases even less than 5%.
Understanding the fact that almost any engine producing 20 HP at 1500 RPM, is capable of producing 30 additional HP on half again as much fuel, gives you the potential benefit of P&G operation. Fuel mileage can be doubled by eliminating all but highest efficiency operational states of the engine.
This is demonstrated by the new 305 HP Mustang that averaged 48 MPG at 48 MPH. I wonder what it would get if it was P&G ed at the same average speed, with engine off coasting.
My guess would be 55-65 MPG.
regards
Mech