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01-13-2007 06:20 AM #1
- Join Date
- Dec 2006
What makes hybrids more efficient?
I have sent inquiries to Ford, Honda, and Toyota, but I got no response. Can anyone explain what makes a hybrid more efficient than a light weight fuel effiecient gasoline or diesel powered vehicle?
Is a hybrid vehicle more fuel-efficient than a similar light-weight gasoline powered vehicle? I canít figure out how it could be. The hybrid has the considerable additional weight of batteries to lug around everywhere. The hybrid also has the weight of the power conversion components and the small but finite losses in converting the mechanical energy from the gasoline engine to electricity and converting electrical energy in the battery into mechanical power at the wheels.
The only advantages I can see for a hybrid are that it can recoup braking energy and that it may be possible to always operate the gasoline engine at itís most efficient RPM. Unless you are driving down a mountain, I canít imagine that regenerative braking could amount to much. Stop and go city driving might also get some gain some efficiency by channeling the vehicleís braking energy back into the battery instead of dissipating it as heat on the brake rotors. Again, I canít imagine much savings here.
Another possible advantage for a hybrid is that the gasoline engine could always run at its most efficient RPM while charging the battery, and that the motor can stop while idling. I donít see much savings here, either. The difference in efficiency in the typical range of driving RPM canít be much. The time spent at a stop is while the motor is stopped, but that must weigh against energy to the starter, and the lost efficiency of the starting process.
The only way I can think of for the vehicle to exceed the fuel efficiency of a comparable gasoline vehicle is to supplement with electric power from the power grid. The vehicle would keep its battery reserve around 10% while running for an extended period. When you get home, you plug your car in and charge it back to full. If the battery capacity is enough, you might not even need the gasoline engine during a short trip.
Are my assumptions reasonable? Are there any engineering details on hybrid vehicles?