Hybrid-electric vehicles are primarily propelled by an internal combustion engine, just like conventional vehicles. However, they also convert energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor. The electric motor is used to assist the engine when accelerating or hill climbing and in low-speed driving conditions where internal combustion engines are least efficient. Some HEVs also automatically shut off the engine when the vehicle comes to a stop and restart it when the accelerator is pressed. This prevents wasted energy from idling.
Ok now my question is why not diesel engines? Just think what your mpg's would be!
Maybe it cant be done with a diesel engine? (would the shutting off of the engine while its idling hurt it?)
You would think they could do something if its just a battery assist .
A hybrid that includes a diesel motor (instead of a gasser) does not reap the advantages of the low-speed assistance that an electric motor provides. A diesel typically has greater torque at lower RPM than a gasser does, so it does not need the assist from the electric motor at low RPM's. Diesels also use only 1/3 of the fuel a gasser does at idle so it won't conserve as much if the motor is switched off at idle. In addition, a diesel takes more electricity to start due to it's higher compression so you won't gain much there either.
A more efficient set-up involving diesels would be similar to that found on trains and ships - a diesel-electric power plant. In this type of plant, the diesel turns over at a constant speed and spins a generator (diesels are far more efficient at constant RPM's), which in turn feeds either a bank of batteries or directly into an electric motor which turns the wheels (or propellor, as the case may be). This would eliminate the need for much of a transmission since electric motors have a very wide RPM and torque range, and the throttle for the diesel could be completely automatic, increasing or decreasing as it perceived the need for either more juice to the electric motor, charging the batteries, or letting the batteries supply the motor and let the diesel idle down. The traditional foot pedal accelerator would control the juice to the electric motor, and the computer controller would decide if that juice would come from either the generator or the batteries. Combine that with regenerative braking and I think it would be quite efficient.
The generator and electric motor drive system is less efficient than a car type driveline. What makes it ideal in a locomotive or large truck would not make it feasible in an automobile.
I would beg to differ on that, Big Al. The primary reason diesel-electric locos came into being was the NEED for smooth but powerful transfer of horsepower to the driving wheels (automatic trannys or stick shifts coupled to big-ass diesels were out of the question). Even the monstrous dump trucks at open pit mines benefited from this combination (one diesel-generator-motor for each wheel).
For a much smaller application such as a sedan or SUV, a small turbo-charged diesel engine coupled to a generator that:
provides power to electric motors that drive the wheels (2WD or 4WD)
provides power to charge a bank of batteries that acts as a float source of power
provides power to vehicle's electric components
can be a very efficient setup. If the float source is small, the diesel will have to run almost continuously. If the float source is large, the diesel can be shut off, then be restarted when the float source decreases to a set threshold. A diesel engine is ideal because of its efficiency compared to a gasoline engine -- a turbo-charged diesel just takes it up another notch or two. Use computer(s) to monitor and control the setup for optimum performance. An electric motor is ideal because of its ability to convert electricity into mechanical energy quietly, very smoothly, and very very efficiently.
Exciting times coming up ahead with the price of gas/diesel going through the roof... necessity and invention (past the theoretical part, at least).
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