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Diesel-Battery-Electric
This is not exactly an electric car. It is close to being a Diesel-Electric but for one very important feature - energy storage. And it is not a parallel hybrid either. | |
A car needs considerable power only for a few minutes at a time to climb hills or to accelerate up to speed. It does not require much if any power going down hill, slowing, or standing still. At cruising speed on the level, a car only needs enough power to overcome air resistance and a relatively small
rolling resistance.
The purpose of a gas-electric hybrid is to use each power source when it is more efficient and to combine them when needed for maximum performance. Electric power works best at lower speeds and in stop-and-go traffic as regenerative braking greatly improves efficiency. Higher speeds require more and lasting power to overcome air resistance so trips between cities make greater use of the gas engine. Hard acceleration and hill climbing are examples where both are used together. Note that Toyota’s Prius gets better fuel economy in town than on the highway.
The purpose of this Diesel-Battery-Electric option is to increase efficiency by averaging out the effects of stop-and-go traffic and the normal ups-and-downs on the road. Side benefits include reduced overall weight and fewer components. It is an electric car with a small Diesel-electric generator. Stopping regenerates power back into the battery similar to a hybrid car. The battery, which is similar to a hybrid’s in size, is topped up as needed by the Diesel-electric generator.
Diesel > electric generator > storage battery > electric drive motors
The source of the power is Diesel but the four wheels are each driven independently by electric motors built into the rims. Only electric wires are needed to get the power from the battery to the wheels. There are no clutches, transmissions, drive shafts, or differentials to add weight or to take up space. The battery is larger than what is found in a conventional car today because it does more than just start a motor. However, it is not nearly as big as what is required in all-electric vehicles.
The fully charged battery would be large enough to provide engine-less power for about five to eight minutes of hard driving so it is not useful as an electric-only car. The Diesel engine only charges the battery so it can be designed to run at maximum efficiency at a constant load and RPM. The engine can shut down at times or run continuously when needed.
The four electric motors combined would be strong enough to overcome the power requirements of a vehicle travelling at a speed of 140 kph (87 mph) to account for head winds at legal speeds. The Diesel engine needs to be large enough to keep the battery charged under these conditions.
Dodge Intrepid ESX
http://www.allpar.c.../intrepid-esx3.html
baked [acurafan07, Jan 18 2007]
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Baked. Dodge experimented with this idea in the Intrepid ESX [link]. It worked almost exactly as you said (with an engine to power the batteries which power the motors). |
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This would be less effiecient than driving the wheels direct from the generator as there is always a loss at each step of the process, you would be losing energy during the charging phase rather than direct drive like a locomotive utilizes. Also I believe the current generation of locomotives have incorporated batteries into their system, but the are charged with the excess power and the recouped braking energy. |
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[-]This is just a series hybrid like the Dodge in the link or the new Chevrolet Volt concept car. I don't see an original idea here. |
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Yup, this is a series hybrid. The other system you've mentioned is a parallel hybrid. |
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Long baked but not yet quite mouldy: compare the Edwardian Lohner-Porsche. |
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The great advantage of what is effectively an electric transmission is that the electric motors can be more powerful than the diesel or petrol engine, so that one operates at a net charge loss while accelerating rapidly. The charge is restored while not accelerating rapidly. |
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Ok. I hadn't heard the terms parallel and series when describing hybrid vehicles before but they make sense. The Dodge Intrepid ESX example seems to me to rely way too much on a large battery, much like a pure electric car. The vehicle is a large one to start with so the fuel economy they were getting was quite good. Since they spent relatively little time and money on this project, I suspect a lot of tweeking could be done to enhance the result. |
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Reduction of weight was a large factor in the high cost of the Dodge tests. But the forces to overcome have very little to do with weight. Greater weight will affect rolling resitance but since it is relatively small when compared to air resitance at normal highway speeds, the extra cost to reduce weight likely yields little or no net benefit. |
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In physics class you will discover that the energy required to accelerate a given mass up to a given speed is not actually spent - it is transferred to the moving mass. Zero energy is lost assuming zero resitance from such things as friction or air resistance. This means that we should be working on reducing rolling resistance and especially aerodynamic drag. The Toyota Prius shows that we can make vehicles that commercially use regenerative braking to average out the cost of street light to street light city type driving. |
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Hills should be no different. It takes energy to lift a given mass a given distance (as against gravity when hill climbing) but that same energy is then stored in the mass. The down hill coast should be capable of regenerating all of the energy required to climb, again assuming zero resistance. |
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Zero resistance is obviously not the world we live in but the point I am making is that we only have to use energy to overcome the typical resistances found with a rolling mass. Minimizing rolling resitance and aerodynamic drag should be much more important than minimizing weight since that moving and/or elevated weight is a significant energy source. As aerodynamic as the Toyoto Prius is, the vehicle still gets better fuel economy in the city than out on the highway which speaks volumes about what needs the most work. |
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Averaging out the energy requirements makes sense to me. A small reasonably aerodynamicly efficient car should require about 6 horsepower to roll down the level road at a constant 80 kph on a calm day. Using even a smallish 80 hp motor to deliver that 6 hp on a conventional-powered car is very wastefull yet it is occationally required to accelerate the vehicle and to climb hills. But accelertion and hill climbing result in stored energy that can be tapped. There is a net cost to climbing and accelerating but this cost is more related to rolling resistance and aerodynamic drag. |
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There is friction and heat losses in electric motor-generators but overall, they are much more efficient than internal combustion engines and they remain relatively efficient through a wide range of RPMs. To deliver the 6 hp to the wheels, I would guess that a 30 hp internal combustion engine would be sufficent to deliver an average of 24 hp to the wheels on this car given efficiencies of 90% each for the generator and motors. The 24 hp would be needed only for extended periods of high-speed driving or driving against a strong headwind or climbing a mountain. Obviously, driving with a strong tailwind or down the mountain would require little or no effort. So, although the 30 hp engine is much more than needed at times, it will shut down for extended periods. When it is running, the engine operates at a designed for maximum efficiency RPM and load. |
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Also, electric motors give their highest torque when starting from a dead stop, which is the opposite of an IC piston engine. This is one of the advantages of the parallel hybrid - the two engine's power ranges complement each other, and consequently each can be made smaller. |
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