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  1. #1
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    Dec 2006
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    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?

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  3. #2
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    Quote Originally Posted by Engr_m View Post
    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. ...
    I think you are assuming that the gasoline engine does nothing but run a generator which then charges the batteries and/or supplies power to the electric motors which drive the wheels. In that case, I think you would be correct in that it would be difficult to be more efficient than a light-weight, low-power engined car. But most hybrids are set up so that the engine drives the wheels of the car and has an electric motor mechanically attached (either in series or parallel) with the engine.

    So where do efficiencies come from? First, the fuel-powered engine can be made smaller than would normally be put in a given sized car. This allows better fuel economy when the car is cruising on the flat, but the electric motor can be used to give additional boost during acceleration. This makes for a driving experience that most drivers have come to expect from their vehicles. Second, as you've already noted, the motor can be used for regenerative braking during deceleration to recover some of the car's momentum as power. Third, the gasoline engine can be shut off at stoplights to avoid using fuel while idling. The electric motor is then used to move from start with the gas engine kicking in after the car is moving.

    In general, if most of your driving is highway cruising, a hybrid will not give you much better mileage than an efficient gas-powered vehicle. But most cars are optimized for both acceleration and cruising so the smaller-engined hybrid will usually get better highway mileage, too. Their biggest advantage comes from in-town driving as I outlined in the previous paragraph.

    Bob

  4. #3
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    Mar 2007
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    I would also add that LRR tires, CVTransmission, design for air flow over/around the veh, light weight wheels with a semi - closed design to reduce wind drag, undercarriage close-out panels to reduce wind drag, 0-20 oil usage and internal engine design to reduce friction/drag would also add to increased MPG.

  5. #4
    Quote Originally Posted by Engr_m View Post
    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?
    Here's what i've read:
    ---------------------
    Benefits of the hybrid design include:

    Current hybrid vehicles reduce petroleum consumption (compared to otherwise similar ICE vehicles) primarily by using three mechanisms: a) Reducing wasted energy during idle/low output, generally by turning the internal combustion engine off; b) Recapturing waste energy (i.e. regenerative braking); c) reducing the size and power of the ICE engine, and hence inefficiencies from under-utilization, by using the better torque response of electric motors to compensate for the loss in peak power output from the smaller internal combustion engine. Any combination of these three primary hybrid technologies may be used for different fuel usage, power, emissions, weight and cost profiles.
    Hybrids may also make more aggressive use of other fuel-saving techniques, such as reduced weight; these are not advantages of the hybrid design, but engineering choices made for various reasons, including marketing to consumers conscious of these issues.
    Trade-offs include higher weight for electric motors and batteries, which may reduce fuel efficiency at highway speeds compared to otherwise equivalent ICE vehicles, or even result in lower fuel efficiency at highway speeds than in urban use; for this reason, hybrids may be considered to be particularly well suited to urban applications.
    The internal-combustion engine in a hybrid vehicle is smaller, lighter, and more efficient than the one in a conventional vehicle, because the combustion engine can be sized for slightly above average power demand rather than peak power demand. A standard combustion engine is required to operate over a range of speed and power, yet its highest efficiency is in a narrow range of operationóin a hybrid vehicle, the combustion engine operates within its range of highest efficiency. The power curve of electric motors is better suited to variable speeds and can provide substantially greater torque at low speeds compared with internal-combustion engines.
    Like many electric cars, but in contrast to conventional vehicles, braking in a hybrid is controlled in part by the electric motor which can recapture part of the kinetic energy of the car to partially recharge the batteries. This is called regenerative braking and contributes to the higher efficiency of hybrid cars. In a conventional vehicle, braking is done by mechanical brakes, and the kinetic energy of the car is wasted as heat.
    Hybrids' greater fuel economy has implication for reduced petroleum consumption and vehicle air pollution emissions worldwide[15]
    Reduced wear on the gasoline engine, particularly from idling with no load.
    Reduced wear on brakes from the regenerative braking system use.
    Reduced noise emissions resulting from substantial use of electric motor at low speeds, leading to roadway noise reduction and beneficial noise health effects. Note, however, that this is not always an advantage; for example, people who are blind or visually-impaired, and who rely on vehicle-noise while crossing streets, find it more difficult to do safely.
    Reduced air pollution emissions due to lower fuel consumption, leading to improved human health with regard to respiratory and other illness. Composite driving tests indicate total air pollution of carbon monoxide and reactive hydrocarbons are 80 to 90 percent cleaner for hybrid versus conventional vehicles[6]. Pollution reduction in urban environments may be particularly significant due to elimination of idle-at-rest.
    Increased driving range without refueling or recharging, compared with electric vehicles and perhaps even compared with internal-combustion vehicles. Limitations in range have been a problem for traditional electric vehicles. Hybrids may have substantially longer "operating hours" per unit of petroleum in certain conditions than the mileage-rated fuel efficiency figures may indicate, due to the reduction of idle-at-rest.
    --------------------------
    Source: http://en.wikipedia.org/wiki/Hybrid_car#Technology

  6. #5
    Guest

    i like hybrids :)

    i like hybrids

  7. #6
    Guest

    Hybrids are more appealing

    Hybrids are more appealing at the moment, they run cheap they are green and they are the next steep into the future. For this reason i`m considering getting one for myself, and i`m thinking that if i would do something like this i should also think about auto donations or selling my very old car. Come to think about it, i do more harm with it then i would consider, seeing the hybrid specs.

  8. #7
    Guest

    Hybrids are more appealing

    Hybrids are more appealing at the moment, they run cheap they are green and they are the next steep into the future. For this reason i`m considering getting one for myself, and i`m thinking that if i would do something like this i should also think about auto donations or selling my very old car. Come to think about it, i do more harm with it then i would consider, seeing the hybrid specs.

  9. #8
    Guest

    Hybrids are more appealing

    Hybrids are more appealing at the moment, they run cheap they are green and they are the next steep into the future. For this reason i`m considering getting one for myself, and i`m thinking that if i would do something like this i should also think about auto donations or selling my very old car. Come to think about it, i do more harm with it then i would consider, seeing the hybrid specs.

  10. #9
    Guest

    All-electric cars are very

    All-electric cars are very attractive to me, but they are impractical for long distance driving due to battery limitations, availability of charging stations and charging time. Has anyone been able to build a hybrid car that is driven by an electric motor which is powered by a generator and small, highly efficient gasoline engine which generate enough charge to continuously run the electric motor indefinitely? The Chevy Volt runs on this principal but has an "extended" range of only 360 miles. Why the mileage limit? Is this based on how far a single tank of gas will get the car or some sort of limitations on battery or charging capacity? If the engine and generator generate sufficient charge to power the electric motor, lights and accessories, it should have an unlimited range as long as there is gas in the gas tank, correct? This is the same principal as diesal-electric locomotives. Why isn't this same principal applicable 100% to automobiles?

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