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Advanced Course in Hybrid Engineering

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Comments

  • peraltaperalta Posts: 94
    "Whay try to re-invent the wheel when the Toyota design engineers already have a production solution. "

    Here are my answers:

    - Less number of motor/genrator (minus 1)
    - less weight = better acceleration = better Fuel Economy
    - cheaper to build
    - Better weight distribution
    - Free up more space under the hood

    This sounds like a good commercial!!!

    Peace
  • devsiennadevsienna Posts: 69
    I think you're ignoring what it would take to make a transaxle that runs the length of the car, plus the various linkages that would be necessary to move MG2 to the rear. On a larger car, like the Highlander, you might have the necessary clearances under the car to do such a thing, but I'm guessing that the added weight of the transaxle and linkages is more than the weight of MG2, or in the case of the Highlander and Lexus RX400h, MG3.
  • peraltaperalta Posts: 94
    As I mentioned before, there is additional weight on relocation of MG2, but minimal. My guess is about 75 lbs max. and that consist of a single planetary gear drive with integral differential and two half shafts. The connection of MG2 to the front are electrical cables and wirings. There are no propeller shafts that tunnels from the front to the rear.
  • devsiennadevsienna Posts: 69
    Are you forgetting that MG2 is mechanically tied to the outer ring of the PSD? The ICE, MG1 and MG2 are all mechanically tied to eachother and the drive wheels. You can't just move MG2 to the rear without having a transaxle that runs the length of the car. Otherwise yer not talking about just moving MG2 to the rear, but re-engineering the HSD system completely.

    I suggest that you look at one of the prius planetary gear simulators to get a better idea of why they are all tied together and how they work with eachother to provide optimal gearing for keeping the ICE running in it's most effcient range.

    Also keep in mind that if you relocate MG2 to the rear, and mechanically disconnect it from the PSD/front wheels, that you lose the ability to drive in reverse. MG1 isn't powerful enough to move the car, and the ICE only spins in one direction...
  • devsienna is right. peralta's suggestion would turn HSD into something else (series dominant) -- generate electricity in the front (MG1) and feed that electricity to the back (MG2). Some mechanical power can go to the front wheels through PSD. Front wheels will be partially powered by ICE and rear wheels powered by electric motor (MG2). To control the power split between front and rear, you'll need to manage MG1 speed and Battery pack. The more MG1 generates electricity, the less power goes to the front wheels. MG1 electricity can charge the battery and/or power the rear wheels.

    Like devsienna pointed out, front wheel will be only able to turn one direction (forward). For the car to go backward, your design will need to depend on the pure battery power -- in order for MG2 to spin backward. If the battery SOC runs low, the ICE will be forced to turn on. The front wheels will want to go forward and rear wheels will want to go backward -- not pretty or efficient.

    I think this design can work but the HV battery might need to be bigger. Regen braking might not be able to capture as much because the weight shifts to front and MG2 is in the rear wheels. You will also need to worry about cooling MG2 in the back. Will it be all worth it to have AWD? I am not sure.

    Dennis
  • peraltaperalta Posts: 94
    Let me simplify how HSD works. ICE power is split 72/28 at the PSD. The 72 part goes to a shaft that powers the differental (via a chain drive). The 28 part goes to MG1 to generate current and then goes to MG2 to convert back to mechanical energy. The MG2 and the output shaft from 72 part joins together to drive the front differential. My suggestion is that the MG2 does not have to join the front output shaft but power the rear instead. No need for transaxle that runs the lenght of the car.

    As I mentioned in "more bags of tricks", it can be more flexible and can run on all mechanical mode for max economy at steady cruising or it can have max acceleration by reprograming the MG! as a second booster.

    I haven't seen the estima HSD system but I guess that it has similar system as my suggestion since has enough room to accomodate the belt drive CVT and it has a standard AWD set up.
  • toyolla2toyolla2 Posts: 158
    Welcome to the board devsienna,

    actually the redesign would not be necessary if MG2's gearing of 4.13:1 was preserved and the braking system was able to prevent the rear overspinning when traction was lost. However, I think you killed peralta's suggestion stone dead when you brought up the small matter of driving in reverse.

    Of course the 59lbs-ft from the front wheels in the forward direction (assume the engine was started because of a depleted battery) would be opposed by the 259 lbs-ft from MG2 in reverse applied to the rear wheels. However (playing devil's advocate here) should the rear lose traction then the rear braking system will not save the day and the vehicle will take off in the forwards direction. Good luck defending an accident from that one in court ! You might argue that the braking system could go to work on the front wheels and block any forwards motion when the drivers intention is to move backwards. Any conscientious designer would walk away from that one. I can see now why Toyota included both MG2 nd MG3. But it was a good attempt to produce an AWD-lite. Knowing what won't work and why helps in exploring for the better solutions. My personal opinion is that it is difficult enough to diagnose problems with HSD's interconnected electrical and mechanical system without bringing in the braking system as well - as peralta has suggested.
    T2
  • toyolla2toyolla2 Posts: 158
    You wrote : -
    "As I mentioned in "more bags of tricks", it can be more flexible and can run on all mechanical mode for max economy at steady cruising or it can have max acceleration by re programing the MG1 as a second booster."

    Since there is only 28Hp of battery available MG1 can never be a power booster unless you can tell me where the 67Hp of electricity for MG2 is coming from at the same time ?

    Peralta, take a minute and look at the electrical power flowing. That 28% of torque split that you quote often is actually 22lbs-ft (28% of 80lbs-ft) and it is able to propel MG1 at 10,000rpm at least until the vehicle reaches 51.28mph. At which time MG1's rpm must begin steadily reducing because the ICE has maxxed out at 5000 rpm and the vehicle is still needing to go faster. Because remember the equation I stated over on the 2004+ board ?

    But what has MG1 been generating during this time ?
    Well, 22lbs-ft @ 10,000rpm = 304v @ 100 amps = 42.2 Hp. It is this power added to 25Hp from the battery which is able to give MG2 its full power of 67Hp. It is able to do this only from 20mph to 51.28mph. Beyond 51.28mph MG1 is still permitted 22lbs-ft but at steadily reducing rpms as I just mentioned, until at 100mph and 2400rpm it can produce barely 10.2 Hp which is sent over to MG2 along with 28Hp from the battery. In the unlikely event that more than two minutes were to elapse then only MG1 would still be in business continuing to feed MG2 with 10.2 Hp.

    Since the Prius will not require its full ICE power of 76Hp to cruise at 100mph. The ICE will have slowed down considerably and so will MG1, in fact MG1 may now be going backwards as a motor with power generated by MG2 operating in the so-called heretical mode in order to depress the ICE speed to a suitable low level for cruising. See Yahoo toyota prius site c. August 2001 for discussions. A scan tool showed in later postings that 35% of a particular commute was actually spent in this mode.

    By the way there is no useful mechanical mode, 59lbs ft of direct thru' mechanical torque requires MG1 to act as a generator with 22lbs-ft. But let's say we were to freeze MG1's rotor as you suggested then ICE rpm will equal 2.6/3.6 MG2.

    At 60mph MG2=3600rpm therefore ICE=2600rpm. Since the ICE likes to run at close to full torque at all times in order to reduce needless mechanical engine motion, this rpm would appear to be racing the engine albeit 38hp would be instantly available on tap if needed, which with the HSD is a useless advantage since the HSD can instantly invent whatever gear it needs to be in. Again scan tools show the ICE settles at 1211 rpm mostly until more than 8.5kw is desired. This order of power will cruise the Prius on level road at 60mph. Using MG1 and MG2 at all times is probably the most efficient way to run this vehicle as Toyota engineers intended. Did I just agree with MidCow ?
    T2
  • peraltaperalta Posts: 94
    toyolla2,

    I agree with almost all of your statements. There is no need for my suggested "bags of tricks" since the THS is well engineered, well thought, and very much optimized and my suggestions were not mathematically based.

    There is one thing that I do not totally agree since I see a solution to it. You mentioned;

    "Of course the 59lbs-ft from the front wheels in the forward direction (assume the engine was started because of a depleted battery) would be opposed by the 259 lbs-ft from MG2 in reverse applied to the rear wheels. However (playing devil's advocate here) should the rear lose traction then the rear braking system will not save the day and the vehicle will take off in the forwards direction. Good luck defending an accident from that one in court !"

    The prius engine is not running when in reverse and it is almost always in that case since reversing usually takes only a few feet (it rarely depletes your battery). Another reason is that it is weaker with the engine running since there is an opposing forward torque from the engine. When reversing, you are not using full power, you are inching to your destination. Just a very short warm up after starting the engine should be good enough charge to use for reversing.

    Other problem is that you lose the AWD in reversing. Yes, but there is a fix. With the engine not running and braked, the MG1 can rotate forward pushing the final drive in reverse and multiplying the MG1's torque by 2.57 (72/28). Remember, you reverse by inches at a time, not at full power.

    Peace
  • peraltaperalta Posts: 94
    By retaining the original computer logic plus the addition of 4ETS-like program, I guess the rear mounted MG2 is viable.

    Backing up, it needs some minor mods as mentioned above but is still doable, reversing in all electric AWD mode. I am assuming that battery SOC is not a concern since the THS's logic on battery SOC is full charge at zero or low speed and partial charge at high speed. And you only back up few feet most of the time (not miles).
  • peraltaperalta Posts: 94
    It looks like my suggestion has already been used by toyota in the THS-C. After researching, I found out that toyota has gone to great lenght in different combinations of hybrid system.

    These were the ff;

    THS-I,
    THS-II (current prius),
    THS-M (mild hybrid, non-US),
    THS-C (Estima hybrid)

    There may be other iterations that I am not aware of.

    The THS-C is similar to my suggestion except that it went the extra mile of putting a denso belt drive CVT at the front. It has one motor in the front and one motor at the rear.

    http://metropolis.japantoday.com/carsbikes/389/carsbikesinc.htm

    http://www.hybrid-vehicles.net/toyota-estima-hybrid-minivan.htm

    My suggestion is not novel anymore but I was right all along that it works.
  • peraltaperalta Posts: 94
    http://www.electrifyingtimes.com/mini.html

    Enjoy...

    Toyota started producing Hybrid estima (AWD) with THS-C in 2001.

    It is puzzling since they have a different AWD later in 2005 in the form of RH/HH with MG-rear.

    However, the gossip is still on that there may be a sienna hybrid in 2007 having a 2.4L engine similar to that of the Estima.

    By the way, the C stands for CVT (belt drive) and the M stands for mild (similar to saturn hybrid).
  • devsiennadevsienna Posts: 69
    The prius engine is not running when in reverse and it is almost always in that case since reversing usually takes only a few feet (it rarely depletes your battery). Another reason is that it is weaker with the engine running since there is an opposing forward torque from the engine. When reversing, you are not using full power, you are inching to your destination. Just a very short warm up after starting the engine should be good enough charge to use for reversing.

    This is not true. I frequently have my engine come on while I'm reversing out of the driveway or a parking spot. With the current HSD system, there is nothing that prevents the engine from being on while in reverse.
  • devsiennadevsienna Posts: 69
    http://www.electrifyingtimes.com/mini.html

    Enjoy...

    Toyota started producing Hybrid estima (AWD) with THS-C in 2001.

    It is puzzling since they have a different AWD later in 2005 in the form of RH/HH with MG-rear.

    However, the gossip is still on that there may be a sienna hybrid in 2007 having a 2.4L engine similar to that of the Estima.

    By the way, the C stands for CVT (belt drive) and the M stands for mild (similar to saturn hybrid).


    From what I can tell, Toyota has abandoned the THS-C design for the Estima. The new Estima in Japan uses THS-II now.

    Why they abandonded THS-C is anybody's guess. My guess is the added complexity of the cone/belt CVT plus the clutch that was being used in the front drive system wasn't very efficient or cost effective. The link you provided unfortunately lacks suffcient details about the system to make a determination.
  • stevedebistevedebi LAPosts: 3,784
    "With the current HSD system, there is nothing that prevents the engine from being on while in reverse."

    I think some people get confused on this issue. The ICE is not used in reverse, but will run if the battery needs charging.
  • peraltaperalta Posts: 94
    Can you site any source that says alphard/estima abandoned the THS-C and now uses THS-II?

    From what I found, a 2005 version of Alphard have been reviewed at "Japan Today" and it still uses THS-C.

    http://www.theautochannel.com/news/2003/11/09/172502.html
  • "I think some people get confused on this issue. The ICE is not used in reverse, but will run if the battery needs charging."

    Prius can go reverse without using battery. PSD will allow ICE to spin forward while the wheel spinning backward (negative gear ratio). MG1 has to spin very fast in order to achieve this. Play with the THS simulator below. Note that the Classic Prius (THS) MG1 max out at 6,500 RPM while HSD allows up to 10,000 RPM.

    http://homepage.mac.com/inachan/prius/planet_e.html

    If you set the ICE(engine) to 1,000 RPM and MG2 (motor) to -1,100 RPM, you can see the car is going in reverse at -30 km/h. Effective transmission ratio is -0.91. Cool huh?

    Dennis
  • "Can you site any source that says alphard/estima abandoned the THS-C and now uses THS-II?"

    Here you go: http://www.toyota.co.jp/en/news/05/1011_1.html

    The ESTIMA HYBRID CONCEPT
    A new generation of stylish minivan that combines the latest hybrid system, THS II, with electric 4WD to achieve both environmental and driving performance

    ▪ The refined exterior is designed to evoke the identity of the Estima Hybrid in a sophisticated one-motion form.
    ▪ The interior feels clean and open. It is accented by a high-tech-looking central panel and is equipped with comfortable second-row seats with built-in footrests and power foldaway third-row seats that allow you to transform the space to your liking. Electrical appliances can be run on the provided 1,500-watt power supply system.
    ▪ From the perspective of environmental performance, the ESTIMA HYBRID CONCEPT is equipped with the THS II, Toyota's latest, highly efficient hybrid system, and an exhaust heat recovery system in the pursuit of low CO2 and other emissions.
    ▪ In addition to the quiet and smooth acceleration indicative of a hybrid vehicle, the ESTIMA HYBRID CONCEPT achieves increased driving pleasure through VDIM—a system that seamlessly supports the vehicle operations of running, turning and stopping for all conditions from normal through to extreme driving. The combination of VDIM with E-Four (electric four-wheel drive) provides even higher levels of drivability.
  • stevedebistevedebi LAPosts: 3,784
    "If you set the ICE(engine) to 1,000 RPM and MG2 (motor) to -1,100 RPM, you can see the car is going in reverse at -30 km/h. Effective transmission ratio is -0.91. Cool huh?"

    Simulators are not real life. Unless the software engineer was privy to Toyota software code, it would include items that did not represent actual Prius programming. For one thing, I suspect that the ECU would limit reverse speed to well below 30 kmph.

    Two questions:

    1. Has anyone actually done this in real life?

    2. Why would anyone want to do this in real life?

    I suppose I should have said that the electric motor is used in reverse "under normal conditions".
  • Anybody going to hybridfest?
    http://www.hybridfest.com/

    Sounds like a big event and include advanced engineering demonstrations on the hybrid drivetrain by representatives of the hybrid venders themselves.
    Lots of things to do and see, people are attending from all around the country.

    Hope to see you there!
  • bkuchbkuch Posts: 1
    My understanding of Hybrid vehicles is limited, but I have this question. Why couldn't wind power be used to recharge batteries? All you would need is to add a wind scoupe either on the hood, front or side of the vehicle. The wind would turn turbines connected to an alternator which would in turn charge the batteries.

    A vehicle traveling at highway speeds should be almost self reliant, shouldn't it? Why not?
  • dhanleydhanley Posts: 1,531
    That won't work because the drag on the wind turbine would be greater than the energy the wind turbine would produce. Conservation of energy.
  • gagricegagrice San DiegoPosts: 28,891
    You would have a better net gain with ultra thin low drag solar panels glued to the roof of the car. It would have the added benefit of charging the batteries while parked. As long as the sun is shining.
  • Because perpetual motion doesn't exist
  • toyolla2toyolla2 Posts: 158
    This is a redo of the earlier posts #115,6

    CAMRY HYBRID PRELIMINARY SPECIFICATIONS

    ENGINE
    Gasoline Engine Type 2.4-liter, 4-cylinder
    Aluminum alloy block with aluminum alloy head
    Bore and Stroke 3.48 x 3.78 inches
    Displacement 2,362 cc Expansion Ratio 12.5:1
    Valve Train Twin-cam, 4-valve/cylinder with VVT-i

    Max Power 147 Hp @ 6,000 rpm (129lbs-ft)
    Max Torque 138 lb-ft @ 4,400 rpm

    Recommended Fuel Regular unleaded
    Emission Control AT-PZEV

    ELECTRIC MOTOR/GENERATOR
    Motor Type Permanent Magnet Synchronous
    MG2 105 kW (141Hp) 167lbs-ft @ 4,500 RPM
    199 lb-ft 0-1,500 RPM
    MG1 72kw 36lbs-ft @14700 RPM

    POWER STORAGE
    Battery Type Nickel-Metal Hydride
    Nominal Voltage 244.8 V (204 cells, 1.2V/cells)
    Capacity 6.5 ampere hour
    Weight 150lbs
    Battery 45 Horsepower Peak Rating (33kw)
    45 because 192-147 = 45 presumably

    This is commensurate with the Prius battery weighing 100lbs
    and delivering 28.5Hp

    Max Bus voltage 650v

    Is it just me but these text windows seem to be getting smaller and smaller. Entering this post feels like I'm fitting a ship in a bottle :-)

    Anyway, doing some analysis here ; we know that the engine torque is around 129 lbs ft so IF the same PSD ratio as Prius is used here then MG1 will exert 36lbs-ft. We know also that MG2 can use 105kw at 4500rpm and above. Since the battery supplies 33kw then 72kw must come from MG1. From this we can infer that 72kw @ 36lbs-ft will require a speed of 14700rpm.

    To determine the speed at which the vehicle develops max power we use the equation

    MG1= 3.6 * ICE - 2.6 * (MG2/2.47)

    The ICE is now goes to 6000rpm which with MG1 at 14700rpm gives (MG2/2.47) = 2423 rpm

    Then IF 4.113 ring gear to wheel axle ratio is same as Prius where 1200rpm=20MPH, then 2423rpm will be 40MPH.

    This is a big improvement over the Prius which did not come up to full power until as late as 51.28MPH. MG2 will be rotating at 5984rpm which is well above the base speed of 4500rpm quoted.

    I make max speed for MG2 as 14820rpm at 100MPH. If that 4.113 figure is lower for the Camry the appropriate correction can be made.

    Someone quoted 12,400rpm max for MG2 and around 50lbs-ft less torque (on the West Virginia U. website) down from 295lbs-ft of the Prius but I make it even lower at 167Lbs-ft go figure. The spec says MG2 puts out 199 lbs-ft at 1500rpm perhaps it does, but at 4500rpm for 105kw it has to be 167lbs-ft.

    Anyway that new 2.47 planetary ratio brings it back up to a respectable 412lbs-ft. To which you must add 129-36 or 93lbs-ft of direct mechanical support.

    The interest for me is that you get 192 Hp at 40mph, a good 10mph lower than when Prius reaches its max power and then like the Prius will hold steady until you hit 100MPH !

    T2
  • toyolla2toyolla2 Posts: 158
    ...is the fact that it can recover the energy typically lost in braking.

    "No , that fact is not beautiful at all, gearhead_greg", I wrote.

    Regeneration, the recapture of mechanical power by converting to electric power for storage on board is a good idea if : -

    You are operating a battery electric vehicle.

    You are operating a gasoline electric hybrid upgraded to a PHEV because either
    1. gas is $15 a gallon - the economic reason.
    2. Hydro-electric power generated in your area - off oil/ anti-pollution statement
    3. Electric power derived from nuclear energy - same as above

    And is a bad idea : -

    For the current batch of hybrid cars on the market.

    It is my considered opinion that it is not an economic decision now and almost
    never will be to install a storage battery for the recapture of kinetic or potential energy on any gasoline hybrid propelled vehicle.

    To be clear - I am not against regenerative braking - I am just simply questioning the storage of reclaimed energy in a battery that you are about to install for that express purpose. Gains are modest at best and lugging 100lbs around when you didn't hafta' starts to be a big negative on prolonged hiway driving.

    For new designs a superior idea is to dissipate the power from light braking in a resistive device commonly referred to as a dynamic braking resistor, yeah no kidding. For industrial electronic drives these are the component of choice. They are low cost and compact, in this application about the size of a video cassette when mounted to a heat sink. A single transistor or relay contacts can bring them into circuit as necessary.

    The advantage of hybridisation is to extract more power from a given engine than can be done with a multi-gear gearbox. The electrical system avoids the adoption of a mechanical CVT which is not predictable over time and over the temperature fluctuations experienced in most of North America. This fact permits the current Toyota HSD system to use a 2.4 L in place of a 3.3L in the case of the Camry for example. The superior performance is not all attributable to 40 Hp of battery power. It is more to do with the fact that the Camry 140Hp engine is able to exert its full power from 40 mph all the way up to maximum speed in a seamless manner which is not interrupted by gear changes which would otherwise keep pushing the engine back down its power curve at each change.

    The other advantage of hybridisation is to reduce the frictional losses on a given engine by using the electrical system to present a load to the engine which always seems to the engine to be a higher torque but at lower RPM than the same engine would experience in a non hybrid car for whatever power happens to be be required at the time. The effect of engine friction is thereby reduced since every piston stroke generates more useful power per stroke than it would be called upon to do in the typical non hybrid application.

    The ability for the engine control unit to stop and start the engine can't be discounted either but the above two paragraphs are key to the main advantages of the hybrid.

    Comments welcome
    T2
  • tpetpe Posts: 2,342
    I am just simply questioning the storage of reclaimed energy in a battery that you are about to install for that express purpose. Gains are modest at best and lugging 100lbs around when you didn't hafta' starts to be a big negative on prolonged hiway driving.

    For the most part your post seems very knowledgeable but you are dead wrong on this point. Carrying an extra 100lbs is going to have a very, very small effect on highway mileage. Extra weight's negative impact is primarily during acceleration. However this is offset to a large extent by having this additional kinetic energy to recapture through regenerative braking. With that said if your driving consists of almost exclusive highway mileage there isn't much to be gained by going hybrid.
  • toyolla2toyolla2 Posts: 158
    Thanks for responding TPE, perhaps I can change your point of view.

    "Carrying an extra 100lbs is going to have a very, very small effect on highway mileage."

    That's what I thought too. It is a small effect but not insignificant as it turns out.

    Someone posted that at 60mph the rolling losses for the Prius battery were 200 watts.
    Recaptured energy from braking the Prius to rest is 540Kjoules. So if the battery was carrying this restored energy while at 60 mph it would be depleted to zero in 45 minutes.

    But even if the battery held no recaptured charge - it used it all up re-accelerating to 60mph again - this 540 KJ of energy is expended every 45 minutes. I brought this up on a Yhoo board some months ago and someone else - using a sophisticated equation punched in the numbers and came back with only 115 watts, but he was no longer a skeptic. His calculation omitted the aerodynamic loss which may have been included in the earlier 200W figure.

    "With that said if your driving consists of almost exclusive highway mileage there isn't much to be gained by going hybrid."

    The second reason to go hybrid covers just this situation. The engine is constrained to go as slow as possible at high torque by means of MG1 and the PSD. Engine frictional losses in this super overdrive are substantially lower. The engine will be kept away from actually lugging but unlike a fixed mechanical gear the servo MG1 can instantly cause the engine revs to rise quickly for more power when the need arises.

    The only problem I have with this is that in order to depress engine revs, MG1 has to become a motor obtaining its electrical power from MG2 which becomes a generator. This caused some uproar in Aug 2001 when original analysis (reverse engineering) was being done. The fact that the main traction motor MG2 could be in a generating condition when cruising at 60mph was regarded as "heretical" but was eventually accepted. Subsequently MG2 was said to be operating in "heretical mode" whenever MG1 was forced to be a motor.

    Heretical mode is when MG1 is negative from the eqn : -

    MG1 = ICE * 3.6 - MG2 * 2.6 (MG2 = 1200rpm per 20mph)

    Of course power must always be transferred between MG1 and MG2 in one direction or another while there is to be a positive torque applied to the road wheels. Direct engine to wheels power is a maximum of only 6.6 Hp per 10 mph for the Prius. But only a fraction of this is needed at 60 mph cruising so the electrical power circulating between MG1 and MG2 is similarly low probably less than 5kw, and this implies that losses will be low too.

    Hopefully the engine frictional losses that are saved by the slower running engine will swamp the electrical losses incurred by those MG1 and MG2 transfers; otherwise a tall gear manual transmission would be more efficient I agree. The fact that the HSD system has allowed a smaller than usual engine to be used should also be factored in.

    T2
  • tpetpe Posts: 2,342
    Someone posted that at 60mph the rolling losses for the Prius battery were 200 watts.
    Recaptured energy from braking the Prius to rest is 540Kjoules. So if the battery was carrying this restored energy while at 60 mph it would be depleted to zero in 45 minutes.


    The extra rolling friction would seem to be the only loss associated with extra weight. I don't see how it could induce an aerodynamic loss. In fact if it forced the car to sit slightly lower there might be a minute aerodynamic gain.

    200 watts is roughly equivalent to 1 mile lost every hour. With the Prius rated at 51 mpg on the highway this would come out to 1 mile for ever 1.18 gallons burned. You state that the amount recaptured from braking would be used up in 45 minutes. What if you stopped twice in this hour? Wouldn't that give you a net gain?

    Here's something that I'm not sure about. Is this battery pack the only battery on the Prius or is there a second battery that performs the function of starting the engine? If its the only battery then it really doesn't represent an additional 100 lbs because you have to consider what a traditional battery would have weighed. And I'm not entirely sure why this battery weighs that much to begin with. It only stores about 1 kWh of energy. You should be able to do that in a 20-25 lb Li-ion battery or <40 lb NiMH battery. I say that because the Toyota RAV4 EV had a battery pack that could store 27 kWh and it weighed slightly more than 900 lbs. This pack consisted of 24 12V NiMH batteries. Maybe I'm missing something but is seems like if you used just one the weight would be less than 40 lbs.

    One last point. Rolling resistance can be significantly reduced by choosing the right tires. Does the Prius come standard with low resistance tires? It probably does.
  • Here's something that I'm not sure about. Is this battery pack the only battery on the Prius or is there a second battery that performs the function of starting the engine? If its the only battery then it really doesn't represent an additional 100 lbs because you have to consider what a traditional battery would have weighed. And I'm not entirely sure why this battery weighs that much to begin with. It only stores about 1 kWh of energy. You should be able to do that in a 20-25 lb Li-ion battery or <40 lb NiMH battery. I say that because the Toyota RAV4 EV had a battery pack that could store 27 kWh and it weighed slightly more than 900 lbs. This pack consisted of 24 12V NiMH batteries. Maybe I'm missing something but is seems like if you used just one the weight would be less than 40 lbs. One last point. Rolling resistance can be significantly reduced by choosing the right tires. Does the Prius come standard with low resistance tires? It probably does.</i>

    The high-voltage battery pack is indeed used to start the engine via MG1. The only other battery in the car is the small 12-volt battery which is there mostly to boot up the computers and run various 12-volt items when the main battery isn't connected (radio, lights, keyless entry, alarm, etc). When the main high-voltage battery is connected, all of those items are powered via it through an step-down transformer. MG1 is also used to generate electricty which in turn can be used to recharge the battery or provide extra electricity to run MG2, or do both at the same time.

    The battery pack is rated at 1.3kWh. The weight of the pack is listed as 45kg, or about 100 pounds.

    And yes, the car comes with low rolling resistance tires.
This discussion has been closed.