Mazda’s Capacitor Based Automotive Regenerative Braking System

Discussion in 'In the News' started by xcel, Nov 25, 2011.

  1. brick

    brick Answers to "that guy."

    You're probably right about the Insight II steady state FE numbers (smaller car, smaller engine, better SS FE), but you're wrong about the EPA test. The real reason the raw numbers are so high is that EPA tests are conducted at low speeds, where the Prius drive train is most effective. Once it gets warm (and I think the test starts with a warm engine?) the engine shuts down any time power isn't needed below 40-45mph (depending on if we're talking 2nd or 3rd generation.) That's an awful lot of ICE-off driving in the city cycle in situations where it would still be turning in an IMA-type hybrid.

    One thing you have to understand is that HSD is set up not to deplete the battery by using it for propulsion except in extremely slow stop & crawl. I start and end every journey with SoC within a percent or two of 60%. The farther below that level the battery gets, the harder the system works to get it back up through greater use of the ICE and less use of electric motor. The opposite true the higher SoC is above 60%. This strategy ensures that there is room to capture regen energy or provide assist or a short run of low-speed crawling, whichever is needed.

    What was this thread about? A capacitor-based BAS-type system? I'm happy to see it come to market, especially when coupled to Mazda's excellent new engines. Chemical batteries do get the job done, but I think it will be hard to get around the need to treat them with extreme care in order to make them last the life of the vehicle. Heat degrades them, cold makes them not work, too much current degrades them (and makes them hot), too much or too little charge can cause degradation while they aren't even being used...fussy stuff. Capacitors have their own issues, but in this application I think they make a huge amount of sense.
  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    The EPA tests are mixed cold and warm starts.

    The EPA tests can start with a full battery, but any difference between the start and end SoC are taken into account.
  3. phoebeisis

    phoebeisis Well-Known Member

    Let me split hairs a bit.But not wanting to start a battle.
    Really, really tiny motors won't get waaaaay better FE.
    A 4 stroke 250 Twin-NO TURBO- would make maybe 20 rwhp at 10000 RPMS- barely enough to hold 60 mph in a very small car.
    It would NOT get better FE than a 500cc twin making 40 hp.The 500 could make the required 20 hp at 5000 RPMS.They would both be at full throttle-so pumping losses about the same-slightly favoring the 500..
    BUT friction losses would be much higher with the 250- KE = 1/2 MV^2-double the piston speed and you increase friction by 4x.

    Of course eventually you get such big motors that pumping losses from the closed throttle will be too high.My 5.7 V-8 for example
    The beauty of the 1.4 turbo is it allows lower RPMS(as if it is a bigger motor)-and it gives more peak power when needed.
    Fords 3.5 turbo vs GMs 5.3-the 3.5 gets just 7% better FE-1 HY 2 CITY-DESPITE BEING MUCH SMALLER.
    Smaller does get better FE- but not "way" better(Yes Ford did have to produce big HP and Torque numbers to make the 3.5 attractive-more than they needed really-cost them some FE probably)

    Look at what Toyota did with the Prius-increased size to 1.8(from 1.5) but got better FE.
    True the 1.5 probably could get better FE-my guess is they had the Prius V (heavier)in mind-and USAers like acceleration.

    Manufacturers are finally mining smaller motor FE-but small has its limits
    RPMS are poison, but so are pumping losses-the turbo allows you to cheat-throttle plate open- but rpms down
  4. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    The electric motor in IMA provides high torque as part of the design. That torque means the engine doesn't need to provide torque at low speeds. In other words it matches the key problem with gasoline engines, the key reason why cars in the USA have larger engines than equivalent European models: US drivers demand rapid acceleration.

    So, sure you could put a conventional 1.0L engine in the Insight (II) and hypermilers would love it, but the rest of the nation would complain about the poor acceleration. You could do what Ford are doing with their 1.0L and turbocharge it. But it would be worse in the city. Then you could add an equivalent of i-stop and i-eloop and it would still be worse in the city because those times it's using assist with IMA it's now going to use the turbo and that smart alternator can't help it propel the vehicle.

    Mazda's system's advantage is not efficiency. It's cost.

    Well, I don't know about the JC08 cycle. But I know that start-stop makes zero difference to the EPA ratings.

    Let's consider those three things (although I think you're ignoring low-speed efficiency):
    - Engine idle at stop: both extremely helpful, but the A/C in IMA vehicles can run for a short time with the engine stopped. Other start-stop systems shut the engine down but provide an override switch so the driver can turn the engine back on to run the A/C.
    - Regenerative braking: the i-eloop system will be efficient but limited in capacity; the captured energy can only be used to run low-power auxiliary systems; the IMA system allows the captured energy to move the car.
    - Engine stop at speed: i-stop+i-eloop can cut fuel to the engine as long as there is no traction demand and it does not need to be on to run A/C; IMA systems can cut fuel to the engine if there is low traction demand and can run the A/C for some time off the battery.

    So, it won't be able to claim back that whole 25%.

    Also, note that it's the JC08. In the USA, the EPA cycles do not include start-stop yet IMA system hold a significant advantage over ICEV alternatives.

    NiMH battery or Lithium in the HCH.

    You're right, it's an inefficient process. Yet still IMA increases efficiency. Engine efficiency increased though downsizing and more opportunity to vary the engine cycles.

    The above statement is entirely false.

    As I've noted in my replies to you, the IMA system helps reduce engine displacement and therefore fuel economy. Wayne and other hypermilers here can get excellent FE out of IMA hybrids because they can keep the engine running efficiently. They also find high-speed pulse and glide much easier in IMA hybrids: the Gen 3 Prius is particularly finicky.

    Those real-world FE numbers are closer together. However, do remember that the Prius is a larger, heavier vehicle and has much greater market acceptance. It makes it more difficult to compare.
  5. phoebeisis

    phoebeisis Well-Known Member

    On another subject did Mazda mention how much this adds to the price?
    If you drive 12000 miles/yr 30 mpg then 400 gallons/yr-save 1% 4 gallons-5% 20 gallons-
    $80/yr at 5%- better not be too expensive-
    $400-$600 would be ok
  6. lightfoot

    lightfoot Reformed speeder

    Key word = "often"

    I think we can agree that accelerating to say 40mph, driving to a traffic light which was already visible and red, and braking to a stop at it wastes energy relative to accelerating to 25mph so that one arrives at the light after it changes to green, thus not having to use the brakes. With a hybrid (or this new Mazda system) one recoups part of the braking energy but not all.

    If you're driving along at 40mph and a green light suddenly turns red without any way you could have foreseen that, obviously you brake to a stop. This also wastes energy, but (assuming the PSL is 40 or higher) the use of brakes is not a sign of inefficient driving.

    Hope that's clearer.
  7. lightfoot

    lightfoot Reformed speeder

    The weight of the IMA system isn't as great as people think:
    - the electric motor is actually a motor-generator, so it replaces the alternator: hybrids don't have an alternator. This offsets a good part of the weight of the IMA motor.
    - since the motor-generator is also used for most ICE starts, the size of the 12V starter might also be reduced in the IMA system???
    - don't know about the other hybrids, but the Insight-I battery weighs only about 85lbs. One guy can easily lift it (we had three of them out today installing charging harnesses)

    FWIW, the Prius is Atkinsonized, the Insight-I uses VTEC and lean burn, and the HCH uses cylinder inactivation with valve lifting to reduce pumping losses. All of these are incorporated to help the ICE be more efficient at lower power outputs while still able to produce higher power levels when needed.

    The point is that a major factor in mpg is how efficiently (as in how little fuel burned) an ICE can produce the 10-15hp?? needed for cruise, while remaining flexible enough to produce higher levels of HP and torque when needed (which is where the electric motors come in). It's virtually impossible to make an ICE capable of producing 300hp also produce 15hp efficiently. Or, at least, as efficiently as a smaller ICE with a much lower max hp output. IOW, people like to talk about peak power/weight ratios, but it's more a question of fuel efficiency at cruise power, with reducing weight being a separate issue.

    As far as regen goes, my experience has been that most of the regen comes from background charging during cruise, not from braking. Which makes sense, because the kinetic energy of a 3300lb car moving at 35mph is only about 0.05 kwh (assuming I calculated correctly) - and not all of that will be captured and returned either by a hybrid or by a vehicle with this capacitor system.

    The good news (for hybrids) is that bursts of assist during typical accelerations do not take much energy either - high wattage but short term.
    Last edited: Nov 28, 2011
  8. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    The Insight-II battery is 45lb.
  9. lightfoot

    lightfoot Reformed speeder

    According to the Honda website, the Civic Hybrid battery weighs 48.5 lbs and the IMA motor weighs 42.5 lbs.

    Looking at overall weights, the basic Civic Hybrid is listed at 2853 lbs, the most comparable non-hybrid model feature-wise (the HCH normally has higher-end features that may add weight) is the basic EX w/AT, which weighs 2765 lbs, or only 88lbs less.

    Even the stripped-down-for-max-mpg Civic HF weighs 2698lbs.

    Much less difference than I thought. Another IMA hybrid myth blown away.

    So I started wondering about HSD hybrids. The Toyota Camry LE w/AT weighs 3190 lbs; the Camry LE Hybrid weighs 3435 lbs, or 245 lb more, features look about the same from a POV of weight. EPA on the LE is 28mpg, EPA on the LE hybrid is 41mpg, 2.5L engine in both cases. So the HSD hybrid system way more than overcomes the weight difference, netting a 46% improvement in fuel economy rating.
    Last edited: Nov 28, 2011
  10. herm

    herm Well-Known Member

    The eAssist mild hybrid has similar functionality, in Canada is a $690 option for the LaCrosse.. its not sold as an option in the US so no idea how that translates... but anything over $300-$400 for Mazda seems like is not a good deal. eAssist replaces the starter and alternator.
  11. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Herm:

    Canada pricing is a bit out of touch as they have such high up-front costs and I am not exactly sure why.

    In any case, eAssit is a $2,000 mark-up over its non-eAssist equipped brethren (Buick Regal vs. Buick Regal with eAssist) here in the states.

    The eAssist option also adds:
    • 17" low-rolling-resistance tires on lightweight machined-alloy wheels
    • Axle with a 2.64 final drive ratio to maximize highway fuel economy.
    • Heavy-duty, 438-cold-cranking-amp battery for surer winter starts.
  12. herm

    herm Well-Known Member

    post #9 here, not bad for such a luxurious car:

    "I did one dedicated highway segment that yielded 35.2 mpg in a steady 65-70 mph cruise covering 160 miles. Commuting to/from work two days in stop and go traffic for 140 total miles yielded 27.7 mpg. The other 300 miles or so was a mix of everything in short bursts with many cold start mornings below freezing (the eAssist doesn't function fully until the engine is warm - takes 3-4 miles for that point to be hit from a cold start) and the overall average was 28.2 mpg for the week and 600 miles. "

    I went to the Canadian Buick website and tried to configure a LaCrosse .. this is what I got:

    "Selection of Engine: 2.4L Direct Injection I4 SFI VVT
    Requires that you choose:
    Transmission: Electronic 6-Speed Auto w/OD
    eAssist 2.4L Package
    Tires: P235/50R17
    2.64 Axle Ratio
    Non-Variable Effort Electric Power Steering
    Flush Mount Lip Spoiler
    115 Volt eAssist Power Pack
    Single Turned Down Hidden Exhaust
    SiriusXM Satellite Radio
    Driver 4-Way Power Lumbar
    Requires that you remove:
    Tires: P245/50R17 AS Blackwall

    The total price of this vehicle will increase by $1,015"

    They advertise the option at $690 but apparently you cant get it, and if you select the 2.4L engine then it cost $1015 more than the V6 option and it includes eAssist.

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