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2008 Sienna Hybrid - Do you want 4 cylinders or 6?



  • Hi Tex,

    You've consistently voted for the 6 cylinder-hybrid combination since your first post in June. Most of the engineers who have replied have had various formulas that conclude that even 200hp is more power than is really needed, even for climbing hills.

    Remember that the hybrid engine WILL work simultaneously with the ICE. A hybrid does have two engines, pretty redundant if the electric engine could work full time. If you do need the power, the electric engine will kick in while climbing a hill and provide extra boost. In my opinion, it's a shame not to use that feature in order to downsize the ICE.

    Your comments do speak to reality, however. There are some people who remember the sluggishness of the 4-cylinder minivans sold in the 1980s and 1990s. Convincing those consumers, and you, that a 4-cylinder ICE plus an electric engine is NOT equivalent to the old 4-cylinder minivans is probably a lost cause. No amount of information, either technical or advertising, is going to change your mind.

    By the way, Bob Lutz, Vice-Chairman at GM, said that the Chevy Volt is likely to come out with a 1-liter, 3-cylinder ICE in addition to its electric engine. I have no idea what HP that converts to, but its not a lot. Yes, the Volt won't be a 2-ton minivan with another ton of passengers or payload, but it does speak to the over powering that we have gotten used to. The Volt is said to have 0-60 times of 8 seconds, which is enough for passing and merging into traffic. Yes, it won't beat the BMW 535 up a hill. But you also won't be able to buy today's version of the 535 in 2020 when CAFE requirement go to 35mpg.

    In my opinion, I hope that Toyota comes out with a Sienna that maxes out its fuel economy potential. It may not suit every consumer's need, but it might be the best choice for consumers looking for fuel efficiency.
  • ateixeiraateixeira Posts: 72,587
    In practice, the supercharged I4 in the Previa minivan was very, very inefficient.

    The 2GR 3.5l V6 blows it away in terms of fuel economy. No contest. It's also much quicker.

    I don't see a reason to go back to a supercharged I-4.
  • wwestwwest Posts: 10,706
    Yes, absent the variable speed capability an SC only means PERFORMANCE, not efficiency. With the variable speed, INFINITELY variable boost capability, the SC would only be used on the hwy where the hybrid capability is less efficient. The hybrid capability would be reserved for city stop and go traffic where its efficiency is STELLAR.

    Keep in mind that this would not be a LARGE high capacity SC, just enough HP boost to bring the ICE up to "snuff" for light acceleration or uphill travel. Passing acceleration would still require the hybrid "boost" aid.
  • ateixeiraateixeira Posts: 72,587
    How would you engage and disengage the supercharger?

    Currently they run off of serpentine belts that leech efficiency from the engine even when you don't need the boost.

    How would it disengage?

    And if it did, wouldn't it partically block the air intake path? Or would you let it freewheel?

    Even then, I imagine it would create a small amount of drag on the intake air while not under boost.

    It just sounds incredibly complex and expensive.
  • wwestwwest Posts: 10,706
    Do you know how the Prius sits non-moving with the ICE running and the e-CVT fully "engaged" ?

    Think of the ICE driving one end of an open differential and the electric motor driving the other. If the electric motor turns in the direction OPPOSING the ICE input then the output of the differential remains stationary.

    So that's the basic idea, one input of the e-CVT (diff'l) would be belt driven via the ICE and the "opposite" end via the synchronous AC motor. In our case, as with the actual E-CVT, we would use a planetary gearset with a 3:1 ratio so that when the engine reaches 5,000 RPM the synchronous motor would be turning at 15,000 RPM.

    To close the intake airflow and "choke" the ICE off the synchronous AC motor would turn at exactly 3 times the speed of the ICE (as it slows to 0) but in the opposing direction, the SC would therefore remain motionless and the ICE would be choked of all intake airflow.

    No traditional throttle valve required.
  • ateixeiraateixeira Posts: 72,587
    I thought the Prius shut off the ICE when the car stopped moving. I guess under high loads, when the battery is drained, it's gotta run to supplement power.
  • wwestwwest Posts: 10,706
    Or to heat the coolant or the catalyst.
  • 5gators5gators Posts: 1
    I think everyone needs to change their paradigm on these hybrids.

    Right now Toyota's hybrids are all Parallel hybrids, meaning that propulsion is achieved by both an ICE and an electric motor.

    They need to move to a Series Hybrid, meaning that propulsion is provided entirely by electric motor, with electricity generated by an ICE (gas, diesel, hydrogen, nat gas).

    This allows maximum torque to be provided by the electric motor at very low speeds as well as cruising speed. The on-board generator would not have peaks and valleys like it would if it were providing propulsion directly. Therefore, it can always run in it's most efficient range. This would also allow a much smaller engine to provide charging power.

    This also is the ideal setup for the future, allowing plug-in capability as well as an easy change to alternative fuels as they develop since the ICE is not as significant a portion of the total car.

    Ideally (especially for a van), the electric motors could be installed in the wheel hubs themselves, freeing up weight and space in a true one box vehicle.

    The technology is here now, you don't even need the lithium batteries for this setup. They would only be needed in a plug-in scenario.

    The VOLT is a series hybrid.

    Whoever puts the series hybrid technology into place in mass quantities first, will take the lead in the Eco/Green/hybrid race.

    Just my 2 cents worth.
  • jim314jim314 Posts: 491
    And in addition a series hybrid would employ a simpler, cheaper, and less failure prone transmission, wouldn't it?

    But what about highway fuel efficiency? Doesn't a parallel hybrid get better mpg at highway speed?
  • ateixeiraateixeira Posts: 72,587
    Ideally (especially for a van), the electric motors could be installed in the wheel hubs themselves, freeing up weight and space in a true one box vehicle.

    One concern I see would be unsprung weight - you are adding mass to the wheels that bounce around each time you hit a pothole. It would be hard to tune that suspension and the shocks would be working overtime.

    It certainly frees up packaging tremendously, but car makers use light alloy wheels for a reason.

    Another concern is the electric motors would get wet in puddles, and would be exposed to the elements.
  • timothyhtimothyh Posts: 11
    The Dept of Transportation just published their proposed CAFE minimums for 2011-15. Toyota is supposed to average 26 mpg for their light trucks in 2012, rising to 28mpg in 2015.

    The current Sienna averages 19mpg according to the EPA.

    Come on Toyota. Give us a more efficient van for our families!!
  • wwestwwest Posts: 10,706
    [quote name='diver1972' date='Tuesday, Apr 22, 2008 @ 03:36 PM' post='146287']
    Exactly how much safety are you trying to achieve? What exactly are you wanting to protect against?

    The Tundra is RWD and therefore will be significantly safer in overall operation on adverse, ice or packed snow, roadbed conditions.

    Yeah, I've heard rumors ranging from 2010 MY to 2012 MY. Like the other hybrids, it's likely to achieve real MPG gains only in stop-go-stop-go-stop-go traffic conditions (i.e. where the ICE can shut off). Since the ICE is still needed to push it down the road on the interstate, highway MPG isn't likely to improve much,

    Well, not really. With the "electrics" along to act as an ICE SuperCharger the ICE can not only be downsized (lower frictional losses), but made more efficient at fuel "burn" using the Atkinson Cycle technique or simply derated as in the HL and RX.

    if any, over what it is now. No matter how you look at it, it's still a 4,000-pound vehicle with a 3.5L 6-cylinder, not a 2,500-pound Cavalier with a 2.2L 4-cylinder. More liters drink more fuel. :sad:

    "..with a 3.5L 6-cylinder, not a..."

    That's the point, or at least partially so...

    The turbocharged 2.3L I4 in the Acura RDX produces 260HP....

    Think about what could, MIGHT, be done with a hybrid 2.0L I4 using the Miller Cycle via an engine driven Supercharger. But with the positive displacement composite (carbon fiber) SC speed/boost controlled independently of the engine RPM using the Toyota HSD CVT concept. During hwy cruise the ICE would just "loaf" along with the SC providing enough, "just" enough, the exact right amount (NO throttle plate), of intake airflow for the level of engine performance required/needed.

    Okay, now put your foot "into it", the lightweight carbon fiber SC spools up virtually instantly putting the ICE "on boost" and the electrics "kick in" their extra TORQUE.

    Zoom, ZOOM,....ZOOM...!!

    And all with absolutely STELLAR FE.

    Now just add a CNG conversion kit w/tank (carbon fiber) and refill the CNG tank overnight at home using PHILL.

    Using CNG (~100 octane equivalence) would not only increase the "standard" ICE's HP/torque substantially, but would allow the compression ratio to be increased to an even higher level..

    Maybe we wouldn't need a LARGE 2.0L ice, maybe a 1.5L would suffice.
  • timothyhtimothyh Posts: 11
    VERY unfortunately, Toyota is not going to put an Acura (Honda) engine in one of its vehicles.

    It should.

    The Camry 4-cylinder (2.4L) gets 155hp. As you noted, the 2.3L Acura turbo charged 4-cylinder gets 260hp. The Acura TSX without a turbo gets 207hp.

    When I first started this thread, I was hoping that SOMEONE at Toyota would focus on a highly efficient large vehicle. The Highlander falls short. And as Atexeria pointed out, it would not be for everyone. If you need to tow something, don't get a hybrid. If you want good acceleration, get a Highlander hybrid or don't get a hybrid.

    As they did with the Prius, would Toyota make a large vehicle that focuses on fuel economy. The Prius has a 1.1% market share of all vehicles sold in the US. Every other hybrid combined also has a 1.1% market share.

    Fuel efficiency doesn't turn everyone on. But if its very important to 1% of the new car buyers - one's with families -

    Come'on Toyota!! Let us have it!
  • ateixeiraateixeira Posts: 72,587
    CAFE uses unadjusted EPA fuel economy numbers.

    They've been lowered twice, yet CAFE still uses the very outdated higher numbers from the 1980s.

    The Sienna would probably get 23-24mpg on that old scale.
  • V-6's are rough enough, especially in 90 degree configuration and without counterbalancers. Coming from my last three cars with rotary, inline 6, and V-8 motors, the current Sienna motor doesn't feel particularly smooth to me. The last thing I'd want is a large unbalanced inline 4 booming away under the hood. Inline fours are not in primary balance, nor are 90 V-6's. The only way to get them to be truly smooth is use counterbalancers, which add weight and mechanical complexity. At least a decent V-6 is smoother than an inline 4.
  • wwestwwest Posts: 10,706
    "The only way to get them to be truly smooth...."

    Yes, that's likely very true for I4/inline, but what about "boxer" style..??

    Wouldn't those be even more "perfectly" balanced vs any "V" engine..??
  • jim314jim314 Posts: 491
    There is negligible additional complexity in having twin counter rotating balance shafts to smooth out an inline 4-cyl. I know Chrysler used them on its now superceded 2.5L 4-cyl. I suppose that the European mfgrs use them on their 2.0 L 4-cylinder engines.
  • ateixeiraateixeira Posts: 72,587
    The chain-driven 2GR V6 isn't exactly known for being quiet. The 3MZ was actually more quiet.

    It's worth the trade-off for all the extra horsepower, but still.

    FWIW Toyota added sound insulation to the fire wall and along the door sills to offset the extra noise from the V6.

    Hybrids often shave weight by removing sound deadening, though.
  • ateixeiraateixeira Posts: 72,587
    People are asking for an AWD descrition in this thread:

    Can you please hop over there?
  • wwestwwest Posts: 10,706
This discussion has been closed.