1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Surprising Critics, New Prius Improves Both Power, Efficiency

Discussion in 'Gen 3 Prius Technical Discussion' started by usbseawolf2000, May 19, 2010.

  1. usbseawolf2000

    usbseawolf2000 HSD PhD

    Joined:
    Sep 22, 2004
    14,487
    2,994
    0
    Location:
    Fort Lee, NJ
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    I found an excellent article with juicy information for the development and engineering of 2010 Prius. I am not copying everything but this is a lot of interesting (good to know) stuffs:

    “Because of the late intake valve closing,†Yerace explains, “the compression stroke doesn’t start taking effect until the valve closes, and it allows a longer expansion stroke on the other side. You have an asymmetric cycle that enables this engine to run at a higher compression ratio of 13:1.

    “Because the intake valve stays open longer, you’re allowing charge from the engine to go back up into the intake manifold. This doesn’t let it make very good power but does allow it to run much more efficiently.

    “That is why most gas/electric hybrid system engines use it, and also the reason why this engine has variable valve timing only on the intake side, where other Toyota engines have both intake and exhaust VVT.â€

    Also, with the intake valve closing so late, a higher throttle opening is required to make an equivalent amount of torque compared with a conventional engine. That higher throttle opening reduces the pumping work at a part-throttle condition, which also improves efficiency.

    And this may be the global auto industry’s only totally beltless engine. “The oil pump is gear-driven,†Yerace says, “but beyond that everything is electric. Engineers really tried to eliminate all parasitics.â€

    It was a challenge to get an electric water pump with the (flow rate) capability and the low-energy requirement they were looking for, Yerace says. So one major task for the team was mapping out what was required for the cooling system under all different conditions.

    It was tuned to have sufficient capacity to cool the engine, yet avoid overkill.

    Another significant improvement over the previous engine is much lower friction. Cooled exhaust gas recirculation is yet another upgrade that allows very good performance at higher loads and higher engine speeds.

    “The heat exchanger that the exhaust gas is going into is water cooled, which reduces its temperature before it goes back into the cylinders. This reduces combustion temperatures and helps reduce spark knock at high loads, which also enables us to run that high 13:1 compression ratio. It also helps us from having to do fuel enrichment, so we can run stoichiometric, much leaner than we could before.â€

    For a look at the rest of the ’10 Synergy Drive system, we asked Advanced Powertrain Program Manager Justin Ward what was new and different. “From a propulsion point of view,†he says, “one big difference is the gear reduction.

    “We bumped the voltage up from 500 volts to 650 and were able to use a much higher-speed traction motor, which optimizes efficiency in its operating zones,†Ward says. “You lose some low-end torque with that higher speed, but you gain it back with the gear reduction, and you get some loss-reducing advantages in the system.â€

    “We also improved thermal management of the battery pack, so we can get a little more out of it.†Another significant difference is the “power-split†electric continuously variable transmission’s direct gear-to-gear interface, which replaces the previous unit’s chain drive. “That helps on many levels, including noise and durability.â€

    And there still is room for further efficiency improvements down the road. “One thing (the engine team) will try to do is expand the minimum fuel consumption areas of the (fuel) map even more,†Yerace says. “That was one of the really big differences between the previous engine and this one.â€

    However, adding direct injection is not on the immediate to-do list.

    “Because of the way DI works, I’m not sure it is complimentary with the Atkinson cycle,†he says. “Typically, to get the most out of DI, you have some kind of earlier injection strategy. But when you’re pushing some of your intake charge back out, I don’t think the benefit is there.â€

    “Power electronics are huge,†Ward kicks in. “We made a tremendous effort on power electronics and were able to make a massive improvement this time, but we still have a way to go. There is also still a lot of opportunity on the traction motor side.â€

    Surprising Critics, New Prius Improves Both Power, Efficiency

    [​IMG]
    [​IMG]
     
    3 people like this.
  2. usbseawolf2000

    usbseawolf2000 HSD PhD

    Joined:
    Sep 22, 2004
    14,487
    2,994
    0
    Location:
    Fort Lee, NJ
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base