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

Prius Prime and the mg1/mg2 situation

Discussion in 'Gen 5 Prius Technical Discussion' started by The Red Baron, Feb 15, 2023.

  1. The Red Baron

    The Red Baron Junior Member

    Joined:
    Sep 24, 2022
    17
    11
    0
    Location:
    Athens Greece
    Vehicle:
    2022 Prius
    Model:
    Touring
    Toyota/Lexus and other manufacturers are implementing the dual motor drivetrain with or without mechanical energy flow to more and more vehicles. It seems that this drivetrain tech has lots to offer.

    We do see that the mg1/mg2 combo is powering front engined front wheel drive vehicles and when awd is required the rear motor is powered through the battery. Lexus rwd platforms are using mechanical connection to power the rear axle. The question i have is this, why the mg1 cannot power a rear postitioned motor? the two motors has to be in close contact for some reason? they cannot exchange power through a wire or something?

    Having a front engined rear wheel drive layout without the need of a mechanical connection (if possible) would be great for efficiency, packaging, and performance.
     
  2. john1701a

    john1701a Prius Guru

    Joined:
    Jan 6, 2004
    12,754
    5,245
    57
    Location:
    Minnesota
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    While in hybrid mode, MG1 interacts with the gas-engine when operating in split-mode as a generator and as a starter. To fulfill that role, it must be physically attached to the gas-engine.
     
  3. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    22,068
    11,533
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    In addition to the above, the system varies the input and output of MG1 to create the variable gear ratios in the transmission for hybrid mode.
     
    john1701a and The Red Baron like this.
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,921
    15,548
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    That sounds like an oversimplification of where the power to the rear motor is coming from.

    Of course they can, and that's your actual answer. The "frame wire" is a pair of heavy orange cables running from front to rear of the car.

    All three MGs are able to function either as motors or as generators at different times, and electrical power coming from any MG as a generator can go to any other MG as a motor, or into the battery, and also power from the battery can be taken and added to that from a generator, when more motor power is needed.

    Even in the FWD versions, by the way, it is not always MG1 doing the generating in normal driving. At higher-speed cruise, MG2 is generating and MG1 is motoring. The overall point remains; they can either be in exact balance, one generating and one motoring at the exact same power level, or there can be a difference. When there is a difference, that power can flow from or into the battery or to MGR.

    The electrons all look the same; you can't stop them as they pass through MGR and say "these came from the battery, and these came from MG1". (Or, "these were available from the battery because MG2 didn't need them because others came from MG1".)
     
    #4 ChapmanF, Feb 15, 2023
    Last edited: Feb 15, 2023
    CR94, john1701a and The Red Baron like this.
  5. TGTGUUD

    TGTGUUD Member

    Joined:
    Dec 15, 2022
    72
    63
    0
    Location:
    San Francisco
    Vehicle:
    2024 Prius
    Model:
    LE
    Not sure I get what you are implying but I assume you mean a longitudinal engine up front as the generator (or range extender) and a bigger rear motor to put down the power?
    Interesting thinking as it definitely will move weight towards the rear and open up room for double wishbone front suspension, etc.
    But I suspect it will be less efficient. The overall package will be heavier (bigger rear motor, battery may need to be bigger), no regenerative braking in the front which will hurt the efficiency a lot. And very difficult to drive the front wheels if that’s needed.
    So from what I can understand it does not make sense to do that. FWD seems to be the more efficient layout for THS. And for that sake the rear motors are small and mostly do nothing in normal driving situation in these AWD models.
     
    The Red Baron likes this.
  6. The Red Baron

    The Red Baron Junior Member

    Joined:
    Sep 24, 2022
    17
    11
    0
    Location:
    Athens Greece
    Vehicle:
    2022 Prius
    Model:
    Touring
    Thank you all for your replies. You pointed out some of the not so apparent drawbacks that make good enough reasons to avoid such a layout. On the other hand all tech comes with pros and cons. As ChapmanF suggested, it can be done, (btw electrons dont like going through a battery :)) so for argument sake lets build a case scenario, or two.

    First we try implementing this into Lexus IS300h, we scrap the planetary gear set and the drive shaft. The mg1 gets all the power from the ice, which is around 180hp and sends it to the 225hp mgr. The main drawback would be a limited top speed? Maybe a planetary rear diff could help with the top speed issue. Apart from this it could work, am i the only one seeing potential here?

    Second try is the awd Nissan Xtrail, it could come with a 200hp mgr powered from mg1, having the battery complementing both front and rear when needed.
     
  7. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    22,068
    11,533
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    What you are proposing is a series hybrid. They've been around for some time in trains and ships. The first cars using such system were over a hundred years ago.
    A Brief History Of Hybrid Cars - CarsDirect
    Series hybrids were the next big thing 100 years ago: Are they any more likely today?

    More recently, the i3 REx and Nissan's ePower system are series hybrids. For a PHEV with an electric range approaching 100 miles or more, it is a cost effective way of adding a range extender, and the drawbacks aren't a big deal because of infrequent use. In a hybrid, the conversion losses of going mechanical to electric to mechanical add up, and the highway efficiency drops. That's why the Volt ended up with a mechanical connection between the wheels and engine. I don't think a ePower hybrid has been sold outside Japan, where the average street speeds are lower.

    In the HSD, the MG1 is maybe 50hp. Getting full power from MG2 always meant pulling energy from the battery. For a series hybrid, MG1 would need to be upsized.
     
  8. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,921
    15,548
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    If I seemed to suggest it can be done, my apologies ... what I meant to say is that it already is done.
     
  9. The Red Baron

    The Red Baron Junior Member

    Joined:
    Sep 24, 2022
    17
    11
    0
    Location:
    Athens Greece
    Vehicle:
    2022 Prius
    Model:
    Touring
    Well we have nissans epower in europe. The problem with the lack of mechanical flow is the extremely low efficiency on highway speeds. In that case i am going to remove the mg2, keep the planetary gear set in order to have mechanical energy flow to the front wheels while mg1 powers the mgr with a little help of the battery thus having an awd drivetrain with mechanical flow to the front and electrical flow to the back wheels. Or to simply put it, send the mg2 to the rear.

    On Prius specs we could get a maximum of 150hp to the front wheels on highway speeds through the ice, 160hp to the back wheels through the mgr (mg1+battery) and around 200hp on full throttle. Doable?

    Efficiency should be almost the same but driving dynamics could be interesting.
     
  10. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    If you want 300 HP, just lift the drive train of a RAV4 Prime, all the design is done for you all you need is to implement it.

    Mind you, efficiency is going to resemble the RAV4, not the Prius.

    RPM of M/G 2 is the limiting factor for top speed, although there are situations where M/G 1 and the internal combustion engine have red lines that limit you as well. (Gen 2 Prius were much more likely to be limited by the RPM of M/G1, later Prius solved that)

    I am not really understanding what goal you are having that a current PHEV is not solving for you, can you explain what you want?

    This explanation of a Gen2 is the most understandable to me, perhaps it will be to you as well.
     
  11. The Red Baron

    The Red Baron Junior Member

    Joined:
    Sep 24, 2022
    17
    11
    0
    Location:
    Athens Greece
    Vehicle:
    2022 Prius
    Model:
    Touring
    The goal is having a rwd biased hybrid drivetrain which would give interesting driving dynamics by putting a large hp motor to the back wheels.
     
  12. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    With that goal, I suspect you have purchased the wrong car, however, M/G R from a hybrid Highlander has 43 hp and 89 ft lbs of torque. I bet you will need the rear inverter and considerable fabrication skills. (A gen 4 AWD Prius only has 7 hp in the rear, 41 ft lbs)
     
  13. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,921
    15,548
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    I would say that the videos by Prof. Kelly (like that one), and the one by Niels Blaauw (Prius Hybrid Drive Explained | PriusChat) have strengths and weaknesses that complement each other.

    Where Prof. Kelly's videos really shine is in showing what the pieces really look like and how they go together, in great detail. He says a little about the theory of operation but never at more than a "and it goes kinda like this" level, never working through the actual directions and proportions of power flow in the different operating modes. That just isn't his focus, and you can't blame him for picking what to focus and not focus on.

    In particular, his videos usually (it's at 1:45 to 2:02 in this one, but I've seen the same in his other videos) will describe how MG1 can be used as a generator, and then how MG1 can be used as a motor to impart torque to the rest of the system.

    But I have never seen him drive home the key point that as a generator it also imparts torque, and in fact very important modes of the transmission's operation involve using it as a generator, not as a motor, to impart torque.

    It is very hard for a good understanding of the transmission to start falling into place before grokking that key point. Until then, a person tends to be stuck in a sort of artificially-separated understanding of "MG1 generates for doing this thing or this thing" or "MG1 motors for doing this or this other thing". Once the person starts to get the picture that also generation is used, and even often, for the torque it involves, then the picture starts to solidify that there aren't distinct regimes the transmission is kind of clicking between, but a single set of algebraic relations that apply all the time, without a discontinuity, across all the rotation directions, torque directions, and power flow directions that arise.

    The Niels Blaauw video has exactly the complementary strengths and weaknesses. It's an animation, not real-life photos, so it is nowhere near as good as Prof. Kelly's for showing you how things really look. That isn't Blaauw's focus. But the video is all about explaining what is going on with the power and why it is done that way, and it does a top-notch job. Because it's an animation, it can even build up the explanation through a series of simpler "transmissions" that show the pieces of the explanation even though they wouldn't be possible to physically build.

    The way you know when you're really starting to get how the transmission works is when you can pick any operating conditions and points on the nomograph and work out both the direction and amount of power taking each of the electrical and mechanical path. The Blaauw video doesn't quite go as far as showing you that math, but it takes you pretty much right up to that point. Getting the rest of the way is much easier from there than if you have only seen the videos from Prof. Kelly.
     
    CR94 likes this.
  14. The Red Baron

    The Red Baron Junior Member

    Joined:
    Sep 24, 2022
    17
    11
    0
    Location:
    Athens Greece
    Vehicle:
    2022 Prius
    Model:
    Touring
    The mg2/mgr of the outlander are 115/135 hp respectively. Still the rear motor is powered through the battery. Have not seen yet a drivetrain with the back motor powered directly from mg1.
    Thats why i started this topic asking why they dont reverse the motors placement, or powering if you like.
    In the outlander (or prius prime) case rear powered from mg1, front from battery.
     
  15. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    I suspect that the reluctance of designers to run 600 VAC lines the length of the wheel base has to do with safety and product liability.

    First Responders are never going to approach such a car after a wreck. The AC cables are as short as possible
     
  16. Trollbait

    Trollbait It's a D&D thing

    Joined:
    Feb 7, 2006
    22,068
    11,533
    0
    Location:
    eastern Pennsylvania
    Vehicle:
    Other Non-Hybrid
    MG1 can directly power MGr now.
    The system tries to avoid putting energy into the battery and taking it out because of conversion losses. But MG1 is a small motor. It can't fully power MG2, let alone another motor at the rear. So when the system needs more power from MG2 or MGr than MG1 can provide, it draws it from the battery.
     
  17. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,921
    15,548
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Still oversimplified; that use of "directly" is muddying the waters. Having the MGR connected at the rear of the car where the battery and its connection to the frame wire are found does not mean it's only powered "through the battery." Power from either MG at the front transaxle still gets there.

    The only thing that would be more "direct" would be if the buck conversion in the front inverter from 600ish to lower volts were to be skipped, but that's no way necessary for the power from MG1 to be reaching MGR.

    Note that it's only the voltage bucking that you could skip anyway, not the rectification to DC. Even on the more "direct" path between MG1 and MG2, the power still gets rectified onto the inverter's internal DC bus and re-inverted to AC for the other MG. It has to, as the MGs are usually turning at different speeds.
     
  18. hill

    hill High Fiber Member

    Joined:
    Jun 23, 2005
    19,862
    8,167
    54
    Location:
    Montana & Nashville, TN
    Vehicle:
    2018 Chevy Volt
    Model:
    Premium
    perhaps what you really mean is - get in a long line of folks waiting for availability or/and paying the $5,000 above MSRP premium. There are plenty of easier ways to get over 300 HP in a plugin without doing that
    ;)
    .
     
  19. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    I confess I would have looked for a broadsided RAV4, your way works as well.
     
  20. CR94

    CR94 Senior Member

    Joined:
    Dec 2, 2014
    2,642
    1,137
    0
    Location:
    Northwestern S.C.
    Vehicle:
    2011 Prius
    Model:
    Two
    That's right, and those algebraic relations aren't as complicated as people might imagine. If one doesn't "get" them, one can't understand what's going on mechanically. You don't even have to know what a planetary gear set in general looks like, although that might help.

    Specifically, the following algebraic relations apply, regardless of the direction (e.g., algebraic sign) of torque and direction of speed:
    1. Torques on the three shafts of the gearset are always at the same fixed ratios (ignoring friction losses). In the case of a regular FWD 3rd generation Prius, MG1 torque is always the fraction 1/3.6 times engine torque . Torque of the ring gear (which is geared to the wheels at a fixed ratio, and to MG2 at a different fixed ratio) is always the fraction 2.6/3.6 times engine torque.
    2. Relative speeds of the three shafts follow a related simple rule or equation. 3.6 times engine speed always equals 2.6 times the ring gear speed plus MG1 speed.

    Those specific numbers may vary between generations, etc.

    That's the simple mechanical side. The magic is in the complex electronics which interact with the mechanical side to manage moving energy between the engine, MG1, MG2, the battery, and other loads as needed to cover every situation. Under low-speed, limited-traction circumstances, on cars so equipped, MGR takes a portion of the power that would go through MG2 to the front wheels in a FWD version, and delivers it instead to the rear wheels