Honda Clarity : Power-split

Discussion in 'Clarity' started by Sai Prudhvi Nagireddy, Jan 5, 2018.

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  1. Hi everyone,

    This is Sai, I'm new to this forum. I'm a Master's student at Michigan Technological University and an Hybrid Electric Vehicles enthusiast.

    I'm interested in knowing about the hybrid technology that is being used in the 2018 Honda Clarity Plug-in Hybrid. We know that the Hybrid Architecture in the vehicle is Power split.
    I want to know which type of powersplit it is. Is it Compound Power split/ Multi mode power split or anything else.

    Thanks is advance.
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  3. JyChevyVolt

    JyChevyVolt Active Member

    Yes. The Clarity PHEV is actually the Accord PHEV.
    Domenick likes this.
  4. dstrauss

    dstrauss Well-Known Member

    Pretty sure the Accord has a smaller battery than the Clarity - it is Hybrid only, with little to no pure EV mileage. It can nearly equal a Prius in MPG so it is a very unique for a Hybrid. At 3:20 mark Alex explains it is a 1.3kWh traction battery.

    Domenick likes this.
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  6. Thanks @JyChevyVolt & @dstrauss for sharing those videos.
    Well, assuming that the same technology is being used in 2018 Honda Clarity (with higher battery capacity of 17 kW-h), it makes it a 'single-mode power split' hybrid vehicle. Correct me if I'm wrong. Thanks.
    Domenick likes this.
  7. ab13

    ab13 Active Member

    These are the presentations regarding the 2 motor hybrid system. It seems to only refer to power split at a "gearbox," not referencing any particular type. Also they show where they determined the range where direct mechanical ICE drive is more efficient.

    Slide presentation from EVS (electric vehicle symposium) conference:

    Paper from EVS conference:
  8. Kendalf

    Kendalf Active Member

    That's a great find, ab13! Lots of technical goodness to look over in that paper and presentation. I found this slide to be very helpful in understanding the theoretical basis for the interoperation of the engine and the battery.
  9. Viking79

    Viking79 Well-Known Member

    I am pretty sure the hill graph shows that it is a multi-mode transmission.
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  11. ab13

    ab13 Active Member

    The interesting part to note is the intermittent operation, as it can switch between direct drive to charge the battery then move to ev which consumes the battery and then back again. So this method alternates charging and discharging using the ev traction motor and not the generator.
  12. bfd

    bfd Active Member

    Though their systems are relatively the same age, Toyota and Honda took different paths with the Prius and the first Insight. I think that plays out to our benefit in the Clarity.
  13. ab13

    ab13 Active Member

    I found this video of the 1 motor Japanese Fit hybrid, it's good because of the animations showing the gearing. After I watched it I realized they designed these based on the dual clutch transmission. They basically attached the EV motor to one of the transmission input shafts directly because the AC motor is it's own clutch. So while a DCT has two input shafts each shaft with it's own clutch, this design has 2 mechanical clutches and one electrical "clutch". This is a 1 EV motor hybrid so it needs a full transmission for the ICE.

    In the 2 motor design, the extra gears are removed and there is only 1 mechanical clutch but still two input shafts, one from the ICE and one from the EV. This is pretty clever, since the output gear of the DCT doesn't care if the input is from a ICE or EV source. They bypass all the complexity and stayed with a "manual" transmission, which is what a DCT is, just automatically shifted.

  14. I believe that's similar to what Hyundai does in the Ioniq (though with a 6-speed DCT).
  15. ab13

    ab13 Active Member

    Hyundai uses a permanent magnet design. I believe it won't work the same way. This design lets Honda directly couple the EV motor to the output gear without any gearing changes. Based on what I could find out about the Ioniq system, it lets you shift gears, which indicates it is likely not directly driving the output gear. I thought I read they used a DCT because it could be more direct feeling to the driver than the CVT Toyota was using, and not droning.
  16. ab13

    ab13 Active Member

    What I wrote here might be somewhat inaccurate, since I can't determine what the difference is in the motor Hyundai uses compared to the one in the Honda design, based on information that's available. However, there is no reason to shift gears when the EV motor is driving the vehicle, that's what implies to me the Hyundai uses the transmission in a conventional manner.
  17. Yeah, I believe the Ioniq has the motor essentially in the flywheel position, so its output is always through the transmission
    Electric motors vary in efficiency with speed, too. If you're the DCT for the engine anyhow, perhaps the electric motor can benefit from a narrower band of operating speeds.
  18. ab13

    ab13 Active Member

    That's probably the reason other cars in the higher price range will go to 4 wheel drive. So they can use a different gearing on the front versus rear axle. This is still simpler probably than including a transmission since the transmission is quite large.

    As a note, here are some of the Honda US Patents regarding the design. They reference switching between the electric motor and gas engine to drive the output shaft. Kind of long links unfortunately. The first is one of the earlier ones I found, the received it in 2006, but it was filed in 2003, so they had already selected this path a long time ago. When they started the replacement for the IMA hybrid, they couldn't or didn't choose to use the method Toyota and others use.
  19. insightman

    insightman Well-Known Member Subscriber

    Does that slide accurately represent what goes on in our Clarity PHEV's? I compulsively corrected the spelling and re-rendered that chart (see below).

    The most interesting thing I see is the "Engine (Charge)" segment. I didn't realize that when you have attained a constant speed that qualifies as high-speed cruising, the starter-motor/generator stops generating and the drive-motor starts generating.

    If the drive-motor is generating electricity to recharge the battery, the engine alone must be powering the car. So that must be when the clutch connects the engine through a set of gears to the wheels, right? (I wish I knew Honda's internal term for this "gear icon" mode.)

    Why is there "No torque" for the starter/generator motor when in the "Engine (Charge)" segment? There is no way to disconnect the starter/generator motor from the engine is there?

    I knew the drive-motor had to be the one regenerating power when the car decelerates because it's the motor connected to the wheels. What occurred to me is that the drive-motor can probably generate more power than the starter/generator motor because it's larger. Does that mean "Engine (Charge)" high-speed cruising recharges the battery faster than HV Charge mode? Or does the drive-motor NOT generate more power because it turns slower than the starter/generator motor?

    Wouldn't it be great to find the secret Easter-egg display that reveals the i-MMD status depicted in this chart as you're driving?

  20. ab13

    ab13 Active Member

    Based on some of the other charts in the journal article, the ICE will run at on optimal RPM. Any excess power from it beyond what is needed to maintain the road load (cruising speed) will be drawn by the drive motor. Therefore there is some speed at which the ICE output meets the road load and you don't generate any excess. Based on Car and Driver the top speed is 105, not sure how accurate that is, but if you go faster than the optimal RPM (based on the fixed gear ratio and road load), then the traction motor may need to add some driving torque. This is what I got from the article.
  21. bpratt

    bpratt Active Member

    The ICE will only run at an optimal RPM when the clutch is not engaged and the engine is being used to run the generator. When the clutch is engaged, the ICE is tied directly to the drive motor which is tied through fixed gears to the wheels and it has to run at the speed determined by the speed of the car.

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