PHEV Design

Discussion in 'PHEV or Plug-in Hybrid Electric Vehicle' started by CRT1, Dec 24, 2012.

  1. CRT1

    CRT1 Newbie McNewbster

    OK Clean MPG Team,

    It seems likely that PHEVs will be a very large part of the market at some point as people get used to plugging in their cars. Many will still need at least one long range vehicle and until we have the EV quick charge infrastructure in place, PHEVs will be big.

    It also seems to me that all of the PHEVs that are on the market or approaching release are existing HEVs with a bigger battery pack. Obviously, this is the cheapest and easiest way for the automakers to get a PHEV to market but it seems to me that this is an back-asswards approach to PHEV design.

    The EV drivetrain in and HEV is designed to supplement the efficiency of the ICE, whereas in a PHEV, the car should drive just fine in EV mode and the ICE should be designed to as-efficiently-as-possible extend the range when needed.

    So, what do you guys think the most efficient PHEV design would look like if you started with a clean sheet of paper? What wheels are your driving by what means? How big would you make the EV motor, ICE, Battery, Gas tank, what would the drivetrain layout be (clutches, gearbox)?

    Whatever we come up with, I want one for Christmas. Is that too much to ask? :)
  2. xcel

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

    Hi CRT1:

    Darn you have been busy here this morning :)

    I am thinking a PHEV with a separate clutched single traction motor design similar to the VW Jetta Hybrid and Hyundai/Kia Sonata/Optima designs currently. HSD is bulletproof but in its current design, you cannot separate the drivetrain from the wheels and thus everything continues to either spin or power is consumed to keep it from spinning. At higher speeds, the power consumed overwhelms the efficiency that the pack should provide. I suspect that Honda's new 2 motor PHEV works something like Hyundai/Kia's but its details have not yet been released. Given the preliminary numbers of mid to high 40 mpgUS city/highway for the Accord HEV, it sounds like a winner as Honda's EPA's are usually a lot easier to achieve than other brands. I am speaking in reference to the C-MAX and Fusion HEV issues currently being bantered about. The Accord PHEV-15 and a tank size of at least 16 gallons (meaning 18 to 19 actual in a Honda) would be state of the art imho.

  3. herm

    herm Well-Known Member

    My guess that Honda's new system will be an HSD clone, why not?.. the patents expired. I like the Jetta and Hyundai hybrids, if you accept that they wont be 100% electric all the time (motor not big enough) then just adding a big pack would work well..
  4. RedylC94

    RedylC94 Well-Known Member

    We could add a clutch to deal with that drawback, although it would add cost, weight, and potential problems.

    Another theoretically good but expensive and complicated solution would be something Volt-like, except with a smaller, lighter engine---with only enough power to maintain 70 mph or so on level.

    If there were an easy answer, we'd have agreed on it by now.
  5. xcel

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

    Hi RedylC94:

    There is also the Volvo design with the pack driving the rear wheels and the turbo diesel engine driving the front.

    I look at the Hyundai/Kia and VW designs as being superior with the VW actually doing it one better as they somehow use that single big motor to not only assist or actually drive the car down the road electrically but it also spins up the ICE and feeds power to the pack when it is below threshold. Hyundai/Kia use the small belt driven HSG to spin the engine up and fill the pack.

    Saying all of that, the Prius' HSD continues to offer 51/48 mpgUS city/highway which nobody using any other architecture has matched to date showing it may still in fact be the most fuel efficient hybrid system even with the 47 to 48 mph limitation under charge sustaining mode and 62 mph under charge depletion mode.

  6. herm

    herm Well-Known Member

    The Mahle range extender is very interesting, 30kW @ 4000rpm, 150lbs and tiny.. its possible BMW will offer it as an option on the I3 BEV.


    "The engine is a “clean sheet” design optimized for cost, weight, NVH, package size and installation flexibility. It is a 900cc, twin-cylinder, 4-stroke gasoline unit with an output of 30 kW at 4,000 rpm. An axial flux generator has been fully integrated within the crankcase to provide a compact modular solution. Fuel consumption of the engine is 240 g/kWh minimum, and it meets Euro 6 emission requirements."
  7. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    I think that, especially with volume, for Volt-style PHEVs where the battery and motor can do everything the car needs, manufacturers will focus more on a combination of EV efficiency and simplification and potentially even serialization of the range extender rather than straining to improve hybrid mode operation.

    Quite simply, the greater the AER, the less important CS efficiency becomes. Reduce the weight of the car and you get greater efficiency in EV and CS. Make the car more aerodynamic and you get greater efficiency in EV and CS. Increase efficiency in EV you increase the AER and therefore drive fewer CS miles.
  8. RedylC94

    RedylC94 Well-Known Member

    Substitute that small Mahle engine into a Volt and it could have better all-electric range, better all-electric acceleration, more room, probably better mileage on gasoline, and maybe a lower price.

    Admittedly, it would not be able to speed all the way up a long, steep mountain grade as fast after the battery is depleted, but so what? That should be a rare circumstance for most people if a reasonable fraction of battery capacity is kept in reserve for hills and acceleration.
  9. herm

    herm Well-Known Member

    The Volt was designed to cruise at 100 mph on the range extender, that is why they required 50kW (67 hp) .. I'm sure we would throttle that Mahler down to 20kW.. the other interesting thing about the I3 (IIRC) is that it will have a 2 gallon tank.
  10. CRT1

    CRT1 Newbie McNewbster

    Some cool ideas. I don't like the idea of a range extender purely for charging the battery in a true PHEV. Power from the engine should go straight to the wheels for extended highway driving for efficiency's sake. BMW concept for range extended is really for an EV with a big pack and people with money to burn, not for a low-cost PHEV which will get more use out of the ICE.

    I think the drivetrain should be have a large EV motor and a very small ICE (600-800cc). EV operation should be possible up to ~80 mph with a full pack. ICE should boost the EV at higher speeds. EV motor should be clutched so the you can freewheel when you lift off the accelerator. Up stream of the EV motor should be a gearbox, another clutch and ICE. So you have: wheels-clutch-EV motor-gearbox-clutch-ICE

    My thought is that you could use the EV mode exclusively from 0-25 mph, thus negating the need for gears 1 & 2 on the ICE. So you could pair the ICE with a simple (cheap/small) single planetary gear-set 3-speed automatic that is geared to be the same as a typical gear 3,4 & 5. If the ICE is small enough and since it is is coupled to the EV motor and since we are not using it for low speed operation, I think we could do without a torque converter?

    As far as pack size, I am thinking about 25 mile range would be ideal for me but it would be cool to offer folks a few different pack sizes to meet their personal needs. Maybe a 12, 18 or 25 mile pack?

    Obviously this thing would not drive all that well with a depleted pack, so in order to manage the pack charge users would have the option of driving without entering destination and the car would keep pack SOC pretty high, or the option of entering destination and whether or not they will be charging at said destination. Trip computer could estimate pack demands based on logged history and perhaps road and elevation maps to manage SOC to get up big hills, etc.

    Instead of driving around EV until pack is depleted and then switch over to HEV mode, which then requires a full-size ICE, the idea is to blend in the amount of EV to get you where you are going as efficiently as possible. If you are driving within the pack range, the you are all EV. But if you are exceeding the pack range, then the computer can increasingly rely on the ICE to get you where you are going, but never to the point you are driving on ICE alone.

    Oh, and for us hypermilers, we would require buttons to control EV mode, ICE on/off, SOC display, etc.

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