Featured Electric cars could spell end of front-wheel drive, VW exec says

Discussion in 'Prius, Hybrid, EV and Alt-Fuel News' started by Tideland Prius, Dec 10, 2018.

  1. austingreen

    austingreen Senior Member

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    I tried looking it up, but got a bunch of horse pages. What does it mean?


    This is more of the full original -
    https://www.motortrend.com/news/volkswagen-abandons-front-wheel-drive-evs/
    Pretty simple - if you are doing a single axle drive, the rear one makes more sense if you are using a high torque electric motor. Driving dynamics are improved. It's not the 70s anymore, there is stability control and better tires to have rwd work well in slipery conditions, but if you are electric and care about it having awd if not that much more expensive.
    That's what vw is admitting it did with the e-golf. If they do it from the ground up it would be rwd or awd in the future.
     
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  2. Trollbait

    Trollbait It's a D&D thing

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    Cost will come down. I posted an article about a spoke motor design that would benefit hub motors.

    But motors mounted in the car body will still have a cost advantage in that their design doesn't have to meet the requirements of fitting in a smaller space. Plus, they don't increase unsprung weight. Hub motors adds weight to the wheels, which reduces efficiency, and could have negative affects on handling.
     
  3. WilDavis

    WilDavis Senior Member

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    Nice, apart from the thumpy-bumpy musak crap festering all over what passes for a soundtack! :confused:
     
  4. austingreen

    austingreen Senior Member

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    The biggest problem with hub motors is as you say unsprung weight. If you are putting 80 kw on each axis, perhaps you can do a 40 kw hub on each front wheel. That would add roughly 80 kg of unsprung weight to the front wheels of the car. Porsche thought about it, then decided to have more traditional motors in their 918. That much weight definitely hurts handling. Say you only want to do something like the 2018 rav4 hybrid power 15 kw on each of the lower powered wheels? That might only add 30 kg, but it won't provide enough power at higher speeds, so its a more limited awd, mainly for low speed slippery conditions, not rain or mud when traveling at higher speeds.

    I don't think we need to worry about efficiency that much on the hub, but more of the impact on suspension and braking.

    Either way we can look at the tesla model 3D for cost/weight estimates. The tesla added a relatively heavy 200 hp ac motor (no rare earth's to the front axle) and guestimates are it added $2500 to cost and added 267 lbs (121 kg) for the motor, gearing, inverter, and suspension changes. On a simpler 200 hp car, we can think of having maybe 120 hp on each axis geared to be efficient at different speeds, versus one 200 hp engine. My guess is such a design would add less than 100 lbs and $1000 to cost. The car company would still need to make a profit, so lets say $1500 added price to the buyer. As hp goes up for the car, if the awd is made to accelerate similarly to the rwd or fwd, the added cost drops (as smaller motors and inverters are less expensive and having two different gearings will help optimize the motors. The model 3 did take an efficiency hit - 116 mpge versus 130 mpge for awd versus rwd, but the awd accelerates much faster and handles slick conditions better making it a reasonable trade off. My guess is the weight and efficiency hit would be much less if they were designed to accelerate the same.
     
    #24 austingreen, Dec 13, 2018
    Last edited: Dec 13, 2018
  5. Robert Holt

    Robert Holt Senior Member

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    My experience riding front hub motor, rear hub motor, and middle-drive motors on BEV bicycles confirms profound effects on the handling depending on where the motor is located. Front hub motors (8-12 motor pounds on a 50-pound bicycle) lead to noticeably heavier steering moments, PLUS the weird, unexpected, and potentially dangerous phenomenon of being yanked into the turn by the front wheel. Rear hub motors make the bicycle noticeably heavier toward the rear, particularly if the rider is also seated upright and aft-of-center, which creates an oddly “light” steering feel on he front wheel, and this feeling is exacerbated particularly under hard acceleration if the bicycle also has a suspension. Middle motor location keeps the motor weight more forward, particularly if the battery is also mounted forward on the frame, and thus does not affect the handling and cornering as much as front or rear hub locations, and also does not affect the steering feel as much—steering feel is much closer to normal although the total all-up weight of the bicycle is still noticeably heavier. Because the weight of motor + battery = around 22 pounds for the ebikes I have built, the relative weight is HUGE compared to BEV automobiles and these handling shifts correspondingly large (and potentially dangerous).
    (That said, no BEV car that I know of can pop a wheelie off the line, whereas the more powerful ebikes can, which is also dangerous, but fun.)
     
  6. ETP

    ETP Ancient sloth foot

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    Exactly! Cheaper, better, and easier to make a rear wheel direct drive. Very smart to do this. Like my old go carts.

    So question of the day! Are people FWD or RWD?:ROFLMAO:
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I've only built one e-bike so far. It was a while ago, so lame tech. 70lb lead battery on the back, 15lb hub motor on the front. I had fun riding NYC on it. That front motor had some weird handling but where it really amazed me was beach riding. Soft sand was surprisingly easy to handle.

    Motors on both ends of a car sounds good to me. Smaller cheaper parts, better weight distribution.

    But I have to agree- hub motors are best left to unsprung, unmanned or lower speed vehicles.
     
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  8. austingreen

    austingreen Senior Member

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    When in a grocery store, people push carts they don't pull them. This is rear foot drive. In the himalaya's the sherpa's care things on thier heads, really a mid foot drive configuration. The front foot drive rickshaw is now out of favor, but pedicab's are front pedial drive ;-)

    As for the Cheaper, Better, Easier, a bev is going to have a high torque motor, or multiple motors. If you are going to have traction control and anti-lock brakes, rwd should be less expensive for similar performance. A limited slip differencial can be approximated in software by a less expensive open differencial + braking of the slipping wheel. This is what tesla does. For handling this makes the front of the car easier, there is no torque steer attempting to provide high power to the front wheels, and the front of the car can just be designed for steering feel. No extra suspension and software tuning is needed for that unsprung weight of 2 hub motors and 2 inverters. The tesla roadster does look like it will have 2 rear motors (regular not hub), and probably can get away with mainly doing torque vectoring in software. It will be a very expensive car though. Just to add, a rwd bev will not be able to take as much regen braking as fwd or awd because brake force is normally foward biased (70% front/30% rear is a good guestimate), that menas for max range in heavy braking applications a rwd driver should anticipate braking needs more than a fwd driver.

    AWD well that seems like a no brainer if ability to handle in slick conditions is important for a bev. The added cost for similar non slippery performance is quite low, but will give a weight penalty..
     
    #28 austingreen, Dec 18, 2018
    Last edited: Dec 18, 2018
  9. walterm

    walterm Active Member

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    But for better handling you want to minimize unsprung weight - witness the infamous Jaguar E-type rear end where the brake discs and calipers were mounted inboard on the differential rather than out at the wheels. It did make brake work less convenient though...
     
  10. Trollbait

    Trollbait It's a D&D thing

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    Which will be partially compensated through better regen braking.
     
  11. padroo

    padroo Senior Member

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    Horse Power was originally up front pulling a wagon, nuf said. lol
     
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  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Sorry I didn't catch this sooner. VW ran full page ads in LIFE magazine from the late 1950s through 1960s, and one early one touted the VW design's rear engine/rear drive arrangement with that line.

    I'm kind of surprised nobody has done a rear-engine PHEV. It seems so obvious... put the noisy engine back in the back, it'll only need a foot of tailpipe and won't heat up the whole belly of the car. The belly can be structure or batteries or both, with the whole front wide open for electric power.

    I'd go back to VW for a new Transporter with a range extender engine in the back where it belongs. I know the T6 was recently released, but I gotta dream.
     
  13. 3PriusMike

    3PriusMike Prius owner since 2000

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    Yeah, I've never seen a horse pushing a wagon...and as a kid everyone pulled wagons if you wanted control of them since they had front wheel steering

    Mike
     
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  14. bisco

    bisco cookie crumbler

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    if leaf is rear wheel drive, so be it
     
  15. padroo

    padroo Senior Member

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    The only flat engine that comes to mind is Subaru and they are water cooled. Most rear engine cars that I remember were air cooled. You shorten the exhaust but then you need a radiator and all that plumbing.
    Then there is weight distribution, handling and steering. Even VW gave up on air cooled engines.
     
  16. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I never said anything about air-cooled. I'm well versed in why those won't be coming back. Nobody says the radiator has to be on the front. Extreme example, the Bugatti Veyron. 9 of its 10 radiators are not in the front of the car.

    And nobody said it had to be a flat engine either. VW themselves built plenty of rear-mount inline engine cars.

    In the case of a range extender? You get even more flexibility. Make it any weird shape, cram it in. Every motor safety agency is going to insist on an exhaust pipe going outside aft of the rear-most opening window. That surrenders a few less CO-lovers to Darwin. With the gear at the back of the car, that can be a 1lb pipe assembly.

    The big advantage is that you aren't going to waste 1/3 of your undercar area on a hot exhaust pipe with a part-time job.
     
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  17. Trollbait

    Trollbait It's a D&D thing

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    The i3 REx has the engine, and motor, in the rear.

    The 911s use water cooled rear engines. An EV is going to be running plumbing through out the car for cooling the motor and inverter, if not the battery, anyway. Then coolant piping is no where near as hot as the exhaust.
     
  18. hill

    hill High Fiber Member

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    or - if you really want to pick your nits, horses push .... AND engines push.... & everything pushes. Even waves of gravity reach up & around and push from the other side (high school physics) ... just like when a locomotive couples on to the car behind it, the coupling is reaching around from the other side of the box car, & pushing.
    hey, if we're going to derail a tread .... see what I did there? Derail? Train?
    :D
    On a serious note, if the oil industry has its way, we will never have to worry about electric cars diminishing front wheel drive - ever - at all.
    .
     
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  19. mikefocke

    mikefocke Prius v Three 2012, Avalon 2011

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    Porsche from the '60s to the present. 4s and 6s. VWs. Owned 5.
     
  20. padroo

    padroo Senior Member

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    When I was referring to a flat engine I war referring to an opposed engine. This type of engine is the only one that will fit under the trunk deck and still have usable space above it. All inline engines I have ever seen have an upright position or mostly like the Chrysler slant six would not leave you with a usable trunk. I don't think people are ready for a mainstream car to use an air cooled engine.
    What is the chances an air cooled hybrid vehicle making it?
     
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