Possible smallest range extender engine

Discussion in 'General' started by The chord, Feb 6, 2018.

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  1. The chord

    The chord New Member

    Does anyone know what is the smallest engine needed to move a car at a reasonable maximum speed?
    Let's consider a medium sized car like the leaf or the note.
    If I'd equip it with a small 20kwh battery and a small range extender engine of i.e. 300cc, what would be the maximum speed in a highway when the battery charge is finished? Could it still reach let's say 100km/h in "e-power" mode ?
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  3. Kendalf

    Kendalf Active Member

    The size of the battery is not the (primary) limiter for maximum speed, rather is the power of the electric motor. For example the Honda Clarity PHEV only has a 17kWh battery, but it can reach it's maximum 160km/h on EV alone because it has a pretty powerful motor. Now it will take awhile to get there on battery charge only.

    Other cars that have smaller electric motors might need the ICE to provide sufficient power to reach high speed, but 100km/h is something that any EV should easily handle on battery alone.

    Sent from my HTC 10 using Tapatalk
  4. The chord

    The chord New Member

    You didn't get me.
    Consider a simple epower hybrid then. What would the maximum speed of the note in a freeway if the engine was only 300cc ?
  5. Kendalf

    Kendalf Active Member

    Okay, I think I get your question now. You're asking how fast can the car go with no charge remaining in the battery?

    For a series hybrid like the Nissan Note e-Power and BMW i3 REx, the ICE does not provide any power to the wheels; it is solely used to recharge the battery. So the car never actually runs without charge at any point (at least, until you run out of petrol), and the moving force is produced solely by the electric motor. I haven't seen any published figures for the top speed of the Note e-Power, but I have seen that it will sustain 100km/h just fine.

    But if you're talking about the kind of hybrid where the ICE takes over when battery is depleted (rather than simply charging the battery), I doubt that you would be able to reach any reasonable speed with a 300cc engine. Even with a top-tuned sport bike engines that can make about 30 hp, that's simply not enough to safely accelerate even a small size car from rest to highway speeds. About the smallest engine in a car on the road today is the Tata Nano with a 624cc engine. There are Japan only "Kei" cars that have smaller engines, but those only go like 50 km/h.

    Which is why the only hybrid cars you see in actual production with these small motors are the series hybrid ones where the engine only recharges the battery.
  6. The chord

    The chord New Member

    Considering a standard use of cars, which is small distances everyday and long distances sometimes, I'm just trying to understand how little the engine can be for emergency situations only when you can't find any charging points. In case of most hybrids the ice is good for regular use too, with top speed as high as a standard car.
    That's why I thought of a 300cc engine, it would take so little room, not adding weight nor costs but how fast would the note be for example?
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  8. The chord

    The chord New Member

    My question could probably be summarized as "how many hp / kw would an epower note have with 300cc engine"?
  9. Kendalf

    Kendalf Active Member

    As I noted earlier, even the best 300cc engines make 30hp (most are less), which is great for a motorcycle but insufficient for a car. The smallest size engine that is used to drive a car is over 600cc, and that's for a car that is significantly smaller than even the Note.
  10. The chord

    The chord New Member

    Logbook: BMW i3
    Engine 125kW electric motor (equivalent to 168bhp, 184lb ft), with 647cc 2-cyl petrol range extender

    Nissan's new e-Power series-type hybrid propulsion system uses a 1.2-L three-cylinder gasoline ICE running at a constant 2,500 rpm combined with a 1.5-kWh lithium ion pack and a Nissan Leaf 80-kW traction motor.

    Bmw: 647cc -> 125kw
    Nissan: 1200cc -> 80kw

    Correct? It looks inversely proportional
  11. Kendalf

    Kendalf Active Member

    The 125kW and 80kW power ratings you are referring to are for the electric motors of the two vehicles. The BMW range extender engine actually only makes 38 hp (28kW) (source) while the Note's engine makes 78 hp (58kW) (source). But that's incidental because both these cars are series hybrids, meaning that the gasoline engine does not actually drive the wheels. They only recharge the battery. The power rating of these engines only determines how quickly they recharge the battery, and does not effect the speed or acceleration of the vehicle.

    Plug-in Hybrids (like the Chevy Volt and Honda Clarity PHEV), where the ICE can help to drive the wheels, in general all have larger engines, but even then the ICE supplements the electric motor which still provides the majority of the power. And "full" hybrids, where the car can run solely on the ICE when battery is depleted, tend to have even larger engines.
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  13. NeilBlanchard

    NeilBlanchard Active Member

    Serial hybrids need their genset to meet or exceed the average consumption to operate the car. The genset needs to start up at a point where there is enough charge left in the battery to buffer the times when it takes more energy to operate the car, than the genset can produce.
  14. The chord

    The chord New Member

    If the engine is undersized, the electronics could just make the car run slower right?
    Considering a 20/40kwh equipped car, I bet we can go below 600cc (4 strokes) and equipe all cars with such technology to meet current ice cars price tags while we wait for chargers to spread all over
    Last edited: Feb 7, 2018
  15. Kendalf

    Kendalf Active Member

    And that's why the BMW i3 REx can use a much smaller ICE than the Nissan Note e-Power. The i3 has a significantly larger battery than the Note (33kWh vs a tiny 1.5kWh) and with it's larger battery the i3 has much more "buffer" and can get by with a smaller and slower charging ICE to maintain usable capacity for the electric motor. Whereas the Note has much less buffer capacity and thus needs a bigger engine to recharge the battery faster. On the flip side, the i3 has a very small (9L) gas tank so the ICE can only extend the range by about 120km, whereas the Note has a 40L fuel capacity and thus has an extended range of 650-800km. Very interesting to contrast the way these two companies balanced the components of their two vehicles, even though they use similar in principal series hybrid powertrains.
  16. Kendalf

    Kendalf Active Member

    You're pretty much describing the BMW i3 REx (33kWh battery, 650cc 2 stroke engine). But unfortunately, this combination only works if you have a large enough battery capacity (as described above), and that greater battery capacity adds significantly to the overall cost of the vehicle. A cheaper car with a small battery (like the Note e-Power) requires a larger ICE to keep the battery sufficiently charged for normal driving.
  17. The chord

    The chord New Member

    I usually think of serial hybrids as sailboats: they hardly ever use petrol, so rarely that speed does not matter at all when using the backup energy source.
    By reducing the note ice size and increasing the battery to the "good old" standard capacity of 20kwh (perfect for city use) the note's price wouldn't be affected.
  18. NeilBlanchard

    NeilBlanchard Active Member

    The i3 REx is a 2 cylinder, 4 stroke engine - essentially a BMW motorcycle engine adapted for this application.

    And yes, the speed is limited when the battery gets below a certain level. This can happen on extended climbs up a mountain. It could be avoided by starting the REx earlier, leaving enough charge to get over the mountain without going below that threshold. Apparently, this is not possible (without hacking) because they want it to meet regulations in some places that it is sold.
  19. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    It's going to depend on the energy required to move the car down the road at a reasonable speed. It also depends on the driving conditions.

    Note that the range extender used in the BMW i3 REx isn't sufficient to move the car at a reasonable speed when mountain-climbing. Owners of that car have reported that when in range-extended mode -- that is, powered by the small gas motor rather than the battery pack -- speed drops to as low as 25 MPH when going up an extended incline such as climbing into a mountain pass.

    According to Wikipedia: "An optional a petrol/gasoline range extender engine is marketed as REx and is powered by the same 647 cc two-cylinder engine used in the BMW C650 GT maxi-scooter."


    Compare with the Chevy Volt, which seems to be fully functional in either EV mode or gas-powered mode. Googling the car's original specs, from the 2011 model year, I find "1x 63 kW (84 hp); 1398 cc".
  20. The chord

    The chord New Member

    25mph to climb a montain pass is not that bad, you won't do that everyday unless you live there
    I'd be more interested to know freeway max speed when rex is engaged
    Last edited: Feb 8, 2018
  21. bwilson4web

    bwilson4web Well-Known Member Subscriber

    On a flat road on a 'standard day,' our 2014 BMW i3-REx maintains the battery SOC at 70 mph. Go up a hill, the battery loses charge that is recovered on the back side descent. The car easily handles a local, 525 ft (160 m) hill, taking ~5% SOC. For more technical details:

    Add air conditioning or heater loads and the car loses charge at 70 mph but works at 65 mph. FYI, I coded the car to enable REX at 75% SOC 3-4 blocks away from the seller and never looked back.

    If you'd like to discuss technical things in more detail: http://ecomodder.com

    Bob Wilson
    Last edited: Feb 8, 2018
  22. Kendalf

    Kendalf Active Member

    To clarify, the i3 REx engine does not actually power the wheels. It only recharges the battery. There is no actual transmission between the engine and the wheel axle. The engine comes on to try to maintain the State Of Charge in the battery, but if the load is great (like when climbing an extended incline) then the computer will reduce speeds so that the electric motor does not discharge the battery faster than the ICE can recharge it, lest the car become completely incapacitated because the battery has become completely discharged.
  23. The chord

    The chord New Member

    By using navigation datas about altitudes and traffic, you could probably avoid the rex to work alone.
    If a trip is about 150kms flat and 100kms mountains, the rex could be always on from the beginning to avoid having an empty battery while climbing.
    Is it already working like that on the i3?
    I know this way the total range (ev+rex) might be lower due to a higher consumption of gasoline (thats because you would never go into limited speed mode) but you can probably find a fuel station half way through your journey for a refill
    Last edited: Feb 8, 2018

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