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Is there a reason not more popular to create hybrids that have no traditional powertrain? IT seems like it would be cost effective. i.e. the petrol engine effe

by Dennip 2y ago

Is there a reason not more popular to create hybrids that have no traditional powertrain? IT seems like it would be cost effective. i.e. the petrol engine effectively just runs a generator to the batteries. You don't need prop shafts/gearboxes/transfer case/axles/alternator/starter etc. If you can integrate the motor assembly into the wheel hub you don't need any kind of axle at all. If/when the batteries degrade and lose capacity, you can just rely on the engine more. The engine won't ever have to 'work' too hard, because when you accelerate hard the energy dump can just come from the battery reserve. Like it could just idle along at a more-or-less fixed rpm.

sandworm101 2y ago
Such a setup is vastly less efficient for small engines. If the combusion engine is turning, the best way to use that power is directly to the wheels, as opposed converting it back and forth to electricity.
- Dennip 2y ago
  It would be interesting to see the numbers I guess. For one, the manufacturer is offloading that energy burden onto the owner, not themselves. IIRC A large portion of the carbon created by a car is during the manufacture, so if you're not forging a prop shaft and machining a gearbox, is it acceptable to reduce engine efficiency by some measure? Especially given the engine won't run all the time, just when the battery drop to some margin the car feels it should start charging. Potentially (theorising here) Your EV will last longer before getting crushed into a cube, as it can compensate for battery degradation, your engine will last longer as it will have a fairly stable usage load (revs etc) and won't be used much
- _visgean 2y ago
  my understanding was that you can run the gas engine in optimal speed to charge the electric engine which makes it more efficient.
  - bluGill 2y ago
    You can also add more gears in the transmission to make it more efficient as well. Gears are very efficient than conversion to/from electric (that is a series model, not even charging a battery.) The only way to make this work is if the engine is very undersized - the more load an engine is under the higher the efficiency, with gears alone though you would end up with an engine that takes unacceptably long to get up to speed, and slows down when going uphill, or into a headwind. If you are going ICE to battery you can have that undersized engine, and make up the extra losses by using the battery when needed, hence a hybrid car.
- bluGill 2y ago
  Such a setup can be more efficient - but only if everything is tuned perfectly. ICE engines are generally most efficient at low RPM and high throttle settings (last time I saw the graphs it was 1950RPM at 87% throttle peaked at 43% efficient, but that was one particular engine: yours will be different) - so you the entire system tuned around this, mistakes mean you either are running lower throttle or spinning extra mass not needed. Very few companies have the ability to design an engine around their exact needs - only the large automakers can really pull it off and they typically trade engines with other auto makers so they can offer more engine options in their cars than they have designed.
  - 4gotunameagain 2y ago
    > ICE engines are generally most efficient at low RPM and high throttle settings Which is why modern cars are much more likely to include a sixth gear -> drop the rpm, increase the torque = higher efficiency
  - Dennip 2y ago
    I guess the principle would be that you just don't care. The cost savings of not designing a powertrain/gearbox, not manufacturing it, reduced moving parts needing maintenance, etc etc. The trade-off _might_ be worth it.
    - bluGill 2y ago
      The geabov is cheap to design compared to the engine. Not free but cheap.
- WalterBright 2y ago
  But isn't that the same as a diesel-electric locomotive, which is very efficient?
- hwillis 2y ago
  Not true. What a series hybrid does is give you big-engine power for small-engine efficiency. Pull onto the highway and you get 350 hp from the battery, which the engine recharges at a steady 50 hp. If you have a big engine you are only losing efficiency.
- mapt 2y ago
  This is not necessarily true, but it is often true for consumer car models that are already designed in quite complex ways around driveshaft power, with abundant compromises and costs. It's never "directly" transferred; Not even close. Something like an automatic transmission is a miracle of engineering perspicacity over the decades. If you're going to spend thousands of dollars including one based on driveshafts, then electric conversion looks a bit silly. In locomotives, some ships, and now tanks they're replacing the whole drivetrain with copper wire driven by an ICE alternator. Even with zero energy storage this permits a dramatic simplification of the vehicle, and often we're more than willing to pay the cost of mechanical->electric->mechanical conversion efficiency in exchange for losing a bunch of cams, gears, and 90 degree joints that each eat a little energy, take up space in the design, and weigh a significant amount. And it is very often the case that adding energy storage (a very simply bolt-on + software changes) permits dramatically reducing the size of the engine needed.
  - sandworm101 2y ago
    Small engines are very different than big. They have very different needs re weight and complexity. A locomotive drive engine is basically mated to its power generating engine, moving in lockstep. Everything gets more complicated when one also wants to charge a battery. (Fyi, many locomotives have huge banks of resisters specifically for dumping energy into heat, which is not an option for cars.) Separating charge and power deliver requires two motors, a power-harvesting generator connected to the combustion engine and a separate drive motor. Those would need to be electrically separated since they would be always turning at different rates. That means totally separate charge and discharge circuitry, possibly even separate battery banks. Harvesting from the wheels might even require a third circuit to simultaneously charge from two sources. And the drive motor equipment would have to be sized large enough to cover the entire rated power output. Secondly, such a battery-in-line arrangement may create a battery-essential system whereby if the battery failed/discharged/overheated, the vehicle would just stop despite still having a working combustion engines. (The power direct from the generator may not be compatible with the drive motor.) Modern hybrids bypass all these problems by routing the IC engine to the wheels. The electrical system is then a single motor and an additional sprocket in the transmission. Power is then added or removed through a single motor and associated circuitry with no need to generate and provide electrical power simultaneously (F1 cars used to work like this). Add an extra differential, aka a "hybrid transmission", and you can run either motor alone or together (as in the Prius).
numpad0 2y ago
That's Nissan e-POWER system. Alas, Toyota THS is cheaper, probably lighter, and slightly more efficient.
hnuser123456 2y ago
chevy volt
chakintosh 2y ago
Audi built and competed with a Rally car using a regular TFSI engine that's generating power for the battery. https://www.youtube.com/watch?v=7ZhtGlwHlLs https://www.youtube.com/watch?v=7ZhtGlwHlLs
schmidtleonard 2y ago
Isn't that the idea behind EREVs (Extended Range EVs) which are wildly popular in China and probably just taking time to reach other markets?
- blacksmith_tb 2y ago
  There have been several popular cars available in the US and EU with this design, like the Chevy Volt and BMW i3.
seltzered_ 2y ago
The issue with an EREV conversion is going to be weight, practicality, and thermal management of the battery. Weight: You're adding about 500 lbs to the car to do this with ~20 miles of ev range. Suspension may need to be altered to support this. Practicality: the batteries have to go somewhere and they can't go under the hood since the engine is still there, so they may go in the bottom of the trunk. From the examples I've seen there's usually less cargo capacity, and the spare tire is removed. Some vehicles that are already hybrids (e.g. Toyota sienna 2022-) have an already tight layout with exhaust and all that it becomes a design challenge to fit a larger battery. Thermals: a li-ion battery for an EREV likely needs thermal management so it doesn't lose range prematurely, so you either need a dedicated cooling line setup that works with the ac compressor (bmw i3) or an aircooled setup where the battery is in the trunk and relies on cabin ac/heat (various toyota hybrid models do this).
- hwillis 2y ago
  > Weight: You're adding about 500 lbs to the car to do this with ~20 miles of ev range. No. The drive unit of a Tesla + 4 battery modules weighs 500 lbs. That's 21 kWh, 80 miles of range and 500 horsepower. And 300 lbs of that is in the drive unit; more common conversion kits weigh ~150 lbs. You could use 500 lbs of regular lead car batteries and still get way more than 20 miles. https://stealthev.com/product/tesla-performance-rear-drive-unit/ https://stealthev.com/product/tesla-performance-rear-drive-u... https://www.evwest.com/catalog/product_info.php?cPath=40&products_id=583 https://www.evwest.com/catalog/product_info.php?cPath=40&pro...
  - horsawlarway 2y ago
    I'm not sure I agree. You would need 24 LFP prismatic EVE cells (Which are EV rated) to get to ~20kWh (72v at ~300ah). They weigh about 5.5kg/cell. That's nearly 300lbs in cells alone (not accounting for wiring/support/cooling). I would pretty easily see total weight hitting 500lbs (or more). You can do it more efficiently with different chemistries, and you can scale down your storage for less range - but 500lbs seems pretty reasonable for a retrofit. Ex - your own linked kit doesn't include any storage, and the motor alone weighs 120lbs. There is NO WAY you're getting away with 150 lbs when the motor alone eats 120lbs. Lead acid... come on... a 100ah 12v lead acid (1.2kWh - of which only .6kWh is really usable because of chemistry) weighs 70lbs on a good day. A normal EV will do 3-4/kwh. 5kWh of usable charge (20 mile range) from those things is going to run you 10 batteries, for 660lbs. And that's NOT including any other parts of the retrofit (like that 120lb motor, or the wiring [thick wire is heavy] or the electronics).
WalterBright 2y ago
Having a small engine (lawnmower size) that doesn't generate enough power to operate the car, but will charge the battery, would seem like a nice convenience because you won't necessarily need a charging station to continue your trip.
- bogwog 2y ago
  I know BMW had (has?) a hybrid that does this using a small motorcycle motor.
hwillis 2y ago
> i.e. the petrol engine effectively just runs a generator to the batteries. You don't need prop shafts/gearboxes/transfer case/axles/alternator/starter etc. But you can't take advantage of that without handling every specific make of car. You need to design a specific solution for each engine. > If you can integrate the motor assembly into the wheel hub you don't need any kind of axle at all. This has a lot of downsides; the unsprung weight is very high which makes the ride much harsher. It's also very hard on the motors because of the shaking. There's only a few inches of space to claim in a normal wheel well by replacing and widening the tire. If you replace the suspension knuckle you have to make it work for all different makes. All that said, I do think there's an underserved opportunity for a drop-in solution that just replaces the engine. Basically the same thing you're proposing, but why keep the old engine? Replace it, and you can make a series-parallel hybrid, which is the ideal type. It's an engine connected by a clutch and single reducer to the driveshaft, with a motor connected to the engine (or by gears). At low throttle the motor acts like a generator, using the opportunity to increase engine load, charge the battery, and run the engine in a more efficient torque. At high throttle the motor joins the engine, increasing power. At cruise, the motor freewheels. For short trips the engine disconnects and the car runs on battery. You don't need an additional generator, the engine gets an efficient shaft connection, and it can still run battery-only. Best of all worlds and IMO worth trashing the engine. If you drop in a full unit with batteries etc you might need a few configurations for different engine bays, but you can just have a variety of mounting points for different makes. Plug into the radiator for cooling. Give a serpentine belt wheel for accessories, or just have an AC onboard and use a spool valve to split some off to col the batteries better.

by Dennip 2y ago

sandworm101 2y ago

Such a setup is vastly less efficient for small engines. If the combusion engine is turning, the best way to use that power is directly to the wheels, as opposed converting it back and forth to electricity.

Dennip 2y ago
It would be interesting to see the numbers I guess. For one, the manufacturer is offloading that energy burden onto the owner, not themselves. IIRC A large portion of the carbon created by a car is during the manufacture, so if you're not forging a prop shaft and machining a gearbox, is it acceptable to reduce engine efficiency by some measure? Especially given the engine won't run all the time, just when the battery drop to some margin the car feels it should start charging. Potentially (theorising here) Your EV will last longer before getting crushed into a cube, as it can compensate for battery degradation, your engine will last longer as it will have a fairly stable usage load (revs etc) and won't be used much
_visgean 2y ago
my understanding was that you can run the gas engine in optimal speed to charge the electric engine which makes it more efficient.
- bluGill 2y ago
  You can also add more gears in the transmission to make it more efficient as well. Gears are very efficient than conversion to/from electric (that is a series model, not even charging a battery.) The only way to make this work is if the engine is very undersized - the more load an engine is under the higher the efficiency, with gears alone though you would end up with an engine that takes unacceptably long to get up to speed, and slows down when going uphill, or into a headwind. If you are going ICE to battery you can have that undersized engine, and make up the extra losses by using the battery when needed, hence a hybrid car.
bluGill 2y ago
Such a setup can be more efficient - but only if everything is tuned perfectly. ICE engines are generally most efficient at low RPM and high throttle settings (last time I saw the graphs it was 1950RPM at 87% throttle peaked at 43% efficient, but that was one particular engine: yours will be different) - so you the entire system tuned around this, mistakes mean you either are running lower throttle or spinning extra mass not needed. Very few companies have the ability to design an engine around their exact needs - only the large automakers can really pull it off and they typically trade engines with other auto makers so they can offer more engine options in their cars than they have designed.
- 4gotunameagain 2y ago
  > ICE engines are generally most efficient at low RPM and high throttle settings Which is why modern cars are much more likely to include a sixth gear -> drop the rpm, increase the torque = higher efficiency
- Dennip 2y ago
  I guess the principle would be that you just don't care. The cost savings of not designing a powertrain/gearbox, not manufacturing it, reduced moving parts needing maintenance, etc etc. The trade-off _might_ be worth it.
  - bluGill 2y ago
    The geabov is cheap to design compared to the engine. Not free but cheap.
WalterBright 2y ago
But isn't that the same as a diesel-electric locomotive, which is very efficient?
hwillis 2y ago
Not true. What a series hybrid does is give you big-engine power for small-engine efficiency. Pull onto the highway and you get 350 hp from the battery, which the engine recharges at a steady 50 hp. If you have a big engine you are only losing efficiency.
mapt 2y ago
This is not necessarily true, but it is often true for consumer car models that are already designed in quite complex ways around driveshaft power, with abundant compromises and costs. It's never "directly" transferred; Not even close. Something like an automatic transmission is a miracle of engineering perspicacity over the decades. If you're going to spend thousands of dollars including one based on driveshafts, then electric conversion looks a bit silly. In locomotives, some ships, and now tanks they're replacing the whole drivetrain with copper wire driven by an ICE alternator. Even with zero energy storage this permits a dramatic simplification of the vehicle, and often we're more than willing to pay the cost of mechanical->electric->mechanical conversion efficiency in exchange for losing a bunch of cams, gears, and 90 degree joints that each eat a little energy, take up space in the design, and weigh a significant amount. And it is very often the case that adding energy storage (a very simply bolt-on + software changes) permits dramatically reducing the size of the engine needed.
- sandworm101 2y ago
  Small engines are very different than big. They have very different needs re weight and complexity. A locomotive drive engine is basically mated to its power generating engine, moving in lockstep. Everything gets more complicated when one also wants to charge a battery. (Fyi, many locomotives have huge banks of resisters specifically for dumping energy into heat, which is not an option for cars.) Separating charge and power deliver requires two motors, a power-harvesting generator connected to the combustion engine and a separate drive motor. Those would need to be electrically separated since they would be always turning at different rates. That means totally separate charge and discharge circuitry, possibly even separate battery banks. Harvesting from the wheels might even require a third circuit to simultaneously charge from two sources. And the drive motor equipment would have to be sized large enough to cover the entire rated power output. Secondly, such a battery-in-line arrangement may create a battery-essential system whereby if the battery failed/discharged/overheated, the vehicle would just stop despite still having a working combustion engines. (The power direct from the generator may not be compatible with the drive motor.) Modern hybrids bypass all these problems by routing the IC engine to the wheels. The electrical system is then a single motor and an additional sprocket in the transmission. Power is then added or removed through a single motor and associated circuitry with no need to generate and provide electrical power simultaneously (F1 cars used to work like this). Add an extra differential, aka a "hybrid transmission", and you can run either motor alone or together (as in the Prius).

numpad0 2y ago

That's Nissan e-POWER system. Alas, Toyota THS is cheaper, probably lighter, and slightly more efficient.

hnuser123456 2y ago

chevy volt

chakintosh 2y ago

Audi built and competed with a Rally car using a regular TFSI engine that's generating power for the battery. https://www.youtube.com/watch?v=7ZhtGlwHlLs https://www.youtube.com/watch?v=7ZhtGlwHlLs

schmidtleonard 2y ago

Isn't that the idea behind EREVs (Extended Range EVs) which are wildly popular in China and probably just taking time to reach other markets?

blacksmith_tb 2y ago
There have been several popular cars available in the US and EU with this design, like the Chevy Volt and BMW i3.

seltzered_ 2y ago

The issue with an EREV conversion is going to be weight, practicality, and thermal management of the battery. Weight: You're adding about 500 lbs to the car to do this with ~20 miles of ev range. Suspension may need to be altered to support this. Practicality: the batteries have to go somewhere and they can't go under the hood since the engine is still there, so they may go in the bottom of the trunk. From the examples I've seen there's usually less cargo capacity, and the spare tire is removed. Some vehicles that are already hybrids (e.g. Toyota sienna 2022-) have an already tight layout with exhaust and all that it becomes a design challenge to fit a larger battery. Thermals: a li-ion battery for an EREV likely needs thermal management so it doesn't lose range prematurely, so you either need a dedicated cooling line setup that works with the ac compressor (bmw i3) or an aircooled setup where the battery is in the trunk and relies on cabin ac/heat (various toyota hybrid models do this).

hwillis 2y ago
> Weight: You're adding about 500 lbs to the car to do this with ~20 miles of ev range. No. The drive unit of a Tesla + 4 battery modules weighs 500 lbs. That's 21 kWh, 80 miles of range and 500 horsepower. And 300 lbs of that is in the drive unit; more common conversion kits weigh ~150 lbs. You could use 500 lbs of regular lead car batteries and still get way more than 20 miles. https://stealthev.com/product/tesla-performance-rear-drive-unit/ https://stealthev.com/product/tesla-performance-rear-drive-u... https://www.evwest.com/catalog/product_info.php?cPath=40&products_id=583 https://www.evwest.com/catalog/product_info.php?cPath=40&pro...
- horsawlarway 2y ago
  I'm not sure I agree. You would need 24 LFP prismatic EVE cells (Which are EV rated) to get to ~20kWh (72v at ~300ah). They weigh about 5.5kg/cell. That's nearly 300lbs in cells alone (not accounting for wiring/support/cooling). I would pretty easily see total weight hitting 500lbs (or more). You can do it more efficiently with different chemistries, and you can scale down your storage for less range - but 500lbs seems pretty reasonable for a retrofit. Ex - your own linked kit doesn't include any storage, and the motor alone weighs 120lbs. There is NO WAY you're getting away with 150 lbs when the motor alone eats 120lbs. Lead acid... come on... a 100ah 12v lead acid (1.2kWh - of which only .6kWh is really usable because of chemistry) weighs 70lbs on a good day. A normal EV will do 3-4/kwh. 5kWh of usable charge (20 mile range) from those things is going to run you 10 batteries, for 660lbs. And that's NOT including any other parts of the retrofit (like that 120lb motor, or the wiring [thick wire is heavy] or the electronics).

WalterBright 2y ago

Having a small engine (lawnmower size) that doesn't generate enough power to operate the car, but will charge the battery, would seem like a nice convenience because you won't necessarily need a charging station to continue your trip.

bogwog 2y ago
I know BMW had (has?) a hybrid that does this using a small motorcycle motor.

hwillis 2y ago

> i.e. the petrol engine effectively just runs a generator to the batteries. You don't need prop shafts/gearboxes/transfer case/axles/alternator/starter etc. But you can't take advantage of that without handling every specific make of car. You need to design a specific solution for each engine. > If you can integrate the motor assembly into the wheel hub you don't need any kind of axle at all. This has a lot of downsides; the unsprung weight is very high which makes the ride much harsher. It's also very hard on the motors because of the shaking. There's only a few inches of space to claim in a normal wheel well by replacing and widening the tire. If you replace the suspension knuckle you have to make it work for all different makes. All that said, I do think there's an underserved opportunity for a drop-in solution that just replaces the engine. Basically the same thing you're proposing, but why keep the old engine? Replace it, and you can make a series-parallel hybrid, which is the ideal type. It's an engine connected by a clutch and single reducer to the driveshaft, with a motor connected to the engine (or by gears). At low throttle the motor acts like a generator, using the opportunity to increase engine load, charge the battery, and run the engine in a more efficient torque. At high throttle the motor joins the engine, increasing power. At cruise, the motor freewheels. For short trips the engine disconnects and the car runs on battery. You don't need an additional generator, the engine gets an efficient shaft connection, and it can still run battery-only. Best of all worlds and IMO worth trashing the engine. If you drop in a full unit with batteries etc you might need a few configurations for different engine bays, but you can just have a variety of mounting points for different makes. Plug into the radiator for cooling. Give a serpentine belt wheel for accessories, or just have an AC onboard and use a spool valve to split some off to col the batteries better.