4 ms·

Excellent and well-written answer. I hadn't considered the dead weight of the generator. It's more proof that questions with seemingly simple answers rarely e

by deeg 6y ago

Excellent and well-written answer. I hadn't considered the dead weight of the generator. It's more proof that questions with seemingly simple answers rarely exist in the real world. As a friend of mine (a data analyst) likes to say: "the real world is messy".

SigmundA 6y ago
Yes most people don't seem to realize the hybrid system tends to just shut down at highway speeds. The reason a hybrid car has good highway mileage is because it has skinny tries and good aerodynamics, if you ripped out the hybrid gear its would get even better highway mileage due to less weight. There is another aspect specifically of gas hybrids they typically use Atkinson cycle engines to increase efficiency but have reduced torque. This makes it ideal for a hybrid setup as the electric motor can make up for the lack of torque off the line. Notice there are basically no diesel hybrids, this is because a diesel engine is more efficient than a Atkinson cycle gas and has even better torque than a Otto gas but they weigh more and cost more, so it makes little sense to add more weight and cost to a diesel drivetrain that is already very efficient and has plenty of torque. City buses are the exception due to the extreme stop and go low speed duty cycle that can really take advantage of a hybrid drivetrain.
- hinkley 6y ago
  You can have Atkinson cycle with diesel, so 1) do they, and 2) how much does that offset the transmission losses?
  - SigmundA 6y ago
    I have never heard of a Diesel-Atkinson and technically Diesel is a cycle, so if its a Atkinson burning diesel fuel its no longer a Diesel engine although the terms get fuzzy between the fuel and cycle.
- Reason077 6y ago
  > "they typically use Atkinson cycle engines" Only the early-model Toyota Prius used Atkinson cycle engines, up until 2003 or so. You'd be hard pressed to find a modern hybrid using Atkinson cycle. Any modern Prius uses conventional engines with variable valve timing.
  - SigmundA 6y ago
    Well they use the variable valve timing to operate in a Atkinson cycle but can change valve timing back towards Otto. Most still seem to refer to these engines as Atkinson cycle even Toyota themselves: "The Prius retains its 1.8-liter VVT-i equipped Atkinson cycle petrol engine (2ZR-FXE)" https://global.toyota/en/detail/9827044 https://global.toyota/en/detail/9827044 https://en.wikipedia.org/wiki/Toyota_ZR_engine#2ZR-FXE https://en.wikipedia.org/wiki/Toyota_ZR_engine#2ZR-FXE
  - avmich 6y ago
    > You'd be hard pressed to find a modern hybrid using Atkinson cycle. Kia Niro? https://futuresuvs.com/2021-kia-niro/ https://futuresuvs.com/2021-kia-niro/ "The centerpiece of the 2021 KIA Niro PHEV is a 1.6-liter Atkinson cycle four-cylinder petrol unit."
- zepearl 6y ago
  > Notice there are basically no diesel hybrids, this is because a diesel engine is more efficient than... Thx for the nice explanations. About diesel engines I read long time back that it's as well because they need to be "hot" in order to be able to filter their exhaust fumes (don't know how to say this correctly - the thing that is done by the catalyzer in the exhaust pipe) => as a hybrid engine is meant to be switched off quite often, the catalyzer of a diesel engine would have to be kept very hot by the battery, reducing therefore range/effectiveness/etc... of the hybrid system.
  - SigmundA 6y ago
    Hard to say with modern diesels but I am sure it does contribute to the cost benefit, DPF filters will need more regeneration (and fuel use) if the exhaust temps are not high enough which is typical of diesel used for short trips vs longer highway trips.
  - nanomonkey 6y ago
    The term that you are looking for is "wet stacking", and is due to the fact that diesels utilize the heat and pressure in the pistons and cylinder walls to induce combustion (there is no spark plug). That being said, one could inject the bare minimum to "idle" the motor and maintain this temperature, losing a bit of efficiency from completely stopping the motor entirely. There are a few diesel hybrid prototypes, if memory serves me there was a two stroke diesel hybrid motorcycle called the eCycle that got something like 160mpg.
- zkms 6y ago
  > Yes most people don't seem to realize the hybrid system tends to just shut down at highway speeds. There's still an advantage to having a hybrid system onboard even at highway speeds. The continuously-variable ratio of the hybrid transmission allows increased freedom of the ECU to select {instantaneous gasoline engine RPM, instantaneous gasoline engine torque}, which permits operation in more favorable parts of the BSFC map more often. Furthermore, the battery/motor-generators allow the ECU to temporarily run the gasoline engine at lower or higher output (without loss of traction power and without waste) than the power required at the wheels, further expanding the area of the BSFC map that the gasoline engine can operate at. It is true that mechanical-electrical-mechanical conversion is more lossy than an all-mechanical system, but topologies such as the Toyota hybrid system allow for significant power transfer without electrical conversion; and spending significantly more time in more efficient regions of the BSFC map makes up for the conversion losses incurred. Also, hybrids tend to have electrically powered coolant pumps and electrically powered air conditioning compressors, allowing for more aggressive fuel cut off (on a downhill section of the highway, say).
  - SigmundA 6y ago
    CVT transmissions are not only available on hybrids although the Prius CVT is a thing of beauty utilizing the electric motors with planetary gears for continuous ratio. None of the other things you mention have more than negligible effect on the highway at cruise speeds where the combustion engine will be providing all the power to run all systems either directly or indirectly at typically ideal rpm most of the time. Also electrical cooling pumps and power steering etc again are not tied to hybrids and many non hybrids are going that route. A/C again does not need a hybrid but would exceed the capability of a standard alternator and direct mechanical compressor drive with a clutch is not that inefficient, again that would mostly be for stop and go urban driving at steady highway speed it probably more efficient to run mechanically off the engine. A small diesel car and Atkinson hybrid will have similar highway mileage mainly due to the combustion efficiency of the cycles not the hybrid systems. However the hybrid systems allow a Atkinson gasoline engine to have acceptable performance in the city while the diesel doesn't need it. An Otto gas car will be behind but the cost saving can buy a lot of gasoline.

by deeg 6y ago

SigmundA 6y ago

Yes most people don't seem to realize the hybrid system tends to just shut down at highway speeds. The reason a hybrid car has good highway mileage is because it has skinny tries and good aerodynamics, if you ripped out the hybrid gear its would get even better highway mileage due to less weight. There is another aspect specifically of gas hybrids they typically use Atkinson cycle engines to increase efficiency but have reduced torque. This makes it ideal for a hybrid setup as the electric motor can make up for the lack of torque off the line. Notice there are basically no diesel hybrids, this is because a diesel engine is more efficient than a Atkinson cycle gas and has even better torque than a Otto gas but they weigh more and cost more, so it makes little sense to add more weight and cost to a diesel drivetrain that is already very efficient and has plenty of torque. City buses are the exception due to the extreme stop and go low speed duty cycle that can really take advantage of a hybrid drivetrain.

hinkley 6y ago
You can have Atkinson cycle with diesel, so 1) do they, and 2) how much does that offset the transmission losses?
- SigmundA 6y ago
  I have never heard of a Diesel-Atkinson and technically Diesel is a cycle, so if its a Atkinson burning diesel fuel its no longer a Diesel engine although the terms get fuzzy between the fuel and cycle.
Reason077 6y ago
> "they typically use Atkinson cycle engines" Only the early-model Toyota Prius used Atkinson cycle engines, up until 2003 or so. You'd be hard pressed to find a modern hybrid using Atkinson cycle. Any modern Prius uses conventional engines with variable valve timing.
- SigmundA 6y ago
  Well they use the variable valve timing to operate in a Atkinson cycle but can change valve timing back towards Otto. Most still seem to refer to these engines as Atkinson cycle even Toyota themselves: "The Prius retains its 1.8-liter VVT-i equipped Atkinson cycle petrol engine (2ZR-FXE)" https://global.toyota/en/detail/9827044 https://global.toyota/en/detail/9827044 https://en.wikipedia.org/wiki/Toyota_ZR_engine#2ZR-FXE https://en.wikipedia.org/wiki/Toyota_ZR_engine#2ZR-FXE
- avmich 6y ago
  > You'd be hard pressed to find a modern hybrid using Atkinson cycle. Kia Niro? https://futuresuvs.com/2021-kia-niro/ https://futuresuvs.com/2021-kia-niro/ "The centerpiece of the 2021 KIA Niro PHEV is a 1.6-liter Atkinson cycle four-cylinder petrol unit."
zepearl 6y ago
> Notice there are basically no diesel hybrids, this is because a diesel engine is more efficient than... Thx for the nice explanations. About diesel engines I read long time back that it's as well because they need to be "hot" in order to be able to filter their exhaust fumes (don't know how to say this correctly - the thing that is done by the catalyzer in the exhaust pipe) => as a hybrid engine is meant to be switched off quite often, the catalyzer of a diesel engine would have to be kept very hot by the battery, reducing therefore range/effectiveness/etc... of the hybrid system.
- SigmundA 6y ago
  Hard to say with modern diesels but I am sure it does contribute to the cost benefit, DPF filters will need more regeneration (and fuel use) if the exhaust temps are not high enough which is typical of diesel used for short trips vs longer highway trips.
- nanomonkey 6y ago
  The term that you are looking for is "wet stacking", and is due to the fact that diesels utilize the heat and pressure in the pistons and cylinder walls to induce combustion (there is no spark plug). That being said, one could inject the bare minimum to "idle" the motor and maintain this temperature, losing a bit of efficiency from completely stopping the motor entirely. There are a few diesel hybrid prototypes, if memory serves me there was a two stroke diesel hybrid motorcycle called the eCycle that got something like 160mpg.
zkms 6y ago
> Yes most people don't seem to realize the hybrid system tends to just shut down at highway speeds. There's still an advantage to having a hybrid system onboard even at highway speeds. The continuously-variable ratio of the hybrid transmission allows increased freedom of the ECU to select {instantaneous gasoline engine RPM, instantaneous gasoline engine torque}, which permits operation in more favorable parts of the BSFC map more often. Furthermore, the battery/motor-generators allow the ECU to temporarily run the gasoline engine at lower or higher output (without loss of traction power and without waste) than the power required at the wheels, further expanding the area of the BSFC map that the gasoline engine can operate at. It is true that mechanical-electrical-mechanical conversion is more lossy than an all-mechanical system, but topologies such as the Toyota hybrid system allow for significant power transfer without electrical conversion; and spending significantly more time in more efficient regions of the BSFC map makes up for the conversion losses incurred. Also, hybrids tend to have electrically powered coolant pumps and electrically powered air conditioning compressors, allowing for more aggressive fuel cut off (on a downhill section of the highway, say).
- SigmundA 6y ago
  CVT transmissions are not only available on hybrids although the Prius CVT is a thing of beauty utilizing the electric motors with planetary gears for continuous ratio. None of the other things you mention have more than negligible effect on the highway at cruise speeds where the combustion engine will be providing all the power to run all systems either directly or indirectly at typically ideal rpm most of the time. Also electrical cooling pumps and power steering etc again are not tied to hybrids and many non hybrids are going that route. A/C again does not need a hybrid but would exceed the capability of a standard alternator and direct mechanical compressor drive with a clutch is not that inefficient, again that would mostly be for stop and go urban driving at steady highway speed it probably more efficient to run mechanically off the engine. A small diesel car and Atkinson hybrid will have similar highway mileage mainly due to the combustion efficiency of the cycles not the hybrid systems. However the hybrid systems allow a Atkinson gasoline engine to have acceptable performance in the city while the diesel doesn't need it. An Otto gas car will be behind but the cost saving can buy a lot of gasoline.