First Drive: 2016 Hyundai Sonata Hybrid and Plug-In
06-03-15, 10:29 AM
#31
Lexus Fanatic
iTrader: (20)
Hell my new v6 vehicle gets 25% better gas mileage than my old v8 vehicle and it makes me feel good, but it's delusional because of the huge cost of the new vehicle itself.
06-03-15, 07:15 PM
#32
Lexus Test Driver
Don't get me wrong, I do appreciate Honda's effort here in improving hybrid vehicle fuel economy (I admit, I can be very critical of some of Honda's efforts). But as an engineer, I am always asking how and why. It seems that Honda re-thought the various hybrid driving modes (no doubt with knowledge gained from their own hybrid experience and the hybrid experiences of Toyota and Ford) and optimised each to the use of the electric motor, gasoline engine, or both.
I find it curious, though, how directly coupling the engine to the drive wheels at higher speeds, thus allowing the car to drive as a normal gasoline-engined car, can save fuel -- there is a direct mechanical connection between engine and wheels, with no CVT effect (constant engine rpm). It was my understanding that an engine turning an electric generator is very efficient, more efficient than an engine turning wheels through a mechanical gearset. Perhaps (in Toyota's hybrid system) routing engine power through a generator, through the power control unit to the electric drive motor wastes more power (and that is leaving the battery out of the picture) than the simple mechanical connection of engine to drive wheels in Honda's system.
I find it curious, though, how directly coupling the engine to the drive wheels at higher speeds, thus allowing the car to drive as a normal gasoline-engined car, can save fuel -- there is a direct mechanical connection between engine and wheels, with no CVT effect (constant engine rpm). It was my understanding that an engine turning an electric generator is very efficient, more efficient than an engine turning wheels through a mechanical gearset. Perhaps (in Toyota's hybrid system) routing engine power through a generator, through the power control unit to the electric drive motor wastes more power (and that is leaving the battery out of the picture) than the simple mechanical connection of engine to drive wheels in Honda's system.
But I do appreciate good engineering, especially mechanical engineering, as I spend far too much time tinkering with computers. I guess engines are most efficient when run at a set rpm as a generator; that's why both Honda and Toyota hybrid systems use the engine to generate extra power for the traction motor at low speeds, instead of driving the wheels directly.
At highway speeds, it's a compromise between EV mode efficiency (from engine to generator to traction motor) and the engine's efficiency directly driving the wheels, and I guess the engine wins out. You can't run on battery only because the charge would be depleted pretty fast, not unless you had a much larger battery pack. You would also need a larger motor and beefier cooling to run on EV mode only, just like with a Model S. I'm not sure how the Honda system blends power at high speed when both the engine and the traction motor are running, like when overtaking on the highway.
You can see the charging vs rpm behavior in the ES300h by changing the custom settings to show the tach in all modes. I think it idles at 1500 rpm for idle charging, goes up to 3000 rpm for generator assist at low speeds and shoots up to the 6000 rpm redline when full power is called for. I do wish we had more control over the hybrid modes like on VW hybrids.
06-03-15, 07:43 PM
#33
Lexus Champion
I'm not an engineer But I do appreciate good engineering, especially mechanical engineering, as I spend far too much time tinkering with computers.
I guess engines are most efficient when run at a set rpm as a generator; that's why both Honda and Toyota hybrid systems use the engine to generate extra power for the traction motor at low speeds, instead of driving the wheels directly.
At highway speeds, it's a compromise between EV mode efficiency (from engine to generator to traction motor) and the engine's efficiency directly driving the wheels, and I guess the engine wins out. You can't run on battery only because the charge would be depleted pretty fast, not unless you had a much larger battery pack. You would also need a larger motor and beefier cooling to run on EV mode only, just like with a Model S. I'm not sure how the Honda system blends power at high speed when both the engine and the traction motor are running, like when overtaking on the highway.
You can see the charging vs rpm behavior in the ES300h by changing the custom settings to show the tach in all modes. I think it idles at 1500 rpm for idle charging, goes up to 3000 rpm for generator assist at low speeds and shoots up to the 6000 rpm redline when full power is called for. I do wish we had more control over the hybrid modes like on VW hybrids.
But I do appreciate good engineering, especially mechanical engineering, as I spend far too much time tinkering with computers. I guess engines are most efficient when run at a set rpm as a generator; that's why both Honda and Toyota hybrid systems use the engine to generate extra power for the traction motor at low speeds, instead of driving the wheels directly.
At highway speeds, it's a compromise between EV mode efficiency (from engine to generator to traction motor) and the engine's efficiency directly driving the wheels, and I guess the engine wins out. You can't run on battery only because the charge would be depleted pretty fast, not unless you had a much larger battery pack. You would also need a larger motor and beefier cooling to run on EV mode only, just like with a Model S. I'm not sure how the Honda system blends power at high speed when both the engine and the traction motor are running, like when overtaking on the highway.
You can see the charging vs rpm behavior in the ES300h by changing the custom settings to show the tach in all modes. I think it idles at 1500 rpm for idle charging, goes up to 3000 rpm for generator assist at low speeds and shoots up to the 6000 rpm redline when full power is called for. I do wish we had more control over the hybrid modes like on VW hybrids.
Since the Accord Hybrid's power-split device mechanically couples the engine to the drive wheels, the speed of the car would be reflected in the engine rpm (even if the engine is assisting the electric motor). But if the power is not needed, and without a variable ratio gearset available between the engine and the wheels to tailor available power, any unneeded power would have to be bled off somehow.
The generator does that. As in the Toyota Hybrid Synergy Drive, the generator balances power needed to drive the car. If less power is needed than what the engine is providing, the excess power is bled off to turn the generator, and as power needed increases, less power goes to the generator, making more available to drive the car.
And since in the Toyota system, the engine is never mechanically connected to the drive wheels, the generator is what allows the PSD to act as a CVT: the engine maintains a constant rpm with the generator balancing power. If you need less power at lower speeds, the generator absorbs the extra power, and as power needs increase, less power goes to the generator.
06-04-15, 05:31 AM
#34
Lexus Test Driver
Actually, the Honda system uses a clutch to couple the engine to the drive shaft. When it's acting as a generator at low to medium speeds, it's decoupled; the clutch only engages above 60 mph and the engine effectively runs at a single ratio up to redline.
Toyota's system has the engine always coupled to the planet carrier with no clutch in between. The power split happens between the sun, planet, carrier and ring gears... Apparently the engine can remain stopped while the sun-MG1 and ring-MG2 gears rotate. Better to look up a Prius drivetrain simulation to see how the different power sources come together.
ORNL analysis of 2007 Camry Hybrid: http://info.ornl.gov/sites/publicati...es/Pub7568.pdf
Toyota analysis of Prius 2 system: http://www.evworld.com/library/toyotahs2.pdf
Toyota's system has the engine always coupled to the planet carrier with no clutch in between. The power split happens between the sun, planet, carrier and ring gears... Apparently the engine can remain stopped while the sun-MG1 and ring-MG2 gears rotate. Better to look up a Prius drivetrain simulation to see how the different power sources come together.
ORNL analysis of 2007 Camry Hybrid: http://info.ornl.gov/sites/publicati...es/Pub7568.pdf
Toyota analysis of Prius 2 system: http://www.evworld.com/library/toyotahs2.pdf
Last edited by chromedome; 06-04-15 at 07:11 AM.
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