|
|
|
|
|
|
by zkms
2081 days 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). |
|
|
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.