In hybrid vehicles, I know the battery can be recharged using regenerative braking, but I also see them sometimes recharge the battery using the engine directly. Why would they do this? It seems like it would be better to use the motor just to move the vehicle. Why go gas -> engine -> battery -> wheels?
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Depends on how exactly it’s set up, but often a hybrid needs both the gas engine combined with the electric engine at the same time to work. In order to increase fuel efficiency, the gas engine will be running on the Atkinson cycle as opposed to the Otto cycle, (which is the one pure gas engines normally run.) The benefit is that the Atkinson cycle can extract more energy from a given quantity of fuel. The downside of the Atkinson cycle is that it doesn’t generate as much power in the moment and worse, it creates inconsistent power throughout the revolution of the crankshaft. Basically, instead of smooth acceleration your car would jerk like the transmission is shifting every revolution of the crankshaft. In order to get around this, an electric motor is integrated into the block and computer controlled to feed power at exactly the point in the revolution that the power delivery in the Atkinson cycle would drop off, with the effect of smoothing it out. An electric motor needs power so some of the energy from running is stored. On balance the energy saved by running the Atkinson cycle more than makes up for any losses associated with charging a battery and running an electric motor. This sort of the system that Honda uses.
The Ford Maverick and Toyota Prius, OTOH, use an ECVT transmission. It’s a super simple transmission that’s centered around a planetary gearset but requires a gasoline engine as well as 2 electric motors that all input power into the transmission at different speeds. A computer calculates and controls the speed and direction that each motor needs to turn at to get the proper wheel speed.
In every case, the power to run the electric motors must come from somewhere and if the only source of energy going into your vehicle is gasoline then some of that energy must be scavenged from the gas engine at some point or form. If you can recapture otherwise wasted energy (regenerative braking) or simply run the engine in the most optimum (efficient) range for longer then overall otherwise lost energy gan be used and your overall efficiency goes up.
Other hybrid systems are just electric cars with a range extender. A small gas engine to charge a battery, but the drivetrain is otherwise all electric. Like the Chevy Volt. Most power is needed to do things like accelerate. Actually cruising down the highway takes a surprisingly little amount of power. We have ‘big’ engines in cars sized to meet the huge power demands of a few moments. Why not let the electric motor do all the heavy lifting and have a tiny, efficient, gas motor just keep the battery topped up?
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