Welcome to Hybrid theory 101. Hybrid cars operate differently depending on your current driving modes. We can divide your typical driving into 5 different modes. Your hybrid car acts differently in each of these 5 driving modes, in some modes the electric motor is operating, and some modes the gasoline engine is operating, and sometimes both are operating. Knowing how your hybrid vehicle operates under each mode is crucial to getting the most gas mileage, and minimizing emissions output. Of course the car makers don't tell you this, they just make it sound like you always get super high gas mileage like a Bingo free spot, no matter how you drive, but that may not be the case. Here are the 5 hybrid vehicle driving modes and their theory of operation:
1) Full Stop: At a full stop, like at a red traffic light or stop sign, the gas engine usually shuts off to eliminate idling, and reduce emissions. The electric motor is now ready to propel the car when push on the gas pedal. This is usually pretty seamless, and you might not even notice without seeing it on the power monitor indicator. In crowded cities with lots of stop and go traffic like the opening scene of Office Space, this can save you a lot of fuel.
2) Low Speed/Initial acceleration from a stop: First of all, I should point out that being a scofflaw maniac driver, I never drive in this mode. Starting from a stop, and driving in a normal sane, just-like-your-grandmother acceleration from the stop line, the electric motor usually propels your car, powered by the electric motor's battery pack. This type of downtown stop and go traffic is where you save the most fuel with hybrids, counter intuitive to normal gas engines, where you burn the most fuel. The electric motor works up until about 15 MPH without any help from the gas engine. The gas engine turns on and off as needed while you drive. I have zero patience for losers at stoplights. If you have a life to live and a lead foot like me, your hybrid SUV will be less efficient in this mode, because flooring the accelerator will demand extra power, causing the gas engine to kick in. This eliminates the fuel savings potential offered to you by your electric motor during this driving mode. Also, if you spend all day in stop and go traffic, the constantly used electric motor battery may discharge quicker, causing the gas engine to turn back on to charge the battery. So your fuel economy savings for hybrids may really only benefit you in a much more narrower range of operating conditions than the car makers will admit. Moral of the story: If you don't drive your hybrid car like you are supposed to, don't expect to get the advertised fuel economy.
3) Heavy Acceleration: This is my personal favorite mode of operation. This mode quickly puts a lot of forward distance between you and the aforementioned losers at stoplights, stuck there during indecision attacks when the light turns green. Here your power comes from both the gas engine, AND the high torque electric motor, typically through some type of power splitting device. During this mode, you probably will not be saving as much fuel as you expect from all the advertising.
4) Highway Driving: This is where the fuel efficiency of Hybrid cars and SUV's works counter intuitive to what you would expect. The reason is that in this driving mode, the car is typically powered only by the gas engine, which may be charging your electric motor battery pack at the same time. So the electric motor is not typically contributing during highway driving, meaning your hybrid vehicle is just another gas guzzling, car at highway speeds. If you are a highway commuter that drives an hour to work each way on the open highway with no stop and go traffic, a hybrid vehicle will probably offer you little fuel savings.
5) Braking, Coasting and Deceleration: When you brake or coast, forward kinetic energy that in standard car normally gets dissipated as heat is instead converted to electric energy. This is accomplished by using the old reliable spinning electrical motor in it's other role, now as a generator to charge the battery pack. This is why hybrid cars never need to be plugged in, despite old wives tales you might hear. This process of charging the battery is known as regenerative braking.
6) Backing Up: Ok I lied, there's a sixth mode, but who really counts going in reverse as a driving mode? In reverse the gas engine does not operate, the electric motor does all the work. Not that this will add huge amounts of fuel savings for you. I drive about 50 feet max in reverse on a daily basis. Now maybe if you're Burt Reynolds...
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