There are two main types of hybrid cars: series hybrid cars and parallel hybrid cars.
Parallel hybrid cars work by using a combination of a traditional gas engine and a high output electric motor. The different elements of the engine start working at higher or lower levels of output are required. If the car is being driven carefully and accelerating at a reasonable level the electric motor will work on its own until a greater output is needed at a higher speed. Then the small high performances, in terms of fuel economy that is, gas engine takes over. This is a seamless almost unnoticeable process with a smooth transition of control from electric to gas power. Hot Car Forum
As the acceleration is powered by the electric motor the gas engine can be much smaller and more economical. There is no need for a great deal of energy, merely enough to keep the car at a steady speed, or to move the car from a mid range, around 40 mph to a higher speed. This requires a lot less energy than the initial movement from a standstill and consequently can be achieved with a lower level of power.
The parallel system of using both the gas engine and electric motor for hybrid cars means that there is less loss of power as when the car is traveling at higher speeds. As the energy is not required to go through the batteries and electric motor before providing power to the car. When traveling in this mode there is no need for the electric motor to operate and this also allows it to be recharged by the gas engine as the vehicle is traveling along. All ready for when the hybrid car slows and switches back to the electric motor.
Series Hybrid Cars: a series design works by powering the vehicle through an electric motor. The batteries supply the power to the motor. As the power arrives at the motor through the battery, series hybrid cars need a substantially larger reserve of power and consequentially a greater amount of batteries need to be carried in the car.
The motor only uses the exact amount of power required for the task in hand. If you spend hours in a traffic jam, you may get a little hot under the collar but your car will not be overheating. An electric motor does not need to tick over or idle when sitting in a jam; it will simply start turning when you start moving. When driving hybrid cars there will be no power (although maybe a little hair) lost even in the most extreme of gridlocks. As the motor will not be working when the vehicle is still, there is no need for the batteries to be recharged until power is again being lost when the car starts to move forward.
The large battery supply that is required for series hybrid cars is kept supplied with energy by a generator that runs from the main gas power unit. This only needs to operate when the batteries are in need of extra power so for much of urban driving there is no need for the motor to operate as only low levels of power are required. This allows the hybrid cars engine to run without emissions for city driving, especially if some higher powered driving, as for highways or main routes is done, and the consequent loss of power means that the hybrid cars batteries are brought upon to their full power supply by the gas motor when out of the urban environment.
There are advantages to both systems, but overall the parallel system is the most flexible for hybrid cars as it allows for the option of either power source to be transferred directly to drive the car without going through another separate means of transmission to the wheels.
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