Combustion engines in hybrids are very similar to combustion engines in other cars -- typically gas-combusting, overhead cams with a bank of four inline cylinders, very much like other economy cars. However, a combustion engine in a hybrid considers the ability for electric power to subsidize power production from the gas engine under heavier loads, minimizing the overall reliance on combustion.
By definition, hybrid cars use multiple sources of power to propel them. The most commercially accepted configuration is a gas engine combined with an electrical motor, where both mechanical and electrical power move the car. Hybrids have many systems that differ from standard gas-powered cars. They also have discrete components or systems within their own configuration. Though the systems are discrete or separate in function, they are also designed to interact with one another.
Battery, Generator, Electric Motor
Most hybrids also have a battery, generator and electric motor. Each of these is a discrete components, but to create the benefits of the hybrid car, they are functionally interactive and interdependent. The battery isn't just a starter battery; it's a way of temporarily storing energy from mechanical power. Most of the energy stored in the battery comes from the operation of the gas engine, converted to electricity under optimum operating conditions of the engine. A generator is connected to the gas engine. The generator engages the engine to convert a portion of its mechanical power to electricity to be stored in the battery. Once stored in the battery, the battery can power an electric motor, converting back from electricity to mechanical power. The electric motor is used to prevent the gas motor from having to increase its power and emission output when straining up a hill, for example.
A power splitter is a device capable of using multiple sources of power input to send to the car's drive-line. Instead of having a simple gear, for example, that forced the car to either run on gas power or electrical power coming from the electric motor, the power splitter allows each power source to contribute simultaneously, thereby reducing the load or power requirement on the other.
Brake Energy Recapturing
Many hybrids have a discrete component to capture brake energy. To understand these systems, think about the turning wheel not as something being powered by an engine but as just a source of mechanical energy. The brake is stopping the energy. In most cars, the energy exerted by the wheels under braking simply dissipates, mostly into heat, and is wasted. Hybrid braking systems are essentially additional generators that convert a portion of the braking force back into electricity. In effect, stopping the car creates some of the electricity to help accelerate the car.