The growing threat of global warming, excessive petrol dependence and ever increases prices in fuel are reasons among others that led to the development of Hybrid Electric Vehicles (HEV). Also, some government backing has offered support to HEV technology with the introduction of restrictive legislation particularly concerned with the reduction of CO2 emissions.
The first ever HEV was built in 1898, and there were several automotive companies who were selling HEVs in the early 1900s. The production of HEVs did not last. Henry Ford initiated the mass production of combustion engine vehicles; making them widely available and affordable. In contrast, the price of less efficient EVs continues to rise. Another problem was the requirement for a smooth coordination between the engine and the motor, which was not possible due to the use of only mechanical controls.
Global warming, the continual rise in fuel prices, and the threat of oil reserves drying up altogether led to interest in more efficient and environmentally means of transport, particularly in the area of HEV. With advances in battery technologies and onboard computer systems, the option of a plausible HEV has become reality, and a number of models like Honda (Civic and Insight) and Toyota (Prius) have been available now since 2000. The increased interest and legislative movements has made clean and efficient transportation not only a vision for the future but for today.
A Hybrid Electric Vehicle is powered by two or more energy sources, one of which is an electrical source. The two most common sources of power in an HEV are mechanical (ICE) and electrical (from batteries). The addition of an electric motor in an HEV means that the size of the gasoline engine can be reduced.
HEVs do not need to be plugged into an external source as all recharging is done whilst the vehicle is in operation. The electric motor acts as a generator through the process of regenerative braking in order to recharge the batteries with the energy which would once have been lost through heat and frictional dissipation. Regenerative braking occurs whilst the vehicle is slowing down. Through the combination of both the direct drive from the engine and the recaptured energy through regenerative braking the energy stored within the batteries will be a sufficient amount for the vehicle to operate. (we will explain regenerative braking in the article HEV part two)
I-1 Gasoline Engine:
The gasoline engine in a HEV is similar to a conventional ICE Engine. Gasoline engines in HEVs are usually much smaller than ones found in comparable conventional vehicles. Larger engines are primarily heavier, requiring extra energy during accelerations or climbing inclinations; pistons along with other components are heavier in a larger engine, which decrease the efficiency and add to the overall weight of the vehicle. The gasoline engine is the primary source of power for the vehicle, and the electric motor is the secondary source of power.
I-2 Electric Motors:
The electric motor is primarily used to drive HEVs at low speeds, and assist the gasoline engine when additional power is required. The electric motor can even act as a generator and convert energy from the engine or through regenerative braking into electricity, which is then stored in the battery. This functionality works as the electric motor applies a resistive force to the drivetrain which causes the wheels to slow down. The energy from the wheels then begin to turn the electric motor, making it operate as a generator, converting this normally wasted energy through coasting and braking into electricity.
In a series configured HEV (discussed later in the article part two) only the electric motor is connected to the wheels. A series HEV has a separate generator which is coupled with the gasoline engine. The engine/generator set supplies the electricity required by the batteries, in turn feeding the electric motor. The coupled generator and engine maintain the efficient usage of the battery system during operation.
I-4 Battery technologies:
The batteries are an integral component within HEVs. Electrical energy can be drawn from the batteries to the electric motor; also this process can operate in reverse by recapturing energy through regenerative braking. The only time there is a large requirement for electrical energy is during electric only mode, the majority of the time the electrical loads are easily managed within the whole vehicular system. Due to the high cost increment of the battery for energy storage, it is far more cost effective to use the engine as the primary power source for the vehicle at higher loads, rather than increasing the amount of energy storage. Continued efforts must concentrate on improving the existing battery technologies in order to make them more efficient, rather than just increasing their sizes to gain a greater output.
In this article, we will treat Lithium-Ion batteries because they have the biggest energy density [120-150] Wh/kg. The Lead-acid batteries have been treated in a previous article in our website (see category Auto parts, sub-category: Batteries).
Lithium-ion batteries have a reasonably low maintenance, offering an advantage that most other battery chemistries cannot. There is no memory or scheduled cycling requirements in order to prolong the overall life of the battery.
There are some drawbacks: Lithium-Ion batteries is a fragile technology, which requires a protection circuit in order to maintain the safe operation of the technology type. The inclusion of a protection circuit does however ensure the voltage and current limits remain within their safe limits. Lithium-Ion batteries become susceptible to aging especially when not in use, and are expensive. For example: They are 40% more expensive to manufacture than Ni/Cd batteries.