Entrance
Introduction
Development
Problems
Future
References

http://www.amazingadgets.com/wp-content/uploads/2007/10/hybrid-cars001.jpgHybrid Vehicles are vehicles propelled by two or more sources of power.[1]
Most hybrid vehicles on modern automobile markets are Hybrid Electric Vehicles (HEV). A typical HEV consists a conventional internal combustion engine (ICE) and a rechargeable energy storage system (RESS). [2] There are also various other forms of hybrid vehicles. Other sources of power also includes hydrogen, propane, CNG (Compressed natural gas), and solar energy.

For road vehicles, power required in different running condition varies a lot, combustion engine in conventional vehicles rarely works on it's most efficient condition due to this reason, thus some fuel are relatively wasted in these situations. Modern Hybrid Electric Vehicles are usually powered by one power source on open road and the other power source only work when maximum power is needed, for example when the vehicle is going uphill or overtaking other cars. Very high acceleration can be achieved by internal combustion engine and electric motor are working at the same time if needed. Engines can run in a more efficient speed with the aid of electric motor. The internal combustion engines of the Hybrid Electric Vehicles can be shut down by computer control system when they are idle or redundant engine power can be used to recharge batteries. The engines needed are usually smaller than those in conventional vehicles, engines that are more efficient but with lower torque engines may also be used . Batteries are recharged by regenerative braking or electrical generator driven by internal combustion engine, usually no external recharging resource is needed. Regenerative braking is also one of the major advantage of Hybrid Vehicle, when the car is braking or going down hill, kinetic energy can be converted to electric energy and recharge the batteries by electric motor, while conventional vehicles have to slow down via braking system which will convert kinetic energy to useless heat, when it is going down long hill engine braking has to be applied to avoid overheating of the braking system, which would also cost fuel.  All these facts clearly indicates that HEVs can reduce the emission and fuel consumption by a large scale.


Main categories of  Hybrid power:

  • Parallel hybrid
    In this type of HEVs, electric motor and ICE can either run on their own or work in parallel. Electric motor usually works alone in low power situation like reversing or low speed running. The internal combustion engine only comes in for higher speed situation or when battery needs to be recharged.
    On open road,  internal combustion engine will be the main power source for the vehicle, usually for maximizing the battery life. electric motor will come in when maximum acceleration or propulsion is required.
     

  • Mild hybrid
    The electric motor in mild hybrid vehicles doesn't run independently, it only assists the internal combustion engine when extra power is needed.
     

  • Plug-in hybrid electrical vehicle (PHEV)
    This design usually provides a larger electricity storage capacity, it emphasis the ability of recharging the battery from external sources rather than from the internal combustion engine.
     

  • Series Hybrid
    In series hybrid vehicles, combustion engine doesn't provide energy directly to the wheels. Instead it is running on its most efficient speed and drives a electric generator and indirectly provides electricity for recharging the battery, recharging the capacitor and drives the electric motors. Theoretically a series hybrid vehicle does not necessarily require a battery, a capacitor is enough for the operation.


 The video below gives a basic demo of the Hybrid theory

 (Another excellent illustration of hybrid vehicle can be found here)

The following table shows a comparison of fuel consumption (miles per gallon) between Hybrid and conventional vehicles.


The table below shows the comparison of fuel cost and emission of the most common Hybrid vehicles on sale at the moment.[4]
 

 
2007
Honda Accord Hybrid
2007
Honda Civic Hybrid
2007
Lexus GS 450h
2007
Nissan Altima Hybrid
2007
Saturn Aura Hybrid
2007
Toyota Camry Hybrid
2007
Toyota Prius
Side-by-Side
MPG
 (city)
28
49
 
25
42
28
40
60
MPG (hwy)
35
51
 
28
36
35
38
51
MPG (comb)
31
50
 
26
39
30
39
55
Annual
Greenhouse
Gas Emissions
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9

 
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
 

 
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
 
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
 
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
 
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
 Worst
Best 
Graph showing tons of greenhouse gases.
14.9
2.9
6.8 tons
4.4 tons
8.0 tons
4.7 tons
6.0 tons
4.8 tons
3.4 tons

It is clearly shown that hybrid models have obvious advantages in fuel consumption rates. It has no doubt that Hybrid vehicles is an excellent choice for more economical and environmental friendly solution.


Chen Chen | starikki@2008 University of Bath
starikki@hotmail.com | http://www.starikki.co.uk