Hybrid Vehicles

1)ABSTRACT

      With the advanced technique emerging in automotive industry the passenger cars and even heavy vehicles are getting more and more refined, within a past couple of years almost each and every system of  vehicles, right from structure, suspension, steering, braking, ignition, transmission etc. have undergone many improvements.

It is evident from the history of automobiles that the lust for passion, power, comfort, stability & safety has always dominated the trends in the developments of automobiles. One such development is HYBRID VEHICLES. Transmission system used in hybrid vehicles is bound to different as it has to deal with both engine power as well as power from battery.

HYBRID VEHICLES is  a combination of electric drive and CVT,  used in vehicles such as Toyota Prius, Toyota Highlander and Camry Hybrid etc. gives synergy between Engine power and Battery power. Hybrid vehicles replaces a normal geared transmission with an electromechanical system. Hybrid vehicles achieves high levels of compatibility between environmental performance and increases the power output upto 1.5 times.

Hybrid system consists of motive power sources of high efficiency gasoline engine that utilizes Atkinson cycle, a permanent magnet AC synchronous motor, a generator, high performance NiMH battery and a power control unit. In the discussion that follows we will see working, performance, development and Future scope of Hybrid vehicles.

2)INTRODUCTION

Since the introduction of the first car there have constantly been new innovations in the automotive industry.  With each new line of automobiles there are new ideas and concepts, introduced to help make our lives easier and make the vehicles more efficient.

The newest innovation from the automotive industry is the hybrid car.  This vehicle is designed to use different forms of energy, not just gasoline.  There has been plenty of talk about hybrid cars some even confused them with cars running on Biodiesel or some kind of Recycling ideology.

What do you mean by hybrid car?

Hybrids are cars that run off a rechargeable battery and gasoline, rather than just gasoline.
Hybrid batteries help to reduce fuel emissions because the hybrid engine draws on the battery and not gasoline when accelerating. Hybrid gasoline motors can shut off when the car is stopped and run off their electricity.

Why Hybrid and Not All-Electric?
Most electric cars cannot go faster than 50-60 mph, and need to be recharged every 50-100 miles. Hybrids bridge the gap between electric and gasoline-powered cars by traveling further and driving faster.

How Hybrids Save Energy and Gasoline:

Hybrid engines are much smaller than those on conventional cars. A hybrid car engine is built small to accommodate the 99% of driving time when a car is not going up hills or accelerating quickly. When extra acceleration power is needed, it relies on the battery to provide additional force.

Hybrid gasoline motors can shut off when the car is stopped and run off their electric motor and battery.

Hybrid cars are lighter, which their tires create half the drag of conventional cars because they are stiffer and inflated to a higher pressure.

Hybrid cars often recover braking energy. Electric hybrid motors take the kinetic energy lost in braking and use it to charge the battery.

Hybrid cars are often more aerodynamic, reducing wind resistance. Hybrids burn less gasoline per mile, so they release much less pollution and fewer greenhouse gases.

How Hybrid Cars Work?

An internal combustion engine is "fueled" by a hybrid's electric generator, which acts as the starter, and is used when first switching the car on. Once the engine is heated up, it automatically shuts itself off and the electric motor takes over.

A computer within the hybrid is responsible for determining how much power is needed from the engine and how much should be used from the electric engine, depending on how fast the car is going. Signals are sent to a gearbox known as the power split device, which uses a series of intricate gears that connect both the gas and electric engines/motors together.

The electric portion of the hybrid draws its power from a set of nickel hydride batteries.

Technology and Hybrid Cars

Hybrid cars implement some new technology that has not been seen in the automotive industry. Most of these advances are strictly for hybrid cars, to ensure they operate correctly and safely.

Automatic start and shut-off is a feature that automatically shuts off the engine when the car has come to a stop, then restarts it when the accelerator is touched. This eliminates the need to waste energy by resting the engine.

The hybrid's electric motor gives the car the added power it needs when accelerating, passing, or climbing hills, which is called electric motor drive. With this extra assistance, a smaller, more fuel efficient engine can be used.

Regenerative braking recycles energy when the cars brakes are applied. The electric motor is designed to exert resistance to the car's drive train, which then causes its wheels to slow down. Energy from the wheels is then used to fuel the electric motor, which acts as a generator, converting the energy that would otherwise be wasted while braking into electricity that is stored in the battery until needed.

Hybrid structure:

In hybrid vehicles the power from both the sources can be combined in different ways. One way known as parallel hybrid has a fuel tank which supplies gasoline to the engine. But it also has a set of batteries that supplies gasoline to the engine. Both the engine and electric motor that drives the transmission then turns wheels.

            By contrast in a series hybrid the gasoline turns a generator and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus the gasoline engine never directly powers the engine.

3)Hybrid Components

Hybrid cars contain the following parts:

·        Gasoline engine: The hybrid car has a gasoline engine much like the one you will find on most cars. However the on a hybrid is smaller and uses advanced technologies to reduce emissions and increase efficiency.

·        Fuel tank: The fuel tank in a hybrid vehicle is the energy storage device for the gasoline engine. Gasoline has much higher energy density than batteries do. For example it takes about 1000 pounds of batteries to store as much energy as 1 gallon (7 pounds) of gasoline.

·        Electric motor: The electric motor on a hybrid car is very sophisticated. Advanced electronics allow it to act as a motor as well as generator. For example, when it needs to , it can draw energy from batteries to accelerate the car. But acting as a generator, it can slow down the car and return energy to batteries.

·        Generator: The generator is similar to an electric motor but it acts only to produce electrical power. It is used mostly on series hybrids.

·        Batteries: The batteries in a hybrid car are energy storage device for the electric motor. Unlike the gasoline engine in the fuel tank, which can only power the gasoline engine, the electric motor on a hybrid car can put energy into the batteries as well as draw energy from them.

·        Transmission: The transmission on a hybrid car performs the same basic function as the transmission on a conventional car. Some hybrids, like the Honda Insight, have conventional transmissions. Others like the Toyota prius have radically different ones.

 HOW DO HYBRID WORKS?

Hybrid electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors and can be configured to obtain different objectives, such as improved fuel economy, increased power or additional auxiliary power for electronic devices and power tools.

Some of the advanced technologies typically used by HEVs include:

Regenerative Braking: The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.

Electric Motor Drive/Assist: The electric motor provides additional power to assist the engine in accelerating, passing or hill climbing. This allows a smaller, more efficient engine to be used. In some vehicles, the motor alone provides power for low-speed driving conditions where internal combustion engines are less efficient.

Automatic Start/Shutoff: Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This prevents wasted energy from idling.

Why to use hybrid cars?

            You must be thinking why to build such a complicated vehicle when we are using gasoline powered cars with ease. The reason is twofold: to reduce tailpipe emissions and to improve mileage. These goals are actually tightly interwoven.

            Emissions standards dictate how much of each type of pollution a car is allowed to emit. The amount is usually specified in grams per mile (g/mi). for example, the low emissions vehicle (LEV) standard allows 3.4 g/mi of carbon monoxide.

                        The key thing here is that the amount of pollution allowed does not depend on the mileage your car gets. But a car that’s twice as much gas to go a mile will generate approximately twice as much pollution. That pollution will have to be removed twice as much pollution. That pollution will have to be removed by the emissions control equipment on this car. So decreasing the fuel consumption of car is one of the surest ways to decrease emissions.

            Carbon dioxide (CO₂) is another type of pollution a car produces. The U.S. government does not regulate it, but scientists suspect that it contributes to global warming.

EVOLUTION OF THE HYBRID

            The hybrid can be called as a compromise. It attempts to significantly increase the mileage and reduce the emissions of a gas powered car while overcoming the shortcomings of an electric car.

4)PROBLEMS WITH GAS POWERED CARS

            To be useful to you or me, a car must meet certain minimum requirements. The car should be able to:

·        Drive at least 300 miles (482 km) between re-fuelling

·        Be refueled easily

·        Keep up with the other traffic on the road

A gasoline car meets these requirements but produces a relatively large amount of pollution and generally gets poor gas mileage. An electric car, on the other hand, produces almost no pollution, but it can only go 50 to 100 miles (80 to 160 km) between charges. And the problem has been that it is very slow and inconvenient to recharge.

A driver’s desire for quick acceleration causes our cars to be much less efficient than they could be. You may have noticed that a car with a less powerful engine. The amazing thing is that most of what we require a car to do uses only a small percentage of its horsepower. When you are driving along the freeway at 60 mph, your car engine has to provide the power to do three things:

·        Overcome the aerodynamic drag caused by pushing the cars through air

·        Overcome all of the friction in the car’s components such as the tires, transmission, axels, and brakes

·        Provide power for accessories like air conditioning, power steering and headlights

For most cars, doing all this requires less than 20 horsepower. So why do you need a car with 200 horsepower? So you can floor it which is the only time you use all that power. The rest of time, you use considerably less power than you have available.

Smaller Engines are More Efficient

            Most cars require a relatively big engine to produce enough power to accelerate the car quickly. In a small engine, however the efficiency can be improved by using smaller, lighter parts, by reducing the number of cylinders and by operating the engine closer to its maximum load.

There are several reasons why smaller engines are more efficient than big ones:

·        The big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill

·        The pistons and other internal components are heavier, requiring more energy each time they go up and down in the cylinder

·        Bigger engines usually have more cylinders and each cylinder uses fuel every time the engine fires even if the car isn’t moving.

This explains why two of the same model cars with different engines can get different mileage. If both cars are driving along the freeway at the same speed , the one with smaller engine uses less energy. Both engines have to output the same amount of power to drive car, but the small engine uses less power to drive itself.

 5)KEY INNOVATION POWER CONTROL UNIT WITH THE BOOST CONVERTER

Power Control Unit

Power Control Unit with DC/AC inverter and Voltage-Boosting Converter

HYBRID SYNERGY DRIVE is equipped with a Power Control Unit that consists of an inverter, a Voltage-Boosting Converter and an AC/DC converter to run the car on electric motors.

Inverter
An inverter converts DC supplied by the battery to AC to turn the electric motors and to use in the generator.
Conversely, it converts AC generated by the electric motors and the generator into DC to recharge the battery.

Voltage-Boosting Converter
The Voltage-Boosting Converter steplessly increases the normal 201.6 V DC supply voltage to a maximum of 650 V(*1) to feed the electric motors and the generator as required. This means more power can be generated from a small current to bring out high performance from the high output motors, enhancing overall system efficiency. It also means that the inverter could be made smaller and lighter.

DC/DC Converter
The DC/DC converter steps down the 201.6 V supply voltage from the battery to 12 V, to be used by ancillary systems and electronic devices like the ECU.

 6)ECU

The Brain: Running the car safely, comfortably and at maximum efficiency.The various devices of the car are centrally controlled by the ECU*, which could be said to be the car's "brain". HYBRID SYNERGY DRIVE uses the ECU to constantly monitor the operational status of these devices, and of energy consumption, on a real-time basis. This enables it to execute quick, precise and comprehensive management to run the car safely, comfortably and with maximum efficiency.
- Monitors operational status of each hybrid component (gas/petrol engine, generator, electric motors, battery)
- Monitors braking data received via car's control network
- Monitors instructions (accelerator pedal opening angle, gear shift position) from the driver
- Monitors energy consumption of driver assisting -operated systems (e.g. air-conditioning, headlamps, navigation system etc.)
- Controls each device electronically, based on information derived from monitoring

7)GENERATOR

Generator:

High speed rotation for higher maximum power output.

As with the electric motors, HYBRID SYNERGY DRIVE uses a synchronous AC generator which can turn faster than the previous model, and therefore increases the maximum power output. The rotor is also made to withstand stronger forces. As a result, the generator power band for maximum output has been extended to 10,000 r.p.m.
Use of a synchronous AC generator capable of high speed axial rotation has made it possible to produce substantial electrical power while the car is running in the mid-speed range. Toyota has put together the ideal generator, high output electric motors and gas/petrol engine combination that enhances low to mid-speed range acceleration.

8)ENGINE

The engine of hybrid car is a comlicated structure. It consist of lot of things combined together to generate power.In this engine we can see the IC engine coupled with generator through a power split device.This whole combination of motors and engine generate the power for the vehicle.

 The Prius has an internal combustion engine (ICE) which is unusually small for a car of this size (1300 kg).  This is made possible by the presence of the electric motors and battery, which supplement the ICE when power demand is high.  A conventional car, with an engine sized for hard acceleration and climbing steep hills, almost always operates that engine with low efficiency. 

Maximum efficiency generally occurs at around half of the engine's peak power output.  A small engine can operate closer to this maximum efficiency because power demands encountered in normal driving are a larger fraction of its peak power.  The possibility of using a small engine in a hybrid vehicle is called "engine downsizing".

In addition to being downsized, the Prius engine uses many techniques to improve efficiency and broaden the range of conditions under which high efficiency is achieved.  The engine uses the Atkinson cycle, rather than the usual Otto cycle, which improves efficiency particularly at lower power by reducing "pumping loss". 

 Limiting the maximum spin rate (to 4500 r.p.m. in the Generation II Prius (2000 - 2003) and 5000 r.p.m in the Generation III Prius (2003 onwards)) allows lightweight parts to be used, reducing inertia and friction losses.  The crankshaft is offset from the cylinder axes so that during the combustion stroke the force from the piston is transmitted to the crankshaft through a straight rather than tilted connecting rod.  The valves have narrow stems and low force springs to reduce energy lost in operating the valves.

   The diagram below is a schematic of the Prius powertrain.  "Schematic" means that it shows the essential features, but takes liberties with detail.  In particular, the way in which the internal combustion engine (ICE) drives the planet gears in the power split device (PSD) and the way that the ring gear is connected to the silent chain sprocket and motor/generator 2 (MG2) has been grossly simplified. It is, however, accurate that the shaft from the Petrol Engine (blue) passes through the shaft of MG1 and the sun gear (green) in order to reach the planet carrier on the other side of the PSD.

 9) BATTERY :

Highlander Hybrid Nickel Metal Hydride Battery :

Newly developed modular metal casing for compact packaging and improved cooling

The Ni-MH battery used in Highlander Hybrid is packaged in the newly developed metal battery casing.
Although it is only 0.014㎥ (240 cells) in volume, it can deliver high voltage of 288 V. The improved cooling performance reduces loss of efficiency due to heat generation, ensuring that the battery can supply required electric power to the motors at all times.
The battery Monitoring Unit manages discharge and recharging by the generator and motors to keep the charge level constant while the car is running.

10)Series Parallel Hybrid System:

Driving the wheels with the electric motors and the gas/petrol engine, yielding electricity via the generator to self-charge the battery

With the Series Parallel Hybrid System, it is possible to drive the wheels using the dual sources of power (electric motors and/or gas/petrol engine), as well as to generate electricity while running on the electric motors.
         

  The system runs the car on power from the electric motors only, or by using both the gas/petrol engine and the electric motors together, depending on the driving conditions. Since the generator is integrated into the system, the battery can be charged while the car is running.
            

The basic components of the system are the electric motors, the gas/petrol engine, the generator, the power split device and the power control unit (inverter/converter). The power split device transfers part of the power produced by the gas/petrol engine to drive the wheels, and the rest to the generator to either provide electric power for the electric motors or to recharge the battery.
         

   This system takes advantage of the energy-efficient electric motors when the car runs in the low speed range, and calls on the gas/petrol engine when the car runs in the higher speed range. In other words, the system can control the dual sources of power for  optimum energy-efficient operation under any driving conditions.

Digramatic representation of parallel hybrid system:

11)REGENERATIVE BRAKING:

Reuse of kinetic energy by using the electric motors to regenerate electricity

HYBRID SYNERGY DRIVE can reuse kinetic energy by using its electric motors to regenerate electricity in what is called "regenerative braking".
Normally, electric motors are turned by passing an electric current through it. However, if some outside force is used to turn the electric motors, it functions as a generator and produces electricity. This makes it possible to employ the rotational force of the driving axle to turn the electric motors, thus regenerating electric energy for storage in the battery and simultaneously slowing the car with the regenerative resistance of the electric motors.

The system coordinates regenerative braking and the braking operation of the conventional hydraulic brakes so that kinetic energy, which is normally discarded as friction heat when braking, can be collected for later reuse in normal driving mode.
Typically, driving in city traffic entails a cycle of acceleration followed by deceleration. The energy recovery ratio under these driving conditions can therefore be quite high.
To take advantage of this situation, the system proactively uses regenerative braking when running the car in the low speed range. Taking Prius as an example, the system can save the energy equivalent of 1ℓ of gas/petrol while running in city traffic for 100 km.

12)MOTOR:

The Prius has two electric motor/generators.  They are very similar in construction, but different in size. Both are three-phase synchronous AC permanent magnet motors. This sounds more complicated than it really is. The rotor (the part that spins the shaft) is a just a big, powerful magnet and has no electrical connections. The stator (the part that stays still and is fixed to the rest of the car) contains three sets of windings. When current is passed in one direction through one set of windings the rotor is attracted to a particular position. By passing current sequentially through each set of windings first on one direction and then in the other the rotor can be made to move from one position to the next and therefore rotate. This is a simplistic explanation, but captures the essence of this type of motor.
 
If the rotor is spun by an outside force, an electric current flows in each set of windings in turn and can be used to charge the battery or power the other motor. Thus, the same device can be a motor or a generator depending on whether current is pushed into the windings to attract the rotor magnet or drawn out and something else spins the rotor around. This is even more simplistic, but will serve for the depth of these explanations.
 
Motor/generator 1 (MG1) is connected to the sun gear of the power split device. It is the smaller of the two and is rated at a maximum power of about 18 kW. Traditionally, its role is described as starting the ICE and controlling the ICE spin rate by generating a variable amount of electrical power. Motor/generator 2 (MG2) is connected to the ring gear of the power split device and therefore to the reduction gears and hence the wheels. Thus it is capable of directly powering the car. It is the larger of the two and is rated at a maximum power of 33 kW in the Generation II Prius and 50 kW in the Generation III Prius. It is sometimes described as the "traction motor" and its traditional role is to power the car as a motor or recover braking energy as a generator.  Both motor/generators are water-cooled.

13)Hybrid Performance

            The key to a hybrid car is that the gasoline engine can be much smaller than the one in a conventional car and therefore more efficient. But how can this smaller engine provide the power your car needs to keep up with the more powerful cars on the road?

            Let’s compare a conventional car like to our hybrid car with its small gas engine and electric motor. The engine in the conventional car has more than enough power to handle any driving situation. The engine in the hybrid car is powerful enough to move the car along the freeway, but when it needs to get the car moving in a hurry, or go up a steep hill, it needs help. That help comes from the electric motor and battery this system steps in to provide the necessary extra power.

            The gas engine on a conventional car is sized for the peak power requirement. In fact most drivers use the peak power of their engines less than one percent of the time. The hybrid car uses much smaller engine one that is sized closer to the average power requirement than to the peak power.

14)HYBRID EFFICIENCY

Besides a smaller more efficient engine todays hybrids use many other tricks to increase the fuel  efficiency. Some of those tricks will help any type of car get better mileage, and some only apply to a hybrid. To squeeze every last mile out of a gallon  of gasoline , a hydrid car cad:

Recover energy and store it in the battery - Whenever you step on the brake , pedal in your car, you are removing energy from the car. The faster a car is going , the kinetic energy it has. The brakes of a car remove this energy and dissipates it is in the form of heat. A hydrid car capture some of this energy and store it in the battery to use later. It does this by using regenerative braking. That is, instead of just using the brakes to stop the car, the electric motor that drives the hydrid can also slow the car. In this mode the electric motor act as a generator and charges the batteries while the car is slowing down.

Sometimes shut down the engine – a hybrid car does not need to rely on the gasoline ehgine all of the time because it has an alternate power source – The electric motor batteries. So the hybrid car can sometimes turn off the gasoline engine, e.g. when the vehicle is stopped at red light

Used advanced aerodynamic to reduce drag – When you are driving on the free way most of the work your engine does goes into pushing the car throug the air this force is known as aerodynamic drag this drag force can be reduced in variety of ways.

One sure way the frontal of the car. Think of how a big SUV has to push a much greater area through the air than a tiny sport car.

Reducing disturbance around object that stick out of the car or eliminating them all together can also help the aerodynamics.For example, covers over the wheel housing smooth the air flow and reduce drag. And sometimes mirrors are replaced by small cameras.

Used low- rollihg resistance tires – The tires on most cars are optimised to give a smooth drive minimised noise and provide good traction in variety of wheather condition. But they are rarely optimised  of effiency. In fact the tires caused a surprising amount a drag while you are driving.

Light weight materials – Reducing the overall weight of a car is one easy way to increse mileage. A ligher vehicle uses less energy each time you acceratela or drive up a hill. Composite material like carbon fibre or light weight material like aluminium and magnesium can be used to reduce weight.

15)MATERIALS USED :

Ultra high strength sheet steel and hot stamped material have been adopted in the pillar reinforcements and roof cross members in order to achieve a simultaneously strong and light weight body.

Ultra high strength steel has aprroximately 1.6 times the strength of conventional high strength sheet steel. Further more the hot stamped material is approximately 2.5 times stronger. Therefore to provide the same strength of high strength sheet steel a weight reduction of 40% is achieved by using ultra high strength sheet steel and 60% by using hot stamped material.

Aluminium has been adopted as the material for the bonnet and the rear hatch pannel. As a result a weight reduction of 36% for the bonnet, 43% for the rear hatch has been achieved compared to same parts made of steel.

Aluminium is also employed in the brake cylinder together with a phenol resin piston. Aluminium is also alloy of choice for the steering knuckles, which reduces unsprung mass and weught.

16)WHAT’S AVAILABLE NOW?

            Three hybrid cars are now available in the United States the Honda civic hybrid, the honda insight and the toyota prius. We will be discussing the latter two, and although both of these cars are hybrids, they are actually quite different in character.

The honda insight price starts around $ 19,750, and the toyota prius starts around $20,510. Both cars have a gasoline engine an electric motor and batteries but what is where the similarities end.

The  honda insight which was introduced in early 2000 in U.S. , is designed to get the best possible mileage. The insight is small lightweight two seater with a tiny high effiency gas engine.

17)HYBRID MAINTENENCE

Both the Honda and the Toyota have long warrenties on the hybrid systems.

1.      The motors and batteries in these cars don’t require any maintenance over the life of the vehicle.

2.       The engine doesn’t require any maintenance over the life of vehicle.

3.       Because both hybrids have regenerative braking, the brake pads may even last a little longer than those in most cars.

However if you do have to replace the batteries after the warranty expires, it will most likely cost you several thousand dollars.

Like the insight the prius never needs to be recharged; the on board generator automatically maintains the proper level of charge in the batteries.

18)ADVANCED HUMAN/MACHINE INTERFACE:

Some of the features of human/machine interface in the hybrid cars are:

1.Multi info display:

In addition to the front digital cluster the main human/machine interface is provided by the multi information display (EMV: Electronic Multi Vision) in combination with voice control and the multi functional steering wheel switches.

The 7-inch EMV display screen is touch sensitive and allows much better hand eye coordination by allowing the user to make the selection directly on screen and not through  a knob.

2. Voice control:

The EMV display is also equipped with a voice recognition system, optional with the navignational system. It offers the control of navigation, audio systems and the AC by almost 300 voice commands, allowing the driver to operate systems while drving with full concentration.

3. Steering switches:

These switches on the steering pad control the following functions:

·        Audio controls

·        Air conditioning controls

·        Car navigation controls

·        Voice recognition controls

·        Hands free controls

·        Air recycling controls

   4. Blue tooth hands free phone systems:

Blue tooth is an advanced wireless communication system working on a very high frequency (2.4 ghz). This is used here to enable the user to make or receive calls and talk hands free on mobile by operating steering pad switches.

 5. Egronomic shift lever:

A fingertip for easy shifting of gears easily operate this lever.

19)FUTURE FOR HYBRID VEHICLES AND CONCLUSION

Reference to an ultimate eco-car call to mind electric vehicles (EV) and fuel cells (FC). However, hybrid vehicles are not for mass production of Evs or FCs. Hybrid sytems improve the overall efficiency of any power train and can be used with petrol diesel or fuel cell system.

Unlike petrol and diesel engines the hybrid system is a technology and still has a lot of room for improvement. In any case this technology further the use of environmental technologies while delivering comforts and driving pleasure.

No matter which theory regarding the size of fossil fuels reserves one subscribes to it is certain that someday the reserves will run out. At that point cars will be certain to adopt systems such as hydrogen fuel cells. The hybrid technologies will be indispensable in making that system efficient.

Conclusion

Hybrid cars are perfect solution to the increasing levels of pollution.

It is a very good substitute and replacement for a conventional vehicle.    

REFERENCES

www.fueleconomy.gov/feg/byclass/Sport_Utility_Vehicle2007

www.toyota.com

  www.google.com

http://www.businessweek.com/innovate/