HYBRID CAR
Abstract
When most people are perfectly happy with their gasoline-powered cars. The reason is twofold: to reduce tailpipe emissions and to improve mileage. The current standards require that the average mileage of all the new cars sold by an automaker should be 27.5 mpg (8.55 liters per 100 km). This means that if an automaker sells one hybrid car that gets 60 mpg (3.92 liters per 100 km), it can then sell four big, expensive luxury cars that only get 20 mpg (11.76 liters per 100 km)! when a car pulled up to the gas pump lately and been shocked by the high price of gasoline? As the pump clicked past $20 or $30, maybe you thought about trading in car for something that gets better mileage. Or maybe worried that the car is contributing to the greenhouse effect. The auto industry has the technology to address these concerns. It's the hybrid car. You're probably aware of hybrid.
Any vehicle is a hybrid when it combines two or more sources of power. This is an improvement over the electric car, which uses gasoline engine along with electric motor powered by batteries. In the series system of the hybrid car engine driven generator is employed to recharge the batteries while the electric motor drives the car. Where as in parallel system the heat engine is directly connected to the electric motor.
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.
INTRODUCTION
We might wonder why anyone would build such a complicated machine when most people are perfectly happy with their gasoline-powered cars. The reason is twofold: to reduce tailpipe emissions and to improve mileage. The emissions standards dictate how much of each type of pollution a car is allowed to emit in to atmosphere. The amount is usually specified in grams per mile (g/mi). 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 of the car gets. But a car that burns twice as much gas to go a mile will generate approximately twice as much pollution. That pollution will have to be removed by the emissions control equipment on the car. So decreasing the fuel consumption of the car is one of the surest ways to decrease emissions. Carbon dioxide (CO2) is another type of pollution a car produces. The government does not regulate it, but scientists suspect that it contributes to global warming. Since it is not regulated, a car has no devices for removing CO2 from the exhaust, so a car that burns twice as much gas adds twice as much CO2 to the atmosphere. Automakers have another strong incentive to improve mileage. They are required by law to meet Corporate Average Fuel Economy (CAFE) standards. The current standards require that the average mileage of all the new cars sold by an automaker should be 27.5 mpg (8.55 liters per 100 km). This means that if an automaker sells one hybrid car that gets 60 mpg (3.92 liters per 100 km).
What is hybrid?
Any vehicle is a hybrid when it combines two or more sources of power. In fact, many people have probably owned a hybrid vehicle at some point. For example, a mo-ped (a motorized pedal bike) is a type of hybrid because it combines the power of a gasoline engine with the pedal power of its rider.
Hybrid vehicles are all around us. Most of the locomotives we see pulling trains are diesel-electric hybrids. We have diesel-electric trains -- these can draw electric power from overhead wires or run on diesel when they are away from the wires. Giant mining trucks are often diesel-electric hybrids.
The gasoline-electric hybrid car is just that -- a cross between a gasoline-powered car and an electric car.
How hybrid car works:
The below figure shows a gas-powered car. It has a fuel tank, which supplies gasoline to the engine. The engine then turns a transmission, which turns the wheels. an electric car, which has a set of batteries that provides electricity to an electric motor. The motor turns a transmission, and the transmission turns the wheels.
Hybrid structure:
Two types of hybrid system have been employed
1.Parallel system:
it has a fuel tank, which supplies gasoline to the engine. But it also has a set of batteries that supplies power to an electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels. a typical parallel hybrid car notice that the fuel tank and gas engine connect to the transmission. The batteries and electric motor also connect to the transmission independently. As a result, in a parallel hybrid, both the electric motor and the gas engine can provide propulsion power.
2.Series system:
By contrast, in a series hybrid the gasoline engine 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 vehicle.
Hybrid car configuration:
a hybrid concept vehicle
Gasoline engine - The hybrid car has a gasoline engine much like the one you will find on most cars. However, the engine on a hybrid is smaller and uses advanced technologies to reduce emissions and increase efficiency.
Fuel tank - The fuel tank in a hybrid is the energy storage device for the gasoline engine. Gasoline has a much higher energy density than batteries do. For example, it takes about 1,000 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 a generator. For example, when it needs to, it can draw energy from the batteries to accelerate the car. But acting as a generator, it can slow the car down and return energy to the 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 the energy storage device for the electric motor. Unlike the gasoline 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 have conventional transmissions. Others radically different ones.
Hybrid system operates in four phases:
Start/Stop - When we turn the ignition key of the Hybrid car, the electric motor comes to life. The electric motor, in turn, starts the gasoline engine. The car then performs a series of checks to determine if it can switch to electric-only operation: It checks to see if the batteries are charged, if the operating temperatures are okay and if interior climate control settings are in the appropriate range (the air conditioning's maximum setting requires the gasoline engine to run). If everything checks out, the engine will then shut off, leaving the car running under electric-only power. This process only takes a second or two.
When we come to a stop in the Hybrid car, the gasoline engine actually shuts off. The car runs on electric-only while you're at a stoplight or waiting in line at the drive-thru. The hybrid put a lot of effort into making the gasoline engine on-off cycles as smooth and seamless as possible, but testers reported a discernible shudder in the vehicle when the engine went on or off. This is common to all hybrid cars.
Electric Drive - As the Hybrid car accelerates from a stop, it does so under electric power. Electric motors are good at generating torque at lower rpm ranges, so they're perfect for this purpose. At about 25 mph, the gasoline engine starts back up. If we are driving in heavy city traffic, we could go all day using only electric power. The electric motor and gasoline engine operate in tandem up to highway cruising speeds.
Regenerative Braking - Whenever we apply the brakes on a car, the kinetic energy of the car's movement is dissipated as heat. In a hybrid car, the brakes take some of that energy and, using the electric motor as a generator, put power back into the batteries. This is why hybrids actually get better mileage in start/stop city driving than they do on open highways. Every red light recharges the batteries.
Electric Assisted Cruising - At highway cruising speeds (roughly 50 to 70 mph or 80 to 110 kph), the gasoline engine does most of the work. It's most efficient at this speed range. But because the Hybrid car has a small, four-cylinder engine, it needs a little help when passing. When a speed boost is called for, the electric motor kicks in and adds its horsepower to that of the gasoline engine.
The "Power Split Device"
The power split device is the heart of the hybrid car. This is a clever gearbox that hooks the gasoline engine, generator and electric motor together. It allows the car to operate like a parallel hybrid -- the electric motor can power the car by itself, the gas engine can power the car by itself or they can power the car together.
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The power split device also allows the car to operate like a series hybrid -- the gasoline engine can operate independently of the vehicle speed, charging the batteries or providing power to the wheels as needed. It also acts as a continuously variable transmission (CVT), eliminating the need for a manual or automatic transmission. Finally, because the power split device allows the generator to start the engine, the car does not need a starter.
The power split device is a planetary gear set . The electric motor is connected to the ring gear of the gear set. It is also directly connected to the differential, which drives the wheels. So, whatever speed the electric motor and ring gear spin at determines the speed of the car.
The generator is connected to the sun gear of the gear set, and the engine is connected to the planet carrier. The speed of the ring gear depends on all three components, so they all have to work together at all times to control the output speed.
Driving mechanism
When you accelerate, initially the electric motor and batteries provide all of the power. The ring gear of the power split device is connected to the electric motor, so it starts to spin with the motor. The planet carrier, which is connected to the engine, is stationary because the engine is not running. Since the ring gear is spinning, the planets have to spin, which causes the sun gear and generator to spin. As the car accelerates, the generator spins at whatever speed it needs to in order for the engine to remain off. You can see all of this in Figure.
Once the car reach about 40 mph (64 kph), the gasoline engine will turn on. The generator suddenly changes speed, causing the planet carrier to turn and start the engine. Once the engine is running, it settles into a constant speed while the generator varies its speed to match the output speed with the electric motor. If you are really accelerating hard, the motor will draw extra power from the batteries. Once you are up to freeway speed, the car will move under a combination of gas and electric power, with all of the electricity coming from the generator.
Efficient Engines for hybrid car
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:
ŽThe big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill.
ŽThe pistons and other internal components are heavier, requiring more energy each time they go up and down in the cylinder.
ŽThe displacement of the cylinders is larger, so more fuel is required by each cylinder.
ŽBigger engines usually have more cylinders, and each cylinder uses fuel every time the engine fires, even if the car isn't moving.
ŽThis 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 the smaller engine uses less energy. Both engines have to output the same amount of power to drive the car, but the small engine uses less power to drive itself.
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 car with its big V-8 engine, to our hybrid car with its small gas engine and electric motor. The engine in the in V-8 has more than enough power to handle any driving situation. The engine in the hybrid car is powerful enough to move the car along on 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 (those few times when you floor the accelerator pedal). In fact, most drivers use the peak power of their engines less than one percent of the time. The hybrid car uses a much smaller engine, one that is sized closer to the average power requirement than to the peak power.
Hybrid Efficiency
Besides a smaller, more efficient engine, today's hybrids use many other tricks to increase 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 hybrid car can:
Recover energy and store it in the battery - Whenever we step on the brake pedal in your car, we are removing energy from the car. The faster a car is going, the more kinetic energy it has. The brakes of a car remove this energy and dissipate it in the form of heat. A hybrid car can 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 hybrid can also slow the car. In this mode, the electric motor acts as a generator and charges the batteries while the car is slowing down.
Sometimes shut off the engine - A hybrid car does not need to rely on the gasoline engine all of the time because it has an alternate power source -- the electric motor and batteries. So the hybrid car can sometimes turn off the gasoline engine, for example when the vehicle is stopped at a red light.
Figure 5. The frontal area profile of a small and large car
Advanced aerodynamics to reduce drag - When we are driving on the freeway, most of the work we`r engine does goes into pushing the car through the air. This force is known as aerodynamic drag. This drag force can be reduced in a variety of ways. One sure way is to reduce the frontal area of the car (Figure 5). Think of how a big SUV has to push a much greater area through the air than a tiny sports car.
Reducing disturbances around objects that stick out from the car or eliminating them altogether can also help to improve the aerodynamics. For example, covers over the wheel housings smooth the airflow and reduce drag. And sometimes, mirrors are replaced with small cameras.
Low-rolling resistance tires - The tires on most cars are optimized to give a smooth ride, minimize noise, and provide good traction in a variety of weather conditions. But they are rarely optimized for efficiency. In fact, the tires cause a surprising amount of drag while you are driving. Hybrid cars use special tires that are both stiffer and inflated to a higher pressure than conventional tires. The result is that they cause about half the drag of regular tires.
Lightweight materials - Reducing the overall weight of a car is one easy way to increase the mileage. A lighter vehicle uses less energy each time you accelerate or drive up a hill. Composite materials like carbon fiber or lightweight metals like aluminum and magnesium can be used to reduce weight.
Conclusion
Over the past four years, more than 100,000 hybrids have been sold in the United States. Even though that's not a huge percentage of the more than 17 million new cars and trucks that are sold in the U.S. each year, it's enough of an incentive to get more manufacturers on the hybrid bandwagon. Analysts suggest that the market this year, alone, could muster up the sales of the past four combined.
Three hybrid cars are now available at present -- the Honda Civic Hybrid, the Honda Insight and the Toyota Prius.
