ALT-5 How Hybrid Cars Work
When we hear the word Hybrid, we think of new and innovative, but hybrids have been around for awhile. A mo-ped is a type of hybrid because it combines the gas engine with the pedal power of the rider. Most locomotives pulling trains are diesel-electric hybrids. Cities like Seattle have diesel-electric buses that can draw electric power from overhead wires or run on diesel when away from the wires. Submarines are hybrids...some are nuclear-electric and some are diesel-electric. Any vehicle that combines the use of two or more sources of power that can directly or indirectly propel the vehicle is a hybrid. Most of the hybrids on our roads right now are gasoline-electric.
A gasoline-electric hybrid car is a cross between a gasoline-powered car and an electric car. In a typical gas-powered car, the fuel tank supplies gas to the engine which turns a transmission which turns the wheels. An electric car has a set of batteries that provide electricity to an electric motor which turns the transmission which turns the wheels. A hybrid is a compromise between the two. It's goal is to increase the mileage and reduce the emissions of a gas-powered car and overcome the shorcomings of the electric car.
To be of any use to the driver, a car must have minimum requirements such as being able to drive at lease 300 miles before re-fueling; refueling must be quick and easy; and you should be able to keep up with the other traffic on the road. A gas car meets these requirements but produces pollution and usually gets poor gas mileage. An electric car produces almost no pollution, but can only go 50-100 miles before it needs to be recharged. The electric car has typically been very slow and inconvenient to recharge.
A gasoline-electric car is trying to combine the best of both worlds using both gas power and electric power. The gasoline engine on a hybrid is similar to what we are used to but is smaller and reduces emissions and increases efficiency. The fuel tank is the energy storage device in a hybrid's gas engine. The electric motor on a hybrid car acts as a motor and a generator. It can draw energy from the batteries to accelerate, and it can slow down the car and return energy back to the batteries. The generator is similar to an electric motor but is only to produce electrical power. The batteries in a hybrid store the energy for the electric motor. The electric motor on a hybrid can put energy into the batteries and also draw energy from them. The trasmissions on a hybrid car are many times conventional transmissions. Some, like the Toyota Prius, have radically different ones.
A parallel hybrid has a fuel tank that supplies the gasoline to the engine and a set of batteries that supplies the power to the electric motor. Both the engine and the electric motor can turn the transmission at the same time and the transmission turns the wheels. In a series hybrid, the gas engine turns a generator which can charge the batteries or power an electric motor that drives the transmission. This means the gas engine never directly powers the vehicle.
In a hybrid car, the gasoline engine can be much smaller and more efficient than in a conventional car. The hybrid engine is powerful enough to move on the freeway, but if it needs to go up a steep hill, or accelerate quickly, it needs help which comes from the electric motor and battery-giving the extra power needed.
Today's hybrids also have a few tricks to increase fuel efficiency. A hybrid can recover energy and store it in the battery. When you step on the brake in your car, you remove energy from the car. The faster a car is going, the more kinetic energy it has. The brakes 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 for later use. Instead of just using the brakes to stop the car, the electric motor can slow the car and act as a generator and charges the batteries while the car is slowing down. This is called regenerative braking. Sometimes the hybrid car will turn off the gas engine and use the electric motor and batteries to save fuel, usually when stopped at a red light. Tires on most cars are optimized to give a smooth ride, and provide good traction in various weather conditions while minimizing noise. But they creat a lot of drag when you are driving. Hybrid cars use special tires that are stiffer and inflated to a higher pressure than conventional tires which causes about half the normal drag. Some hybrids use composite materials like carbon fiber or aluminum and magnesium to reduce weight.
The Toyota Prius came out in Japan at the end of 1997 and is designed to reduce emmissions in urban areas. It uses a specially designed parallel hybrid powertrain to do this. The Prius meets California's low emission standard and the powertrain is capable of accelerating the car to speeds up to 15 mph on electric power alone. This gives better city mileage. The Prius has two feature to optimize efficiency and reduce emissions. 1. Its engine can accelerate to 15 mph before switching on the gas engine. Once the engine starts, it operates in a narrow speed band. 2. Its uses a unique power split device which keeps the engine in its most efficient load and speed range most of its driving time. The 1.5-liter engine runs at a maximum speed of 5,000 rpm making 76 horsepower. Keeping the maximum speed of the engine low allows for the use of lighter component that improve efficiency. The electric motor on the Prius is rated at 67 horse power from 1,200 to 1,540 rpm. It produces 295 pound-feet of torgue from 0 to 1,200 rpm without using the gas engine.(http://auto.howstuffworks.com/hybrid-car7.htm)
The power split device is a gearbox that hooks the gas engine, generator and the electric motor together. It allows the car to operate like a parallel hybrid (the electric motor or the gas engine can power the car by itself, or they can operate together). The power split device can also operate like a serice hybrid (the gas engine can operate no matter how fast you are driving and charges the batteries or provides power to the wheels when needed.) It also acts as a continuously variable transmission (CVT) which eliminates the need for a manual or automatic transmission. And since the generator starts the engine, the car doesn't 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.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." (http://auto.howstuffworks.com/hybrid-car7.htm)
"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. " (http://auto.howstuffworks.com/hybrid-car7.htm)
When you accelerate, the electric motor and batteries provide all of the initial power. As the car accelerates, the generator spins at whatever speed it needs to...to keep the engine off. Once you reach about 40 mph the gas engine will turn on. Once the engine is running, it uses a constant speed while the generator varies its speed to match the output speed with the electric motor. If you are accelerating hard, the motor will draw extra power from the batteries. Once up to highway speed, the car will use a combination of gas and electric power with all of the electricity coming from the generator. The Prius never needs to be recharged. The onboard generator automatically keeps the batteries charged. The Prius has an 8 year-100,000-mile warranty on the battery and hybrid systems. The motors and batteries usually don't require any maintenance over the life of the car.
Sources..How Hybrids work...http://www.fueleconomy.gov/Feg/hybridtech.shtmlHow Hybrid cars work...http://www.howstuffworks.com/hybrid-car.htmhttp://www.hybridcenter.org/hybrid-center-how-hybrid-cars-work-under-the-hood.htmlhttp://www.hybrid-car.org/hybrid-cars-work.html
