Hybrid Power Systems

Introduction


For thousands of years, propulsion for personal transportation was provided by a beast of burden hitched to a wooden wagon or sled. Then, about a hundred years ago, someone got the bright idea to attach a new-fangled contraption called the "internal combustion engine" to that wagon, creating "the horseless carriage." And so the automotive industry was born and with it came ongoing improvements to the piston-driven internal combustion engine until it evolved into the incredible, fuel-efficient, power plant that propels our modern vehicles. Yet, refinements aside, the governing principles behind the basic functioning of the typical modern automotive engine are identical to those of the Model-T Ford.

It is not that we haven't tried to come up with alternatives to the piston engine. We have developed numerous systems. In fact, electric cars have been around for as long as the piston engine. We have also tried steam, gas turbines, rotary engines and solar powered cars. But none of these could rival the power and efficiency of the internal combustion piston engine, fed by fossil fuel and connected to a transmission that turns the drive wheels through a series of shafts and gears.

Unfortunately, nagging problems like fuel shortages and air pollution necessitate a renewed search for alternative power sources for our personal transportation needs. While engineers have been ingenious in proposing new ideas for propulsion systems that are far more efficient than anything that we have today, the problem is that most of these technologies rely on fuels other than gasoline and there is no system in place to deliver these fuels to us at anything close to the price that we now pay for gas.

Can we build an infrastructure to deliver a better fuel, whatever it may be? Probably. But who will build it? The oil companies say that they will build such a system as soon as there are enough cars to make it profitable, but who will buy one of these cars before the required fuel is available? It's the classic catch-22.

Government intervened in California by requiring a percentage of cars sold to be zero-emission vehicles by a specified date. The only currently available technology that could meet the zero emissions goal was an electric car, so manufacturers dutifully designed and built electric cars for sale in California and even subsidized the cost of these vehicles to make them attractive for consumers. The program was a dismal failure. Few people wanted to bear the inconvenience of a car with a range of less than 100 miles, after which they had to plug it into an outlet for hours of recharging. The answer looked like it might have to to come from some kind of liquid or gaseous fuel that could be dumped into a vehicle in minutes and provide a range of a few hundred miles before the process had to be repeated. So we're back to the catch-22.

There is a partial answer to this conundrum available today in the form of an innovative technology that uses existing fuel supplies more efficiently. This promising technology combines a gasoline engine with an electric motor to stretch a gallon of gas further than ever before possible. The vehicles that use this technology are called Hybrids because they use a combination of a very efficient gasoline engine and a hi-tech electric motor to propel the vehicle.

The Concept: How the hybrid system works in simple terms

Despite the fact that they use electric motors that draw their power from a battery, hybrid vehicles do not have to be plugged in to recharge... Ever. The battery is recharged from two sources, and herein lies this system's advantage. The first source is from a generator powered by the internal combustion engine. The second source is through reclaiming the energy that is normally wasted slowing and stopping the vehicle. Let's look at the second method first because that is the most intriguing.

When you step on the brakes to slow a vehicle, you are counteracting the energy of a one or two ton projectile that wants to keep going because of inertia. In order to slow the vehicle, you must convert the energy of inertia into a different form: heat. The brakes heat up, absorbing the energy of the speeding vehicle, and the air that is directed around them then dissipates the heat, carrying it into the surroundings.

Many of us complain about how much it costs to heat a house, but here we are throwing all of our braking energy to the wind. What if we could capture some of that energy and use it later on to propel the vehicle? Well, that is exactly what a hybrid vehicle does. It uses a property that is inherent in all electric motors: the fact that electric motors and generators are exactly the same. If you send electricity through wires into a motor, it will cause the shaft of the motor to turn, but if you find another way to turn the shaft of an electric motor, it will generate electricity back through those wires.

The more work that a motor has to perform, the more electricity it requires. In the same way, the more electrical power you demand of a generator, the harder it is to turn the shaft. So, if we set the system up so that when you first step on the brakes, it connects this motor/generator to the battery in order to charge it, the effect will be to slow the vehicle down and, voila, we have free energy that we just stored in the battery to be used later to propel the car.

On the other side of the equation, the gasoline engine can be smaller because, when it needs extra power, the electric motor is there to assist in the acceleration using the free energy in the battery that was captured the last time that the brakes were applied. Because the engine doesn't have to be as powerful, it can be more compact and deliver much better gas mileage.

The Cars: What it's like to drive them
As of this writing, there are two, very affordable vehicles that you can buy that use hybrid technology, the Toyota Prius and the Honda Insight, with several more on the way.

The Toyota Prius, which is a 4-door, 5-passenger sedan, gets an EPA rating of 52 mpg city and 45 mpg highway while the Honda Insight, a small 2-passenger coupe gets 61 mpg city and 68 mpg highway. In the spring of 2002, you will also see a new Honda Civic hybrid that will match the 4-door 5-passenger layout of the Prius. The powertrain layout for the new Civic will be similar to the Insight. Ford will join the fray in 2003 with a hybrid version of the Escape SUV.

These cars are also environmentally friendly. Both the Prius and the Insight with the CVT (Automatic) transmission have earned an SULEV emissions rating. This means that if you were able to collect all the pollution that was emitted from one of these cars over 100,000 miles, you would just about fill a tea cup.

The Prius. Three components make up the powertrain of the Prius, a 4 cylinder high efficiency gasoline engine, a generator and an electric motor. These components are tied together with a single planetary gear set. There is no transmission beyond that simple gear arrangement.

To start the Prius, you turn the ignition switch to the start position, just like a normal car, but you don't hear anything. Did the car start? The indicators on the graphical display panel say that the car is running, but there is silence. Ok, on a leap of faith you put the Selector Lever in Drive and step on the accelerator pedal and, sure enough, the car takes off silently as though a large invisible hand is pushing you from behind.. As you reach about 15 mph, you notice that the gasoline engine is running though you did not hear it start.

During normal cruising above 15 mph, the gasoline engine is doing most of the work while the generator tops off the charge in the battery. Whenever you release the throttle or step on the brake, the electric motor doubles as a generator and charges the battery through regenerative braking. If more power is needed for accelerating or climbing a hill, the electric motor immediately kicks in to assist the gasoline engine using the energy that is stored in the battery. As you slow down and come to a stop, you realize that the gasoline engine is no longer running and the car is dead quiet, an eerie feeling that would have you breaking out into a cold sweat in an ordinary car.

Another thing that you notice as you accelerate is that this car does not shift. The planetary gear set acts as an infinitely variable transmission that gradually transitions from low gear to high gear in a smooth steady flow. The effect is that, while the car picks up speed, the engine seems to stay at its most efficient rpm.

Backing up is handled completely by the electric motor which serves to simplify the system and eliminate the need for a reverse
ear.

The Prius rides and handles like a typical Toyota Corolla, which is to say, competently. The exterior is about the size of a Corolla as well. Interior space, however, is more like that of a Camry with plenty of room for 5 adults to ride in comfort. There is also a reasonably sized trunk, despite the fact that there is a pretty large battery pack hidden back there.

The Toyota Prius is an environmentally friendly family sedan, that is quite pleasant to drive and easy to live with. Acceleration is a bit leisurely for some of the more aggressive drivers that I know, but it is competent and will handle most traffic situations without a problem.

The brake feel takes a bit of getting used to. The car stops well, but the brake pedal feel is unusual. On a normal car, the harder that you press on the brake pedal, the stronger the stopping action, but on the Prius, a light pressure on the brake will start with a light braking action that increases in severity even though pedal pressure hasn't changed. I'm not saying that this a safety issue at all, more of an idiosyncrasy. You will adapt to it after a while and learn to compensate until you barely notice it.

Overall, this is a nice family sedan that will make you feel good about yourself.

Click here for more photos of the Toyota Prius