Hybrid Power Systems
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
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
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 gear.
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.
The Insight: The Honda Insight is a small two seat commuter car that gets great gas mileage and is a blast to drive and be seen in. It weighs in at a featherweight 1,887 pounds due to a lightweight aluminum body and frame that is 47-percent lighter than an equivalent steel body. Powering the Insight is a 1.0 liter, 3-cylinder VTEC engine coupled to an ultra-thin electric motor that is mounted between the engine and the transmission. The electric motor provides additional power to help the engine when it's needed during acceleration. When slowing down, the motor does double duty as a generator to recharge the battery pack. This "regenerative braking" captures energy that is normally lost through the brakes and stores it in the battery for later use to help propel the car.
Unlike the Prius, the Insight has a transmission, either a 5-speed manual or, for 2002, a new CVT automatic, and drives like a normal economy car. The engine is always running when the vehicle is moving, but will sometimes shut itself off when you stop in order to conserve fuel. As soon as you depress the clutch, the engine instantly restarts. The single electric motor is used as an assist to the 3 cylinder gasoline engine, which is the primary source of power. The electric motor becomes a generator when the computer calls upon it to charge the battery.
This system is elegant in its simplicity and certainly delivers the goods with an EPA rating of 61 mpg city and 68 mpg highway for the standard transmission model. These figures earn the Insight top billing as the most fuel efficient car sold in America. The CVT Equipped Insight comes in at a respectable 57 mpg city and 56 mpg highway.
During my week-long test drive of the stick-shift model, I rarely drove it like an economy car in my quest to find its performance potential. I was surprised by the better than 50 mpg average that this car delivered despite all the flogging,
Despite the great gas mileage, this car has good acceleration and is as much fun to drive on winding country roads as it is to dart around in city traffic.
There is only room in this car for two people and their bare essentials since there is very little storage space. As is typical for Honda, the handling and steering feel are excellent. The ride is another story, however. You will feel all the bumps and irregularities of the road surface as you drive this featherweight. Part of the reason for the choppy ride is the small, high-pressure tires that are tailored for the lowest rolling resistance possible.
If you are looking for a commuter car that won't break the bank, look no further. This is your puppy. If you like Honda but need a car that has more room, a new Civic Hybrid is just around the corner. The Honda Civic Hybrid has a new 1.3-liter i-DSI 4-cylinder engine and more advanced version of the Integrated Motor Assist (IMA) system that powers the Insight. Gas mileage is expected to be around 50 MPG for both city and highway driving and there will be room for 5.
The Toyota Prius: The components that are used to perform this magic on the Toyota Prius include: a 4 cylinder high efficiency gasoline engine and two combination generator/motors. One is mounted to the gasoline engine where the flywheel normally sits. Toyota calls this one a generator although it also serves as a starter motor. The other motor is connected to the drive wheels and is used to move the car at low speeds and assist the engine when more power is required. This motor does double duty as a generator whenever the car is coasting or slowing down. All three components (gasoline engine and 2 motor/generators) are connected through a planetary gear set. There is also a 274 volt nickel-metal hydride battery that is mounted between the back seat and the trunk.
As you can see from the picture, the combination gasoline engine,generator and electric motor forms a very compact unit that drives the frontwheels.
As I mentioned before, the generator that is mounted to the back of the engine does double duty as a starter motor. To start the engine, the VVTi system increases valve overlap to reduce compression. The generator/motor then spins the engine up to about 1000 rpm. As soon as the engine is spinning up to speed, compression is brought back on line along with spark and fuel and the engine is running. No typical starter noise, no bucking, no lurching, just a smooth, almost unnoticed transition of power from electric drive to gasoline engine power.
The diagram below shows how the three components are connected through the planetary gear (power split device). The engine is connected to the planetary carrier, the generator is connected to the sun gear and the output shaft and motor are both connected to the ring gear.
If there is no load on the generator, then the engine will simply spin the generator through the planetary gears and not be able to move the car. This is what happens when the selector is in Neutral or Park. If a load is placed on the generator, either to charge the battery or to directly power the electric motor, then a portion of the engine's power will be directed through the planetary gear to the drive wheels to move the vehicle. By regulating the load on the generator, the engine RPM can be held constant while accelerating the car, thereby acting like an infinitely variable transmission. Pretty ingenious, isn't it?
By adding that second motor/generator and a single planetary gearset, Toyota was able to completely eliminate the transmission and still have the effect of a continuously variable transmission. But what about reverse gear? Simple. Backing up is handled entirely by the electric motor.
The following diagrams show the power system for the Toyota Prius
The Honda Insight powertrain is fairly straight forward front-wheel drive arrangement, consisting of a small three cylinder high-efficiency engine that is coupled to an ultra-thin electric motor mounted between the engine and either a conventional 5-speed standard shift transmission or a new Continuously Variable Automatic Transmission (CVT). The battery is a 144 volt Nickel Metal Hydride (Ni-MH) unit that contains 120 cells of 1.2 volts each
The Insight has an all-aluminum body structure that is about half the weight of an equivalent steel body. The total weight of the Insight is a remarkable 1,856 pounds
Hybrid technology is an interim solution that can lessen, but not eradicate, our dependence on fossil fuel. There is another new technology called "Fuel Cells" that should be available by the end of the decade that will eliminate our dependence on non-renewable resources.
Fuel cells convert hydrogen and oxygen to electricity without going through a combustion process; thereby virtually eliminating emissions. They also operate at much higher efficiencies than internal combustion engines, producing double the amount of energy.
Most of the world's auto manufacturers have a fuel cell project in progress and virtually all of them agree that fuel cells are the propulsion system of the future.
Honda is saying that by 2010, you should expect mid-sized sedans with all the trimmings and power that we enjoy today, fueled by hydrogen that you can produce yourself in your garage using a Home Energy Station connected to your natural gas supply line. Not only will this Home Energy Station produce Hydrogen for your fuel-cell car, it will also help to heat your home.
Watch for our in-depth article on fuel cells, coming soon.