| Sustainable Transportation Options |
Diana Volovelskay, San Francisco Marketing Coordinator
Car Sharing
Flexcar, a no-frills, self-serve car sharing company established in Seattle in 1999, stocks 40% of its fleet with hybrid cars. You can choose from a Honda Civic, Toyota Prius or Honda Accord. This service reduces congestion, air pollution, and energy use, increases use of public transit, and contributes to sustainable communities. Both the Glumac Portland office and the Seattle office have been utilizing Flexcar since 2001, and the San Francisco office has joined in the initiative this year. In addition, the San Francisco office has purchased a Toyota Prius company car for use by employees.
There are several hybrid cars to choose from at Flexcar, from a Honda Civic, a Honda Accord, or a Toyota Prius. The hourly fee rate covers gas, insurance, and unlimited miles. Each vehicle has its own reserved parking space in parking lots located throughout the city. An assigned keycard is all that is required to open the vehicle once reserved it via the internet at Flexcar or over the phone.
Hybrid Types
Hybrid cars are a growing environmentally conscious, sustainable trend in large cities. Using 50 percent electrical power and 50 percent gasoline, you get 20 to 30 more miles per gallon, which is a great alternative to the standard automobile.
There are two types of hybrid cars that combine the two power sources of electricity and gasoline in different ways. The first, known as a parallel hybrid, has a fuel tank that supplies gasoline to the engine and a set of batteries that supplies power to the electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels.
The second is a series hybrid, where 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.
The key to a hybrid car is that the gasoline engine is smaller than that of a conventional car, and is therefore more efficient. Most cars require a large engine to produce enough power to accelerate quickly, and most drivers only use the peak power of their engines less than one percent of the time. However, in a small engine, the efficiency is improved by using smaller, lighter parts, by reducing the number of cylinders, and by operating the engine closer to its maximum load, thus sizing the engine closer to the average power requirement than to the peak power.
Hybrid Structure
Gasoline-electric 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 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, like the Honda Insight, have conventional transmissions. Others, like the Toyota Prius, have radically different ones.
Fuel Efficiency
Hybrids increase fuel efficiency by:
- 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 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.
- Partial engine shut off - 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.
- Advanced aerodynamics to reduce drag - When you are driving on the freeway, most of the work your 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. 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.
Source
1. Julia Layton and Karim Nice, "How Stuff Works," n.d., <http://www.howstuffworks.com/hybrid-car.htm> (21 June 2006)
