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Is a hybrid car, one that uses a small petrol engine to charge batteries only?

Is it more efficient to have hybrid cars with engines that charge batteries to drive the wheels, or an engine that directly drives the wheels but has a electric motor as a standby ?

Public Comments

1. Usually a hybrid car has a normal petrol engine, but a set of batteries and a SMALL electric motor for use at low speeds or (supposedly) for a boost of power.
2. Some hybrid cars such as the Lexus LS600h (5.0L V8) have quite large petrol engines. As previously answered, the principle of a hybrid petrol/electric car is that the electric motor gets the car moving from a stop or very slow speed, this is a time when a petrol engine is particularly inefficient and an electric motor with it's linear torque output is at it's most advantageous over a petrol engine. Once the car has reached a certain speed the petrol engine starts up and delivers power to the wheels as well, this continues to a stage where at steady cruising speed the petrol engine is delivering all the power and the electric motor has shut off. At this time the petrol engine is charging the motors batteries up as well. Hybrid cars therefore only show significant fuel consumption benefits on cars that experience a fair amount of slow and stop start town driving. The difference in fuel consumption between a standard car and a hybrid mostly used on long distance motorway driving would be much smaller and maybe negligable.
3. All of the hybrid cars on the road today are driven by a standard transmission which is connected to both an electric motor and a conventional gas engine. The Chevrolet Volt due out in 2010 will probably be the first car that will be driven only by an electric motor. The engine will only drive a generator.
4. It depends on what you consider hybrid. The Chevy Volt is considered to be a series hybrid like you are describing. GM prefers to call it an Extended Range Electric Vehicle (ER-EV). In the Volt there is only an electric motor for propulsion, the engine/generator only helps the battery out when it runs low. For the first 40 miles the car runs on electricity from your home (much cheaper in the long run) thus no gas is used if your daily trip is shorter than 40 miles. Statistics show 80% of Americans will not need to buy fuel. The Prius is a parallel hybrid. Either or both the gas engine and electric motor can drive the wheels through a complex transmission. The electric motor is only there to fill in the gas engine's deficiencies. You can buy a kit (plug-in conversion) to beef up the battery allowing a longer all electric range but if you want to go faster than 35 or you stomp on the gas to hard the engine kicks in. The stock Toyota Prius goes nowhere without gas. A gas engine turning a generator making electricity to turn a motor to turn the wheels will never be as efficient as a transmission. As gas car is only 20% efficient at best, 80% of that energy you paid for goes to pushing the car forward. In the all electric car over 80% of that energy goes to pushing the car forward and as a bonus it is 1/10 the cost to go a mile. Why don't we have electric cars? The existing system will make less money in fuel sales, vehicle sales, repairs and maintenance.