24 Aug 00
Cars which combine a conventional petrol engine with an electric motor to deliver improved fuel economy, reduced carbon dioxide emissions and, increasingly, improved performance.
Besides the general improvements in economy and emissions mentioned above, most have the advantage of being able to run in electric-only - and therefore zero-emissions - mode at city speeds and during stop-start low-speed motoring. They attract lower tax bandings than petrol counterparts, and are usually exempt from schemes such as London's congestion charge. They are also very fashionable, especially in the USA, as a way of boasting your eco-friendliness - Prince Charles, for example, has just taken delivery of a Toyota Prius, as also owned by many a Hollywood star. This makes them a relatively good investment, as secondhand demand has been very high and thus residual (resale) values remain strong.
Toyota Prius
As the petrol engine tends to be relatively small for the type of car, and the batteries and extra electric powertrain heavy, the engine has to work hard at higher speeds, and fuel economy can suffer. Hybrids are not suitable for people doing mainly motorway mileage. And in the city, battery life tends to be limited before the petrol engine has to kick in again, so range in electric-only mode is only short. Overall, given the high purchase costs compared to a mainstream car, a comparable diesel-engined model is often cheaper to run - and emits less carbon dioxide. The financial incentives are also less attractive now than they were, since the discontinuation of the government's Powershift grants scheme. Also, because of the extra space needed for the electric powertrain and batteries, boot space can be limited a little, with less scope for clever folding/sliding seats and so on in some models.
The main motive source is our good friend the internal combustion engine. But to eke out each gallon of fuel, the wheels are also driven by an electric motor. Depending upon road conditions, demand on the engine etc, a computer decides whether to use petrol or electric power - or both. Hence the name 'hybrid' - it's a cross between a petrol car and an electric car.
Different hybrid systems work in different combinations. The Honda Insight, for example, will use the petrol engine only when moving off from rest and at low speeds, but when accelerating, its computer asks the electric motor to chip in with extra help. As cruising speeds are reached, the electric motor is turned off, leaving petrol power only. As the driver starts to slow down - and this is the clever bit - the electric motor becomes a generator and transfers the kinetic energy of the car into the battery as electric power. This is called 'regenerative braking'. Whenever the car comes to a stop, the computer turns off the engine to save fuel and CO2 emissions.
