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Just what is a hybrid car? Andrew English is confused...

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By Andrew English

03rd October 2007

My Oxford English Dictionary tells me a hybrid is the ‘offspring of two plants or animals’. If only the automotive world was so simple. Hybrids were a major theme of last month’s Frankfurt Motor Show – you couldn’t move for concepts of them. Mercedes had 15 and I spent the day tripping over gorgeous, pouting TV presenters introducing “der neue Mercedes hybrid Coelacanth”, or the “Ford hybrid Sideboard”. At least that’s what they sounded like. But what is a hybrid?


	The industry is calling everything a hybrid, whether it produces enough power to drive the car or run an iPod

Car makers are fond of muddying the waters, especially if they can put an environmental spin on their products. The Smart stop/go system, for instance, is termed a ‘hybrid’, but is nothing of the sort. Toyota has been trading on its hybrid credentials to hide the fact that its European fleet average carbon dioxide emissions are greater than Ford’s. Yet General Motors doesn’t call its E-Flex plug-in serial hybrid a hybrid. GM boss Rick Wagoner named it: “The electrification of the automobile.”

There’s nothing new in dual power. Diesel/electric railway engines have been around for years, and most quarry trucks and excavators use diesel and electric or hydraulic units. One of the earliest hybrids was on the 1901 Lohner Chaise Radnabenmotor, designed by a young Ferdinand Porsche – it used a battery pack and four in-wheel motors. The petrol/electric driveline was cumbersome, but eventually found its way to Mercedes, which sold it as the Mixte. As the packaging benefits of petrol and diesel power became clear, hybrids disappeared, until the oil shortages of the Seventies prompted more research. Later, production cars such as Audi’s 1989 A4-based Duo and Volkswagen’s Golf hybrid of the early Nineties proved the concept, if not the economics.

In automotive terms, hybrid means twin power sources, and the primary one can be diesel, petrol or fuel cell. The second is mostly electricity, stored in batteries or ultra capacitors, although research is being done on flywheel-based energy-recovery systems by Xtrac and Torotrak for the new Formula One rules.

The idea is that the power sources complement each other. In the world’s most popular hybrid – the Toyota Prius – electricity generation, storage and drive systems propel the vehicle in low-speed manoeuvres and keep the petrol engine running at its most efficient rpm. The electrical set-up also increases overall efficiency as the car can use a smaller petrol engine.

Honda’s hybrid system is called Integrated Motor Assist, because that’s what it does. Electricity is generated from the primary engine, which runs the generator to top up the batteries, or the car’s kinetic energy, which also drives the generator when decelerating and braking. In the latter mode, the hybrid’s energy is free, as in a normal car such energy is wasted as heat by the brakes.

However, when the battery is full, there is nowhere for the electricity to go, so it is wasted as heat. And as you must slow down or brake to generate this ‘free’ power, if you simply drive at a steady speed there is no advantage to having a hybrid. The balance of battery and engine size against charging capacity is crucial to the success of a hybrid design.

Not that you would have learned any of the above from Frankfurt, where the industry reacted to pleas from politicians that “something must be done” by calling everything a hybrid, whether it produces enough power to drive the car or run an iPod. “I do admire you lot,” said one PR, “trying to explain the intricacies of hybrids to the general public. I just find it bewildering.” So do I. Will someone please tell me what a hybrid actually is?