HYBRID FLAVORS
You’ve no doubt noticed that as gas prices have risen during the past year, so has interest in hybrid vehicles - both those currently on sale, and those that are in the pipelines of a variety of manufacturers.
But there seems to be a bit of confusion about the definition of a hybrid – and also about the divisions among the hybrid family.
So let’s start from first principles to clear that up.
According to the
SAE International, a leading society of engineers, a hybrid vehicle is one that has "both a rechargeable energy storage system (RESS) capable of releasing and capturing energy and an energy generating device that converts consumable fuels into propulsion energy."
So if a vehicle has two power sources, one of which is an RESS such as a battery pack, it is, by definition, a hybrid.
But because hybrids are separated into types - series, parallel and series/parallel- and because there are also plug-in hybrids, mild hybrids and full hybrids, a further bit of explanation is in order.
First, a series hybrid is one in which two power sources work in series, with only one of them, an electric motor, connected to the drive wheels. The other, a gas engine, for instance, turns a generator to power the electric motor or to provide a charge for that motor’s batteries. Chevrolet’s Volt, and also Chrysler Corp.’s recently announced gas/electric concept cars, are series hybrids.
A parallel hybrid is a vehicle that has two power sources – a gas engine and an electric motor, for instance - and draws power from both of them, such as the Honda and some GM systems do. The power sources parallel each other, in other words.
A series/parallel hybrid is one that has two power sources and that can operate in either series or parallel mode, depending upon the situation.
In other words, the gas engine can drive the vehicle’s wheels directly, the electric motor can drive the vehicle’s wheels directly, or the two can work in tandem to drive the wheels. This is the way
Toyota’s Hybrid Synergy Drive works in our Prius and in our other hybrid vehicles.
A plug-in hybrid is any of the above types that has, in addition to its on-board power-generation capabilities, high-capacity batteries – these may be of various chemistry types – that provide an extended electric-only mode. Plug-in hybrids can be connected to an electrical outlet so that batteries can be recharged while the vehicle is at rest. Toyota will begin U.S. fleet tests of our Prius plug-in hybrid in 2009, and GM and Chrysler also have announced plans for plug-in hybrids.
A mild hybrid relies on a conventional gas engine to move the vehicle and an electric motor, sometimes built into the vehicle’s alternator and sometimes incorporated into its transmission, for providing acceleration assistance when that’s needed, and to start the gas engine, which shuts down automatically when the vehicle is stopped or is slowing. Both Honda and GM offer such systems.
A full hybrid, such as the Prius or the Ford Escape, is one that can be powered solely by its electric motor, solely by its gas engine, or jointly by both, as needed.
It’s clear that as the hybrid has gained public acceptance, each manufacturer has developed its own idea of which hybrid type is the right one for today’s drivers. We hope that the information presented here will help illustrate the differences between the various hybrid approaches. Ultimately consumers will decide which approach is best for them.