Cooley On Cars
Car Tech 101, Hybrid systems explainedCNET's Brian Cooley explains the differences in hybrid technologies and how they efficiently manage fuel consumption and power.
I'm gonna simplify here and put hybrids in four categories -- mile, full or strong, plug-in, and performance. First, what's a hybrid? It's a car with two power plants. That could be any two kinds of power plants, but in modern parlance, it means a combustion engine and an electric motor. These two power plants can either work in parallel, both helping move the car at the same time, or in series, handing off back and forth to each other. Another key trait is regeneration, not growing a new leg but charging the battery when you brake or coast. The electric motor then flips modes and turns into a generator as the car's momentum turns it. And of course, hybrids have a large motive battery separate from the auxiliary battery that you see in your current car or toss on the side of the road. Let's look at the parts that make up a hybrid powertrain. Now, you start with a combustion engine and a fuel supply just like any other car. And by the way, it's almost always a gas engine. There are diesel hybrids out there. They're exceedingly rare. There's a motor generator. That's that motor that sometimes works as a generator, typically wedged in between the gas engine and the transmission. Working one way, it's a motor. Being worked by the car, it becomes a generator to put juice back in the battery. A motive battery, usually nickel-metal hydride, but increasingly lithium-ion and these are big batteries, much bigger than the one you get jump started, not unlike a very large version of what's in your laptop or your smartphone. An extra cooling system. That battery has got to be maintained at a critical temperature and it can't share the cooling system for the engine because this runs way hotter than the battery would be happy at. A battery wants things substantially cooler. Then, you get to the inverter and converter. The inverter changes DC to AC. Batteries store DC. The motor wants AC. The converter changes voltage stepping up or down depending who is asking for what within the hybrid system. You've got an ECU. It's an electronic control unit that makes all this stuff work together, and finally, if you've got a plug-in hybrid, there's an onboard charger which is not just the cable that goes to the wall, but its circuitry inside the car that pulses that juice to the battery the way it wants it. Now, I think you can see why they charge a few grand more for a hybrid. Now, the four ways all this tech hits the road. Mild hybrids. A mild hybrid basically uses an electric motor to help the combustion engines, but never take over moving the car by itself. It may be mild, but it's a useful architecture because combustion engines are really lousy at generating a lot more power when you need it right now, like from a stop or when you're passing. Electric motors are really good at giving an instantaneous push at exactly those times. So, they jump in to help the combustion engine. Mild hybrids usually have more modest electric motors and motive batteries, so they tend to have less of a hybrid premium cost. Examples of mild hybrids include the GM eAssist system which you'll find on the Chevy Cruze Eco, for example. So simple. It works easily like an alternator, helping the engine through a flexible belt. And the Honda Insight also made headlines as being one of the first really affordable, dedicated hybrid models after the Prius which brings us to full or strong hybrids. Strong hybrids have the option to run on electric only for meaningful distances and speeds, let's say up to a handful of miles at city speeds. These kinds of hybrids have larger batteries and motors and typically more sophisticated power blending system where the engine and the electric motor power meet. Now, when you talk about full hybrids, you're talking about the sweet spot of the market that, of course, brings you to the Prius now available in three variants. It's a family unto itself and it pretty much outsells all other hybrids combined, but also costs like the Ford Fusion and other mainstream models that now offer highly efficient hybrid variants that are getting some market traction. So, what's a plug-in hybrid? A plug-in, as the name suggests, can be plugged in. That allows it to use a larger battery pack than even a strong hybrid, larger than regeneration alone could ever sustain. So, plug-ins are sort of stronger hybrids offering up to tens of miles of electric range head up to highway speeds. You may not use gas at all for your commute if you just plug in daily. Now, when it comes to plug-in hybrids, the best known and the best selling is the Chevy Volt which, by the way, is also a range extender, kind of a corollary or an adjunct to hybrids. If you wanna learn about that, go see all about it in episode four CNET On Cars. Another well-known but very new plug-in hybrid is the Ford C-Max Energi. That is the plug-in version of a car that's also available as a non-plug-in hybrid. Now, what about performance hybrids? Hybrids aren't all for tree hugging. Some are for curve hugging. Unlike gas engines, electric motors deliver all of their torque from 1 RPM instead of having to rev up to peak power. And torque is what makes accelerating fun. So, by biasing a hybrid power system towards that aim, you can get tremendous acceleration as well as decent MPG. For example, when the Lexus GS Hybrid came out, it actually had worst highway MPG than the conventional V6, yet it was as fast as the V8. Now, when it comes to performance hybrids, this gets into a matter of some interpretation, but I definitely think that the Lexus GS Hybrid is one that was among the first to say electric is fast, not just efficient, and also Porche's 19. This car is going to have nearly 900 horsepower, but they won't all come from its V8. Almost 300 will come from its electric motors. Now, as you know, almost every hybrid model has its own MSRP, typically a few grand or more than a comparable combustion model. If you wanna run your own calculation on how long it will take to earn back the so-called hybrid penalty, we've got some calculator links at cnetoncars.com.