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Power Train

Is there a future for hybrid vehicles? Part 2

September 13, 2010 | David Swanson | 222901081
Is there a future for hybrid vehicles? Part 2 David Swanson, Principal Engineer, STMicroelectronics looks at what regenerative braking and energy harvesting solutions bring to hybrid vehicle powertrain technology.
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Part 1 of this feature looked at the "conservation of energy" and the hybrid mystique.

The other thing that hybrid vehicle powertrain technology brings to the table is regenerative braking—converting some of a car's forward motion back into electrical energy to be used later. There are a few methods or strategies to do this. In each technique not all of the forward motion is returned to electrical energy. Some is consumed in ICE (internal combustion engine) compression (using the engine as a brake), a good portion is converted into electricity, while the remaining is converted into heat by the brake pads.

Regenerative braking takes the electric motor and drives it in such a way that instead of behaving like a motor driving the wheels, it behaves like a generator where the wheels drive it. Regenerative braking is not limited to hybrid powertrains. It can be used in any powertrain where electric motors are used. So a fully electric vehicle would also take advantage of regenerative braking.

Of the two methods, parallel and series (or sequential), parallel is the easiest to control as everything is somewhat linear. Pedal pressure increases both mechanical and electrical braking forces. Series systems must hold off the mechanical braking until the regenerative braking mechanism has done all it can. This is not so simple.

Regenerative braking explained

So between keeping the ICE in the sweet spot and regenerative braking, we gain quite a bit of efficiency. Hybrids do fill a need. Hybrid automobiles can be reasonable little cars that get decent to good gas mileage—for a price.

ICE: Not dead yet
However, there are some new ICE technologies, or new applications of gasoline engine technologies, that might make a big dent in the hybrid universe.

As and example, from 1980 to 1986 I owned a very small and economical 1974 model car. I bought it used before I started college and it got me through those lean years. It was first owned by a mechanic who had done some tweaking to it to improve the gas mileage. I was able to get 45 - 50 mpg out of the thing driving the back roads of North Carolina (there weren’t too many highways in NC back then). I will have to admit, it was a very small car with 12-inch wheels and a little bit more than enough power to get out of its own way. My point is, that in 1980 someone was able to use 1974 technology to make a better than 45 mpg vehicle. Don’t you think that we could do that and more using variable valve technology, gasoline direct injection, and turbo boosting? I would think it could be done for a lot less money and hassle than making a hybrid powertrain.

There are people in the industry who are thinking similarly. Recently, I learned of a major U.S. car manufacturer that is developing a small powerplant using these technologies that will produce over 120 hp and get into upper 40s mpg. I can’t imagine that this configuration will cost nearly as much as a hybrid, or weigh as much or be as nearly complex, either. And it won’t be consuming nasty materials like those found in nickel metal hydride or lithium ion batteries. (Even lead acid batteries are nasty.)

This reminds me of the trusty old 12V Lundell alternator. A few years ago some of us predicted that old (for automotive) 1960s technology would go the way of the dinosaurs in lieu of the 42V system. The mantra went, “Vehicle electrical demands were becoming too great for the Lundell technology to support it at 12V”. In the end the costs and complexity of the conversion to 42V was too much. Motivated by the cost penalties and the technical hurdles associated with 42V systems, the vehicle OEMs were able to trim the fat a bit, electronics efficiencies improved, and the alternator manufacturers were able to enhance the alternator a bit and, mmm, we don’t even hear of 42V vehicles any more.

The hybrid electric vehicle has come a lot farther than the 42V systems. There are several production vehicles on the road today. When we ask the smart guys (analysts) with the crystal balls and Tarot cards about what to expect in the future regarding hybrid electric vehicles, they tell us that HEVs will not be increasing much in demand even six years from now. Across the board, HEVs are still going to be just a small fraction of the total car production.

I think we could say that hybrids are really only purchased by those who believe in the technology and can afford it. I know of one family that owns a bright shiny red luxury roadster, a fully optioned out minivan, and a hybrid. I am not thinking that they bought the hybrid for the mileage.

Most of us are just trying get from one place to another without it costing too much. If we can do that in a non-hybrid technology car for much less money (tax breaks aside) we will. The OEMs understand this and are working on the ICE technology that can compete with hybrid. It will take trimming the fat here, adjusting there, but I think it can be done. Like the Lundell alternator, the ICE will be a hard one to beat.

A better future

In reality the affordable fuel cell is what is going to change things dramatically. Where refueling is not much different than what happens today. You will hook up a hose to your car and obtain the stuff that will make it go. It won’t be recharging (which takes hours) or replacing a depleted battery pack by popping in a charged one (which means you don’t know the quality of the battery you just installed). The batteries, perhaps along with ultracapacitors, will only be needed for acceleration and braking energy storage so there won’t be the need for so many of them.

The two biggest hurdles for fuel cell technology are making it industrialize-able (read affordable and reliable) and producing a fuel that is not based on hydrocarbons (i.e. not extracting hydrogen from fossil fuels). Truly, the hydrocarbons used to make hydrogen will be much more efficiently used than if burned in an ICE (an internal combustion engine is terribly inefficient). But the resulting efficiency improvement alone from fuel cells will be worth it even if we have to first use hydrocarbons to make it work. In the long run though, we will need to make hydrogen, or whatever we end up using, from something other than fossil fuels.

Then we can have a true electric vehicle that has the range and performance similar to what we have grown accustomed to with gasoline engines. That technology will be well accepted by the masses. At that point hybrids will either evolve to include fuel cells as an alternative to massive battery packs and charging systems—or become an interesting moment in our history.

David Swanson is principal engineer at STMicroelectronics.

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