In a move that highlights the rise of micro-hybrid technology in next-generation vehicles, General Motors (GM) has chosen to stick with start-stop technology on its 2014 Chevy Malibu, while discarding a more costly mild hybrid system.
GM said that it made the decision because start-stop, along with certain engine enhancements, can provide similar fuel economy benefits, while eliminating the need for customers to pay for a feature that includes an extra lithium-ion battery. The start-stop (or micro-hybrid) version of the mid-sized sedan would use a pair of small lead-acid batteries and a 12V electrical architecture. ”A start-stop system with a 12V lead-acid battery is very cost effective, especially if you’re able to combine it with enhancements to your internal combustion engine,” GM spokesman Kevin Kelly told Design News.
The 2014 Chevy Malibu offers start-stop technology by employing lead-acid batteries in the front and rear. (Source: General Motors)
The new Malibu uses a 2.5-liter V-6 engine that includes fuel-saving features, such as direct injection and variable valve timing. Each of those features is said to provide a fuel efficiency boost of a few percent. When combined with start-stop technology, in which the engine is turned off at traffic lights and stop signs, a fuel efficiency gain of as much as 15 percent is possible.
Chevrolet previously offered a version of the Malibu that included a feature called eAssist, which is generically described as a “mild hybrid” technology. A mild-hybrid incorporates a start-stop system, regenerative braking technology, and a power-assist for the engine. To do that, the vehicle needs additional components, including a belted alternator-starter, lithium-ion battery, and a higher-voltage electrical architecture (GM’s e-Assist uses a 110V architecture). GM said it will keep the eAssist system on other vehicles, including the Buick LaCrosse, Buick Regal, and Chevy Impala.
Up until now, the auto industry has considered mild-hybrid technology to be a stepping stone between the micro-hybrid and full hybrid (such as the Toyota Prius). In general, micro-hybrids offered a 5 percent efficiency bump, whereas mild-hybrids offered 15 percent. Industry analysts are now saying that engine advancements are potentially blurring the line between the two.
”As internal combustion engines get more efficient -- smaller displacement, less cylinders, and turbocharging -- they give a substantial boost to fuel efficiency, which is then made even better by micro-hybridization,” Lux Research analyst Cosmin Laslau wrote in an email to Design News. “That’s what happened with the Chevy Malibu: The micro-hybrid became so good, it matched the more expensive mild hybrid, so there was no reason to keep the latter around. Look for this trend to continue -- mild hybrids are an endangered species.”
One question that I have regarding this start/stop technology is: when the car shuts down (like at a stoplight) is there a delay when you want to go?
This also has me wondering, is the increase in mpg targeting city driving for start/stop and the engine efficiency increases for overall increase in mpg, but especially the highway mpg? How is the advancement in transmissions aiding in this pursuit?
Cap'n, this is a good decision. Large battery packs and more complex mechanism add costs, weight and complexity. The ICE advances and the ability to use lower weight materials is a way to go for near term increases in efficiency. I am especially impressed with the increased efficiency of ICE engines. Some of these are due primarily to the control system. This means that current engines can, in many cases, be improved by just reprogramming. Since the only measure that really counts is Total Cost of Ownership (TCO), which most engineers should be familiar with. Until battery technology changes dramatically, the ICE will always have an edge here. With lots of new oil supply coming on-line, the price will stabalize and then come down. As much of that new supply is in more stable parts of the world, we could see fairly dramatic drops in fuel prices.
Very interesting point, naperlou. If oil prices do what you say, then it's going to be hard for plug-in hybrids and pure electrics to get as good a foothold. In that case, I think we'll see a lot of interest in micro-hybrids. On the other hand, if gasoline reaches $6 per gallon over the next decade, most studies show that EV sales will rise.
What about accessories driven by the engine ? I have a hybrid Aspen and my wife has a Prius hybrid. When stopped in traffic, or in slow moving traffic, the battery drives the vehicle and accessories, like air conditioning. When a micro-hybrid stops, doesn't the air conditioning compressor also stop ? This may seem like a minor inconvience, but what will the customer reaction be if they lose air conditioning when stuck in traffic on a hot day ?
Excellent question, GlennA. I won't speak for GM here, since I didn't ask them that question directly, but I can say that suppliers have various ways of handling it. The simplest way is to use an ambient temperature sensor, which enables the vehicle to "decide" if it needs to be restarted for comfort reasons. This seems to be the prevailing way to deal with it today. A more advanced solution involves the use of a cooling storage evaporator, piggybacked atop the AC evaporator. The cooling storage evaporator allows drivers to continue cooling the vehicle for 50 seconds, or maybe even a minute.
What a pitiful situation, not being able to survive if the air conditioning switches off for a minute. Those folks get no sympathy at all from me.
The other engine driven accessories are a large problem, power steering and power brakes. Of course it used to be that much heavier cars had neither of these, and it is still possible to build cars that don't need them. Really, a vehicle designed to not use power assisted brakes would be quite a bit more reliable. But if they had to be included, a vacuum reservoir would be a logical solution. The challenge would be finding a space for it. Electric assisted power steering has been around for many years and that would quickly solve the other part of the problem, in addition to getting rid of the power steering pump would reduce fuel consumption. Another option is to change the steering ratio a bit and adjust the wheel alignment for non-powered steering, which used to be the way that all cars were made. Power steering is not a thing that everybody needs, it is something that is very aggressively sold.
Getting rid of those two loads would allow switching the engine off and coasting a lot, which could easily provide a much greater reduction in fuel consumption, at least in some driving conditions.
William K; What about when traffic stops for 5 minutes or more ? If you add a larger battery to compensate, you have moved from micro- to mild hybrid. One of the reasons that I like my hybrid Aspen because the battery can drive the truck and accessories in slow or stopped traffic with the engine off. I'm guessing that after a few stories of drivers stuck in traffic in cars that shut down the engine and accessories the micro-hybrid will lose some of its appeal.
The start and coast works in slow traffic as well if the engine starts well, I have done that with my Neon a few times. And non-assisted brakes and steering have been with us for a long time, but they have fallen out of favor. But the knowledge of how to provide them is still oround.
What will probably reduce the effectiveness of stop-start more than anything else will be air conditioning, and all of those soft people who refuse to live without it.
A half century ago, cars were still built by people, not robots. Even on some of the country’s longest assembly lines, human workers installed windows, doors, hoods, engines, windshields, and batteries, with no robotic aid.
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