Technology Defines Mercedes-Benz' Road to the Future, From DiesOtto Engine to Fuel Cell EVs
By John O'Dell June 13, 2008
By John O'Dell, Senior Editor
HUELVA, Spain -- I've been sitting in Mercedes-Benz' exotic F-700 – facing backward in the research car's multi-position rear seat and watching the engine-power display on a 20-inch flat-screen monitor as driver Peter Lehmen slowly takes us around the track at Circuito Monteblanco.
We’re at this track, 30 miles east of Seville, for an event Mercedes calls "the Road to the Future."
In fact, it's a demonstration of a number of technologies the German luxury-car maker has been showing off around the globe for many months. The neatest stuff, of course, is years away from being production-ready.
A display with the same name at last September's Frankfurt Motor Show in Germany featured 19 clean and green Mercedes-Benz vehicles including the F-700 research car.
My interests are several, starting with the DiesOtto engine that powers the F-700 – a gasoline engine that works much like a diesel, providing low emissions, substantial fuel economy and power in a pretty small package.
Mercedes has promised to fill us in on advances made since the prototype engine was unveiled at the Frankfurt show.
The automaker also has gathered experts to talk about the whole range of its green car efforts, including clean diesels, fuel cell vehicles, battery-electric cars and the company's breakthrough development that will let it be the first to put a lithium-ion battery pack into a production hybrid car when the S-400 BlueHybrid is introduced next year.
Turbo, Torque, Thrift
But let's get to the DiesOtto, Mercedes' name for an engine that uses the technology everyone else calls homogeneous charge combustion ignition, or HCCI. Other big players working hard on an HCCI engines are General Motors Corp., Volkswagen and Honda Motor Co.
Mercedes has opted to pair the relatively small 1.8-liter, four-cylinder with a small electric motor for extra assist, making the F-700 a hybrid. A dual-stage turbocharger that works at both low and high engine speeds helps keep things exciting. It's a powerful package, with the gas engine producing 238 horsepower and the electric motor another 20 hp. Working in tandem, they provide 295 pound-feet of torque.
That's enough to propel the hefty 3,748-pound package from standstill to 62 miles per hour in 7.5 seconds and to an electronically governed top speed of 125 mph.
It does so while delivering a thrifty, Mercedes-estimated fuel economy of 45 miles per gallon and spewing just 45 pounds of CO2 per 100 miles.
How It Works
The simplest explanation of an HCCI engine is that it works like a spark-fired direct-injection gasoline engine during acceleration phases and like a compression-fired diesel engine when it is cruising and there's no big demand for quick power.
(DiesOtto is the contraction of Diesel and Otto, the official names of the intake-compression-combustion-exhaust stroke cycles of conventional diesel and gasoline engines, respectively.)
In Mercedes' engine, gasoline is injected deeply into each cylinder, which ensures better atomization, less unburned fuel, fewer nitrogen oxide emissions and more energy in each combustion cycle.
The gas-air mixture is fired by a spark plug when power is needed for acceleration. The engine reverts to diesel-like operation at low speeds and while cruising.
The diesel cycle's process -- the air-fuel mixture is compressed in the cylinders until it ignites form the heat of compression – uses very little fuel compared to spark-ignition, so it helps boost mileage. Combustion also occurs at relatively low temperatures compared to spark-ignition, so fewer nitrogen oxides are formed.
Progress, Challenges
Günter Karl, DiesOtto project leader at Mercedes' engine research center, said that the engine is still a long way from being production-ready.
"We need to work on cost-optimization, and some components are not ready because of durability" issues, he said.
Improved cylinder pressure sensor is left of valve in DiesOtto engine cutaway.
Since the engine bowed-in at the Frankfurt show, though, Karl and his team have improved a number of key components including the valve train, the cylinder pressure sensors and the interaction of the four separate electronic control modules.
Those modules now individually oversee engine combustion, valve train and variable crankshaft operation and the hybrid system's interface with the gas engine.
A more efficient, but much more elaborate, system would control everything from a single, unified program, Karl said.
"The interaction of the [powertrain's] different systems is a big challenge," he said, adding that his team's greatest progress, so far, has been in getting the hybrid system to work seamlessly with the gas engine.
Thanks, Honda
Asked how long Mercedes has been working on the DiesOtto concept, and where the idea came from, Karl looks a little sheepish.
Turns out that the idea came from Japan's Honda Motor Co., about 15 years ago, when Honda showed a concept two-stroke motorcycle engine that used HCCI technology, Karl said.
"That was in 1993," he said, " and we started working [on the DiesOtto concept] the same year."
Honda never put its motorcycle engine into production – there is one on display in the Honda museum in Japan, though – and now is one of the companies vying with Mercedes to perfect HCCI technology for automobiles.
Batteries
Mercedes' parent, Daimler AG, recently made a big splash with the announcement of a "breakthrough" in lithium-ion battery technology that would enable it to be first to market with the advanced technology batteries in a hybrid car – the 2009 S400 BlueHybrid sedan due out next year.
The batteries initially will be used in so-called mild hybrids like the S400 that don't require massive battery packs.
That's intentional, as lithium-ion cells can heat up, sometimes dangerously so, and the more cells stuffed into a battery pack – to increase power sand energy storage – the greater the risk of what battery engineers like to call "thermal events."
The battery pack that Mercedes will use in the S400 was developed for Daimler by Johnson Controls-Saft, a French-American venture. It uses a proprietary lithium ion chemistry and battery cell construction technique that minimizes heat build-up, said Mercedes hybrid systems specialist Peter Antony.
Germany's Continental AG designed the battery management electronics while Mercedes-Benz' contribution to the mild hybrid system was to figure out a way of connecting the battery pack to the car's heating and cooling system so the range of operating temperatures could be closely controlled.
Size Matters
Lithium-ion cells are much smaller and lighter than conventional nickel metal-hydride cells with the same storage and power output capacity, so the S400's hybrid battery pack – which contains 35 cells, weighs 53 pounds and can deliver up to 25 kilowatts of power -- is about the same size as the car's standard 12-volt accessories battery.
With so little surface area to deal with, it was relatively easy for Mercedes engineers route the big luxury sedan's heating and air conditioning lines through the pack's housing.
Temperature sensors tell the battery management software how to adjust the AC or the heat in the housing to keep everything on an even keel.
After the S400, Daimler will turn its attention to the upcoming battery-electric version of its Smart micro-mini car.
There's no well-defined timeline, but several executives said that the nickel metal-hydride batteries now used in the test versions of the electric Smart and slated to be used in production versions, ultimately will be replaced with lithium-ion battery packs. It could be 2015, though, before that shift occurs.
Fuel Cells
Daimler believes hydrogen fuel-cell vehicles ultimately will replace battery-electrics as the ultimate alternative fuel vehicle, and in Spain the company reiterated its intent to replace the A-class fuel cell vehicles it now is using as test beds for the technology with larger B-Class models in 2010.
The B-class fuel-cell electric cars will use a next generation system that is smaller but more powerful than the system in the A-Class models, said Herbert Kohler, Daimler's chief environmental officer and advanced engineering guru.
The new system will produce about 55 percent more power than the A-class system: 123 horsepower versus 85 hp and 236 pound-feet of torque versus 155.
Sat the same time, maximum range is expected to more than double, to 250 miles from 100 miles, and fuel economy is expected to increase by 30 percent, to the hydrogen equivalent of almost 75 miles per gallon.
It Takes Money
To keep all of this technology moving forward, Mercedes-Benz has been among the industry's biggest spenders on R&D, Kohler said, budgeting 4.1 billion euros, or about $6 billion, in 2007 alone.
"For the upcoming years, 2008 through 2010, we will invest close to 14 billion euros" more, he said.
It is an investment, said Kohler, not only in technology but, more important, "in our future."
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