The Truth About Cars » 2 mode The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Sun, 05 Jul 2015 18:22:25 +0000 en-US hourly 1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars » 2 mode A 2nd Look at the 2-Mode Hybrid – It Could Have Saved More Gas Than The Prius Thu, 20 Feb 2014 13:00:21 +0000 The photo illustrating Zombie McQuestionbot’s query about what would it take to get you to buy a hybrid was of a Chevy Silverado hybrid pickup truck. I bet some of you seeing that picture didn’t know that Chevy even sold fullsize hybrid pickups and those of you who are familiar with them, may have dismissed […]

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The photo illustrating Zombie McQuestionbot’s query about what would it take to get you to buy a hybrid was of a Chevy Silverado hybrid pickup truck. I bet some of you seeing that picture didn’t know that Chevy even sold fullsize hybrid pickups and those of you who are familiar with them, may have dismissed the concept. It was called the 2-Mode hybrid system, introduced with great promise and fanfare but in the end it became the Rodney Dangerfield of hybrid drives. That’s too bad. Had the 2-Mode system been embraced by consumers on a wide scale, it might have saved more gasoline than all the Chevy Volts and Toyota Priuses put together.

Actually, the Dangerfield crack isn’t fair to Jacob Cohen, who in real life had a long and illustrious career, once he got his big break on the Ed Sullivan show. In contrast, the 2-Mode hybrid has come and pretty much gone in half a decade. Maybe part of the problem was that instead of first bringing it to the market on pickup trucks, GM introduced it as a package on it’s big body-on-frame SUVs. Perhaps the image of something that consumes combustibles as conspicuously as a Cadillac Escalade does, kitted up with four foot long “HYBRID” decals, evoked too much cognitive dissonance for critics and consumers to swallow but as contradictory as the idea sounds and looks, it made some sense.

There was a time when, unlike Mr. Cohen’s comedic persona, the 2-Mode system actually got some respect. Enough respect that in 2005 both Daimler-Chrysler and BMW joined General Motors in partnering to bring the system to production. There are vehicles from all four of those manufacturers using the 2-Mode system on the road today. Automobile magazine even named it the technology of the year in 2007.


The 2-Mode hybrid system is based around what is a sophisticated electromechanical automatic transmission. General Motors has long had a core competency in the development of automatic gearboxes. GM developed the first mass produced fully automatic transmission, Oldsmobile’s Hydramatic, and the corporation currently has two divisions devoted just to developing and building transmissions, Hydramatic, which produces gearboxes for cars and light trucks, and Allison, which makes transmissions for big commercial trucks. It was an Allison development for city buses that was the basis of the 2-Mode hybrid.

Two-Mode Full Hybrid GM-DCX Cooperation

GM 2ML70 hybrid transmission

A conventional single mode hybrid system, like Toyota and Ford developed independently, uses a planetary gear arrangement to connect both a combustion engine and one or more electric motors to a single driveshaft. Conventional hybrids can run on pure electric drive, combustion drive, or a combination of the two. That mode is known as “input split mode”. A second hybrid mode called “compound split mode” is more suitable for highway speeds, and always uses the combustion engine to drive the wheels, aided by the electric motors.

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Is “sophisticated” another word for “complicated”?

In the late 1990s, Allison developed a 2-mode hybrid transmission system for transit buses, now called the H 40/50 EP Series, that by now has been installed in over 5,000 buses around the world. Their latest hybrid transmission model is the H3000, for medium and heavy duty trucks.


Allison H40 EP hybrid transmission. Note “Electric Drives” embossed on the case.

With Toyota’s Prius gaining traction in the market and giving that company some green cred, GM decided to implement a variation on the Allison design that would initially be used in fullsize rear wheel drive body on frame trucks and SUVs and later developed in FWD form suitable for passenger cars. What would become known as the GM 2ML70 transmission (in the BMW ActiveHybrid X6 and the Mercedes-Benz ML450 BlueHybrid it’s called the Allison AHS-2) added four fixed gear ratios to the mix. It has two 82 kW (110 hp peak) three phase permanent magnet AC motors, three planetary gear sets, and four selectively engaging friction clutches. A dampener replaces a conventional automatic’s torque converter.

Two-Mode Input and Compound Split Transmission

The transmission operates as two different continuously variable transmissions in one case. Electronic controls coordinate the electromechanical symphony, switching between the two modes to provide the ideal power, torque and fuel efficiency for the circumstances. One feature of the 2-Mode system making it particularly suitable for pickups and SUVs is that it allows moderate towing capabilities. Another advantage is that by locating the motor/generators where they are in the power chain, it amplifies their torque output the same way a conventional transmission amplifies the torque of an internal combustion engine, allowing the use of more compact motors, making it possible to fit it all inside the dimensions of a conventional automatic transmission. A more complete explanation, courtesy of and Wikipedia is can be downloaded here (Word doc), and one suitable for transmission mechanics can be found here.

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GM and their partners were hoping for a 50% improvement in city gas mileage, with a lesser but significant increase in highway mileage. The system was introduced on 2008 Chevy Tahoes and Cadillac Escalades. Reviews from the time uniformly praise the system as working seamlessly and smoothly, yielding a real world improvement in fuel economy of about 25%.


Despite the technical success of the system and the significant fuel savings, a lot of observers scratched their heads at GM’s strategy. What was getting headlines at the time were hybrids that were earning EPA ratings with big numbers, not SUVs that got 20 mpg. A hybrid SUV seemed like a rolling oxymoron. The thing, though, is that there was some reason to GM’s strategy if you look at the American fleet. The pickup trucks upon which those hybrid SUVs were based represent the largest segment of America’s fleet of cars and light trucks. Fullsize pickups are the best selling vehicles in America and have been for decades. They’re also the part of the fleet that gets the worst fuel economy. Improving the fuel economy of pickups from 15 mpg overall to 20 mpg saves a lot more fuel than improving the mileage of a compact car by a similar percentage. The small car is already getting better mileage so the same percentage increase is a smaller amount of saved fuel. Over 100 miles, going from 15 to 20 mpg saves 1.66 gallons of gasoline. Over the same distance, going from 30 mpg to 40 mpg saves half that amount, 0.83 gallons.

BMW's version. Note the AWD transfer case.

BMW’s version. Note the AWD transfer case.

Getting American pickups a 25% real world improvement in fuel economy would save huge amounts of fuel. Because it was pretty much a bolt in replacement for a conventional Hydramatic product (the 300 volt battery pack was mounted under the back seat), implementation was relatively simple, also allowing for the use of normal all wheel drive transfer cases.

However, when the latest generation of GM fullsize pickups were introduced in late 2013, they didn’t include a hybrid variant and none is planned. GM also stopped development on a front wheel drive version of the transmission. Chrysler discontinued the few models offering the 2-mode system and in mid 2009, Daimler and BMW  withdrew from the partnership. The 2-Mode today, if it’s known at all, is known as a bit of a technological dead end, not a tour de force. Considering that the thing worked and indeed saved significant amounts of fuel, what went wrong?

Two-Mode Hybrid Transmission Display

In a word, money. Well, mostly it was money, in a variety of ways, but there were other factors. To begin with, the 2ML70/AHS-2 is possibly the most sophisticated transmission ever made for a passenger vehicle. It was expensive to develop (the operational software to coordinate all that activity can’t be very simple) and expensive to build, which is why GM solicited partners in the project. I’ve seen the figure $10,000 cited as the manufacturer’s cost for a single transmission. A hybrid Silverado started at just under $40,000, a substantial increase over a similarly equipped four door Chevy pickup with a conventional drivetrain, just as the United States was about to enter one of the deepest and longest economic recessions in its history. Also, the first 2 Mode vehicles were introduced to the market in late 2007, for the 2008 model year, as General Motors was already on its inexorable path to bankruptcy. During 2008 and then going through the bankruptcy many programs’ development budgets were slashed or, like the Cadillac V8, were eliminated altogether.

Money wasn’t the only issue. The 2-Mode system went into production the same year that GM revealed that they were working on the Chevy Volt, an extended range electric car. A lot of the public and media’s attention that the 2-Mode hybrids could have gotten went instead to the higher profile Volt project. Inside GM, resources were being shifted. As a matter of fact, some of the same engineers who developed the 2-Mode system were granted patents that are at the heart of the Volt.

In addition to the paradox of trying to market a big SUV or pickup as an environmentally conscious consumer choice, GM’s marketers faced the fact that the 2-Mode system worked well at saving fuel in real life, but didn’t show outstanding results on the EPA test cycle. The 2013 Chevy Tahoe hybrid was rated by the EPA at 20 mpg in the city and 23 highway, which doesn’t sound very impressive compared to 16/23 for the conventional Tahoe. Apparently, advertising a 25% increase in real world gas mileage isn’t as appealing as touting big empeegees. New ICE technologies like direct injection and variable valve timing have come onstream, and with 6, 8, 9 and 10- speed transmissions coming on line, V6 and even V8 powered trucks can get very impressive government ratings, without the added cost and complexity of the 2-Mode system.

Since then, hybrids of all sorts, including million dollar supercars like the McLaren P1 and the Porsche 918, have proliferated. The idea of a $40,000+ luxury hybrid SUV doesn’t seem so outlandishly contradictory these days. I was at a Toyota media ride & drive for the new Highlander that Bark M reviewed here at TTAC recently and they told us that the hybrid Highlander starts at $47,900. The idea of an Escalade or Tahoe hybrid seemed to offend some folks just a few years ago, but Toyota only offers the hybrid drivetrain on the Highlander’s most expensive, Limited, trim level. The 2013 Tahoe hybrid, in a bigger, more expensive class of vehicles, started at $53,620, not that much of a stretch from what a Highlander Hybrid costs just a year later. From behind the wheel of a new Highlander hybrid, the big GM hybrids seem less silly than they did just a few years ago. Maybe they were just ahead of their time.

I wouldn’t write the 2-Mode off as some kind of technological dead end. One thing that’s true after over a century of people making cars and trucks is that what is old often becomes new again. Technologies and designs formerly rejected can be improved and implemented as materials science and control devices improve. I won’t be surprised if we see the 2-Mode hybrid or something similar appears at some time again in the future.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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