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GM, DaimlerChrysler and BMW Advanced Hybrid System: Two Variable Modes and Four Fixed-Gear Ratios

Advanced Hybrid System

Daimler Chrysler, GM and BMW are providing more detail on the new advanced hybrid system the three companies are co-developing.

Because of its low- and high-speed electric continuously variable transmission (ECVT) modes, the system is commonly referred to as the 2-mode hybrid. (Earlier post.) However, the system also incorporates four fixed-gear ratios for high efficiency and power-handling capabilities in a broad variety of vehicle applications.

During the two ECVT modes and four fixed-gear operations, the hybrid system can use the electric motors for boosting and regenerative braking.

The four fixed gears overlay two ECVT modes for a total of six operating functions:

  1. Input-split ECVT mode, or continuously variable Mode 1, operates from vehicle launch through the second fixed gear ratio.

  2. Compound-split ECVT mode, or continuously variable Mode 2, operates after the second fixed gear ratio.

  3. First fixed-gear ratio with both electric motors available to boost the internal combustion engine or capture and store energy from regenerative braking, deceleration and coasting.

  4. Second fixed-gear ratio with one electric motor available for boost/braking,

  5. Third fixed-gear ratio with two electric motors available for boost/braking.

  6. Fourth fixed-gear ratio with one electric motor available for boost/braking.

The full hybrid system has an overall mechanical content and size similar to a conventional automatic transmission, yet this full hybrid transmission can operate in infinitely variable gear ratios or one of the four fixed-gear ratios.

An electronic control module constantly optimizes the entire hybrid powertrain system to select the most efficient operation point for the power level demanded by the driver.

Traditional hybrid systems typically have only one torque-splitting arrangement and no fixed mechanical ratios (“one-mode” hybrids). Due to their less capable mechanical content, one-mode hybrids need to transmit a significant amount of power through an electrical path that is 20% less efficient than a mechanical path, according to the three.

This usually requires a substantial compromise in vehicle capability or reliance on larger electrical motors, which can create cost, weight and packaging issues.

The use of the four fixed mechanical ratios within the two ECVT modes reduces the power transmission through the less efficient electrical path. Consequently, the electric motors are more compact and less dependent on engine size.

The combination of two ECVT modes and four fixed gear ratios eliminates the drawbacks of one-mode hybrid systems to allow for efficient operation throughout a vehicle ’s operating range, at low and high speeds. It also allows for application across a broader variety of vehicles. It is particularly beneficial in applications that require larger engines, such as towing, hill-climbing or carrying heavy loads.

Existing internal combustion engines can be used with relatively minimal alteration because the full hybrid system imposes no significant limitation on the size or type of engine. It enables the three global automakers to package internal combustion engines with the full hybrid transmissions more cost-effectively and offer the fuel-saving technology across a wider range of vehicles.

Initial applications are suitable for front-engine, rear- and four-wheel-drive vehicle architectures, but the full hybrid system has the flexibility to be used in front-engine, front-wheel-drive architectures in the future as well.

General Motors, DaimlerChrysler and the BMW Group have formed a cooperative effort called the Global Hybrid Cooperation, which is actively developing this next generation hybrid powertrain system. Currently full hybrid systems are under development for front- and rear-wheel-drive passenger cars, and light-duty truck and SUV applications.



It'll never fly.

Max Reid

They have to apply this tech in a smaller and popular vehicle like Saturn-Vue, PT-Cruiser, etc and price it without jazzy features.

It will send ripples into Toyota, Honda camp.

John Ard

This would work well if it is actually used in a truck and not wasted on the LX platform (Charger, Magnum, 300). We recently traded our Ram 1500 Hemi Quadcab for a 2500 Cummins Turbo Diesel because of the Hemi's poor fuel economy and horrible towing performance. This system could fix that problem.

For the record, I live in Alabama where Average Joe needs a truck just to navigate our county roads. The Hemi's fuel economy maxed out at about 12mpg while the Cummins regularly returns 20+mpg. Both are 2WD and Quadcab.

Rafael Seidl

Lucas - I don't think the transmission is supposed to leave the vehicle :-)

The design is a downscaled version of the one GM's Allison division developed for buses. Note the absence of a torque converter. The system's many modes make it at least as complex as and probably heavier than a straight dual clutch tranny with an electric motor attached to the shaft for the even gears. However, this triumvirate clearly placed a premium on a form factor that permits the drop-in replacement of a traditional AT. Expect to see it deployed in large rear-wheel drive vehicles.

As with any hybrid, you have to combine engine downsizing with advanced turbocharging, early gear shift points and a power-centric electric energy store to achieve really significant overall fuel economy gains. Limiting the weight and component cost of the electric energy store are also critical. In a regular hybrid, all-electric range is irrelevant to anyone but CARB - but then again, they are the ones writing the rules.

The first-gen Allison system fared rather more poorly than advertised in this regard:

GM presumably invited DCX and BMW to come on-board not just to reduce R&D cost and time but also because of their control systems engineering expertise.

gerald earl

It will never swim either??????????

Ron Fischer

GM, DCX and BMW reduce hybrid to "transmission" and thus reject re-engineering the whole vehicle to improve efficiency. This approach also rejects the idea that a hybrid vehicle could be mechanically simpler.

There is a reason Toyota calls theirs the SYNERGY drive...

This "dual mode" (six mode?) system also requires much more complex software to make it switch modes appropriately without destroying itself. Watch the warranty costs on this one...


Hey, if they can use this to produce a midsize car that gets 50-60 mpg, I'll be sufficiently impressed.


GM? In your dreams.


They don't know how to build a car like that and are unwilling to learn.

gerald earl

They steal candy from babies.


When gas is $4.00 a gallon this stuff will really take off. It amazes me when we Americans act like victims because gas cost $3/gallon; meanwhile driving around in 4,000 lb vehicles with 300hp. It will take market forces to get people to demand 50mpg, this technology will work as long as we consumers don't ask it to go from zero to 60 in 6seconds.
It isn't really GM's fault, we keep buying this stuff.

Furthermore babies shouldn't eat candy!


The explanation could not be more complicated and sugar coated for a "souped up" 4-speed automatic transmission!

hampden wireless

Tell us how many hp the electric side has. Can it run on electric only mode? Does it need a starter as well or does this unit alone start the engine. Real details please.


A truck is required in Alabama? hahahahha...sure, this is how people rationalize their decisions when they start to feel bad about a poor choice. I lived in Rural Georgia (just about 20 miles east of the Alabama border) for a few years and never had a need for anything more than the average compact or mid-size vehicle. Never once did I have problems on dirt roads through rolling hills when it was heavily raining.

richard schumacher

Jeez. Now we know they'll do anything to avoid paying royalties to Toyota.

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