Global Hybrid Cooperation

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Global Hybrid Cooperation (formerly called Advanced Hybrid System 2 or AHS2) is a set of hybrid vehicle technologies jointly developed by General Motors, Daimler, and Chrysler LLC, with BMW joining in 2005. It uses 2 or 3 sets of planetary gears in an automatic transmission: One for the internal combustion engine(input split) and 1 or possibly 2 additional gearsets to multiply the power of a pair of electric motors. General Motors has stopped using the "AHS2" name as of 2006, preferring to call it simply a "two-mode hybrid system".

Toyota's Hybrid Synergy Drive is similar in that it also combines the power from a single engine and a pair of electric motors, although it uses only one planetary gearset (input split only). Honda's Integrated Motor Assist uses a more traditional ICE and transmission where the flywheel is replaced with an electric motor.


The GM/DaimlerChrysler partnership was announced on December 13, 2004 with Dieter Zetsche of DaimlerChrysler joining Rick Wagoner of GM on stage with a prototype. The agreement was not signed until the following August, however.

GM is reportedly responsible for development of rear- and four-wheel drive truck and front wheel drive car systems while DaimlerChrysler is focused on a rear wheel drive luxury car application.

It was announced on September 7, 2005 that BMW would also join the alliance, likely using archrival DaimlerChrysler's rear wheel drive system.

The three companies have formed an organization called Global Hybrid Cooperation with engineering and management centered at the GM, DaimlerChrysler and BMW Hybrid Development Center in Troy, Michigan. Recent reports indicate that the three automakers will spend one billion US dollars between them on the development of the front- and rear-wheel drive hybrid transmissions.[1]


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The technology is referred to as "two-mode" hybrid transmission due to the ability to extend the abilities of both electrical and mechanical paths of power.[2]The two modes of operation are:

  1. Input-split mode — At low speeds, the vehicle can move with either the electric motor/generators, the internal combustion engine, or both, making it a so-called full hybrid. All accessories will still remain functioning on electric power, and the engine can restart instantly if needed. In this mode, one of the motor/generators (M/G 1) acts as a generator, while the other operates as a motor (M/G 2). This mode is operational using the first and second gear ratios of the transmission.
  2. Compound-split mode — At higher speeds or heavier loads, the internal combustion engine always runs, and the system uses advanced technologies like Active Fuel Management and late intake valve closing to optimize engine and fuel efficiency.

This mode begins at the point where one of the motor/generators reaches zero speed; at this point some clutches within the system engage while others disengage to alter the physical configuration of the transmission, and the velocity is Vshift. Immediately after the shift, both electric machines operate as motors and the first gear ratio is employed. At a given velocity above Vshift, the second gear ratio is employed, and M/G 2 begins to operate as a generator, while also slowing down its angular speed. When the angular speed of M/G 2 is zero, the third gear ratio is employed, and M/G 1 begins to operate again as a generator. As the vehicle velocity increases, the fourth gear ratio is employed, and M/G 1 begin to operate as a generator and M/G 2 as a motor again.

Although the transmission mechanically has only four conventional gear ratios, the electric motors allow it to function as a continuously variable transmission. This variable ratio functions in addition to the torque multiplication of the planetary gears.

A special automatic transmission incorporates two 55-100 kW (75-133 hp) three phase induction motors, three planetary gearsets, and four selectively-engaging friction clutches. This system amplifies the output of the electric motors similarly to the way in which a conventional transmission amplifies the torque of an internal combustion engine. It also, when required, permits transfer of more of the engine's torque to the wheels, making the transmission more efficient even without the electric motors in use. Finally, the whole system fits into the space of, and indeed appears as, a conventional Allison model 1000 automatic transmission.

A 300 volt battery pack is housed elsewhere in the vehicle to store energy.



The system was first used in the New Flyer transit buses deployed in 2001.

RWD/4WD truck

The longitudinal system for light trucks from General Motors will be manufactured at Baltimore Transmission by GM's Allison Transmission division. The nickel-metal hydride batteries will be manufactured by Panasonic EV of Japan.

The system was introduced for the 2008 model year in the full-sized Chevrolet Tahoe and GMC Yukon SUVs as a specific 2-Mode Hybrid model.It is available in both two and four wheel drive models. GM will reportedly offer an identical 2-mode hybrid system in its full-size 2009 model 1/2-ton pickup trucks (aka GMT900) in Q:4 2008.


Latest developments

On March 1, 2007, BMW and DaimlerChrysler announced that they are expanding their partnership and moving quickly to develop a mild hybrid module for rear wheel drive premium cars. They plan to roll out the new system within the next three years on BMW and Mercedes-Benz vehicles produced.

GM is not part of this expanded partnership, and has not announced plans to develop a hybrid RWD system for cars.[4]



See also

External links