Global Hybrid Cooperation

Global Hybrid Cooperation (formerly called Advanced Hybrid System 2 or AHS2) is a set of hybrid vehicle technologies jointly developed by General Motors and DaimlerChrysler, with BMW joining in 2005. It uses two sets of gears in an automatic transmission: One for the internal combustion engine and another 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. Honda's Integrated Motor Assist uses a more traditional ICE and transmission where the flywheel is replaced with an electric motor.

Cooperation

When GM and DaimlerChrysler engineers realized how similar their hybrid work was, they decided to join forces and share technology. 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.

Technology

Cutaway of the longitudinal GHC transmission

The group touts its technology as "two-mode" to differentiate it from the Toyota, Honda, and Ford "single-mode" systems. The two modes of operation are:

1. Input-split mode — At low speeds, the vehicle can move with either the electric motors, 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. 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 fuel efficiency. This mode can use all four gear ratios, with each tuned to a different condition:

• First gear with both electric motors
• Second gear with one electric motor
• Third gear with both electric motors
• Fourth gear with one electric motor

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.

Despite the "two-mode" marketing pitch, however, it is the packaging of the first application of the system which is unique. A special automatic transmission incorporates two 60 kW (80 hp) DC electric motors, two planetary gearsets, and two 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 transfers 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 4L60-E automatic transmission.

A 300 volt battery pack is housed elsewhere in the vehicle to store energy. Most applications will also include 120 volt AC power outlets as on the 2004 Chevrolet Silverado hybrid.

The two-mode transmission seems to resemble at least some, if not most, aspects of the SEL Transmission, researched and documented by TU Chemnitz under a public research grant, in July 2000.

Applications

Buses

The system was first used in the General Motors transit buses deployed in 2004.

• City bus system by Allison Transmission
  • Albuquerque, New Mexico (twelve busses announced December 21, 2004)
  • Indianapolis, Indiana IndyGo (two busses announced January 24, 2005)
  • Yosemite National Park National Park Service (18 Gillig busses announced April 25, 2005)
  • Shreveport, Louisiana SporTran (one bus announced June 9, 2005)
  • Charlotte, North Carolina Charlotte Area Transit System (2 busses announced June 9, 2005)
  • Springfield, Massachusetts Pioneer Valley Transit Authority (one bus announced October 14, 2005)
  • Aspen, Colorado Roaring Fork Transportation Authority (seven busses announced December 9, 2005)
  • Consortium of 11 transit agencies in California, Nevada and New Mexico (157 busses announced March 20, 2006)

RWD truck

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

The system was to be introduced for the 2007 model year in the full-sized GM SUVs, but these were delayed for one year for unspecified reasons.

• Rear wheel drive truck system
  • GMC Graphyte Hybrid SUV concept (shown at the 2005 NAIAS)
  • 2008 Cadillac Escalade
  • 2008 Chevrolet Tahoe
  • 2008 GMC Yukon
  • 2008 Dodge Durango

FWD car

• Front wheel drive car system
  • Opel Astra Diesel hybrid concept (shown at the 2005 NAIAS)

References

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See also

• Hybrid car
• Hybrid Synergy Drive

External links

• Hybrid Cars and Vehicles — MixedPower.com
• Comparative Assessment of Hybrid Vehicle Power Split Transmissions
• Electrically variable transmission having two planetary gear sets with one fixed interconnection, US Patent Application 2006/0111213 A1

Formerly known as Advanced Hybrid System 2 (AHS2)

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