Hybrid Car Review

BMW Group, GM and DaimlerChrysler got together to create the Global Alliance for Hybrid Drive Development. GM and DaimlerChrysler signed binding, definitive agreements on August 22, 2005. BMW Group signed on September 7, 2005. Their goal was to research and create a base two-mode hybrid design. Today they announced success.

They've developed a low and high-speed electric continuously variable transmission (ECVT), commonly known as the 2-mode hybrid. They've also put in place four fixed gear ratios for higher efficiency and power handling.
In summary, the four fixed gears overlay two ECVT modes for a total of six operating functions:

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

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

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.

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

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

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

The full hybrid system being co-developed by General Motors, DaimlerChrysler and the BMW Group 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.

A sophisticated 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. These systems are often called “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 percent less efficient than a mechanical path. This requires usually substantial compromise in vehicle capability or reliance on larger electrical motors, which can create cost, weight and packaging issues.

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.

The Global Alliance for Hybrid Drive Development is centered in Troy, Michigan at the "GM, DaimlerChrysler and BMW Hybrid Development Center"

The group hopes to move into production of the two-mode hybrid next year.

Source: Press Release