June 19, 2006 UPDATED with extensive image and diagram library Details of the hybrid drive system under co-development by General Motors, DaimlerChrysler and BMW have been released and the new system is quite a technological feat due to the full integration of electric motors with a fixed-gear transmission. As a result of its low- and high-speed electric continuously variable transmission (ECVT) modes, the system is commonly referred to as the 2-mode hybrid. The system also incorporates four fixed gear ratios for high efficiency and power-handling capabilities. During the two ECVT modes and four fixed gear operations, the hybrid system can use the electric motors for boosting and regenerative braking. Traditional “one-mode” hybrid systems typically have only one torque-splitting arrangement and no fixed mechanical ratios. 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. Working collaboratively, the group has conceived a full hybrid system featuring four fixed mechanical ratios, within the two ECVT modes, to reduce power transmission through the less efficient electrical path. Consequently, the electric motors are more compact and less dependent on engine size.
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