|MY 2007 Aspen.|
The new Aspen full-size SUV will join the Dodge Durango as Chrysler’s first volume production hybrids next year. Both vehicles will use a 5.7-liter HEMI engine coupled with the advanced two-mode hybrid technology being co-developed by GM, DaimlerChrysler and BMW (earlier post).
The HEMI engine will continue to feature Chrysler Group’s Multi-displacement System (MDS), which allows the engine to alternate between four-cylinder mode when less power is needed and V-8 mode when more power is in demand.
The new 5.7-liter HEMI Hybrid is expected to deliver an overall fuel economy improvement of more than 25%, including an improvement of nearly 40% in the city. The current 2007 Aspen (2WD) carries an EPA rating of 15 mpg city, 20 mpg highway, 17 mpg combined.
The advanced two-mode hybrid system is optimized for use in a large SUV or pickup, with a particular focus on being able to support towing applications.
The two-mode system is an electrically variable transmission which uses two electric motors to operate at any nearly any speed ratio through the transmission. The electric motors support hybrid functions: electric vehicle operation, electric boost and regenerative braking, as well as engine starting.
The two-mode system also is an automatic transmission, without the torque converter but with conventional hydraulically-applied wet plate clutches to allow automatic shifting among two continuously variable modes and four fixed gears for a total of six mechanical configurations.
Towing puts an especially heavy load in two main areas: increased steady state cruising and increased grade loads. The fixed gears in the two-mode increase the ability of the system to support towing without excessive electrical path losses or motor heating.
Typically, the increased road load would force a conventional transmission top operate near a 1:1 ratio condition for highway cruise...The fixed gear 3 [in the two-mode] with a ratio of 1.0 provides optimum fuel economy for trailer cruise by reducing the need to process power electrically. Fixed gear 2, with a ratio of 1.7, is useful for trailering on a grade at highway speeds, and fixed gear 1, with a ratio of 3.69, provide high torque to accelerate the vehicle at low speeds.—“Defining the General Motors 2-Mode Hybrid Transmission”
With all the complexity and possible choices, the key to the success, including the driver experience, of the two-mode is the control system, according to Tim Grewe, GM’s chief engineer for the two-mode hybrid system. Full rule-based on-line optimizers are constantly (100 times per second) searching for the best efficiency.
GM is rolling out its own full-size SUV hybrids late this year.
Defining the General Motors 2-Mode Hybrid Transmission (SAE 2007-01-0273)