The unusual technological alliance between DaimlerChrysler, BMW
2007 Dodge Durango
Chrysler Group's largest SUVs, the Durango and the Aspen will get hybrid drivetrains starting next year. (Photo: Chrysler Group)
and General Motors that started in 2005 has resulted in a major groundbreaking advancement in terms of hybrid drivetrains. Each of the three firms invested approximately one billion dollars in the research and development, which was conducted in Michigan at the DaimlerChrysler, GM and BMW Hybrid Development Centre. A Two-Mode Hybrid System is the result, first shown in Chevy's Tahoe Hybrid and then in a number of DCX concept vehicles. Now it is heading for production in a Dodge and a Chrysler. The Two-Mode Hybrid System has been designed to be used on almost every type of vehicle made, ranging from a compact front-wheel drive car, to a midsize SUV, to a large pickup truck. With DCX, the first version of this system will be arriving on the market starting 2008.

The 2008 Dodge Durango Hybrid and 2008 Chrysler Aspen Hybrid will be the first gasoline-electric production vehicles that Chrysler Group has made, which should help spur
Two-Mode Hybrid System
In the shell of a standard hydramatic automatic gearbox lies all the gadgetry and motors that make this hybrid possible. (Photo: GM)
interest in the brand’s large SUVs.

Being that the Durango and Aspen are sought after for their high towing capabilities and ample on-road performance, Chrysler Group decided to make the 5.7-litre HEMI V8 engine the centerpiece of the new drivetrain system. Besides offering the muscle needed in a large sport utility vehicle, this HEMI also offers MDS cylinder deactivation, which seamlessly shuts off four cylinders under lighter loads. Combined with the hybrid assist, Chrysler Group estimates that the Two-Mode Durango and Aspen will have 25-percent better fuel economy than their non-hybrid counterparts. The biggest gains will be observed in the city, where the engine-stop and electrical assist are expected to reduce these large SUVs’ thirst by up to 40-percent!

What makes the Two-Mode hybrid system different than Toyota’s Hybrid Synergy Drive or Honda’s Integrated Motor Assist is its layout. It still has a gasoline motor, a starter/generator and
Two-Mode Hybrid System
It'll run on electric power and/or gasoline, but these electric motors are what give the system the ability to function like a CVT. (Photo: GM)
batteries, and can shut off at stoplights, but the main difference is that it has two sets of gears in its automatic transmission; one set is used for the HEMI V8 with four fixed ratios (i.e. a four-speed automatic), while the other is used for the twin electric motors. The combination of the motors and transmissions yields two different operating modes. The first is at low speeds, where the vehicle can be powered by either the gasoline engine, the electric motor or both. It uses the first two speeds in the automatic transmission. The second mode is more complex, and revolves around higher speeds and engine loads. In this situation, the gasoline engine always runs, but the electric motors kick in at different points with different ratios, creating the effect of a CVT transmission for better efficiency.

The Two-Mode system is a rather complicated drivetrain, but it will ease the thirst and emissions of large sport utility vehicles. We’re very curious to see how the system functions, and how the vehicle will drive, but we’ll have to wait until the Durango and Aspen Hybrids arrive in 2008. Shortly thereafter, General Motors’ version of the system will debut in the Tahoe and Yukon, as well as in its half-ton pickup truck lineup.