GM introduced two applications of its two-mode hybrid system at NAIAS: the Graphyte SUV and the Opel Astra Diesel Hybrid. The two concept cars demonstrate the packaging versatility of the two-mode hybrid system that is the basis for the development partnership between GM and Daimler Chrysler (earlier post).

The two-mode system packages two electric motors into the transmission. The motors work with traditional transmission gears and electronic controls to provide two modes or ranges of infinitely variable gear ratios. The input split mode is used for launching the vehicle from a stop, driving at low speeds and providing superior performance and moderate load trailer towing. In this mode, the system can operate just with the engine, just with the motor, or with any combination of the two. In this mode, one motor acts as a generator, while the other provides drive (motor) power.

In the compound split mode, both motors, managed by the control unit,  selectively operate in motoring or generating modes depending upon the vehicle speed and working in conjunction with the other engine technologies,such as Displacement on Demand. The electric motors not only regulate the power flow, but also aid in extending DoD operation well beyond what is capable without hybrid assist. The purpose of the second mode is to optimize fuel consumption at higher speeds.

GM designed its two-mode full hybrid technology to fit within the space of a conventional automatic transmission, with a battery pack providing the electric power. Future variants of the two-mode hybrid system include rear-, front- and all-wheel drive versions for cars, trucks and other vehicles.

The GMC Graphyte concept vehicle (picture at right) is a midsize SUV that combines a 5.3-liter V-8 with Displacement on Demand (DoD) technology with two electric motors integrated within the transmission case. A 330-volt NiMH battery pack is located beneath the rear sear.

The engine (a Vortec 5300) is the same used currently in the Tahoe and Yukon, as well as other SUVs, and delivers 300 hp (223.5 kW) of power and 325 lb-ft (449 Nm) of torque. The hybrid system delivers a 25% improvement in fuel economy, according to GM.

GM feels it is best to employ hybrid technology first on large vehicles, such as buses and SUVs, because they generally are the largest consumers of fuel. With the Graphyte, we’ve demonstrated its integration into a type of vehicle where its fuel-saving technology will do the most good, while maintaining all the utility for which GMC trucks and SUVs are known.

The promise of the Graphyte’s hybrid technology is guilt-free performance. It provides a real and dramatic improvement in fuel economy without compromising the reasons customers want to use their SUV.

—Tom Stephens, group vice president for GM Powertrain

The Opel Astra diesel hybrid (picture at right) front-wheel drive concept is based on the production-version Opel Astra GTC.  The hybrid combines a 1.7-liter turbo diesel engine that delivers 125 hp (92 kW) of power and 206 lb-ft (280 Nm) torque with two electric motors, rated at 30 kw and 40 kw, respectively. GM expects the Astra Diesel Hybrid to deliver zippy 0-62 mph acceleration of less than 8 seconds.

Fuel consumption of the Astra hybrid is less than 4-liters/100km (58.8 mpg)—25% more fuel-efficient than comparable diesel models.

We decided to use a diesel-powered car as a starting point because in the mid-term, we don’t see a demand for gasoline hybrids in Europe. Our state-of-the-art CDTI engines already deliver impressive dynamics and low fuel consumption. The Astra concept demonstrates that fuel efficiency and vehicle dynamics can be significantly improved by hybrid technology.

—Hans H. Demant, GM European engineering vice president and Opel managing director

The release of the vehicles together highlights the design point that both GM and DaimlerChrysler stressed upon making their partnership announcement: the packaging of the two-mode system as essentially a transmission replacement will allow the application of the system in a wide variety of vehicle formats. This is one way to bring hybrid technology to a wide range of vehicles more quickly.

It also appears that GM plans to deploy the hybrid systems without downsizing the standard ICE powerplants in the target vehicles. This is the same approach taken by Honda in its Hybrid Accord, although not the same approach it took with the Civic hybrid. The result is equivalent or even more performance to the conventional models, with a lesser reduction in fuel consumption.

Many consumers will agree with Tom Stephens—this is “guilt-free performance”. What’s not to like? You have the platform of your choice, it drives the same—if not better—and it uses less fuel.

The larger question, though, is whether or not that level of improvement in fuel consumption will make enough of a difference. Relative improvements do not necessarily equate to the necessary quantitative improvements.

Let’s take the Yukon as an example. GM has already announced that the Yukon and Tahoe will receive the two-mode hybrid system in 2007. Assuming the 25% improvement in fuel consumption, adding the two-mode hybrid system to the current Yukon with the same engine as the Graphyte would produce a vehicle that delivers 20 mpg rather than 16 mpg. That would be a big relative improvement. A 25% improvement. But it is still a lot of fuel.