GM and DaimlerChrysler are working together on a two-mode, full hybrid system that could support a range of applications, from compact cars to large SUVs, including front-wheel and read-wheel drives, and using a variety of powertrains including diesel, gasoline, and possibly alternative fuel systems.

When participating on a conference panel in Oct 2003, mid-level engineering managers from both companies discovered that they had similar notions and work in progress on the design of such a hybrid drive. That conference planted the seed for the cooperation announced today. 

The two-mode full hybrid system described is conceptually an implementation of GM’s Advanced Hybrid System II, currently used in its diesel-hybrid transit buses, and planned for implementation in a downsized version in the Tahoe and Yukon SUVs in 2007. At the announcement, both companies were very careful to state that while GM has numerous patents in this area, Chrysler has significant work in process as well; in other words, this is not a tech licensing or transfer deal from GM to DaimlerChrysler. Both companies have cooperated together in the past on the development of transmissions.

The proposed system is, in essence, an electrically variable transmission with two hybrid drive modes provided by a variable pairing of two electric motors. The first mode is for low-speed, stop-and-start, in-city driving. The second is for highway driving—an area in which other single-mode hybrids have not performed as well as expected. As noted in this earlier post, in road-testing, Mercedes’s F500 MIND diesel hybrid prototype delivered worse fuel economy in highway driving than the conventional diesel. The two-mode architecture is intended to correct that type of result.

This system will reduce fuel consumption at highway speeds much more effectively than available single-mode systems and achieve at least a 25% improvement in composite fuel economy in full-size truck applications.

—Tom Stephens, Group Vice President, GM Powertrain

The system relies on two electric motors coupled to two gearsets rather than a single motor to provide a more flexible range of operating power, control and efficiency than obtained with a single-motor implementation. By using gearing to selectively amplify the power from the electric motors, the system can use smaller motors, inverters and batteries, thereby reducing mass and cost while maintaining or increasing hybrid efficiency.

In the first mode, for low-speed and light loads, 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 second, both motors selectively operate in motoring or generating modes depending upon the vehicle speed.

By taking this approach, the companies are increasing the mechanical complexity of the system and the accompanying requirements for sophisticated engine control software.

The first products stemming from this partnership will be the GM Yukon and Tahoe SUVs in 2007, followed shortly thereafter by the Dodge Durango. The partnership isn’t accelerating the arrival of the first new full hybrid models to market, but it presumably is helping (a) to ensure that those first vehicles will roll out as previously announced, (b) that they can be manufactured in sufficient volume to meet demand and (c) that the companies can accelerate the implementation of the hybrid drive across multiple platforms more quickly and cost-effectively.

One of the major pragmatic advantages of this approach, according to both companies, is the reduced size required to package the system due to the use of smaller components. Ultimately, they’d like to be able to take an existing powertrain and replace the conventional transmission with the appropriate two-mode hybrid drive and get comparable tractive results while dramatically reducing fuel consumption and emissions. The ability to package the system in a compact form factor is an essential element to achieve that goal.

Neither company in the past has been an outspoken avocate of hybrid technology—almost the opposite. GM has focused visibly on fuel cells and DaimlerChrysler on clean diesels as well as fuel cells. Yet their hybrid work had been ongoing, as evidenced by the 60+ patents GM holds in the area and by the work DaimlerChrysler was doing with its diesel-hybrids. Despite the very low market penetration that hybrids currently have, the two companies now foresee rapid market growth to perhaps 15%+ in the coming years. Definitely a market size of substantial interest, and one that they cannot afford to cede to the competition—especially Toyota and Honda.

We see the world fragmenting into many technologies...we are working across many at DaimlerChrysler: clean diesel, displacement on demand, the role of internal combustion engines, hybrids...

—Eric Ridenour, Executive Vice President of Product Development, Chrysler Group

GM has an advanced propulsion technology strategy...we are trying to improve fuel economy, and we’d like to take emissions down to zero. There is no silver bullet. We have to work on every on of these fronts [fuel cell vehicles, hybrids, alternative fuel vehicles, clean diesel, gasoline]. The issue is how do we improve fuel economy? How do we reduce CO₂? How do we move forward with more environmentally friendly vehicle applications? Hybrids are not a silver bullet. But as the market grows, DaimlerChrysler and GM will partner together, collaborate together, and have a very important presence in that market.

—Tom Stephens, Group Vice President, GM Powertrain