GM-DaimlerChrysler's Two-Mode Full Hybrid System – Versatile for any Market

DETROIT – General Motors Corp. (GM) and DaimlerChrysler AG (DCX) will co-develop the world's first two-mode full hybrid and advance the state of hybrid technology in the automotive industry.

The flexible and cost-effective two-mode full hybrid system will leverage automatic transmission technology and electronic controls in an integrated, powerful and compact system that can be used with a variety of engines, both gas and diesel. The system will easily configure to rear-, front- and all-wheel drive versions for cars, trucks and other vehicles, making the two-mode full hybrid one of the most versatile, best performing and cost effective packages in the industry. The technology is expected to improve acceleration performance while also improving vehicle fuel economy and range.

Both companies have been working independently on their own hybrid propulsion systems for their range of passenger vehicles. Working together, the two companies will draw on their combined technical expertise to achieve higher fuel savings and cost efficiencies and deliver a two-mode full hybrid system to market quickly.

“It is both companies' goal to build the two-mode full hybrid system as one of the leading hybrid systems globally in the industry,” said Tom Stephens, group vice president for GM Powertrain.

GM previously announced its first application of a full hybrid would be launched in late 2007 in two of GM's most popular full-size SUVs, the Chevrolet Tahoe and GMC Yukon. Chrysler Group will introduce the two-mode full hybrid system in the Dodge Durango shortly following the GM SUVs. Mercedes will focus on high-tech propulsion systems in rear-wheel drive passenger cars in the luxury segment.

Combining the hybrid development efforts of DaimlerChrysler and GM will position both companies for leadership in this technology. The wide-ranging program will allow opportunities for additional partners, and could become a hybrid source for other auto manufacturers.

“The ability to offer a common full hybrid architecture with the flexibility to configure in rear-, front- and all-wheel-drive packages, for both gasoline and diesel engines, gives us the best opportunity for expanding the technology globally. It also provides the basis for co-development with DaimlerChrysler and potential collaborations with other manufacturers,” Stephens added.

A two-mode full hybrid plays an important role in GM's comprehensive advanced propulsion strategy to apply relevant and meaningful technologies to improve efficiency and reduce emissions. In the near-term, GM is applying innovations on both gas and diesel internal combustion engines and transmissions. In the middle of the decade and into the future, GM will focus considerable resources to bring to market affordable and effective hybrid technologies, offering three hybrid propulsion systems across a broad portfolio of products, including the two-mode full hybrid cooperation with DaimlerChrysler. Long-term, GM is committed to delivering commercially viable fuel cell technology.

Patented two-mode full hybrid

GM's two mode full hybrid system has been established as the starting point for the GM-DaimlerChrysler collaboration. The design integrates proven automatic transmission technology with a patented hybrid-electric drive system to deliver the world's first two-mode full hybrid. In full-size truck and SUV applications, the system enables at least 25 percent fuel economy savings and superior performance.

Two-mode system innovations also allow for more compact packaging because its compact and powerful electric motors are designed to fit within the approximate space of a conventional automatic transmission – an efficiency advantage compared with today's typical single-mode systems that rely on much larger electric motors.

“It's the optimal merging of full hybrid and state-of-the-art automatic transmission technologies,” said Stephens. “The system is essentially an electrically variable transmission with two hybrid drive modes. We've taken the two-mode hybrid technology that we are using in transit buses and improved it further for use in our popular rear-wheel drive SUVs and pickups, and front-wheel drive cars. Single-mode systems can't provide the range of operating efficiencies that our two-mode system can. Our system reduces fuel consumption at highway speeds much more effectively.”

Compact and powerful electric motors are integrated into the transmission and 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. The compound split mode is used primarily when the vehicle is at higher speeds to provide efficient cruising.

The drive modes alternate seamlessly between the input split mode and a compound split mode. In the input split mode the vehicle can operate on electric, mechanical or a combination of the two. The vehicle operates as a full hybrid when the engine is shut off at low speed and light loads, as leaving the engine off for extended periods of time and moving under electric power is key to reducing fuel consumption in stop and go traffic.

Coupled with the efficient compound split mode, the electronic controller seamlessly integrates with other fuel-saving technologies of advanced engines, such as ultra-high compression ratio, Late Intake Valve Closing (LIVC), Cam Phasing and Displacement on Demand (DoD) to regulate cylinder deactivation. Electric motors not only regulate the power flow, but also aid in extending DoD operation well beyond what is capable without hybrid assist. In addition to electric assist, full –size engine power is on tap whenever higher-load situations demand it, such as towing, climbing steep grades, etc.

“It all happens without the driver realizing it,” said Larry Nitz, executive director of GM's hybrid program. “There are no discernible steps between modes or DoD transitions. The two-mode full hybrid simply optimizes power and torque for the given driving conditions, and all the driver feels is the satisfaction of low fuel consumption and the exceptional reserve power and performance.”

The addition of a second mode to the drive system improves efficiency and reduces the need for exceedingly large electric motors, typical with today's single-mode systems. The resulting scaleable architecture enables faster proliferation of the technology to a wide range of engines and vehicles, from compact cars to trucks and even 60-foot buses.

“Typical single-mode systems depend on large electric power loops between two large electric motors, resulting in inefficiency and ultimately less continuous power,” said Nitz. “The two-mode full hybrid delivers seamless, dependable power on demand and in a more efficient power flow – and is packaged with motors less than half the size of single-mode systems.”

A sophisticated controller determines when the vehicle should operate in either mode of the two-mode drive system. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors. The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission to propel the vehicle. But unlike conventional continuously variable transmissions, the two-mode full hybrid's electrically controlled system uses no mechanical belts or bands. Shifts between the two modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth accelerations.

The 300-volt battery pack provides electric power for the system, and while it is larger than a typical automotive battery, it is designed to fit in the vehicle without compromising passenger space. Special converters located under the vehicle's hood convert the motors' AC output to DC current and power conventional 12-volt accessories, such as interior lighting, climate control and the radio. The vehicle's internal combustion engine provides power to charge the battery pack, so the vehicle doesn't have to be plugged in to keep the battery pack maintained.

Story by GM