(August 9, 2009) As General Motors moves forward with four core brands in North America including Buick, it will be expanding the product lineup for its entry premium brand. The next new addition will be a compact crossover based on the outgoing Saturn Vue. The new crossover will debut in late 2010 with conventional 2.4-liter and 3.0-liter direct injected four and six cylinder engines.

Sometime in 2011, a plug-in hybrid (PHEV) will join the lineup using the front wheel drive two-mode hybrid system developed initially for the Vue. A non-plug two-mode vue was due for launch in late 2008 but was cancelled due to GM's financial turmoil.

The powertrain for the Buick will be a modified version of the system planned for the Vue. The 3.6-liter V6 engine with direct injection is being retained but it will now have flex-fuel capability added. Larry Nitz, director of hybrid powertrain development at GM, told GFF the decision to make the PHEV flex-fuel was made "not too long ago. It's part of the whole E85 and flex fuel initiative. We really wanted to focus on displacing petroleum."

"Two main ways that we see at the company to do it was through biofuels and also plug-in. So putting those two technologies together was really a showcase for our two ways of displacing petroleum."

To date no other automaker has done a production flex-fuel (FFV) hybrid although Ford has been field testing FFV versions of the Escape hybrid. The new crossover will be both the first hybrid and the first direct injected FFV. This poses new challenges for the GM engineers because of the "lower lubricity of the fuel and the higher pressure fuel pump." Nitz tells GFF that so far we haven't seen an issue in bringing it all together.

The charge cooling effects of direct injection allow engine designers to run higher compression ratios without risking detonation. This aids both torque production and efficiency. E85 has a significantly higher octane rating than pump gasoline, making it even more resistant to detonation. Since this PHEV is normally aspirated it can't take advantage of using higher boost the way a turbocharged engine could, Nitz acknowledges that it could use more spark advance than the gas only version. This could help close some of the gap in fuel mileage between running on gasoline and E85 that results from ethanol's lower energy content.

While GM cancelled production of the two-mode Vue, the powertrain engineers continued working to optimize the hardware for future applications. Nitz says that the engineers have been able to take advantage of lessons learned on the Volt program. This has allowed some cost reduction of the system. The electric drive motors are sized the same as the original Vue.

The Buick PHEV will now use the AC power inverter developed for the Volt rather than the used on the GMT900 (full-size truck) hybrids. The newer second generation inverter is smaller, lighter and has higher efficiency.

Another area where GM has been able leverage the Volt development is the battery pack. In early 2007 GM began working with Johnson-Controls-Saft and Cobasys-A123 Systems on development lithium ion packs for the Vue PHEV. The production Buick will instead use the same LG Chem sourced lithium polymer cells that will go into the Volt. Nitz explained that "economies of scale and engineering learnings from the Volt program" were the main reasons for the change. The other suppliers' cells work, but with all the work done on the Volt it made sense at this point to move forward with that choice.

The PHEV pack will use the same type of liquid cooling system for the pack that will be applied to the Volt. While GM has opted to build the Volt battery pack in-house with the LG Chem cells, the Buick pack will be built buy LG Chem subsidiary Compact Power Inc.

In spite of the different usage pattern in a parallel power-split hybrid compared to an extended range EV, Nitz believes there will be problem with pack durability. "It operates over the same range of state of charge as the Volt." The PHEV pack uses half the number of cells of the Volt pack. The pack will use the same management system as the Volt, including conditioning of the pack in less than ideal temperatures.
 
The packaging configuration will differ from the Volt allowing it to fit under the rear load floor of the crossover but Nitz says the design principles will be the same.

One of the big questions that remains for all plug-in hybrid and extended range electric vehicles is how the efficiency will be rated. The EPA has not finalized the procedure but such combined plug-in vehicles are expected to carry two numbers, a mileage number representing the charge sustaining or depleted mode and another representing electrical energy content. In the case of an ER-EV like the Volt which operates purely on electric drive, the latter number will get a special consideration and display electric range. A blended drive vehicle like the PHEV will not get an electric range number.

In the case of the PHEV, the test protocol becomes difficult because the mileage of such vehicles are more highly dependent on the duty cycle than conventional vehicles. If the test cycle stays largely below the maximum electric drive speed of the hybrid system, the mileage numbers can go up dramatically. Conversely, average speeds above that threshold cause the number to drop as does the length of the test cycle. If the drive cycle is long enough to deplete the battery plug-in charge, the mileage also falls off.

Sizing the battery becomes critical here. The automakers are trying to provide enough capacity to meet the needs of a significant number of drivers with little or no leftover charge. If a significant amount of charge goes unused the driver has paid a heavy initial price premium for battery capacity that is not used.

The Buick PHEV will be able to get over 30 mph in electric only drive. However, rating the electric driving range is problematic. According to Nitz "in a blended plug-in, you're not trying to be an EV, you're trying to be super-efficient. So you are looking for opportunities to discharge the battery where it would be efficient, not discharge it particularly to make it an EV."

"People always ask that question, 'how many miles can you drive electrically?' The engineers almost cringe in coming up with a number because that's not really the mission. It's about 10 miles but that's not really the mission."

"Because the engine can start to run the tests (the OBD-II diagnostics) during the drive cycle we have to start it." "The first key on, the engine will start the first little bit of driving. You may have a silent start, but then give it another thirty seconds and the engine is going to light off." Once the diagnostics are completed and the catalyst has been warmed up, then the drivetrain can revert to more electric operation. "The blended plug-in operation is very, very different from the ER-EV, and the challenges are very different. It certainly exciting engineering to learn how to do both."

"The idea is to come home empty so we are trying to use up all the electric power available in the first 20 miles." Given that Nitz expects up to a fifty percent improvement in fuel economy from a conventional hybrid version when running prior to plug-in charge depletion and under certain lower speed conditions, up to double the fuel economy. The original non-plug-in two-mode Vue was projected to get a rating of 28 mpg city and 31 mpg highway. That would put expected mileage of the plug-in somewhere in the low to mid 40 mpg range.

Nitz emphasizes that going forward customers will have to look more carefully at their driving behavior when considering what type of powertrain to buy. For people who drive relatively short distances, plug-ins will be a great option. For others who regularly drive farther, they may not be the best choice.