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GM Sheds Light on Volt's Greatest Problems, How it Hopes to Overcome Them
Jason Mick (Blog) - November 18, 2009 12:19 PM
The 2011
Chevy Volt has handled crash testing well, with the passenger compartment, and the battery system both being sufficiently safeguarded. (Source: GM)
Noise, vibration, and harshness (NVH) have been a more significant challenge for GM, though. The company still isn't happy with the
vehicle's NVH performance and is still making changes. (Source: GM)
GM has tweaked the Volt's battery chemistry and is currently satisfied with it. Its now working to optimize the supporting system and its software to provide maximum battery life. The vehicle is overweight, so an optimized system is even more critical. (Source: GM)
GM's engineers are hard at work fixing the upcoming vehicle's flaws and improving the battery system
Chief Engineer Andrew Farah and Battery Engineering Group Manager Bill Wallace recently gave members of the press an update on the
status of the 2011 Chevy Volt and its battery pack. Designed with the goal of providing a 40 mile range from a 16 kWh (8 kWh usable) charge, the pack and its supporting systems have evolved greatly over the past couple years.
Initially, GM was considering a four-partner arrangement with LG Chem providing cells for CPI to assemble into packs, and A123 Systems producing cells for Continental (which owns the former Siemens VDO) to assemble into packs. The arrangement was significantly altered when GM deemed A123 Systems not ready for this generation, opting to
go solely with LG Chem. Subsequently GM also decided to handle the battery pack assembly itself at a new assembly facility located in Brownstown, Michigan.
Since GM arrived at these decisions, it has been hard at work cooking up the Volt packs. The packs it's currently producing are third generation packs -- the first generation was for the Malibu-body mules, the second generation for the Cruze-body mules, and the current generation for the
pre-production (IVER) body Volts. Thus far, the Brownstown facility has built 80 IVER Volts and 300 production battery packs.
When it comes to the Volt battery, tweaking the system's software and hardware to efficiently manage it is as important, or more so than the design of the battery itself, and that's what GM is currently focusing on. With the first product and process validation
vehicles (PPV) set to be produced at the Detroit-Hamtramck assembly plant in March 2010, and with the manufacturing validation build (MVB) landing between August and November of next year, GM has only a small window to perfect the battery system.
Still, the results thus far have been promising, with 300,000 miles logged in GM's Volt full vehicle simulator (more than the life of many components of the vehicle) and no major problems or failures reported thus far. The batteries also completed a 65 percent calibration ride, recently, with no "show-stopping" issues.
With over 50,000 cells produced since the first generation, Mr. Wallace offers the impressive claim that not one failure (that he knows of) has occurred, on the cell level, module level, or pack level evaluations. With so many miles of simulated road testing and charging cycles, GM and its partner LG Chem have gained some
insight and tweaked the battery chemistry slightly to provide better life with similar performance. The result design is now finalized, in terms of chemistry, according to Mr. Wallace.
The cells have thus far endured torturous testing under extreme conditions. One test called the crush and impact test looks at the response to a collision, looking at whether the battery's seal is maintained. A second test, looks at corrosion by smearing salt on the pack and putting it in a heated chamber. Overcharge testing is also being performed.
These battery-specific tests are in addition to full-vehicle crash tests, rough road, and hot-cold testing. Early indicates from the full vehicle tests look promising, with a 40 mph collision with a barrier at a 30 degree angle unable to intrude upon the pack's area.
The pack weighs in at a final weight of 200 kg (440 lb) according to GM. The car as a whole, however, has a problem unfortunately shared by many Americans -- it weighs more than they would like. GM at this point has conceded that its probably too late to fully fix this by production time and hope to negate its effects on performance and roll out reductions over the vehicle's full production cycle.
One problem GM is looking to tackle is improving cold weather performance. One strategy it is employing is to pre-warm the car while its J1772 connector is plugged in, to ready it for road use. The vehicle employs an electric heater, as well as
heated seats, which will sap the battery, likely reducing the all-electric
mileage in the winter.
Aside from the cold, another major issue is noise, vibration and harshness when running with the range extender (gasoline engine). To minimize the noise GM's engineers have come up with new bushings such as switching rubber for hydraulics for mounting the engine/generator. The body's aerodynamics also produced unpleasant noises, so venting has been implemented, as well. This work is ongoing and not complete.
A couple Volt-related questions still remain unanswered, though, in addition to the vehicle's final weight. GM engineers still won't reveal the size of the final gas tank for use with the range extending gasoline engine. They also stop short of saying whether
The Detroit News report that GM had
given the Converj concept a production go-ahead was true. Mr. Farrah did comment that it was a great concept and that he was looking forward to getting to work on it, indicating that production indeed may be in store, though no official word has come yet.
