They may not know about everything under the hood of Ford’s new Fusion hybrid electric vehicle, but U-M researchers enjoy an up-close look at what’s under the back seat. Ford has supplied one of its most advanced batteries to a team of electrical, mechanical and chemical engineers. In collaboration with Ford and General Electric, (GE) the team is beginning a project that will monitor the thermal and mechanical stresses on battery cells and develop a battery management scheme to reduce those stresses and prolong battery life.
|The complete battery pack in its steel case.|
First, they removed the cover of the control module that monitors the voltages of the cells and connects the battery to the vehicle communication system. “This is as far as a dealer can go,” said Jason Siegel, a research scientist in mechanical engineering. Anything to do with the battery itself has to be done by Ford’s experts.
|The control module and a nest of wires is revealed. “This is as far as a dealer can go,” said Siegel.|
The team then removed the connector covers from one side, revealing the tops of the cells and the black channel that runs down the center of the module. At the bottom of that channel, the batteries are designed with a weak spot, “like that thin little foil on a Capri Sun,” said Monroe.
If a cell fails - due to overcharging, for example - and its pressure rises high enough to burst, it will break at the weak point so that the gasses will flow straight out of the pack and into a special exhaust vent.
|Four rows of orange connection covers, with black marking the breakers. The breakers can divide the 300 volt battery into six safer 50 volt batteries.|
|Battery cells “shoot out” of the module. One of the spacers that allow air to flow between the cells sticks out. The black channel running down the center of the pack can safely carry gasses from burst cells into the exhaust vent.|
Finally down to the cell level, the team has begun liberally applying sensors, provided by GE, under the translucent green electrical insulating film. For the heat maps, they will attach 48 tiny temperature sensors, just a fraction of a millimeter thick, to each side of a cell.
With the battery segment inside, Stefanopoulou and Siegel’s contingent will test straight charge-discharge cycles and also mimic the demands expected when the battery is installed in a real car, simulating the varying currents that the battery must supply or absorb. The group will run similar tests after rigging a cell up with strain sensors to see how the battery expands and contracts during charging and discharging.
|Stefanopoulou numbers the cells while Siegel and colleagues measure voltages on the cells.|
|Monroe’s team stripped away the cell casing to reveal the electrical and chemical system.|
After the models have been proven against the data taken in Stefanopoulou and Siegel’s lab, the team will streamline them so that they are much faster but still accurate. “We’re trying to take this sensor data and use it for real-time, on-the-car battery management systems,” said Monroe.
|The layers within a cell. The team seeks to understand the basic mechanical and chemical properties of the cells in order to build an accurate model of the battery.|
Siegel admits that if Ford’s design is as good as it looked when they took the battery apart, it will be tough to improve on it with sensors and software. If they succeed, a version of their method may one day be incorporated into the energy management systems of hybrid electric vehicles. But at the very least, their measurements will reveal how and where mechanical strains and heat build up in the battery – information that could improve the next generation design.