Managing battery packs for electrified powertrains is a major challenge, but battery management has been relatively ignored by teams designing the majority of cars with internal combustion engines. That’s changing swiftly as stop/start technology begins to gain market acceptance.
When engines in so-called microhybrids turn off at red lights and other times, it’s essential to ensure that batteries have enough energy to restart the vehicle. That’s prompting a range of chip and system developers to focus on this technology, which is expected to gain widespread acceptance as fuel conservation demands grow.
Bosch, Hella, Denso, Valeo, and Delphi are among the systems suppliers who have entered the market. Chip and sensor makers are also getting into the act. For example, Freescale Semiconductor recently unveiled an intelligent battery sensor that monitors lead/acid batteries. The chip adds more precision so battery conditions can be more closely monitored and managed.
“In start/stop, you definitely need to know the state-of-health and state-of-charge of the battery,” Antonio Leone, Product Line Manager at Freescale Semiconductor’s RF, Analog and Sensor Group. “We measure in microseconds compared to systems in use today that monitor in milliseconds.”
Other chipmakers are also tightening precision, pushing forward in both hardware and software. Monitoring the battery’s state-of-charge plays an important role to guarantee the start/stop function.
“The monitoring device needs a very precise coulomb charging algorithm,” said Joseph Notaro, Director Market Development for STMicroelectronics' North America Automotive Business Unit. “The current measurement has a very wide range to handle. Therefore, nowadays, the system requires a 16-bit analog-to-digital converter for current measurement.”
Along with precision, pricing and packaging are also important issues. Sensor makers are employing new solutions that trim cost and make it easy for designers to house components in crowded engine compartments.
“Now, battery-current sensors are based on shunts, which are too expensive,” said Robert Racz, a Product Marketing Engineer at Melexis. “Hall Effect sensors are less expensive and don’t generate as much heat. They’re also small, so they can be packaged in the battery harness or other conductors like bus bars.”