Chevy Volt teardown reveals future battery pack upgrades and safety monitoring systems
UBM Electronics, as part of their Drive For Innovation tour, recently conducted a teardown of the Chevy Volt down to the nuts and bolts. The disassembly team looked mostly at the on-board electronics, finding an extensive sprinkling of microprocessor control systems all through the car. While the team estimates that over 40% of the Chevy Volt value is in the electronics, we're most interested in what it showed about the battery pack safety systems, given the recent Volt battery pack fire furor.
UBM's Drive For Innovation tour is a one year project to showcase electronics innovation and automotive system design in which EE Times Editorial Director Brian Fuller drove a Chevy Volt to "innovation hubs" around the U.S. to conduct interviews. In a one-hour webinar today, the team presented a high level overview of the circuit boards, the chips on the boards, and the connecting cables between subsystems. The overview came from details the team learned by tearing the Volt down to its component parts, then examining each board to identify major chip part numbers, and manufacturers, as well as the overall function of the system. The purpose was to better understand the Chevy Volt, as well as the future of automotive technology.
Of course our primary interest is to learn what the team discovered about Chevy Volt battery pack safety. We'll get to that in a minute.
The team found the Volt to demonstrate a trend in automotive engineering where more and more of the value in an automobile is electronics systems. In the 1980's they said perhaps 5% of the value of a car was in the electronics. In that era computerized controls were first began appearing in cars, and today they are common. The team estimates that, in the Chevy Volt, 40% of the value is the electronics systems, and that a modern 2012 gasoline powered car has 20% of its value in the electronics systems. Clearly, modern electronics are becoming more powerful every week (it seems) and the presence of automobile manufacturers at January's Consumer Electronics Show (CES) and this weeks Mobile World Congress demonstrates all the automakers are looking hard at modern including electronics features in new cars.
The Chevy Volt was described as an example of an extremely sophisticated vehicle. Over 100 microprocessors were used among in the various subsystems, to control each system. The majority of these controlling microprocessors were in the battery pack (for the battery management system) and the inverter controlling the motor. The UBM team estimates over 10 million lines of software code are used to drive these microprocessors, and draw a comparison to fighter jets whose control systems require perhaps 6 million lines of software code.
An electric car like the Volt has many systems that need to be controlled and modulated during operation and charging. As we see in the Chevy Volt, battery pack monitoring, management and cooling, as GM designed it, requires extensive computerized control systems.
We start with the battery pack. This is a T-shaped unit, the long part of the T is the tunnel running down the center of the passenger compartment, and the short part of the T is immediately behind the rear seats. The pack is constructed of 288 individual cells, grouped in four modules. One modules is 120 volts, two are 96 volts, and the last is 72 volts. The 288 cells are grouped as 96 cells in series, and each cell is actually three cells in parallel. Radio controlled vehicle aficionados would describe this as a 96S3P arrangement.
Each module contains a battery management board, and there is a master control board, the Energy Control Module, that manages the battery pack as a whole. Each cell is individually monitored for voltage and current flow, and there are temperature sensors all through the pack. Monitoring voltage at each cell allows the battery management system to ensure each cell is evenly charged, ensuring the pack works well and to lengthen its life. Each of these five boards has its own microprocessor and other circuitry.
The Volt has an extensive cooling system on-board, with four separate loops for coolant to flow through different subsystems. The battery pack has one of the coolant systems, and of course it was the coolant in the battery pack which was implicated as a prime cause for the battery pack fire. The system monitors the battery pack temperature, keeping temperature within a narrow range both during charge and discharge. To do so the system not only cools the battery pack, but heats it if needed, using what the UBM team described as a hefty heating unit. The other three coolant loops go to the radiator on the gas engine, the AC-DC converter used to charge the battery pack, and the main power inverter for the electric motor.