26 March 2012
SAN JOSE, Calif. — Love it or loathe it, the Chevy Volt is a marvel of electronics and automotive engineering. This week at DESIGN West, we're peeling back the onion on this innovative General Motors design.
In three sessions, Tuesday through Thursday, Al Steier of Munro and Associates and John Scott-Thomas of TechInsights will walk you through what we found when we pulled apart the car for three days at Munro's Troy, Mich., facilities. If you're nearby, you should make a point of attending these sessions and have a chance to question Steier and Scott-Thomas about what they found.
Here's a sneak peek:
The battery pack is split into four major sections. The rear section consists of two modules with 72 cells on the right and 54 cells on the left, which are connected with a short buss bar. The front module contains 90 cells, the middle module 72 cells. At the very front of the pack are the high current relays and vehicle cable, wiring and coolant line interfaces. Each section of the battery has a single electronic module to monitor temperatures and voltages.
The battery pack consists of 288 cells, which are grouped by connecting three cells in parallel to create 96 individual sub modules. These 96 sub-modules are distributed into the four main battery modules. The left rear battery pack monitoring system is shown to the right, the other three packs are designed similarly.
Initial voltage readings taken after removal:
+Front Cell:120.8 VDC
+Middle Cell: 96.6 VDC
+Right Rear Cell: 96.7 VDC
+Left Rear Cell: 72.5 VDC
+Total Battery Pack Voltage: 386.6 VDC
The battery pack front module (electronics pictured, right) contains a circuit board, which is used to control the high current relays, coolant heater and the coolant pump for battery temperature control. The module also contains a current sensor on the DC output circuits. The module is contained in an aluminum die casting with numerous injection molded brackets for component attachment. It is sealed around the outer perimeter to the cover and at the bottom to the large stamped steel battery support member.
The Chevy Volt’s charging system can be divided into three primary systems:
The inverter is located directly over the transmission in the engine compartment. A large “beauty” cover is placed over the module. Interestingly, the cover also contains the high voltage circuit interlock. All of the high voltage cable connections have their own discreet interlock, while the inverter uses the cover to replace/eliminate five of them. The module contains two three-phase connections to each of the transmission drive motor/generators and two DC connections: one to the battery pack and the other to the electric A/C compressor. On the front of the module are a pair of 40 pin cam lock connectors for low current/voltage IO interfaces to the vehicle and components.
The inverter’s two low-current connectors (40 pins each) provide interface to low current/voltage IOs. Based on service manual documentation, a total of at least seven serial communication lines are used connecting to the other hybrid-related components. Inputs to the module include a pair of resolvers for each electric motor and temperature sensors for monitoring the motors. Additional inputs include engine crank sensor (engine speed), ignition switch input signals and the typical 12 volt power and ground connections.
The high voltage DC to low voltage DC module is located in the trunk of the vehicle under the cargo floor. It replaces the belt driven alternator on the internal combustion engine, converting the battery pack high voltage DC to 12-14 volt DC. The module is air cooled using plastic ducting and has its own fan for air flow. The low voltage connector provides engine run/crank inputs and communication links.
The deep dive
This is just a peek at what's under the Volt's hood. Register for DESIGN West and come see it in person. We'd love to see you and hear your questions.