21 May 2012
Third in the Teardown series
By John Scott-Thomas
For the designers of the Chevrolet Volt – GM’s signature hybrid automobile – the infotainment system presented an interesting dilemma. On the one hand, the infotainment system is the primary interface between the driver and the automobile, and as such, it should be a highlight of the vehicle. On the other hand, no one is buying a Volt because of its infotainment; they want to buy a car that runs on a battery and does not burn a lot of gas.
GM recognized this challenge, and its solution was to design an information system that shines a spotlight on the Volt’s novelty, with generous graphics that encourage the occupants to be excited about driving an electric car. In this article, we look at how they did it and peek inside some of the electronics and firmware used for the design.
Play the EV Game
In previous articles (Volt Battery Teardown; Powertrain Teardown), we looked inside the battery and powertrain of the Volt. At its simplest, the Volt is powered by an on-board lithium-ion battery pack and 1.4L gasoline engine that are controlled by highly complex electronics. The electronics continuously monitor the battery, engine, brake and accelerator pedal position, and car speed with the goal of using as much electric power (and as little gas) as possible. The infotainment graphics display plenty of information, encouraging the driver to play in this game. Acceleration and braking habits, the state of charge of the battery, when to charge the battery (many states have cheaper power rates at particular times of the day), the number of miles driven on electricity or gas, and other information are all provided in easy to understand graphics.
We decided to open up a 2012 Volt’s dashboard to see what was inside (here's a 42:08 video from our infotainment teardown session at Design West in March or see the embedded video nearby). The first step in tearing down the system was a visual inspection of the dashboard. Figure 1 shows the information consoles available to the driver. The instrument panel in front of the driver uses a seven inch LCD and has a conventional look and feel.
In addition to speed, odometer, engine and battery charge information, an “efficiency driving style feedback meter” is visible on the right. The goal for the driver is to keep the ball centered and spinning in a reassuring green on the vertical gauge. Accelerating or braking too heavily causes the ball to rise or drop and turn yellow; when this happens, energy is being dissipated needlessly.
The center stack mechanical design is quite modern, using a moulded plastic housing with curved lines to create a future-spacecraft-like appearance. People seem to have strong opinions on the center stack; some love it, others don’t. The stack has navigation, passenger compartment, radio and video controls. Haptic touch sensitive buttons are used for the settings.
Prominently placed to the left of the stack is the “Leaf” button that provides the driver with all the information about the battery state, battery charging controls, driving statistics, and internal power management that allow economical driving. When the Leaf button is engaged, the LCD provides information to the driver about the power management and distribution in the vehicle.
The right inset of Figure 1 shows one of three possible Leaf display modes; the “Power Flow” display. This mode has an icon of the battery pack, gas engine, and car wheels. As the car is driving, green power pulses flow between the components. Most of the time, power is flowing from the battery pack to the wheels, but during regenerative braking, the pulses reverse direction as the battery captures kinetic energy from the car. The inset shows a pulse flowing from the gas engine to the inverter.
|Figure 1: The Infotainment
consoles of the Volt
|Figure 2: The Video Control
PCB in the Center Stack
|Figure 3: The Instrument
|Figure 4: The Communications
As we began to disassemble the consoles, it was clear GM had taken great care in the design to reduce electromagnetic interference. Sensitive telematics must be well-shielded from the powerful currents flowing through the drive train. All modules are enclosed in aluminum or steel grounded housings. Additionally, the power electronics and the electric motors are heavily shielded and high power cables have internal shielding to prevent electromagnetic emissions.
The center stack contains two printed circuit boards (PCBs); one for radio and audio functions and one dedicated to video and control of the LCD touch screen display. The radio PCB has mechanical tuning knobs soldered directly on the board and blue surface mount LEDs to illuminate the touch sensitive switches. A slot is cut through the center of the PCB allowing DVDs and CDs to pass through to the player.
The back of the PCB has two Cypress programmable SOCs (Part # CY8C21534-24PVXA) that have configurable blocks of analog and digital circuitry. An 8 bit microcontroller (Part # D78FD535A, manufacturer not identified) is also on the board. A buzzer on the back of the PCB provides audio feedback for the button controls.
The video PCB is shown in Figure 2. The board acts as the main interface between the LCD touch screen and the rest of the vehicle. Two integrated circuits (ICs) play central roles on this board. A Sony GCIF Receiver (Part # CXB1458R) uses gigabit video interface technology that receives high speed uncompressed digital video over single twisted pair cabling.
A Renesas 32/16 bit microprocessor is the main controller for the display; it has 1 MB of address space and is specifically designed to withstand electromagnetic interference.
The instrument cluster PCB controls the main dashboard LCD in front of the driver. A Freescale display controller (Part # SPC5121YVY400B) integrates an e300 CPU based on Power Architecture Technology with peripheral functions focused on automobile communications (CAN and Ethernet). Figure 3 shows the front of the PCB.
The communications module PCB is one of the more interesting control boards on the Volt. Mounted in a metal shielded box under the instrument panel on the passenger side, this module provides the interface between the Volt and a smartphone. The Volt is designed to become an extension of a smartphone, allowing the driver to perform hands-free calls using voice recognition and access GM’s OnStar system.
Smartphone apps allow the driver to remotely charge the car, turn on the air conditioning, and monitor the car status. The communications PCB is shown in Figure 4. An LG Bluetooth transceiver (Part # LBMA-2C66B7) connects the board to a smartphone. A Spansion 512 Mb Mirrorbit Flash (Part # S29GL512P10TE) holds the firmware for the PCB.
We were intrigued by the firmware on the communications PCB. The Spansion flash (Part # S29GL512P10TE) was desoldered and the firmware dumped to a viewer. The operating system is QNX. Vehicle status variables were clearly named, including tire pressure, battery voltage, engine oil life, fuel level, and odometer. This information can be transmitted to a smartphone giving the driver a “remote view” of the vehicle.
A search through the code revealed many of the key players in the firmware development. Code contributors include a board support package from MEN Mikro Elektronik, a digital signal controller driver from Freescale, a firmware update manager from the Open Mobile Alliance (OMA), a help page for the WiMAX Forum Network Architecture and Funambol open source for mobile cloud synching. The Funambol source code allows the entertainment system to connect to the cloud using WiFi.
Chevrolet has been announcing for some time the release of their Mylink telematics system. MyLink allows the driver to access Internet services, such as Pandora, Stitcher SmartRadio and Gracenote through the smartphone. We could not find any firmware related to MyLink; GM’s latest availability date is Spring 2012.
The Volt’s infotainment system uses a broad range of IC suppliers compared to other systems on the car for which the main socket holder is Freescale. ICs from Renesas, Sony, Cypress, Zentel, Spansion and LG are on board. The graphical user interface highlights the “electric car” nature of the vehicle, providing feature-rich graphics about minute details of the power distribution. Perhaps equally significantly, the communications systems are designed to evolve rapidly as the automobile becomes yet another extension of the Internet over the next few years.
Please view our live teardown video of the infotainment system (42:08).