With increasing frequency, car buyers are spending big for the convenience of in-car navigation. Not unusual for factory-optioned navigation, the Prius' GPS-based mapping and guidance system adds almost $2,000 to the sticker price.
As a practical matter, what the driver perceives as the navigation "system" is really a composition of two distinct subsystems, one the GPS navigation unit itself and the other a visual interface by which the driver can see and interact with mapping functions.
The Prius' visual user interface (VUI) comes by way of a Toshiba liquid-crystal display and associated electronics located middash. The touchscreen LCD panel is an important and standard part of any Prius bought today (it's present even if the navigation option is not chosen), serving as the interface for energy monitoring, climate control and car audio. The trend in cars and aircraft today is to migrate much of the traditional gauge and button user interfaces to a centralized "glass cockpit," and the Prius is no exception.
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Communication with the engine control module (ECM), hybrid vehicle engine control unit (HVECU) and other convenience control subsystems occurs within the VUI, allowing the touch panel to serve many roles, depending on the selected use mode (activated via the buttons to either side of the LCD). While speed, gear, fuel-level and odometer functions are delivered via a vacuum-fluorescent display (VFD) assembly, the bulk of interaction in the Prius comes through the VUI.
A pair of components based on the multi-OS-capable Naviem partnership between Denso and Toshiba creates the master graphical display and control interface. Joining with the Naviem devices are 32 Mbytes of NOR flash from Sharp and 64 Mbytes of DDR SDRAM from Elpida to create what can be considered the general-purpose compute system responsible for touchscreen and monitoring and command I/O. The VUI box is cooled by a pair of fans, hinting at the processor horsepower within.
Pony up the extra money for the navigation unit (NU), and the MAP/Voice and DEST mode buttons become active alongside the standard VUI mode selects. With the navigation option, a box housing the navigation-specific electronics and accompanying DVD-ROM drive for map data gets installed under the driver's seat at build time. The factory navigation unit supports more than just mapping information, however. Voice recognition allows hands-free address and navigation command entry, and voice prompts provide spoken driving directions, among other functions.
The navigation subsystem is standalone, other than the visual interface. To complete the connection to the VUI for visual aspects of operation, a Sony CXB1457R Gigabit Video Interface transmitter pipes data up to the VUI for display. A corresponding Sony CXB1458R Gigabit Video Interface receiver is found within the VUI box to bring in navigation unit information for that.
A GPS antenna installed under the dash cover is positioned to allow line of sight to GPS satellites through the front windshield, and a coax cable then snakes its way back to the underseat navigation box. The RF front end for GPS constitutes quite a small portion of the navigation electronics, based here on a Panasonic AN18401A downconverter to get to a de-modulated GPS input signal. From there, a sizable Renesas HD6473810 processor is responsible for all of the GPS baseband work needed to calculate the present position for joining with local mapping data. But GPS data crunching is only part of the required processor function, since all of the voice recognition and voice prompting are also done in the NU.
Within the NU, 96 Mbytes of total DDR SDRAM is found spread across three 32-Mbyte Elpida chips, and 1 Mbyte of Spansion NOR flash serves for local code store. Both the NU and VUI are among the few modules in the Prius that use sizable stores of discrete memory. Likewise, IC packaging steps up to high-pin-count BGA devices from the QFP packaging found in the more conservatively designed modules.
The mix of cabin-internal use environments, more-modern design and less-mission-critical attributes for the NU and VUI probably contributes to the latter's closer engineering resemblance to traditional consumer electronics (CE). Indeed, it is in infotainment where we see much of the growth in automotive electronics and convergence with the gadgetry we're accustomed to seeing outside the car.
David Carey is President of Portelligent. The Austin, Texas company produces teardown reports and related industry research on Wireless, Mobile, and Personal Electronics. (www.teardown.com)
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