Navigation Computer: Overview
The navigation computer is located in a bracket under the RH front seat, immediately behind the CD autochanger. The navigation computer contains all the hardware and software required for control of the navigation system, including the GPS receiver and a solid state piezo gyro. Using the gyro, and inputs from the GPS antenna and the vehicle K bus, the navigation computer determines the vehicle's current position, direction and speed.
The navigation computer also houses a CD-ROM drive. The drive is used to read map data from country specific CD's and also to load software into the computer. A button, adjacent to the CD slot, is provided to eject the CD from the unit. If the ignition is on, one press of the button will eject the CD. If the ignition is off, two presses are required, one to wake up the system and the second to eject the CD. Access to the CD-ROM drive is from the rear of the RH front seat.
The Navigation computer is delivered pre-loaded with operating software, 2 languages and the Off Road navigation software. The 2 pre-loaded languages are:
- UK English (Female)
- German (Male)
Software loading can be achieved at any time by inserting a software CD into the CD-ROM drive. The navigation computer compares the version of software on the CD with that currently loaded. If the software version on the CD is a later version it automatically loads the new software. The status of software loading is shown on the display unit. On completion of software loading, the CD is automatically ejected. The user is prompted to remove the CD and confirm. The computer then resets and restarts with the new software.
The piezo gyro measures the motion of the vehicle around its vertical axis using the Coriolis force. The Coriolis force is a force which accelerates a body moving away from the rotational axis against the direction of rotation of that axis.
In operation, a mass inside the sensor is excited to a point where it begins to vibrate, similar to a tuning fork. The vibrations travel perpendicular to the rotational axis and cause continuous potential charge of the mass in relation to the rotational axis. The forces are measured and converted into a yaw rate to calculate direction.
The sensor is supplied with a current from a driver stage. The current induces vibrations in the driver elements and retaining elements. As the vehicle turns a corner, the rotational motion is detected by the retaining elements due to the Coriolis force, and a small electrical voltage is produced.
The voltage is passed to an amplifier and the amplified signal is then passed to a phase detector. The phase detector establishes the direction of rotation and passes a signal to a frequency filter. Because the gyro sensor is subject to vibrations produced by means other than cornering, the frequency filter analyses the signals and removes signals not produced by cornering forces. The filtered signal is passed from the frequency filter to the navigation computer, which uses it to calculate the direction of travel.