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System Description

WARNING: This page is about a different car, the 2007 Lexus GX 470. However, it is still accessible from the selected car via links, so may be relevant.
  1. NAVIGATION SYSTEM OUTLINE 
    1. Vehicle position tracking methods
      1. It is essential that the navigation system correctly tracks the current vehicle position and displays it on the map. There are 2 methods to track the current vehicle position: autonomous (dead reckoning) and GPS* (satellite) navigation. Both navigation methods are used in conjunction with each other.

        HINT:

        *: GPS (Global Positioning System)

      Fig 1: Identifying Navigation System Outline Diagram
      G05266325Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      OPERATION DESCRIPTION

      Operation Description
      Vehicle Position Calculation Navigation ECU calculates current vehicle position (direction and current position) using direction deviation signal from gyro sensor and running distance signal from vehicle speed sensor, and creates driving route.
      Map Display Processing Navigation ECU processes vehicle position data, vehicle running track, and map data from map disc.
      Map Matching Map data from the map disc is compared to vehicle position and running track data. Then, vehicle position is matched with nearest road.
      GPS Correction Vehicle position is matched to position measured by GPS. Then, measurement position data from GPS unit is compared with vehicle position and running track data. If the position is very different, GPS measurement position is used.
      Distance Correction Running distance signal from vehicle speed sensor includes error caused by tire wear and slippage between tires and road surface. Distance correction is performed to account for this. Navigation ECU automatically offsets running distance signal to make up for difference between it and distance data of map. Offset is automatically updated.
      Fig 2: Identifying Combination Of Autonomous & GPS Navigation
      G04945443Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      HINT:

      The combination of autonomous and GPS navigation makes it possible to display the vehicle position even when the vehicle is in places where the GPS radio wave cannot receive a signal. When only autonomous navigation is used, the mapping accuracy may slightly decline.

    2. Autonomous navigation

      This method determines the relative vehicle position based on the running track determined by the gyro and vehicle speed sensors located in the navigation ECU.

      1. Gyro sensor

        Calculates the direction by detecting angular velocity. It is located in the navigation ECU.

      2. Vehicle speed sensor

        Used to calculated the vehicle running distance.

    3. GPS navigation (Satellite navigation)

      This method detects the absolute vehicle position using radio waves from a GPS satellite*.

      HINT:

      *: GPS satellites were launched by the U.S. Department of Defense for military purposes.

      Fig 3: Identifying GPS Radio Wave Navigation
      G05266327Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      SATELLITE MEASUREMENT DESCRIPTION

      Number of satellites Measurement Description
      2 or less Measurement impossible Vehicle position cannot be obtained because number of satellites is not enough.
      3 2-dimensional measurement is possible Vehicle position is obtained based on current longitude and latitude (this is less precise than 3-dimensional measurement).
      4 3-dimensional measurement is possible Vehicle position is obtained based on current longitude, latitude and altitude.
    4. Map matching

      The current driving route is calculated by autonomous navigation (according to the gyro sensor and vehicle speed sensor) and GPS navigation. This information is then compared with possible road shapes from the map data in the map disc and the vehicle position is set onto the most appropriate road.

      Fig 4: Identifying Map Matching
      G04945224Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. MULTI-DISPLAY OUTLINE 
    1. Touch switch

      Touch switches are touch-sensitive (interactive) switches operated by touching the screen. When a switch is pressed, the outer glass bends to contact the inner glass at the pressed position. By doing this, the voltage ratio is measured and the pressed position is detected.

      Fig 5: Identifying Touch Switch
      G04945225Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. DVD (DIGITAL VERSATILE DISC) PLAYER OUTLINE (for Navigation Map) 
    1. The navigation ECU uses a laser pickup to read the digital signals recorded on a DVD.
    CAUTION: Because the navigation system uses an invisible laser beam, do not look directly at the laser pickup. Be sure to only operate the navigation as instructed.
    NOTE:
    • Do not disassemble any part of the navigation ECU.
    • Do not apply oil to the navigation ECU.
    • Do not insert anything but a DVD into the navigation ECU.
  4. DVD (Digital Versatile Disc) PLAYER OUTLINE (for DVD Changer Models) 
    1. The DVD player can only play DVD videos that have any of the following marks:
    Fig 6: Identifying DVD Videos Symbols
    G04945226Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Precaution for use of discs
    NOTE:
    • PAL or SECAM color television standard discs cannot be played. (Only NTSC discs can be played.)
    • Keep the discs away from dirt. Be careful not to damage the discs or leave fingerprints on them.
    • Hold discs by the outer edge and center hole with the label side up.
    • Leaving the disc exposed halfway out of the slot for a long time after pressing the disc eject button may cause deformation of the disc, marking the disc unusable.
    • Do not use odd-shaped CDs because these may cause player malfunctions.
    • Do not use discs whose recording portion is transparent or translucent because they may not be inserted, ejected, or played normally.
    • DualDiscs that mate DVD recorded material on one side with CD digital audio material on the other cannot be played.
  5. "BLUETOOTH" OUTLINE 
    1. "BLUETOOTH" is a trademark owned by "Bluetooth" SIG, Inc.
    2. "Bluetooth" is a new wireless connection technology that uses the 2.4 GHz frequency band. This makes it possible to connect a cellular phone ("Bluetooth" capable phone*) to the multi-display ("Bluetooth" system is built-in), and use a handsfree function with the cellular phone in a pocket or bag. As a result, it is not necessary to use a connector for the cellular phone.

      HINT:

      *: The communication performance of "Bluetooth" may vary depending on the "Bluetooth" version, obstructions or radio wave conditions between communication devices, electromagnetic radiation, communication device sensitivity, or antenna capacity.

    Fig 7: Identifying Bluetooth Communication Diagram
    G05266331Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  6. AVC-LAN DESCRIPTION 
    1. What is AVC-LAN?
      Fig 8: Identifying AVC-LAN Diagram
      G05266332Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      AVC-LAN, an abbreviation for "Audio Visual Communication Local Area Network", is a united standard developed by the manufacturers in affiliation with Toyota Motor Corporation. This standard pertains to audio and visual signals as well as switch and communication signals.

    2. Purpose:

      Recently, car audio systems have rapidly developed and the functions have vastly changed. The conventional car audio system is being integrated with multimedia interfaces similar to those in navigation systems. At the same time, customers are demanding higher quality from their audio systems. This is merely an overview of the standardization background. The specific purposes are as follows:

      1. To solve sound problems, etc. caused by using components of different manufacturers thorough signal standardization.
      2. To allow each manufacturer to concentrate on developing products they do best. From this, reasonably priced products can be produced.

        HINT:

        • If a short +B or short to ground is detected in the AVC-LAN circuit, communication is interrupted and the audio system will stop functioning.
        • If an audio system is equipped with a navigation system, the multi-display unit acts as the master unit.

        If the navigation system is not equipped, the audio head unit acts as the master unit instead. If the multi-display is equipped, it is the navigation ECU master unit.

  7. COMMUNICATION SYSTEM OUTLINE 
    1. Components of the navigation system communicate with each other via the AVC-LAN.
    2. Radio receiver assembly has enough resistance (60 to 80 Ω) necessary for transmitting the communication. This is essential for communication.
    3. If a short circuit or open circuit occurs in the AVC-LAN circuit, communication is interrupted and the navigation system will stop functioning.
  8. DIAGNOSTIC FUNCTION OUTLINE 
    1. The navigation system has a diagnostic function (the result is indicated on the master unit).
    2. A 3-digit hexadecimal component code (physical address) is allocated to each component on the AVC-LAN. Using this code, the component in the diagnostic function can be displayed.
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