System Description

1. Conventionally, 2 separate devices, a "radio and display assy" and a "navigation ECU" are used. This model has adopted a new type, combining these devices into a single unit.

Fig 1: Identifying Radio & Navigation Assy

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1. Vehicle position tracking methods

   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.

   *GPS (Global Positioning System)

   Fig 2: Identifying GPS System

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   Fig 3: Identifying GPS Description

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   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, however, the mapping accuracy may slightly decline.

   Fig 4: Identifying GPS Satellite Connectivity

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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 radio and navigation assy.

   2. Vehicle speed sensor

      Used to calculate the vehicle running distance.

3. GPS navigation (Satellite navigation)

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

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

   Fig 5: Identifying GPS Satellite Positioning

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   Fig 6: GPS Description

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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 7: Identifying Map Matching

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5. Touch switch

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

Fig 8: Identifying Switch Contact

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1. The navigation ECU uses a laser pickup to read the digital signals recorded on a DVD.

HINT:

• Do not disassemble any part of the navigation system.
• Do not apply oil to the navigation system.
• Do not insert anything but a DVD into the navigation system.

1. A compact disc player uses a laser pickup to read digital signals recorded on a compact disc (CD). By converting the digital signals to analog, it can play music and other things. In general, CD players can play 4.7-inch (12 cm) or 3.2-inch (8 cm) discs.

HINT:

• Do not disassemble any part of the CD player.
• Do not apply oil to the CD player.
• Do not insert anything but a CD into the CD player.

1. What is AVC-LAN?

   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.

   Fig 9: AVC-LAN Description Table

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2. Purpose:

   Recently, car audio systems have rapidly developed and the functions 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 through signal standardization.
   2. To allow each manufacturer to concentrate on developing products they do best. From this, reasonably priced products can be produced.
3. Above is the purpose of the AVC-LAN. Under this standardization, system errors caused by a new product development should not occur.

HINT:

• If a +B or GND short 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 radio and navigation assy is equipped, it is the master unit.
• The radio and navigation assy provides resistance to make communication possible.
• The car audio system with an AVC-LAN circuit has a diagnostic function.
• Each component has a specified number (3-digit) called a physical address. Each function has a number (2-digit) called a logical address.

1. Components of the audio system communicate with each other via the AVC-LAN.
2. The master component of the AVC-LAN is a radio and navigation assy with a 60 to 80 Ω resistor. This is essential for communication.
3. If a short circuit or open circuit occurs in the AVC-LAN circuit, communication is interrupted and the audio system will stop functioning.

1. The audio 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.