System Description

NAVIGATION SYSTEM OUTLINE

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 Global Positioning System (GPS) (satellite) navigation. Both navigation methods are used in conjunction with each other.

Fig 1: Navigation System Outline

Courtesy 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 the running distance signal from vehicle speed sensor. Then driving route is created.
Map Display processing	Navigation ECU displays vehicle track on map by processing vehicle position data, vehicle running track, and map data from map disc.
Map Matching	Map data from 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 position is widely 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.

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 2: Vehicle Position Tracking Method

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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.

GPS navigation (Satellite navigation)

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

HINT:

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

Fig 3: Identifying GPS Navigation (Satellite Navigation)

GPS NAVIGATION (SATELLITE NAVIGATION)

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.

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 to the most appropriate road.

Fig 4: Identifying Map Matching
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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.
  HINT:
  - 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.
    CAUTION: Do not look directly at the navigation system's laser pickup. Be sure to only operate the navigation as instructed.
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 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 5: Identifying Touch Switch Of Multi-Display Outline
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
AVC-LAN DESCRIPTION
1. What is AVC-LAN?
  AVC-LAN, an abbreviation for "Audio Visual Communication Local Area Network", is a unified standard developed by manufacturers in collaboration with Toyota Motor Corporation. This standard pertains to audio and visual signals as well as switch and communication signals.
  
  Fig 6: Identifying AVC-LAN
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Purpose:
  Recently, car audio systems have rapidly developed and functions has 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 audio systems. The following is a brief overview of the standardization. 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.
    HINT:
    - When a short circuit or circuit breakdown occurs in the AVC-LAN circuit, the audio system does not operate normally due to the communication cutoff.
    - If an audio system is equipped with a navigation system, the multi-display unit acts as the master unit.
    - The radio receiver assy provides resistance to make communication possible.
    - Car audio systems with AVC-LAN circuits have diagnostic functions.
    - Each component has a specified number (3-digit) called a physical address. Each function has a number (2-digit) called a logical address.
COMMUNICATION SYSTEM OUTLINE
1. Components of the navigation system communicate with each other through the AVC-LAN.
2. The radio receiver has a of 60 to 80 Ω, which is necessary for transmitting the communication. This is essential for communication.
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.
3. If a short circuit or open circuit occurs in the AVC-LAN circuit, communication is interrupted and the audio system will stop functioning.
BLUETOOTH OUTLINE
1. BLUETOOTH is a new wireless connection technology that uses the 2.4 GHz frequency band. This makes it possible to remotely connect a cellular phone (BLUETOOTH capable phone*) to the multi-display (BLUETOOTH system is built in), and use a hands-free function with the cellular phone in a pocket or bag.
  HINT:
  
  *: Some versions of BLUETOOTH capable cellular phones may not function with this vehicle.
  
  NOTE: The communication performance of BLUETOOTH may vary depending on obstructions or radio wave conditions between communication devices, electromagnetic radiation, communication device sensitivity, or antenna capacity.
  
  Fig 7: Identifying BLUETOOTH Outline
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002