Navigation system outline

(a) 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)

GPS satellite

GPS satellite

Location by GPS navigation

GPS Antenna

Receive satellite radio wave

Detect the measurement position

Location by GPS navigation

GPS Antenna

Receive satellite radio wave

Detect the measurement position

Vehicle Speed Sensor

Detect vehicle running distance

Detect direction change

Gyro Sensor

Map matching correction

Navigation

Gyro Sensor

Navigation

Gyro Sensor

Location by autonomous navigation

Radio and Navigation Assembly

GPS correction

\

1

Create the cu position track

rrent vehicle ng data

Navigation screen

Map and current vehicle position data processing

Map disc

Map scrolling Map scale switching

Operation

Description

Vehicle Position Calculation

The radio and navigation assembly calculates the current vehicle position (direction and current position) using the direction deviation signal from the gyro sensor and the running distance signal from the vehicle speed sensor and creates the driving route.

Map Display Processing

The radio and navigation assembly displays the vehicle track on the map by processing the vehicle position data, vehicle running track, and map data from the map disc.

Map Matching

The map data from the map disc is compared to the vehicle position and running track data. Then, the vehicle position is matched with the nearest road.

GPS Correction

The vehicle position is matched to the position measured by GPS. Then, the measurement position data from the GPS unit is compared with the vehicle position and running track data. If the position is widely different, the GPS measurement position is used.

Distance Correction

The running distance signal from the vehicle speed sensor includes the error caused by tire wear and slippage between the tires and road surface. Distance correction is performed to account for this. The radio and navigation assembly automatically offsets the running distance signal to make up for the difference between it and the distance data of the map. The offset is automatically updated.

Autonomous Navigation and GPS Wave Navigation p I100028E07

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. (b) 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 radio and navigation assembly.

(1) Gyro sensor

Calculates the direction by detecting angular velocity. It is located in the radio and navigation assembly.

(2) Vehicle speed sensor

Used to calculate the vehicle running distance.

(c) GPS navigation (Satellite navigation)

This method detects the absolute vehicle position using radio waves from a GPS satellite. * GPS satellites were launched by the U.S. Department of Defence for military purposes.

Current longitude/latitude/altitude is determined using the radio wave arrival time from four satellites.

I100029E03

Number of satellites

Measurement

Description

2 or less

Measurement impossible

Vehicle position cannot be obtained because the number of satellites is not enough.

3

2-dimensional measurement is possible

Vehicle position is obtained based on the current longitude and latitude. (This is less precise than 3-dimensional measurement.)

4

3-dimensional measurement is possible

Vehicle position is obtained based on the current longitude, latitude and altitude.

(d) 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.

Start

Start

Matching

The system compares the shape of the roads L1, L2 and L3 to the estimated running track after the vehicle makes a right turn. At point A, the vehicle position differs enough from the shape of L1 that the display switches to the road L2.

Matching

(e) 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.

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