Vehicle navigation apparatus

Abstract: A vehicle navigation apparatus comprises a self-contained positioning system, GPS positioning system, and a controller for performing arithmetic operation on the basis of the output of any one of the self-contained positioning system and the GPS positioning system so as to display various navigation information on a displayer. The controller corrects the bearing data based on the self-contained positioning system with respect to that based on the GPS positioning system if the bearing data of self-contained positioning system differs from that of the GPS positioning system by more than a predetermined value when a vehicle velocity determined on the basis of the position data from any one of the positioning systems exceeds a predetermined value.

Description: The present invention relates to a vehicle navigation apparatus according to the preamble of claim 1. It is well known that the GPS positioning system is superior in accuracy to the self-contained positioning system. US-A 4 903 212 discloses a GPS self-contained combination type navigation system. This conventional vehicle navigation apparatus normally displays various pieces of navigation information based on position data from the GPS positioning system, and displays the information from the self-contained positioning system when proper navigation information is not available from the GPS positioning system for various reasons. In this way the navigation information can be supplied from either the GPS positioning system or the self-contained positioning system to the displayer. However, geomagnetism is usually very weak and therefore a geomagnetic sensor as a bearing sensor used in the self-contained positioning system is quick susceptible to external disturbances. Thus, error results when the geomagnetic sensor is magnetized, the vehicle is magnetized, or when the vehicle runs along a railway or runs across a railway. The gyro used as a bearing sensor in the self-contained positioning system tends to be affected by external disturbances and results in errors that accumulate. In order to correct the bearing data of the bearing sensor in the self-contained positioning system, it is necessary not only to reset the offset values but also to correct the bearing sensor against some more accurate reference. This is an inconvenient and time consuming task. SUMMARY OF THE INVENTION The present invention was made in view of the aforementioned drawbacks. An object of the invention is to provide a vehicle navigation apparatus in which the bearing data of the bearing sensor in the self-contained positioning system is automatically corrected with respect to that of the GPS positioning system as well as the accumulated error is minimized. In a vehicle navigation apparatus according to the present invention, when the vehicle velocity calculated on the basis of the output of the self-contained positioning system or GPS positioning system is over a predetermined value, a decision is made based on whether the error in bearing data based on the self-contained positioning system with respect to the GPS positioning system is greater than a given value. If the error in bearing data of the self-contained positioning system is greater than a given value, then the bearing data of the self-contained positioning system is corrected by the bearing data from the GPS positioning system. BRIEF DESCRIPTION OF THE DRAWINGS Features and other objects of the invention will be more apparent from the detailed description of the preferred embodiment with reference to the accompanying drawings in which: Fig. 1 is a block diagram showing a general configuration of an embodiment of a vehicle navigation apparatus according to the present invention; and Fig. 2 is a flowchart showing the operation of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Fig. 1 is a block diagram showing the general configuration of an embodiment of a vehicle navigation apparatus according to the present invention. A GPS receiver 3 receives the waves from at least three satellites so as to determine the present position of the vehicle. A CPU 5 receives the present position data from the GPS receiver 3 via an I/O 4. Transmitting and receiving the data between an arithmetic logic unit 6 and a RAM 8, the CPU 5 performs calculation of various data to be supplied to the displayer under control of the system program stored in a ROM 7. When the vehicle is running on a road, the navigation system displays at each moment various navigation information based on the present position of the vehicle such as the velocity of the vehicle and the bearing or direction in which the vehicle is running. Meanwhile, a self-contained positioning system consists of a vehicle velocity sensor 2 such as a pulse generator and a geomagnetic sensor 1. The CPU 5 receives the data from the geomagnetic sensor 1 and the vehicle velocity sensor 2 via an I/O 4. Transmitting and receiving the data between the arithmetic logic unit 6 and the RAM 8 under control of the system program stored in a ROM 7, the CPU 5 calculates various data such as the position data indicative of the present position of the vehicle velocity, bearing data or direction in which the vehicle is running, and supplies to the displayer. Generally, the GPS positioning system is much more accurate than the self-containing system. When the vehicle is running at a reasonably high speed, for example 10 km/h, the GPS positioning is reasonably accurate. However, when the vehicle is running at a speed much slower than 10 km/h, GPS positioning is not quite accurate because the distance the vehicle traveled in a given time length is too short to be detected accurately. In which case, the self-contained positioning system is much more reliable than the GPS positioning system. In the present invention, the bearing correction data is calculated on the basis of the error in bearing data of self-contained positioning system with respect to the bearing data obtained from the GPS positioning system, and is stored into the RAM. This bearing correction data is used to correct the bearing data of the self-contained positioning system when the information from the GPS positioning system is not properly obtained. A microcomputer-based display-drive circuit 10 receives the outputs of the CPU 5 and the map data in the CD-ROM 9, and edits the map data so as to display the map information on a displayer 11. The I/O 4, CPU 5, arithmetic logic unit 6, ROM 7, and RAM 8 constitute a microcomputer-based controller as a whole which controls associated devices such as the CD-ROM 9, drive circuit 10, and displayer 11. Operation Fig. 2 is a flowchart showing the operation of the present invention. First, a decision is made based on whether or not proper data from the GPS positioning system is available (step 1). If the data is available, the CPU receives the respective data from both self-contained positioning system and GPS positioning system, and stores the data into the RAM 8 (step 2). At step 3, if the vehicle velocity data determined on the basis of the output from either the self-contained positioning system or the GPS positioning system is above a predetermined value, for example, 10 km/h, then the arithmetic logic unit 6 calculates the error O in bearing data of the self-contained positioning system with respect to the GPS positioning system (step 4). Then, a decision is made based on whether the absolute value of the error O in bearing data is greater than a predetermined value, for example, 30 degrees (step 5). If the error is more than 30 degrees in step 5, then the CPU produces a bearing correction data for the self-contained positioning system with respect to the GPS positioning system and then stores it into the RAM 8 as well as outputs the respective data to the drive circuit 10 (step 6). Then, the program returns to step 1. If the proper data is not available from the GPS positioning system at step 1, or if the vehicle velocity is below, for example, 10 km/h at step 3, the bearing data of the self-contained system is corrected by the bearing correction data stored in the RAM and is outputted to the drive circuit 10 together with other data (step 7), then the program returns to step 1. If the error in bearing data is less than 30 degrees, then the CPU 5 outputs the respective data received from the GPS positioning system to the drive circuit 10 (step 8), and then the program returns to step 1. The drive circuit 10 receives the respective data from the CPU 5 and outputs to the displayer 11. The drive circuit 10 also edits the map data read from the CD-ROM 9 as required on the basis of the data from the CPU 5 so as to display map information on the displayer 11. While the above embodiment has been described with respect to an apparatus in which the arithmetic logic unit 6 and the CPU 5 are formed of separate devices, respectively, the CPU 5 may be arranged to perform the role played by the unit 6.

Claims: A vehicle navigation apparatus comprising a self-contained positioning system based on a bearing sensor (1), a vehicle velocity sensor (2), a GPS positioning system based on a GPS receiver (3), and a controller (5, 6) for performing arithmetic operation on the basis of outputs from any one of the self-contained positioning system and the GPS positioning system so as to display various navigation information on a display, CHARACTERIZED in that said controller (5, 6) is adapted to calculate and store bearing correction data for the self-contained positioning system based on bearing data from self-contained positioning system and bearing data from the GPS positioning system (ST6) , if the bearing data of self-contained positioning system differs from the bearing data from the GPS positioning system by more than a predetermined value (ST4, ST5) when a vehicle velocity determined based on the outputs of any one of said self-contained positioning system and GPS positioning system is above a predetermined value (ST3).

Inventors: ENDO ISAO, HONDA TSUTOMU, KAWASAKI KENICHIRO, SAKAGUCHI SHOZABURO, TAKEMURA SHINICHI, ENDO, ISAO, HONDA, TSUTOMU, KAWASAKI, KENICHIRO, SAKAGUCHI, SHOZABURO, TAKEMURA, SHINICHI, ENDO, ISAO, C/O PIONEER ELECTRONIC CORP., HONDA, TSUTOMU, C/O PIONEER ELECTRONIC CORP., KAWASAKI, KENICHIRO, C/O PIONEER ELECTRONIC CORP., SAKAGUCHI, SHOZABURO, C/O PIONEER ELECTRONIC CORP., TAKEMURA, SHINICHI, C/O PIONEER ELECTRONIC CORP.
Applicants: PIONEER ELECTRONIC CORP, PIONEER ELECTRONIC CORPORATION
Application year: 1991
Main classification: G01S5
IPC codes: G08G1, G01S5, G01C21