Abstract:
A navigation system is proposed which stores data concerning the motion states of the motor vehicle. The navigation system is usable as a trip recorder, in particular as an accident data recorder.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a navigation system. 
     BACKGROUND INFORMATION 
     A navigation system is described in a periodical Funkschau 5/96, pages 74 et seq. This navigation system, which is intended for installation in a motor vehicle, in particular an automobile, includes several devices for location determination, a permanent memory unit, an input/output unit, and a control system, all of which are located on board the vehicle. Location determination is accomplished on the one hand via Global Positioning System (GPS), which is based on satellites. In addition, compass sensors and wheel rotation sensors are present for relative position determination. A destination can be input under menu control via the input/output unit. The permanent memory unit, a CD-ROM, makes available electronic road and city maps from which the controller calculates a suggested route for the best connection between the current location and the destination. 
     Conventional trip recorders record the speed of a vehicle over a period of many hours, for example, on a card. These devices are designed, however, so that they record short-term speed changes only after a certain delay. Small changes in speed, and short time intervals, are also very difficult to resolve. 
     SUMMARY OF THE INVENTION 
     An arrangement according to the present invention is advantageous in that the motion state of the motor vehicle can be understood with high accuracy in space and time. This becomes particularly significant for determining culpability in the event of an accident. The navigation system is thus simultaneously advantageous as an accident recorder. 
     It is advantageous additionally to record the speed of the vehicle, since this creates a certain redundancy in the data so that recording errors can easily be corrected. 
     It is advantageous to store data regarding the motion state of the vehicle, such as position or direction of travel, in a nonvolatile memory, so that the data are retained even if an interruption in power supply occurs. 
     It is furthermore particularly advantageous, when the memory has been completely filled, to overwrite the oldest data record with the newest one, so that the data most relevant to an explanation of the cause of an accident are available with a high probability. 
     The memory capacity of the navigation system is used particularly efficiently if vehicle states which remain constant for a long period are stored only twice. 
     It is advantageous to play back the memory contents via means which are present on the navigation system, for example, via a display, since simple questions about the previous trip can thereby be answered without complex data transfer to other analysis systems. 
     Moreover, it is particularly advantageous to disable overwriting of the memory either manually, in particular, by actuation of a control element, or by way of a predetermined event, for example, an extreme deceleration or the triggering of an airbag. This ensures that the relevant data for explaining the cause of an accident are available after the accident. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an exemplary embodiment of a navigation system according to the present invention. 
     FIG. 2 illustrates a flowchart of the operation of the exemplary embodiment of the navigation system according to the present invention. 
     FIG. 3 illustrates a flowchart of the operation of another exemplary embodiment of the navigation system according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a navigation system according to the present invention. The number  1  designates a navigation system whose operation is similarly described, for example, in the article cited initially. Navigation system  1  contains a control system  4 , a device  2  for position determination, and a device  3  for determining direction of travel. Further mechanisms  5  are combined in FIG. 1 into one unit. A nonvolatile memory  8 , which in an exemplary embodiment according to the present invention illustrated here is configured as a random access memory (RAM) with battery backup, is connected to navigation system  1 . Data transfer between navigation system  1  and backed-up memory  8  can be influenced by an accident sensor  10 , and interrupted in some circumstances. A timing module  9  is also connected to navigation system  1 . Navigation system  1  has an interface  7  through which data can be read out. The data that can be read out include both the data currently being processed in navigation system  1 , and the memory contents of backed-up memory  8 . 
     The manner in which navigation system  1  operates is explained with reference to the flow chart in FIG. 2. A data processing cycle, controlled by control system  4 , begins with position determination  20  by navigation system  1 . Position determination  20  is immediately followed by time determination  22 . This is accomplished, in the exemplary embodiment according to the present invention illustrated here, with the aid of timing module  9 . Alternatively, however, the time can also be taken from the GPS signal. In a subsequent step  23 , the data record comprising position data and the associated time is written into nonvolatile memory  8 . If all the memory regions already have data records written to them, the oldest data record is erased and is replaced by the data record being written. 
     Data storage is disabled as soon as an indication of an accident is present. In the present example, this is the triggering of an airbag, which is reported by accident sensor  10 . Data storage can also be deactivated manually. Alternatively, accident sensor  10  can also be configured as an acceleration sensor, and can thus report an extraordinary operating state. In the event of an accident, the memory contents can be read out via interface  7 . The data can then be processed further using conventional means, for example, in a different computer. From the data records including position and time data it is possible, for example, to calculate the speed and the deceleration or acceleration of the vehicle. 
     As an alternative to this, the instantaneous speed can be calculated in navigation system  1  and written, together with the associated position and time, into nonvolatile memory  8 . The functional sequence resulting from this is depicted in FIG.  3 . In a first step  20 , a first position is measured, and in a second step  21  it is stored temporarily. This is followed by a waiting step  24  which lasts for a short time interval DT, which is measured by timing module  9  and advantageously is predefined. Another position determination is made in a subsequent step  20 , followed by a temporary storage step  21  in which the second position is also stored in the temporary memory. In calculation step  25 , the speed is calculated from these two data records, by dividing the distance traveled by the time interval. In a following step  27 , the data record—made up of the position at the end of the time interval, the speed, and the time of the second position determination—is stored in nonvolatile memory  8 . As in the previous example, the oldest data record is overwritten as soon as nonvolatile memory  8  is full. 
     The present invention contemplates many possibilities for modifying the examples set forth above. For example, it is equivalent to the functionality presented above to store a data record comprising the position at the beginning of the time interval, the speed, and the time at the beginning of the time interval. 
     Since the direction of travel has already been acquired by the navigation system, it is both possible and desirable to store the direction of travel. On the one hand, it is conceivable that the direction of travel may be relevant for explaining the cause of an accident; on the other hand, the speed in a curve can be calculated more accurately from the position data, since there is no need to resort to a linear interpolation in order to calculate the distance traveled. 
     A further possible embodiment according to the present invention results from the fact that navigation system  1  has devices for measuring speed. This simplifies operation, since the measured speed can be stored, along with a position determined at the same time and the particular time, as a data record 
     A further possible embodiment according to the present invention results from the fact that the contents of the nonvolatile memory are personalized. In this context, data about the driver or the vehicle can be input at the beginning of the trip or at any desired later time. This can be done using the same input device of navigation system  1  that is already present for inputting a desired destination. The data that are input can then, preferably together with the time at which they were input, also be stored in the nonvolatile memory. In this case it is advantageous to exempt these personalization data from overwriting of the respective oldest data record. 
     Moreover, a further possible embodiment according to the present invention which has the advantage of using memory  8  more efficiently results from the fact that the control system compares the position in the last two stored data records with the position in the new data record that is to be stored, and stores the new data record only if at least two of the three positions contained in the data records differ from one another. This prevents the memory from being filled up with redundant information when the vehicle is stationary for long periods.