Abstract:
A method for rating road classifications in navigational systems using fixed average speeds input into the system, to be replaced by or, if necessary, supplemented with continuously corrected, i.e., updated speed values.

Description:
BACKGROUND INFORMATION 
     Although applicable to any information systems which involve rating of specific, time-variable system parameters, the present invention, as well as its underlying problem definition, are clarified with reference to a navigational system located on board an automobile. 
     Present-day navigational systems are essentially composed of the following subsystems: digital map, computational module for automatic route determination, position-finding device, system management, automotive sensor technology for recognizing vehicle movements, as well as input unit and output unit for the operation and guidance system. 
     In navigational systems having route guidance, to calculate the travel path, also referred to in the following as route, from the geographic coordinate S, usually representing the vehicle position, to another coordinate Z, as the destination, which is usually specified by the location, road or intersection and, in some instances by other information such as street number, one must rate (evaluate) the roads to be traveled, to achieve an “optimal” route guidance in accordance with a predefined criterion. 
     If the user of the system chooses “short route” as optimal, for example, then the criterion “search for the shortest drivable route” is stipulated for the system to calculate a route. Usually, however, such a stipulation (input) does not lead to an effective route guidance, for example when it comes to many overland routes via country roads or in larger cities having many “30 k.p.h. zones”. 
     For that reason, a “fast” connection from S to Z is often considered to be optimal. In this context, “fast” means that for the route computation, the roads are classified by type, such as expressway, national highway, country road, etc. The individual road classifications in related-art navigational systems are then assigned fixed average speeds, such as 100 km/h for superhighways, 80 km/h for national highways, etc. The route computation is then set up to calculate a route having altogether a shortest possible driving time. 
     In addition, there is also information about the probable period of time until the destination is reached. This can be output to the user of the system, whether it be as a time span or as an estimated time of arrival. 
     Navigational systems of this kind are, however, static with respect to external conditions. They do not take into account the actual average speeds which are driven and which can be reached on the route. Furthermore, systems of this kind are not able to incorporate the user&#39;s driving habits in the route planning. For these reasons, they usually only provide imprecise information about the time until the destination is reached. 
     In addition, such a static assignment of average speeds to specific road sections often results in longer routes than a system user would desire or would select if he/she were to use a road map. Moreover, depending on the average speeds selected, the routes calculated by the system are often characterized by an unjustified preference for major roads, such as superhighways or national highways. 
     SUMMARY OF THE INVENTION 
     The method of the present invention has the advantage that, following a certain “transient recovery time”, (“response time”) the route calculation is able to generate better routes for the most frequently driven surrounding area. In most cases, this is associated with a shorter driving time. In addition, the routes calculated by the system are better adapted to the user&#39;s individual driving behavior. As a result, the time needed to reach a destination, as queried of the system or output by the system, is more accurate. 
     An idea underlying the present invention is for the above described, static rating of the road classifications using fixed average speeds input into the system, to be replaced by or, if necessary, supplemented with continuously corrected, i.e., updated speed values. In other words, instead of the fixed and invariably predefined road-classification speeds of the related art, actually reached speeds learned by the system during vehicle operation are, to an extent, used as a basis for route planning and estimating arrival time, etc. Because such average driving-speed values learned by the system are stored in a non-volatile memory, they are also available for a new route planning after the system is turned off. 
     For this, the information available during the driving operation, pertaining to the currently driven road classification and speed, is repeated, for instance at intervals of one second or longer, and set against one another, separately for each road classification. As a starting value for such a calculation, one may use, for example, the fixed average speed indicated above, or alternatively thereto, a speed to be entered by the driver into the system. 
     Thus, in accordance with the general aspect of the present invention, a dynamically adapted average value of the vehicle speed is used for calculating the route for one or more partial sections K of a particular driven road. The corresponding linking of database fields implemented in the navigational system is, therefore, also dynamic. The system adapts itself to the actually existing conditions. 
     In accordance with one preferred embodiment, a filtering takes place over time, in order to recalculate the average vehicle-speed value that is relevant to the rating. Such a filtering constitutes an especially simple implementation. In principle, however, other algorithms are also possible. 
     Another preferred embodiment provides for weighting the influence of this adaptation, variably, with respect to the recalculation. This makes it possible to minimize the effects of a “self-learning process” of the navigational system on the stored attribute values for the average speed of a particular road section K. This can be useful in the event of snowfall or other adverse weather conditions, so that rare, exceptional events do not become the basis of a self-learning process for the navigational system. In one simple variant, the user may choose, for example, between heavy, average, and weak weighting. Alternatively, other weighting factors may also be input by the user. 
     For this, the following schema is given: 
     When v(tO,K) is the fixed average speed preset for road classification K at the first system start-up; v(tn,K) is the adapted average speed calculated for road classification K at instant tn; v(tn+1) is the instantaneously driven speed and x the weighting factor, with which the old value in the particular case is linked to the new value, then, at instant tn+1, the instantaneously adapted average speed is obtained for K as 
     
       
           v ( t   n+1   r,K )=(1 −x ). v ( t   n   ,K )+ x.v ( t   n+1 ). 
       
     
     In this context, it does not matter whether the road classifications are actually rated in the “km/h” unit; what is important is the change in ratings as a function of values which are actually attained. 
     To be able to continue to use the values calculated within one driving cycle later on, provision is made to store them in a non-volatile memory. 
     Likewise provided is the introduction of upper and lower limits for each of the learned speeds; generally, this is more likely to result in unfavorable route proposals, for example, if the rating of an expressway were lower than that of a country road. 
     In accordance with another preferred embodiment, the method of the present invention may be improved by undertaking a separation into a so-called short-term and long-term adaptation, including different time constants and/or weightings xshort and xlong, respectively: the case of short-term adaptation, the intervals between tn and tn+i lie in the seconds range, and, in the case of long-term adaptation, in the minutes range. In accordance with this separation, the driven speed may be calculated within the selected period of time. The above-mentioned weighting factor x may also be selected to be greater or smaller, depending on whether it is practical to give the active speed value a greater or smaller influence in the recalculation of the average value. The values from the long-term adaptation are preferably used for the route calculation, and those from the short-term adaptation are used for updating the time indication until the destination is reached. 
     In accordance with another preferred embodiment, a starting value may be proposed by the system user for recalculating the average value that is relevant to the rating, and be entered by him/her into the system. This makes the system more flexible in its response to individual driving habits and to the configuration of individual road sections. 
     In accordance with another preferred embodiment, the method of the present invention may be simplified by an adaptation, without explicit consideration of the road classifications, only with respect to the average vehicle speed, including appropriate percentage increase or decrease in the rating factors of the individual road classifications. The average vehicle-speed value is then calculated on the basis of the current average vehicle-speed value, and the weighting of road classifications, preset by the system, loses influence. A measure of this kind likewise enhances the flexibility of the navigational system. 
     Another preferred embodiment provides for the user to be given a variably adjustable way to influence route proposals generated by the system, in order to minimize or eliminate the influence of values learned by the system. The method of the present invention may be supplemented in this manner using statistics pertaining to the length of the calculated routes and analysis thereof. when the user drives frequently in the neighborhood of his/her residence, for example in a congested area, then, due to increased traffic volume, such as rush-hour traffic, the adapted values are more likely to become low for the road classification rating. When the intention is to calculate a route to a more distant destination, it can then happen, under unfavorable conditions, that an inexpert route selection is made, for example, due to strong consideration of minor roads. In such a case, given such atypical destination distances, it would be more beneficial, for example, for part of the adaptation to be carried out by overriding the values learned by the system, towards starting values acquired from long-term experience or preset by the user. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention are illustrated in the drawings and are elucidated in the following description. 
     FIG. 1 shows a detail of a vehicle&#39;s navigational system including elements important to the present invention. 
     FIG. 2 shows a schematic block diagram including the steps of importance to the present invention, during travel, in accordance with a preferred exemplary embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a detail of a vehicle&#39;s navigational system including elements important to the present invention. 
     A processor  10  is linked to an input device  12  for inputting starting and destination locations, as well as for inputting other data. An output for the driver may follow optically and acoustically via an output device  14 . This essentially includes a display and associated speakers. 
     In addition, processor  10  is connected to a memory  16 . Processor  10  has read/write access to memory  16 . Memory  16  is advantageously set up as a non-volatile memory. As described in greater detail below, it is intended for values of the instantaneous average vehicle speed, updated during travel, to be read out of this memory, and new values are to be written into it. 
     In addition, processor  10  is connected via an averaging unit  18  to the motor vehicle&#39;s speed signaling device  20 . By way of the averaging unit, which may be a suitable, related-art logic circuit having integrating action, active, instantaneous speed values are read off from speed signaling device  20  and, following appropriate time intervals, combined to form an arithmetic, i.e., integrated average value that is of significance to the particular time interval. 
     FIG. 2 shows a schematic block diagram including the steps of importance to the present invention, during travel, in accordance with a preferred exemplary embodiment. 
     In a step  200 , the user starts the system and, in a step  205 , allows the system to determine road classification K. He/she may then enter the destination. 
     In accordance with the preferred functional sequence of the exemplary embodiment, as illustrated in FIG. 2, method steps for a specific road section K, treated as a unit, are repeated in an outer loop, whose loop body begins after step  200  and ends at decision  240 . The average driving-speed values are repeated at specific instances tn, n=0, 1, 2 . . . This repetition is shown in the inner loop, beginning with step  215  and ending with step  240 . 
     In step  210 , n is set to 0, and all values specific to road section K (section of the driven road classification) are read in from the navigational system&#39;s database, in order to initialize all quantities which are important to the method. In a further step  215 , n is increased by 1. 
     At the first pass through the inner loop, in a step  220 , the above-mentioned starting value for the average speed is read out of memory  16 . Subsequently, in a step  225 , the average speed value present in averaging unit  18 , which is based on the actually just driven speed specifications (data) from speed signaling device  20 , is recorded by processor  10 . 
     Average vehicle-speed value v(t n+1 ,K), which is decisive for the rating, is subsequently calculated in accordance with the following formula: 
     
       
           v ( t   n+1   r,K )=(1 −x ). v ( t   n   ,K )+ x.v ( t   n+1 ). 
       
     
     This newly calculated value is then stored as an updated value in memory  16 , in step  235 , and may now be used by the system for route calculations and/or to indicate the probable arrival time at the destination. 
     It is quite evident that, after one single pass through the inner loop, this newly calculated value is still not accurate enough. It is then determined in a step  240 , whether the motor vehicle is still located on the same partial section or road section K. If this is not the case, the system loops back to step  215 , and the method is continued, following the same sequence,—assuming a normal travel characteristic—the value stored in memory  16  becoming more and more realistic with every pass-through. 
     If this is not the case, preparations are made to be able to process the next partial section K. Depending on the navigational system&#39;s implementation method, the values relevant to this partial section K are read out of the database, and the system loops back to step  205 . The method is then continued for this partial section, following the same principle. 
     The method ends with the switching off of the system. 
     The inner loop may preferably be passed through relatively often, per minute. Preferred values lie within an interval of between 60 times per minute and two times per minute. 
     The outer loop is repeated as many times as there are different road sections K on the route. 
     In the following, the advantageous effect of the method of the present invention is demonstrated on the basis of an exemplary calculation for a section from S to Z, it being possible to cover the section via two alternative routes. 
     Route A includes a 10 km country road (assumed average speed v(tO, county road) =60 km/h), 80 km of expressway (100 km/h), and, again, of 10 km county road. 
     The alternative route B includes, altogether, 30 km of county road and 60 km of national highway (80 km/h). 
     Given fixed average speeds, this yields route A over the expressway (fast route), which is, however, 10 km longer than route B: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Route A 
                   
               
               
                   
                 20 km county road 
                 20 min 
               
               
                   
                 80 km expressway 
                 48 min 
               
               
                   
                   
                 68 min 
               
               
                   
                 Route B 
               
               
                   
                 20 km county road 
                 30 min 
               
               
                   
                 60 km national highway 
                 45 min 
               
               
                   
                   
                 75 min 
               
               
                   
                   
               
             
          
         
       
     
     The road classification rating in accordance with the given exemplary embodiment is now able to distinguish among different cases: 
     The user frequently drives in an area and at a time of day in which the expressway is usually congested; the average speed is “learned downward” to 80 km/h; therefore, the path via the national highway proves to be the better route: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Route A 
                   
               
               
                   
                 20 km county road 
                 20 min 
               
               
                   
                 80 km expressway 
                 60 min 
               
               
                   
                   
                 80 min 
               
               
                   
                 Route B 
               
               
                   
                 20 km county road 
                 30 min 
               
               
                   
                 60 km national highway 
                 45 min 
               
               
                   
                   
                 75 min 
               
               
                   
                   
               
             
          
         
       
     
     Even when the national highways driven at average speeds appear to be faster than expected (95 km/h), the rating, altered by adaptation, leads to route B, even though the advantage is minimal in this example. 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Route A 
                   
               
               
                   
                 20 km county road 
                 20 min 
               
               
                   
                 80 km expressway 
                 48 min 
               
               
                   
                   
                 68 min 
               
               
                   
                 Route B 
               
               
                   
                 30 km county road 
                 30 min 
               
               
                   
                 60 km national highway 
                 37 min 
               
               
                   
                   
                 67 min 
               
               
                   
                   
               
             
          
         
       
     
     If the system user prefers a speedy style of driving and if available expressways are found—the average speed is raised to 120 km/h —, the error at the 11% level in the route&#39;s time indication is compensated through adaptation of the road&#39;s rating: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Fixed values 
                   
               
               
                   
                 20 km county road 
                 20 min 
               
               
                   
                 80 km expressway 
                 48 min 
               
               
                   
                   
                 68 min 
               
               
                   
                 Adapted values 
               
               
                   
                 20 km county road 
                 20 min 
               
               
                   
                 80 km expressway 
                 40 min 
               
               
                   
                   
                 60 min 
               
               
                   
                   
               
             
          
         
       
     
     The short-term adaptation mentioned and described above is able to correct the time indication in the event of traffic jams even more effectively and make the adaptation to the prevailing road condition. 
     Although the present invention is described above with reference to a preferred embodiment, it is not limited thereto, but instead may be modified in a variety of ways. 
     For example, the frequency with which the inner loop is passed through may be adapted to the navigational system&#39;s computing capacity. In addition, other mathematical algorithms may be employed to provide values which are usable to the system from the multiplicity of average speed values read in from the speed signaling device via the average-value generator. In this case, various filter functions may be useful. 
     In addition, the system may be equipped in a practical manner with an additional option which allows one to temporarily discontinue with the method of the present invention and, instead, to revert to standard road-classification rating values present in the system. Here, the benefit is derived that the system does not learn “incorrectly”, for example, when the driver stops somewhere along the route to purchase something, or if he/she makes some other kind of atypical intermediate stop. 
     When the vehicle is turned off (ignition off), the navigational unit is usually switched off and/or is set to a stand-by mode. A temporary method for switching off the unit may also be provided during operation as a towing vehicle (towing, trailer towing).