Patent Publication Number: US-2012029803-A1

Title: Fuel-consumption projecting apparatus, fuel-consumption projecting method, fuel-consumption projecting program, and recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a fuel-consumption projecting apparatus, a fuel-consumption projecting method, a fuel-consumption projecting program, and a recording medium that estimate vehicle fuel efficiency. However, use of the invention is not limited to the fuel-consumption projecting apparatus, fuel-consumption projecting method, fuel-consumption projecting program, and the recording medium above. 
     BACKGROUND ART 
     Conventionally, various methods have been proposed to project fuel consumption of a vehicle in transit (see, for example, Patent document 1). Patent document 1 discloses technology that retrieves a route for which fuel consumption is low. The disclosed technology stores according to vehicle type, fuel consumption information corresponding to traveling speed, and uses link data and the fuel consumption information to calculate a route for which the least amount of fuel is consumed. Additionally, Patent document 1 discloses a method that correlates traveling speed and the fuel consumption information collected from a fuel consumption detector and that uses the correlated information in subsequent fuel-consumption projections. 
       FIG. 12  is a graph of vehicle speed and fuel consumption. In  FIG. 12 , the vertical axis indicates fuel consumption and the horizontal axis indicates traveling speed. The relation between traveling speed and fuel consumption is commonly known to be expressed by the equation below, for example. 
       fc= m 1+ m 2· x 2+ m 3· x 3+ m 4· x  
 
     Here, fc represents fuel consumption per unit time; x represents average speed for a unit interval; and m1 to m4 are constants.
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2005-172582   

     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     However, the conventional technology above does not take vehicle acceleration into account when projecting fuel consumption, arising in a problem of low projection accuracy. The effect vehicle acceleration has on fuel consumption is not small. For example, if acceleration during travel is out of the ordinary, the projection accuracy of the conventional technology above becomes poor. The shape and slope of the traveled road, driving technique (abrupt acceleration, etc.) may also cause the margin of error to increase between the actual and the projected fuel consumption. Furthermore, since the frequency of acceleration is high on winding roads, when such roads are traveled, projection accuracy becomes poor. 
     Means for Solving Problem 
     To solve the problems above and achieve an object, a fuel-consumption projecting apparatus according to claim  1  projects fuel consumption by a vehicle for a given interval. The fuel-consumption projecting apparatus includes a projecting unit that using a first equation, projects the fuel consumption before travel begins along the given interval; an estimating unit that using a second equation that sets vehicle acceleration occurring during travel as a variable, estimates the fuel consumption occurring during travel; a correcting unit that corrects the first equation, based on the fuel consumption projected by the projecting unit and the fuel consumption estimated by the estimating unit. 
     Further, a fuel-consumption projecting method according to claim  11  is a method of projecting fuel consumption by a vehicle for a given interval. The fuel-consumption projecting method includes projecting the fuel consumption before travel begins along the given interval, by using a first equation; estimating the fuel consumption occurring during travel, the fuel consumption being estimated by using a second equation that sets vehicle acceleration occurring during travel as a variable; and correcting the first equation, based on the fuel consumption projected at the projecting and the fuel consumption estimated at the estimating. 
     A fuel-consumption projecting program according to claim  12  causes a computer to execute the fuel-consumption projecting method according to claim  11 . 
     Further, a recording medium according to claim  13  stores therein the fuel-consumption projecting program according to claim  12 . 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a functional configuration of a fuel-consumption projecting apparatus according to an embodiment; 
         FIG. 2  is a flowchart of a fuel-consumption projecting process of the fuel-consumption projecting apparatus; 
         FIG. 3  is a block diagram of a hardware configuration of a navigation apparatus; 
         FIG. 4  is a schematic of an example of a fuel consumption projecting process by the navigation apparatus; 
         FIG. 5  is a schematic of an example of the fuel consumption projecting process by the navigation apparatus; 
         FIG. 6  depicts a coefficient table retained by the navigation apparatus; 
         FIG. 7  is a graph of coefficient k 1  and displacement; 
         FIG. 8  is a graph of coefficient k 2  and vehicle weight; 
         FIG. 9  is a graph of coefficient k 3  and displacement; 
         FIG. 10  is a schematic of acceleration of a vehicle traveling a road that has a slope; 
         FIG. 11  is a flowchart of the fuel-consumption projecting process performed by the navigation apparatus  300 ; and 
         FIG. 12  is a graph of vehicle speed and fuel consumption. 
     
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     With reference to the accompanying drawings, preferred embodiments of a fuel-consumption projecting apparatus, a fuel-consumption projecting method, a fuel-consumption projecting program, and a recording medium according to the present invention will be described in detail. 
     Embodiment 
       FIG. 1  is a block diagram of a functional configuration of a fuel-consumption projecting apparatus according to an embodiment. A fuel-consumption projecting apparatus  100  projects vehicle fuel consumption for a given interval and includes a projecting unit  101 , an estimating unit  102 , a correcting unit  103 , an average-speed information acquiring unit  104 , and a traveling-speed information acquiring unit  105 . Here, a given interval is, for example, a route linking a user set starting point and destination. Hereinafter, the interval for which the fuel-consumption projecting apparatus  100  projects fuel consumption is referred to as the “projection-target interval”. 
     The projecting unit  101  uses a first equation and projects fuel consumption, before the vehicle begins to travel the projection-target interval. The first equation is function that sets vehicle speed as a variable and for example, is equation (1). Fuel consumption calculated using equation (1) indicates instantaneous fuel consumption. Consequently, the total amount of fuel consumed when the projection-target interval is traveled is obtained by the summation of equation (1). 
       fc 1 ( x )= h ·( m   1   +m   2   ·x   2   +m   3   ·x   3   +m   4   ·x )  (1)
 
     Where, 
     fc 1 : fuel consumption per unit time (cc/sec) 
     x: 
     
       
         
           
             speed 
              
             
                 
             
              
             
               ( 
               
                 km 
                 
                   h 
                    
                   
                       
                   
                 
               
               ) 
             
           
         
       
     
     h: correction coefficient 
     m 1  to m 4 : constants 
     To project fuel consumption, the projecting unit  101  substitutes into the first equation, average speed information (average speed information for each unit interval in the projection-target interval) acquired by the average-speed information acquiring unit  104  described hereinafter. Further, configuration may be such that to recalculate fuel consumption, the projecting unit  101  substitutes into the first equation, speed information that is acquired by the traveling-speed information acquiring unit  105  during travel along the projection-target interval. 
     The estimating unit  102  uses a second equation that regards vehicle acceleration during travel along the projection-target interval as a variable and estimates the amount of fuel consumed for travel along the projection-target interval. The second equation is a function that sets vehicle acceleration and speed as variables and is equation (2), for example. Fuel consumption calculated using equation (2) indicates instantaneous fuel consumption. Consequently, the total amount of fuel consumed when the projection-target interval is traveled is obtained by the summation of equation (2). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               fc 
                               2 
                             
                              
                             
                               ( 
                               x 
                               ) 
                             
                           
                            
                           
                               
                           
                           = 
                           
                             
                               k 
                               1 
                             
                             + 
                             
                               
                                 k 
                                 2 
                               
                               · 
                               x 
                               · 
                               
                                 ( 
                                 
                                   
                                     
                                        
                                       x 
                                     
                                     
                                        
                                       t 
                                     
                                   
                                   + 
                                   
                                     
                                       g 
                                       · 
                                       sin 
                                     
                                      
                                     
                                         
                                     
                                      
                                     θ 
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               
                                 k 
                                 3 
                               
                               · 
                               
                                 G 
                                  
                                 
                                   ( 
                                   x 
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             G 
                              
                             
                               ( 
                               x 
                               ) 
                             
                           
                           = 
                           
                             
                               x 
                               3 
                             
                             + 
                             
                               
                                 a 
                                 1 
                               
                               · 
                               
                                 x 
                                 2 
                               
                             
                             + 
                             
                               
                                 a 
                                 2 
                               
                               · 
                               x 
                             
                           
                         
                       
                     
                   
                   } 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Where, 
     fc 2 (x): fuel consumption per unit time (cc/sec) 
     x: speed 
     
       
         
           
             ( 
             
               km 
               h 
             
             ) 
           
         
       
     
     
       
         
           
             
               
                  
                 x 
               
               
                  
                 t 
               
             
              
             
               : 
             
              
             
                 
             
              
             acceleration 
              
             
                 
             
              
             
               ( 
               
                 km 
                 
                   h 
                   · 
                   s 
                 
               
               ) 
             
           
         
       
     
     g: gravitational acceleration 
     
       
         
           
             ( 
             
               = 
               
                 35.3 
                  
                 
                   ( 
                   
                     km 
                     
                       h 
                       · 
                       s 
                     
                   
                   ) 
                 
               
             
             ) 
           
         
       
     
     θ: slope of traveled road (radian) 
     k 1 : coefficient based on fuel consumption when vehicle is stopped with engine running 
     
       
         
           
             ( 
             
               cc 
               s 
             
             ) 
           
         
       
     
     k 2 : coefficient based on fuel consumption during acceleration 
     
       
         
           
             ( 
             
               
                 cc 
                 · 
                 
                   h 
                   2 
                 
               
               
                 km 
                 2 
               
             
             ) 
           
         
       
     
     k 3 : coefficient based on drag and rolling resistance 
     
       
         
           
             ( 
             
               
                 cc 
                 · 
                 
                   h 
                   3 
                 
               
               
                 
                   km 
                   3 
                 
                 · 
                 s 
               
             
             ) 
           
         
       
     
     a 1 =−100 (km/h) 
     a 2 =6000 (km/h 2 ) 
     In equation (2), time is indicated in units of hours (h) and seconds (s) because distance per hour (km/h) is adopted as the unit for speed and seconds (s) are adopted as the unit of time for estimating fuel consumption. Appropriate calculations are performed on the values if the units of time are to be made uniform. 
     The correcting unit  103  corrects the first equation, based on the fuel consumption projected by the projecting unit  101  and the fuel consumption estimated by the estimating unit  102 . The correcting unit  103 , for example, calculates a correction coefficient from the fuel consumption projected by the projecting unit  101  and the fuel consumption estimated by the estimating unit  102  and appends the calculated correction coefficient to the first equation to thereby correct the first equation. The correction coefficient is, for example, the ratio of the fuel consumption projected by the projecting unit  101  and the fuel consumption estimated by the estimating unit  102 . In this case, a correction coefficient h is expressed by equation (3), where Σ indicates the summation of instantaneous fuel consumption of intervals traveled by the vehicle. 
     
       
         
           
             
               
                 
                   h 
                   = 
                   
                     
                       ∑ 
                       
                         
                           fc 
                           2 
                         
                          
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                     
                       ∑ 
                       
                         
                           fc 
                           1 
                         
                          
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The correcting unit  103 , for example, regards the ratio of the fuel consumption projected by the projecting unit  101  before travel along the projection-target interval begins and the fuel consumption estimated by the estimating unit  102  during travel along the projection-target interval as the correction coefficient. Further, for example, during travel along the projection-target interval, if the projecting unit  101  recalculates the fuel consumption by substituting into the first equation, speed information (speed information acquired by the traveling-speed information acquiring unit  105 ) for the vehicle in transit, configuration may be such that the correcting unit  103  regards the ratio of the recalculated fuel consumption and the fuel consumption estimated by the estimating unit  102  as the correction coefficient. 
     Further, configuration may be such that when, for example, during travel along the projection-target interval, the type of the road traveled by the vehicle does not change for a given distance or longer, or for a given period or longer, the correcting unit  103  corrects equation (1). When the road type changes, vehicle speed/acceleration may significantly change and if the acceleration information and speed information before the change is used, the accuracy of the fuel consumption estimate may drop. Further, configuration may be such that the correcting unit  103 , for example, corrects the first equation at given periods during travel along the projection-target interval. 
     The average-speed information acquiring unit  104  acquires for each unit interval in the projection-target interval, average speed information. A unit interval, for example, is a link in map data. Further, average speed information is the distance of a unit interval divided by the average time required to traverse the unit interval. The average-speed information acquiring unit  104 , for example, reads out average speed information included in map data to acquire the average speed information. 
     The traveling-speed information acquiring unit  105  acquires acceleration information and speed information for the vehicle in transit. The traveling-speed information acquiring unit  105 , for example, acquires acceleration information and speed information output from an accelerometer and speedometer equipped on the vehicle. If an accelerometer and speedometer are equipped on the fuel-consumption projecting apparatus  100 , the acceleration information and speed information from these sensors may be acquired. Further, configuration may be such that the traveling-speed information acquiring unit  105  itself can measure (or calculate) acceleration and speed. 
       FIG. 2  is a flowchart of a fuel-consumption projecting process of the fuel-consumption projecting apparatus. In the flowchart depicted in  FIG. 2 , in the fuel-consumption projecting apparatus  100 , the average-speed information acquiring unit  104  acquires average speed information for the projection-target interval, before travel along the projection-target interval begins (step S 201 ); and the projecting unit  101  uses the first equation to project fuel consumption for the projection-target interval (step S 202 ). 
     The fuel-consumption projecting apparatus  100  remains in standby until the vehicle begins to travel (step S 203 : NO) and when the vehicle begins to travel (step S 203 : YES), the traveling-speed information acquiring unit  105  acquires acceleration information and speed information for the vehicle (step S 204 ). Subsequently, in the fuel-consumption projecting apparatus  100 , the estimating unit  102  uses the second equation to estimate fuel consumption of the vehicle in transit (step S 205 ). 
     Further, in the fuel-consumption projecting apparatus  100 , the correcting unit  103  calculates a correction coefficient (step S 206 ) and corrects the first equation used by the projecting unit  101  to project fuel consumption (step S 207 ). The correction coefficient calculated at step S 206 , for example, is the ratio of the fuel consumption projected by the projecting unit  101  before travel along the projection-target interval begins and the fuel consumption estimated by the estimating unit  102  during travel along the projection-target interval. Further, the correction coefficient, for example, may be the ratio of the fuel consumption recalculated by substituting into the first equation (1), actual speed information (the speed information acquired at step S 204 ) for the vehicle in transit and the fuel consumption estimated by the estimating unit  102 . 
     The projecting unit  101  uses the first equation corrected at step S 207  and again projects fuel consumption (step S 208 ). For example, the projecting unit  101  substitutes into the corrected first equation (1), average speed information for the remaining portion of the projection-target interval and thereby calculates fuel consumption for the remaining portion of the projection-target interval. 
     Until the vehicle completes travel along the projection-target interval (step S 209 : NO), the fuel-consumption projecting apparatus  100  returns to step S 204  and continues the processes therefrom. When the vehicle completes travel along the projection-target interval (step S 209 : YES), the fuel-consumption projecting apparatus  100  ends the process according to the present flowchart. 
     As described, the fuel-consumption projecting apparatus  100  corrects the equation used in the projection of fuel consumption, by an estimated value of fuel consumption obtained using actual acceleration information and speed information for the vehicle in transit. Consequently, fuel consumption can be projected with consideration of vehicle acceleration, enabling accurate projection of fuel consumption even if acceleration changes greatly during travel along the road, such as along a road that has numerous curves, a steep slope, etc. 
     Further, after the vehicle begins travel, the fuel-consumption projecting apparatus  100  estimates fuel consumption using speed information and acceleration information for the vehicle, slope information for the road traveled by the vehicle, and equation (2) to estimate fuel consumption. Consequently, the fuel-consumption projecting apparatus  100  can reflect to the fuel consumption projection, changes in vehicle speed and acceleration, changes in potential energy according to the vehicle, etc., enabling more accurate projection of fuel consumption. 
     Example 
     An example of the present invention will be described. Here, an application example of the present invention will be described where a navigation apparatus  300  equipped on a vehicle is applied as the fuel-consumption projecting apparatus  100 . 
     (Hardware Configuration of Navigation Apparatus  300 ) 
     A hardware configuration of the navigation apparatus  300  will be described.  FIG. 3  is a block diagram of a hardware configuration of the navigation apparatus. As depicted in  FIG. 3 , the navigation apparatus  300  includes a CPU  301 , ROM  302 , RAM  303 , a magnetic disk drive  304 , a magnetic disk  305 , an optical disk drive  306 , an optical disk  307 , an audio I/F (interface)  308 , a microphone  309 , a speaker  310 , an input device  311 , a video I/F  312 , a display  313 , a camera  314 , a communication I/F  315 , a GPS unit  316 , and various sensors  317 , all components respectively connected through a bus  320 . 
     The CPU  301  governs overall control of the navigation apparatus  300 . The ROM  302  stores therein various programs such as a boot program, a route retrieving program, etc. The RAM  303  is used a work area of the CPU  301 , i.e., the CPU  301  while using the RAM  303  as a work area, executes various programs stored in the ROM  302  to govern overall control of the navigation apparatus  300 . 
     The magnetic disk drive  304  controls the reading and the writing of data with respect to the magnetic disk  305  under the control of the CPU  301 . The magnetic disk  305  records data written thereto under the control of the magnetic disk drive  304 . As the magnetic disk  305 , for example, an HD (hard disk), FD (flexible disk), etc. may be used. 
     The optical disk drive  306  controls the reading and the writing of the data with respect to the optical disk  307 , under the control of the CPU  301 . The optical disk  307  is a removable recording medium from which data is read under the control of the optical disk drive  306 . The optical disk  307  may be a writable recording medium. As the removal recording medium, a medium other than the optical disk  307  can be employed, such as an MO and a memory card. 
     Information recorded on the magnetic disk  305  and the optical disk  307  may be, for example, content data and map data. Content data, for example, is music data, still image data, moving picture data, etc. Map data includes background data indicative of terrestrial objects (features) such as buildings, rivers, and ground surfaces, and road-shape data indicative of the shapes of roads; the data being divided into data files according to region. 
     The audio I/F  308  is connected to the microphone  309  for audio input and the speaker  310  for audio output. Sound received by the microphone  309  is subjected to A/D conversion at the audio I/F  308 . The speaker  310  outputs sound subjected to A/D conversion at the audio I/F  308 . 
     The input device  311  may be, for example, a remote controller having keys used to input characters, numerical values, or various kinds of instructions, a keyboard, a mouse, or a touch panel. Further, the input device  311  may be implemented by any one, or more, of the remote controller, the keyboard, and the touch panel. 
     The video I/F  312  is connected to the display  313 . The video I/F  312  is made up of, for example, a graphic controller that controls the display  313 , a buffer memory such as VRAM (Video RAM) that temporarily stores immediately displayable image information, and a control IC that controls the display  313  based on image data output from the graphic controller. 
     The camera  317  captures images inside and outside the vehicle. The images may be still images or moving images. For example, images taken by the camera  317 , capturing views and terrestrial objects outside the vehicle and the behavior of passengers inside the vehicle are stored through the video I/F  312  to a recording medium such as the magnetic disk  305  and the optical disk  307 . 
     The display  313  displays icons, a cursor, menus, windows, or various data such as text and images. Map information may be drawn on the display  313  two-dimensionally or 3-dimensionally. A mark representing the current position of the vehicle on which the navigation apparatus  300  is equipped may be displayed superimposed on the map information displayed on the display  313 . The current position of the mobile object is calculated by the CPU  301 . A TFT liquid crystal display, an organic electroluminescence display, and the like may be employed as the display  313 . 
     The communication I/F  315  wirelessly connected to a network and functions as an interface between the navigation apparatus  300  and the CPU  301 . Further, the communication I/F  315  communicates data with nearby electronic devices, by short distance communication such as infrared communication, Bluetooth (registered trademark), etc. The communication I/F  315  further receives television and radio broadcasts. Broadcasts received by the communication I/f  315  are output, via the audio I/F  308  and the video I/F  312 , as audio information/video information by the speaker  310  and the display  313 . 
     The GPS unit  316  receives signals from GPS satellites and outputs information indicating the position of the vehicle. The information output by the GPS unit  316  is used together with values output from the various sensors  317 , described hereinafter, in the calculation of the current position of the vehicle, by the CPU  301 . Information indicative of current position includes, for example, information indicating one point on map information, such as latitude, longitude, altitude, etc. 
     The various sensors  317  include a vehicle speed sensor, an acceleration sensor, and an angular speed sensor that respectively output information used to determine the position and behavior of the vehicle. Values output from the various sensors  317  are used by the CPU  301  to compute the current position and compute changes in speed, direction, etc. 
     Functions of the projecting unit  101 , the estimating unit  102 , the correcting unit  103 , the average-speed information acquiring unit  104 , and the traveling-speed information acquiring unit  105  of the fuel-consumption projecting apparatus  100  depicted in  FIG. 1  are implemented by using programs and data recorded on the ROM  302 , the RAM  303 , the magnetic disk  305 , the optical disk  307  of the navigation apparatus  300  depicted in  FIG. 3 , to execute a given program on the CPU  301  and control the respective components of the navigation apparatus  300 . 
     (Overview of Fuel Consumption Estimation by Navigation Apparatus  300 ) 
     The fuel-consumption projecting process performed by the navigation apparatus  300  will be described. In the description, “the amount of fuel consumed” and “fuel consumption” have the same meaning. Although the navigation apparatus  300  has a function of retrieving a route linking a starting point and a destination set by a designated user, the navigation apparatus  300  according to the present embodiment additionally has a function of projecting the amount of fuel consumed for travel along the retrieved route. For example, before the vehicle begins to travel along the route, the navigation apparatus  300  uses the first equation to project the amount of fuel consumed for travel along the route and after travel along the route has begun, the navigation apparatus  300  uses the second equation, which sets actual speed information and acceleration information of the vehicle as variables, to estimate the actual amount of fuel consumed for travel along the route. Subsequently, the navigation apparatus  300  uses the estimated fuel consumption to correct the fuel consumption projecting equation (first equation). 
     [Fuel Consumption Projection Before Travel Begins] 
     Before the vehicle begins to travel along a route, the navigation apparatus  300  projects the amount of fuel consumed for travel along the route. For example, the navigation apparatus  300  uses equation (1) below to calculate fuel consumption. Equation (1) is called “the fuel consumption projecting equation” and the fuel consumption calculated using equation (1) is called “projected fuel consumption”. In equation (1), h represents a correction coefficient and before travel begins, is assumed as h=1, for example. 
       fc 1 ( x )= h ·( m   1   +m   2   ·x   2   +m   3   ·x   3   +m   4   ·x )  (1)
 
     In equation (1), although speed x is an independent variable, since the actual traveling speed is unknown before travel begins, the speed x is assumed as the average traveling speed along the route. The average traveling speed, for example, is calculated by dividing the distance of the route, by the average time required to travel the route. For the average time required to traverse a given interval, for example, average-required-time data recorded in the navigation apparatus  300  as a database is used. The route may be divided into a given number of intervals (e.g., a node, which is a unit interval) and the average traveling speed may be calculated for each interval. 
     [Fuel Consumption Estimation after Travel Begins] 
     When the vehicle begins travel, the navigation apparatus  300  acquires acceleration information and speed information for the vehicle in real-time and calculates fuel consumption that reflects the actual traveling state of the vehicle. For example, the navigation apparatus  300  uses equation (2) below to calculate fuel consumption that takes acceleration of the vehicle into consideration. Equation (2) is called “fuel consumption estimating equation” and fuel consumption calculated using equation (2) is called “estimated fuel consumption”. The fuel consumption estimating equation is not limited to equation (2) and may be that which enables acquisition of vehicle acceleration information and speed information in real-time and estimation of fuel consumption. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               fc 
                               2 
                             
                              
                             
                               ( 
                               x 
                               ) 
                             
                           
                            
                           
                               
                           
                           = 
                           
                             
                               k 
                               1 
                             
                             + 
                             
                               
                                 k 
                                 2 
                               
                               · 
                               x 
                               · 
                               
                                 ( 
                                 
                                   
                                     
                                        
                                       x 
                                     
                                     
                                        
                                       t 
                                     
                                   
                                   + 
                                   
                                     
                                       g 
                                       · 
                                       sin 
                                     
                                      
                                     
                                         
                                     
                                      
                                     θ 
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               
                                 k 
                                 3 
                               
                               · 
                               
                                 G 
                                  
                                 
                                   ( 
                                   x 
                                   ) 
                                 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             G 
                              
                             
                               ( 
                               x 
                               ) 
                             
                           
                           = 
                           
                             
                               x 
                               3 
                             
                             + 
                             
                               
                                 a 
                                 1 
                               
                               · 
                               
                                 x 
                                 2 
                               
                             
                             + 
                             
                               
                                 a 
                                 2 
                               
                               · 
                               x 
                             
                           
                         
                       
                     
                   
                   } 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Where, 
     fc 2 (x): fuel consumption per unit time (cc/sec) 
     x: speed 
     
       
         
           
             ( 
             
               km 
               h 
             
             ) 
           
         
       
     
     
       
         
           
             
               
                  
                 x 
               
               
                  
                 t 
               
             
              
             
               : 
             
              
             
                 
             
              
             acceleration 
              
             
                 
             
              
             
               ( 
               
                 km 
                 
                   h 
                   · 
                   s 
                 
               
               ) 
             
           
         
       
     
     g: gravitational acceleration 
     
       
         
           
             ( 
             
               = 
               
                 35.3 
                  
                 
                   ( 
                   
                     km 
                     
                       h 
                       · 
                       s 
                     
                   
                   ) 
                 
               
             
             ) 
           
         
       
     
     θ: slope of traveled road (radian) 
     k 1 : coefficient based on fuel consumption when vehicle is stopped with engine running 
     
       
         
           
             ( 
             
               cc 
               s 
             
             ) 
           
         
       
     
     k 2 : coefficient based on fuel consumption during acceleration 
     
       
         
           
             ( 
             
               
                 cc 
                 · 
                 
                   h 
                   2 
                 
               
               
                 km 
                 2 
               
             
             ) 
           
         
       
     
     k 3 : coefficient based on drag and rolling resistance 
     
       
         
           
             ( 
             
               
                 cc 
                 · 
                 
                   h 
                   3 
                 
               
               
                 
                   km 
                   3 
                 
                 · 
                 s 
               
             
             ) 
           
         
       
     
     a 1 =−100 (km/h) 
     a 2 =6000 (km/h 2 ) 
     In equation (2), time is indicated in units of hours (h) and seconds (s) because distance per hour (km/h) is adopted as the unit for speed and seconds (s) are adopted as the unit of time for estimating fuel consumption. Appropriate calculations are performed on the values if the units of time are to be made uniform. 
     Further, from the ratio of the projected fuel consumption calculated using equation (1) and the estimated fuel consumption calculated using equation (2), the navigation apparatus  300  calculates the correction coefficient h expressed by equation (3) below. 
     
       
         
           
             
               
                 
                   h 
                   = 
                   
                     
                       ∑ 
                       
                         
                           fc 
                           2 
                         
                          
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                     
                       ∑ 
                       
                         
                           fc 
                           1 
                         
                          
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
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     The navigation apparatus  300  substitutes the calculated correction coefficient h into equation (1) to correct the fuel consumption projecting equation and uses the corrected fuel consumption projecting equation to again project fuel consumption for the remaining portion of the route (correction of fuel consumption). Consequently, fuel consumption reflecting the actual acceleration and speed during travel can be projected. The effect vehicle acceleration has on fuel consumption is not small. Like the navigation apparatus  300 , actual acceleration information is used to correct fuel consumption, whereby more accurate fuel consumption can be projected. 
     Correction of the fuel consumption projecting equation is performed periodically, at a given timing, e.g., every 10 minutes. Further, for example, if the type of the road traveled by the vehicle does not change for a given period or longer, or for a given distance or longer, correction of the fuel consumption projecting equation may be performed. When the road type changes, vehicle speed/acceleration may significantly change and if the acceleration information and speed information before the change is used, the accuracy of the fuel consumption estimate may drop. 
     [Detailed Example of Fuel Consumption Projecting Process] 
     &lt;First Method&gt; 
       FIGS. 4 and 5  are schematics of the fuel consumption projecting process by the navigation apparatus. For example, if a route R, which starts at a starting point A passes through a point B to a destination C, is traveled, the navigation apparatus  300  uses equation (1) to calculate the projected fuel consumption L 1AC  before travel along the route R begins, as depicted in  FIG. 4 . 
     For example, the navigation apparatus  300  uses the projected required time T AB  and the average traveling speed V AB  for the interval between A and B to calculate the projected fuel consumption L 1AB  between A and B. L 1AB  is expressed by equation (4) below using equation (1). Further, the navigation apparatus  300  uses the projected required time T BC  and the average traveling speed V BC  for the interval between B and C to calculate the projected fuel consumption L 1BC  between B and C. L 1BC  is expressed by equation (5) below using equation (1). Fuel consumption L AC  for the route R is expressed by equation (6) using L 1AB  and L 1BC . In equations (4) and (5), h 1  represents the correction coefficient for the starting point A and is set as h 1 =1. 
         L   1AB   =h   1   ·T   AB ·fc 1 ( V   AB )  (4)
 
         L   1BC   =h   1   ·T   BC ·fc 1 ( V   BC )  (5)
 
         L   AC   =L   1AB   +L   1BC   (6)
 
     As depicted in  FIG. 5 , when travel begins, the navigation apparatus  300  acquires acceleration information and speed information indicative of the actual acceleration and speed of the vehicle and uses equation (2) to calculate the estimated fuel consumption. The estimated fuel consumption is the instantaneous fuel consumption and therefore, by a summation of the instantaneous fuel consumption between A and B, the fuel consumption between A and B can be calculated. For example, the estimated fuel consumption L 2AB  between A and B is expressed by equation (7) below. In equation (7), v AB  represents information indicative of the actual speed and Σ indicates summation of the value of fc 2  for the interval between A and B. 
         L   2AB =Σfc 2 ( v   AB )  (7)
 
     Further, the navigation apparatus  300  uses equation (1) and calculates the projected fuel consumption based on information indicative of the actual speed. For example, when point B is reached, the navigation apparatus  300  uses the actual required time t AB  for travel between A and B and the average value v AB     —     av  of the actual speed v AB  between A and B (average speed between A and B) to calculate the projected fuel consumption L 1rAB  expressed by equation (8) below. 
         L   1rAB   =h   1   ·t   AB ·fc 1 ( v   AB     —     av )  (8)
 
     As indicated by equation (9), the ratio between the projected fuel consumption and the estimated fuel consumption respectively calculated from information indicative of the actual speed is set as the correction coefficient h 2 , whereby, the relation between the fuel consumption calculated from the average speed and the fuel consumption calculated taking into account the actual speed and acceleration, can be appropriately corrected. 
         h   2   =L   1rAB   /L   2AB   (9)
 
     The navigation apparatus  300  applies the correction coefficient h 2  calculated as described to equation (1) and again projects the amount of fuel consumed between B and C (projected fuel consumption). The projected fuel consumption L 1hBC  again projected for the interval between B and C is expressed by equation (10). Further, for the fuel consumption between A and B, the value (L 2AB ) of equation (7) is used, whereby the newly estimated fuel consumption L AC  for the route R is expressed by equation (11) below. 
         L   1hBC   =h   2   ·T   BC ·fc 1 ( V   BC )  (10)
 
         L   AC   =L   2AB   +L   1hBC =Σfc 2 ( v   AB )+ h   2   ·T   BC ·fc 1 ( V   BC )  (11)
 
     &lt;Second Method&gt; 
     Although, in the first method above, the navigation apparatus  300  uses information indicative of the actual speed after travel begins, to project the re-projected fuel consumption and calculate the correction coefficient, configuration may be such that the projected fuel consumption projected before travel begins is used as is to calculate the correction coefficient. In other words, the ratio of the estimated fuel consumption L 2AB  between A and B (equation (7)) calculated at point B and the projected fuel consumption L 1AB  between A and B calculated at point A (equation (4)) before travel, is used as the correction coefficient. In this case, the correction coefficient h 3  is expressed by equation (12) below. 
         h   3   =L   1AB   /L   2AB   (12)
 
     The first method is meaningful if there are numerous curves along the road between A and C. Along a road having numerous curves, even if the traveling speed does not vary, acceleration and deceleration occurs frequently and the magnitude thereof is large. Consequently, the fuel consumption calculated by equation (2) increases. In this case, correction that takes the effects of curves in the road into account, can be performed by substituting into equation (1), speed information indicative of the actual speed, again projecting the fuel consumption and calculating the correction coefficient. 
     Meanwhile, the second method is meaningful if congestion occurs frequently along the road between A and C. Along a congested road, the traveling speed of the vehicle becomes slow. Consequently, the fuel consumption calculated by equation (2) becomes small. However, travel at a slow speed consequent to congestion and simply traveling at a slow speed affect fuel consumption differently. Consequently, by the second method, correction that takes the effects of congestion into account, can be performed by using the average speed information and the projected fuel consumption as is. 
     Although adoption of either the first method or the second method is arbitrary, configuration may be such that, for example, when a road is retrieved, link-shape data concerning the road is referred to and if curvature is a given rate or more, the first method is adopted. Further, for example, configuration may be such that congestion information concerning the road is referred to and for an interval where congestion occurs, the second method is adopted. Configuration may be such that along the same route, the first method and the second method are switched between according to interval. Further, configuration may be such that even if the first method and the second method are adopted, for example, during travel along the projection-target interval, if the type of the road being traveled by the vehicle does not change, equation (1) is corrected. 
     (Concerning Second Fuel Consumption Estimating Equation) 
     Equation (2), which is a second fuel consumption estimating equation, will be described in detail. Equation (2) is an equation that can stably calculate highly accurate fuel consumption by using information related to vehicle idling, information related to vehicle acceleration, and resistance occurring when the vehicle travels alone as variables. Further details are described hereinafter. 
     [Concerning Coefficients k 1  to k 3 ] 
     Coefficients k 1  to k 3  of equation (2) are described.  FIG. 6  depicts a coefficient table retained by the navigation apparatus. In a coefficient table  600  depicted in  FIG. 6 , vehicle type  601  identifying the type of vehicle and model information  602  for each vehicle type are recorded, where coefficients (k 1  to k 3 )  606  respectively corresponding thereto are further recorded. Displacement  603 , vehicle weight  604 , and specific fuel consumption  605  are further correlated with the vehicle type  601  and the model information  602 , respectively. 
     Coefficients k 1  to k 3  vary according to vehicle type and model. The navigation apparatus  300  reads from the coefficient table  600 , the coefficients k 1  to k 3  that correspond to the vehicle on which the navigation apparatus  300  is equipped. For example, if the navigation apparatus  300  can identify the vehicle type and model of the vehicle on which the navigation apparatus  300  is equipped, the navigation apparatus  300  selects the corresponding vehicle type  601  and model information  602 , and reads out the coefficients correlated thereto. 
     If the navigation apparatus  300  cannot identify the vehicle type and model, but can identify the displacement and/or vehicle weight, the navigation apparatus  300  selects the corresponding displacement  603  and vehicle weight  604 , and reads out the coefficients correlated thereto. Further, if the navigation apparatus  300  can identify the specific fuel consumption for the vehicle, the navigation apparatus  300  selects the corresponding specific fuel consumption  605 , and reads out the coefficients correlated thereto. 
     Although an example has been given in which if the vehicle type and model cannot be identified, the coefficients are read out using the displacement and/or an approximate fuel consumption, configuration is not limited hereto. For example, even if the vehicle type and model can be identified, configuration may be such that data for naturally aspirated gasoline, diesel engine, turbo engine, etc. and information related to approximate fuel consumption, vehicle weight, displacement, etc. are used and the coefficients corresponding to a similar vehicle type and/or model are read out. 
     Next, the meaning of the respective coefficients k 1  to k 3  will be described. k 1  is a coefficient that indicates fuel consumption during idling (when the vehicle is not in motion). k 2  is a coefficient that indicates fuel consumption during acceleration. k 3  is a coefficient that is based on resistance occurring when the vehicle is in motion. The resistance that occurs when the vehicle is in motion includes drag and rolling resistance. Rolling resistance includes resistance that occurs accompanying rotation of the tires and rotation inside the engine. 
       FIG. 7  is a graph of coefficient k 1  and displacement. The vertical axis indicates the value of coefficient k 1  and the horizontal axis indicates displacement. As depicted in  FIG. 7 , the coefficient k 1  and displacement are positively correlated. In other words, typically, the greater the displacement of the vehicle, the greater the fuel consumption is during idling and thus, the coefficient k 1  is a coefficient reflecting fuel consumption during idling. 
       FIG. 8  is a graph of the coefficient k 2  and vehicle weight. The vertical axis indicates the value of coefficient k 2  and the horizontal axis indicates vehicle weight. As depicted in  FIG. 8 , the coefficient k 2  and vehicle weight are positively correlated. In other words, typically, the greater the vehicle weight, the greater the fuel consumption is during acceleration and thus, the coefficient k 2  is a coefficient reflecting fuel consumption during acceleration. 
       FIG. 9  is a graph of coefficient k 3  and displacement. The vertical axis indicates the value of coefficient k 3  and the horizontal axis indicates displacement. As depicted in  FIG. 9 , no correlation can be seen between the coefficient k 3  and displacement. This phenomenon is consequent to the coefficient k 3  being a coefficient based on resistance that occurs when the vehicle is in motion and therefore, coefficient k3 has a stronger correlation with vehicle shape than with displacement. 
     [Method for Databasing Coefficients k 1  to k 3 ] 
     The databasing of the values of the coefficients k 1  to k 3  will be described. A coefficient table (coefficient database) such as that depicted in  FIG. 6  is built by the following procedure, for example. 
     &lt;First Procedure&gt; 
     Actual traveling data for a representative vehicle type is measured and substituted into equation (α) below. Multi-regression analysis of equation (α) into which the actual traveling data has been substituted derives coefficients k 1 , k 2 , k 3 , k 4 , and k 5 . Here, k 1  is a coefficient based on the fuel consumption during idling; k 2  a coefficient based on the fuel consumption during acceleration; k 3  a coefficient based on drag and rolling resistance; and k 4  and k 5  are coefficients for engine torque characteristics and transmission efficiency. Further, in equation (α), fc represents fuel consumption (cc/sec), x represents speed (km/h), dx/dt+g·sin θ represents resultant acceleration (vehicle acceleration and gravitational acceleration). 
       fc( x )= k   1   +k   2 ·( dx/dt+g ·sin θ)· x+k   3   ·x   3   +k   4   ·x   2   +k   5   ·x   (α)
 
     &lt;Second Procedure&gt; 
     Among k 1  to k 5  obtained from the first procedure, k 3  to k 5  are used to derive a 1  and a2 in equation (2). a 1  and a2 are, for the most part, values common to all vehicle types and therefore, by setting these values as constants, the number of parameters can be reduced, e.g., a 1 =k 4 /k 3 , a2=k 5 /k 3 . 
     &lt;Third Procedure&gt; 
     For the coefficients k 1  to k 3  for vehicle types that are not typical equation (β) below is used and multi-regression analysis of the actual traveling data is performed. In equation (β), the parameters have been narrowed to three and the coefficients k 1  to k 3  obtained for each vehicle type, displacement, engine model, etc. are entered into a database. 
       fc( x )= k   1   +k   2 ·( dx/dt+g ·sin θ)· x+k   3 ·( x   3   +a   1   ·x   2   +a 2· x )  (β)
 
     [Concerning Road Slope θ] 
     Next, the road slope θ, which is the second term on the right of equation (2) will be discussed.  FIG. 10  is a schematic of acceleration of a vehicle traveling a road that has a slope. As depicted in  FIG. 10 , for a vehicle to travel on a hill having a slope of θ, acceleration (dx/dt)A according to the vehicle motion and the traveling direction component (g·sin θ)B of gravitational acceleration g are needed. The second term on the right of equation (2) represents the resultant acceleration C of the acceleration A according to vehicle motion and the traveling direction component B of gravitational acceleration g. 
     If consideration is not given to the road slope θ when fuel consumption is estimated, the margin of error would be small for an area where the road slope θ is small, however, for an area where the road slope θ is large, the margin of error would be large. Consequently, the navigation apparatus  300  estimates fuel consumption with the consideration of road slope. 
     The slope of the road traveled by the vehicle, for example, can be known using an inclinometer equipped on the navigation apparatus  300 . If an inclinometer is not equipped on the navigation apparatus  300 , for example, slope information for roads included in map data can be used. 
     If slope information is not included in the map data, altitude data in the map data can be used or if the navigation apparatus is capable of three-dimensional positioning, altitude information of the positioning results can be used to estimate fuel consumption for sloped interval. For example, an approximation equation such as equation (13) below is used to estimate fuel consumption (sloped-interval fuel consumption) for a sloped interval. 
       sloped-interval fuel consumption=fuel consumption for interval constantly of 0+ k   2   ·g·(altitude at end of interval-altitude at start of interval)   (13)
 
     The first term on the right of equation (2) “fuel consumption (for interval constantly of 0)” is a value that is the summation of the instantaneous fuel consumption for a given interval (the value of equation (2)). The second term on the right (altitude at end of interval-altitude at start of interval) represents variations in potential energy. Fuel consumption approximation for a sloped interval by equation (14) is demonstrated as follows. 
       interval fuel consumption=Σfc·Δ T  
 
       =Σ{ k   1   +k   2   ·x ·( dx/dt+g ·sin θ)+ k   3   ·G ( x )}Δ T  
 
       = k   1   ·ΣΔT+k   2   ·Σx ( dx/dt+g ·sin θ)Δ T+k   3   ·ΣG ( x )Δ T   (14)
 
     Taking a closer look at the second term in equation (14), 
       Σ V ( dx/dt+g ·sin θ) ΔT=Σx·dx/dt·ΔT+g ·Σ( x ·sin θ)Δ T   (15)
 
     can be deduced, where the second term on the right in equation (15) “Σ(x·sin θ)ΔT” is displacement in the direction of altitude in the interval. The first term on the right in equation (15) is fuel consumption with respect to acceleration energy when the slope is taken as constantly 0 and therefore, integration with other parameters unrelated to slope, enables “interval fuel estimation calculated with a slope of constantly 0”. Consequently, even if no inclinometer is provided, if the latitude and longitude of the starting point and of the ending point of the interval are obtained, fuel consumption estimated with consideration of road slope becomes possible by referring to altitude data. Alternatively, if the navigation apparatus is capable of three-dimensional positioning, altitude information for the starting point and the ending point of the interval is referred to, whereby fuel consumption can be estimated with consideration of road slope. 
     [Effect of Fuel Cuts] 
     In equation (2), if any of the conditions below are met consequent to the effects of fuel cuts, the value of fc is taken to be as follows. 
       fc= k   1 , if fc 2   &lt;k   1   [1]
 
     
       
         
           
             
               
                 
                   
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     Here, conditional expression [1] above is a prescribed condition based on the notion that the fuel consumption to be projected does not take on a positive value less than the fuel consumption during idling or a negative value. Therefore, for example, if the fuel consumption to be projected takes on a positive value less than k 1  or a negative value, according to conditional expression [1], the fuel consumption to be projected takes on the value of k 1 . Conditional expressions [2] and [3] above are prescribed conditions related to fuel consumption during vehicle deceleration. According to vehicle type, when the vehicle decelerates without manipulation of the accelerator, there are occasions when fuel is not sent to the engine and if the actual fuel consumption and the projected fuel consumption differ, there are occasions when use of this condition for correction is meaningful. The values of fc in conditional expressions [1] to [3] above are merely examples and are appropriately adjusted according to vehicle type. 
     In this case, fc is not included in conditional expressions [2] and [3]. For example, if a given determination is to be made without obtaining the value of fc, these conditional expressions are particularly meaningful. For example, if the estimated fuel consumption is transmitted to a server, and statistical processing thereof is to be performed, the values of the conditional expressions k 1  to k 3  are separated from other values and processed. Thereafter, when the values of conditional expressions k 1  to k 3  are updated, the amount of calculations to be performed can be greatly reduced and as can recalculation of the conditional expressions. 
     (Fuel-Consumption Projecting Process Performed by Navigation Apparatus  300 ) 
     Next, the fuel-consumption projecting process performed by the navigation apparatus  300  will be described.  FIG. 11  is a flowchart of the fuel-consumption projecting process performed by the navigation apparatus  300 .  FIG. 11  depicts the first method (refer to  FIGS. 4 and 5 ) in the fuel consumption projecting process. 
     In the flowchart depicted in  FIG. 11 , the navigation apparatus  300  retrieves a route to the destination designated by the user (step S 1101 ). Upon retrieving a route, the navigation apparatus  300  uses the average traveling speed for the route and equation (1) to calculate fuel consumption (projected fuel consumption) for the entire route (step S 1102 ), and displays the projected fuel consumption on the display  313  (step S 1103 ). 
     The navigation apparatus  300  remains in standby until the vehicle begins to travel (step S 1104 : NO). When the vehicle begins to travel (step S 1104 : YES), the navigation apparatus  300  acquires speed information and acceleration information for the vehicle (step S 1105 ). Until the time for correction arrives (step S 1106 : NO), the navigation apparatus  300  returns to step S 1105  and continues to acquire the speed information and acceleration information. 
     When the time for correction arrives (step S 1106 : YES), the navigation apparatus  300  uses the speed information and acceleration information acquired at step S 1105  and equation (2) to calculate the estimated fuel consumption (the amount of fuel consumed thus far traveling along the route) (step S 1107 ). Further, the navigation apparatus  300  uses the speed information acquired at step S 1105  and calculates by equation (1), the projected fuel consumption based on the actual speed (step S 1108 ). The navigation apparatus  300  calculates the correction coefficient from the estimated fuel consumption calculated at step S 1107  and the projected fuel consumption that is based on the actual speed and calculated at step S 1108  (step S 1109 ). 
     The navigation apparatus  300  uses equation (1) to which the correction coefficient has been applied, to recalculate the projected fuel consumption for the remaining portion of the route (step S 1110 ). The navigation apparatus  300  sums the estimated fuel consumption (the amount of fuel consumed thus far to travel along the route) calculated at step S 1107  and the fuel consumption calculated, at step S 1110 , for the remaining portion of the route, and displays, on the display  313 , the sum as fuel consumption for the entire route (step S 1111 ). Rather than display as fuel consumption for the entire route, the amount of fuel consumed thus far and the amount of fuel to be consumed for the remaining portion of the route may be displayed separately, or any one of the amounts may be displayed alone. 
     Until the vehicle reaches the destination (step S 1112 : NO), the navigation apparatus  300  returns to step S 1105  and repeats the steps therefrom. When the vehicle reaches the destination (step S 1112 : YES), the process according to the flowchart ends. In the flowchart, although the estimated fuel consumption is calculated at the time for correction, configuration may be such that the estimated fuel consumption is calculated as necessary during travel. 
     In the fuel consumption projecting process, in the case of the second method, without performing the process (calculation of the projected fuel consumption that is based on the actual speed) at step S 1108 , the correction coefficient may be calculated using the projected fuel consumption calculated at step S 1102 . 
     As described, the navigation apparatus  300  uses acceleration information corresponding to actual travel to correct an equation (equation (1)) used for projecting fuel consumption before travel begins. Consequently, fuel consumption can be calculated, taking vehicle acceleration into consideration. For example, even if the vehicle travels a road along which acceleration changes drastically, such as a road having a lot of curves or a steep slope, fuel consumption can be estimated with favorable accuracy. 
     Further, after travel begins, the fuel-consumption projecting apparatus  100  estimates fuel consumption by equation (2), which uses speed information and acceleration information for the vehicle and slope information for the traveled road. Consequently, the navigation apparatus  300  can reflect to the fuel consumption estimate, changes in vehicle traveling speed and acceleration, as well as changes in potential energy according to the vehicle, etc., enabling more accurate estimation of fuel consumption. 
     The fuel projecting method described in the present embodiment may be implemented by executing a prepared program on a computer such as a personal computer and a workstation. The program is stored on a computer-readable recording medium such as a hard disk, a flexible disk, a CD-ROM, an MO, and a DVD, read out from the recording medium, and executed by the computer. The program may be a transmission medium that can be distributed through a network such as the Internet. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
           100  fuel-consumption projecting apparatus 
           101  projecting unit 
           102  estimating unit 
           103  correcting unit 
           104  average-speed information acquiring unit 
           105  traveling-speed information acquiring unit