Abstract:
A fuel-saving driving system which gradually decreases a target vehicle speed from a start of control to passage of a descending-slope starting point in a linear form and can obtain fuel-saving and smooth driving feeling without repeating fuel-cut and injection. A vehicle-position specifying device is provided for specifying the position of a vehicle, a storage device for storing data of a descending slope located in the vehicle traveling direction, a vehicle speed measuring device for measuring a speed of the vehicle, and a controller The controller has a function of determining a target speed of the vehicle from the vehicle speed and the data of the descending slope.

Description:
The present invention relates to an automatic control system for fuel-saving driving of an automobile and particularly to automatic control which can further reduce fuel consumption when driving changes to descending. 
     BACKGROUND OF THE INVENTION 
     As a prior art, a fuel-saving system that effectively promotes fuel-saving driving using road gradient information and a control method thereof are disclosed (See Patent Document 1, for example). 
     In the prior art (Patent Document 1), improvement in fuel efficiency is promoted by using acceleration energy on a descending slope or in more detail by performing speed-reduction control before the descending slope. 
     In the prior art (Patent Document 1), an advice position for fuel-cut before the descending slope (a position where an advice is given to a driver) or a control position for fuel-cut in an automatic fuel-saving driving system (a position where fuel is cut by automatic control) is determined by a vehicle speed (a car speed), a gradient before the descending slope and the gradient of the descending slope. And the gradient before the descending slope and the gradient of the descending slope are determined by a three-dimensional map. 
     Thus, in order to reduce the speed to a targeted vehicle speed at start of the descending slope, the gradient before the descending slope and the gradient of the descending slope need to be mapped precisely, and the advice position for fuel-cut or the control position for fuel-cut in the automatic fuel-saving driving system also need to be mapped precisely. 
     However, even if the map is to be improved precisely, the gradient at an actual traveling position is not necessarily constant. 
     Also, in the case of a cargo vehicle, its mass is greatly varied whether the vehicle is empty or loaded, and thus, deceleration is largely different at the fuel-cut between the empty vehicle and the loaded vehicle, and it has been difficult to reduce the speed to a requested vehicle speed (target vehicle speed) at start of the descending slope both in the empty vehicle and the loaded vehicle. 
     Here, in the case of the automatic fuel-saving driving mode, at a requested vehicle speed or less, control is performed such that fuel is automatically injected so that the vehicle speed is not reduced excessively. Because of such control, fuel might be injected immediately before entering the descending slope, and in that case, a vehicle behavior becomes jerky, and a driver would have a sense of discomfort, which is a problem. At the same time, there is also a problem of a bad influence on the fuel efficiency. 
       FIG. 5  shows a traveling distance, a vehicle speed and a fuel injection amount in the control at a point to change to descending during the automatic fuel-saving driving according to the prior art. 
     In  FIG. 5 , reference character P 1  denotes a control start position, reference character P 2  for a peak point changing from ascending to descending (descending-slope starting point), reference character Vd for a requested vehicle speed, reference character Va for an actual vehicle speed, reference character Vt for a target vehicle speed when entering the descending slope, and reference character q for a fuel injection amount. Here, a distance from the control starting point to a descending starting point is 300 m (constant), for example. 
     In  FIG. 5 , reference character by indicates a difference between the actual vehicle speed Va and the target vehicle speed Vd. 
       FIG. 5  shows a case in which the gradient on the ascending side is steeper than that in data stored in a database or a vehicle mass is small. 
     In the case shown in  FIG. 5 , the speed is lost before reaching the descending-slope starting point P 2 , and the vehicle speed Va becomes lower than the target vehicle speed Vt at entering the descending slope. Thus, the fuel injection amount q is temporarily injected. By means of this temporary fuel injection q, the vehicle speed Va rapidly increases and becomes higher than the target vehicle speed Vt at entering the descending slope, but since fuel is cut immediately after the fuel injection amount q is temporarily injected, the vehicle speed Va is decreased again. 
     As a result, a driving feeling before and after the descending-slope starting point P 2  becomes jerky, and fuel efficiency is deteriorated by the temporary fuel injection. 
       FIG. 6  shows the traveling distance, the vehicle speed, and the fuel injection amount in control at a point of time changing from ascending to descending in the automatic fuel-saving driving of the prior art as well as shown in  FIG. 5 . However,  FIG. 6  shows a case in which the gradient on the actual ascending side is gentler than that in the data stored in the database or the vehicle mass is larger. 
     In the case shown in  FIG. 6 , the actual vehicle speed Va does not fully slow down but the actual vehicle speed Va at the descending-slope starting point P 2  exceeds the target vehicle speed Vt at entering the descending slope and a frequency of operating an auxiliary brake in the middle of the slope is increased, which deteriorates the fuel efficiency. 
       FIG. 7  shows a case in which in order to solve the problem in  FIG. 5 , the control start position P 1  is brought close to the descending-slope starting point P 2  and the distance from the control starting point to the descending starting point is set short. 
     In  FIG. 7 , it is not necessary to temporarily inject the fuel injection amount q before reaching the descending-slope starting point P 2  as in the case shown in  FIG. 5 . However, similarly to the case shown in  FIG. 6 , the actual vehicle speed Va at the descending-slope starting point P 2  exceeds the target vehicle speed Vt at entering the descending slope, and the frequency of operating the auxiliary brake in the middle of the descending slope is increased and thus, the problem of deterioration in fuel efficiency still remains.
     Patent Document 1: JPA (Non-examined publication) No. 2007-156704   

     SUMMARY OF THE INVENTION 
     Problem to be solved 
     The present invention was created in view of the above-mentioned problems of the prior art and has an object for providing a fuel-saving driving system in which a target vehicle speed from start of control to passage of a descending-slope starting point is gradually decreased linearly, and a smooth driving feeling can be obtained without repeating fuel-cut and injection while saving fuel consumption. 
     Solution Means for Problem 
     A fuel-saving driving system ( 100 ) of the present invention has a vehicle-position specifying device ( 2 : GPS, for example) which specifies the position of a vehicle, 
     a storage device (database  11 , for example) which stores data of a descending slope located in the vehicle traveling direction, 
     a vehicle speed measuring device (vehicle speed sensor  3 ) which measures a speed (vehicle speed Va) of a vehicle ( 1 ), and 
     a controller (controller of the fuel-saving driving system side: control unit  10 ), 
     the controller ( 10 ) has a function of determining (calculating) a target speed (requested vehicle speed Vd) of the vehicle ( 1 ) from the vehicle speed (Va) and the data of the descending slope (a distance L from the current position to the descending-slope starting point and the target vehicle speed Vt at the descending-slope starting point and the like, for example) (claim  1 ). 
     In the present invention, the controller (controller of the fuel-saving driving system side: control unit  10 ) preferably has a function of calculating the target speed (Vd) at a spot where the vehicle ( 1 ) is traveling on the basis of the vehicle speed (Va) at the spot where the vehicle ( 1 ) is traveling and the distance (L) to the descending-slope starting point so that the speed (Va) of the vehicle ( 1 ) at a point of time when the vehicle ( 1 ) reaches the descending-slope starting point (P 2 ) becomes the target speed (Vt) at the descending-slope starting point (claim  2 ). 
     Here, the controller (controller of the fuel-saving driving system side: control unit  10 ) preferably has a function of executing control of decreasing the target speed (Vd) at the spot where the vehicle ( 1 ) is traveling gradually (so that the deceleration characteristic becomes linear) so that the speed (Va) of the vehicle at the point of time when the vehicle ( 1 ) reaches the descending-slope starting point (P 2 ) becomes the target speed (Vt) at the descending-slope starting point P 2  (claim  3 ). 
     Said controller (controller of the fuel-saving driving system side: control unit  10 ) preferably has a function of transmitting a control signal to a vehicle-side controller (engine controller  4 ) that controls an engine via an information network ( 5 ) of the vehicle so as to have the vehicle-side controller ( 4 ) transmit a control signal to inject fuel in an injection amount corresponding to the control signal to a fuel injecting device (claim  4 ). 
     Advantageous Effects of Invention 
     According to the present invention provided with the above-mentioned constructions, since the present invention is constructed to determine (calculate) the target speed (requested vehicle speed Vd) of the vehicle from the vehicle speed (Va) and the data of the descending slope (the distance L from the current position to the descending-slope starting point, the target vehicle speed Vt at the descending-slope starting point and the like), the target speed (Vd) at the spot where the vehicle ( 1 ) is traveling can be decreased linearly (claim  2 ), and the target speed (Vd) at the spot where the vehicle ( 1 ) is traveling can be decreased linearly (gradually) (claim  3 ), repetition of fuel-cut and fuel injection before the descending-slope starting point P 2  can be suppressed. 
     That is, the fuel-cut or the fuel injection makes a vehicle behavior unstable (jerky) and gives a sense of unstableness or a sense of discomfort to a vehicle passenger, but since the repetition of fuel-cut and fuel injection is suppressed in the present invention, a sense of unstableness or a sense of discomfort is prevented from being given to the vehicle passenger. 
     Moreover, according to the present invention, since the target speed (Vd) at the spot where the vehicle ( 1 ) is traveling can be decreased linearly (gradually) (claim  3 ), a starting point (P 1 ) where the vehicle traveling speed (Va) is decreased can be set at a position away from the descending-slope starting point (P 2 ) as compared with the prior art. 
     That is, since the distance for which the vehicle ( 1 ) travels with a decreased speed (the distance L from the point P 1  where deceleration is started to the descending-slope starting point P 2 ) can be made longer than that in the prior art, deviation between the vehicle speed (Va) and the target speed (V) at the descending-slope starting point becomes smaller even in the case shown in  FIG. 6 , and a frequency of braking in the middle of the descending slope becomes fewer. Thus, energy is not wasted by braking and fuel efficiency of the vehicle is improved. Also, since the distance for which the vehicle can travel while being subjected to braking can be made shorter, the fuel-saving effect can be exerted further effectively. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an embodiment of the present invention. 
         FIG. 2  is a block diagram of a controller used in the embodiment. 
         FIG. 3  is a diagram illustrating characteristics of a traveling distance, a vehicle speed, and fuel injection when changing from ascending a slope to descending a slope in a fuel-saving driving system according to the embodiment. 
         FIG. 4  is a flowchart illustrating driving control according to the embodiment. 
         FIG. 5  is a diagram illustrating characteristics of a traveling distance, a vehicle speed, and fuel injection when changing from ascending a slope to descending a slope in a prior art. 
         FIG. 6  is a diagram illustrating characteristics of a traveling distance, a vehicle speed, and fuel injection when changing to descending a slope in a prior art different from that in  FIG. 5 . 
         FIG. 7  is a diagram illustrating characteristics of a traveling distance, a vehicle speed, and fuel injection when changing from ascending a slope to descending a slope in a prior art different from that in  FIGS. 5 and 6 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described below by referring to the attached drawings. 
     In  FIG. 1 , a fuel-saving driving system according to the embodiment of the present invention is indicated in entirety by reference numeral  100 . 
     The fuel-saving driving system  100  has a vehicle  1 , a GPS  2 , which is a vehicle position specifying device, a vehicle speed sensor  3 , an engine controller  4 , an in-vehicle communication network  5 , and a control unit  10 , which is control means of the automatic fuel-saving driving system. 
     In this embodiment, the position of the vehicle is specified by using a Global Positioning System, and the GPS  2 , which is a vehicle position specifying device, receives position information or the like from a satellite of the Global Positioning System. 
     The in-vehicle communication network  5  connects the control unit  10  to the vehicle speed sensor  3  and the engine controller  4 . 
       FIG. 2  illustrates a construction of the control unit  10 . 
     In  FIG. 2 , the control unit  10  has a database  11 , a current-position specification portion  12 , a calculation portion (distance calculation portion)  13  for calculating a distance from the current position to a descending-slope starting point, a target-speed determination portion  14 , an instruction-signal transmission timing determination portion  15 , and an interface  16 . 
     The information relating to the current position of the vehicle from the GPS  2  is inputted into the current-position specification portion  12  via a line L 1 . 
     In the database  11 , map data obtained by a requested vehicle speed (target vehicle speed) at the descending-slope starting point and the information obtained so far from the GPS, for example, is stored. If the map data stored in the database  11  is to be updated, new map data is sent from the GPS  2  to the database  11  via the line L 2 . 
     The distance calculation portion  13  is constructed to have a function of calculating the distance “L” (See  FIG. 3 ) from the (current position of the) vehicle  1  to the descending-slope starting point from the current position information of the vehicle  1  obtained from the current-position specification portion  12  via a line L 3  and the map information obtained from the database  11  via a line L 4 . 
     Into the target-speed determination portion  14 , the distance L from the current position to the descending-slope starting point calculated by the distance calculation portion  13  is inputted via a line L 5 . Also, into the target-speed determination portion  14 , the current vehicle speed Va measured by the vehicle speed sensor  3  is inputted via the in-vehicle communication network  5 . Moreover, into the target-speed determination portion  14 , the requested vehicle speed (target vehicle speed when entering the descending slope) Vt at the descending-slope starting point stored in the database  11  is inputted via a line L 6 . 
     The target-speed determination portion  14  has a function of calculating the requested vehicle speed (target vehicle speed) Vd on the basis of the distance L from the current position to the descending-slope starting point, the current vehicle speed Va, and the target vehicle speed Vt when entering the descending slope. 
     The instruction-signal transmission timing determination portion  15  has a function of determining timing at which a control signal to achieve the target vehicle speed Vd is transmitted. 
     If the target vehicle speed Vd determined by the target-speed determination portion  14  is inputted via a line L 7 , the instruction-signal transmission timing determination portion  15  transmits a control signal (control signal to achieve the target vehicle speed Vd) to the engine controller  4  via a line L 8 , an interface  16 , and the in-vehicle communication network  5  in accordance with the timing determined by the instruction-signal transmission timing determination portion  15 . 
     Then, the engine controller  4  transmits the control signal to a fuel injecting device, not shown, and adjusts or controls a fuel injection amount and injection timing so that the vehicle speed becomes the target vehicle speed Vd. 
     In  FIG. 2 , a timer  17  measures a control interval. In the control unit  10 , the distance “L” from the current position of the vehicle to the descending-slope starting point and the target vehicle speed (requested vehicle speed; Vd) are calculated at every predetermined control interval measured by the timer  17 . 
     As described above, in the prior art, when changing from ascending to descending, from a constant distance (300 m, for example) before the descending-slope starting point, the speed (requested vehicle speed) of the vehicle  1  is determined and the fuel injection amount is adjusted on the basis of the gradient on the ascending side and the gradient on the descending side of the spot (according to the map information stored in the database) and the vehicle speed at the start of control (300 m before the descending-slope starting point) and so that the vehicle can travel on the ascending slope to the descending-slope starting point. 
     However, as described above by referring to  FIGS. 5 to 7 , there were cases in which the speed is lost before the descending-slope starting point P 2  due to the difference between the gradient information of the database and the actual gradient and the vehicle weight and the fuel injection amount is temporarily injected ( FIG. 5 ) or in which the actual vehicle speed at the descending-slope starting point P 2  exceeds the target vehicle speed when entering the descending slope and an auxiliary brake is operated ( FIGS. 6 and 7 ). 
     Thus, the purpose of improving fuel efficiency cannot be achieved in some cases. 
     In order to cope with that, in the fuel-saving driving system  100  according to the illustrated embodiment, the speed (requested vehicle speed) of the vehicle  1  is determined on the basis of the actual vehicle speed Va from the vehicle speed sensor  3 , the target vehicle speed Vt when entering the descending slope, and the distance L from the current position to the descending-slope starting point, and the fuel injection amount is adjusted. Also, in the fuel-saving driving system  100  according to the illustrated embodiment, since the speed is decreased linearly (gradually) so that the target vehicle speed Vt is achieved at a descending-slope starting point P 2 A, the situation in which the vehicle speed Va falls under the target vehicle speed Vt when entering the descending slope at a stage before reaching the descending-slope starting point P 2 A (See  FIG. 5 ) can be prevented. 
     Similarly, in the fuel-saving driving system  100  according to the illustrated embodiment, since the distance for which the vehicle  1  travels at a reduced speed (the distance L from the point P 1  where deceleration is started to the descending-slope starting point P 2 A) can be made longer than that in the prior art, the situation in which the speed is not fully decreased before reaching the descending-slope starting point P 2 A and the vehicle speed Va largely exceeds the target vehicle speed Vt when entering the descending slope at the descending-slope starting point P 2 A (See  FIGS. 6 and 7 ) can be prevented. 
     That is, according to the illustrated embodiment, since the distance L to the descending-slope starting point P 2 A is considered, the requested vehicle speed Vd of the vehicle  1  can be determined by considering whether or not the vehicle speed Va at the current position is appropriate for achieving the target vehicle speed Vt when entering the descending slope. 
     Thus, an error between the vehicle speed Va at the descending-slope starting point P 2 A and the target vehicle speed Vt when entering the descending slope can be made small. 
     In other words, according to the illustrated embodiment, since in each control cycle, the speed when the vehicle  1  moves from the current position to the descending-slope starting point P 2 A can be expected by considering the distance L to the descending-slope starting point P 2 A, the requested vehicle speed or the target vehicle speed Vd of the vehicle  1  can be determined by referring to the expected value. This means that the requested vehicle speed or the target vehicle speed Vd of the vehicle  1  can be corrected at every control cycle. 
     Therefore, in the illustrated embodiment, even if the distance from the point P 1 A where the control is started to the descending-slope starting point P 2 A is long, the fuel injection amount is adjusted by correcting the requested vehicle speed or the target vehicle speed Vd at every control cycle and thus, an error between the vehicle speed Va at the descending-slope starting point P 2 A and the target vehicle speed Vt when entering a descending slope can be made small by reducing an error between the vehicle speed Va and the target vehicle speed Vt when entering a descending slope. 
     In the illustrated embodiment, as a numerical value of the distance L from the point P 1 A where the control is started to the descending-slope starting point P 2 A, 400 to 500 m, for example, can be set. 
     On the basis of the flowchart in  FIG. 4  and also by referring to  FIGS. 2 and 3 , control of the fuel-saving driving system  100  will be described. 
     In  FIG. 4 , the control unit  10  reads the vehicle speed data (Step S 1 ) from the information from the vehicle speed sensor  3 , the position information (Step S 2 ) of the descending-slope starting point P 2 A (See  FIG. 3 ) during traveling from the database  11 , and reads the current position of the vehicle  1  from the GPS  2 . (Step S 3 ). 
     The order of reading each data, that is, the order of Steps S 1  to S 3  is not limited by the above. Also, Steps S 1  to S 3  can be executed at the same time. 
     At Step S 4 , on the basis of the position information of the descending-slope starting point P 2 A (Step S 2 ) during traveling and the current position of the vehicle  1  (Step S 3 ), the distance calculation portion  13  calculates the distance L between the descending-slope starting point P 2 A and the current position. 
     At Step S 5 , the control unit  10  determines whether or not the distance L between the descending-slope starting point P 2 A and the current position is not more than a constant (400 to 500 m, for example). 
     If the distance L between from the current position to the descending slope starting point P 2 A is not more than the constant (YES for Step S 5 ), the routine proceeds to Step S 6 . 
     On the other hand, if the distance L from the current position to the descending slope starting point P 2 A is larger than the constant (NO for Step S 5 ), Step S 1  and after is repeated. 
     At Step S 6 , using parameters of the vehicle speed Va, the target vehicle speed Vt when entering the descending slope, and the distance L from the current position P 1  to the descending slope starting point P 2 , the requested vehicle speed (target vehicle speed) Vd is calculated. Then, the routine proceeds to Step S 7 . 
     At Step S 7 , a control signal for controlling the fuel injection amount so that the requested vehicle speed Vd is achieved is outputted to the engine controller  4  via the in-vehicle communication network  5 . Then, the engine controller  4  transmits a control signal relating to the fuel injection amount to the fuel injecting device, not shown, so as to achieve the requested vehicle speed Vd. 
     Then, Step S 1  and after is repeated. 
     As described above, the illustrated fuel-saving driving system  100  is constructed to determine the target vehicle speed (requested vehicle speed Vd) from the vehicle speed Va, the data of the descending slope (the position of the descending-slope starting point P 2 A and the target vehicle speed Vt when entering the descending slope, for example) and the distance L from the current position to the descending-slope starting point P 2 A. 
     According to the fuel-saving driving system  100  as above, since the target vehicle speed Vd and the vehicle speed Va at a spot where the vehicle  1  is traveling can be controlled as shown in  FIG. 3 , repetition of fuel-cut and fuel injection before the descending-slope starting point P 2 A or a frequency at which the auxiliary brake is operated during the descending slope can be suppressed. 
     Since fuel-cut and fuel injection are not repeated, according to the illustrated fuel-saving driving system  100 , the vehicle behavior does not become unstable or jerky or give a sense of unstableness or a sense of discomfort to a driver. 
     Also, according to the illustrated fuel-saving driving system  100 , a frequency at which the auxiliary brake is operated in the middle of the descending slope is reduced. This means full deceleration has been achieved before reaching the descending-slope starting point P 2 A and also that the fuel consumption is saved in the illustrated fuel-saving driving system  100 . 
     That is, according to the illustrated embodiment, the fuel-saving driving is achieved. 
     The present invention may be applied to traveling changing from a flat road to the descending slope, for example, other than changing from ascending to descending. 
     The illustrated embodiment is only an example, and the description is not intended to limit the technical scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  vehicle 
               2  vehicle-position specifying device/GPS 
               3  vehicle speed measuring device/vehicle speed sensor 
               4  vehicle-side controller/engine controller 
               5  vehicle information network 
               10  controller/control unit 
               11  storage device/database 
               12  current-position specification portion 
               13  calculation portion for distance from current position to descending slope staring point/distance calculation portion 
               14  target-speed determination portion 
               15  instruction signal transmission timing determination portion 
               16  interface 
               17  timer