Vehicle navigator

Abstract: A vehicle navigator in a vehicle displays the vehicle's present position on a road map on a scrren, and marks a guide route between a start point (S) and a destination (O) which is determined so as to provide a low cost route. Return routes for returning the vehicle to the guide route should it deviate from the guide route are determined, as are the costs for the vehicle to return to the guide route via the return routes, and the vehicle is prevented from entering a return route depending on the cost calculated. For example, when the vehicle reaches a point in the guide route at which a deviation would result in a high cost return route, an alarm may be given to warn the driver of this.

Description: This invention relates to a vehicle navigator for constantly indicating the present position of a vehicle in a road map displayed on a screen as the vehicle travels, thereby aiding navigation of the vehicle along a predetermined route set on the road map. A vehicle navigator of this type has conventionally been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 58-70117, in which a start point, a destination, and crossings which the vehicle is to pass on the way from the start point to the destination are previously designated as a guide route on a road map displayed on a screen by inputting data thereof, and then the present position of the vehicle on the road map is constantly displayed to thereby navigate the vehicle along the guide route. Further, an improved vehicle navigator has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 1-138409, in which in setting a guide route for a vehicle from a start point to a destination on a road map, the guide route is automatically set to the optimum one which is most advantageous in distance and travel cost, such as a toll, of possible routes connecting between the start point and the destination. In these vehicle navigators, when the vehicle deviates from the guide route during travel, a possible solution to this deviation is to return to the guide route originally set, or to set a new guide route to the destination, thereby continuing the travel (hereinafter, the route for returning to the original guide route or the newly set guide route will be referred to as "return route"). EP-A-583773 and US-A-5291414 disclose similar systems. Anyway, the return route is disadvantageous due to a resulting increased cost ascribable to increases in the distance, time, and money. A possible solution to this inconvenience is to notify the driver of a course to be taken whenever the vehicle comes near a point, such as a crossing, at which the vehicle can deviate from the guide route. However this can be an annoyance to the driver when a large number of crossings and the like are frequently notified on the way. Therefore, the problem to be solved is that when the vehicle deviates from a guide route during travel, it is not so inconvenient so long as the cost resulting from the return route is small, but it is very disadvantageous when the cost resulting from the return route is large, and guide messages frequently delivered for prevention of deviation from the guide route can be an annoyance. The invention provides a vehicle navigator which is capable of cautioning the driver of a possibility of deviation of the vehicle from the route, only when deviation from a point of the guide route results in a large increase in the travel cost. According to a first aspect of the invention, there is provided a vehicle navigator for aiding navigation of a vehicle comprising: map displaying means for displaying a road map on a screen; present position-indicating means for indicating a present position of said vehicle on said road map on said screen; and guide route-determining/indicating means for determining a guide route connecting a start point of said vehicle and a destination of said vehicle which are set in advance, and indicating said guide route on said road map; the navigator being characterised in that it further comprises: possible deviation-determining means for determining possible deviations of said vehicle from said guide route; return route-selecting means for selecting a return route for returning said vehicle to said guide route according to said possible deviations of said vehicle from said guide route; cost-calculating means for calculating cost required for said vehicle to return to said guide route via said return route; and prevention means for preventing said vehicle from entering a deviation, depending on the cost of the return route for the deviation calculated by said cost-calculating means, said prevention means including warning means for issuing a warning for prevention of said vehicle from entering said deviation. Preferably, the prevention means comprises determining means for determining whether or not the cost exceeds a predetermined value, and the warning means issue a warning for prevention of the vehicle from entering the deviation when the cost of the return route exceeds the predetermined value. Preferably, the cost includes a time period and a toll which are required for the vehicle to return to the guide route via the deviation. The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description given by way of example only, taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram showing the basic arrangement of a vehicle navigator according to an embodiment of the invention; Fig. 2 is a diagram showing an example of a display screen for vehicle navigation; Fig. 3 is a diagram showing an example of a return route to be taken when the vehicle deviates from a guide route; Fig. 4 is a flowchart of processing for searching for a return route and determining the travel cost of the return route; Fig. 5 is a flowchart of processing carried out when the present position of the vehicle has deviated from the guide route; and Fig. 6 is a flowchart of processing carried out when a deviating course selection range has changed. Referring first to Fig. 1, there is shown the basic arrangement of a vehicle navigator according to an embodiment of the invention. The vehicle navigator is comprised of a distance sensor 1 for delivering a signal pulse whenever the vehicle travels a unit distance, based on rotations of wheels of the vehicle, a direction sensor 2 for detecting a change in the angular velocity in a yawing direction to thereby deliver a signal proportional to an amount of change in the traveling direction, a signal processor 3 formed of a microcomputer for measuring the travel distance covered by the vehicle by counting the number of signal pulses received from the distance sensor 1, and for determining a change in the traveling direction based on the signal output from the direction sensor 2, to thereby determine, by computation, the present position of the vehicle on X-Y coordinates whenever the vehicle travels a predetermined distance, as well as performing the overall control of the whole vehicle navigator, a travel path storage unit 4 for sequentially storing data of the present position determined on each occasion by the signal processor 3 as a finite sequence of positional information, a map information-storing medium 5 storing road map information formed of digital map data, a storage medium reader unit 6 for selectively reading road map information necessary for an area in which the vehicle is traveling, from the map information-storing medium 5, a display device 7 for displaying a predetermined road map on a screen based on the road map information read by the storage medium reader unit 6 and indicating the present position of the vehicle on the road map displayed together with the advancing direction, as the vehicle travels, an operating device 8 which can give directions to the signal processor 3, as to selection and display of a map on the screen, setting of a start point and a destination of the vehicle on the map displayed and automatic setting of the optimum guide route therebetween, selective designation of the covered route display, change of settings of display modes, such as selection of a display scale, and other directions, and a warning device 9 for producing a guide message, e.g. by alarm in the form of synthesized voice. According to this arrangement, a road map selectively read is displayed on the display device 7, and the present position of the vehicle on the X-Y coordinates is calculated every moment based on the scale of the map set in advance by the signal processor 3 as the vehicle travels from a start point S set on the displayed map. Results of the calculation are sequentially delivered to the travel path storage unit 4 to update the contents of storage therein, which are then read out therefrom and delivered to the display device 7. The display device 7 displays thereon in a manner following up and reflecting the state of travel of the vehicle, e.g. as shown in Fig. 2, a mark M1 indicating the present position of the vehicle on the displayed map, a mark M2 indicating the advancing direction of the vehicle in the present position, and covered route-indicating marks M3 indicating a route covered from the start point S to the present position indicated by the mark M1, as the vehicle advances. In the signal processor 3, based on map data read from the map information-storing medium 5, the optimum guide route is searched for, which is advantageous in respect of travel cost taken when the vehicle travels from the start point S to the destination O both set on the map, and the optimum guide route thus determined is indicated e.g. in a special color, thereby performing navigation for the driver of the vehicle such that the present position thereof can be on the guide route when the vehicle travels from the start point S. It should be noted that in the present embodiment, a conventional method of searching for the optimum guide route is used as it is, which is the minimum in travel cost when the vehicle travels from the start point to the destination O. According to the present invention, in the vehicle navigator, especially in the signal processor 3, there are provided means for selecting a return route when the vehicle deviates from the guide route, means for calculating a travel cost to be incurred in following the selected return route and determining whether or not the travel cost calculated exceeds a threshold value, and means for generating a caution or warning or a guide message to prevent the vehicle from deviating into the return route during travel when the travel cost of the return route exceeds the threshold value. More specifically, first the start point S and the destination O are set on the map, and then, based on this setting, the optimum guide route is searched for. Data on the optimum guide route are stored into a guide route-storing block of an internal memory within the signal processor 3. Then, a deviating route selection range is determined along the guide route, and within this range, possible deviating courses into which the vehicle can deviate are selected. In doing this, routes having higher possibility of deviation are selected preferentially according to a predetermined determination algorithm, which takes into consideration road circumstances, e.g. closeness of a crossing at which the vehicle should turn to the right to another crossing, etc. The routes thus selected are stored together with the order of priority depending upon the possibility of deviation, into a deviating course-storing area of the internal memory within the signal processor 3. Then, a return route to be taken when the vehicle deviates into one of the selected deviating courses is searched for, and the travel cost of the return route is calculated. Then, it is determined whether or not the travel cost thus calculated exceeds the threshold value, e.g. by the following procedure: Now, let it be assumed that the routes are expressed as follows: Po: guide route P: return route Po∩P: common part of the guide route and the return route Po - Po∩P: part of the guide route which is not common with the return route P - Po∩P: part of the return route which is not common with the guide route, The travel cost C(P) of the return route P is determined from an average time period required for the vehicle to travel along the return route P, and a toll, if any, as follows: Cd(P): estimated average time period required for the vehicle to travel along the return route (the sum of distances of route sections x respective estimated average speeds along the route sections ) Ct(P): total of tolls to be paid for the return route Conditions for determining whether or not the travel cost of the return route is reasonable are defined as follows: ▵Cd(P) = Cd(P-Po∩P) - Cd (Po-Po∩P) > 15 minutes ▵Ct(P) = Ct(P-Po∩P) - Ct(Po-Po∩P) > 0.1Ct(Po-Po∩P). When the travel cost of a return route determined to be taken for a deviating course into which the vehicle can deviate from the guide route fulfills the above conditions, it is determined that the travel cost of the return route is high. More specifically, referring to Fig. 3 for example, assuming that the vehicle deviates from a guide route Po at a point X and then returns to the guide route Po via a return route P, it is determined that the travel cost of the return route is high, if an average time period required for the vehicle to travel through a section B over which the vehicle deviates from the guide route minus an average time period required for the vehicle to travel through a regular section A of the guide route is above 15 minutes, or if the total of tolls becomes higher by 10% or more when the vehicle travels through the section B than when the vehicle travels through the section A. If it is determined that the travel cost of the return route P is high, an alarm or a guide message in the form of a synthesized voice is delivered from the warning device 9, before the present position of the vehicle reaches the point X at which there is a high possibility of deviation of the vehicle from the guide route. Fig. 4 shows a program for selecting deviating courses, searching for a return route, and determining whether or not the travel cost of the return route is high. First, at a step S1, a deviating course selection range is determined according to a guide route previously set, and possible deviating courses into which the vehicle can deviate within the determined deviating course selection range are enumerated into a deviating course group. At the following step S2, the possible deviating courses of the deviating course group are lined up in the order of higher possibility of deviation. At the following step S3, the deviating course group is stored into the memory block. Then, it is determined at a step S4 whether or not there still remains a deviating course for which a return route has not been searched for. If the answer to this question is negative (NO), the program is immediately terminated, whereas if the answer is affirmative (YES), the program proceeds to a step S5. At the step S5, a return route which has not been searched for the deviating course is searched for, and the travel cost of the return route (return cost) searched out is calculated. At the following step S6, the return route and the return cost are stored into the return route-storing block. Then, the program proceeds to a step S7. At the step S7, it is determined whether or not the return cost is above a threshold value. If the answer to this question is negative (NO), the program returns to the step S4, whereas if the answer is affirmative (YES), the program proceeds to a step S8. At the step S8, an alarm or a guide message is issued by the warning device 9 before the vehicle reaches a point at which the vehicle can deviate into the deviating course of which the return cost is determined to be high at the step S7. Further, during travel of the vehicle, if the present position of the vehicle actually deviates from the guide route, the signal processor 3 prepares an updated guide route according to a return route searched according to the deviation course, whereby the data stored in the guide route-storing block is updated. Then, according to the updated guide route, the processing described above is continued. Fig. 5 shows a program for this processing. First, at a step S11, it is determined whether or not the present position of the vehicle has deviated from the guide route. If the answer to this question is negative (NO), the program returns to the step S11, whereas if the answer is affirmative (YES), a return route is searched for according to the deviating course, and the return route searched out is stored into the guide route-storing block as an updated guide route to thereby continue vehicle navigation at a step S12. After the guide route has been updated due to deviation of the vehicle, the deviating course selection range is updated accordingly. Within the updated range, courses having possibility of deviation are selected, and the data stored in the deviating course-storing block in the internal memory of the signal processor 3 is updated. Then, based on the courses having possibility of deviation thus selected, the processing described hereinabove is carried out. Fig. 6 shows a program for the updating processing. First, at step S21, it is determined whether or not the deviating course selection range has been changed. If the answer to this question is negative (NO), the program returns to the step S21, whereas if the answer is affirmative (YES), the program proceeds to a step S22, where the Fig. 4 return route search routine is started again (the routine is stopped and started again if it is already being executed).

Claims: A vehicle navigator for aiding navigation of a vehicle, comprising: map displaying means (7) for displaying a road map on a screen; present position-indicating means (3) for indicating a present position (M1) of said vehicle on said road map on said screen; and guide route-determining/indicating means (3) for determining a guide route connecting a start point (5) of said vehicle and a destination (0) of said vehicle which are set in advance, and indicating said guide route on said road map; the navigator being characterised in that it further comprises: possible deviation-determining means for determining possible deviations of said vehicle from said guide route; return route-selecting means (3) for selecting a return route for returning said vehicle to said guide route according to said possible deviations of said vehicle from said guide route; cost-calculating means (3) for calculating cost required for said vehicle to return to said guide route via said return route; and prevention means (3) for preventing said vehicle from entering a deviation, depending on the cost of the return route for the deviation calculated by said cost-calculating means, said prevention means including warning means (9) for issuing a warning for prevention of said vehicle from entering said deviation. A vehicle navigator according to claim 1, wherein said prevention means comprises determining means for determining whether or not said cost exceeds a predetermined value, and issues said warning for prevention when said cost exceeds said predetermined value. A vehicle navigator according to claim 1 or 2, wherein said cost includes a time period and a toll which are required for said vehicle to return to said guide route via said return route.

Inventors: SAWADA YASUHIRO, SAWADA, YASUHIRO, Sawada, Yasuhiro, c/o Honda R &amp; D Co., Ltd.
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1995
Main classification: G01C21
IPC codes: G01C21, G09B29, G08G1, G10L13