Current position calculating system having a function for correcting a distance factor

Claim 1

A current position calculating system for installation on a vehicle moving in accordance with a wheel rotation and calculates a current position of the vehicle, said system comprising: means for storing road data representing a road map; a headed direction detecting means for detecting a headed direction of the vehicle; a rotational speed detecting means for detecting a wheel rotational speed; a travelled distance calculating means for calculating a travelled distance of the vehicle in accordance with the wheel rotational speed detected by the rotational speed detecting means and a predetermined distance factor; a current position estimating means for estimating a current position on a road where the vehicle exists thereon, in accordance with the detected ravelled distance, the detected head direction and the road map represented by the road data; a left/right turning determining means for determining whether the vehicle turns left or right from a first road to a second road; a distance factor correcting means for obtaining at a time of turning left or right, based on the detected travelled distance, the detected headed direction and the road data of the road map, a distance error amount which is an error in an output from the travelled distance calculating means with respect to an actual value it should be, and for correcting the distance factor in order to reduce the distance error amount; a storing means for accumulating a combination of data items obtained at a plurality of previous sequential points in time, said data items including the detected travelled distance, the detected headed direction and the current position where the vehicle exists, said distance factor correcting means estimating a moving path of vehicle positions whether the positions are on or off a road, according to the combination of said data items, after completing a left or a right turn, checking whether said moving path overshoots or undershoots the second road on the road map, and obtaining an amount of either of the overshoot and the undershoot as said distance error amount; means for obtaining a width of said second road according to the road data; and means for correcting said distance error amount in accordance with the width of said second road.

Claim 7

A method for correcting a distance factor for obtaining a vehicle travelled distance based on a wheel rotational speed, in a current position calculating system for installation on the vehicle to obtain a current position of the vehicle, comprising: when the vehicle turns left or right at approximately right angle and moves from a first road to a second road, estimating a moving path of vehicle positions on or off a road according to the travelled distance determined based on headed directions sequentially obtained by a headed direction detecting means and a travelled distance determined based on travelled distances sequentially obtained according to the distance factor and the wheel rotational speed; checking whether the estimated moving path of vehicle positions overshoots or undershoots the second road on a road map; and decreasing the distance factor depending on an amount of the overshoot when the moving path is an overshoot, and increasing the distance factor depending on an amount of the undershoot, when the moving path is an undershoot, wherein a width of said second road is checked according to the road data, and each amount of the overshoot and the undershoot is corrected in accordance with the width of said second road.

Claim 8

A method for correcting a distance factor for obtaining a vehicle travelled distance based on a wheel rotational speed, in a current position calculating system for installation on the vehicle to obtain a current position of the vehicle, comprising: when the vehicle turns left or right at approximately right angle and moves from a first road to a second road, estimating a moving path of vehicle positions on or off a road according to the travelled distance determined based on headed directions sequentially obtained by a headed direction detecting means and a travelled distance determined based on travelled distances sequentially obtained according to the distance factor and the wheel rotational speed; checking whether the estimated moving path of vehicle positions overshoots or undershoots the second road on a road map; and decreasing the distance factor depending on an amount of the overshoot when the moving path is an overshoot, and increasing the distance factor depending on an amount of the undershoot, when the moving path is an undershoot, wherein a width of said second road is checked according to the road data, and each amount of the overshoot and the undershoot is corrected in accordance with the width of said second road.