Vehicle orientation detection method and vehicle orientation detection apparatus

1. A vehicle orientation detection method detecting a vehicle orientation on a basis of data measured at each predetermined time interval when a vehicle travels, the vehicle including a GPS receiver that receives a signal of a GPS satellite, a yaw rate sensor that detects a yaw rate, a lateral acceleration sensor that detects a lateral acceleration and a vehicle speed sensor that detects a vehicle speed, the vehicle orientation detection method comprising:

detecting the vehicle orientation of the vehicle which travels less than a reference speed on a basis of the yaw rate detected by the yaw rate sensor when a detection speed of the vehicle speed sensor is less than the reference speed, the vehicle orientation being a heading orientation toward which the vehicle travels;

performing drift determination to determine whether the vehicle is in a drift state when the detection speed of the vehicle speed sensor is equal to or greater than the reference speed;

when the vehicle is not determined to be in the drift state in the drift determination, detecting the vehicle orientation on a basis of the signal received by the GPS receiver; and

when the vehicle is determined to be in the drift state in the drift determination, detecting the vehicle orientation of the vehicle which travels at or greater than the reference speed on the basis of the yaw rate detected by the yaw rate sensor.

2. The vehicle orientation detection method according to claim 1 , wherein:

when a value of a difference between the lateral acceleration detected by the lateral acceleration sensor and an acceleration in a lateral direction obtained from the yaw rate and the vehicle speed is equal to or greater than a drift determination value, the drift determination determines that the vehicle is in the drift state;

the yaw rate sensor detects the yaw rate; and

the vehicle speed sensor detects the vehicle speed.

3. The vehicle orientation detection method according to claim 2 , wherein:

when the drift state is detected in the drift determination, and when the value of the difference is equal to or less than a drift end determination value that is smaller than the drift determination value, an end of the drift state is detected.

4. The vehicle orientation detection method according to claim 2 , wherein:

when the yaw rate detected by the yaw rate sensor is equal to or greater than a drift determination angular speed, the drift determination determines that the vehicle is in the drift state.

5. The vehicle orientation detection method according to claim 1 , wherein:

when the vehicle orientation based on the yaw rate is switched to the vehicle orientation based on the signal received by the GPS receiver at a time of an end of the drift state, and when an orientation difference occurs between the vehicle orientation based on the yaw rate and the vehicle orientation based on the signal received by the GPS receiver, an interpolation process is performed so as to disperse and add the orientation difference on each orientation data of the vehicle based on the yaw rate during a drift period.

6. The vehicle orientation detection method according to claim 5 , wherein:

the interpolation process equally disperses and adds a value of the orientation difference on the each orientation data of the vehicle based on the yaw rate during the drift period.

7. The vehicle orientation detection method according to claim 1 , wherein:

when a signal obtained from a value of a difference between the lateral acceleration detected by the lateral acceleration sensor and an acceleration obtained from the yaw rate detected by the yaw rate sensor and the vehicle speed detected by the vehicle speed sensor through a low pass filter is equal to or greater than the drift determination value, the drift determination determines that the vehicle is in the drift state.

8. A vehicle orientation detection apparatus that detects a vehicle orientation of a vehicle on a basis of a GPS signal that a GPS receiver receives from a GPS satellite at each predetermined time interval, a yaw rate detected by a yaw rate sensor at each predetermined time interval, a lateral acceleration detected by a lateral acceleration sensor at each predetermined time interval, and a vehicle speed detected by a vehicle speed sensor at each predetermined time interval, the vehicle orientation detection apparatus comprising:

a vehicle speed determination portion determining whether the vehicle speed detected by the vehicle speed sensor is equal to or greater than a reference speed regarding each data at each predetermined time interval;

a drift determination portion determining whether the vehicle is in a drift state when the vehicle speed determination portion determines that the vehicle speed is equal to or greater than the reference speed; and

a vehicle orientation detection portion

detecting the vehicle orientation of the vehicle which travels less than the reference speed on a basis of the yaw rate of the yaw rate sensor when the vehicle speed determination portion determines that the vehicle speed is less than the reference speed, the vehicle orientation being a heading orientation toward which the vehicle travels,

detecting the vehicle orientation on a basis of the yaw rate of the yaw rate sensor when the drift determination portion has determined that the vehicle is in the drift state, and

detecting the vehicle orientation on a basis of a signal received by the GPS receiver other than a case where the vehicle speed determination portion determines that the vehicle speed is less than the reference speed and a case where the drift determination portion determines that the vehicle is in the drift state.