Autonomous driving system

1. An autonomous driving system configured to perform an autonomous driving of a vehicle, comprising:

a database that stores map information;

a global positioning sensor (GPS) that obtains a position of the vehicle on a map;

a vehicle speed sensor that detects a vehicle speed; and

an electronic control unit (ECU) including a processor programmed to:

determine a necessity of an operation intervention for a lane change of the vehicle by a driver of the vehicle during the autonomous driving based on a target route of the autonomous driving, the position of the vehicle on the map, and the map information;

determine that it is necessary for the driver to perform the operation intervention for the lane change of the vehicle when a length of a lane changeable section for the vehicle is shorter than a distance sufficient for the lane change by the autonomous driving, wherein the distance sufficient for the lane change by the autonomous driving is changed according to the vehicle speed of the vehicle;

request the driver to perform the operation intervention for the lane change of the vehicle when the determination is made that it is necessary to perform the operation intervention for the lane change of the vehicle by the driver;

switch a steering torque mode for a lane keep control in the autonomous driving from a normal steering torque mode to a weak steering torque mode when the driver is requested to perform the operation intervention for the lane change of the vehicle,

switch an area for the autonomous driving, based on an amount of operation intervention by the driver during the autonomous driving, from among: (i) an ignorance area where the vehicle is caused to travel by the control of the autonomous driving even if there is an operation intervention by the driver, (ii) a cooperation area where the vehicle is caused to travel under a cooperation between the operation intervention by the driver and the control of the autonomous driving, and (iii) a cut-off area where the vehicle is caused to travel by the operation intervention by the driver without reflecting the control of the autonomous driving,

switch the area to the cooperation area if the amount of operation intervention by the driver becomes equal to or greater than a first threshold value, and switch the area to the cut-off area if the amount of operation intervention by the driver is equal to or greater than a second threshold value which is greater than the first threshold value, and

wherein the first threshold value and the second threshold value are switched to smaller values in the weak steering torque mode than that in the normal steering torque mode,

wherein the weak steering torque mode is a mode of the lane keep control that (i) weakens, compared to that in the normal steering torque mode, a steering torque in a direction of the lane change of the vehicle among a right direction and a left direction of the vehicle, and (ii) strengthens, compared to that in the normal steering torque mode, a steering torque in a direction opposite to the direction of lane change.

2. The autonomous driving system according to claim 1 , wherein the lane changeable section for the vehicle is a section where a traveling lane of the vehicle and a lane of a lane change destination are adjacent to each other.