Vehicle steering assist device

A vehicle steering assist device comprising:

• a turning device configured to turn a turning wheel in accordance with a steering operation amount applied to a steering input member by a driver, and configured to apply a return torque for urging the steering input member to a neutral position to the steering input member, the return torque being a torque that increases as the steering operation amount increases;
• a control steering torque generating device that generates a control steering torque for correcting the return torque;
• a control unit that controls the control steering torque generating device;
• a curvature degree acquisition device that acquires a curvature degree of a traveling road in front of a vehicle;
• a vehicle speed detecting device;
• and
• a steering assist switch,
• wherein when the steering assist switch is turned on, the control unit calculates a target steering angle for causing the vehicle to travel along a traveling road based on the curvature degree of the traveling road acquired by the curvature degree acquisition device and a vehicle speed detected by the vehicle speed detecting device,
• wherein the control unit calculates a target steering guide torque for facilitating a steering angle to become the target steering angle by reducing the return torque in an area where the steering angle is smaller than the target steering angle,
• wherein the control unit is configured to control the control steering torque generating device to cause the control steering torque generating device to generate the control steering torque including the target steering guiding torque,
• wherein the control unit calculates an actual steering angular velocity based on the steering angle when the steering assist switch is turned on,
• wherein the control unit calculates a target steering angular velocity based on the target steering angle,
• wherein when the actual steering angular velocity is higher than the target steering angular velocity, the control unit calculates a target steering angular velocity control torque acting in a direction opposite to a direction in which the actual steering angle changes, and
• wherein the control unit controls the control steering torque generating device to cause the control steering torque generating device to generate a control steering torque including a sum of the target steering guide torque and the target steering angular velocity control torque,
• wherein the control unit is configured to:
• calculate a determination reference value for a steering angular velocity based on a maximum steering angular velocity when the vehicle travels on a curve of the traveling road, in a situation where the steering assist switch is turned off,
• reduce a magnitude of the target steering guide torque when the actual steering angular velocity is smaller than the target steering angular velocity and an index value of the actual steering angular velocity is higher than the determination reference value, in a situation where the steering assist switch is turned on;
• and
• control the control steering torque generating device to cause the control steering torque generating device to generate a control steering torque that includes the target steering guide torque with a reduced magnitude of the target steering guide torque and that does not include the target steering angular velocity control torque.