Driving assist apparatus

1. A driving assist apparatus comprising:

a driver monitor sensor which detects a state of a driver of an own vehicle installed with the driving assist apparatus; and

an electronic control unit configured to:

determine whether the driver is in a drowsy state, based on the state of the driver detected by the driver monitor sensor;

determine that a light collision occurs when a light collision determination condition that at least one collision index value representing a level of a collision of the own vehicle is larger than a light collision determination threshold at which an airbag is not developed, is satisfied; and

execute a secondary collision damage mitigation control to apply a braking force to the own vehicle or limit a driving force applied to the own vehicle when the electronic control unit determines that (i) the driver is in the drowsy state, and (ii) the light collision occurs.

2. The driving assist apparatus as set forth in claim 1 , wherein:

the electronic control unit is configured to execute the secondary collision damage mitigation control when the electronic control unit determines that the light collision occurs until a predetermined amount of time elapses since the electronic control unit determines that the driver is not in the drowsy state.

3. The driving assist apparatus as set forth in claim 1 , wherein:

the driving assist apparatus further comprises at least one rear monitor sensor which detects a state behind the own vehicle; and

the electronic control unit is configured to:

determine whether there is a following vehicle moving behind the own vehicle in a predetermined area near the own vehicle, based on the state behind the own vehicle detected by the rear monitor sensor;

apply the braking force to the own vehicle in executing the secondary collision damage mitigation control when the electronic control determines that there is not the following vehicle in the predetermined area near the own vehicle; and

limit the driving force applied to the own vehicle without applying the braking force to the own vehicle in executing the secondary collision damage mitigation control when the electronic control determines that there is the following vehicle in the predetermined area near the own vehicle.

4. The driving assist apparatus as set forth in claim 3 , wherein:

the predetermined area is set such that an inter-vehicle distance between the own vehicle and the following vehicle in the predetermined area is longer than or equal to a predetermined distance.

5. The driving assist apparatus as set forth in claim 4 , wherein:

the predetermined distance is set to a distance which increases as a moving speed of the own vehicle increases.

6. The driving assist apparatus as set forth in claim 1 , wherein:

the at least one collision index value includes at least one of (i) an acceleration of a body of the own vehicle and (ii) a value varying, depending on the acceleration.

7. The driving assist apparatus as set forth in claim 1 , wherein:

the at least one collision index value includes at least one of (i) an acceleration of a body of the own vehicle and (ii) an integration value of the acceleration.

8. The driving assist apparatus as set forth in claim 1 , wherein:

the at least one collision index value includes (i) an acceleration of a body of the own vehicle and (ii) an integration value of the acceleration.

9. The driving assist apparatus as set forth in claim 1 , wherein:

the airbag is developed when the at least one collision index value is larger than an airbag development determination threshold; and

the light collision determination threshold is smaller than the airbag development determination threshold.