Parking assist device

1. A parking assist device, comprising:

an electronic control unit configured to:

perform parking assist of a vehicle to automatically park the vehicle at a target position, while restricting a vehicle speed to an upper limit or lower in accordance with an instruction of a user who is outside the vehicle, and control a first brake device configured to brake the vehicle or a second brake device that is configured to brake the vehicle, when the vehicle is braked during the parking assist, and wherein the second brake device is different from the first brake device;

determine whether or not the vehicle moves on a road surface having a downhill grade along a travelling direction of the vehicle by the parking assist;

set the upper limit in a case where the vehicle is determined to move on the road surface having the downhill grade to be smaller than the upper limit in a case where the vehicle is not determined to move on the road surface having the downhill grade; and

control the second brake device to brake the vehicle when an abnormality occurs during the parking assist, the abnormality being a failure in controlling the first brake device to brake the vehicle, wherein

the first brake device is hydraulic,

the second brake device is different from a hydraulic brake device, the second brake device being allowed to operate under a situation where the vehicle speed is smaller than a specified allowable value while being prohibited to operate under a situation where the vehicle speed is larger than the allowable value; and

the electronic control unit is further configured to:

set the upper limit in the case where the vehicle is determined to move on the road surface having the downhill grade to be equal to or lower than a value obtained by subtracting an increment of the vehicle speed from the allowable value, the increment of the vehicle speed being assumed on a supposition that the vehicle not braked by the first brake device moves on a road surface with a largest downhill grade over a prescribed period, the road surface with the largest downhill grade being preset as a road surface where the parking assist is applicable, and

the prescribed period is a period required for starting operation of the second brake device after occurrence of the abnormality.

2. The parking assist device according to claim 1 , wherein

the electronic control unit is further configured to determine whether or not the abnormality occurs based on the upper limit in the case where the vehicle is not determined to move on the road surface having the downhill grade.

3. A parking assist device, comprising:

an electronic control unit configured to:

perform parking assist of a vehicle to automatically park the vehicle at a target position, while restricting a vehicle speed to an upper limit or lower in accordance with an instruction of a user who is outside the vehicle, and control a first brake device configured to brake the vehicle or a second brake device that is configured to brake the vehicle, when the vehicle is braked during the parking assist, and wherein the second brake device is different from the first brake device;

determine whether or not the vehicle moves on a road surface having a downhill grade along a travelling direction of the vehicle by the parking assist;

set the upper limit in a case where the vehicle is determined to move on the road surface having the downhill grade to be smaller than the upper limit in a case where the vehicle is not determined to move on the road surface having the downhill grade; and

control the second brake device to brake the vehicle when an abnormality occurs during the parking assist, the abnormality being a failure in controlling the first brake device to brake the vehicle, wherein

the first brake device is hydraulic,

the second brake device is different from a hydraulic brake device, the second brake device being allowed to operate under a situation where the vehicle speed is smaller than a specified allowable value while being prohibited to operate under a situation where the vehicle speed is larger than the allowable value;

at a time of determining whether or not the vehicle moves on the road surface with the downhill grade, acquire a grade of the road surface where the vehicle moves by the parking assist; and

set the upper limit in the case where the vehicle is determined to move on a road surface having a specified downhill grade to be equal to or lower than a value obtained by subtracting an increment of the vehicle speed from the allowable value, the increment of the vehicle speed being assumed on a supposition that the vehicle not braked by the first brake device moves on the road surface with the specified downhill grade over a prescribed period, and

the prescribed period is a period required for starting operation of the second brake device after occurrence of the abnormality.

4. The parking assist device according to claim 3 , wherein

the electronic control unit is configured to set the upper limit in the case where the vehicle is not determined to move on the road surface having the downhill grade to be equal to or lower than the allowable value.

5. A parking assist device, comprising:

an electronic control unit configured to:

perform parking assist of a vehicle to automatically park the vehicle at a target position while controlling a vehicle speed to follow after a target value in accordance with an instruction of a user who is outside the vehicle, and control a first brake device configured to brake the vehicle or a second brake device that is configured to brake the vehicle, when the vehicle is braked during the parking assist, and wherein the second brake device is different from the first brake device;

determine whether or not the vehicle moves on a road surface having a downhill grade along a travelling direction of the vehicle by the parking assist;

set the target value in a case where the vehicle is determined to move on the road surface having the downhill grade to be smaller than the target value in a case where the vehicle is not determined to move on the road surface having the downhill grade; and

control the second brake device to brake the vehicle when an abnormality occurs during the parking assist, the abnormality being a failure in controlling the first brake device to brake the vehicle, wherein

the first brake device is hydraulic,

the second brake device different from a hydraulic brake device, the second brake device being allowed to operate under a situation where the vehicle speed is smaller than a specified allowable value while being prohibited to operate under a situation where the vehicle speed is larger than the allowable value; and

set the target value in the case where the vehicle is determined to move on the road surface having the downhill grade to be equal to or lower than a value obtained by subtracting an increment of the vehicle speed from the allowable value, the increment of the vehicle speed being assumed on a supposition that the vehicle not braked by the first brake device moves on a road surface with a largest downhill grade over a prescribed period, the road surface with the largest downhill grade being preset as a road surface where the parking assist is applicable, and

the prescribed period is a period required for starting operation of the second brake device after occurrence of the abnormality.

6. The parking assist device according to claim 5 , wherein

the electronic control unit is configured to, when the vehicle is determined to travel on the road surface having the downhill grade, set the target value to be smaller as an absolute value of the downhill grade of the road surface becomes larger.

7. A parking assist device, comprising:

an electronic control unit configured to:

perform parking assist of a vehicle to automatically park the vehicle at a target position while controlling a vehicle speed to follow after a target value in accordance with an instruction of a user who is outside the vehicle, and control a first brake device configured to brake the vehicle or a second brake device that is configured to brake the vehicle, when the vehicle is braked during the parking assist, and wherein the second brake device is different from the first brake device;

determine whether or not the vehicle moves on a road surface having a downhill grade along a travelling direction of the vehicle by the parking assist;

set the target value in a case where the vehicle is determined to move on the road surface having the downhill grade to be smaller than the target value in a case where the vehicle is not determined to move on the road surface having the downhill grade; and

control the second brake device to brake the vehicle when an abnormality occurs during the parking assist, the abnormality being a failure in controlling the first brake device to brake the vehicle, wherein

the first brake device is hydraulic,

the second brake device is different from a hydraulic brake device, the second brake device being allowed to operate under a situation where the vehicle speed is smaller than a specified allowable value while being prohibited to operate under a situation where the vehicle speed is larger than the allowable value;

at a time of determining whether or not the vehicle moves on the road surface with the downhill grade, acquire a grade of the road surface where the vehicle moves by the parking assist; and

set the target value in the case where the vehicle is determined to move on a road surface having a specified downhill grade to be equal to or lower than a value obtained by subtracting an increment of the vehicle speed from the allowable value, the increment of the vehicle speed being assumed on a supposition that the vehicle not braked by the first brake device moves on the road surface with the specified downhill grade over a prescribed period, and

the prescribed period is a period required for starting operation of the second brake device after occurrence of the abnormality.

8. The parking assist device according to claim 5 , wherein

the electronic control unit is configured to set the target value in the case where the vehicle is not determined to move on the road surface having the downhill grade to be equal to or lower than the allowable value.