CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-179645 filed Sep. 30, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a travel controller for performing travel control of a host vehicle.

BACKGROUND ART

There is currently a trend to develop elemental technologies for automating the driving of vehicles that ease the burden of drivers regarding driving operation. A travel control technology called adaptive cruise control (ACC) is one known elemental technology for achieving automated driving.

In a travel controller with an ACC (adaptive cruise control) function, travel control is achieved by controlling a drive system and braking system of a host vehicle in an integrated manner, wherein the travel control includes (i) constant speed travel control that controls a host vehicle to travel at constant speed in accordance with a target vehicle speed, and (ii) headway travel control that controls a host vehicle to travel by following another vehicle travelling ahead, wherein a predetermined inter-vehicle distance is maintained with the other vehicle.

An example of such a travel controller is shown in Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2017-043237), in which the travel controller prohibits ACC operation when the likelihood of brake fade occurring reaches a predetermined critical level (Patent Literature 1, paragraph 0069).

According to the travel controller of Patent Literature 1, because ACC operation is prohibited when the likelihood of brake fade occurring reaches a predetermined critical level, the travel controller can prevent brake fade from occurring while the travel control of ACC is in operation.

According to the travel controller of Patent Literature 1, when the likelihood of brake fade occurring exceeds a first threshold, a brake fade flag is turned on and ACC operation is prohibited (i.e., cancelled) (Patent Literature 1, paragraph 0069).

Furthermore, according to the travel controller of Patent Literature 1, if the level of likelihood of brake fade occurring drops below a second threshold that is lower than the first threshold, the brake fade flag is turned off and ACC operation is resumed (Patent Literature 1, paragraph 0044, 0060).

However, the travel controller according to Patent Literature 1 does not disclose nor suggest a travel controller that reduces the level of likelihood of brake fade occurring while ACC (travel control) is in operation. Thus, there exists a need for improvement in terms of extending an operation period of ACC as much as possible and contributing to improving the operation rate of ACC.

SUMMARY

The disclosure has been made in view of the abovementioned situation. It is an object of the disclosure to provide a travel controller that extends the operation time of travel control as much as possible while the travel control is in operation and contributes to improving the operation rate of travel control.

In order to solve the above problems, the disclosure is a travel controller for performing travel control of a host vehicle, wherein the travel controller includes the following main features. The travel controller includes an information acquisition part that is configured to acquire brake state information of a braking device that the host vehicle is equipped with and a travel control part that is configured to perform travel control. The travel control performed includes constant speed travel control, headway travel control, or constant speed travel control and headway travel control. The constant speed travel control is configured to control the host vehicle to travel at constant speed in accordance with a target vehicle speed, and the headway travel control is configured to control the host vehicle to travel by following another vehicle travelling ahead so that a target inter-vehicle distance is maintained with the other vehicle. In the constant speed travel control, when an actual vehicle speed drops below the target vehicle speed, the travel control part is configured to (i) calculate target acceleration based on a difference between the target vehicle speed and the actual vehicle speed and (ii) perform the constant speed travel control so that the actual vehicle speed is brought closer to the target vehicle speed. When the target acceleration is calculated, if a braking performance index based on the brake state information acquired with the information acquisition part has declined relative to a predetermined evaluation threshold while the constant speed travel control has been in operation, then the target acceleration is corrected so that (a) the target acceleration is reduced compared to if the braking performance index has not declined relative to the evaluation threshold and (b) the constant speed travel control is performed so that the actual vehicle speed is brought closer to the target vehicle speed based on the corrected target acceleration.

A travel controller according to the disclosure is capable of extending an operation time of travel control as much as possible while the travel control is in operation and contributing to improving an operation rate of the travel control.

