INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2019-053395 filed on Mar. 20, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a vehicle battery controller.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2018-069900 discloses a battery controller mounted on a vehicle configured to execute autonomous driving. The battery controller includes a lead-acid battery and a lithium ion battery. The lead-acid battery supplies electric power to electric equipment such as accessories. The lithium ion battery is used for backing up the autonomous driving. In this battery controller, when the autonomous driving is requested while charging the lead-acid battery in a state in which the lithium ion battery is disconnected from a power supply line, the lithium ion battery is connected to the power supply line with its voltage reduced to an open-circuit voltage of the lithium ion battery. Therefore, only the lead-acid battery can be charged in a state in which both the lithium ion battery and the lead-acid battery are connected to the power supply line. Thus, the battery controller described in Japanese Unexamined Patent Application Publication No. 2018-069900 secures backup power necessary during a limp home mode of the autonomous driving using the lithium ion battery, and prevents a delay in the charging of the lead-acid battery.

SUMMARY

In the battery controller described in Japanese Unexamined Patent Application Publication No. 2018-069900, when the autonomous driving is requested, the autonomous driving is executed without checking the power storage amount of the battery. To secure the safety of the vehicle, it is desirable to determine, when the autonomous driving is requested, whether the lithium ion battery can output the backup power necessary during the limp home mode before the autonomous driving is executed. This determination generally requires a long time because of a necessity to temporarily discharge the battery such that the current to be consumed in the limp home mode is actually caused to flow, and then charge the battery to a predetermined power storage amount. Therefore, the autonomous driving cannot immediately be executed even if the autonomous driving is requested by a driver or the like.

The present disclosure provides a vehicle battery controller in which autonomous driving requested by a driver or the like can be executed quickly.

One aspect of the present disclosure relates to a vehicle battery controller including a sensor, a DC-DC converter, a switching unit, and a control unit. The sensor is configured to acquire information related to a current, a voltage, and a temperature of a subordinate battery configured to back up a main battery during autonomous driving. The DC-DC converter is provided between the main battery and the subordinate battery. The switching unit is configured to switch a connection state of the subordinate battery between a connection state for manual driving and a connection state for the autonomous driving. The control unit is configured to control charging and discharging of the subordinate battery by controlling the DC-DC converter and the switching unit based on the information acquired by the sensor. The control unit is configured to tentatively determine, by executing a first battery control during a period of the manual driving after an ignition is turned ON, whether the subordinate battery is able to output backup power necessary during a limp home mode of the autonomous driving. The control unit is configured to permit the autonomous driving when determination is made, through the first battery control, that the subordinate battery is able to output the backup power. The control unit is configured to execute the autonomous driving in response to a request after the autonomous driving is permitted. The control unit is configured to determine, by executing a second battery control after the autonomous driving is permitted, whether the subordinate battery is able to output the backup power. The second battery control has higher accuracy than accuracy of the first battery control.

According to the vehicle battery controller described above, when determination is tentatively made that the subordinate battery can output the backup power necessary during the limp home mode before the driver or the like requests the autonomous driving, the requested autonomous driving can quickly be executed after the autonomous driving is permitted.

