Idling stop control device and idling stop control method

Abstract

In this idling stop control device, a controller 10 calculates a first discharge SOC, calculates a present SOC after the start of the current travel, sets a permission threshold for permitting the idling stop and a non-permission threshold for not permitting the idling stop, permits the idling stop when the present SOC is equal to or more than a permission SOC threshold, and does not permit the idling stop when the present SOC is equal to or less than a non-permission SOC threshold.

Description

Idling stop control device and idling stop control method

[0001] The present invention relates to an idling stop control device and an idling stop control method.

[0002] Conventionally, systems have been known that automatically stop an internal combustion engine when an idle stop condition of a vehicle is met and quickly start the internal combustion engine when the vehicle is restarted. For example, a system described in Patent Document 1 includes a means for measuring the battery voltage and current while the starter motor is running, a means for calculating the internal resistance of a lead battery from the battery voltage and current, and a means for estimating the degree of deterioration of the lead battery from the calculated internal resistance, which is used as a prohibition condition or a permission condition for idle stop control.

[0003] Japanese Patent Application Laid-Open No. 2007-331716

[0004] The system described in Patent Document 1 uses the degree of deterioration to determine whether to allow idling stop, and allows idling stop if it is determined that the battery has returned to a good condition, but it is not a system that prevents battery deterioration.

[0005] The problem to be solved by the present invention is to provide an idling stop control device and an idling stop control method that prevent deterioration of a battery.

[0006] The present invention solves the above problem by calculating a first discharge SOC, calculating the current SOC after the start of the current driving, setting an authorization threshold that permits idling stop and a non-authorization threshold that prohibits idling stop, and permitting idling stop when the current SOC is equal to or greater than the authorization SOC threshold, and not permitting idling stop when the current SOC is equal to or less than the non-authorization SOC threshold.

[0007] According to the present invention, deterioration of the battery can be prevented.

[0008] Fig. 1 is a block diagram of an idling stop control system according to an embodiment of the present invention. Fig. 2 is a graph showing a transition of SOC according to a running state of a vehicle. Fig. 3 is a flowchart showing a control flow of an idling stop control method according to this embodiment. Fig. 4 is a flowchart showing a control flow of an idling stop control method according to this embodiment.

[0009] An idling stop control device and an idling stop control method according to an embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of an idling stop control system according to an embodiment of the present invention. The idling stop control system 100 is mounted on a vehicle equipped with an engine and controls idling stop in accordance with the vehicle's running state and the state of the battery. The idling stop function is a function that stops the engine when the vehicle speed drops below a predetermined speed. Note that an apparatus including the controller 10 corresponds to the "idling stop control device" of the present invention, and the idling stop control method executed by the controller corresponds to the "idling stop control method" of the present invention.

[0010] As shown in FIG. 1, the idling stop control system 100 includes a battery 1, a current sensor 2, a voltage sensor 3, an alternator 4, an inverter 5, a DC-DC converter 6, a starter motor 7, a relay switch 8, a controller 10, an IS permission determination controller (15), and ECUs 20 and 30.

[0011] The battery 1 is a low-voltage power source for operating the starter motor 7 and auxiliary devices. The battery 1 is a battery of 50 volts or less, for example, a 12 V battery. The battery 1 is a secondary battery such as a lithium-ion battery or a lead battery. The battery 1 is electrically connected to the alternator 4 and the starter motor 7. A recommended SOC range for use of the battery 1 (hereinafter also referred to as the recommended SOC range) is set in advance. The recommended SOC range is a range of use of the battery 1 defined by SOC within which the battery 1 is less likely to deteriorate, and is determined experimentally based on the structure and battery performance of the battery 1, for example. The recommended SOC range for use is set to a range of, for example, 70% to 86%.

[0012] The current sensor 2 and the voltage sensor 3 are connected to the battery 1. The current sensor 2 detects the charge / discharge current flowing through the battery 1. The voltage sensor 3 detects the terminal voltage of the battery 1. The current sensor 2 and the voltage sensor 3 output their detected values ​​to the controller 10. The alternator 4 is electrically connected to the battery 1 via an inverter 5 and a DC / DC converter 6. The alternator 4 charges the battery 1 by supplying generated power to the battery 1. The alternator 4 generates electricity using energy obtained from the engine and / or the high-voltage battery. The engine and / or the high-voltage battery are installed in the vehicle depending on the vehicle's powertrain.

[0013] The inverter 5 is a power converter that converts the power generated by the alternator 4 into DC power. The DC-DC converter 6 is connected between the battery 1 and the inverter 5, converts the output voltage of the inverter 5, and outputs it as a charging voltage for the battery 1.

[0014] The starter motor 7 is a motor for cranking the engine. When the relay switch 8 is turned on, power is supplied from the battery 1 to the starter motor 7, driving the starter motor 7. The relay switch 8 is connected between the battery 1 and the starter motor 7, and switches between electrical connection and disconnection from the battery 1 to the starter motor 7. The relay switch 8 is switched on and off by a control command from a controller 10.

[0015] The controller 10 is a control unit (ECU) that controls the idling stop. The controller 10 is a processor for executing various functions, such as a function for managing the state of the battery 1, a function for setting criteria for permitting or disallowing (prohibiting) idling stop, a function for determining whether idling stop is permitted or not, a function for controlling charging and discharging of the battery 1, and a function for controlling idling stop, and executes programs stored in a memory in the control unit. The controller 10 has, as functional blocks, an SOC calculation unit 11, a threshold setting unit 12, a permission unit 13, and a battery control unit 14. Note that the controller 10 is not limited to the functions of each functional block such as the SOC calculation unit 11, and may also have other functions. Furthermore, the controller 10 does not necessarily have to be composed of a single ECU, but may be composed of multiple ECUs.

[0016] The SOC calculation unit 11 calculates the SOC (state of charge) of the battery 1 based on the current detected by the current sensor 2 and the voltage detected by the voltage sensor 3. When the battery 1 is in an unloaded state, the SOC calculation unit 11 acquires the voltage detected by the voltage sensor 3 as the open-circuit voltage and calculates the SOC by referring to a map showing the correlation between the open-circuit voltage and the SOC of the battery 1. When the battery 1 is in a loaded state, the SOC calculation unit 11 calculates the charge or discharge amount of the battery 1 by integrating the charge / discharge current of the battery 1 using the current detected by the current sensor 2. The SOC calculation unit 11 calculates the current battery capacity by adding the calculated charge or discharge amount to the battery capacity (remaining capacity) at the start of charging or discharging the battery 1. Then, the SOC calculation unit 11 calculates the current SOC by dividing the full charge capacity of the battery 1 by the current battery capacity. Note that other methods may be used to calculate the SOC of the battery 1.

[0017] The threshold setting unit 12 sets an allowable SOC threshold that allows idling stop and a disallowable SOC threshold that disallows idling stop. The allowable SOC threshold is a threshold that uses SOC as an index to determine whether idling stop is allowed. The disallowable SOC threshold is a threshold that uses SOC as an index to determine whether idling stop is not allowed (prohibited). When the current SOC of the battery 1 is equal to or higher than the allowable SOC threshold, idling stop is permitted. When the current SOC of the battery 1 is equal to or lower than the disallowable SOC threshold, idling stop is not permitted (prohibited).

[0018] The permissible SOC thresholds include a first permissible SOC threshold and a second permissible SOC threshold. The first permissible SOC threshold is a determination threshold for permitting the first idling stop, and the second permissible SOC threshold is a determination threshold for permitting the second or subsequent idling stop. The first idling stop is the first idling stop performed after the vehicle has finished parking and started moving.

[0019] The threshold setting unit 12 sets a first permitted SOC threshold based on the SOC of the battery 1 that has decreased while the vehicle is parked, the SOC at the start of vehicle travel, and the SOC that has decreased due to battery discharge during idling stop. The threshold setting unit 12 sets the first permitted SOC threshold to an SOC that can ensure, relative to the SOC at the start of the vehicle, the SOC that has decreased due to discharge while parked and the SOC that will decrease due to the first idling stop. The threshold setting unit 12 also sets the SOC at the start of the previous idling stop to the second permitted SOC threshold. The threshold setting unit 12 sets the second permitted SOC threshold so that the SOC at the start of the current idling stop will not be equal to or lower than the SOC at the start of the previous idling stop. Note that specific methods for setting the first permitted SOC threshold and the second permitted SOC threshold will be described later.

[0020] The threshold setting unit 12 sets a disallowed SOC threshold based on the SOC at the start of the idling stop and the SOC that decreases due to battery discharge during the idling stop. The disallowed SOC threshold is a lower limit value of the SOC that prohibits idling stop due to a decrease in the SOC during the idling stop. The threshold setting unit 12 calculates the disallowed SOC threshold by subtracting the SOC that decreases due to battery discharge during the idling stop from the SOC at the start of the idling stop.

[0021] The permission unit 13 permits idling stop based on the current SOC and the permission SOC threshold. Specifically, if the current SOC is equal to or greater than the permission SOC threshold, the permission unit 13 permits idling stop. If the current SOC is less than the permission SOC threshold, the permission unit 13 does not permit idling stop. Furthermore, if the current SOC becomes equal to or less than the non-permission SOC threshold during idling stop, the permission unit 13 determines that idling stop is not permitted. The permission unit 13 transmits the determination result of whether or not to permit idling stop to the idling stop (IS) permission determination controller 15. Note that it is sufficient for the permission unit 13 to transmit at least the determination result of non-permission of idling stop to the idling stop (IS) permission determination controller 15.

[0022] The battery control unit 14 controls the charging of the battery 1 so that the current SOC of the battery does not fall below the lower limit of the recommended use SOC range. Furthermore, when the current SOC is equal to or higher than the upper limit SOC of the recommended use SOC range, the battery control unit 14 controls the charging and discharging of the battery 1 so as to maintain the current SOC. When charging the battery 1, the battery control unit 14 outputs a control command to the alternator 4 so as to increase the power generated by the alternator 4. When discharging the battery 1, the battery control unit 14 outputs a control command to the alternator 4 so as to decrease the power generated by the alternator 4.

[0023] The idling stop (IS) permission determination controller 15 performs idling stop when idling stop conditions are satisfied while idling stop is permitted. Furthermore, when the IS permission determination controller 15 receives idling stop non-permission from any one of the permission unit 13 and the ECUs 20 and 30, it prohibits idling stop even if the idling stop conditions are satisfied. That is, the IS permission determination controller 15 manages idling stop non-permission (prohibition) from each ECU, such as the permission unit 13, the ECUs 20 and 30, and prohibits idling stop when idling stop is not permitted by at least one ECU. The idling stop conditions are defined by vehicle speed, whether or not the brakes are applied, engine rotation speed, etc. For example, the idling stop conditions are when the vehicle speed is zero, the brakes are applied, and the engine rotation speed is less than a predetermined rotation speed threshold. The idling stop condition may also be when the vehicle is traveling at a predetermined speed or less. If the vehicle state does not satisfy the idling stop conditions during idling stop, or if the permission unit 13 has denied idling stop, the IS permission determination controller 15 turns on the relay switch 8 to drive the starter motor 7. This cancels the idling stop and restarts the engine. If the idling stop conditions are not satisfied, the ECUs 20 and 30 send a control command to the permission determination controller 15 to the effect that the idling stop conditions are not satisfied. Note that a control command to the effect that the idling stop conditions are not satisfied corresponds to idling stop denial. The idling stop conditions include multiple conditions such as vehicle speed and engine rotation speed, and the determination of whether the idling stop conditions are satisfied is made by multiple ECUs, such as the ECUs 20 and 30.

[0024] The idling stop period (the period during which the engine is stopped) is predetermined, for example, one minute. The IS permission determination controller 15 cancels the idling stop when the elapsed time of the idling stop reaches the idling stop period. The ECUs 20 and 30 are, for example, a controller that controls the engine or a controller that controls the brake / accelerator.

[0025] Next, a method for setting the first allowable SOC threshold value, the second allowable SOC threshold value, and the non-allowable SOC threshold value will be described with reference to FIG. 2 . FIG. 2 is a graph showing the transition of SOC depending on the vehicle driving state. The vehicle state is assumed to transition in the order of the previous driving state, the parked state, and the current driving state. To simplify the explanation of the SOC transition shown in FIG. 2 , it is assumed that the battery 1 is charged by power generation by the alternator 4 while the vehicle is driving. However, during an idle stop, the amount of power consumed by the battery 1 during the idle stop (the amount of discharge of the battery 1) is greater than the amount of charge of the battery 1 generated by the alternator 4, so it is assumed that the battery 1 is discharged. Furthermore, during parking, dark current flows from the battery 1, and the SOC of the battery 1 decreases due to self-discharge.

[0026] When the current SOC of the battery 1 is within the recommended SOC range, the controller 10 performs the following control. First, the SOC calculation unit 11 calculates the SOC at the end of the previous driving (time t １ ) SOC is recorded, and the SOC at the end of the previous run is １ The SOC calculation unit 11 calculates the SOC at the start of the current run (time t ２ ) from the open circuit voltage, the SOC at the start of this run ２ Calculate the SOC at the start of this trip. ２ corresponds to the SOC when the ignition switch is turned on. The SOC calculation unit 11 calculates the SOC at the end of the previous run. １ And the SOC at the start of this run ２ From the difference, the first discharge SOC (SOC ｄ１ ) is calculated. ｄ１) is the SOC (the amount of change in the SOC) that has decreased due to the discharge of the battery 1 while the vehicle is parked from the end of the previous run to the start of the current run. The SOC calculation unit 11 calculates the first discharge SOC (SOC ｄ１ ) may be calculated.

[0027] The vehicle ２ The vehicle starts to travel at this time (current travel). While the vehicle is traveling, the SOC calculation unit 11 calculates the current SOC of the battery 1 (current SOC: SOC ｎ The threshold value setting unit 12 calculates the SOC (SOC ２ ), the first discharge SOC (SOC ｄ１ ) and the second discharge SOC (SOC ｄ２ ) to obtain the first allowable SOC threshold (SOC ｐ１ ) is calculated. ｄ２ ) is the SOC (amount of change in the SOC) that has decreased due to the discharge of the battery 1 during idling stop. That is, the second discharge SOC (SOC ｄ２ ) corresponds to the SOC that decreases during the idling stop period (the period when the engine is stopped). ｄ２ ) may be a fixed value of SOC (for example, 1%) according to the idling stop period. When the idling stop period is a fixed period (for example, 1 minute), the value obtained by converting the discharge amount during the fixed period into SOC is the second discharge SOC (SOC ｄ２ ) and SOC ２ , the first discharge SOC (SOC ｄ１ ) and the second discharge SOC (SOC ｄ２ ) SOC ３ is the first permitted SOC threshold (SOC ｐ１ ) That is, the first allowable SOC threshold (SOC ｐ１ ) is the SOC at the start of this run (SOC ２ ) with respect to the first discharge SOC (SOC ｄ１ ) and second discharge SOC (SOC ｄ２ ) is added to the SOC. As a result, the threshold value setting unit 12 sets the first allowable SOC threshold value (SOC ｐ１) is set. ｐ１ ) is used to determine whether or not the first idling stop is permitted. ３ At this time, the current SOC of battery 1 (SOC ｎ ) is the first permitted SOC threshold (SOC ｐ１ = SOC ３ ), the permission unit 13 permits the first idling stop.

[0028] Time t ４ Assume that the idling stop condition is satisfied at time t. The IS permission determination controller 15 executes idling stop. The SOC calculation unit 11 ４ The SOC at the start of idling stop (SOC ４ The threshold value setting unit 12 calculates the SOC (SOC ４ ) to the second discharge SOC (SOC ｄ２ ) to obtain the disallowed SOC threshold (SOC ｎｐ ) is calculated. That is, the unacceptable SOC threshold (SOC ｎｐ ) is the SOC (SOC ４ ) to the second discharge SOC (SOC ｄ２ In the example of FIG. 2, the SOC ５ is the disallowed SOC threshold (SOC ｎｐ ) at the start of idling stop. ４ ) is the second allowable SOC threshold (SOC ｐ２ ) is set as the second allowable SOC threshold (SOC ｐ２ ) is used to determine whether the second idling stop is permitted. The first permitted SOC threshold (SOC ｐ１ ), second permitted SOC threshold (SOC ｐ２ ) and the disallowed SOC threshold (SOC ｎｐ The method for setting the threshold value is the same as the method for setting the threshold value for the second idling stop.

[0029] Time t ４During the subsequent idling stop, the power of the battery 1 is consumed by auxiliary devices, etc., and the SOC of the battery 1 decreases. ５ At this time, the SOC of battery 1 is below the disallowed SOC threshold (SOC ｎｐ ) or less, the permission unit 13 does not permit the idling stop. The idling stop is released, and the SOC of the battery 1 increases by charging using the power generated by the alternator 4. Then, the current SOC of the battery 1 ｎ is the second permitted SOC threshold (SOC ｐ２ = SOC ４ ), the permission unit 13 permits a second idling stop (time t6).

[0030] The threshold setting unit 12 sets the lower limit of the recommended SOC range as a non-permitted SOC threshold (SOC ｎｐ ) and the current SOC of the battery 1 is set as the unauthorized SOC threshold (SOC ｎｐ ), the permission unit 13 does not permit idling stop. As a result, if the current SOC of the battery 1 is equal to or lower than the lower limit SOC of the recommended use SOC range, idling stop is not permitted. Then, if the current SOC of the battery 1 becomes higher than the lower limit SOC while the vehicle is running, the controller 10 executes the above control.

[0031] In addition, when the SOC at the start of vehicle running is equal to or higher than the upper limit SOC of the recommended use SOC range, or when the current SOC of the battery 1 becomes equal to or higher than the upper limit SOC of the recommended use SOC range while the vehicle is running, the threshold setting unit 12 calculates a second discharge SOC (SOC ｄ２ ) is subtracted from the SOC and is called the disallowed SOC threshold (SOC ｎｐ During idling stop, the SOC decreases and the discharge amount of the battery 1 reaches the second discharge SOC (SOC ｄ２), idling stop is not permitted and is therefore cancelled. Furthermore, if the current SOC is equal to or higher than the upper limit SOC of the recommended use SOC range, the battery control unit 14 controls the charging and discharging of the battery 1 so as to maintain the current SOC. This allows the SOC of the battery 1 to be maintained at the upper limit SOC of the recommended use SOC range.

[0032] Next, a control flow of the idling stop control method will be described with reference to Figures 3 and 4. Figures 3 and 4 are flowcharts showing the control flow of the idling stop control method. The controller 10 starts the control flow when the vehicle starts traveling. Note that when the SOC of the battery 1 is within the recommended use SOC range, the controller 10 may execute the following control flow.

[0033] In step S1, the SOC calculation unit 11 calculates a first discharge SOC (SOC ｄ１ In step S2, the SOC calculation unit 11 calculates the current SOC (SOC ｎ In step S3, the threshold setting unit 12 determines whether or not the first idling stop (first IS) has been performed. If the first idling stop (first IS) has been performed, the controller 10 executes the control flow from step S21 onwards, which will be described later.

[0034] If the first idling stop has not been performed, the threshold setting unit 12 sets the SOC at the start of the current run, the first discharge SOC (SOC ｄ１ ), second discharge SOC (SOC ｄ２ ) based on the first permitted SOC threshold (SOC ｐ１ ) (step S4). In step S5, the permission unit 13 sets the current SOC (SOC ｎ ) is the first permitted SOC threshold (SOC ｐ１ ) or more. ｎ ) is the first permitted SOC threshold (SOC ｐ１), idling stop is not permitted, and the controller 10 executes the control flow of step S15.

[0035] Currently SOC (SOC ｎ ) is the first permitted SOC threshold (SOC ｐ１ ) or more, the permission unit 13 permits idling stop in step S6. In step S7, the IS permission determination controller 15 determines whether the current vehicle state satisfies the idling stop conditions. If the idling stop conditions are not satisfied, the controller 10 executes the control flow of step S15.

[0036] If the idling stop condition is satisfied, the IS permission determination controller 15 executes idling stop (step S8). In step S9, the threshold setting unit 12 calculates the SOC at the start of idling stop and the second discharge SOC (SOC ｄ２ ), based on the disallowed SOC threshold (SOC ｎｐ In step S10, the SOC calculation unit 11 calculates the current SOC (SOC ｎ In step S11, the permission unit 13 calculates the current SOC (SOC ｎ ) is the disallowed SOC threshold (SOC ｎｐ ) or less. ｎ ) is the disallowed SOC threshold (SOC ｎｐ ), the permission unit 13 does not permit idling stop. ｎ ) is the disallowed SOC threshold (SOC ｎｐ ), the IS permission determination controller 15 determines whether the current vehicle state satisfies the idling stop condition. If the idling stop condition is satisfied, the idling stop is continued, and the controller 10 returns to step S10 and executes the control flow. If the idling stop condition is not satisfied, the process proceeds to step S14.

[0037] In step S14, the IS permission determination controller 15 cancels the idling stop. That is, during the idling stop, the current SOC (SOC ｎ ) is the disallowed SOC threshold (SOC ｎｐ ) or below, or if the current vehicle condition does not meet the idling stop conditions, the idling stop will be canceled.

[0038] In step S15, the controller 10 determines whether the vehicle has stopped traveling. If the vehicle has stopped traveling, the controller 10 ends the control flow. On the other hand, if the vehicle is still traveling, the controller 10 returns to step S2 and executes the control flow.

[0039] Returning to step S3, if the first idling stop (first IS) has already been performed, the control flow proceeds to the flow shown in FIG.

[0040] In step S21, the SOC calculation unit 11 calculates the current SOC (SOC ｎ In step S22, the threshold value setting unit 12 calculates the SOC (SOC ４ ) is the second allowable SOC threshold (SOC ｐ２ In step S23, the permission unit 13 sets the current SOC (SOC ｎ ) is the second allowable SOC threshold (SOC ｐ２ ) or more. ｎ ) is the second allowable SOC threshold (SOC ｐ２ ), the controller 10 executes the control flow of step S24. ｎ ) is the second allowable SOC threshold (SOC ｐ２ ), idling stop is not permitted, and the controller 10 executes the control flow of step S33. Note that the control flow of steps S24 to S33 is the same as the control flow of steps S6 to S15, and therefore the description thereof will be omitted.

[0041] As described above, in the idling stop control device or idling control method according to this embodiment, the controller 10 calculates the first discharge SOC, calculates the current SOC after the start of the current driving, sets an authorization threshold for permitting idling stop and a non-authorization threshold for disallowing idling stop, and permits idling stop when the current SOC is equal to or greater than the authorization SOC threshold, and disallows idling stop when the current SOC is equal to or less than the non-authorization SOC threshold. The authorization SOC thresholds include a first authorization SOC threshold set for the first idling stop and a second authorization SOC threshold set for the second or subsequent idling stops. The first authorization SOC threshold corresponds to the SOC obtained by adding the first discharge SOC and the second discharge SOC to the SOC at the start of the current driving. The second discharge SOC indicates the SOC reduced by discharging the battery 1 during idling stop. The second permitted SOC threshold corresponds to the SOC at the start of the previous idling stop, and the non-permitted SOC threshold corresponds to the SOC at the start of idling stop minus the second discharge SOC. That is, in this embodiment, when the battery 1 is charged after the vehicle starts traveling and the SOC becomes equal to or higher than the first permitted SOC threshold, idling stop is permitted, and when the SOC becomes lower than the SOC at the end of the previous traveling, idling stop is prohibited. This narrows the SOC control range and enables idling stop, thereby preventing battery degradation. Furthermore, since idling stop is permitted while the battery 1 is charged, fuel economy is improved. As a result, this embodiment can achieve both improved fuel economy and battery protection.

[0042] Furthermore, in this embodiment, when the current SOC is equal to or higher than the upper limit SOC of the recommended use SOC range, the battery control unit 14 controls the charging and discharging of the battery 1 to maintain the current SOC. If the SOC is sufficiently high when the vehicle starts traveling, idling stop is permitted while maintaining a high SOC, which increases the number of idling stop operations and improves fuel economy. Even when idling stop is performed, idling stop is not permitted before the discharge amount of the battery 1 during idling stop reaches the second discharge SOC. Therefore, the SOC can be maintained at a high level even when idling stop is performed.

[0043] In this embodiment, the permission unit 13 prohibits idling stop when the current SOC is equal to or lower than the lower limit SOC of the recommended use SOC range. In other words, if the SOC is low when the vehicle starts to travel, idling stop is not permitted. This allows the battery 1 to be protected.

[0044] In this embodiment, the threshold setting unit 12 may set the SOC calculation value obtained by adding the first discharge SOC and the second discharge SOC to the SOC at the start of the current traveling as the first permission SOC threshold, or may set the SOC obtained by adding a predetermined SOC equivalent to a margin to the SOC calculation value as the first permission SOC threshold. In other words, the first permission SOC threshold may be a value equivalent to the SOC obtained by adding the first discharge SOC and the second discharge SOC to the SOC at the start of the current traveling.

[0045] Furthermore, threshold setting unit 12 may set the SOC at the time of the previous start of idling stop as the second permissible SOC threshold, or may set the SOC obtained by adding a predetermined SOC equivalent to a margin to the SOC at the time of the previous start of idling stop as the second permissible SOC threshold. In other words, the second permissible SOC threshold may be any value that corresponds to the SOC at the time of the previous start of idling stop.

[0046] The threshold setting unit 12 may set the SOC calculation value obtained by subtracting the second discharge SOC from the SOC at the start of idling stop as the disallowed SOC threshold, or may set the SOC obtained by adding a predetermined SOC equivalent to a margin to the SOC calculation value as the disallowed SOC threshold. In other words, the disallowed SOC threshold may be any value equivalent to the SOC obtained by subtracting the second discharge SOC from the SOC at the start of idling stop.

[0047] In this embodiment, the controller 10 does not need to execute all of the control flows of steps S1 to S15 and steps S21 to S33, and the execution order of the control flows may be changed.

[0048] REFERENCE SIGNS LIST 1 Battery 2 Current sensor 3 Voltage sensor 4 Alternator 5 Inverter 6 DC-DC converter 7 Starter motor 8 Relay switch 10 Controller 11 SOC calculation unit 12 Threshold value setting unit 13 Permission unit 14 Battery control unit 15 Idling stop permission determination controller 100 Idling stop control system

Claims

1. An idling stop control device that controls idling stop, which stops the engine when the vehicle speed is equal to or lower than a predetermined vehicle speed, comprising: an SOC calculation unit that calculates a current SOC indicating the current state of charge of a battery; a threshold setting unit that sets an allowed SOC threshold that permits the idling stop and a disallowed SOC threshold that disallows the idling stop; and a permission unit that permits the idling stop based on the current SOC and the allowed SOC threshold that permits the idling stop, wherein the SOC calculation unit calculates a first discharge SOC that indicates the SOC that has decreased due to discharging of the battery while the vehicle is parked from the end of the previous driving to the start of the current driving, and calculates a current SOC that indicates the current SOC of the battery after the start of the current driving, and the threshold setting unit sets a first allowed SOC threshold that is the allowed SOC threshold for a first idling stop, a second allowed SOC threshold that is the allowed SOC threshold for a second or subsequent idling stop, and a disallowed threshold that disallows the idling stop, an idle stop control device, wherein the first permitted SOC threshold corresponds to an SOC obtained by adding the first discharge SOC and the second discharge SOC to the SOC at the start of the current running, the second discharge SOC indicating an SOC that has decreased due to discharging of the battery during the idle stop, the second permitted SOC threshold corresponds to an SOC at the start of the previous idle stop, and the disallowed SOC threshold corresponds to an SOC obtained by subtracting the second discharge SOC from the SOC at the start of the idle stop, and the permitting unit permits the idle stop when the current SOC is equal to or greater than the permitted SOC threshold, and disallows the idle stop when the current SOC is equal to or less than the disallowed SOC threshold.

2. An idling stop control device according to claim 1, further comprising a battery control unit that controls charging and discharging of the battery, wherein the battery indicates an SOC range that is recommended for use, and wherein the battery control unit controls charging and discharging of the battery so as to maintain the current SOC when the current SOC is equal to or higher than an upper limit SOC of the SOC range that is recommended for use of the battery.

3. An idling stop control device according to claim 1 or 2, wherein the permission unit does not permit the idling stop when the current SOC is equal to or lower than a lower limit SOC of an SOC range recommended for use.

4. An idling stop control method executed by a controller for controlling idling stop, which stops the engine when the vehicle speed is equal to or lower than a predetermined vehicle speed, wherein the controller: calculates a first discharge SOC indicating the SOC that has decreased due to battery discharge while the vehicle is parked from the end of the previous driving to the start of the current driving; calculates a current SOC indicating the current SOC of the battery after the start of the current driving; sets a permission threshold for permitting the idling stop and a non-permission threshold for disallowing the idling stop; permits the idling stop when the current SOC is equal to or higher than the permission SOC threshold; and disallows the idling stop when the current SOC is equal to or lower than the non-permission SOC threshold; the permission SOC thresholds include a first permission SOC threshold set for a first idling stop and a second permission SOC threshold set for a second or subsequent idling stop; and the first permission SOC threshold corresponds to an SOC obtained by adding the first discharge SOC and the second discharge SOC to the SOC at the start of the current driving. an idle stop control method, wherein the second discharge SOC indicates an SOC that has decreased due to discharge of the battery during the idle stop; the second permitted SOC threshold corresponds to an SOC at the time of the previous start of the idle stop; and the non-permitted SOC threshold corresponds to an SOC obtained by subtracting the second discharge SOC from the SOC at the time of the start of the idle stop.

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