Vehicle battery control device

Abstract

To reduce a speed at which a battery deteriorates.SOLUTION: A battery control device for a vehicle controls the charge and discharge of a battery in the vehicle. The battery control device includes: causing a charger for supplying a direct-current power to the battery to output an output voltage of a first voltage value or an output voltage of a second voltage value lower than the first voltage value; acquiring a battery capacity in the battery; and changing the output ratio between the first voltage value and the second voltage value by comparing the acquired battery capacity with a target capacity value in the battery. The target capacity value has an upper limit value and a lower limit value. The battery control device outputs the output voltage so that the first voltage value and the second voltage value are alternately switched when the acquired battery capacity is smaller than the upper limit value and larger than the lower limit value.SELECTED DRAWING: Figure 4

Description

Technical Field

[0005] ,

[0001] The present invention relates to a battery control device for a vehicle.

Background Art

[0002] An electric vehicle includes an auxiliary battery which is a secondary battery that generates a voltage of about a dozen volts, for example. The auxiliary battery is a lead-acid battery. The auxiliary battery is charged from the motor drive battery by a DC-DC converter so that the battery capacity becomes the target capacity value.

Prior Art Documents

[0006] To solve the above-mentioned problems and achieve the objective, the vehicle battery control device according to the present invention is a vehicle battery control device that controls the charging and discharging of a battery in a vehicle, and is connected to a charging device that supplies DC power to the battery, The aforementioned battery is charged. Output voltage of the first voltage value, or lower than the first voltage value. The battery is discharged. The output voltage of the second voltage value, which is a voltage value, is output, the battery capacity of the battery is obtained, and the output ratio of the first voltage value and the second voltage value is changed by comparing the obtained battery capacity with the target capacity value of the battery. [Effects of the Invention]

[0007] According to the present invention, the rate at which batteries degrade can be mitigated. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a diagram showing the configuration of the battery-related parts in a vehicle according to the embodiment. [Figure 2] Figure 2 shows an example of the voltage waveform generated by a DC-DC converter. [Figure 3] Figure 3 shows an example of the relationship between the output ratio and battery capacity. [Figure 4] Figure 4 is a flowchart showing the processing flow of the controller. [Figure 5] Figure 5 shows an example of an upper limit ratio map. [Figure 6] Figure 6 shows an example of a lower limit ratio map. [Figure 7] Figure 7 is a waveform diagram showing an example of changes in battery capacity and output voltage. [Figure 8] Figure 8 is a flowchart showing the process of resetting the lower limit by the controller. [Modes for carrying out the invention]

[0009] The embodiments will be described below with reference to the drawings.

[0010] Figure 1 shows the configuration of the battery components in a vehicle 10 according to an embodiment. The vehicle 10 includes a main battery 22, an auxiliary battery 24, a DC-DC converter 26, and a controller 30.

[0011] The main battery 22 is, for example, a lithium-ion battery, and is powered by an electric vehicle charging station or the like. The main battery 22 generates a DC voltage of, for example, several hundred volts. The main battery 22 supplies power to the motor, etc.

[0012] The auxiliary battery 24 is a rechargeable battery (secondary battery), such as a lead-acid battery. The auxiliary battery 24 is charged by power transferred from the main battery 22. The auxiliary battery 24 generates a DC voltage of, for example, several tens of volts. The auxiliary battery 24 supplies power to electrical system devices in the vehicle 10, such as the onboard computer, power windows, headlights, and air conditioner.

[0013] The DC-DC converter 26 functions as a charging device that receives DC power from the main battery 22 and supplies DC power to the auxiliary battery 24. The DC-DC converter 26 steps down the DC voltage generated from the main battery 22 to a DC voltage corresponding to the indicated voltage value and supplies it to the auxiliary battery 24.

[0014] The controller 30 is implemented through the functions of the battery control module in the ECU. The controller 30 acquires the State of Charge (SOC), which is the battery capacity of the auxiliary battery 24. The SOC represents the charge state of the auxiliary battery 24 and is expressed as a value between 0% and 100%. 0% represents a state where no power is charged, and 100% represents a fully charged state.

[0015] Based on the acquired battery capacity, the controller 30 provides an instruction voltage value to the DC-DC converter 26. Thereby, the controller 30 causes the DC-DC converter 26 to output an output voltage corresponding to the instruction voltage value, and causes the DC-DC converter 26 to supply DC power of the output voltage corresponding to the instruction voltage value to the auxiliary battery 24.

[0016] FIG. 2 is a diagram showing an example of the waveform of the voltage generated from the DC-DC converter 26.

[0017] The controller 30 provides the DC-DC converter 26 with a first voltage value or a second voltage value as the instruction voltage value. That is, the controller 30 causes the DC-DC converter 26 to output an output voltage of the first voltage value or an output voltage of the second voltage value.

[0018] The first voltage value is a voltage value at which the auxiliary battery 24 is charged even when the auxiliary battery 24 is supplying power to the electrical equipment in the vehicle 10. As an example, the first voltage value is 13.5V.

[0019] The second voltage value is a voltage value lower than the first voltage value, and is a voltage value at which the auxiliary battery 24 is discharged even when the auxiliary battery 24 is supplying the minimum power to the electrical equipment in the vehicle 10. As an example, the first voltage value is 12.5V. The first voltage value and the second voltage value are preset in the controller 30.

[0020] Therefore, the auxiliary battery 24 is charged with power and the battery capacity is increased during the period when the output voltage of the first voltage value is output from the DC-DC converter 26. Also, the auxiliary battery 24 discharges power and the battery capacity is decreased during the period when the output voltage of the second voltage value is output from the DC-DC converter 26.

[0021] The controller 30 then compares the battery capacity of the auxiliary battery 24 with the target capacity value of the auxiliary battery 24 and changes the output ratio between the first voltage value and the second voltage value. The controller 30 changes the output ratio between the first voltage value and the second voltage value, for example, every certain period T.

[0022] If the ratio of the first voltage value over a certain period T is less than the ratio of the second voltage value (0% or more, but less than 50%), the auxiliary battery 24 will discharge power over the entire period T. Therefore, in this case, the auxiliary battery 24 will have a reduced battery capacity over the entire period T.

[0023] Furthermore, the auxiliary battery 24 charges power over the entire period T if the ratio of the first voltage values ​​over the entire period T is greater than the ratio of the second voltage values ​​(greater than 50% and less than or equal to 100%). In this case, the auxiliary battery 24 increases its battery capacity over the entire period T.

[0024] Furthermore, the controller 30 may continuously change the output ratio instead of changing it every T over a fixed period.

[0025] Figure 3 shows an example of the relationship between the output ratio and battery capacity.

[0026] The target capacity value of the battery has an upper limit and a lower limit. The controller 30 has the upper and lower limits set in advance. The lower limit is a value lower than the upper limit. For example, the controller 30 may have a target capacity value set, with the upper limit being a value that is a predetermined percentage greater than the target capacity value, and the lower limit being a value that is a predetermined percentage less than the target capacity value.

[0027] The controller 30 continues to output an output voltage of a first voltage value from the DC-DC converter 26 if the acquired battery capacity is below the lower limit. In other words, if the acquired battery capacity is below the lower limit, the controller 30 sets the output ratio of the output voltage of the first voltage value to 100% and the output ratio of the second voltage value to 0%. As a result, if the acquired battery capacity is below the lower limit, the controller 30 can charge the auxiliary battery 24 and increase the battery capacity.

[0028] Furthermore, if the acquired battery capacity is above the upper limit, the controller 30 continues to output the output voltage of the second voltage value from the DC-DC converter 26. That is, if the acquired battery capacity is above the upper limit, the controller 30 sets the output ratio of the output voltage of the first voltage value to 0% and the output ratio of the second voltage value to 100%. As a result, if the acquired battery capacity is above the upper limit, the controller 30 can discharge the auxiliary battery 24 and reduce the battery capacity.

[0029] The controller 30 then outputs an output voltage that alternates between a first voltage value and a second voltage value when the acquired battery capacity is less than the upper limit and greater than the lower limit. This allows the controller 30 to output an output voltage that causes the auxiliary battery 24 to alternately charge and discharge. Therefore, when the acquired battery capacity is less than the upper limit and greater than the lower limit, the controller 30 can charge or discharge the auxiliary battery 24 so that the battery capacity changes gradually.

[0030] Furthermore, after the battery capacity falls below the lower limit, the controller 30 increases the output ratio of the first voltage value to that of the second voltage value until the battery capacity rises above the upper limit. In other words, after the battery capacity falls below the lower limit, the controller 30 sets the output ratio of the first voltage value to be greater than 50% and less than or equal to 100% until the battery capacity rises above the upper limit.

[0031] As a result, when the battery capacity falls below the lower limit, the controller 30 can gradually change the battery capacity of the auxiliary battery 24 in the charging direction until the battery capacity rises above the upper limit. Therefore, when the battery capacity is near the lower limit, the controller 30 can eliminate the need for control that causes a rapid discharge of the auxiliary battery 24.

[0032] Furthermore, after the battery capacity exceeds the upper limit, the controller 30 increases the output ratio of the second voltage value compared to the output ratio of the first voltage value until the battery capacity falls below the lower limit. In other words, after the battery capacity exceeds the upper limit, the controller 30 sets the output ratio of the first voltage value to less than 50% and above 0% until the battery capacity falls below the lower limit.

[0033] As a result, when the battery capacity exceeds the upper limit, the controller 30 can gradually change the battery capacity of the auxiliary battery 24 in the discharge direction until the battery capacity falls below the lower limit. Therefore, when the battery capacity is near the upper limit, the controller 30 can eliminate the need for control that would rapidly charge the auxiliary battery 24.

[0034] Furthermore, for example, if the controller 30 increases the output ratio of the first voltage value compared to the output ratio of the second voltage value when the battery capacity falls below the lower limit, it may decrease the output ratio of the first voltage value, i.e., increase the output ratio of the second voltage value, as the battery capacity approaches the upper limit. This allows the controller 30 to slow down the charging speed as the battery capacity approaches the upper limit when changing the battery capacity of the auxiliary battery 24 in the charging direction.

[0035] Furthermore, for example, if the controller 30 increases the output ratio of the second voltage value compared to the output ratio of the first voltage value because the battery capacity exceeds the upper limit, it may decrease the output ratio of the second voltage value, that is, increase the output ratio of the first voltage value, as the battery capacity approaches the lower limit. This allows the controller 30 to slow down the discharge rate as the battery capacity approaches the lower limit when changing the battery capacity of the auxiliary battery 24 in the discharge direction.

[0036] Figure 4 is a flowchart showing the processing flow of the controller 30. The controller 30 controls the output voltage of the DC-DC converter 26 in the flow shown in Figure 4, for example.

[0037] First, in S11, the controller 30 performs a startup process.

[0038] Next, in S12, the controller 30 determines whether the full charge determination flag is ON or OFF. The full charge determination flag is OFF when the auxiliary battery 24's battery capacity is fully charged, i.e., 100%, and ON when the battery capacity is not fully charged, i.e., less than 100%. If the full charge determination flag is not ON, i.e., the battery capacity is fully charged (No in S12), the controller 30 waits in S12 before proceeding. If the full charge determination flag is ON, i.e., the battery capacity is not fully charged (Yes in S12), the controller 30 proceeds to S13.

[0039] In S13, the controller 30 sets the upper limit flag to ON. The upper limit flag is set to ON if the battery capacity of the auxiliary battery 24 is above the upper limit, or if the battery capacity has exceeded the upper limit but has not yet fallen below the lower limit. The upper limit flag is set to OFF if the battery capacity of the auxiliary battery 24 is below the lower limit, or if the battery capacity has fallen below the lower limit but has not yet exceeded the upper limit.

[0040] Next, in S14, the controller 30 determines whether the upper limit flag is ON or OFF. If the upper limit flag is ON (Yes in S14), the controller 30 proceeds to S15. If the upper limit flag is OFF (No in S14), the controller 30 proceeds to S18.

[0041] In S15, the controller 30 sets the output ratio of the first output voltage and the second output voltage based on the upper limit ratio MAP. The method for setting the output ratio based on the upper limit ratio MAP will be described later with reference to Figure 5.

[0042] Next, in S16, the controller 30 determines whether the battery capacity is below the lower limit. If the battery capacity is not below the lower limit (No in S16), the controller 30 returns to S15 and repeats the processes in S15 and S16 until the battery capacity is below the lower limit. If the battery capacity is below the lower limit (Yes in S16), the controller 30 proceeds to S17.

[0043] In S17, the controller 30 sets the upper limit flag to OFF. After completing S17, the controller 30 returns to processing S14.

[0044] Meanwhile, in S18, the controller 30 sets the output ratio of the first output voltage and the second output voltage based on the lower limit ratio MAP. The method for setting the output ratio based on the lower limit ratio MAP will be described later with reference to Figure 6.

[0045] Next, in S19, the controller 30 determines whether the battery capacity is above or below the upper limit. If the battery capacity is not above or below the upper limit (No in S19), the controller 30 returns to S18 and repeats the processes in S18 and S19 until the battery capacity is above or below the upper limit. If the battery capacity is above or below the upper limit (Yes in S19), the controller 30 proceeds to S20.

[0046] In S20, the controller 30 sets the upper limit flag to ON. After completing S20, the controller 30 returns to processing S14. The controller 30 continues these processes until the operation of the vehicle 10 is completed.

[0047] Figure 5 shows an example of an upper limit ratio MAP. The upper limit ratio MAP is a table that shows the output ratio of the first voltage value and the second voltage value to the difference obtained by subtracting the battery capacity (SOC) from the target capacity value. The upper limit ratio MAP is pre-set in the controller 30.

[0048] In this example, the target volume value is the midpoint between the upper and lower limits. In this example, the lower limit is -1.0% of the target volume value, and the upper limit is +1.0% of the target volume value.

[0049] In step S15 of Figure 4, the controller 30 determines the output ratio by referring to the upper limit ratio MAP shown in Figure 5.

[0050] For example, if the difference value is -1.0% or less, the controller 30 sets the output ratio of the first voltage value to 0% and the output ratio of the second voltage value to 100%. If the difference value is greater than -1.0% and -0.8% or less, the controller 30 sets the output ratio of the first voltage value to 5% and the output ratio of the second voltage value to 95%. If the difference value is greater than -0.8% and -0.5% or less, the controller 30 sets the output ratio of the first voltage value to 10% and the output ratio of the second voltage value to 90%. If the difference value is greater than -0.5% and 0% or less, the controller 30 sets the output ratio of the first voltage value to 20% and the output ratio of the second voltage value to 80%. If the difference value is greater than 0% and 0.5% or less, the controller 30 sets the output ratio of the first voltage value to 30% and the output ratio of the second voltage value to 70%. The controller 30 sets the output ratio of the first voltage value to 40% and the output ratio of the second voltage value to 60% if the difference value is greater than 0.5% and less than or equal to 0.8%. The controller 30 sets the output ratio of the first voltage value to 45% and the output ratio of the second voltage value to 55% if the difference value is greater than 0.8% and less than 1.0%.

[0051] By setting it in this way, when the battery capacity exceeds the upper limit, the controller 30 can make the output ratio of the second voltage value greater than the output ratio of the first voltage value until the battery capacity falls below the lower limit. Furthermore, by setting it in this way, when the battery capacity exceeds the upper limit and the controller 30 makes the output ratio of the second voltage value greater than the output ratio of the first voltage value, it can make the output ratio of the second voltage value smaller, that is, the output ratio of the first voltage value larger, as the battery capacity approaches the lower limit. Note that the controller 30 may calculate the output ratios of the first and second voltage values ​​not only using a table like the one shown in Figure 5, but also using, for example, a pre-set function.

[0052] Figure 6 shows an example of a lower limit ratio MAP. The lower limit ratio MAP is a table that shows the output ratio of the first voltage value and the second voltage value to the difference obtained by subtracting the target capacity value from the battery capacity (SOC). The lower limit ratio MAP is pre-set in the controller 30.

[0053] In step S18 of Figure 4, the controller 30 determines the output ratio by referring to the lower limit ratio MAP shown in Figure 6. The specific values ​​of the lower limit ratio MAP are the same as those in the table obtained by swapping the first and second voltage values ​​in the upper limit ratio MAP of Figure 5.

[0054] By setting it in this way, when the battery capacity falls below the lower limit, the controller 30 can make the output ratio of the first voltage value greater than the output ratio of the second voltage value until the battery capacity rises above the upper limit. Furthermore, by setting it in this way, when the battery capacity falls below the lower limit and the controller 30 makes the output ratio of the first voltage value greater than the output ratio of the second voltage value, it can decrease the output ratio of the first voltage value, that is, increase the output ratio of the second voltage value, as the battery capacity approaches the upper limit. Note that the controller 30 may calculate the output ratios of the first and second voltage values ​​not only using a table like the one shown in Figure 6, but also using, for example, a pre-set function.

[0055] Figure 7 is a waveform diagram showing an example of changes in battery capacity and output voltage. The controller 30 controls the voltage of the DC-DC converter 26 when the full charge determination flag is ON.

[0056] The period during which the upper limit flag is ON is the period during which the battery capacity is greater than or equal to the upper limit, or the period from when the battery capacity is greater than or equal to the upper limit until it falls below the lower limit. During the period when the upper limit flag is ON, if the battery capacity is less than the upper limit and greater than the lower limit, the controller 30 alternately switches between the first voltage value and the second voltage value, and makes the output ratio of the second voltage value greater than the output ratio of the first voltage value. Therefore, during this period, the controller 30 can gradually reduce the battery capacity of the auxiliary battery 24 by alternately discharging and charging in small amounts.

[0057] Furthermore, the period during which the upper limit flag is OFF is the period when the battery capacity is below the lower limit, or the period from when the battery capacity falls below the lower limit until it rises above the upper limit. During the period when the upper limit flag is OFF, if the battery capacity is less than the upper limit and greater than the lower limit, the controller 30 alternately switches between the first voltage value and the second voltage value, and makes the output ratio of the first voltage value greater than the output ratio of the second voltage value. Therefore, during this period, the controller 30 can gradually increase the battery capacity of the auxiliary battery 24 by alternately repeating small amounts of discharge and charge.

[0058] As described above, the controller 30 can eliminate rapid discharge or charging by repeatedly controlling the auxiliary battery 24 to gradually decrease its battery capacity from the upper limit to the lower limit, and then gradually decrease its battery capacity from the lower limit to the upper limit. In this way, the controller 30 can prevent the auxiliary battery 24 from being discharged to a deep depth of discharge, thereby mitigating the rate at which the auxiliary battery 24 deteriorates.

[0059] Figure 8 is a flowchart showing the process of resetting the lower limit by the controller 30. For example, the controller 30 may reset the lower limit in the flow shown in Figure 8.

[0060] First, in S31, the controller 30 determines whether or not it has detected deterioration of the auxiliary battery 24 based on information regarding the operation of the auxiliary battery 24. For example, the controller 30 may obtain a value that serves as an indicator of the degree of deterioration of the auxiliary battery 24 and compare this indicator with a preset threshold. The controller 30 may then detect that the auxiliary battery 24 has deteriorated if the indicator value exceeds the threshold. Alternatively, the controller 30 may obtain information from another device indicating that the auxiliary battery 24 has deteriorated.

[0061] If the controller 30 has not detected deterioration of the auxiliary battery 24 (No in S31), it waits in S31 before proceeding. If the controller 30 has detected deterioration of the auxiliary battery 24 (Yes in S31), it proceeds to S32.

[0062] In S32, the controller 30 adds a predetermined amount (α) to the lower limit and resets the lower limit with the predetermined amount (α) added as the new lower limit. After completing the process in S32, the controller 30 terminates this flow.

[0063] Such a controller 30 raises the lower limit of the battery capacity when the auxiliary battery 24 deteriorates compared to when the auxiliary battery 24 is not deteriorated. This allows the controller 30 to avoid a deeper discharge depth due to errors in the estimated battery capacity when the auxiliary battery 24 deteriorates. In this way, the controller 30 can perform appropriate charge and discharge control according to the deterioration state of the auxiliary battery 24.

[0064] Although embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. Various modifications can be made to the embodiments. [Explanation of Symbols]

[0065] 10 vehicles, 22 main batteries, 24 auxiliary batteries, 26 DC-DC converters, 30 controllers

Claims

1. A vehicle battery control device that controls the charging and discharging of the vehicle's battery, A charging device that supplies DC power to the battery outputs an output voltage of a first voltage value at which the battery is charged, or an output voltage of a second voltage value that is lower than the first voltage value at which the battery is discharged. The battery capacity of the battery is obtained, and the obtained battery capacity is compared with the target capacity value of the battery to change the output ratio between the first voltage value and the second voltage value. A vehicle battery control device.

2. The aforementioned target capacity value has an upper limit and a lower limit. When the acquired battery capacity is less than the upper limit and greater than the lower limit, the output voltage is output, in which the first voltage value and the second voltage value alternate. A battery control device for a vehicle according to claim 1.

3. The system detects battery degradation based on information regarding the operation of the battery, and if battery degradation is detected, it resets the lower limit value. A battery control device for a vehicle according to claim 2.

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