Discharge system

Abstract

To provide a discharge system for accurately measuring a secondary battery while suppressing decrease in residual quantity of the secondary battery.SOLUTION: A discharge system for making a chargeable secondary battery discharge includes: a discharge circuit for making the secondary battery discharge; and a discharge control part for controlling the discharge circuit in a manner to make the secondary battery discharge in a predetermined pattern. The discharge circuit changes a current value of a current flowing from the secondary battery according to the control of the discharge control part when the secondary battery discharges.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a discharge system.

Background Art

[0002] As an invention for detecting the state of a rechargeable battery (hereinafter referred to as a secondary battery) mounted on a vehicle, there is, for example, a secondary battery state detection device disclosed in Patent Document 1. This device pulsates the secondary battery with a discharge means after the engine stops, fits the time change of the voltage value when the secondary battery pulsates with a predetermined function to calculate the parameters of the function, and detects the state of the secondary battery based on the calculated parameters.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the device disclosed in Patent Document 1, pulse discharge is performed in a state where the engine is stopped and the secondary battery is not charged. If the current value when discharging the secondary battery by pulse discharge is increased, the state can be detected accurately, but if the current value of the pulse discharge is increased, power is consumed, and there is a risk that the voltage of the secondary battery will decrease and power cannot be supplied to the load.

[0005] The present invention has been made in view of the above, and an object thereof is to accurately measure the secondary battery while suppressing a decrease in the remaining amount of the secondary battery.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a discharge system according to the present invention is a discharge system that discharges a rechargeable secondary battery, and includes a discharge circuit that discharges the secondary battery, and a discharge control unit that controls the discharge circuit so that the discharge from the secondary battery is performed in a predetermined pattern. The discharge circuit changes the current value of the current flowing from the secondary battery in accordance with the control of the discharge control unit when the secondary battery discharges.

[0007] In a discharge system according to an aspect of the present invention, the discharge circuit includes a plurality of discharge paths each including a resistance element connected to the secondary battery and a switching element connected in series to the resistance element. The resistance elements of the plurality of discharge paths have different resistance values, respectively. The discharge control unit may select at least one of the switching elements of the plurality of discharge paths to discharge the secondary battery when discharging the secondary battery in a predetermined discharge pattern.

[0008] In a discharge system according to an aspect of the present invention, the discharge control unit may select a plurality of the switching elements among the switching elements of the plurality of discharge paths to discharge the secondary battery.

[0009] In a discharge system according to an aspect of the present invention, the current values of the currents flowing from the secondary battery in the plurality of discharge paths are different from each other. Among the discharge paths having the closest current values of the flowing currents, the current value of the current in one discharge path may be equal to or less than twice the current value of the current in the other discharge path.

[0010] In a discharge system according to an aspect of the present invention, the discharge circuit has a discharge path including a resistance element connected to the secondary battery and a PNP type transistor connected to the resistance element, and has a plurality of paths each including a resistance element connected to the base of the PNP type transistor and a switching element connected in series to the resistance element. The current values of the currents flowing in the plurality of paths may be different from each other.

[0011] In a discharge system according to an aspect of the present invention, the discharge circuit has a current mirror circuit composed of a pair of transistors, and the current mirror circuit discharges the secondary battery. The discharge control unit may control the current flowing through the current mirror circuit.

[0012] In a discharge system according to an aspect of the present invention, the discharge circuit has a discharge path composed of a resistance element connected to the secondary battery and a switching element connected to the resistance element. The discharge control unit may output a PWM signal to the switching element and control the duty ratio of the PWM signal.

Effects of the Invention

[0013] According to the present invention, it is possible to accurately measure the secondary battery while suppressing a decrease in the remaining amount of the secondary battery.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiments described below. Also, in the description of the drawings, the same or corresponding elements are appropriately assigned the same reference numerals.

[0016] [First Embodiment] (Configuration of the First Embodiment) FIG. 1 is a diagram showing the power supply system of a vehicle V according to an embodiment of the present invention. The secondary battery 20 is a rechargeable battery having an electrolyte, and is constituted by, for example, a lead-acid battery, a lithium-ion battery, a nickel-cadmium battery, or a nickel-metal hydride battery. The secondary battery 20 is charged by the alternator 25, drives the starter motor 27, and supplies power to the load 28. The starter motor 27 is constituted by, for example, a DC motor, generates a rotational force by the power supplied from the secondary battery 20, and starts the engine 26. The engine 26 is constituted by, for example, a reciprocating engine such as a gasoline engine and a diesel engine, or a rotary engine. The engine 26 is started by the starter motor 27, drives the drive wheels via the transmission, gives a propulsive force to the vehicle V, and drives the alternator 25. The alternator 25 is driven by the engine 26 to generate AC power, and converts the generated AC power into DC power by a rectifier circuit to charge the secondary battery 20. The load 28 is constituted by, for example, an electric steering motor, a defogger, a seat heater, an ignition coil, a car audio, and a car navigation, and operates by the power supplied from the secondary battery 20.

[0017] In addition, the vehicle V includes an ECU (Electronic Control Unit) 2 which is a higher-level device that controls the main control of the drive system of the vehicle V, a state detection device 1 that detects the state of the secondary battery 20, a voltage sensor 21, a current sensor 22, a temperature sensor 23, and a discharge circuit 24. The state detection device 1 and the discharge circuit 24 are an example of a discharge system that discharges the secondary battery 20.

[0018] The voltage sensor 21, the current sensor 22, and the temperature sensor 23 are sensors used to detect the state of the secondary battery 20. The voltage sensor 21 measures the terminal voltage of the secondary battery 20 and outputs a signal indicating the measured voltage to the state detection device 1. The current sensor 22 measures the charging current and the discharging current of the secondary battery 20 and outputs a signal indicating the measured current to the state detection device 1. The temperature sensor 23 measures the temperature of the electrolyte of the secondary battery 20 or the temperature around the secondary battery 20 and outputs a signal indicating the measured temperature to the control unit 10.

[0019] The discharge circuit 24 is a circuit used to detect the state of the secondary battery 20. The discharge circuit 24 does not supply power to the load 28, but is a circuit for discharging the secondary battery 20 in a predetermined pattern to detect the state of the secondary battery 20, and is controlled separately from the load 28 by the state detection device 1. The discharge circuit 24 is, for example, a circuit configured by connecting a semiconductor switch and a resistance element in series, and discharges the secondary battery 20 in a predetermined (e.g., rectangular wave) pattern by turning the semiconductor switch on / off in response to control from the state detection device 1. The predetermined pattern includes, for example, a pattern in which discharge is performed a predetermined number of times.

[0020] FIG. 2 is a diagram showing the circuit configuration of the discharge circuit 24. The discharge circuit 24 includes resistors R11 to R14, which are an example of resistor elements, and FETs (Field Effect Transistors) 51 to 54, which are an example of switching elements. The resistors R11 to R14 are fixed resistors. The resistance values of the resistors R11 to R14 are different from each other, and the resistance value of resistor R11 < the resistance value of resistor R12 < the resistance value of resistor R13 < the resistance value of resistor R14. Due to the different resistance values of the resistors R11 to R14, for example, the current value of the current flowing through resistor R12 is not more than twice the current value of the current flowing through resistor R11, the current value of the current flowing through resistor R13 is not more than twice the current value of the current flowing through resistor R12, and the current value of the current flowing through resistor R14 is not more than twice the current value of the current flowing through resistor R13. One ends of the resistors R11 to R14 are connected to the positive electrode of the secondary battery 20. The other end of resistor R11 is connected to the drain of FET51, the other end of resistor R12 is connected to the drain of FET52, the other end of resistor R13 is connected to the drain of FET53, and the other end of resistor R14 is connected to the drain of FET54.

[0021] The FETs 51 to 54 are N-channel MOS (Metal Oxide Semiconductor) type field effect transistors. The gates of the FETs 51 to 54 are connected to the control unit 10, and the sources are connected to the shunt resistor SR. The FETs 51 to 54 turn on or off according to the voltage applied to the gates from the control unit 10 described later. In the discharge circuit 24, a current flows through the FET that has a voltage turned on applied to its gate from the control unit 10 and via the resistor connected to the turned-on FET.

[0022] The shunt resistor SR is an example of the current sensor 22. One end of the shunt resistor SR is connected to the control unit 10 and the sources of the FETs 51 to 54, and the other end is connected to the control unit 10 and the negative electrode of the secondary battery 20.

[0023] The state detection device 1 acquires signals output from the voltage sensor 21, the current sensor 22, and the temperature sensor 23 when the secondary battery 20 discharges in a predetermined pattern by the discharge circuit 24, and detects the state of the secondary battery 20 based on the acquired signals. Note that the state detection device 1, the voltage sensor 21, the current sensor 22, the temperature sensor 23, and the discharge circuit 24 may not be separate configurations, and a configuration in which some or all of these are combined may be used as the state detection device.

[0024] FIG. 3 is a block diagram showing an example of the configuration of the state detection device 1. The state detection device 1 includes a control unit 10 including a CPU (Central Processing Unit) 10a, a ROM (Read Only Memory) 10b, and a RAM (Random Access Memory) 10c, a storage unit 11, a communication unit 12, an interface 13, and a bus 14. Note that the control unit 10 may be configured by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or the like instead of the CPU 10a. Here, all elements (control unit 10, storage unit 11, communication unit 12, interface 13) of the state detection device 1 do not necessarily have to be integrated, and for example, the elements may be distributed inside the vehicle V.

[0025] The bus 14 is a group of signal lines that mutually connect the CPU 10a, the ROM 10b, the RAM 10c, the storage unit 11, the communication unit 12, and the interface 13, and enables the exchange of information between them. The communication unit 12 communicates with the ECU 2 and exchanges various types of information. The interface 13 converts the signals supplied from the voltage sensor 21, the current sensor 22, and the temperature sensor 23 into digital signals and acquires them, and outputs a control signal for controlling the discharge circuit 24.

[0026] The memory unit 11 is composed of a non-volatile memory and stores various data used by the CPU 10a for calculations. The ROM 10b is composed of a non-volatile semiconductor memory or the like and stores the program 10ba. The RAM 10c is composed of a semiconductor memory or the like and stores data generated when the CPU 10a executes the program 10ba, measurement results of the voltage sensor 21, current sensor 22, and temperature sensor 23, and various values calculated by the CPU 10a using these measurement results.

[0027] The CPU 10a controls each unit based on the program 10ba stored in the ROM 10b. The functions of the control unit 10 are realized as functional units when the CPU 10a reads and executes the program 10ba from the ROM 10b. FIG. 4 is a functional block diagram showing the configuration of the functions realized in the control unit 10 when the CPU 10a executes the program 10ba. In the control unit 10, an acquisition unit 101, a discharge control unit 102, and an estimation unit 103 are realized.

[0028] The acquisition unit 101 acquires the voltage value of the secondary battery 20 indicated by the signals output from the voltage sensor 21, current sensor 22, and temperature sensor 23 and acquired by the interface 13, the current value of the current flowing from the secondary battery 20, and the temperature of the secondary battery 20. The discharge control unit 102 controls the discharge circuit 24 so that discharge in the secondary battery 20 is performed in a predetermined pattern. Further, the discharge control unit 102 controls the current value of the current flowing from the secondary battery 20 when the secondary battery 20 discharges. The estimation unit 103 estimates the state of the secondary battery 20 based on the voltage value and current value acquired by the acquisition unit 101 when discharge in the secondary battery 20 is performed in a predetermined pattern.

[0029] (Operation example of the first embodiment) Next, the operation example of this embodiment will be described. FIG. 5 is a flowchart showing the flow of the process in which the control unit 10 detects the state of the secondary battery 20. The control unit 10 executes the process shown in FIG. 5, for example, at a predetermined period or at a predetermined timing.

[0030] First, the control unit 10 determines whether the secondary battery 20 is in a standby state (step S101). Here, when the engine 26 is stopped, the control unit 10 determines that it is in a standby state (Yes in step S101). When the engine 26 is not stopped, the control unit 10 determines that it is not in a standby state (No in step S101). Regarding the determination of whether the engine 26 is stopped, for example, the control unit 10 inquires about the state of the engine 26 to the ECU2 via the communication unit 12. When a response of ignition off is obtained from the ECU2, it determines that the engine 26 is in a stopped standby state and proceeds to step S102. When a response of ignition on is obtained from the ECU2, it determines that the engine 26 is not stopped and is in a non-standby state, and ends the process of FIG. 5. Note that when the vehicle V is a hybrid vehicle, the ECU2 may set a state where neither the engine 26 nor the electric motor is operating as a standby state. When the vehicle V is an electric vehicle, the ECU2 may set a state where the electric motor is not operating as a standby state.

[0031] When the control unit 10 determines in step S101 that it is in a standby state, it selects an FET to be used when discharging the secondary battery 20 in a predetermined pattern (step S102). Here, the control unit 10 selects an FET based on, for example, the SOC (State Of Charge) of the secondary battery 20. Specifically, the control unit 10 first estimates the open-circuit voltage of the secondary battery 20. The open-circuit voltage can be estimated, for example, by using the approximate formula disclosed in Japanese Patent No. 4785056. Also, regarding the open-circuit voltage, the terminal voltage of the secondary battery 20 measured by the voltage sensor 21 at the start of the engine 26, or the latest terminal voltage of the secondary battery 20 measured periodically by the voltage sensor 21 and stored in the RAM10c may be estimated as the open-circuit voltage. Further, the open-circuit voltage may be estimated based on the terminal voltage measured at the timing closest to the start of the engine 26, that is, the terminal voltage of the secondary battery 20 measured immediately before the start of the engine 26. The control unit 10 estimates the SOC of the secondary battery 20 by a well-known or publicly known method based on the estimated open-circuit voltage.

[0032] The control unit 10 selects the FET among FETs 51 to 54 that is used to discharge the secondary battery 20 based on the estimated SOC. For example, when the SOC is less than 25%, the control unit 10 selects FET 54; when the SOC is 25% or more and less than 50%, it selects FET 53; when the SOC is 50% or more and less than 75%, it selects FET 52; and when the SOC is 75% or more, it selects FET 51. That is, the control unit 10 selects the FET with a smaller resistance value of the connected resistor as the SOC of the secondary battery 20 is higher. When the FET with a smaller resistance value of the connected resistor is selected, the current value of the current flowing from the secondary battery 20 when the FET is turned on becomes larger. Also, the control unit 10 selects the FET with a larger resistance value of the connected resistor as the SOC of the secondary battery 20 is lower. When the FET with a larger resistance value of the connected resistor is selected, the current value of the current flowing through the discharge circuit 24 when the FET is turned on becomes smaller.

[0033] Next, the control unit 10 controls the gate voltage of the selected FET so that the secondary battery 20 discharges in a predetermined pattern, and estimates the state of the secondary battery 20 (step S103). Here, the control unit 10 calculates the internal resistance value of the secondary battery 20 using the voltage value and current value of the secondary battery 20 acquired by the acquisition unit 101 when the secondary battery 20 is discharging in a predetermined pattern by the discharge circuit 24, and detects the state of the secondary battery 20 based on the calculated internal resistance value.

[0034] Here, the FET to be controlled is selected according to the SOC. When the SOC is high, the FET connected to the resistor with a small resistance value is controlled. In this case, since the voltage change when discharging is in a predetermined pattern becomes large, the internal resistance value can be accurately estimated. Also, when the SOC is low, the FET connected to the resistor with a large resistance value is controlled. In this case, since the current value of the current flowing through the discharge circuit 24 when discharging is in a predetermined pattern becomes small, the power consumption of the secondary battery 20 can be suppressed in a state where the secondary battery 20 is undercharged.

[0035] Next, the control unit 10 notifies the detection result of step S103 to the upper-level device, i.e., the ECU 3 (step S104). The ECU 3 that has obtained the detection result of the state of the secondary battery 20 notifies, for example, the state of the secondary battery 20 on the instrument panel. Note that the notification of the state of the secondary battery 20 is not limited to the notification on the instrument panel, and may be, for example, an alarm sound or voice. Also, these notifications may be performed at the timing when the accessory power supply is turned on in the vehicle V or at the timing of ignition on.

[0036] Note that in the discharge circuit 24, the number of sets of series resistors and FETs may be two, three, or five or more. Also, for the discharge circuit 24, a plurality of FETs may be selected when selecting the FETs to be used when discharging in a predetermined pattern in step S102. By using a plurality of FETs when discharging the secondary battery 20 in a predetermined pattern, current flows through the parallel resistors in the discharge circuit 24, so that the current value of the flowing current can be finely switched.

[0037] [Second Embodiment] Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in that the vehicle V includes a discharge circuit 24A instead of the discharge circuit 24. In the following description, the same components as those of the discharge circuit 24 are denoted by the same reference numerals and the description thereof is omitted.

[0038] FIG. 6 is a diagram showing the circuit configuration of the discharge circuit 24A according to the second embodiment. The discharge circuit 24A has a transistor TR1 and a resistor R15 in addition to the resistors R11 to R13 and the FETs 51 to 53. The resistor R15 is a fixed resistor, one end of which is connected to the positive electrode of the secondary battery 20, and the other end is connected to the emitter of the transistor TR1. The transistor TR1 is a PNP-type transistor, the base of which is connected to the resistors R11 to R13, and the collector of which is connected to one end of the shunt resistor SR. One end of the shunt resistor SR is connected to the control unit 10 and the collector of the transistor TR1, and the other end is connected to the negative electrode of the secondary battery 20.

[0039] The resistors R11 to R13 have one end connected to the base of the transistor TR1. One end of the resistor R11 is connected to the drain of the FET51, one end of the resistor R12 is connected to the drain of the FET52, and one end of the resistor R13 is connected to the drain of the FET53. The gates of the FETs 51 to 53 are connected to the control unit 10, and the sources are connected to the negative electrode of the secondary battery.

[0040] In the second embodiment, when selecting the FET in step S102, similar to the first embodiment, one of the FETs 51 to 53 is selected based on the SOC of the secondary battery 20. That is, the control unit 10 selects the FET in step S102 such that the current flowing from the transistor TR1 to the shunt resistor SR increases as the SOC increases, and the current flowing from the transistor TR1 to the shunt resistor SR decreases as the SOC decreases.

[0041] Note that in the discharge circuit 24A, the number of sets of series resistors and FETs may be two or four or more. Also, for the discharge circuit 24A, a plurality of FETs may be selected when selecting the FET in step S102. By using a plurality of FETs when discharging the secondary battery 20 in a predetermined pattern, the current value of the current flowing through the shunt resistor SW can be finely switched.

[0042] [Third Embodiment] Next, a third embodiment of the present invention will be described. The third embodiment is different from the first embodiment in that the vehicle V includes a discharge circuit 24B instead of the discharge circuit 24. In the following description, the same components as those of the discharge circuit 24 are denoted by the same reference numerals, and the description thereof is omitted.

[0043] FIG. 7 is a diagram showing the circuit configuration of the discharge circuit 24B according to the third embodiment. The discharge circuit 24B includes resistors R11 to R13, FETs 51 to 53, and also FETs 55, 56 and resistor R15. Resistor R15 is a fixed resistor, one end of which is connected to the positive electrode of the secondary battery 20, and the other end of which is connected to the drain of FET56. The gates of FETs 51 to 53 are connected to the control unit 10, and the sources are connected to the drain of FET55 and the gates of FETs 55 and 56.

[0044] FETs 55, 56 are N-channel MOS-type field effect transistors. For FET55, the drain is connected to the gates of FETs 55, 56 and the sources of FETs 51 to 53, the gate is connected to the drain of FET55, the gates of FET56, and the sources of FETs 51 to 53, and the source is connected to the negative electrode of the secondary battery 20. For FET56, the drain is connected to resistor R15, the gate is connected to the gate and drain of FET55 and the sources of FETs 51 to 53, and the source is connected to one end of the shunt resistor SR. FETs 55 and 56 form a current mirror circuit, and the current value of the current flowing through the drain of FET56 is the same as the current value of the current flowing through the drain of FET55.

[0045] In the third embodiment, when selecting an FET in step S102, similar to the first embodiment, one of FETs 51 to 53 is selected based on the SOC of the secondary battery 20. That is, the control unit 10 selects an FET such that the current flowing through the shunt resistor SR via the resistor R15 and FET56 increases as the SOC increases, and the current flowing through the shunt resistor SR via the resistor R15 and FET56 decreases as the SOC decreases.

[0046] In the discharge circuit 24B, the number of sets of a series resistor and an FET may be two or four or more. Also, for the discharge circuit 24B, a plurality of FETs may be selected when selecting an FET in step S102. By using a plurality of FETs when discharging the secondary battery 20 in a predetermined pattern, the current value of the current flowing through the shunt resistor SR can be finely switched.

[0047] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. The fourth embodiment is different from the first embodiment in that the vehicle V includes a discharge circuit 24C instead of the discharge circuit 24.

[0048] FIG. 8 is a diagram showing the circuit configuration of the discharge circuit 24C according to the fourth embodiment. The discharge circuit 24C has a transistor TR2 and a resistor R15. The resistor R15 is a fixed resistor, one end of which is connected to the positive electrode of the secondary battery 20, and the other end is connected to the collector of the transistor TR2. The transistor TR2 is an NPN-type transistor, the base of which is connected to the control unit 10, and the emitter of which is connected to one end of the shunt resistor SR. One end of the shunt resistor SR is connected to the control unit 10 and the emitter of the transistor TR1, and the other end is connected to the negative electrode of the secondary battery 20. In the discharge circuit 24C, the current value when discharging the secondary battery 20 in a predetermined pattern can be changed by changing the duty ratio of the PWM signal supplied by the control unit 10 to the base of the transistor TR1.

[0049] FIG. 9 is a flowchart showing the flow of the process in which the control unit 10 according to the fourth embodiment detects the state of the secondary battery 20. The control unit 10 executes the process shown in FIG. 9, for example, at a predetermined period or a predetermined timing.

[0050] First, the control unit 10 determines whether the secondary battery 20 is in a standby state (step S101). Here, when the engine 26 is stopped, the control unit 10 determines that it is in a standby state (Yes in step S101). When the engine 26 is not stopped, the control unit 10 determines that it is not in a standby state (No in step S101).

[0051] When the control unit 10 determines in step S101 that it is in a standby state, it determines the duty ratio of the PWM signal output to the discharge circuit 24C (step S102a). Here, the control unit 10 determines the duty ratio based on, for example, the SOC of the secondary battery 20. Specifically, the control unit 10 determines the duty ratio such that the current flowing through the shunt resistor SR via the resistor R15 and the transistor TR1 increases as the SOC increases, and the current flowing through the shunt resistor SR via the resistor R15 and the transistor TR1 decreases as the SOC decreases.

[0052] Next, the control unit 10 outputs a PWM signal with the determined duty ratio so that the secondary battery 20 discharges in a predetermined pattern, and estimates the state of the secondary battery 20 (step S103a). Here, the control unit 10 calculates the internal resistance value of the secondary battery 20 using the voltage value and current value of the secondary battery 20 acquired by the acquisition unit 101 when the secondary battery 20 is discharging in a predetermined pattern by the discharge circuit 24C, and detects the state of the secondary battery 20 based on the calculated internal resistance value. Next, the control unit 10 notifies the ECU 3 of the detection result in step S103 (step S104).

[0053] Also in the fourth embodiment, when the SOC is small, since the current value of the current flowing through the discharge circuit 24C becomes small when the discharge is performed in a predetermined pattern, in a state where the charging of the secondary battery 20 is insufficient, the power consumption of the secondary battery 20 can be suppressed when the secondary battery 20 is discharged in a predetermined pattern. Further, in the discharge circuit 24C, the current value when discharging in a predetermined pattern can be changed with a smaller number of components as compared with the discharge circuits 24, 24A, and 24B. Note that in the fourth embodiment, instead of controlling the current flowing through the shunt resistor SR with a PWM signal, the current value of the current supplied by the control unit 10 to the base of the transistor TR2 may be changed to change the current value when the secondary battery 20 is discharged in a predetermined pattern.

[0054] [Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. The fifth embodiment is different from the first embodiment in that the vehicle V includes a discharge circuit 24D instead of the discharge circuit 24.

[0055] FIG. 10 is a diagram showing a circuit configuration of the discharge circuit 24D according to the fifth embodiment. The discharge circuit 24D includes an FET 57, a resistor R15, a resistor R16, and a capacitor C1. One end of the resistor R15 is connected to the positive electrode of the secondary battery 20, and the other end is connected to the drain of the FET 57. The FET 57 is an N-channel MOS-type field effect transistor. The drain of the FET 57 is connected to the other end of the resistor R15, the gate is connected to the resistor R16 and the capacitor C1, and the source is connected to the shunt resistor SR. The resistor R16 is a fixed resistor, one end of which is connected to the control unit 10, and the other end is connected to the capacitor C1 and the gate of the FET 57. One end of the capacitor C1 is connected to the resistor R16 and the gate of the FET 57, and the other end is connected to the negative electrode of the secondary battery 20.

[0056] In the fifth embodiment, the process of FIG. 9 is executed to detect the state of the secondary battery 20. The control unit 10 determines the duty ratio of the PWM signal output to the discharge circuit 24D in step S102a. Here, the control unit 10 determines the duty ratio based on, for example, the SOC of the secondary battery 20. Specifically, the control unit 10 determines the duty ratio such that the current flowing through the shunt resistor SR via the resistor R15 and the FET 57 increases as the SOC increases, and the current flowing through the shunt resistor SR via the resistor R15 and the FET 57 decreases as the SOC decreases.

[0057] Also in the fifth embodiment, when the SOC is small, the current value of the current flowing through the discharge circuit 24D becomes small when the discharge is performed in a predetermined pattern. Therefore, in a state where the secondary battery 20 is insufficiently charged, the power consumption of the secondary battery 20 can be suppressed when the secondary battery 20 is discharged in a predetermined pattern. Further, in the discharge circuit 24C, the current value when the discharge is performed in a predetermined pattern can be changed with a smaller number of components compared to the discharge circuits 24, 24A, and 24B.

[0058] [Modification Example] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the present invention may be implemented by modifying the above-described embodiments as follows. Note that the above-described embodiments and the following modification examples may be combined with each other. The present invention also includes those configured by appropriately combining the components of the above-described embodiments and each modification example. Further, additional effects and modification examples can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiments and modification examples, and various changes are possible.

[0059] In the present invention, when the control unit 10 discharges the secondary battery 20 a plurality of times in a rectangular wave pattern, the control unit 10 may select an FET or determine the duty ratio of a PWM signal so that the current value of the current flowing through the shunt resistor SR becomes large once every several times. According to this modification, since the voltage change becomes large when the discharge is performed in a predetermined pattern, the internal resistance value can be accurately estimated.

[0060] In the present invention, based on the temperature measured by the temperature sensor 23, the control unit 10 may select an FET used when discharging the secondary battery 20 in a predetermined pattern or determine the duty ratio of the PWM signal output to the discharge circuit 24C. For example, when the temperature measured by the temperature sensor 23 is lower than a predetermined threshold value, the control unit 10 may select an FET or determine the duty ratio of the PWM signal so that the current value of the current flowing through the shunt resistor SR becomes small.

[0061] Further, the control unit 10 may select an FET used when discharging the secondary battery 20 in a predetermined pattern so that the current flowing through the shunt resistor SR increases as the temperature measured by the temperature sensor 23 increases and decreases as the temperature measured by the temperature sensor 23 decreases. Further, the control unit 10 may determine the duty ratio of the PWM signal when discharging the secondary battery 20 in a predetermined pattern so that the current flowing through the shunt resistor SR increases as the temperature measured by the temperature sensor 23 increases and decreases as the temperature measured by the temperature sensor 23 decreases. According to this modification, the state of the secondary battery 20 can be estimated with high accuracy even when the temperature changes.

[0062] In the present invention, based on, for example, the size or product number of the secondary battery 20, the control unit 10 may determine the FET used when discharging the secondary battery 20 in a predetermined pattern or the duty ratio of the PWM signal output to the discharge circuits 24C and 24D when discharging the secondary battery 20 in a predetermined pattern.

[0063] In the discharge circuits 24, 24A, and 24B, an IPD (Intelligent Power Device) may be used instead of the FET.

[0064] In the above-described embodiment, the state detection device 1 provided in the vehicle V controls the discharge circuit. However, for example, the ECU 2 may be configured to include the functions of the state detection device 1, and the ECU 2 may control the discharge circuit. FIG. 11 is a block diagram showing the configuration of another embodiment of the discharge system.

[0065] The ECU 2 as an example of the state detection device has a control unit 200, a storage unit 210, an interface 220, and a bus (not shown). The control unit 200 has a CPU, a ROM, and a RAM, similar to the control unit 10. The CPU, ROM, RAM, storage unit 210, and interface 220 are interconnected by a bus and exchange information therebetween.

[0066] The functions of the control unit 200 are realized as functional units by the CPU reading and executing a program from the ROM. By the CPU executing the program stored in the ROM, an acquisition unit 201, a discharge control unit 202, and an estimation unit 203 are realized in the control unit 200.

[0067] The acquisition unit 301 acquires the voltage value of the secondary battery 20, the current value of the current flowing from the secondary battery 20, and the temperature of the secondary battery 20 indicated by the signals output from the voltage sensor 21, the current sensor 22, and the temperature sensor 23 and acquired by the interface 220. The discharge control unit 202 controls the discharge circuit 24 so that discharge is performed in a predetermined pattern in the secondary battery 20. Further, the discharge control unit 202 controls the current value of the current flowing from the secondary battery 20 when the secondary battery 20 discharges. The estimation unit 203 estimates the state of the secondary battery 20 based on the voltage value and the current value acquired by the acquisition unit 201 when discharge is performed in a predetermined pattern in the secondary battery 20.

[0068] Even in this configuration, when discharging is performed in a predetermined pattern by the secondary battery 20, the current value of the current flowing from the secondary battery 20 can be changed.

Explanation of Signs

[0069] 1 State detection device 2 ECU 10a CPU 10b ROM 10ba Program 10c RAM 11 Storage unit 12 Communication unit 13 Interface 14 Bus 20 Secondary battery 21 Voltage sensor 22 Current sensor 23 Temperature sensor 24, 24A~24D Discharge circuit 101, 201 Acquisition unit 102, 202 Discharge control unit 103, 203 Estimation unit R11~R14 Resistor SR Shunt resistor TR1 Transistor

Claims

1. A discharge system for discharging a rechargeable secondary battery, comprising: a discharge circuit for discharging the secondary battery; a discharge control unit for controlling the discharge circuit so that the discharge from the secondary battery is performed in a predetermined pattern; wherein the discharge circuit changes a current value of a current flowing from the secondary battery in response to control of the discharge control unit when the secondary battery discharges. The discharge system.

2. The discharge circuit has a plurality of discharge paths each including a resistance element connected to the secondary battery and a switching element connected in series to the resistance element, the resistance elements of the plurality of discharge paths have different resistance values, respectively, and the discharge control unit selects at least one of the switching elements of the plurality of discharge paths to discharge the secondary battery when discharging the secondary battery in a predetermined discharge pattern. The discharge system according to claim 1.

3. The discharge control unit selects a plurality of the switching elements among the switching elements of the plurality of discharge paths to discharge the secondary battery. The discharge system according to claim 2.

4. The current values of the currents flowing through the plurality of discharge paths are different from each other, and for the discharge paths with the closest current values of the flowing currents, the current value of the current in one discharge path is not more than twice the current value of the current in the other discharge path. The discharge system according to claim 2.

5. The discharge circuit has a discharge path including a resistance element connected to the secondary battery and a PNP-type transistor connected to the resistance element, and has a plurality of paths each including a resistance element connected to the base of the PNP-type transistor and a switching element connected in series to the resistance element, wherein the current values of the currents flowing through the plurality of paths are different from each other. The discharge system according to claim 1.

6. The discharge circuit has a current mirror circuit composed of a pair of transistors, the current mirror circuit discharges the secondary battery, and the discharge control unit controls the current flowing through the current mirror circuit. The discharge system according to claim 1.

7. The discharge circuit has a discharge path including a resistance element connected to the secondary battery and a switching element connected to the resistance element, and the discharge control unit outputs a PWM signal to the switching element and controls a duty ratio of the PWM signal. The discharge system according to claim 1.

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