Battery monitoring apparatus

A battery monitoring apparatus for monitoring a battery condition of an assembled battery. In the apparatus, a monitoring unit is powered by the assembled battery and transitions from a normal mode, in which power supply from the assembled battery to the monitoring unit is maintained, to a dark-current mode, in which the power supply is partially interrupted, in response to a mode-switching instruction signal from a control unit. Upon reception of a mode confirmation signal from the control unit during the normal mode, the monitoring unit transmits a response signal to the control unit. The control unit transmits the mode-switching instruction signal to the monitoring unit, and thereafter transmits the mode confirmation signal to the monitoring unit. Upon reception of the response signal to the mode confirmation signal from the monitoring unit, the control unit determines that the dark-current mode of the monitoring unit is malfunctioning.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2011-230995 filed Oct. 20, 2011, the description of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a battery monitoring apparatus for monitoring a battery condition of an assembled battery formed of a plurality of battery cells connected in series.

2. Related Art

A known battery monitoring apparatus includes, as main components, a monitoring unit that monitors a battery condition, such as an over-charge or over-discharge condition, of each of a plurality of battery cells forming an assembled battery, and a control unit that controls the operation of the monitoring unit.

The monitoring unit of the battery monitoring apparatus is powered by the assembled battery that is a monitored object. Therefore, the consumption of power by the monitoring circuit will lead to a reduction in state of charge (SOC) of each battery cell of the assembled battery. In addition, when the monitoring unit operates unnecessarily, the power consumed by the monitoring unit is increased, which facilitates a reduction in SOC of the assembled battery. This may lead to an over-discharge condition of each battery cell of the assembled battery.

To reduce the power consumed by the monitoring unit, there has been proposed a battery monitoring apparatus as disclosed in Japanese Patent No. 4114310 including a dark-current mode (or a sleep mode) in which power supply from the assembled battery to the monitoring unit is limited when a prescribed condition is met. The disclosed battery monitoring apparatus is configured such that the monitoring unit transitions to the dark-current mode when the control unit is receiving no monitoring results (in the form of monitoring information signals) from the monitoring unit.

In the disclosed battery monitoring apparatus, however, the control unit is unable to diagnose whether or not the dark-current mode of the monitoring unit is functioning normally. Accordingly, when the dark-current mode of the monitoring unit is malfunctioning or functioning incorrectly, the monitoring unit may unnecessarily consume the power of the assembled battery and sufficient power of the assembled battery may not be supplied to electrical loads other than the monitoring unit, such as a vehicle inverter and the like, which may prevent the electrical loads from being driven properly. Malfunction of the dark-current mode of the monitoring unit may occur when an abnormality in a switching element or the like in the monitoring unit prevents the monitoring unit from transitioning to the dark-current mode correctly or when external noise or the like causes false triggering of the monitoring unit during the dark-current mode.

In consideration of the foregoing, it would therefore be desirable to have a battery monitoring apparatus including a monitoring unit that monitors a battery condition of an assembled battery and a control unit that controls the operation of the monitoring unit, where the control unit is capable of diagnosing whether or not a dark-current mode of the monitoring unit is functioning normally.

SUMMARY

In accordance with an exemplary embodiment of the present invention, there is provided a battery monitoring apparatus for monitoring a battery condition of an assembled battery formed of a plurality of battery cells connected in series. The apparatus includes: a monitoring unit that is powered by the assembled battery and monitors the battery condition of the assembled battery; a control unit that acquires a monitoring result indicative of the battery condition of the assembled battery from the monitoring unit and controls the operation of the monitoring unit on the basis of the monitoring result. In the apparatus, the monitoring unit transitions from a normal mode, in which power supply from the assembled battery to the monitoring unit is maintained, to a dark-current mode, in which power supply from the assembled battery to the monitoring unit is partially interrupted, in response to a first mode-switching instruction signal from the control unit for instructing the monitoring unit to transition from the normal mode to the dark-current mode, and transitions from the dark-current mode to the normal mode in response to a second mode-switching instruction signal from the control unit for instructing the monitoring unit to transition from the dark-current mode to the normal mode, and upon reception of a mode confirmation signal from the control unit during the normal mode of the monitoring unit, the monitoring unit transmits a response signal to the mode confirmation signal to the control unit. The control unit transmits the first mode-switching instruction signal to the monitoring unit, thereafter transmits the mode confirmation signal to the monitoring unit, and upon reception of the response signal to the mode confirmation signal from the monitoring unit, determines that the dark-current mode of the monitoring unit is malfunctioning.

The above battery monitoring apparatus is configured such that the response signal to the mode confirmation signal is unable to be transmitted from the monitoring unit to the control unit during the dark-current mode of the monitoring unit. In addition, the mode confirmation signal is transmitted from the control unit to the monitoring unit subsequently to transmission of the first mode-switching instruction signal from the control unit to the monitoring unit. Subsequently to the transmission of the mode confirmation signal, the control unit determines whether or not the response signal to the mode confirmation signal has been received from the monitoring unit. With this configuration, when it is determined that the response signal has been received from the monitoring unit, it can be determined that the dark-current mode of the monitoring unit is malfunctioning (or is not functioning correctly). In the above battery monitoring apparatus, power supply from the assembled battery to the monitoring unit is not fully interrupted during the dark-current mode of the monitoring unit. That is, at least power supply to some elements of the monitoring unit necessary to transition from the dark-current mode to the normal mode are maintained even during the dark-current mode of the monitoring unit.

DESCRIPTION OF SPECIFIC EMBODIMENTS

There will now be explained a battery monitoring apparatus in accordance with one embodiment of the present invention with reference toFIGS. 1 to 3. The battery monitoring apparatus2is applied to a battery control system for an assembled battery, which is a high-voltage battery mounted in a hybrid vehicle or an electrical vehicle. As shown inFIG. 1, main components of the battery control system of the present embodiment are the assembled battery1and the battery monitoring apparatus2.

The assembled battery1of the present embodiment supplies electrical power to various electrical loads, such as an electrical motor (not shown) or the like for driving the vehicle. More specifically, the assembled battery1is a series connection of a plurality of battery cells10each being a lithium-ion battery or the like. The series connection of battery cells10is divided into a plurality of battery blocks B1to Bn each being a series connection of an equal number of battery cells (eight cells per block in the present embodiment). For illustration purposes only,FIG. 1shows only one block B1(1≦i≦n).

The assembled battery1is electrically connected to the battery monitoring apparatus2via sense lines. The battery monitoring apparatus2is operable to monitor a battery condition, such as an over-discharge condition or an over-charge condition, of each battery cell of the assembled battery1(an abnormal condition detection function) and to equalize cell voltages of the respective battery cells10of the assembled battery1(a cell-voltage equalization function). The over-discharge condition is an abnormal condition where a voltage of each battery cell10is too low to ensure reliability of the system. The over-charge condition is an abnormal condition where a voltage of each battery cell10is too high to ensure reliability of the system.

More specifically, the battery monitoring apparatus2includes, as main components, a plurality of monitoring circuits21(each as a monitoring unit or monitoring means) respectively associated with the plurality of battery blocks B and each adapted to monitor a battery condition of a respectively corresponding battery block B, a microcomputer22(as a control unit or control means) adapted to control the operation of each of the plurality of monitoring circuits21, and a plurality of signal transfer circuits23(each as a signal transfer unit or signal transfer means) respectively associated with the plurality of monitoring circuits21and each adapted to transfer communication signals between a respectively corresponding monitoring circuit21and the microcomputer22in an electrically insulating manner.

Each monitoring circuit21is powered by a respectively corresponding high-voltage battery block B that is a monitored object of the monitoring circuit21. The microcomputer22is powered by a low-voltage auxiliary battery (not shown), such as a 12V battery. That is, each monitoring circuit21of the present embodiment is included in a high-voltage system, and the microcomputer22is included in a low-voltage system.

The monitoring circuit21is electrically connected to positive and negative terminals of each battery cell10of the monitored battery block B via sense lines to detect a voltage across the battery cell10. Detected cell-voltage values of the respective battery cells10of the monitored battery block B are outputted from the monitoring circuit21to the microcomputer22. As described above, the plurality of monitoring circuits21correspond one-to-one to the plurality of the battery blocks B1to Bn. Therefore, the explanations regarding a specific one of the plurality of monitoring circuits21corresponding to the battery block Bi that is illustrated inFIG. 1are applicable equally to each of the other monitoring circuits21.

The monitoring circuit21includes a voltage detection circuit211that detects a voltage across each battery cell10of the monitored battery block B, an cell-voltage equalization circuit212that equalizes cell voltages of the respective battery cells of the monitored battery block B, an interface circuit213(as an interface unit or as interface means) that outputs and receives various signals, and a power supply circuit214and others.

The voltage detection circuit211of the present embodiment includes a plurality of selection switches (not shown) each electrically connected to a respectively corresponding battery cell10of the monitored battery block B, a multiplexer (not shown) adapted to select and turn on and off an arbitrary one of the plurality of selection switches, an A/D convertor (not shown) adapted to convert an analog signal (indicative of voltage values) acquired via the multiplexer to digital data, and others.

The cell-voltage equalization circuit212detects cell-to-cell voltage variations in the monitored battery block B with reference to detected voltage values from the voltage detection circuit211and regulates or minimizes the cell-to-cell voltage variations by discharging a battery cell10having the highest cell voltage thereacross among the battery cells10of the monitored battery block B (cell-voltage equalization discharge).

The interface circuit (or input/output circuit)213outputs a signal to and receives a signal from the microcomputer22via the signal transfer circuit23(as a signal transfer unit or as signal transfer means). The interface circuit213includes a first terminal213afor receiving first and second mode-switching instruction signals (which will be described later) from the microcomputer22and a second terminal213bfor outputting to and receiving from the microcomputer22communication signals other than the first and second mode-switching instruction signals. The first terminal213amay be a chip select terminal (CS terminal).

Upon reception of a signal other than the first and second mode-switching instruction signals during a normal mode (which will be described later) via the second terminal213b, the interface circuit213transmits to the microcomputer22a response signal indicative of successful reception of the signal other than the first and second mode-switching instruction signals.

The first mode-switching instruction signal is outputted from the microcomputer22to each monitoring circuit21for instructing the monitoring circuit21to transition from a normal mode, in which power supply from the monitored battery block B to the monitoring circuit21is maintained, to a dark-current mode (or a sleep mode), in which power supply from the monitored battery block B to the monitoring circuit21is partially interrupted. The second mode-switching instruction signal is outputted from the microcomputer22to each monitoring circuit21for instructing the monitoring circuit21to transition from the dark-current mode to the normal mode.

The power supply circuit214of the present embodiment is electrically connected to a positive terminal of the highest-side battery cell10(the top battery cell inFIG. 1) within the monitored battery block B and to a negative terminal of the lowest-side battery cell10(the bottom battery cell inFIG. 1) and converts a voltage across the battery block B into a desired voltage to supply the desired voltage to each of the elements211to213of the monitoring circuit21.

The power supply circuit214includes a mode switcher214afor switching between the normal mode and the dark-current mode of the monitoring circuit21in response to the first or second mode-switching instruction signal from the microcomputer22. The mode switcher214amay include a switching element that electrically connects and disconnects between the power supply circuit214and each of the elements211to213of the monitoring circuit21. It should be noted that, during the dark-current mode of the monitoring circuit21, at least power supply to some elements necessary for transition from the dark-current mode to the normal mode is maintained without being interrupted.

The microcomputer22includes MPU (not shown), ROM (not shown), EEPROM (not shown), RAM (not shown) and others, and is operable to perform various processes in accordance with programs stored in the ROM or the like.

The microcomputer22of the present embodiment transmits various instruction signals to each monitoring circuit21, acquires output signals, such as signals indicative of monitoring results, of each monitoring circuit21, and diagnoses a battery condition of the assembled battery1and/or an abnormality in each monitoring circuit21on the basis of the acquired signals.

The various instruction signals outputted from the microcomputer22to each monitoring circuit21may include a monitoring instruction signal for instructing the monitoring circuit21to monitor a battery condition of each battery cell10of the monitored battery block B, a cell-voltage equalization instruction signal for instructing the monitoring circuit21to perform cell-voltage equalization discharge, in which the battery cells of the monitored battery block B are discharged so that their cell voltages become substantially equal to each other, the first mode-switching instruction signal for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode, the second mode-switching instruction signal for instructing the monitoring circuit21to transition from the dark-current mode to the normal mode, and a mode confirmation signal used in diagnosis of abnormality in the monitoring circuit21.

The monitoring instruction signal and the cell-voltage equalization instruction signal are transmitted from the microcomputer22to each monitoring circuit21, for example, during ON state of a starting switch, such as an ignition switch (not shown), of the vehicle. The first mode-switching instruction signal is transmitted from the microcomputer22to each monitoring circuit21for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode, when the starting switch of the vehicle is turned off. The second mode-switching instruction signal is transmitted from the microcomputer22to each monitoring circuit21for instructing the monitoring circuit21to transition from the dark-current mode to the normal mode, when a prescribed triggering condition is met. Since a cell-voltage of each battery cell10of the assembled battery1is less likely to vary during the OFF state of the starting switch of the vehicle, the microcomputer22transmits to each monitoring circuit21the first mode-switching instruction signal for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode. This allows power consumption to be reduced in each monitoring circuit21.

Each signal transfer circuit23is responsible for signal transfer between a respectively corresponding monitoring circuit21and the microcomputer22in an electrically insulated manner. The signal transfer circuit23of the present embodiment includes a first signal transfer section23afor transferring the first and second mode-switching instruction signals from the microcomputer22to the monitoring circuit21and a second signal transfer section23bfor transferring communication signals other than the first and second mode-switching instruction signals (i.e., the monitoring instruction signal, the cell-voltage equalization instruction signal, the mode confirmation signal, the response signal etc.) between the microcomputer22and the monitoring circuit21. That is, in the signal transfer circuit23of the present embodiment, the first signal transfer section23aand the second signal transfer section23bare separate and independent from each other.

The first signal transfer section23aincludes an optically-coupled insulating element for unidirectionally transferring signals, such as the first and second mode-switching instruction signals, from the microcomputer22to the monitoring circuit21. Since the first and second mode-switching instruction signals don't have to be transferred at a high rate, the optically-coupled insulating element may be a photocoupler. The first signal transfer section23ais powered not by the assembled battery1, but by the auxiliary battery for driving the microcomputer22. This allows the first signal transfer section23ato transfer signals from the microcomputer22to the monitoring circuit21regardless of whether the monitoring circuit21is in the normal mode or in the dark-current mode.

The second signal transfer section23bincludes a pair of optically-coupled insulating elements for bidirectionally transferring signals (other than the first and second mode-switching instruction signals) between the microcomputer22and the monitoring circuit21. Since the second signal transfer section23bmay transfer the signals required to be transferred at a higher rate than the first and second mode-switching instruction signals, each optically-coupled insulating element of the pair may be a photo-IC coupler including a high-speed logic IC for accelerating signal transfer.

The second signal transfer section23bis configured such that the insulating element (including the high-speed logic IC) of the pair, dedicated to signal transfer from the monitoring circuit21to the microcomputer22, is powered by the assembled battery1. Therefore, the second signal transfer section23bis able to transfer the signals (the response signal etc.) from the monitoring circuit21to the microcomputer22, only when the monitoring circuit21is in the normal mode. In other words, when the monitoring circuit21is in the dark-current mode, the second signal transfer section23bis unable to transfer the signals from the monitoring circuit21to the microcomputer22.

There will now be explained operations of the battery monitoring apparatus2in accordance with the present embodiment. The battery monitoring apparatus2of the present embodiment monitors a battery condition of the assembled battery1, equalizes cell voltages of the respective battery cells10of the assembled battery1, and performs diagnosis of abnormality in each monitoring circuit21. The battery monitoring apparatus2further performs an abnormality response measure in response to the abnormality diagnosis.

At first, monitoring and cell-voltage equalization of the assembled battery1performed in the battery monitoring apparatus2will be explained. As described above, the battery monitoring apparatus2of the present embodiment is configured such that each monitoring circuit21is powered by the corresponding battery block B of the assembled battery1and each signal transfer circuit23is partially powered by the power supply circuit21of the corresponding monitoring circuit21. With configuration, the monitoring of the assembled battery1is triggered, for example, by an external command.

The microcomputer22transmits the monitoring instruction signal to each monitoring circuit21via the second signal transfer section23bof the signal transfer circuit23to instruct the monitoring circuit21to monitor a battery condition of each battery cell10of the monitored battery block B. In each monitoring circuit21having received the monitoring instruction signal from the microcomputer22, the voltage detection circuit211detects a battery condition, such as a cell voltage or the like, of each battery cell of the monitored battery block B. Subsequently, the monitoring circuit21transmits an output signal indicative of the battery condition of each battery cell detected by the voltage detection circuit211to the microcomputer22via the second signal transfer section23bof the signal transfer circuit23. The microcomputer22diagnoses a battery condition of each battery cell10of the assembled battery1on the basis of the output signal of each monitoring circuit21.

When it is determined by the microcomputer22that at least one of the cell-to-cell voltage variations of the assembled battery1exceeds a predetermined value, the microcomputer22transmits the cell-voltage equalization instruction signal to each monitoring circuit21via the second signal transfer section23bof the signal transfer circuit23to instruct the monitoring circuit21to equalize cell voltages of the respective battery cells10of the monitored battery block B. In each monitoring circuit21having received the cell-voltage equalization instruction signal from the microcomputer22, the cell-voltage equalization circuit212equalizes cell-voltages of the respective battery cells10of the monitored battery block B by performing the cell-voltage equalization discharge. The cell-voltage equalization discharge is performed repeatedly until the cell-to-cell voltage variations are lowered below the predetermined value.

There will now be explained abnormality diagnosis for diagnosing whether or not the dark-current mode of each monitoring circuit21of the battery monitoring apparatus2is functioning normally with reference toFIG. 2.FIG. 2shows a flowchart of the abnormality diagnosis of the present embodiment performed by the microcomputer22. A control routine shown inFIG. 2is performed when the starting switch of the vehicle is turned off.

At first, as shown inFIG. 2, the microcomputer22transmits to each monitoring circuit21the first mode-switching instruction signal for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode, via the first signal transfer section23aof the signal transfer circuit23, in step S10. Thereafter, in step S20, the microcomputer22waits a predetermined time period, where the predetermined time period is set to a time period required for the monitoring circuit21to transition from the normal mode to the dark-current mode.

Subsequently to step S20, that is, after waiting the predetermined time period, the microcomputer22transmits the mode confirmation signal to the monitoring circuit21via the second signal transfer section23bof the signal transfer circuit23in step S30. Thereafter, in step S40, the microcomputer22determines whether or not the response signal to the mode confirmation signal has been received from the monitoring circuit21.

As far as the dark-current mode of the monitoring circuit21is functioning normally, the insulating element dedicated to signal transfer from the monitoring circuit21to the microcomputer22, of the second signal transfer section23b, is unable to transfer signals from the monitoring circuit21to the microcomputer22. Therefore, the microcomputer22will receive no response signal to the mode confirmation signal from the monitoring circuit21when the monitoring circuit21is in the dark-current mode.

Conversely, when the microcomputer22receives the response signal to the mode confirmation signal from the monitoring circuit21, the insulating element dedicated to signal transfer from the monitoring circuit21to the microcomputer22, of the second signal transfer section23b, is enabled to transfer signals from the monitoring circuit21to the microcomputer22. The dark-current mode of the monitoring circuit21is then considered malfunctioning.

Therefore, if it is determined in step S40that the response signal to the mode confirmation signal has been received by the microcomputer22from the monitoring circuit21, then it is determined in step S50that the monitoring circuit21is in an abnormal condition where the dark-current mode is malfunctioning. Further, in step S50, a mode-abnormality flag, which is indicative of whether or not the dark-current mode of the monitoring circuit21is functioning normally, is set to be “ON” (or “1”), and the flag state “ON” is stored in a memory of the microprocessor22, such as EEPROM. Thereafter, the abnormality diagnosis is ended.

On the other hand, if it is determined in step S40that the response signal to the mode confirmation signal has not been received by the microcomputer22from the monitoring circuit21, then it is determined in step S60that the monitoring circuit21is in a normal condition where the dark-current mode is functioning normally. Further, in step S60, the mode-abnormality flag is set to be “OFF” (or “0”), and the flag state “OFF” is stored in the memory of the microprocessor22. Thereafter, the abnormality diagnosis is ended.

In the abnormality diagnosis performed by the microcomputer22, The operation in step S10is performed by means (or a function) of the microcomputer22for transmitting to each monitoring circuit21the first mode-switching instruction signal for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode. The operation in step S30is performed by means (or a function) of the microcomputer22for transmitting the mode-confirmation signal to each monitoring circuit21after transmission of the first mode-switching instruction signal. The operations in steps S40, S50are performed by means (or a function) of the microcomputer22for determining that the dark-current mode of the monitoring circuit21is malfunctioning when having received from the monitoring circuit21the response signal to the mode-confirmation signal.

There will now be explained an abnormality response measure performed by the microcomputer22subsequently to the abnormality diagnosis with reference toFIG. 3.FIG. 3shows a flowchart of the abnormality response measure of the present embodiment. A control routine shown inFIG. 3is performed by the microcomputer22when the starting switch of the vehicle is turned on subsequently to the abnormality diagnosis ofFIG. 2.

At first, as shown inFIG. 3, it is determined in step S100whether or not the mode-abnormality flag is ON (or 1). If it is determined in step S100that the mode-abnormality flag is OFF (or 0), then abnormality response measure is ended.

If it is determined in step S100that the mode-abnormality flag is ON (or 1), then it is determined in step S200that the monitoring circuit21is in an abnormal condition where the dark-current mode is malfunctioning. Subsequently, a restriction process for suppressing adverse effects caused by malfunction of the dark-current mode is performed in step S300. Thereafter, the abnormality response measure is ended.

In the restriction process of the preset embodiment, an allowable lower limit that limits a state of charge (SOC) of the assembled battery1is raised greater than the allowable lower limit when the mode-abnormality flag is OFF (or 0). For example, assuming that the allowable lower limit of SOC of the assembled battery1when the mode-abnormality flag is OFF (or 0) is approximately 20%, the allowable lower limit is raised in a range of 60% to 80% in the restriction process.

This can prevent the assembled battery1from being over-discharged even when power of the assembled battery1is consumed by the monitoring circuits21.

Further, in the restriction process (step S300) of the present embodiment, transmission of the cell-voltage equalization instruction signal for instructing the monitoring circuit21to perform the cell-voltage equalization discharge is inhibited. This can prevent power of the assembled battery1from being unnecessarily consumed, thereby preventing the assembled battery1from being over-discharged.

In the abnormality response measure performed by the microcomputer22, the operation in step S300is performed by means (or a function) of the microcomputer22for raising the allowable lower limit of SOC of the assembled battery1and inhibiting transmission of the cell-voltage equalization instruction signal to the monitoring circuit21.

The battery monitoring apparatus2of the present embodiment as described above is configured such that the response signal to the mode confirmation signal is unable to be transmitted from the monitoring circuit21to the microcomputer22during the dark-current mode of the monitoring circuit21. The mode confirmation signal is transmitted from the microcomputer22to the monitoring circuit21subsequently to transmission of the first mode-switching instruction signal from the microcomputer22to the monitoring circuit21for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode. Subsequently to the transmission of the mode confirmation signal, the microcomputer22determines whether or not the response signal to the mode confirmation signal has been received from the monitoring circuit21. When it is determined that the response signal has been received from the monitoring circuit21, then it is determined that the dark-current mode is malfunctioning.

As described above, the battery monitoring apparatus2of the present embodiment allows the microcomputer22to diagnose whether or not the dark-current mode of each monitoring circuit21is functioning normally.

There will now be explained some modifications of the above embodiment that may be devised without departing from the spirit and scope of the present invention.

(1) In the abnormality diagnosis of the above described embodiment, the microcomputer22transmits the mode confirmation signal to each monitoring circuit21only once after transmission of the first mode-switching instruction signal for instructing the monitoring circuit21to transition from the normal mode to the dark-current mode. Alternatively, the microcomputer22may transmit the mode confirmation signal to each monitoring circuit21several times at predetermined time intervals after the transmission of the first mode-switching instruction signal. This allows the microcomputer22to determine whether the dark-current mode of the monitoring circuit21is malfunctioning temporarily or continuously.

(2) In the above described embodiment, the first signal transfer section23aincludes a single optically-coupled insulating element, and the second signal transfer section23bincludes a pair of optically-coupled insulating elements. Alternatively, each of these optically-coupled insulating elements may be replaced by an inductively-coupled (transformer coupling) insulating element or by a capacitively-coupled (capacitor coupling) insulating element.

(3) In the above described embodiment, the signal transfer circuit23includes the first signal transfer section23adedicated to transferring of the first and second mode-switching instruction signals from the microcomputer22to the monitoring circuit21. Alternatively, in some embodiments where the mode switcher214aof the power supply circuit214of the monitoring circuit21can be controlled by the first and second mode-switching instruction signals transmitted from the microcomputer22, the second signal transfer section23bof the signal transfer circuit23may be used to transfer the first and second mode-switching instruction signals from the microcomputer22to the monitoring circuit21, where the first signal transfer section23amay be removed.

Preferably, as described above, the second signal transfer section23bincludes a pair of insulating elements adapted to transfer communication signals at a high rate. However, when the communication signals are not required to be transferred at a high rate, the second signal transfer section23bmay include a pair of insulating elements adapted to transfer the communication signals at a lower rate.

(4) Preferably, as described above, when it is determined in the abnormality diagnosis that the monitoring circuit21is in an abnormal condition where the dark-current mode of the monitoring circuit21is malfunctioning, the abnormality response measure is performed upon subsequent turning on of the starting switch of the vehicle. Alternatively, for example, the abnormality response measure may not be performed when malfunction of the dark-current mode is likely to cause less adverse effects.

(5) In the restriction process of the abnormality response measure of the above described embodiment, the allowable lower limit of SOC of the assembled battery1is raised and the cell-voltage equalization in the monitoring circuit21is inhibited. Alternatively, in the restriction process of the abnormality response measure, the allowable lower limit of SOC of the assembled battery1may be raised, or else the cell-voltage equalization in the monitoring circuit21may be inhibited. Further, in the abnormality response measure, a user or maintenance personnel may be informed of occurrence of the abnormality.

(6) Preferably, as described above, the monitoring circuit21includes the cell-voltage equalization circuit212. Alternatively, when cell-to-cell voltage variations are of less concern, the cell-voltage equalization circuit212may be removed. In such an alternative embodiment, measures other than the inhibition of the cell-voltage equalization may be performed in the abnormality response measure.

(7) In the above described embodiment, the diagnosis of abnormality in the monitoring circuit21(the control routine shown inFIG. 2) is performed during the OFF state of the starting switch of the vehicle. Alternatively, for example, the diagnosis of abnormality in the monitoring circuit21may be triggered by an external instruction signal from a control device external to the battery monitoring apparatus2during the ON state of the starting switch of the vehicle.

In the above described embodiment, the abnormality response measure (the control routine shown inFIG. 3) is performed when the starting switch of the vehicle is turned on subsequently to the abnormality diagnosis ofFIG. 2. Alternatively, the abnormality response measure may be performed immediately after it is determined in the abnormality diagnosis that the monitoring circuit21is in an abnormal condition where the dark-current mode of the monitoring circuit21is malfunctioning or may be performed a prescribed time period after the abnormality diagnosis.

(8) In the above described embodiment, the battery monitoring apparatus2is applied to the assembled battery1that is a vehicle-mounted high-voltage battery. Alternatively, the battery monitoring apparatus2may be applied to the other kinds of batteries.