Diagnostic apparatus and diagnostic method

A diagnostic apparatus includes a capacitor capable of being connected in parallel with a first battery, first switches that switch the connection state between a plurality of the first batteries and the capacitor, a detection circuit, a second switch that switches the connection state between the capacitor and the detection circuit, a changeover switch that switches the connection state between a second battery and the capacitor, a controller, and a diagnostic unit. The controller turns on the changeover switch to apply a voltage to the capacitor from the second battery, the detection circuit subsequently detects a potential difference or a discharge current, and the diagnostic unit diagnoses at least one of the capacitor, a lowermost first switch, and the second switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of Japanese Patent Application No. 2018-071107 filed Apr. 2, 2018, Japanese Patent Application No. 2019-016395 filed Jan. 31, 2019, and Japanese Patent Application No. 2019-016397 filed Jan. 31, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a diagnostic apparatus and a diagnostic method.

BACKGROUND

A known flying capacitor type battery monitoring apparatus indirectly measures the voltage of a battery by charging a capacitor with the voltage of the battery, subsequently separating the battery from the capacitor, and detecting the voltage of the capacitor in this state with a voltage detection circuit.

In such a flying capacitor type battery monitoring apparatus, the performance of fault diagnosis of a switch that switches the connection between the capacitor and the voltage detection circuit is known. For example, in patent literature JP 2014-182089 A, a short-circuit fault is judged to have occurred in the switch when the voltage detection circuit detects voltage despite an instruction having been sent to turn off the switch that switches the connection between the capacitor and the voltage detection circuit.

SUMMARY

The aforementioned battery monitoring apparatus uses the battery targeted for voltage detection as the power supply for diagnosis. Hence, the reliability of the diagnosis depends on the battery.

In light of these considerations, the present disclosure aims to provide a diagnostic apparatus and a diagnostic method that can diagnose the state of a flying capacitor or a switch without being dependent on the battery targeted for voltage detection.

To resolve the aforementioned problem, a diagnostic apparatus according to a first aspect includes:

a capacitor capable of being connected in parallel with each first battery among a plurality of first batteries connected in series;

a plurality of first switches configured to switch a connection state between the plurality of first batteries and the capacitor;

a detection circuit configured to detect a potential difference between both terminals of the capacitor or to detect a discharge current from the capacitor;

a second switch configured to switch a connection state between the capacitor and the detection circuit;

a changeover switch configured to switch a connection state between the capacitor and a second battery that differs from the first batteries;

a controller configured to control the first switches, the second switch, and the changeover switch; and

a diagnostic unit configured to diagnose at least one of the capacitor, a lowermost first switch among the plurality of first switches, and the second switch, the lowermost first switch being connected to ground;

wherein the detection circuit detects the potential difference or the discharge current after the controller turns on the changeover switch to apply a voltage to the capacitor from the second battery; and

wherein the diagnostic unit diagnoses at least one of the capacitor, the lowermost first switch, and the second switch.

To resolve the aforementioned problem, a diagnostic method according to a second aspect is a diagnostic method in a diagnostic apparatus including a capacitor capable of being connected in parallel with each first battery among a plurality of first batteries connected in series, a plurality of first switches configured to switch a connection state between the plurality of first batteries and the capacitor, a detection circuit configured to detect a potential difference between both terminals of the capacitor or to detect a discharge current from the capacitor, a second switch configured to switch a connection state between the capacitor and the detection circuit, and a changeover switch configured to switch a connection state between the capacitor and a second battery that differs from the first batteries, the diagnostic method including:

detecting, using the detection circuit, the potential difference or the discharge current after the changeover switch is turned on to apply a voltage to the capacitor from the second battery; and

diagnosing at least one of the capacitor, a lowermost first switch among the plurality of first switches, and the second switch, the lowermost first switch being connected to ground.

To resolve the aforementioned problem, a diagnostic apparatus according to a third aspect includes:

a detection circuit configured to detect voltage or current;

a detection connection circuit capable of connecting a first battery to the detection circuit;

a diagnostic connection circuit capable of connecting a different power supply than the first battery to the detection connection circuit; and

a diagnostic unit configured to connect the diagnostic connection circuit to the detection connection circuit and diagnose the detection connection circuit.

The diagnostic apparatus according to the first aspect can diagnose the state of a flying capacitor or a switch without being dependent on the battery targeted for voltage detection.

The diagnostic method according to the second aspect can diagnose the state of a flying capacitor or a switch without being dependent on the battery targeted for voltage detection.

The diagnostic apparatus according to the third aspect can diagnose the state of a flying capacitor or a switch without being dependent on the battery targeted for voltage detection.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described below in detail with reference to the drawings.

As illustrated inFIG. 1, a diagnostic apparatus100according to an embodiment connects to first batteries200A to200E. The diagnostic apparatus100and the first batteries200A to200E may be mounted in a vehicle such as a vehicle provided with an internal-combustion engine, for example a gasoline engine or a diesel engine, or a hybrid vehicle that can be driven by power from both an internal-combustion engine and an electric motor.

The first batteries200A to200E may be included in a battery pack. The battery pack may include the diagnostic apparatus100. The battery pack may include a battery management system (BMS). The diagnostic apparatus100may function as the BMS or be included in the BMS.

In the example inFIG. 1, the first battery200A, the first battery200B, the first battery200C, the first battery200D, and the first battery200E are connected in series. When no distinction need be made, the first batteries200A to200E are collectively referred to below as the first batteries200.

Five first batteries200are connected in series in the example inFIG. 1, but the number of first batteries200is not limited to five. Any number, greater than one, of first batteries200may be connected in series.

The first battery200may be a secondary battery with a wide state of charge (SOC) bandwidth. The SOC bandwidth of the first battery200may, for example, be 10% to 90%. The first battery200is, for example, a lithium-ion battery, a nickel-hydrogen battery, or the like but is not limited to these examples and may be another secondary battery.

The diagnostic apparatus100includes first switches1A to1K, second switches2A,2B, a fourth switch4, a capacitor10, a resistor11, a detection circuit20, a constant voltage circuit30, a capacitor voltage detection circuit40, a sub-detection circuit50, a controller60, and a storage70.

The capacitor10can connect in parallel to the first batteries200A to200E via the first switches1A to1K. The capacitor10can charge using power supplied from the first battery200. The detection circuit20can detect a potential difference between both terminals of the capacitor10charged by the first battery200. In other words, the capacitor10functions as a flying capacitor for flying capacitor type voltage measurement.

The first switches1A to1K switch the connection state between the first battery200and the capacitor10in response to an instruction from the controller60. When the first switches1A to1K are controlled to turn on, the ends thereof become conductive. When the first switches1A to1K are controlled to turn off, the ends thereof are insulated. For the sake of readability, the control lines from the controller60to the first switches1A to1K are omitted fromFIG. 1.

The first switch1A, the first switch1C, the first switch1E, the first switch1G, and the first switch1J respectively switch the connection state of a positive electrode of the first battery200A, the first battery200B, the first battery200C, the first battery200D, and the first battery200E to a first node10A. The first node10A is a node connected to one end of the capacitor10.

The first switch1B, the first switch1D, the first switch1F, the first switch1H, and the first switch1K respectively switch the connection state of a negative electrode of the first battery200A, the first battery200B, the first battery200C, the first battery200D, and the first battery200E to a second node10B. The second node10B is a node connected to the other end of the capacitor10.

When no distinction need be made, the first switches1A to1K are collectively referred to below as the first switches1. The first switches1may be mechanical switches that have a movable part. Each first switch1may have a contact and be configured to switch between a conducting state and an insulated state by opening and closing of the contact. Each first switch1may, for example, be an electromagnetic relay.

The second switches2A and2B switch the connection state between the capacitor10on one side and the detection circuit20and sub-detection circuit50on the other side in accordance with an instruction from the controller60. When the second switches2A and2B are controlled to turn on, the ends thereof become conductive. When the second switches2A and2B are controlled to turn off, the ends thereof are insulated. For the sake of readability, the control lines from the controller60to the second switches2A and2B are omitted fromFIG. 1.

The second switch2A switches the connection state between the first node10A on one side and the detection circuit20and sub-detection circuit50on the other side. The second switch2B switches the connection state between the second node10B and ground. The second switch2A is also referred to as the upper second switch. The second switch2B is also referred to as the lower second switch.

When no distinction need be made, the second switches2A and2B are collectively referred to below as the second switches2. The second switches2may be mechanical switches that have a movable part. Each second switch2may have a contact and be configured to switch between a conducting state and an insulated state by opening and closing of the contact. Each second switch2may, for example, be an electromagnetic relay.

The fourth switch4switches the connection state between the first node10A and the resistor11in response to an instruction from the controller60. When the fourth switch4is controlled to turn on, the ends thereof become conductive. When the fourth switch4is controlled to turn off, the ends thereof are insulated. The fourth switch4may be a mechanical switch that has a movable part. The fourth switch4may have a contact and be configured to switch between a conducting state and an insulated state by opening and closing of the contact. The fourth switch4may, for example, be an electromagnetic relay. For the sake of readability, the control line from the controller60to the fourth switch4is omitted fromFIG. 1.

One end of the resistor11is connected to the fourth switch4, and the other end is grounded. The fourth switch4is normally controlled to be off. When the fourth switch4is turned on, the capacitor10discharges via the resistor11. In other words, the fourth switch4and the resistor11are configured as a discharge circuit for discharging the charge stored in the capacitor10.

The detection circuit20can detect a potential difference between both terminals of the capacitor10when the second switches2are on. The detection circuit20includes an operational amplifier21and an A/D converter22. The detection circuit20can detect a potential difference between both terminals of the capacitor10based on input to the operational amplifier21.

The detection circuit20can detect the voltage of each first battery200by detecting the potential difference between both terminals of the capacitor10. For example, the detection circuit20can detect the voltage of the first battery200A by detecting the potential difference between both terminals of the capacitor10when the first switch1A and the first switch1B are turned on to charge the capacitor10with the voltage of the first battery200A and are subsequently turned off. The detection circuit20can also detect the voltage of the first batteries200B to200E in a similar way.

The operational amplifier21forms part of a voltage follower in which the negative input terminal and the output terminal are connected. The voltage follower configured to include the operational amplifier21functions as a buffer and outputs the voltage inputted into the detection circuit20to the A/D converter22.

A voltage follower configured by the operational amplifier21upstream from the A/D converter22is only one example. The configuration of the detection circuit20is not limited to this example. Instead of a voltage follower, an amplifier that has a different amplification factor than 1 may be arranged upstream from the A/D converter22. In other words, an amplification circuit having any amplification factor, such as a voltage follower with an amplification factor of one or an amplifier with a different amplification factor than one, may be arranged upstream from the A/D converter22.

The A/D converter22includes an A/D input terminal22A. The A/D converter22converts an analog voltage, inputted to the A/D input terminal22A from the voltage follower configured by the operational amplifier21, to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60.

The A/D converter22also includes A/D input terminals22B,22C. The A/D input terminal22B is connected to the first node10A via a third switch3A and a resistor41. The A/D input terminal22B is grounded via a resistor42. The A/D input terminal22C is connected to the second node10B via a third switch3B and a resistor43. The A/D input terminal22C is grounded via a resistor44.

The A/D converter22converts an analog voltage inputted to the A/D input terminal22B to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60. The A/D converter22converts an analog voltage inputted to the A/D input terminal22C to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60.

The constant voltage circuit30includes a control terminal30A and an output terminal30B. The constant voltage circuit30outputs a constant voltage from the output terminal30B in accordance with a control signal inputted from the controller60to the control terminal30A. The constant voltage circuit30can output constant voltage to the capacitor10. In the present embodiment, the constant voltage circuit30outputs a constant voltage when a high signal is inputted and suspends output of the constant voltage when a low signal is inputted from the controller60to the control terminal30A.

FIG. 2illustrates an example configuration of the constant voltage circuit30. In addition to the control terminal30A and the output terminal30B, the constant voltage circuit30includes a power supply terminal30C, not illustrated inFIG. 1.

The constant voltage circuit30receives a power supply voltage from the power supply terminal30C. As illustrated inFIG. 2, the constant voltage circuit30receives the power supply voltage at the power supply terminal30C from a second battery300via a voltage conversion circuit400, for example.

The second battery300is a different battery from the first battery200. The second battery300may be a secondary battery having a narrower SOC bandwidth than the first batteries200. The second battery300is, for example, a lead-acid battery but is not limited to this example and may be another secondary battery. While not illustrated, the second battery300is connected in parallel with the first batteries200and supplies power to auxiliary equipment in the vehicle.

The voltage conversion circuit400converts the voltage supplied from the second battery300and supplies the converted voltage to the power supply terminal30C of the constant voltage circuit30. For example, the voltage conversion circuit400steps down the 12 V voltage supplied from the second battery300to 5 V and supplies the 5 V voltage to the power supply terminal30C of the constant voltage circuit30.

As illustrated inFIG. 2, the constant voltage circuit30includes an NPN transistor31, a PNP transistor32, a capacitor33, resistors34to38, and a diode39.

When a high signal is received at the control terminal30A of the constant voltage circuit30from the controller60, the base voltage of the NPN transistor31rises, and the NPN transistor31turns on. When the NPN transistor31turns on, the base voltage of the PNP transistor32lowers, and the PNP transistor32turns on. When the PNP transistor32turns on, current can flow from the output terminal30B to the first node10A. When the second switch2B illustrated inFIG. 1is on, for example, the capacitor10can be charged by current provided from the output terminal30B of the constant voltage circuit30. A constant voltage is supplied at this time to the output terminal30B of the constant voltage circuit30. The constant voltage corresponds to the power supply voltage inputted to the power supply terminal30C, reduced by the voltage drop due to the resistor34and the PNP transistor32. In this way, the PNP transistor32can function as a changeover switch that switches the connection state between the second battery300and the capacitor10in response to an instruction from the controller60. When the PNP transistor32is on, the voltage from the second battery300can be applied to the capacitor10. The cathode of the diode39is connected to the first battery200side to prevent current from the first battery200from flowing in reverse.

The constant voltage circuit30thus generates a constant voltage based on the power supply voltage supplied from the second battery300, which is a secondary battery with a narrow SOC bandwidth, such as a lead-acid battery. In this way, the constant voltage circuit30can stably generate a constant voltage of a predetermined magnitude or higher.

The constant voltage outputted by the constant voltage circuit30can be a smaller voltage than the maximum voltage suppliable by the first batteries200A to200E connected in series, i.e. the voltage between the positive terminal of the first battery200A and the negative terminal of the first battery200E. For example, when the maximum voltage suppliable by each first battery200is 2.4 V, the maximum voltage suppliable by the first batteries200A to200E connected in series is 12 V. In this case, the constant voltage outputted by the constant voltage circuit30can be smaller than 12 V. This can reduce the risk of fault in the operational amplifier21of the detection circuit20when the constant voltage outputted by the constant voltage circuit30is inputted to the operational amplifier21.

The constant voltage outputted by the constant voltage circuit30can be larger than the maximum voltage suppliable by each first battery200. For example, when the maximum voltage suppliable by each first battery200is 2.4 V, the constant voltage outputted by the constant voltage circuit30can be larger than 2.4 V. When, during diagnostic processing, the controller60detects the voltage from the constant voltage circuit30that charged the capacitor10, the controller60can thereby confirm that the detected voltage is not the voltage supplied from the first battery200.

The diagnostic apparatus100can perform fault diagnosis using the constant voltage outputted by the constant voltage circuit30. If the voltage of the first battery200, which is the target of detection, were used as a reference voltage when the diagnostic apparatus100performs fault diagnosis, then it might not be possible to correctly detect fault of the capacitor10, the first switches1, the second switches2, and the like when the battery capacity of the first battery200is reduced. The diagnostic apparatus100according to the present embodiment, however, performs fault diagnosis using the constant voltage outputted by the constant voltage circuit30and can therefore diagnose the state of the capacitor10, the first switches1, the second switches2, and the like without depending on the first battery200.

The description returns toFIG. 1.

The capacitor voltage detection circuit40is a circuit for detecting the voltage of both terminals of the capacitor10, i.e. the first node10A and the second node10B, without using the operational amplifier21of the detection circuit20.

The capacitor voltage detection circuit40includes the third switches3A and3B, the resistor41, the resistor42, the resistor43, and the resistor44.

The third switch3A switches the connection state between the first node10A and the resistor41in response to an instruction from the controller60. The third switch3B switches the connection state between the second node10B and the resistor43in response to an instruction from the controller60. When the third switches3A and3B are controlled to turn on, the ends thereof become conductive. When the third switches3A and3B are controlled to turn off, the ends thereof are insulated. For the sake of readability, the control lines from the controller60to the third switches3A and3B are omitted fromFIG. 1.

By being controlled to turn on, the third switch3A can connect the first node10A and the A/D input terminal22B while bypassing the operational amplifier21. By being controlled to turn on, the third switch3B can connect the second node10B and the A/D input terminal22C while bypassing the operational amplifier21. The first node10A is connected to the terminal of the first switch1A, the first switch1C, the first switch1E, the first switch1G, and the first switch1J on the side not connected to the first battery200. The second node10B is connected to the terminal of the first switch1B, the first switch1D, the first switch1F, the first switch1H, and the first switch1K on the side not connected to the first battery200.

When no distinction need be made, the third switches3A and3B are collectively referred to below as the third switches3. The third switches3may be mechanical switches that have a movable part. Each third switch3may have a contact and be configured to switch between a conducting state and an insulated state by opening and closing of the contact. Each third switch3may, for example, be an electromagnetic relay.

One end of the resistor41connects to the first node10A via the third switch3A. The other end of the resistor41connects to the A/D input terminal22B of the A/D converter22and to the resistor42.

One end of the resistor42connects to the A/D input terminal22B of the A/D converter22and to the resistor41. The other end of the resistor42is grounded.

One end of the resistor43connects to the second node10B via the third switch3B. The other end of the resistor43connects to the A/D input terminal22C of the A/D converter22and to the resistor44.

One end of the resistor44connects to the A/D input terminal22C of the A/D converter22and to the resistor43. The other end of the resistor44is grounded.

If one of the first switch1A, the first switch1C, the first switch1E, the first switch1G, and the first switch1J is turned on while the constant voltage circuit30is off and the third switch3A is on, then the voltage on the positive electrode side of the first battery200connected to the first switch1that is on is divided at the resistor41and the resistor42and supplied to the A/D input terminal22B of the A/D converter22.

If all of the first switch1A, the first switch1C, the first switch1E, the first switch1G, and the first switch1J are turned off while the constant voltage circuit30is off and the third switch3A is on, then 0 V is supplied to the A/D input terminal22B of the A/D converter22via the grounded resistor42.

If one of the first switch1B, the first switch1D, the first switch1F, and the first switch1H is turned on while the constant voltage circuit30is off and the third switch3B is on, then the voltage on the negative electrode side of the first battery200connected to the first switch1that is on is divided at the resistor43and the resistor44and supplied to the A/D input terminal22C of the A/D converter22.

If all of the first switch1B, the first switch1D, the first switch1F, and the first switch1H are turned off while the constant voltage circuit30is off and the third switch3B is on, then 0 V is supplied to the A/D input terminal22C of the A/D converter22via the grounded resistor44.

When the third switch3A is turned off, 0 V is supplied to the A/D input terminal22B of the A/D converter22via the grounded resistor42. When the third switch3B is turned off, 0 V is supplied to the A/D input terminal22C of the A/D converter22via the grounded resistor44.

The sub-detection circuit50can detect a potential difference between both terminals of the capacitor10when the second switches2are on. The sub-detection circuit50is a circuit for diagnosing whether the operational amplifier21of the detection circuit20is operating normally. The sub-detection circuit50operates together with the detection circuit20when the detection circuit20is operating.

The operational amplifier51forms part of a voltage follower in which the negative input terminal and the output terminal are connected. The voltage follower configured to include the operational amplifier51functions as a buffer and outputs the voltage inputted into the sub-detection circuit50to the A/D converter52.

The A/D converter52converts an analog voltage, inputted from the voltage follower configured by the operational amplifier51, to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60.

InFIG. 1, the A/D converter52is illustrated as an A/D converter with a different configuration than the A/D converter22.

The controller60connects to each component of the diagnostic apparatus100in a communicable manner by wired or wireless communication. The controller60may output control instructions to each component and acquire information from each component.

The controller60controls the first switches1, the second switches2, the third switches3, and the fourth switch4to be on or off. The controller60controls the constant voltage circuit30to be on or off. When the controller60controls the constant voltage circuit30to be on, the constant voltage circuit30can supply constant voltage to the first node10A.

The controller60can acquire digital signals, from the A/D converter22of the detection circuit20, corresponding to the analog voltages inputted to the A/D input terminals22A,22B,22C. The controller60can acquire digital signals, from the A/D converter52of the sub-detection circuit50, corresponding to the analog voltage inputted to the sub-detection circuit50.

The controller60may be a processor, such as a central processing unit (CPU), that executes programs with prescribed control procedures. When the diagnostic apparatus100is mounted in a vehicle, the controller60may be configured as an electric control unit or engine control unit (ECU) of the vehicle.

The storage70is connected to the controller60and stores information acquired from the controller60. The storage70may also function as a working memory of the controller60. The storage70may store programs executed by the controller60. The storage70may be a semiconductor memory but is not limited to this example. The storage70may be configured as a magnetic storage medium or as another storage medium. The storage70may also be included as a portion of the controller60.

In the present embodiment, the first switch1, the capacitor10, and the second switch2A can function as a detection connection circuit for making the first battery200connectable to the detection circuit20. The constant voltage circuit30can function as a diagnostic connection circuit for making the second battery300connectable to the detection connection circuit.

The controller60of the diagnostic apparatus100can diagnose the constituent elements of the diagnostic apparatus100by following the procedures illustrated in the flowchart ofFIG. 3. The controller60can diagnose whether a fault has occurred in the first switches1, the second switches2, the capacitor10, and the operational amplifier21.

First, the controller60performs diagnosis mainly using the capacitor voltage detection circuit40(step S1). In step S1, the controller60diagnoses the first switches1other than the first switch1K that is the lowermost first switch connected to ground, i.e. the first switches1A to1J. The diagnosis by the controller60in step S1is referred to below as “diagnosis 1”.

Subsequently, the controller60performs diagnosis mainly using the detection circuit20(step S2). The controller60diagnoses the lowermost first switch1K in step S2. The diagnosis by the controller60in step S2is referred to below as “diagnosis 2”.

Subsequently, the controller60performs diagnosis mainly using the constant voltage circuit30(step S3). The controller60diagnoses the capacitor10, the second switches2, the operational amplifier21, and the lowermost first switch1K in step S3. The diagnosis by the controller60in step S3is referred to below as “diagnosis 3”.

Subsequently, the controller60performs diagnosis mainly using the sub-detection circuit50(step S4). The controller60diagnoses the operational amplifier21in step S4. The diagnosis by the controller60in step S4is referred to below as “diagnosis 4”.

When a fault is judged to have occurred in any of the constituent elements of the diagnostic apparatus100in one of the stages from diagnosis 1 to diagnosis 4, the controller60may raise a fault flag and suspend subsequent diagnostic processing.

The controller60is described in the present embodiment as controlling the first switches1, the second switches2, the third switches3, the fourth switch4, and the constant voltage circuit30to be on or off and to diagnose the first switches1, the second switches2, the capacitor10, and the operational amplifier21. However, this configuration is not limiting. For example, a processor may include the controller60and a diagnostic unit. In this case, the controller60may perform control and the like to turn the first switches1, the second switches2, the third switches3, the fourth switch4, and the constant voltage circuit30on or off, and the diagnostic unit may perform a diagnosis and the like of the first switches1, the second switches2, the capacitor10, and the operational amplifier21.

Diagnosis 1 through diagnosis 4 are described in detail below.

Diagnosis 1 includes the following two diagnoses.

Diagnosis 1-1: short-circuit fault diagnosis of first switches1A to1J Diagnosis 1-2: open fault diagnosis of first switches1A to1J

Diagnosis 1-1 is a short-circuit fault diagnosis of the first switches1A to1J other than the lowermost first switch1K. Diagnosis 1-1 is described with reference to the block diagram inFIG. 4. Note thatFIG. 4is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 1-1, the controller60controls the first switches1to be off, the second switches2to be off, and the third switches3to be on. The controller60also controls the constant voltage circuit30illustrated inFIG. 1to be off.

At this time, if a short-circuit fault has occurred in any of the first switches1A to1J, the A/D converter22detects the voltage of the first battery200connected to the first switch1with the short-circuit fault. The A/D converter22detects this voltage at either of the A/D input terminals22B,22C.

As the assumed fault site,FIG. 4illustrates the case of the first switch1A having a short-circuit fault. In this case, the first switch1A remains short-circuited even when controlled to be off. The A/D input terminal22B of the A/D converter22therefore detects the voltage at the positive electrode side of the first battery200A.

When none of the first switches1A to1J has a short-circuit fault, the A/D converter22detects 0 V at both of the A/D input terminals22B,22C.

In other words, when the controller60has controlled the first switches1to be off, the second switches2to be off, the third switches3to be on, and the constant voltage circuit30to be off and then detects a voltage other than 0 V, the controller60can judge that one of the first switches1A to1J possibly has a short-circuit fault. The controller60may judge that a voltage other than 0 V is detected when a voltage equal to or greater than a predetermined threshold is detected.

In the present embodiment, the diagnostic apparatus100performs diagnosis 1-1 as an initial diagnosis and confirms that no short-circuit fault has occurred in the first switches1A to1J. The reason is that if one of the first switches1A to1J has a short-circuit fault, a voltage greater than the voltage tolerated by the operational amplifier21might be applied to the operational amplifier21when the second switches2are turned on, and the operational amplifier21might experience a fault.

The controller60performs diagnosis 1-1 before executing processing to turn the second switches2on. When judging that one of the first switches1A to1J has a short-circuit fault, the controller60maintains the second switches2in the off state and suspends subsequent diagnostic processing. In this way, the diagnostic apparatus100can reduce the risk of the operational amplifier21experiencing a fault due to application of a relatively high voltage.

Diagnosis 1-2 is an open fault diagnosis of the first switches1A to1J other than the lowermost first switch1K. Diagnosis 1-2 is described with reference to the block diagram inFIG. 5and the timing chart inFIG. 6. Note thatFIG. 5is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 1-2, the controller60controls the second switches2to be off and the third switches3to be on. The controller60also controls the constant voltage circuit30illustrated inFIG. 1to be off.

The controller60turns the first switches1connected to both terminals of the first battery200on/off from the low potential side to the high potential side of the first battery200. In other words, from a state in which all of the first switches1are off, the controller60first turns the first switches1J,1K on/off. Subsequently, the controller60controls the first switches1G,1H to be on/off. The controller60continues this processing until the first switches1A,1B are turned on/off.

The controller60may turn the first switches1connected to both terminals of the first battery200on/off from the high potential side to the low potential side of the first battery200instead of from the low potential side to the high potential side.

FIG. 6is a timing chart for when the controller60turns the first switches1A,1B on/off. After turning the first switches1A,1B on, the controller60measures the voltage inputted to the A/D input terminals22B,22C at predetermined measurement timings t1, t2. Subsequently, the controller60turns the first switches1A,1B off. The controller60may calculate the average of the voltages measured at t1, t2and treat the average as the detected voltage.

In the example illustrated inFIG. 6, the controller60measures the voltage at two timings, t1and t2, but the measurement timing is not limited to this example. The controller60may measure the voltage at one timing or measure the voltage at three or more timings. When measuring the voltage at a plurality of timings, the controller60may calculate the average and treat the average as the detected voltage. The number of measurement timings and the calculation of the average are similar in diagnosis 2 and beyond as well. Hence, a description of the number of measurement timings and the calculation of the average is omitted in diagnosis 2 and beyond.

At this time, if an open fault has occurred in any of the first switches1A to1J, then when the first switch1that has the open fault is turned on, the A/D converter22detects 0 V at the A/D input terminal22B or22C to which this first switch1is connected.

FIG. 5illustrates the state when the first switches1A,1B are turned on, assuming that the fault site is an open fault at the first switch1A. In this case, the first switch1A remains open even when controlled to turn on. The A/D input terminal22B of the A/D converter22therefore detects 0 V. Since the first switch1B is on normally, the A/D input terminal22C of the A/D converter22detects the voltage at the negative electrode side of the first battery200A, divided by the resistor43and the resistor44.

The timing chart ofFIG. 6illustrates two states: the case of the first switch1A being in the normal state, and the case of the first switch1A having an open fault. As illustrated inFIG. 6, the A/D input terminal22B of the A/D converter22detects the voltage at the positive electrode side of the first battery200A, divided by the resistor41and the resistor42, when the first switch1A is in a normal state. When the first switch1A has an open fault, the A/D input terminal22B of the A/D converter22detects 0 V.

In other words, the controller60controls the second switches2to be off, the third switches3to be on, and the constant voltage circuit30to be off, and in this state, turns the first switches1on/off in order. If the controller60detects 0 V when one of the first switches1A to1J is turned on, the controller60can judge that this first switch1possibly has an open fault. The controller60may judge that 0 V is detected when a voltage equal to or less than a predetermined threshold is detected.

Diagnosis 2 is an open fault diagnosis of the first switch1K, which is the lowermost switch among the first switches1. Diagnosis 2 is described with reference to the block diagram inFIG. 7and the timing chart inFIG. 8. Note thatFIG. 7is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 2, the controller60controls the third switches3and the constant voltage circuit30illustrated inFIG. 1to be off. The controller60controls the first switches1and the second switches2all to be off before starting diagnosis 2.

FIG. 8illustrates a timing chart in diagnosis 2. The controller60turns on/off the first switches1J,1K connected to both terminals of the first battery200E, which is the battery on the lowest potential side among the first batteries200. Subsequently, the controller60turns the second switches2on and then measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t1to t4. The controller60subsequently turns the second switches2off. The controller60may calculate the average of the voltages measured at t1to t4and treat the average as the detected voltage.

If the first switches1J,1K are in a normal state when the controller60turns the first switches1J,1K on, then the potential difference between both terminals of the capacitor10rises to the voltage of the first battery200E, as illustrated inFIG. 8. Subsequently, even if the controller60turns the first switches1J,1K off, this potential difference is maintained between both terminals of the capacitor10. In this case, after turning the second switches on, the controller60detects a voltage corresponding to the voltage of the first battery200E at the predetermined measurement timings t1to t4.

As the assumed fault site,FIG. 7illustrates the case of the first switch1K having an open fault. In this case, even if the first switches1J,1K are controlled to turn on, the first switch1K remains open. Consequently, the capacitor10is not charged, and the potential difference between both terminals of the capacitor10remains at 0 V, as illustrated inFIG. 8. In this case, after turning the second switches on, the controller60detects 0 V at the predetermined measurement timings t1to t4.

The capacitor10is also not charged if the first switch1J, rather than the first switch1K, has an open fault. When the first switch1J has an open fault, however, an open fault is detected in diagnosis 1-2, and the diagnostic processing is suspended at that point. Accordingly, if diagnosis 2 is performed and 0 V is detected at the predetermined measurement timings t1to t4, the controller60can judge that the first switch1K possibly has an open fault.

The sequence based on the timing chart illustrated inFIG. 8is similar to the sequence when the controller60detects the voltage of the first battery200during normal processing. Accordingly, the controller60can perform diagnosis 2 with a similar sequence to the normal voltage detection sequence of the first battery200.

Diagnosis 3 includes the following seven diagnoses.

Diagnosis 3-1: leak or short-circuit fault diagnosis of capacitor10

Diagnosis 3-2: open fault diagnosis of second switches2

Diagnosis 3-3: output voltage sticking diagnosis (0 V) of operational amplifier

Diagnosis 3-4: short-circuit fault diagnosis of second switch2A

Diagnosis 3-5: short-circuit fault diagnosis of second switch2B

Diagnosis 3-6: short-circuit fault diagnosis of first switch1K

Diagnosis 3-7: output voltage sticking diagnosis (5 V) of operational amplifier

Diagnosis 3-1 diagnoses a leak fault or short-circuit fault in the capacitor10.

Diagnosis 3-1 is described with reference to the block diagram inFIG. 9and the timing chart inFIG. 10. As illustrated inFIG. 9, the target of fault diagnosis in diagnosis 3-1 is the capacitor10.FIG. 9is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-1, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-1.

FIG. 10illustrates a timing chart in diagnosis 3-1. The controller60outputs a high signal to the control terminal30A to turn the constant voltage circuit30on and also turns the second switches2on. After turning the constant voltage circuit30and the second switches2on, the controller60measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t1to t4. The measurement at the predetermined measurement timings t1to t4is also referred to below as “measurement1”.

Subsequently, the controller60outputs a low signal to the control terminal30A to turn the constant voltage circuit30off. After turning the constant voltage circuit30off, the controller60measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t5to t8. The measurement at the predetermined measurement timings t5to t8is also referred to below as “measurement2”.

The controller60may, insofar as possible, match the conditions of the predetermined measurement timings t1to t4and t5to t8to the conditions of the measurement timing when the voltage of the first battery200is detected during normal processing. For example, when the number of measurements during normal processing is four, and the four measurement values are averaged, the controller60may measure four times at timings t1to t4in measurement1as well and average the four measurement values. The controller60may measure four times at timings t5to t8in measurement2as well and average the four measurement values. The controller60may, for example, set the delay time from when the second switches2are turned on until measurement2is started to be the same as the delay time from when the second switches2are turned on until measurement is started during normal processing. When the conditions of the predetermined measurement timings t1to t4and t5to t8during diagnosis 3-1 are matched in this way, insofar as possible, to the conditions of the measurement timing when the voltage of the first battery200is detected during normal processing, the controller60can perform measurement1and measurement2with little error. With regard to the measurements1to6illustrated inFIGS. 12, 14, 16, 18, 20, 22, and 24as well, the conditions of the measurement timings may be matched, insofar as possible, to the conditions of the measurement timings when the voltage of the first battery200is detected during normal processing.

After the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is charged by the constant voltage supplied from the constant voltage circuit30when the capacitor10is in a normal state. During measurement1, the controller60in this case detects a voltage corresponding to the constant voltage supplied by the constant voltage circuit30. The capacitor10can be charged by the constant voltage supplied from the constant voltage circuit30even when the capacitor10has a leak fault. During measurement1, the controller60in this case can detect a voltage corresponding to the constant voltage supplied by the constant voltage circuit30. The capacitor10is not charged even if constant voltage is applied from the constant voltage circuit30when the capacitor10has a short-circuit fault. In this case, the controller60detects 0 V during measurement1.

Subsequently, the controller60turns the constant voltage circuit30off. When the capacitor10is in a normal state, the capacitor10maintains the charged state. During measurement2, the controller60in this case detects a voltage corresponding to the constant voltage supplied by the constant voltage circuit30. When the capacitor10has a leak fault, the charge accumulated in the capacitor10is reduced by leakage. During measurement2, the controller60detects a smaller voltage in this case than the voltage detected in measurement1. When the capacitor10has a short-circuit fault, the controller60continues to detect 0 V during measurement2.

When the voltage detected in measurement1is 0 V, the controller60can judge that the capacitor10possibly has a short-circuit fault. The controller60may judge that 0 V is detected when a voltage equal to or less than a predetermined threshold is detected.

The controller60can judge that the capacitor10is possibly leaking when the difference resulting from subtracting the voltage measured in measurement2from the voltage measured in measurement1is greater than a predetermined threshold. The predetermined threshold may be set to an appropriate value taking into account error in reading the voltage, noise, and the like.

In this way, the controller60can judge that the capacitor10possibly has a leak fault. The controller60can thereby reduce the risk of the voltage of the first battery200being mistakenly read too low during normal processing due to a leak fault in the capacitor10, which would end up overcharging the first battery200.

Diagnosis 3-2 is an open fault diagnosis of the second switches2. Diagnosis 3-2 is described with reference to the block diagram inFIG. 11and the timing chart inFIG. 12. As illustrated inFIG. 11, the targets of fault diagnosis in diagnosis 3-2 are the second switches2A,2B.FIG. 11is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-2, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-2.

FIG. 12illustrates a timing chart in diagnosis 3-2. The controller60controls the constant voltage circuit30to be on/off and the second switches2to be on/off at similar timings to those of the timing chart illustrated inFIG. 10. The controller60performs measurement1at measurement timings t1to t4similar to those of the timing chart illustrated inFIG. 10. The controller60performs measurement2at measurement timings t5to t8similar to those of the timing chart illustrated inFIG. 10.

After the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is charged by the constant voltage supplied from the constant voltage circuit30when the second switch2B is in a normal state. If the second switch2A is in a normal state at this time, then during measurement1, the controller60can detect a voltage corresponding to the constant voltage supplied by the constant voltage circuit30. The capacitor10is maintained in the charged state even if the constant voltage circuit30is turned off. Therefore, during measurement2as well, the controller60can detect a voltage corresponding to the constant voltage supplied by the constant voltage circuit30.

When the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is not charged by the constant voltage circuit30if the second switch2B has an open fault. In this case, the controller60detects 0 V during measurement1and measurement2.

When the controller60turns the constant voltage circuit30and the second switches2on, the voltage of the first node10A is not applied to the A/D input terminal22A of the A/D converter22if the second switch2A has an open fault. In this case, the input terminal on the positive side of the operational amplifier21is grounded via a several kiloohm resistance component, due to wrapping around nearby circuits or the like. The controller60therefore detects 0 V during measurement1and measurement2.

When the voltage detected in measurement1and measurement2is 0 V, the controller60can judge that the second switches2possibly have an open fault. The controller60may judge that 0 V is detected when a voltage equal to or less than a predetermined threshold is detected.

Diagnosis 3-3 diagnoses whether the output voltage of the operational amplifier21is stuck at 0 V. Diagnosis 3-3 is described with reference to the block diagram inFIG. 13and the timing chart inFIG. 14. As illustrated inFIG. 13, the target of fault diagnosis in diagnosis 3-3 is the operational amplifier21.FIG. 13is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-3, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-3.

FIG. 14illustrates a timing chart in diagnosis 3-3. The controller60controls the constant voltage circuit30to be on/off and the second switches2to be on/off at similar timings to those of the timing chart illustrated inFIG. 10. The controller60performs measurement1at measurement timings t1to t4similar to those of the timing chart illustrated inFIG. 10. The controller60performs measurement2at measurement timings t5to t8similar to those of the timing chart illustrated inFIG. 10.

After the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is charged by the constant voltage supplied from the constant voltage circuit30. When the operational amplifier21is in a normal state at this time, the operational amplifier21outputs voltage corresponding to the constant voltage supplied by constant voltage circuit30to the A/D input terminal22A of the A/D converter22. Accordingly, during measurement1, the controller60can detect a voltage corresponding to the constant voltage supplied by the constant voltage circuit30. The capacitor10is maintained in the charged state even if the constant voltage circuit30is turned off. Therefore, during measurement2as well, the controller60can detect a voltage corresponding to the constant voltage supplied by the constant voltage circuit30.

If the output of the operational amplifier21is stuck at 0 V, the operational amplifier21outputs 0 V even when the inputted voltage corresponds to the constant voltage supplied by the constant voltage circuit30. Accordingly, when the output of the operational amplifier21is stuck at 0 V, the controller60detects 0 V during measurement1and measurement2. If the output of the operational amplifier21is stuck at 0 V, the output of the detection circuit20is also stuck at 0 V.

When the voltage detected in measurement1and measurement2is 0 V, the controller60can judge that the output of the operational amplifier21is possibly stuck at 0 V. The controller60may judge that 0 V is detected when a voltage equal to or less than a predetermined threshold is detected.

Diagnosis 3-4 is a short-circuit fault diagnosis of the second switch2A. Diagnosis 3-4 is described with reference to the block diagram inFIG. 15and the timing chart inFIG. 16. As illustrated inFIG. 15, the target of fault diagnosis in diagnosis 3-4 is the second switch2A.FIG. 15is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-4, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-4.

FIG. 16illustrates a timing chart in diagnosis 3-4. The controller60controls the constant voltage circuit30to be on/off and the second switches2to be on/off at similar timings to those of the timing chart illustrated inFIG. 10. The controller60performs measurement1at measurement timings t1to t4similar to those of the timing chart illustrated inFIG. 10. The controller60performs measurement2at measurement timings t5to t8similar to those of the timing chart illustrated inFIG. 10.

The controller60turns the second switches2off and then measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t9to t12. The measurement at the predetermined measurement timings t9to t12is also referred to below as “measurement3”.

The input terminal on the positive side of the operational amplifier21is grounded via a several kiloohm resistance component, due to wrapping around nearby circuits or the like. Therefore, if the second switch2A is in a normal state when the controller60turns the second switch off, the input voltage of the operational amplifier21gradually decreases due to current leaking via this resistance component. During measurement3, the controller60detects a smaller voltage in this case than the voltage detected in measurement2.

When the second switch2A has a short-circuit fault, the second switch2A remains short-circuited even if the controller60executes control to turn the second switches2off. In this case, the input voltage of the operational amplifier21does not change even if the controller60executes control to turn the second switches2off. Accordingly, during measurement3, the controller60detects a similar voltage to the voltage detected in measurement2.

When the difference resulting from subtracting the voltage detected in measurement3from the voltage detected in measurement1or measurement2is zero, the controller60can judge that the second switch2A possibly has a short-circuit fault. The controller60may judge that the difference resulting from subtracting the voltage detected in measurement3from the voltage detected in measurement1or measurement2is zero when the difference is equal to or less than a predetermined threshold.

Diagnosis 3-5 is a short-circuit fault diagnosis of the second switch2B. Diagnosis 3-5 is described with reference to the block diagram inFIG. 17and the timing chart inFIG. 18. As illustrated inFIG. 17, the target of fault diagnosis in diagnosis 3-5 is the second switch2B.FIG. 17is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-5, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-5.

FIG. 18illustrates a timing chart in diagnosis 3-5. The controller60outputs a high signal to the control terminal30A to turn the constant voltage circuit30on. After a predetermined time elapses, the controller60outputs a low signal to the control terminal30A to turn the constant voltage circuit30off. After turning the constant voltage circuit30off, the controller60turns the second switches2on and then turns the second switches2off. The controller60turns the second switches2on and then measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t13to t16. The measurement at the predetermined measurement timings t13to t16is also referred to below as “measurement4”.

When the controller60turns the constant voltage circuit30on while the second switches2are off, the capacitor10is not charged. The reason is that when the second switch2B is in a normal state, the second node10B is not grounded. Accordingly, when the controller60subsequently turns the constant voltage circuit30off and then turns the second switches2on, the controller60detects 0 V.

If the second switch2B has a short-circuit fault, then the capacitor10charges when the controller60turns on the constant voltage circuit30after having turned off the second switches2. The reason is that when the second switch2B has a short-circuit fault, the second node10B is grounded. Accordingly, when the controller60subsequently turns the constant voltage circuit30off and then turns the second switches2on, the controller60detects a voltage corresponding to the constant voltage supplied by the constant voltage circuit30.

When the voltage detected in measurement4is not 0 V, the controller60can judge that the second switch2B possibly has a short-circuit fault. The controller60may judge that a voltage other than 0 V is detected when a voltage equal to or greater than a predetermined threshold is detected.

Diagnosis 3-6 is a short-circuit fault diagnosis of the first switch1K, which is the lowermost switch among the first switches1. Diagnosis 3-6 is described with reference to the block diagram inFIG. 19and the timing chart inFIG. 20. As illustrated inFIG. 19, the target of fault diagnosis in diagnosis 3-6 is the first switch1K.FIG. 19is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-6, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off. The controller60controls the constant voltage circuit30and the second switches2to be off before starting diagnosis 3-6.

FIG. 20illustrates a timing chart in diagnosis 3-6. The controller60controls the constant voltage circuit30to be on/off and the second switches2to be on/off at similar timings to those of the timing chart illustrated inFIG. 18. The controller60performs measurement4at measurement timings t13to t16similar to those of the timing chart illustrated inFIG. 18.

When the controller60turns the constant voltage circuit30on while the second switches2are off, the capacitor10is not charged. The reason is that when the first switch1K is in a normal state, the second node10B is not grounded. Accordingly, when the controller60subsequently turns the constant voltage circuit30off and then turns the second switches2on, the controller60detects 0 V.

If the first switch1K has a short-circuit fault, then the capacitor10charges when the controller60turns on the constant voltage circuit30after having turned off the second switches2. The reason is that when the first switch1K has a short-circuit fault, the second node10B is grounded. Accordingly, when the controller60subsequently turns the constant voltage circuit30off and then turns the second switches2on, the controller60detects a voltage corresponding to the constant voltage supplied by the constant voltage circuit30.

When the voltage detected in measurement4is not 0 V, the controller60can judge that the first switch1K possibly has a short-circuit fault. The controller60may judge that a voltage other than 0 V is detected when a voltage equal to or greater than a predetermined threshold is detected.

Diagnosis 3-7 diagnoses whether the output voltage of the operational amplifier21is stuck at the power supply voltage (such as 5 V). Diagnosis 3-7 is described with reference to the block diagram inFIG. 21and the timing chart inFIG. 22. As illustrated inFIG. 21, the target of fault diagnosis in diagnosis 3-7 is the operational amplifier21.FIG. 21is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 3-7, the controller60controls the first switches1to be off. The controller60also controls the third switches3illustrated inFIG. 1to be off.

FIG. 22illustrates a timing chart in diagnosis 3-7. Before turning the constant voltage circuit30and the second switches2on, the controller60measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t17to t20. The measurement at the predetermined measurement timings t17to t20is also referred to below as “measurement5”.

Before the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is not charged. When the operational amplifier21is in a normal state at this time, the operational amplifier21outputs 0 V to the A/D input terminal22A of the A/D converter22. Accordingly, the controller60can detect 0 V during measurement5.

When the output voltage of the operational amplifier21is stuck at the power supply voltage (such as 5 V), the operational amplifier21outputs 5 V even when 0 V is inputted to the operational amplifier21. Accordingly, when the output of the operational amplifier21is stuck at 5 V, the controller60detects 5 V during measurement5. If the output of the operational amplifier21is stuck at 5 V, the output of the detection circuit20is also stuck at 5 V.

When the voltage detected in measurement5is the power supply voltage of the operational amplifier21(such as 5 V), the controller60can judge that the output of the operational amplifier21is possibly stuck at 5 V. The controller60may judge that a voltage of 5 V is detected when the detected voltage differs from 5 V by an amount equal to or less than a predetermined threshold.

Diagnosis 4 is a fault diagnosis of the operational amplifier21. Diagnosis 4 is described with reference to the block diagram inFIG. 23and the timing chart inFIG. 24. Note thatFIG. 23is a simplified view that omits a portion of the constituent elements of the diagnostic apparatus100illustrated inFIG. 1as appropriate.

In diagnosis 4, the controller60controls the third switches3and the constant voltage circuit30illustrated inFIG. 1to be off. The controller60controls the first switches1and the second switches2all to be off before starting diagnosis 4.

FIG. 24illustrates a timing chart in diagnosis 4. The controller60outputs a high signal to the control terminal30A to turn the constant voltage circuit30on and also turns the second switches2on. After turning the constant voltage circuit30and the second switches2on, the controller60measures the voltage inputted to the A/D input terminal22A of the A/D converter22at predetermined measurement timings t21to t24. In diagnosis 4, the controller60turns the constant voltage circuit30and the second switches2on and then also measures the voltage inputted to the A/D input terminal of the A/D converter52of the sub-detection circuit50at measurement timings t21to t24. The measurement at the predetermined measurement timings t21to t24is also referred to below as “measurement6”.

After the controller60turns the constant voltage circuit30and the second switches2on, the capacitor10is charged by the constant voltage supplied from the constant voltage circuit30. When the operational amplifier21is in a normal state during measurement6, the controller60in this case detects a voltage, from both the detection circuit20and the sub-detection circuit50, corresponding to the constant voltage supplied by the constant voltage circuit30. When an abnormality has occurred in the operational amplifier21, the controller60detects different voltages from the detection circuit20and the sub-detection circuit50in measurement6.

The controller60can judge that the operational amplifier21possibly has a fault when, during measurement6, the difference between the voltage acquired from the detection circuit20and the voltage acquired from the sub-detection circuit50is greater than a predetermined threshold.

[Procedures for Diagnosis 3 and Diagnosis 4]

An example of detailed procedures of step S3(diagnosis 3) and step S4(diagnosis 4) are described with reference to the flowchart inFIGS. 25 to 27.

The controller60of the diagnostic apparatus100starts the flow illustrated inFIGS. 25 to 27after executing control to turn the first switches1, the second switches2, the third switches3, and the constant voltage circuit30off.

The controller60turns the second switches2on (step S101) and the constant voltage circuit30on (step S102) as in the timing chart illustrated inFIG. 10, for example. The controller60may simultaneously execute step S101and step S102. The controller60may execute step S102before step S101.

Based on the results of measurement1and measurement2, the controller60judges whether a fault was detected in diagnosis 3-1, diagnosis 3-2, or diagnosis 3-3 (step S106).

When the voltage detected in measurement1is 0 V, the controller60can judge that there is a possibility of one of the following faults. The controller60may judge that 0 V is detected when a voltage equal to or less than a predetermined voltage is detected.

Short-circuit fault of the capacitor10(diagnosis 3-1)

Open fault of second switches2(diagnosis 3-2)

Output of operational amplifier21stuck at 0 V (diagnosis 3-3)

The controller60can judge that the capacitor10is possibly leaking when the difference resulting from subtracting the voltage measured in measurement2from the voltage measured in measurement1is greater than a predetermined threshold (diagnosis 3-1).

When a fault is detected in diagnosis 3-1, diagnosis 3-2, or diagnosis 3-3 (step S106: Yes), the controller60raises a fault flag (step S107) and ends the diagnostic processing.

When no fault is detected in diagnosis 3-1, diagnosis 3-2, or diagnosis 3-3 (step S106: No), the controller60proceeds to step S108.

The controller60turns the second switches2off (step S108) and performs measurement3(step S109) as in the timing chart illustrated inFIG. 16, for example.

Based on the results of measurements1to3, the controller60judges whether a fault was detected in diagnosis 3-4 (step S110).

When the difference resulting from subtracting the voltage detected in measurement3from the voltage detected in measurement1or measurement2is zero, the controller60can judge that the second switch2A possibly has a short-circuit fault (diagnosis 3-4). The controller60may judge that the difference resulting from subtracting the voltage detected in measurement3from the voltage detected in measurement1or measurement2is zero when the difference is equal to or less than a predetermined threshold.

When a fault is detected in diagnosis 3-4 (step S110: Yes), the controller60raises a fault flag (step S111) and ends the diagnostic processing.

When no fault is detected in diagnosis 3-4 (step S110: No), the controller60proceeds to step S112.

The controller60turns the fourth switch4on to discharge the capacitor10(step S112).

The controller60turns the constant voltage circuit30on and then off (step S113) and turns the second switches2on (step S114) as in the timing chart illustrated inFIG. 18, for example. The controller60performs measurement4(step S115).

Based on the results of measurement4, the controller60judges whether a fault was detected in diagnosis 3-5 or diagnosis 3-6 (step S116).

When the voltage detected in measurement4is not 0 V, the controller60can judge that there is a possibility of one of the following faults. The controller60may judge that a voltage other than 0 V is detected when a voltage equal to or greater than a predetermined voltage is detected.

When a fault is detected in diagnosis 3-5 or diagnosis 3-6 (step S116: Yes), the controller60raises a fault flag (step S117) and ends the diagnostic processing.

When no fault is detected in diagnosis 3-5 or diagnosis 3-6 (step S116: No), the controller60proceeds to step S118.

The controller60turns the fourth switch4on to discharge the capacitor10(step S119). Step S119can be omitted when a fault has not occurred in diagnosis 3-5 or diagnosis 3-6, since there is no charge stored in the capacitor10.

The controller60performs measurement5while the constant voltage circuit30and the second switches2are off (step S120) as in the timing chart illustrated inFIG. 22, for example.

The controller60turns the constant voltage circuit30on (step S121) and the second switches2on (step S122) as in the timing chart illustrated inFIG. 24, for example. The controller60may simultaneously execute step S121and step S122. The controller60may execute step S122before step S121.

Based on the results of measurement5and measurement6, the controller60judges whether a fault was detected in diagnosis 3-7 or diagnosis 4 (step S124).

When the voltage detected in measurement5is the power supply voltage of the operational amplifier21(such as 5 V), the controller60can judge that the output of the operational amplifier21is possibly stuck at 5 V (diagnosis 3-7). The controller60may judge that a voltage of 5 V is detected when the detected voltage differs from 5 V by an amount equal to or less than a predetermined threshold.

The controller60can judge that the operational amplifier21possibly has a fault when, during measurement6, the difference between the voltage acquired from the detection circuit20and the voltage acquired from the sub-detection circuit50is greater than a predetermined threshold (diagnosis 4).

When a fault is detected in diagnosis 3-7 or diagnosis 4 (step S124: Yes), the controller60raises a fault flag (step S125) and ends the diagnostic processing.

When no fault is detected in diagnosis 3-7 or diagnosis 4 (step S124: No), the controller60ends the diagnostic processing.

At the time the controller60raises a fault flag in step S107, step S111, step S117, or step S125and ends the diagnostic processing, the controller60may perform control to suspend subsequent use of the first battery200.

The timing of fault judgment in steps S106, S110, S116, and S124is only a non-limiting example.

For example, in step S106, the following fault judgment may be made at the stage at which measurement1is performed in step S103.

Short-circuit fault of the capacitor10(diagnosis 3-1)

Open fault of second switches2(diagnosis 3-2)

Output of operational amplifier21stuck at 0 V (diagnosis 3-3)

For example, the fault judgment in step S106may be made along with the fault judgment of step S110after measurement3is performed in step S109.

For example, in step S124, the fault judgment of diagnosis 3-7 may be made at the stage at which measurement5is performed in step S120.

In the present embodiment, the detection circuit20has been described as detecting the potential difference between both terminals of the capacitor10, but the detection circuit20may detect the discharge current from the capacitor10.

The diagnostic apparatus100according to the present embodiment can apply a voltage from the second battery300, which differs from the first battery200, to the capacitor10. The detection circuit20detects a potential difference or a discharge current after the controller60turns on the PNP transistor32and applies voltage from the second battery300to the capacitor10. The controller60then diagnoses at least one of the capacitor10, the first switch1K, and the second switches2. The diagnostic apparatus100according to the present embodiment can thereby diagnose the state of the capacitor10, the first switch1K, and the second switches2without depending on the first battery200, which is the target of voltage detection.

The diagnostic apparatus100according to the present embodiment can supply constant voltage to the capacitor10from the constant voltage circuit30when performing fault diagnosis. The threshold for judging whether there is a fault can therefore easily be set.

The diagnostic apparatus100according to the present embodiment diagnoses the capacitor10that functions as a flying capacitor, the first switches1that switch the connection state between the first battery200and the capacitor10, and the second switches2that switch the connection state between the capacitor10and the detection circuit20. Consequently, the diagnostic apparatus100according to the present embodiment can comprehensively perform the necessary fault diagnosis in a configuration with a flying capacitor.

The diagnostic apparatus100according to the present embodiment can maintain the second switches2off and suspend diagnosis of the capacitor10and the second switches2when detecting a short-circuit fault in the first switches1. This can reduce the risk of a fault in the operational amplifier21of the detection circuit20due to a high voltage being applied to the operational amplifier21as a result of the short-circuit fault in the first switches1.

The diagnostic apparatus100according to the present embodiment also includes third switches3capable of connecting the terminal of the first switch1that is not connected to the first battery200and the A/D converter22of the detection circuit20while bypassing the operational amplifier21that functions as an amplification circuit. The diagnostic apparatus100turns the second switches2off and the third switches3on, and in this state, diagnoses the first switches1based on the detection result of the A/D converter22when the first switches1are on or off. The diagnostic apparatus100according to the present embodiment can thereby diagnose the first switches1while bypassing the operational amplifier21. This reduces the risk of a fault in the operational amplifier21, which functions as an amplification circuit.

(Modification to Configuration of Diagnostic Apparatus)

FIG. 28illustrates the configuration of a diagnostic apparatus110according to a modification. The diagnostic apparatus110according to application differs from the diagnostic apparatus100inFIG. 1by inclusion of a detection circuit23in addition to the detection circuit20. The diagnostic apparatus110according to a modification is described focusing mainly on the differences from the diagnostic apparatus100illustrated inFIG. 1.

The detection circuit23includes an A/D converter24. The A/D converter24includes A/D input terminals24A and24B. The A/D converter24converts an analog voltage inputted to the A/D input terminal24A to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60. The A/D converter24converts an analog voltage inputted to the A/D input terminal24B to a digital signal corresponding to the analog voltage and outputs the digital signal to the controller60.

In the diagnostic apparatus110according to a modification, the detection circuit20may function as a first detection circuit, and the detection circuit23may function as a second detection circuit. The A/D converter22may function as a first A/D converter, and the A/D converter24may function as a second A/D converter.

In the diagnostic apparatus110according to a modification, the third switch3A is connected to the A/D input terminal24A of the A/D converter24via the resistor41. The third switch3B is connected to the A/D input terminal24B of the A/D converter24via the resistor43.

The configuration of the diagnostic apparatus110according to a modification can also achieve similar effects to those of the diagnostic apparatus100illustrated inFIG. 1.

In a flying capacitor type battery monitoring apparatus, it is preferable to perform not only fault diagnosis of the switch that switches the connection between the capacitor and the voltage detection circuit, but also fault diagnosis of the switch that switches the connection between the battery and the capacitor and fault diagnosis of the capacitor. PTL 1 is silent, however, regarding fault diagnosis of the switch that switches connection between the battery and the capacitor and fault diagnosis of the capacitor.

In light of this, the diagnostic apparatus according to a fourth aspect, the diagnostic method according to a fifth aspect, and the diagnostic apparatus according to a sixth aspect described below are capable of comprehensively performing the fault diagnosis necessary in a configuration with a flying capacitor.

To resolve the aforementioned problem, a diagnostic apparatus according to a fourth aspect includes:

a capacitor capable of being connected in parallel with each first battery among a plurality of first batteries connected in series;

a plurality of first switches configured to switch a connection state between the plurality of first batteries and the capacitor;

a detection circuit including an A/D converter and configured to detect a potential difference between both terminals of the capacitor;

a second switch configured to switch a connection state between the capacitor and the detection circuit;

a third switch capable of connecting a terminal of the first switches not connected to the first batteries to one of the detection circuit and another A/D converter while bypassing the second switch; and a controller configured to control the first switches, the second switch, and the third switch;

wherein the controller is configuredto diagnose the first switch based on a detection result of one of the detection circuit and the other A/D converter when the first switch is on or off while the second switch is off and the third switch is on; andafter diagnosing the first switch, to turn the third switch off, to turn the second switch from off to on, and to diagnose the capacitor and the second switch.

In the diagnostic apparatus according to the fourth aspect, the controller may be configured to maintain the second switch off and suspend diagnosis of the capacitor and the second switch when a short-circuit fault of the first switch is detected.

In the diagnostic apparatus according to the fourth aspect,

the detection circuit may include an amplification circuit configured to provide output to the A/D converter and may detect the potential difference between both terminals of the capacitor based on input to the amplification circuit;

the third switch may be capable of connecting a terminal of the first switches not connected to the first batteries to one of the A/D converter and the other A/D converter while bypassing the amplification circuit; and

the controller may be configured to diagnose the first switch based on a detection result of one of the A/D converter and the other A/D converter when the first switch is on or off while the second switch is off and the third switch is on.

The diagnostic apparatus according to the fourth aspect may further include

a changeover switch configured to switch a connection state between the capacitor and a second battery that differs from the first batteries; and

after the controller diagnoses the first switch, the controller may turn the third switch off, turn the second switch from off to on, turn the changeover switch on to apply a voltage to the capacitor from the second battery, and subsequently diagnose the capacitor and the second switch based on a detection result of the detection circuit.

The diagnostic apparatus according to the fourth aspect may further include a constant voltage circuit capable of generating a constant voltage from the second battery and of outputting the constant voltage to the capacitor via the changeover switch.

In the diagnostic apparatus according to the fourth aspect, the constant voltage may be smaller than a maximum voltage suppliable by the plurality of first batteries connected in series.

In the diagnostic apparatus according to the fourth aspect, the constant voltage may be larger than a maximum voltage suppliable by each first battery.

In the diagnostic apparatus according to the fourth aspect, the first batteries may be lithium-ion batteries or nickel-hydrogen batteries.

In the diagnostic apparatus according to the fourth aspect, the second battery may be a lead-acid battery, a lithium-ion battery, or a nickel-hydrogen battery.

To resolve the aforementioned problem, a diagnostic method according to a fifth aspect is a diagnostic method in a diagnostic apparatus including a capacitor capable of being connected in parallel with each first battery among a plurality of first batteries connected in series, a plurality of first switches configured to switch a connection state between the plurality of first batteries and the capacitor, a detection circuit including an A/D converter and configured to detect a potential difference between both terminals of the capacitor, a second switch configured to switch a connection state between the capacitor and the detection circuit, and a third switch capable of connecting a terminal of the first switches not connected to the first batteries to one of the detection circuit and another A/D converter while bypassing the second switch, the diagnostic method including:

diagnosing the first switch based on a detection result of one of the detection circuit and the other A/D converter when the first switch is on or off while the second switch is off and the third switch is on; and

turning the third switch off, turning the second switch from off to on, and diagnosing the capacitor and the second switch after diagnosing the first switch.

To resolve the aforementioned problem, a diagnostic apparatus according to a sixth aspect includes:

a capacitor capable of being connected in parallel with each first battery among a plurality of first batteries connected in series;

a plurality of first switches configured to switch a connection state between the plurality of first batteries and the capacitor;

a first detection circuit configured to detect a potential difference between both terminals of the capacitor;

a second switch configured to switch a connection state between the capacitor and the first detection circuit;

a second detection circuit capable of bypassing the second switch to detect a voltage of a terminal of the first switches not connected to the first batteries;

a third switch configured to switch a connection state between the first switches and the second detection circuit; and

a controller configured to control the first switches, the second switch, and the third switch;

wherein the controller is configured todiagnose the first switch based on a detection result of the second detection circuit when the first switch is on or off while the second switch is off and the third switch is on; andafter diagnosing the first switch, turn the third switch off, turn the second switch from off to on, and diagnose the capacitor and the second switch based on a detection result of the first detection circuit.

The diagnostic apparatus according to the fourth aspect can comprehensively perform the necessary fault diagnosis in a configuration with a flying capacitor.

The diagnostic method according to the fifth aspect can comprehensively perform the necessary fault diagnosis in a configuration with a flying capacitor.

The diagnostic apparatus according to the sixth aspect can comprehensively perform the necessary fault diagnosis in a configuration with a flying capacitor.

(Reduction of Risk of Fault in Amplification Circuit that Detects Voltage of Flying Capacitor)

One known configuration of a voltage detection circuit that detects the voltage of a capacitor in a flying capacitor type battery monitoring apparatus is a configuration to amplify the voltage of the capacitor with an amplification circuit, such as an operational amplifier, and convert the analog signal outputted from the amplification circuit to a digital signal using an A/D converter (for example, see JP 2010-78572 A).

In a flying capacitor type battery monitoring apparatus, the switch for switching connection between the battery and the capacitor needs to operate normally. It is therefore necessary to perform fault diagnosis on the switch. In the case of using a flying capacitor type battery monitoring apparatus to monitor the voltage of each battery among a plurality of batteries connected in series, the voltage applied to the amplification circuit is larger than the allowable voltage of the amplification circuit when the switch connected to the high potential battery and the switch connected to the low potential battery simultaneously have a short-circuit fault. The amplification circuit may suffer a fault during fault diagnosis as a result.

In light of this, the diagnostic apparatus according to a seventh aspect, the diagnostic method according to an eighth aspect, and the diagnostic apparatus according to a ninth aspect described below are capable of reducing the risk of a fault in an amplification circuit that detects the voltage of a flying capacitor.

To resolve the aforementioned problem, a diagnostic apparatus according to a seventh aspect includes:

a detection circuit capable of detecting a voltage of each first battery among a plurality of first batteries connected in series, the detection circuit including an amplification circuit and an A/D converter;

a plurality of first switches connected to a positive electrode and a negative electrode of the plurality of first batteries;

a second switch configured to switch a connection state between the plurality of first switches and the amplification circuit of the detection circuit;

a third switch capable of connecting a point between the first switch and the second switch to one of the A/D converter and another A/D converter; and

a controller configured to control the first switches, the second switch, and the third switch;

wherein the controller is configured to diagnose the first switch based on a detection result of one of the A/D converter and the other A/D converter when the first switch is on or off while the second switch is off and the third switch is on.

In the diagnostic apparatus according to the seventh aspect, the controller may be configured to maintain the second switch off when a short-circuit fault of the first switch is detected.

The diagnostic apparatus according to the seventh aspect may further include a capacitor capable of being connected in parallel with each first battery among the plurality of first batteries via the plurality of first switches.

The diagnostic apparatus according to the seventh aspect may further include a fourth switch configured to discharge a charge stored in the capacitor by being turned on.

The diagnostic apparatus according to the seventh aspect may further include a changeover switch configured to switch a connection state between the capacitor and a second battery that differs from the first batteries; and

the controller may turn the changeover switch on to apply a voltage to the capacitor from the second battery and subsequently diagnose the capacitor and the second switch based on a detection result of the detection circuit.

In the diagnostic apparatus according to the seventh aspect, the second battery may be a lead-acid battery.

In the diagnostic apparatus according to the seventh aspect, the first batteries may be lithium-ion batteries or nickel-hydrogen batteries.

To resolve the aforementioned problem, a diagnostic method according to an eighth aspect is a diagnostic method in a diagnostic apparatus including a detection circuit capable of detecting a voltage of each first battery among a plurality of first batteries connected in series, the detection circuit including an amplification circuit and an A/D converter; a plurality of first switches connected to a positive electrode and a negative electrode of the plurality of first batteries; a second switch configured to switch a connection state between the plurality of first switches and the amplification circuit of the detection circuit; and a third switch capable of connecting a point between the first switch and the second switch to one of the A/D converter and another A/D converter, the diagnostic method including:

diagnosing the first switch based on a detection result of one of the A/D converter and the other A/D converter when the first switch is on or off while the second switch is off and the third switch is on.

To resolve the aforementioned problem, a diagnostic apparatus according to a ninth aspect includes:

a first detection circuit capable of detecting a voltage of each first battery among a plurality of first batteries connected in series, the first detection circuit including an amplification circuit and a first A/D converter;

a second detection circuit capable of detecting a voltage of each first battery, the second detection circuit including a second A/D converter;

a plurality of first switches connected to a positive electrode and a negative electrode of the plurality of first batteries;

a second switch configured to switch a connection state between the plurality of first switches and the amplification circuit of the first detection circuit;

a third switch capable of connecting the first switch and the second A/D converter; and

a controller configured to control the first switches, the second switch, and the third switch;

wherein the controller is configured to diagnose the first switch based on a detection result of the second A/D converter when the first switch is on or off while the second switch is off and the third switch is on.

The diagnostic apparatus according to the seventh aspect can reduce the risk of a fault in an amplification circuit that detects the voltage of a flying capacitor.

The diagnostic method according to the eighth aspect can reduce the risk of a fault in an amplification circuit that detects the voltage of a flying capacitor.

The diagnostic apparatus according to the ninth aspect can reduce the risk of a fault in an amplification circuit that detects the voltage of a flying capacitor.

Although embodiments of the present disclosure have been described based on drawings and examples, it is to be noted that various changes and modifications may be made by those skilled in the art based on the present disclosure. Therefore, such changes and modifications are to be understood as included within the scope of the present disclosure. For example, the functions and the like included in the various components may be reordered in any logically consistent way. Furthermore, a plurality of components and the like may be combined into one, or a single component or the like may be divided.

REFERENCE SIGNS LIST